Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Monday 11 January 2016 14:44:54 John Kasunich wrote:

> On Mon, Jan 11, 2016, at 02:00 PM, Gene Heskett wrote:
> > On Monday 11 January 2016 13:10:10 John Kasunich wrote:
> > > SSRs can fail shorted, I don't think this buys you much in terms
> > > of reliability and safety.
> > >
> > > I think there is a little over-kill going on.
> > >
> > > Do you really need a fast bleeder (<1 minute to safe)?  Or would a
> > > five minute bleeder be OK?
> > >
> > > My understanding is that you have two 68000uF caps in series,
> > > charged to about 130V. (If this is incorrect let me know - the
> > > thread is long and rambling and refers to other thread.  I'm
> > > basing this on something written in the first message of this
> > > particular thread.)
> >
> > Actually 10 6800 u-f in parallel, working at their labeled 63 volts
> > ratings.
> >
> > But yes, you have the right idea. :)
> >
> > > Series caps divide, so you have 34000uF.  Let's say that "safe" is
> > > 20V.  So you need to discharge from 130V to 20V, that is to 15% of
> > > the original voltage.  Ln(0.15) is -1.9, so it takes 1.9 RC time
> > > constants to get to a safe voltage.  Call it 2.0 for easy math. 
> > > If you want to get there in 5 minutes, then one time constant is
> > > 2.5 minutes = 150 seconds. T = RC, solve for R, gives you R = T/C
> > > = 4411 ohms.  At 130V, that would draw 29mA and burn 3.8 watts. 
> > > Next lower 10% value is 3.9K, that would draw and burn 4.3 watts.
> > > I like to derate power resistors by 50%, so you want a 3.9K 10W
> > > resistor.
> >
> > I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it
> > right now that I was going to use once the relays get here.  Thats
> > 833 ohms which would drain it even faster than just the one.
>
> The 5K's are across the entire bus, or across each cap?

The bus, since there are 4 toroids and rectifiers, (dictated by the 
toroids I could source for close to nothing,) is arranged as 5 caps per 
group, in a 2 in parallel, stacked two more on top of that so there is 
one 5 k R across each 5 caps. 20 of those 6800x63 caps total. I did not 
have a bar joining the center of the stack, still don't.  So there's a 
possibility of a volt or so's miss-match there.
>
> If across the entire bus, 130V would result in 3.38 watts per
> resistor. Less than the 5W rating, but more than half the rating,
> which is the derate I like to use to keep things from getting too hot
> and ensure long life.

These are 10 watt R's.
>
> I'd suggest 3 of the 5K across each side of the bus.  At 65V across 5K
> each resistor would be running at 0.85W, nice and cool.  Total
> resistance of the 3-parallel 2-series arrangement would be 3.33K, RC
> time constant 113 seconds, bleed-down time from 130V to 20V = 212
> seconds = 3.5 minutes.  And free voltage balancing between the two
> sets of caps.
>
> > And, somewhere
> > on an undermanned galley in the pacific, is a 250 ohm 250 watt
> > resistor which would do the bleed-down even faster, and the current
> > peak would be nominally .5 amps in that case. I can't see that as
> > being capable of welding a relay contact.
>
> Making 0.5A probably won't weld any contacts.  Breaking 0.5A DC on
> a relay designed for AC is another story.  And keep in mind that
> contact bounce = breaking and making.

True, very true.

> I'm just not a big believer in switched bleeders.  Significant hassle
> and risk.  If fixed bleeders can meet your discharge time
> requirements, call it good and move on.

That, once I put in GOOD charge-pump detectors, is exactly what I'm going 
to do.  And when I put the cover back on it, a dymo label that reminds  
me that the minimum safe off time is at least 20 minutes.

> Context - I design large motor drives for a living.  The vast majority
> used permanent bleeders only.  One recent design does augment them
> with a switched bleeder.  But that drive has 90 caps, each rated
> 6800uF 400V, in a 30-parallel by 3-series array, total of 68000uF. 
> Nominal bus voltage is 975V DC.  Stored energy is 32 kilo-joules.  UL
> requires that it discharge below 50V in five minutes.  The fixed
> bleeders would do it in 10.5 minutes, so we added a switched bleeder
> to help it along.
>
> Your unit has 34000uF at 130V, for a stored energy of 287 joules.
>
> > > If you do indeed have two caps in series, they ought to have
> > > balancing resistors anyway, so you could split the bleeder into
> > > two sections. Make each section 2K or 2.2K and 5 watts.
> >
> > That too, I was contemplating, but the 51 ohmmer would need to be
> > dismounted to gain access to the pcb bus connecting them all
> > together. Since I have them already 2 each of the 5k's across each
> > bank would seem to be about right.  They are well discharged atm,
> > and I could do that yet this afternoon.  If my math is correct, at
> > 5k and 63.5 volts=0.80645 watts per, so if I spread them out on the
> > busses, the heat shouldn't hurt the caps.
>
> Agreed.  But why not use all 6 of the 5K?

Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Monday 11 January 2016 13:33:22 Bertho Stultiens wrote:

> On 01/11/2016 06:01 PM, Gene Heskett wrote:
> > 1. put a small tranny delivering say 6 volts AC in series with the
> > resistor and its shorting SSR to encourage that SSR to turn off when
> > the cap voltage has dropped to 6 volts or less.
>
> How do you connect the 6V AC without it bearing a huge (peak) current?
>
> If you have a DC signal in it too, it will feedback into the primary.
> That is a huge problem. Not to speak of the inductance.
>
Probably, I hadn't though it all the way thru.

> > 2. enforce in hal, 2 delay circuits.  An on delay long enough for #1
> > to have completed its job and the short across the resistor no
> > longer exists thru that pair of SSR's.
>
> Enforcing a software solution is a risk. If the software fails, then
> you get potentially fried? You'd normally have an electronic interlock
> to prevent problems.
>
> > 3. Time the short enable so its 5 to 10 seconds after the relay has
> > closed, and time the short disable to take place a second or so
> > before the relay is de-energized, so that SSR is off by the time the
> > switch of the resistors position in the circuit takes place. By
> > placing another timedelay in the relay control, with longer time
> > delays than the shorting time delay would enforce disconnecting the
> > short whose timedelay is set for 1 second, so the resistor is
> > switched back into the circuit well before its transferred to dump
> > the caps duty.
>
> The real problem of shorting the resistor are the huge peak currents.

Miss-conception John. Its shorted after the caps are nearly charged.  
When the final short comes on, the caps are up to 110-teens already, so 
the remaining charge isn't much.  I put an amprobe on the black wire of 
the AC feed, and its a blond one north of 3 amps when the motor is doing 
2500 revs cutting air.

> You said that you have two 68000uF caps in series, or 34000uF
> effectively on it, which suggests that you are handling an average DC
> current somewhere between 30...60A.

No, I just over estimated the u-f's I'd need for a 1HP motor.  The 
current capacity is there should something short it out, but thats a 
fault condition, nothing approaching that will ever occur in normal 
operation even if I should manage to lock the rotor, the servo amp is 
set for a current limit in the 14.5 amp range, 150% of the motors 
nameplate draw at full song.  The toroids might warm up 30 degrees doing 
it for 30 minutes, but Jon's driver will survive that.

> The current peak from the rectifier, just to maintain that DC current
> after the cap, is somewhere between 120...240A (estimated) and even
> higher currents are possible. That will fuse most normal relays.

Rated 410 amps for these 40 amp CCS relays, but that would not be thru 
the relay contacts ever.

With that resistor in circuit for the first 5 or 6 seconds, the max amps 
is nominally 2.5 rms for the first 1/2 second or so, and tapers to very 
little as the caps charge.

> SSRs would probably survive is you get one and stay well below the
> fusing current (specified in the I^2t parameter) and stay below the
> peak current rating.
> However, SSRs do not like to be operated at high 
> peak currents for long periods.
>
> > Does anyone have an data on how sensitive these SSR's are to a false
> > trigger from dv/dt effects applied to the output terminals?
>
> They all have that specified in the datasheet. Most large ones are
> specified at about 500V/us.

These are SSR-40DA's, and the spec sheet I'm looking at makes no 
reference to that, only the maximum "durated" current, which as I read 
the chinglish translation means 1 cycle duration.  I doubt if they'll 
ever see 10% of that.

That doesn't sound appetizing in view of the hard switch the relay would 
make.  So scrub that.

> > Or do I need to use 2 of these relays with a fraction of a second
> > between them, to assure the line side SSR's have time enough to turn
> > off? At 60Hz thats 8. milliseconds after drive has been removed,
> > and the single relay could be faster than that.  All TBD when the
> > relays arrive I guess.  They haven't yet.
>
> Well, it looks like a very complicated and rather risky setup.

Well, with better charge-pump-detectors, what I have after adding those 
dual 5k r's across each cap bank, which is working fairly well, if a 
second or so slow, right now. Off time back to 40 volts is 4 minutes 
even, and is down to 7 volts in about 25 minutes.  I got tired of 
resetting the meter because it was timing out and shutting down.

It was working, and I had taken measurements and sawed off a 4" piece of 
white 1.25" PVC that I am going to bore out to about 1.53" for about 
3/4" on one end for a tight friction fit on the exhaust snout of the 
sander, and turn the OD down to around 1.33" for about an inch on the 
other end, which will serve as the adaptor to hook it up to a vac for 
dust collection.  Where I am right now on these chest lids is a 

Re: [Emc-users] Another crazy idea?

[Erik Christiansen]

On 11.01.16 14:00, Gene Heskett wrote:
> 
> I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it 
> right now that I was going to use once the relays get here.  Thats 833  
> ohms which would drain it even faster than just the one.  And, somewhere 
> on an undermanned galley in the pacific, is a 250 ohm 250 watt resistor 
> which would do the bleed-down even faster, and the current peak would be 
> nominally .5 amps in that case. I can't see that as being capable of 
> welding a relay contact.

There are alternatives to the electromechanical relay or an
SCR/Triac-based SSR, such as opto-coupled FET switches. They switch off,
even on DC. In my junkbox I (think I still) have some

http://documentation.renesas.com/doc/YOUSYS/document/PN10273EJ02V0DS.pdf

With both FETs in parallel, it'll just handle 0.5A, so adding some ohms
in series with the bleeder would be wise in this case. There are
doubtless beefier units out there by now.

Note: If used to switch AC, the FETs need to be used in series, halving
  the current capacity.

That brief technology diversion aside, I'd just go with fixed slow
bleeders, I think.¹ (Though a small relay buffered by a big MOSFET would
solve all your contact welding concerns, and allow a low value bleeder
in the drain circuit. The MOSFET would only switch, obviating your
concerns with running one in the linear region. OK, in the last few
volts, gate drive would fall off, unless you added a diode to keep
charge on the gate.)

¹ Especially given John's suggestion that a split bleeder can serve for
voltage equalisation across series capacitors. You're not doing that,
instead running the electros at full rated voltage? In the Siemens
design labs we were never allowed to design that way. Half of rated was
the allowed max, for reliability. I like to stick to 60% for my own
stuff, still.

Where I'm happier with a switched resistor is as inrush limiter.

Erik

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Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Monday 11 January 2016 21:07:35 John Kasunich wrote:

> On Mon, Jan 11, 2016, at 05:41 PM, Gene Heskett wrote:
> > On Monday 11 January 2016 14:44:54 John Kasunich wrote:
> > > On Mon, Jan 11, 2016, at 02:00 PM, Gene Heskett wrote:
> > > > On Monday 11 January 2016 13:10:10 John Kasunich wrote:
> > > > I actually have, atm, 6 ea 5k 10 watters in parallel clipped
> > > > onto it
> > >
> > > The 5K's are across the entire bus, or across each cap?
> > > If across the entire bus, 130V would result in 3.38 watts per
> > > resistor. Less than the 5W rating, but more than half the rating,
> > > which is the derate I like to use to keep things from getting too
> > > hot and ensure long life.
> >
> > These are 10 watt R's.
>
> My mistake, I somehow read that as 5K 5W.
>
> > > Agreed.  But why not use all 6 of the 5K?
> >
> > I could, if I tied the center points of the stacks together,
> > otherwise I'd need 8 so I could put 2 on each group.
>
> Understood.
>
> Although, since they are 10W, you could put the last two across the
> entire bus to speed up the discharge.

Humm, damn I must be getting slow, I should have thought of that.  Now I 
have to take it all apart again. ;-)  After I collect some ZZ's though.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Another crazy idea?

[John Kasunich]

On Mon, Jan 11, 2016, at 05:41 PM, Gene Heskett wrote:
> On Monday 11 January 2016 14:44:54 John Kasunich wrote:
> 
> > On Mon, Jan 11, 2016, at 02:00 PM, Gene Heskett wrote:
> > > On Monday 11 January 2016 13:10:10 John Kasunich wrote:
> > > I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it
> >
> > The 5K's are across the entire bus, or across each cap?
> > If across the entire bus, 130V would result in 3.38 watts per
> > resistor. Less than the 5W rating, but more than half the rating,
> > which is the derate I like to use to keep things from getting too hot
> > and ensure long life.
> 
> These are 10 watt R's.

My mistake, I somehow read that as 5K 5W.

> > Agreed.  But why not use all 6 of the 5K?
> 
> I could, if I tied the center points of the stacks together, otherwise 
> I'd need 8 so I could put 2 on each group.
> 

Understood.

Although, since they are 10W, you could put the last two across the
entire bus to speed up the discharge.

-- 
  John Kasunich
  jmkasun...@fastmail.fm

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Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Tuesday 12 January 2016 00:37:55 Erik Christiansen wrote:

> On 11.01.16 14:00, Gene Heskett wrote:
> > I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it
> > right now that I was going to use once the relays get here.  Thats
> > 833 ohms which would drain it even faster than just the one.  And,
> > somewhere on an undermanned galley in the pacific, is a 250 ohm 250
> > watt resistor which would do the bleed-down even faster, and the
> > current peak would be nominally .5 amps in that case. I can't see
> > that as being capable of welding a relay contact.
>
> There are alternatives to the electromechanical relay or an
> SCR/Triac-based SSR, such as opto-coupled FET switches. They switch
> off, even on DC. In my junkbox I (think I still) have some
>
> http://documentation.renesas.com/doc/YOUSYS/document/PN10273EJ02V0DS.p
>df
>
> With both FETs in parallel, it'll just handle 0.5A, so adding some
> ohms in series with the bleeder would be wise in this case. There are
> doubtless beefier units out there by now.
>
> Note: If used to switch AC, the FETs need to be used in series,
> halving the current capacity.
>
> That brief technology diversion aside, I'd just go with fixed slow
> bleeders, I think.¹ (Though a small relay buffered by a big MOSFET
> would solve all your contact welding concerns, and allow a low value
> bleeder in the drain circuit. The MOSFET would only switch, obviating
> your concerns with running one in the linear region. OK, in the last
> few volts, gate drive would fall off, unless you added a diode to keep
> charge on the gate.)
>
> ¹ Especially given John's suggestion that a split bleeder can serve
> for voltage equalisation across series capacitors. You're not doing
> that, instead running the electros at full rated voltage? In the
> Siemens design labs we were never allowed to design that way. Half of
> rated was the allowed max, for reliability. I like to stick to 60% for
> my own stuff, still.

Yes, 63 volt rated caps, running at 63 volts.  They have formed up to 
such low leakage that without the bleeders, they are still dangerous 2 
days after the shut down.  No clue how long they will last but I suspect 
they were a decade+ old when I pulled the 20 some I used out a bushel 
sized box.  Dave was going to make hisself a 10 kw PA amp that would 
carry the Grateful Dead from his place clear into Ellamore WV, about 5 
miles. GD was the star attraction at a charity concert he threw at his 
place every summer for nearly 25 years while he was working for me at 
the tv station.  It was called, because the stage was across the road 
from the river, River Rocks.  But he's retired, pushing 70 and 
essentially broke, a small vet pension and SS, but his 40 acres is paid 
for so he hasn't done the concert in 3 or 4 years.  He putters about & 
keeps busy.  I guess that would also describe me. :)

> Where I'm happier with a switched resistor is as inrush limiter.
>
> Erik
>
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Rewiring the BP Again

[Mark]

We had about 10" of snow on the ground before the short melt hit, making 
things a bit soggy.  Then the temps dropped again and we got another 3 - 
4 inches over the last couple of days.  Hopefully, they'll have the 
roads cleared by the time I set out.

Mark

On 01/11/2016 08:14 AM, Peter Blodow wrote:
> Mark, it surely was interesting, when I drove to Traverse City last
> time, some 50 years ago, when I was temporarily a Michigander. Was a
> nice skiing weekend.
>
> Peter
>
> Am 11.01.2016 13:34, schrieb Mark:
>> 8 Degrees and snowing here in Grayling, MI this morning. I have to
>> drive over to Traverse City this morning. Should be interesting. Mark


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Re: [Emc-users] Rewiring the BP Again

[Mark]

On 01/10/2016 04:23 PM, Dave Cole wrote:
> I understand.I'm working out of town and just came back for the
> weekend.
>
> For me this is a good time to be distracted with too much work.
>
> It helps me ignore the wind gusts to 30 mph, the snow, and the temps
> headed to 8 degrees F for tonight.
> Except that I need to drive a long ways in this crap tomorrow morning.
>
> Dave

8 Degrees and snowing here in Grayling, MI this morning.  I have to 
drive over to Traverse City this morning.  Should be interesting.

Mark

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Re: [Emc-users] Rewiring the BP Again

[Peter Blodow]

Mark, it surely was interesting, when I drove to Traverse City last 
time, some 50 years ago, when I was temporarily a Michigander. Was a 
nice skiing weekend.

Peter

Am 11.01.2016 13:34, schrieb Mark:
> 8 Degrees and snowing here in Grayling, MI this morning. I have to 
> drive over to Traverse City this morning. Should be interesting. Mark


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Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Friday 08 January 2016 23:44:43 Gene Heskett wrote:

> On Thursday 07 January 2016 05:27:09 Gene Heskett wrote:
> > On Thursday 07 January 2016 05:07:25 Gene Heskett wrote:
> > > On Thursday 07 January 2016 04:50:35 andy pugh wrote:
> > > > On 7 January 2016 at 03:32, Gene Heskett  
wrote:
> > > > >  > > > >4P DT -1
> > > > > 4-Pin-10A-250VAC-With-Socket-Base-/120897376163?hash=item1c260
> > > > >b8 fa 3:g
> > > > >
> > > > >:3~kAAMXQgPhRkf79>
> > > > >
> > > > > That gives me a 4pdt,
> > > >
> > > > It doesn't mention being force-guided.
> > >
> > > That is a relay term I am not familiar with, please define?
> >
> > I looked it up on wikipedia. It does seem to be a good safety
> > feature. Perhaps I should interlock its operation by assuring it is
> > switched at no load by turning off a series SSR? I'll see what I can
> > cobble up in the hal file.
>
> As an update, sorta. The parts I ordered are trickling in, the
> schottky diodes and tantalum caps have arrived, as has a small 6.3V ct
> filament transformer in case I need to encourage a faster turn off the
> bleeder, but they aren't much use until the smallish hexfets to drive
> relays and SSR's with get here.
>
> I've changed my mind a bit since I'll have a 4pdt relay. The swinging
> contacts of 2 poles will connect both ends of that 51 ohm 200 watt
> resistor in series with the line power to the toroids when enabled,
> and switch it across the caps for a bleeder when de-energized.  The
> 3rd set of contacts will parallel the resistor with an SSR, shorting
> it when the on timeout has expired.
>
> This will also, by interrupting that path as the relay opens, remove
> any possibility of the resistor being shorted when the relay closes.
> The 4th set will feed back to hal, hitting a short timer to make sure
> the softstart done SSR is off before it can be re-enabled, enforcing a
> 1 or 2 second delay in that event.  I haven't located an input pin on
> that BoB, but as thats on the P2 connector of a 5i25, there are
> several pins available on it yet.
>
> I also have sourced a 100 foot roll of 26 conductor ribbon, and a bag
> of db25 connectors of both genders so I can make cables that don't hit
> the wall behind the computer, trying to knock the 5i25 out of its
> socket. The cable has arrived, but the connectors are still on a
> rowboat someplace...
>
> Thanks everybody.
>
> Cheers, Gene Heskett

Continued...

Andy's comment about that relay not being force guided, meaning it 
wouldn't be prevented from a misscue if a contact welded, got me 
thinking.  Which can be entertaining at times...

What if I used it essentially for a dry contact, which has its own 
closure problems, but used the contacts to steer SSR's?

1 set of spdt contacts would swing a 25 volt source thru 2 SSR's control 
terminals. That pair would be wired to connect the line power to one end 
of that resistor, while the other end of the resistor would be connected 
to the toroid power trannies by the 2nd SSR.  When they are off, the 
resistor is isolated, so...

The back, nc side of that same spdt section would connect the resistor 
across the cap bank with 2 more SSR's to serve as a suitable bleeder 
when the relay was de-energized.

The problem with that is that there needs to be a method of turning the 
SSR's off because the 2nd condition is DC and I've no clue as to the 
holding current they need to stay on.

And I will still be shorting the resistor after a turn on delay to charge 
the caps to about 90% of full voltage.

So how about 2 things:

1. put a small tranny delivering say 6 volts AC in series with the 
resistor and its shorting SSR to encourage that SSR to turn off when the 
cap voltage has dropped to 6 volts or less.

2. enforce in hal, 2 delay circuits.  An on delay long enough for #1 to 
have completed its job and the short across the resistor no longer 
exists thru that pair of SSR's.

3. Time the short enable so its 5 to 10 seconds after the relay has 
closed, and time the short disable to take place a second or so before 
the relay is de-energized, so that SSR is off by the time the switch of 
the resistors position in the circuit takes place. By placing another 
timedelay in the relay control, with longer time delays than the 
shorting time delay would enforce disconnecting the short whose 
timedelay is set for 1 second, so the resistor is switched back into the 
circuit well before its transferred to dump the caps duty.

All proved out on the scope before hooking up the power source of course.

That will take one more SSR than I have, but I got those 4 from MPJones 
fairly fast and relatively cheap, like about $9 USD a copy.

Does anyone have an data on how sensitive these SSR's are to a false 
trigger from dv/dt effects applied to the output terminals?

Or do I need to use 2 of these relays with a fraction of a second between 
them, to assure the line side SSR's have time enough to 

Re: [Emc-users] Rewiring the BP Again

[Gene Heskett]

On Monday 11 January 2016 08:35:59 Mark wrote:

> We had about 10" of snow on the ground before the short melt hit,
> making things a bit soggy.  Then the temps dropped again and we got
> another 3 - 4 inches over the last couple of days.  Hopefully, they'll
> have the roads cleared by the time I set out.
>
> Mark
>
Positively balmy down here in WV, 18 degrees this morning, 1/4" of snow 
in the shade.

Winds were high & gusty yesterday though, my 7000 lb WV Cadillac got 
moved sideways about 2 feet at 75 mph, taking me over the right hand 
white line on I-79 as I was approaching the AnnMore turnoff ramp, then 
out of the south when I turned around & went back south to home, 
normally a top gear 75mph trip, it blew the automatic into passing gear 
5 times in that 15 miles to the Jane Lew exit.  Keeps one up on his 
tippy toes for sure. 

OTOH, I learned to drive 66+ years ago in Iowa, and that winter was 
legendary, still remembered by us oldtimers.  Same in Nebraska.  When I 
moved there from Rapid City where I had seen -39F on a tree in front of 
my house in South Canyon back in the middle 60's, the first time I went 
to get a hair cut in a little square block building, grandfathered into 
one edge of a block square city park, the first thing I noticed on the 
wall was a picture taken in 1950, of a smoking stovepipe sticking up out 
of a snowdrift.

Taken from an angle that did not show the front had a shoveled path to 
the front door, it was that barbershop. The stove was by then, in 1971 
propane gas, but it was a coal burning, pot bellied "Warm Morning" in 
1950.  He said he brought 2 buckets with him from his home coal shed 
when he opened up, and again after lunch in those days.

So yeah, WV is balmy.  I think I'll stay till the rapture.:)

> On 01/11/2016 08:14 AM, Peter Blodow wrote:
> > Mark, it surely was interesting, when I drove to Traverse City last
> > time, some 50 years ago, when I was temporarily a Michigander. Was a
> > nice skiing weekend.
> >
> > Peter
> >
> > Am 11.01.2016 13:34, schrieb Mark:
> >> 8 Degrees and snowing here in Grayling, MI this morning. I have to
> >> drive over to Traverse City this morning. Should be interesting.
> >> Mark
>
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Another crazy idea?

[John Kasunich]

SSRs can fail shorted, I don't think this buys you much in terms of
reliability and safety.

I think there is a little over-kill going on.

Do you really need a fast bleeder (<1 minute to safe)?  Or would a
five minute bleeder be OK?

My understanding is that you have two 68000uF caps in series, charged to about 
130V.
(If this is incorrect let me know - the thread is long and rambling and refers 
to other 
thread.  I'm basing this on something written in the first message of this 
particular
thread.)

Series caps divide, so you have 34000uF.  Let's say that "safe" is 20V.  So you 
need to
discharge from 130V to 20V, that is to 15% of the original voltage.  Ln(0.15) 
is -1.9, so
it takes 1.9 RC time constants to get to a safe voltage.  Call it 2.0 for easy 
math.  If you
want to get there in 5 minutes, then one time constant is 2.5 minutes = 150 
seconds.
T = RC, solve for R, gives you R = T/C = 4411 ohms.  At 130V, that would draw 
29mA 
and burn 3.8 watts.  Next lower 10% value is 3.9K, that would draw and burn 4.3 
watts.
I like to derate power resistors by 50%, so you want a 3.9K 10W resistor.  

If you do indeed have two caps in series, they ought to have balancing 
resistors anyway,
so you could split the bleeder into two sections.  Make each section 2K or 2.2K 
and 5 watts.

Something like this can be chassis mounted and wired to the caps:
http://www.digikey.com/product-detail/en/RH0052K000FE02/RHRA-2.0K-ND/1166266
Cost is $5 each, total $10

Even cheaper would be to parallel up some 1W leaded resistors:
http://www.digikey.com/product-detail/en/PR01000101002JR500/PPC10KW-1CT-ND/597177
$2.06 for ten - five in parallel will make 2K 5W, put one set of five across 
each cap.
Might be a nuisance to mount.

If you have can type caps with screw terminals, use power resistors with solid 
axial leads,
crimp/solder them to ring lugs, and mount right on top of the caps:
http://www.digikey.com/product-detail/en/SQP10AJB-2K0/2.0KW-10-ND/18789
$0.64 each, total $1.28

I realize that Digikey might not be your supplier of choice due to shipping 
costs, but my
point is that an always-on bleeder is simple, safe, and at this power level, 
cheap.  As
you get to larger energy levels (more volts or more uF) or if you need a much 
faster
discharge time you might be able to justify a switched fast bleeder.  But that 
will ALWAYS
be less reliable and less safe than an always-on bleeder.  Even if you have a 
switched
bleeder it would be wise to have an permanent bleeder with maybe a 10 minute 
time
constant.  At 10 minutes, the power and cost are negligible, and it serves 
double duty
as the voltage balancing resistors for your series caps.

Inrush limiting is a separate issue.  Separate resistor, bypassed by a 
contactor or relay
for normal operation.  Put it on the AC side so you don't have any issues with 
DC contact
ratings.  The main risk is that if you try to run with the bypass relay open 
you can fry your
resistor.  One way to avoid that is to make the "resistor" a 100W incandescent 
light bulb.

Using bulbs for bleeders is risky because they run all the time, and when they 
burn 
out they leave the caps charged with no indication of the risk.  But using a 
bulb for 
charging is different.  The bulb only lights for a few seconds when you first 
apply 
power.  If it is burned out the caps won't charge.  If you try to run with the 
bypass 
open the light will glow to let you know.

A 100W 120V bulb has a hot resistance of 144 ohms.  With 34000uF the charging
time constant is 4.9 seconds.  As the bus charges the voltage drop across the
bulb goes down, it cools down, and its resistance decreased - that is good, it 
make
the "long tail" of the charging curve go faster.  The inrush during the first 
cycle or
so will be based on the cold resistance of the bulb, but if your switch and 
diodes
can handle a 100W light bulb you know it can handle any size cap bank fed thru
that same 100W light bulb.


-- 
  John Kasunich
  jmkasun...@fastmail.fm

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Re: [Emc-users] Another crazy idea?

[Gene Heskett]

On Monday 11 January 2016 13:10:10 John Kasunich wrote:

> SSRs can fail shorted, I don't think this buys you much in terms of
> reliability and safety.
>
> I think there is a little over-kill going on.
>
> Do you really need a fast bleeder (<1 minute to safe)?  Or would a
> five minute bleeder be OK?
>
> My understanding is that you have two 68000uF caps in series, charged
> to about 130V. (If this is incorrect let me know - the thread is long
> and rambling and refers to other thread.  I'm basing this on something
> written in the first message of this particular thread.)

Actually 10 6800 u-f in parallel, working at their labeled 63 volts 
ratings.

But yes, you have the right idea. :)
>
> Series caps divide, so you have 34000uF.  Let's say that "safe" is
> 20V.  So you need to discharge from 130V to 20V, that is to 15% of the
> original voltage.  Ln(0.15) is -1.9, so it takes 1.9 RC time constants
> to get to a safe voltage.  Call it 2.0 for easy math.  If you want to
> get there in 5 minutes, then one time constant is 2.5 minutes = 150
> seconds. T = RC, solve for R, gives you R = T/C = 4411 ohms.  At 130V,
> that would draw 29mA and burn 3.8 watts.  Next lower 10% value is
> 3.9K, that would draw and burn 4.3 watts. I like to derate power
> resistors by 50%, so you want a 3.9K 10W resistor.

I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it 
right now that I was going to use once the relays get here.  Thats 833  
ohms which would drain it even faster than just the one.  And, somewhere 
on an undermanned galley in the pacific, is a 250 ohm 250 watt resistor 
which would do the bleed-down even faster, and the current peak would be 
nominally .5 amps in that case. I can't see that as being capable of 
welding a relay contact.


> If you do indeed have two caps in series, they ought to have balancing
> resistors anyway, so you could split the bleeder into two sections. 
> Make each section 2K or 2.2K and 5 watts.
>
That too, I was contemplating, but the 51 ohmmer would need to be 
dismounted to gain access to the pcb bus connecting them all together.  
Since I have them already 2 each of the 5k's across each bank would seem 
to be about right.  They are well discharged atm, and I could do that 
yet this afternoon.  If my math is correct, at 5k and 63.5 volts=0.80645 
watts per, so if I spread them out on the busses, the heat shouldn't 
hurt the caps.  And my existing SSR lashup would be fine when the rest 
of the parts to make a decent charge-pump-detector to drive the SSR's 
with do arrive.

I can do that yet this afternoon if I can get high enough on a ladder to 
turn the unit face up so the soldering is easy. There's a 4 footer 
currently parked 3 feet away. :) The problem is the floor real estate to 
spread it out.

> Something like this can be chassis mounted and wired to the caps:
> http://www.digikey.com/product-detail/en/RH0052K000FE02/RHRA-2.0K-ND/1
>166266 Cost is $5 each, total $10
>
> Even cheaper would be to parallel up some 1W leaded resistors:
> http://www.digikey.com/product-detail/en/PR01000101002JR500/PPC10KW-1C
>T-ND/597177 $2.06 for ten - five in parallel will make 2K 5W, put one
> set of five across each cap. Might be a nuisance to mount.
>
The cap busses are nominally a foot long, 3/8" wide 2oz copper

> If you have can type caps with screw terminals, use power resistors
> with solid axial leads, crimp/solder them to ring lugs, and mount
> right on top of the caps:
> http://www.digikey.com/product-detail/en/SQP10AJB-2K0/2.0KW-10-ND/1878
>9 $0.64 each, total $1.28
>
> I realize that Digikey might not be your supplier of choice due to
> shipping costs, but my point is that an always-on bleeder is simple,
> safe, and at this power level, cheap.  As you get to larger energy
> levels (more volts or more uF) or if you need a much faster discharge
> time you might be able to justify a switched fast bleeder.  But that
> will ALWAYS be less reliable and less safe than an always-on bleeder. 
> Even if you have a switched bleeder it would be wise to have an
> permanent bleeder with maybe a 10 minute time constant.  At 10
> minutes, the power and cost are negligible, and it serves double duty
> as the voltage balancing resistors for your series caps.
>
> Inrush limiting is a separate issue.  Separate resistor, bypassed by a
> contactor or relay for normal operation.  Put it on the AC side so you
> don't have any issues with DC contact ratings.

That is what I am doing right now with the SSR's, one to switch on the 
power thru that 51 ohm resistor, and a second SSR about 5 seconds later 
to short out the resistor.

> The main risk is that 
> if you try to run with the bypass relay open you can fry your
> resistor.  One way to avoid that is to make the "resistor" a 100W
> incandescent light bulb.

Which rigid tapping would quickly make history.  The spindle turnaround, 
even if I have it rate restricted, still pumps the supply high enough to 
blow a C7 bulb in 4 or 5 pecks.  

Re: [Emc-users] Another crazy idea?

[Bertho Stultiens]

On 01/11/2016 06:01 PM, Gene Heskett wrote:
> 1. put a small tranny delivering say 6 volts AC in series with the 
> resistor and its shorting SSR to encourage that SSR to turn off when the 
> cap voltage has dropped to 6 volts or less.

How do you connect the 6V AC without it bearing a huge (peak) current?

If you have a DC signal in it too, it will feedback into the primary.
That is a huge problem. Not to speak of the inductance.


> 2. enforce in hal, 2 delay circuits.  An on delay long enough for #1 to 
> have completed its job and the short across the resistor no longer 
> exists thru that pair of SSR's.

Enforcing a software solution is a risk. If the software fails, then you
get potentially fried? You'd normally have an electronic interlock to
prevent problems.


> 3. Time the short enable so its 5 to 10 seconds after the relay has 
> closed, and time the short disable to take place a second or so before 
> the relay is de-energized, so that SSR is off by the time the switch of 
> the resistors position in the circuit takes place. By placing another 
> timedelay in the relay control, with longer time delays than the 
> shorting time delay would enforce disconnecting the short whose 
> timedelay is set for 1 second, so the resistor is switched back into the 
> circuit well before its transferred to dump the caps duty.

The real problem of shorting the resistor are the huge peak currents.
You said that you have two 68000uF caps in series, or 34000uF
effectively on it, which suggests that you are handling an average DC
current somewhere between 30...60A.

The current peak from the rectifier, just to maintain that DC current
after the cap, is somewhere between 120...240A (estimated) and even
higher currents are possible. That will fuse most normal relays.

SSRs would probably survive is you get one and stay well below the
fusing current (specified in the I^2t parameter) and stay below the peak
current rating. However, SSRs do not like to be operated at high peak
currents for long periods.


> Does anyone have an data on how sensitive these SSR's are to a false 
> trigger from dv/dt effects applied to the output terminals?

They all have that specified in the datasheet. Most large ones are
specified at about 500V/us.


> Or do I need to use 2 of these relays with a fraction of a second between 
> them, to assure the line side SSR's have time enough to turn off? At 
> 60Hz thats 8. milliseconds after drive has been removed, and the 
> single relay could be faster than that.  All TBD when the relays arrive 
> I guess.  They haven't yet.

Well, it looks like a very complicated and rather risky setup.


-- 
Greetings Bertho

(disclaimers are disclaimed)

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Re: [Emc-users] calling Todd Z

[Todd Zuercher]

Rob,

We've been running this for a little while now and it seems to be working well 
for us.  Is there any plans to move it to the mainstream (Master or 2.7)?

- Original Message -
From: "Robert Ellenberg" 
To: "Enhanced Machine Controller (EMC)" 
Sent: Tuesday, December 1, 2015 12:31:50 PM
Subject: Re: [Emc-users] calling Todd Z

That's consistent with the changes I made, that "velocity"  from the TP's
perspective is now along the 6D path (instead of just XYZ).

Maybe we could add fields / Hal pins for different interpretations? It
wouldn't be too hard to calculate XYZ-only velocity, and report it on a
separate pin. Or, for backwards compatibility, I could tweak the status
update code so that motion only reports xyz velocity, even though
internally it uses xyzuvw.

On Tue, Dec 1, 2015, 12:14 PM Todd Zuercher  wrote:

> Ok I got to test it again today some, and here is what I've found so far.
> It looks like the g-code with Z and W are running the same as the only Z
> g-code.  The same file runs for the same amount of time both ways.
>
> However I have noticed that it looks like the velocity display on the DRO,
> is adding the velocity of the W axis to the Z, so that when milling at F80,
> the DRO will show that the velocity was more than 80.  I'm not quite sure
> how this could be corrected or if it should be.  There are configurations
> where you may want the W and Z velocities to be additive (such as a knee
> mill) but that situation might be better served by configuring it more like
> 2 joints serving the Z axis.  I don't think it would be right to just
> completely ignore the W velocity either, because there are situations where
> the machine may be using only XYW for carving instead of XYZ or XYZW.
> Maybe some way of only using the most significant velocity of the 2 (Z and
> W) in the velocity calculation, sounds like a recipe for making something
> simple (at least on the surface) into something very complicated.
>
> Again, it is only what is being shown for the velocity on the DRO that I
> think is wrong, the actual movement of the the machine looks right, and the
> run times for the files seem to confirm that.
>
> - Original Message -
> From: "Robert Ellenberg" 
> To: "Enhanced Machine Controller (EMC)" 
> Sent: Friday, November 27, 2015 10:56:44 AM
> Subject: Re: [Emc-users] calling Todd Z
>
> I just tweaked naive cam detection to handle uvw axes too. Can you guys
> give it a spin and see if it makes up the difference?
>
> -Rob
>
> On Wed, Nov 25, 2015, 4:09 PM sam sokolik  wrote:
>
> > the thing that is missing with uvy blends it the nieve cam detector
> > (combining of short line segments..)  so it will run just a bit slower.
> >
> > sam
> >
> > On 11/25/2015 12:17 PM, Todd Zuercher wrote:
> > > Just for perspective the current version of 2.7 using XYZW runs the
> file
> > below in 10min. 44sec.
> > >
> > > - Original Message -
> > > From: "Todd Zuercher" 
> > > To: "Enhanced Machine Controller (EMC)" <
> emc-users@lists.sourceforge.net
> > >
> > > Sent: Wednesday, November 25, 2015 10:17:03 AM
> > > Subject: Re: [Emc-users] calling Todd Z
> > >
> > > Seems to be working great.  I haven't found a problem XYZ and XYZW code
> > seem to run mostly the same now, but not exactly.  The first file I
> tested
> > ran in 7min. 10 sec. using only XYZ code (with the W slaved to Z) and the
> > same file using XYZW code, ran in 7min. 28sec.
> > >
> > > - Original Message -
> > > From: "Robert Ellenberg" 
> > > To: "Enhanced Machine Controller (EMC)" <
> emc-users@lists.sourceforge.net
> > >
> > > Sent: Tuesday, November 24, 2015 11:39:38 PM
> > > Subject: Re: [Emc-users] calling Todd Z
> > >
> > > Ok, i just pushed a fix for that build error, and now it seems to
> compile
> > > and run on my RTAI VM.  Also, I pushed the branch to the main linuxcnc
> > > repository for the buildbot to chew on.
> > >
> > > -Rob
> > >
> > > On Tue, Nov 24, 2015 at 4:16 PM, Robert Ellenberg 
> > wrote:
> > >
> > >> Todd,
> > >>
> > >> I'll troubleshoot the build tonight, it looks like a symbol is missing
> > in
> > >> the RT build that's available in the sim build.
> > >>
> > >> Rob
> > >>
> > >> On Tue, Nov 24, 2015, 4:09 PM Todd Zuercher 
> > >> wrote:
> > >>
> > >>> I think I forgot to do the sudo make setuid.
> > >>> did that now, and this is what it spits out.
> > >>>
> > >>> LINUXCNC - 2.7.2
> > >>> Machine configuration directory is
> > >>> '/home/digital4/linuxcnc/configs/Digital_4_ZZ'
> > >>> Machine configuration file is 'Digital_4w.ini'
> > >>> Starting LinuxCNC...
> > >>> insmod: can't read '/home/digital4/linuxcnc-uvw/rtlib/rtapi.ko': No
> > such
> > >>> file or directory
> > >>> Realtime system did not load
> > >>> Shutting down and cleaning up 

Re: [Emc-users] Another crazy idea?

[John Kasunich]

On Mon, Jan 11, 2016, at 02:00 PM, Gene Heskett wrote:
> On Monday 11 January 2016 13:10:10 John Kasunich wrote:
> 
> > SSRs can fail shorted, I don't think this buys you much in terms of
> > reliability and safety.
> >
> > I think there is a little over-kill going on.
> >
> > Do you really need a fast bleeder (<1 minute to safe)?  Or would a
> > five minute bleeder be OK?
> >
> > My understanding is that you have two 68000uF caps in series, charged
> > to about 130V. (If this is incorrect let me know - the thread is long
> > and rambling and refers to other thread.  I'm basing this on something
> > written in the first message of this particular thread.)
> 
> Actually 10 6800 u-f in parallel, working at their labeled 63 volts 
> ratings.
> 
> But yes, you have the right idea. :)
> >
> > Series caps divide, so you have 34000uF.  Let's say that "safe" is
> > 20V.  So you need to discharge from 130V to 20V, that is to 15% of the
> > original voltage.  Ln(0.15) is -1.9, so it takes 1.9 RC time constants
> > to get to a safe voltage.  Call it 2.0 for easy math.  If you want to
> > get there in 5 minutes, then one time constant is 2.5 minutes = 150
> > seconds. T = RC, solve for R, gives you R = T/C = 4411 ohms.  At 130V,
> > that would draw 29mA and burn 3.8 watts.  Next lower 10% value is
> > 3.9K, that would draw and burn 4.3 watts. I like to derate power
> > resistors by 50%, so you want a 3.9K 10W resistor.
> 
> I actually have, atm, 6 ea 5k 10 watters in parallel clipped onto it 
> right now that I was going to use once the relays get here.  Thats 833  
> ohms which would drain it even faster than just the one. 

The 5K's are across the entire bus, or across each cap?

If across the entire bus, 130V would result in 3.38 watts per resistor. 
Less than the 5W rating, but more than half the rating, which is the derate
I like to use to keep things from getting too hot and ensure long life.

I'd suggest 3 of the 5K across each side of the bus.  At 65V across 5K
each resistor would be running at 0.85W, nice and cool.  Total resistance
of the 3-parallel 2-series arrangement would be 3.33K, RC time constant
113 seconds, bleed-down time from 130V to 20V = 212 seconds = 3.5
minutes.  And free voltage balancing between the two sets of caps.

> And, somewhere 
> on an undermanned galley in the pacific, is a 250 ohm 250 watt resistor 
> which would do the bleed-down even faster, and the current peak would be 
> nominally .5 amps in that case. I can't see that as being capable of 
> welding a relay contact.

Making 0.5A probably won't weld any contacts.  Breaking 0.5A DC on
a relay designed for AC is another story.  And keep in mind that contact
bounce = breaking and making.

I'm just not a big believer in switched bleeders.  Significant hassle and
risk.  If fixed bleeders can meet your discharge time requirements, call
it good and move on.

Context - I design large motor drives for a living.  The vast majority 
used permanent bleeders only.  One recent design does augment them
with a switched bleeder.  But that drive has 90 caps, each rated 6800uF
400V, in a 30-parallel by 3-series array, total of 68000uF.  Nominal bus
voltage is 975V DC.  Stored energy is 32 kilo-joules.  UL requires that
it discharge below 50V in five minutes.  The fixed bleeders would do it
in 10.5 minutes, so we added a switched bleeder to help it along.

Your unit has 34000uF at 130V, for a stored energy of 287 joules.
 
> > If you do indeed have two caps in series, they ought to have balancing
> > resistors anyway, so you could split the bleeder into two sections. 
> > Make each section 2K or 2.2K and 5 watts.
> >
> That too, I was contemplating, but the 51 ohmmer would need to be 
> dismounted to gain access to the pcb bus connecting them all together.  
> Since I have them already 2 each of the 5k's across each bank would seem 
> to be about right.  They are well discharged atm, and I could do that 
> yet this afternoon.  If my math is correct, at 5k and 63.5 volts=0.80645 
> watts per, so if I spread them out on the busses, the heat shouldn't 
> hurt the caps.  

Agreed.  But why not use all 6 of the 5K?

> >
> > Inrush limiting is a separate issue.  Separate resistor, bypassed by a
> > contactor or relay for normal operation.  Put it on the AC side so you
> > don't have any issues with DC contact ratings.
> 
> That is what I am doing right now with the SSR's, one to switch on the 
> power thru that 51 ohm resistor, and a second SSR about 5 seconds later 
> to short out the resistor.
> 
> > The main risk is that 
> > if you try to run with the bypass relay open you can fry your
> > resistor.  One way to avoid that is to make the "resistor" a 100W
> > incandescent light bulb.
> 
> Which rigid tapping would quickly make history.  The spindle turnaround, 
> even if I have it rate restricted, still pumps the supply high enough to 
> blow a C7 bulb in 4 or 5 pecks.  Jon's pwm servo amp is effectively a 
> full 4 quadrant controller, so it dumps