Re: [EVDL] Question about charging small LiIon batteries

[Lee Hart via EV]

Justin Kenny via EV wrote:

Not sure if you understood the previous 2 messages, the Zener diode will
drain your battery, and a diode will not stop it from overcharging. I
really suggest to use the right tool for the job, $3.25 for a
constant-current constant-voltage converter isn't much cost to save your
battery pack from being killed prematurely, or at worst preventing a
fire/destruction by overcharging:  https://www.amazon.com/dp/B00LPK0IKQ


I think we got it, Justin. My suggestion is to use *two* diodes; a zener 
across the PV panel (to clamp its maximum voltage), and a series diode 
between them and the battery to charge. Schematic (view it with a 
fixed-width font like Courier. Periods are just to stop your browser 
from removing the blanks):


+ --o--|>|--- +
| . . . | . . . . . . . . |
PV. . zener . blocking. . Li
panel diode . .diode. . .cell
| . . . | . . . . . . . . |
- --0 -

If you choose the right diodes, it guarantees the Li cell can't go 
overvoltage even in full sun when fully charged. And, it guarantees the 
battery current is zero when there is no sun (won't discharge the battery).


Of course you can design more complicated circuits that work better. But 
sometimes the "perfect" is the enemy of the "good enough".


Lee Hart

--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Lee Hart via EV]

jkenny23 via EV wrote:

Another very important note; diodes don't drop voltage the same at all
current levels. Meaning; they will NOT stop your 4.5V panel from
overcharging your battery to 4.5V if you don't have a dedicated charging IC.

If you want to charge your battery to an unusual voltage, I highly recommend
using an adjustable CC/CV (constant-current/constant-voltage) buck
converter. They're widely available from China on eBay and Aliexpress, and
probably available from the US through Amazon. This way you can set a safe
current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
3.9 or 4.0V). Then you could even use multiple panels in series and not
worry about charging, the input limit for the common LM2596 modules is 35V.

Here's some data for a common 1N5819 Schottky diode illustrating the issue
of voltage drop as current tapers down at the end of charging:
1.0A - 0.41V
0.5A - 0.35V
0.1A - 0.28V
20mA - 0.23V


Yes; diodes are far from "perfect" regulators. But they are predictable 
and reliable (if not misused).


A cheap buck converter will have better regulation; but it will also 
have lots more failure modes. It will also drain the battery when the PV 
panel is not supplying power. The whole point of a series diode is to 
prevent this.


Batteries don't require precision regulation. The 0.2v change for a 50:1 
change in current is pretty good... maybe good enough for Peter's 
application? That's what testing is for. :-)


Lee Hart

--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Justin Kenny via EV]

I've had pretty bad luck with MP2307 boards, a lot of them that I use are
defective. The LM2596 boards I've used have all worked however, they use
the much better 10-turn potentiometers. You could try and replace the
variable resistor with your own potentiometer or fixed one, it is a bit of
a challenging rework since it's such a small SMD part. It won't have any
current limiting either so it might not work very well, but I guess it's
better than diodes.

- Justin

On Tue, Jun 2, 2020 at 9:05 PM  wrote:

> Justin Kenny's suggestion earlier reminded me of something, so I went
> looking through my spare parts and found some regulators boards that have
> variable MP2307 regulators. I originally got them to use with 3.3V
> microcontrollers, but never used them because they have flaky outputs. I'm
> pretty sure the problem with them is the cheap variable resistors, I think
> if I replace those with a fixed voltage divider they might be ok.
>
>
> However, I think the problem with them is the cheap variable resistors
> they use
> June 2, 2020 6:30 PM, justin.sout...@xtra.co.nz wrote:
>
> Peter,
> Can i suggest a lm723 voltage regulator configured as a shunt regulator. I
> have used the datasheet design with solar panels. Lee may be able to
> recommend a better design than the barebones design in the datasheet. As
> the solar panel is a current source of limited output you could probably
> forgo the load resistor and simply dump all the excess energy into a large
> enough power transistor. The standby current of the device is typically
> 1.7ma with 30v source according to the datasheet so id expect it to be
> lower in your application. The addition of an output diode would disconnect
> the reg once the solar input was removed.
> Regards,
> Justin
> On Jun 3, 2020 10:58, Peter VanDerWal via EV  wrote:
>
> Yes, Lee has already pointed this out, so I am looking into putting the
> zener in parallel to the PV panel and then a schottky, etc. in series to
> the battery.
>
> The problem I have with the cheap CV/CC circuits from china is that in my
> experience they have a high failure rate and, just like buttered toast, the
> failures tend to happen in the worst possible mode.
>
> June 2, 2020 3:17 PM, "Justin Kenny"  jkenn...@gmail.com?to=%22Justin%20Kenny%22%20)> wrote:
> Not sure if you understood the previous 2 messages, the Zener diode will
> drain your battery, and a diode will not stop it from overcharging. I
> really suggest to use the right tool for the job, $3.25 for a
> constant-current constant-voltage converter isn't much cost to save your
> battery pack from being killed prematurely, or at worst preventing a
> fire/destruction by overcharging: https://www.amazon.com/dp/B00LPK0IKQ (
> https://www.amazon.com/dp/B00LPK0IKQ)
> - Justin
> On Tue, Jun 2, 2020 at 2:57 PM  e...@vanderwal.us)> wrote: I'm thinking of using two panels, one tilted
> 45 degs to the east, and the other tilted 45 deg to
> the west. That should provide a fairly flat power output through the day
> with something like .375
> ma max. If I put a 4.3V zener across the panel, then that should bypass
> some of the current, so I should only see a swing from perhaps 0.2V to 0.3V
> and the 0.2V will likely occur when the panel voltage is lower.
> At any rate a 0.1V variation is close enough for my purposes.
> I've got a selection of diodes on order, so I'll see what happens when I
> test it on the bench.
>
> Pete.
>
> June 2, 2020 1:51 PM, "jkenny23 via EV"  ev@lists.evdl.org)> wrote:
>
> > Another very important note; diodes don't drop voltage the same at all
> > current levels. Meaning; they will NOT stop your 4.5V panel from
> > overcharging your battery to 4.5V if you don't have a dedicated charging
> IC.
> >
> > If you want to charge your battery to an unusual voltage, I highly
> recommend
> > using an adjustable CC/CV (constant-current/constant-voltage) buck
> > converter. They're widely available from China on eBay and Aliexpress,
> and
> > probably available from the US through Amazon. This way you can set a
> safe
> > current limit (say 400mA), and a voltage limit that is lower than 4.2V
> (say
> > 3.9 or 4.0V). Then you could even use multiple panels in series and not
> > worry about charging, the input limit for the common LM2596 modules is
> 35V.
> >
> > Here's some data for a common 1N5819 Schottky diode illustrating the
> issue
> > of voltage drop as current tapers down at the end of charging:
> > 1.0A - 0.41V
> > 0.5A - 0.35V
> > 0.1A - 0.28V
> > 20mA - 0.23V
> >
> > --
> > Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com
> (http://electric-vehicle-discussion-list.413529.n4.nabble.com)
> > ___
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub (
> http://www.evdl.org/help/index.html#usub)
> > ARCHIVE: http://www.evdl.org/archive/index.html (
> http://www.evdl.org/archive/index.html)
> > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org (
> 

Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Justin Kenny's suggestion earlier reminded me of something, so I went looking 
through my spare parts and found some regulators boards that have variable 
MP2307 regulators. I originally got them to use with 3.3V microcontrollers, but 
never used them because they have flaky outputs. I'm pretty sure the problem 
with them is the cheap variable resistors, I think if I replace those with a 
fixed voltage divider they might be ok.
However, I think the problem with them is the cheap variable resistors they use 
June 2, 2020 6:30 PM, justin.sout...@xtra.co.nz 
(mailto:justin.sout...@xtra.co.nz) wrote:
 Peter, Can i suggest a lm723 voltage regulator configured as a shunt 
regulator. I have used the datasheet design with solar panels. Lee may be able 
to recommend a better design than the barebones design in the datasheet. As the 
solar panel is a current source of limited output you could probably forgo the 
load resistor and simply dump all the excess energy into a large enough power 
transistor. The standby current of the device is typically 1.7ma with 30v 
source according to the datasheet so id expect it to be lower in your 
application. The addition of an output diode would disconnect the reg once the 
solar input was removed.  Regards,  Justin   
On Jun 3, 2020 10:58, Peter VanDerWal via EV mailto:ev@lists.evdl.org)> wrote:
Yes, Lee has already pointed this out, so I am looking into putting the 
zener in parallel to the PV panel and then a schottky, etc. in series to the 
battery.

The problem I have with the cheap CV/CC circuits from china is that in my 
experience they have a high failure rate and, just like buttered toast, the 
failures tend to happen in the worst possible mode.

June 2, 2020 3:17 PM, "Justin Kenny" mailto:jkenn...@gmail.com) (mailto:jkenn...@gmail.com 
(mailto:jkenn...@gmail.com)?to=%22Justin%20Kenny%22%20mailto:jkenn...@gmail.com)>)> wrote:
Not sure if you understood the previous 2 messages, the Zener diode will drain 
your battery, and a diode will not stop it from overcharging. I really suggest 
to use the right tool for the job, $3.25 for a constant-current 
constant-voltage converter isn't much cost to save your battery pack from being 
killed prematurely, or at worst preventing a fire/destruction by overcharging: 
https://www.amazon.com/dp/B00LPK0IKQ (https://www.amazon.com/dp/B00LPK0IKQ) 
(https://www.amazon.com/dp/B00LPK0IKQ (https://www.amazon.com/dp/B00LPK0IKQ))
- Justin
On Tue, Jun 2, 2020 at 2:57 PM mailto:e...@vanderwal.us) 
(mailto:e...@vanderwal.us (mailto:e...@vanderwal.us))> wrote: I'm thinking of 
using two panels, one tilted 45 degs to the east, and the other tilted 45 deg to
the west. That should provide a fairly flat power output through the day with 
something like .375
ma max. If I put a 4.3V zener across the panel, then that should bypass some of 
the current, so I should only see a swing from perhaps 0.2V to 0.3V and the 
0.2V will likely occur when the panel voltage is lower.
At any rate a 0.1V variation is close enough for my purposes.
I've got a selection of diodes on order, so I'll see what happens when I test 
it on the bench.

Pete.

June 2, 2020 1:51 PM, "jkenny23 via EV" mailto:ev@lists.evdl.org) (mailto:ev@lists.evdl.org 
(mailto:ev@lists.evdl.org))> wrote:

> Another very important note; diodes don't drop voltage the same at all
> current levels. Meaning; they will NOT stop your 4.5V panel from
> overcharging your battery to 4.5V if you don't have a dedicated charging IC.
>
> If you want to charge your battery to an unusual voltage, I highly recommend
> using an adjustable CC/CV (constant-current/constant-voltage) buck
> converter. They're widely available from China on eBay and Aliexpress, and
> probably available from the US through Amazon. This way you can set a safe
> current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
> 3.9 or 4.0V). Then you could even use multiple panels in series and not
> worry about charging, the input limit for the common LM2596 modules is 35V.
>
> Here's some data for a common 1N5819 Schottky diode illustrating the issue
> of voltage drop as current tapers down at the end of charging:
> 1.0A - 0.41V
> 0.5A - 0.35V
> 0.1A - 0.28V
> 20mA - 0.23V
>
> --
> Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com 
> (http://electric-vehicle-discussion-list.413529.n4.nabble.com) 
> (http://electric-vehicle-discussion-list.413529.n4.nabble.com 
> (http://electric-vehicle-discussion-list.413529.n4.nabble.com))
> ___
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> (http://www.evdl.org/help/index.html#usub))
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Re: [EVDL] Question about charging small LiIon batteries

[Justin Southam via EV]

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Re: [EVDL] Question about charging small LiIon batteries

[Robert Bruninga via EV]

I agree.  I needed a 2.5v zener reference voltage (half way on a 5v
system).  It took a 3.9v zener to get the 2.5v I needed when biasing it
with something like a 10k resistor...  Bob

-Original Message-
From: EV  On Behalf Of Lee Hart via EV
Sent: Tuesday, June 2, 2020 4:10 PM
To: Electric Vehicle Discussion List 
Cc: Lee Hart 
Subject: Re: [EVDL] Question about charging small LiIon batteries

Peter VanDerWal via EV wrote:
> Wouldn't it be better to have a 3.9V zener across the battery?
> Unless thay have leakage current when off?
>
> If I'm going to put it across the panel then I'd probably want a 4.3V
> zener, and then drop ~0.4V between the panel and the battery?
>
> The result doesn't have to be precisely 3.9V on the battery, just
> somewhere in that neighborhood.

(Warning: Technical discussion to follow. May cause drowsiness...)

True zener diodes only exist below about 6 volts. True zeners have a large
change in their zener voltage versus current. For example, a
1N5335 3.9v 5-watt zener will measure about:

5.1v at 1200ma
4.5v at 600ma
3.9v at 300ma <-- rated current
3.5v at 150ma
3.0v at 50ma
1.0v at 0.3ma

In other words, it draws a *lot* of current even well below its zener
voltage. If connected right across a lithium cell, it would soon discharge
it below 1.0v, and murder it.

In contrast, "zeners" above 6v are in fact "avalance" diodes. A different
mechanism defines their threshold voltage, and they have a far more stable
voltage versus current. For example, a 1N5342 6.8v 5w zener will measure
about:

7.15v at 700ma
6.95v at 350ma
6.8v at 175ma <-- rated current
6.6v at 60ma
4.9v at 0.01ma

Notice that the voltage changes far less with current, and becomes
insignificant (10uA) below 5v.

In between the two (5-6v range), the characteristics gradually transition
from one behavior to the other. That's why you have to "test"
and pick the best parts for the job.

This means you want to use a higher-voltage "avalanche" diode across the
PV panel to limit its max voltage; then knock this down to the desired
cell voltage (and block reverse current) with 1 or more series diodes.

Lee Hart
--
When something bad happens, you have three choices: You can let it define
you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Justin Kenny via EV]

Suit yourself, I hope you are using protected 18650 cells. If not please
use one of these to protect the batteries from overcharging/undervoltage:
https://www.amazon.com/dp/B07KSPYMJ2

- Justin

On Tue, Jun 2, 2020 at 3:58 PM  wrote:

> Yes, Lee has already pointed this out, so I am looking into putting the
> zener in parallel to the PV panel and then a schottky, etc. in series to
> the battery.
>
> The problem I have with the cheap CV/CC circuits from china is that in my
> experience they have a high failure rate and, just like buttered toast, the
> failures tend to happen in the worst possible mode.
>
> June 2, 2020 3:17 PM, "Justin Kenny"  >
> wrote:
>
> Not sure if you understood the previous 2 messages, the Zener diode will
> drain your battery, and a diode will not stop it from overcharging. I
> really suggest to use the right tool for the job, $3.25 for a
> constant-current constant-voltage converter isn't much cost to save your
> battery pack from being killed prematurely, or at worst preventing a
> fire/destruction by overcharging: https://www.amazon.com/dp/B00LPK0IKQ
> - Justin
> On Tue, Jun 2, 2020 at 2:57 PM  wrote:
>
> I'm thinking of using two panels, one tilted 45 degs to the east, and the
> other tilted 45 deg to
> the west. That should provide a fairly flat power output through the day
> with something like .375
> ma max. If I put a 4.3V zener across the panel, then that should bypass
> some of the current, so I should only see a swing from perhaps 0.2V to 0.3V
> and the 0.2V will likely occur when the panel voltage is lower.
> At any rate a 0.1V variation is close enough for my purposes.
> I've got a selection of diodes on order, so I'll see what happens when I
> test it on the bench.
>
> Pete.
>
> June 2, 2020 1:51 PM, "jkenny23 via EV"  wrote:
>
> > Another very important note; diodes don't drop voltage the same at all
> > current levels. Meaning; they will NOT stop your 4.5V panel from
> > overcharging your battery to 4.5V if you don't have a dedicated charging
> IC.
> >
> > If you want to charge your battery to an unusual voltage, I highly
> recommend
> > using an adjustable CC/CV (constant-current/constant-voltage) buck
> > converter. They're widely available from China on eBay and Aliexpress,
> and
> > probably available from the US through Amazon. This way you can set a
> safe
> > current limit (say 400mA), and a voltage limit that is lower than 4.2V
> (say
> > 3.9 or 4.0V). Then you could even use multiple panels in series and not
> > worry about charging, the input limit for the common LM2596 modules is
> 35V.
> >
> > Here's some data for a common 1N5819 Schottky diode illustrating the
> issue
> > of voltage drop as current tapers down at the end of charging:
> > 1.0A - 0.41V
> > 0.5A - 0.35V
> > 0.1A - 0.28V
> > 20mA - 0.23V
> >
> > --
> > Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com
> > ___
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> > ARCHIVE: http://www.evdl.org/archive/index.html
> > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> > Please discuss EV drag racing at NEDRA (
> http://groups.yahoo.com/group/NEDRA)
>
>
>
>
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Yes, Lee has already pointed this out, so I am looking into putting the zener 
in parallel to the PV panel and then a schottky, etc. in series to the battery.

The problem I have with the cheap CV/CC circuits from china is that in my 
experience they have a high failure rate and, just like buttered toast, the 
failures tend to happen in the worst possible mode.

June 2, 2020 3:17 PM, "Justin Kenny" mailto:jkenn...@gmail.com?to=%22Justin%20Kenny%22%20)> 
wrote:
 Not sure if you understood the previous 2 messages, the Zener diode will drain 
your battery, and a diode will not stop it from overcharging. I really suggest 
to use the right tool for the job, $3.25 for a constant-current 
constant-voltage converter isn't much cost to save your battery pack from being 
killed prematurely, or at worst preventing a fire/destruction by overcharging: 
https://www.amazon.com/dp/B00LPK0IKQ (https://www.amazon.com/dp/B00LPK0IKQ)
- Justin  
 On Tue, Jun 2, 2020 at 2:57 PM mailto:e...@vanderwal.us)> 
wrote: I'm thinking of using two panels, one tilted 45 degs to the east, and 
the other tilted 45 deg to
the west. That should provide a fairly flat power output through the day with 
something like .375
ma max. If I put a 4.3V zener across the panel, then that should bypass some of 
the current, so I should only see a swing from perhaps 0.2V to 0.3V and the 
0.2V will likely occur when the panel voltage is lower.
At any rate a 0.1V variation is close enough for my purposes.
I've got a selection of diodes on order, so I'll see what happens when I test 
it on the bench.

Pete.

June 2, 2020 1:51 PM, "jkenny23 via EV" mailto:ev@lists.evdl.org)> wrote:

> Another very important note; diodes don't drop voltage the same at all
> current levels. Meaning; they will NOT stop your 4.5V panel from
> overcharging your battery to 4.5V if you don't have a dedicated charging IC.
>
> If you want to charge your battery to an unusual voltage, I highly recommend
> using an adjustable CC/CV (constant-current/constant-voltage) buck
> converter. They're widely available from China on eBay and Aliexpress, and
> probably available from the US through Amazon. This way you can set a safe
> current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
> 3.9 or 4.0V). Then you could even use multiple panels in series and not
> worry about charging, the input limit for the common LM2596 modules is 35V.
>
> Here's some data for a common 1N5819 Schottky diode illustrating the issue
> of voltage drop as current tapers down at the end of charging:
> 1.0A - 0.41V
> 0.5A - 0.35V
> 0.1A - 0.28V
> 20mA - 0.23V
>
> --
> Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com 
> (http://electric-vehicle-discussion-list.413529.n4.nabble.com)
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Re: [EVDL] Question about charging small LiIon batteries

[Justin Kenny via EV]

Not sure if you understood the previous 2 messages, the Zener diode will
drain your battery, and a diode will not stop it from overcharging. I
really suggest to use the right tool for the job, $3.25 for a
constant-current constant-voltage converter isn't much cost to save your
battery pack from being killed prematurely, or at worst preventing a
fire/destruction by overcharging:  https://www.amazon.com/dp/B00LPK0IKQ

- Justin

On Tue, Jun 2, 2020 at 2:57 PM  wrote:

> I'm thinking of using two panels, one tilted 45 degs to the east, and the
> other tilted 45 deg to
> the west. That should provide a fairly flat power output through the day
> with something like .375
> ma max. If I put a 4.3V zener across the panel, then that should bypass
> some of the current, so I should only see a swing from perhaps 0.2V to 0.3V
> and the 0.2V will likely occur when the panel voltage is lower.
> At any rate a 0.1V variation is close enough for my purposes.
> I've got a selection of diodes on order, so I'll see what happens when I
> test it on the bench.
>
> Pete.
>
> June 2, 2020 1:51 PM, "jkenny23 via EV"  wrote:
>
> > Another very important note; diodes don't drop voltage the same at all
> > current levels. Meaning; they will NOT stop your 4.5V panel from
> > overcharging your battery to 4.5V if you don't have a dedicated charging
> IC.
> >
> > If you want to charge your battery to an unusual voltage, I highly
> recommend
> > using an adjustable CC/CV (constant-current/constant-voltage) buck
> > converter. They're widely available from China on eBay and Aliexpress,
> and
> > probably available from the US through Amazon. This way you can set a
> safe
> > current limit (say 400mA), and a voltage limit that is lower than 4.2V
> (say
> > 3.9 or 4.0V). Then you could even use multiple panels in series and not
> > worry about charging, the input limit for the common LM2596 modules is
> 35V.
> >
> > Here's some data for a common 1N5819 Schottky diode illustrating the
> issue
> > of voltage drop as current tapers down at the end of charging:
> > 1.0A - 0.41V
> > 0.5A - 0.35V
> > 0.1A - 0.28V
> > 20mA - 0.23V
> >
> > --
> > Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com
> > ___
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>
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

I'm thinking of using two panels, one tilted 45 degs to the east, and the other 
tilted 45 deg to
the west. That should provide a fairly flat power output through the day with 
something like .375
ma max. If I put a 4.3V zener across the panel, then that should bypass some of 
the current, so I should only see a swing from perhaps 0.2V to 0.3V and the 
0.2V will likely occur when the panel voltage is lower.
At any rate a 0.1V variation is close enough for my purposes.  
I've got a selection of diodes on order, so I'll see what happens when I test 
it on the bench.

Pete.

June 2, 2020 1:51 PM, "jkenny23 via EV"  wrote:

> Another very important note; diodes don't drop voltage the same at all
> current levels. Meaning; they will NOT stop your 4.5V panel from
> overcharging your battery to 4.5V if you don't have a dedicated charging IC.
> 
> If you want to charge your battery to an unusual voltage, I highly recommend
> using an adjustable CC/CV (constant-current/constant-voltage) buck
> converter. They're widely available from China on eBay and Aliexpress, and
> probably available from the US through Amazon. This way you can set a safe
> current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
> 3.9 or 4.0V). Then you could even use multiple panels in series and not
> worry about charging, the input limit for the common LM2596 modules is 35V.
> 
> Here's some data for a common 1N5819 Schottky diode illustrating the issue
> of voltage drop as current tapers down at the end of charging:
> 1.0A - 0.41V
> 0.5A - 0.35V
> 0.1A - 0.28V
> 20mA - 0.23V
> 
> --
> Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Thanks Lee, I'd just about figured that out by looking at data sheets. :-)



> True zener diodes only exist below about 6 volts. True zeners have a large 
> change in their zener
> voltage versus current. For example, a 1N5335 3.9v 5-watt zener will measure 
> about:
> 
> 5.1v at 1200ma
> 4.5v at 600ma
> 3.9v at 300ma <-- rated current
> 3.5v at 150ma
> 3.0v at 50ma
> 1.0v at 0.3ma
> 
> In other words, it draws a *lot* of current even well below its zener 
> voltage. If connected right
> across a lithium cell, it would soon discharge it below 1.0v, and murder it.
> 
> In contrast, "zeners" above 6v are in fact "avalance" diodes. A different 
> mechanism defines their
> threshold voltage, and they have a far more stable voltage versus current. 
> For example, a 1N5342
> 6.8v 5w zener will measure about:
> 
> 7.15v at 700ma
> 6.95v at 350ma
> 6.8v at 175ma <-- rated current
> 6.6v at 60ma
> 4.9v at 0.01ma
> 
> Notice that the voltage changes far less with current, and becomes 
> insignificant (10uA) below 5v.
> 
> In between the two (5-6v range), the characteristics gradually transition 
> from one behavior to the
> other. That's why you have to "test" and pick the best parts for the job.
> 
> This means you want to use a higher-voltage "avalanche" diode across the PV 
> panel to limit its max
> voltage; then knock this down to the desired cell voltage (and block reverse 
> current) with 1 or
> more series diodes.
> 
> Lee Hart
> -- When something bad happens, you have three choices: You can let it
> define you; let it destroy you; or you can let it strengthen you.
> -- Theodor Seuss Geisel
> --
> Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[jkenny23 via EV]

Another very important note; diodes don't drop voltage the same at all
current levels. Meaning; they will NOT stop your 4.5V panel from
overcharging your battery to 4.5V if you don't have a dedicated charging IC. 

If you want to charge your battery to an unusual voltage, I highly recommend
using an adjustable CC/CV (constant-current/constant-voltage) buck
converter. They're widely available from China on eBay and Aliexpress, and
probably available from the US through Amazon. This way you can set a safe
current limit (say 400mA), and a voltage limit that is lower than 4.2V (say
3.9 or 4.0V). Then you could even use multiple panels in series and not
worry about charging, the input limit for the common LM2596 modules is 35V.

Here's some data for a common 1N5819 Schottky diode illustrating the issue
of voltage drop as current tapers down at the end of charging:
1.0A - 0.41V
0.5A - 0.35V
0.1A - 0.28V
20mA - 0.23V


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Re: [EVDL] Question about charging small LiIon batteries

[Lee Hart via EV]

Peter VanDerWal via EV wrote:

Wouldn't it be better to have a 3.9V zener across the battery?
Unless thay have leakage current when off?

If I'm going to put it across the panel then I'd probably want a 4.3V
zener, and then drop ~0.4V between the panel and the battery?

The result doesn't have to be precisely 3.9V on the battery, just
somewhere in that neighborhood.


(Warning: Technical discussion to follow. May cause drowsiness...)

True zener diodes only exist below about 6 volts. True zeners have a 
large change in their zener voltage versus current. For example, a 
1N5335 3.9v 5-watt zener will measure about:


5.1v at 1200ma
4.5v at 600ma
3.9v at 300ma <-- rated current
3.5v at 150ma
3.0v at 50ma
1.0v at 0.3ma

In other words, it draws a *lot* of current even well below its zener 
voltage. If connected right across a lithium cell, it would soon 
discharge it below 1.0v, and murder it.


In contrast, "zeners" above 6v are in fact "avalance" diodes. A 
different mechanism defines their threshold voltage, and they have a far 
more stable voltage versus current. For example, a 1N5342 6.8v 5w zener 
will measure about:


7.15v at 700ma
6.95v at 350ma
6.8v at 175ma <-- rated current
6.6v at 60ma
4.9v at 0.01ma

Notice that the voltage changes far less with current, and becomes 
insignificant (10uA) below 5v.


In between the two (5-6v range), the characteristics gradually 
transition from one behavior to the other. That's why you have to "test" 
and pick the best parts for the job.


This means you want to use a higher-voltage "avalanche" diode across the 
PV panel to limit its max voltage; then knock this down to the desired 
cell voltage (and block reverse current) with 1 or more series diodes.


Lee Hart
--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Wouldn't it be better to have a 3.9V zener across the battery?  Unless thay 
have leakage current when off?

If I'm going to put it across the panel then I'd probably want a 4.3V zener, 
and then drop ~0.4V between the panel and the battery?

The result doesn't have to be precisely 3.9V on the battery, just somewhere in 
that neighborhood.

-Pete.

June 2, 2020 11:17 AM, "Lee Hart via EV"  wrote:

> Peter VanDerWal via EV wrote:
> 
>> Correction, My panels have 2x12 cells. ~5.5V at VMP, ~7V VOC
>> 
>> Now that I think about it, I don't think just using diodes will work. The 
>> VMP and VOC are two far
>> about to make it practical.
> 
> How about a zener diode across the panel to limit its peak voltage? Then a 
> series diode (needed
> anyway) between it and the Li cell?
> 
> The zener would need a high enough power rating to "dump" the output current 
> of the PV panel in
> full sun. 5w zeners are easy to get; a 5.1v 5w zener could safely shunt about 
> 500ma (de-rated 2:1
> for long life).
> 
> You'd have to play with parts to find the right combination.
> 
> Lee Hart
> 
> -- When something bad happens, you have three choices: You can let it
> define you; let it destroy you; or you can let it strengthen you.
> -- Theodor Seuss Geisel
> --
> Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Lee Hart via EV]

Peter VanDerWal via EV wrote:

Correction, My panels have 2x12 cells.   ~5.5V at VMP, ~7V VOC

Now that I think about it, I don't think just using diodes will work.  The VMP 
and VOC are two far about to make it practical.


How about a zener diode across the panel to limit its peak voltage? Then 
a series diode (needed anyway) between it and the Li cell?


The zener would need a high enough power rating to "dump" the output 
current of the PV panel in full sun. 5w zeners are easy to get; a 5.1v 
5w zener could safely shunt about 500ma (de-rated 2:1 for long life).


You'd have to play with parts to find the right combination.

Lee Hart

--
When something bad happens, you have three choices: You can let it
define you; let it destroy you; or you can let it strengthen you.
-- Theodor Seuss Geisel
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Correction, My panels have 2x12 cells.   ~5.5V at VMP, ~7V VOC

Now that I think about it, I don't think just using diodes will work.  The VMP 
and VOC are two far about to make it practical.

June 2, 2020 10:20 AM, "Peter VanDerWal via EV"  wrote:

> Now why didn't I think of that? 
> The chargers I've been looking at have MPTT(or at least they claim to), 
> however I could just use
> two panels.
> 
> I have a couple dozen panels left over from an abandoned project: 5V @ 240ma, 
> they have conformal
> coating so reducing them to 5 cells instead of 6 would be difficult.
> However, I could run a couple diodes in series...
> 
> June 2, 2020 10:02 AM, "Matt via EV"  wrote:
> 
>> What about no charge control, a solar panel whose Voc is 4.5v (so only 5 
>> series cells) and a
>> schotkey diode to prevent back flow
>> 
>> That would have the effect of limiting max voltage to ~4.2v, but at 4v only 
>> around 20% of Imp would
>> flow (ie charge rate slows right down past 3.6v)
>> 
>> How much power are you thinking?
>> 
>> Sent from Mail for Windows 10
>> 
>> From: Peter VanDerWal via EV
>> Sent: Wednesday, 3 June 2020 12:55 AM
>> To: Electric Vehicle Discussion List
>> Cc: e...@vanderwal.us
>> Subject: [EVDL] Question about charging small LiIon batteries
>> 
>> Somewhat off topic, but I'm hoping someone can help.
>> 
>> I'm building a solar powered weather station and plan to use 1 or 2 18650 
>> cells. There are tons of
>> small solar chargers available for these, however they all charge the cells 
>> to ~4.2V.
>> To maximize life from the LiIon batteries I'd like to keep them between 
>> 40-80% charged.
>> 
>> So what I'm looking for is either a solar module that I can set to only 
>> charge the cells to ~3.9V
>> or a way to make a 4.2V charger work.
>> Since I'm not having any luck finding 3.9V chargers what I've been thinking 
>> about is perhaps using
>> a schottky diode to drop the 4.2V to around 3.9V. however that would prevent 
>> the charger from
>> seeing voltage from the battery and it might not start charging.
>> So I'm thinking maybe putting a 100 ohm resistor in parrel with the diode, 
>> that would allow the
>> charger to see the battery voltage.
>> I still have to figure out how much current the microcontrollers, etc. will 
>> draw, but it's going to
>> be at least 10 mA when idle, with bursts up to several hundred ma when 
>> transmitting.
>> 
>> Does this sound like a reasonable plan? Any better suggestions?
>> 
>> Thanks, Pete.
>> -- next part --
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Re: [EVDL] Question about charging small LiIon batteries

[Matt via EV]

A silicone diode instead of a schotkey would probably do it, though voltage may 
be a little on the high side if you’re expecting the panel to be very cold when 
the battery is full

Sent from Mail for Windows 10

From: Peter VanDerWal via EV
Sent: Wednesday, 3 June 2020 1:21 AM
To: Electric Vehicle Discussion List
Cc: e...@vanderwal.us
Subject: Re: [EVDL] Question about charging small LiIon batteries

Now why didn't I think of that?  
The chargers I've been looking at have MPTT(or at least they claim to), however 
I could just use two panels.

I have a couple dozen panels left over from an abandoned project: 5V @ 240ma, 
they have conformal coating so reducing them to 5 cells instead of 6 would be 
difficult.
However, I could run a couple diodes in series...

June 2, 2020 10:02 AM, "Matt via EV"  wrote:

> What about no charge control, a solar panel whose Voc is 4.5v (so only 5 
> series cells) and a
> schotkey diode to prevent back flow
> 
> That would have the effect of limiting max voltage to ~4.2v, but at 4v only 
> around 20% of Imp would
> flow (ie charge rate slows right down past 3.6v)
> 
> How much power are you thinking?
> 
> Sent from Mail for Windows 10
> 
> From: Peter VanDerWal via EV
> Sent: Wednesday, 3 June 2020 12:55 AM
> To: Electric Vehicle Discussion List
> Cc: e...@vanderwal.us
> Subject: [EVDL] Question about charging small LiIon batteries
> 
> Somewhat off topic, but I'm hoping someone can help.
> 
> I'm building a solar powered weather station and plan to use 1 or 2 18650 
> cells. There are tons of
> small solar chargers available for these, however they all charge the cells 
> to ~4.2V.
> To maximize life from the LiIon batteries I'd like to keep them between 
> 40-80% charged.
> 
> So what I'm looking for is either a solar module that I can set to only 
> charge the cells to ~3.9V
> or a way to make a 4.2V charger work.
> Since I'm not having any luck finding 3.9V chargers what I've been thinking 
> about is perhaps using
> a schottky diode to drop the 4.2V to around 3.9V. however that would prevent 
> the charger from
> seeing voltage from the battery and it might not start charging. 
> So I'm thinking maybe putting a 100 ohm resistor in parrel with the diode, 
> that would allow the
> charger to see the battery voltage.
> I still have to figure out how much current the microcontrollers, etc. will 
> draw, but it's going to
> be at least 10 mA when idle, with bursts up to several hundred ma when 
> transmitting.
> 
> Does this sound like a reasonable plan? Any better suggestions?
> 
> Thanks, Pete.
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Re: [EVDL] Question about charging small LiIon batteries

[Peter VanDerWal via EV]

Now why didn't I think of that?  
The chargers I've been looking at have MPTT(or at least they claim to), however 
I could just use two panels.

I have a couple dozen panels left over from an abandoned project: 5V @ 240ma, 
they have conformal coating so reducing them to 5 cells instead of 6 would be 
difficult.
However, I could run a couple diodes in series...

June 2, 2020 10:02 AM, "Matt via EV"  wrote:

> What about no charge control, a solar panel whose Voc is 4.5v (so only 5 
> series cells) and a
> schotkey diode to prevent back flow
> 
> That would have the effect of limiting max voltage to ~4.2v, but at 4v only 
> around 20% of Imp would
> flow (ie charge rate slows right down past 3.6v)
> 
> How much power are you thinking?
> 
> Sent from Mail for Windows 10
> 
> From: Peter VanDerWal via EV
> Sent: Wednesday, 3 June 2020 12:55 AM
> To: Electric Vehicle Discussion List
> Cc: e...@vanderwal.us
> Subject: [EVDL] Question about charging small LiIon batteries
> 
> Somewhat off topic, but I'm hoping someone can help.
> 
> I'm building a solar powered weather station and plan to use 1 or 2 18650 
> cells. There are tons of
> small solar chargers available for these, however they all charge the cells 
> to ~4.2V.
> To maximize life from the LiIon batteries I'd like to keep them between 
> 40-80% charged.
> 
> So what I'm looking for is either a solar module that I can set to only 
> charge the cells to ~3.9V
> or a way to make a 4.2V charger work.
> Since I'm not having any luck finding 3.9V chargers what I've been thinking 
> about is perhaps using
> a schottky diode to drop the 4.2V to around 3.9V. however that would prevent 
> the charger from
> seeing voltage from the battery and it might not start charging. 
> So I'm thinking maybe putting a 100 ohm resistor in parrel with the diode, 
> that would allow the
> charger to see the battery voltage.
> I still have to figure out how much current the microcontrollers, etc. will 
> draw, but it's going to
> be at least 10 mA when idle, with bursts up to several hundred ma when 
> transmitting.
> 
> Does this sound like a reasonable plan? Any better suggestions?
> 
> Thanks, Pete.
> -- next part --
> An HTML attachment was scrubbed...
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Re: [EVDL] Question about charging small LiIon batteries

[Matt via EV]

What about no charge control, a solar panel whose Voc is 4.5v (so only 5 series 
cells) and a schotkey diode to prevent back flow

That would have the effect of limiting max voltage to ~4.2v, but at 4v only 
around 20% of Imp would flow (ie charge rate slows right down past 3.6v)

How much power are you thinking?

Sent from Mail for Windows 10

From: Peter VanDerWal via EV
Sent: Wednesday, 3 June 2020 12:55 AM
To: Electric Vehicle Discussion List
Cc: e...@vanderwal.us
Subject: [EVDL] Question about charging small LiIon batteries

Somewhat off topic, but I'm hoping someone can help.

I'm building a solar powered weather station and plan to use 1 or 2 18650 
cells. There are tons of small solar chargers available for these, however they 
all charge the cells to ~4.2V.
To maximize life from the LiIon batteries I'd like to keep them between 40-80% 
charged.

So what I'm looking for is either a solar module that I can set to only charge 
the cells to ~3.9V or a way to make a 4.2V charger work.
Since I'm not having any luck finding 3.9V chargers what I've been thinking 
about is perhaps using a schottky diode to drop the 4.2V to around 3.9V. 
however that would prevent the charger from seeing voltage from the battery and 
it might not start charging. 
So I'm thinking maybe putting a 100 ohm resistor in parrel with the diode, that 
would allow the charger to see the battery voltage.
I still have to figure out how much current the microcontrollers, etc. will 
draw, but it's going to be at least 10 mA when idle, with bursts up to several 
hundred ma when transmitting.

Does this sound like a reasonable plan? Any better suggestions?

Thanks, Pete.
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