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Old 07-26-2014, 12:18 AM   #6741 (permalink)
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Old 07-28-2014, 03:44 AM   #6742 (permalink)
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Quote:
Originally Posted by jedsmd View Post
I will connect the j6 wires to a 24volt relay to isolate them from the main contactor which is 12volt.

I normally connect the precharge resistor directly from the battery pack to the controller so that the capacitor bank is always at pack voltage.

Thank-you
Just wondering what pre-charge times are normally experienced by EV'ers that use switched pre-charge resistors?
I know the time will depend on the pre-charge resistor value and the size of the controllers capacitor(s) but just wondering what times people were experiencing.
Are we talking less than a second, 10 seconds, 30 seconds?
Just curious to know what people think is an acceptable time.

I like the idea of switching the pre-charge just because i know eventually i would do something silly and end up being kicked by the charged capacitor.

Paul, does the controller capacitor have some sort of trickle discharge or will it hold its charge indefinitely?

Also wouldn't a 12v contactor coil like jedsmd uses be easier to work with. Simple to get 12v to test it even when stranded miles from home. 24v seems less convenient given the vehicles 12v system.
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Old 07-28-2014, 05:47 AM   #6743 (permalink)
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I use 1 of 1000uF SBE cap, pack voltage is ~184V, precharge resistor is 15 ohm 40W and it takes less than a second to reach more than 90% voltage (RC=0.015s, 5*RC=0.075s, test with scope confirms this). 184/15 gives acceptable ~12A inrush current.
I set precharge time to 2s and it works
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Old 07-28-2014, 09:44 AM   #6744 (permalink)
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Quote:
Originally Posted by z_power View Post
I use 1 of 1000uF SBE cap, pack voltage is ~184V, precharge resistor is 15 ohm 40W and it takes less than a second to reach more than 90% voltage (RC=0.015s, 5*RC=0.075s, test with scope confirms this). 184/15 gives acceptable ~12A inrush current.
I set precharge time to 2s and it works
So the pre-charge is done in about a tenth of a second but you allow a delay of 2 seconds before main contactor energising to give a nice safety margin.
So the pre-charge can be less than what an ICE driver experiences waiting for their motor to crank and catch.
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Old 07-28-2014, 10:32 AM   #6745 (permalink)
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Paul,
The controller has a pre-charge relay connection and the main contactor connection.
Does the software check that the pre-charge has occurred and the capacitor is charged before energising the main contactor or is it just a time delay?
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Old 07-28-2014, 10:55 AM   #6746 (permalink)
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Quote:
Originally Posted by Astro View Post
Paul,
The controller has a pre-charge relay connection and the main contactor connection.
Does the software check that the pre-charge has occurred and the capacitor is charged before energising the main contactor or is it just a time delay?
It's a time delay.
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Old 07-28-2014, 11:48 AM   #6747 (permalink)
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Quote:
Originally Posted by Astro View Post
...
So the pre-charge can be less than what an ICE driver experiences waiting for their motor to crank and catch.
I actually connected things so that my start sequence is:

- turn key to from lock to ignition - nothing happens in HV and controller 12V circuit, rest of 12V systems work in ICE manner (wipers etc.)
- turn further to "start" - precharging occurs, if key is backed to "ign" before 2 sec. period then we're back to previous state...
- ...if "start" held longer than 2 sec. then a relay is latching and providing 12V to controller, contactors and coolant pump as long as OpenRevolt doesn't break it (due to errors) or until ignition switched off.

My intention was to mimick original ICE behaviour of car - one day it'll be anachronism but now we all have this sequence "hard coded" in our minds
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Old 07-28-2014, 11:59 AM   #6748 (permalink)
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Quote:
Originally Posted by flores View Post
It's a time delay.
This actually got me thinking a few weeks ago: "what if something fails im my precharge - fuse, connection or anything; I wouldn't notice the failure until contactor burns or welds itself".
There's JLD404 meter in my car, I'm going to rewire it so that with ignition switched off (during charging for example) it measures voltage at the battery but when key is turned to "ign" or "start" a relay switches measuring points to controller's DC bus. This way I could check precharging at any time without extra equipment, just keep my eye on voltmeter during "cranking" (see above post).
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Old 07-28-2014, 08:48 PM   #6749 (permalink)
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I've done voltage monitoring before, where it only closes the contactor if dv/dt = 0 and v is nonzero. It makes the board bigger, and the voltage monitor circuit adds another $25 or so. It aldo brings high voltage onto the control board. I'm just now finally done with placing the components, and mostly done with routing, and I don't think I could keep the controller the same size as the dc if voltage monitoring were included. There are alternative precharge methods. You could have the precharge wire go thru a hall effect current sensor. If the current never goes to zero, then precharge has failed (or precharge resistor failed open would show up as a different current feedback signature than exponential decay.). What some people do is monitor pack voltage at the cap in the car.
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Old 07-29-2014, 05:00 PM   #6750 (permalink)
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Meanwhile on the raspberry


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