Jay Summet via EV wrote:
On 01/08/2017 09:46 AM, brucedp5 via EV wrote:
So, instead of queuing to work on repairing or upgrading your dead
cursit, I
suggest you line up a robustly-designed controller to purchase when this,
your replacement cursit, dies (start saving your money now, and don't
spend
any $ on your dead cursit).
I agree that better controllers exist on the market. If I had to pay
retail I would spend a bit more for a Zilla 1K or ZEVA or something
along those lines. But since I was able to find a used controller the
ability to just bolt it in with no other changes was a large benefit.
If having a lead foot (strong acceleration use) with the cursit will
cause a
controller failure sooner, then isn't there a simple RC (resistor,
capacitor) circuit one could put at the cursit controller (pot-box) input
(slows the acceleration attack ramp to a slower rise, etc.)?
I can control the lead foot, so an extra resistor (or modifying the
twist pot control on the Curtis) wouldn't be of much extra use (and just
get in the way if I do need to floor it in an emergency).
Sounds like what you need is a bypass contactor. This is an extra
contactor that simply switches *full pack voltage* to the motor. Engage
the bypass contactor with a switch that closes when you floor the
accelerator.
This takes the controller out of the "loop". The current is only limited
by the wiring. It's a good idea to deliberately under-size the wire in
this path to have enough resistance to keep the peak current (into a
stopped motor) below whatever you deem sensible (like the 800 amps you
have mentioned).
Here's now it works. You're at a dead stop, waiting for an opening in
traffic. Aha, there it is! You floor it. The bypass contactor closes,
and hits the motor with 800 amps. Away you go! As the motor picks up
speed, its current naturally drops. When it's below 400 amps (below the
controller's current limit), you can let up the pedal a little. The
bypass contactor opens, and the controller takes over as usual.
But there's one caveat. You must not open the bypass contactor while the
current is above the controller's current limit. If you do, the
controller gets hit with a current substantially above its ratings.
There are a number of solutions for this.
- Live dangerously. Never "blip" the throttle for a fraction of a
second while completely stopped.
- Add a delay to give the motor a second or so to speed up enough
so the current is below 400 amps. (Be sure you also have a switch
to turn off *all* power to the motor when you fully release the
accelerator.)
- Add a second larger freewheel diode that can take the higher peak
current. (Its forward voltage drop needs to be chosen to be higher
than the controller's diodes at low currents, but lower at high
currents. This big new diode is not likely to be fast enough to
efficiently switch at 15 KHz.
- Add one more contactor to disconnect the controller while the bypass
contactor is active. Sense motor current, and don't turn this
contactor back on until motor current is below 400 amp (or whatever
the controller can safely handle).
- Use something like a big old slow "hockey puck" IGBT as your bypass
"contactor". Turn it on hard, but let it turn off slowly (with a
resistor-capacitor-diode network in its gate). That forces the motor
current down so the controller can handle it.
--
Teaching children to program goes against the grain of modern education.
Just imagine the chaos if they learned to think logically, plan, create,
implement, test, and execute!
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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