# precharge and discharge



## Tesseract (Sep 27, 2008)

nikita said:


> we are using kelly controller witth capacitors 6768*10^-6 F.
> my precharge resistor is 2.2 k ohm,20 W.
> when i m calculating the steady state time by T=R*C, it is comming 14.8 sec.
> now my problem is,should i wait for 14 sec to start my car. isn't it weird?


Technically, you should wait at least 3 RC periods - a capacitor is only ~63% charged after 1 RC of time.

So 2.2k is an absurdly high value of precharge resistance for this controller. I would substitute the 2.2k/20W resistor with a 25W or 50W cement filled type of 100 to 220 ohms. This would cut the RC time constant down to 0.7 to 1.5 seconds.


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## nikita (Aug 24, 2013)

yes. you are saying correct, but we have taken values of precharge resistor from the wiring diagramthat kelly controller's technician have provided in their circuit diagram,i f change the values of resistor will it affect our controller??


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## major (Apr 4, 2008)

nikita said:


> yes. you are saying correct, but we have taken values of precharge resistor from the wiring diagramthat kelly controller's technician have provided in their circuit diagram,i f change the values of resistor will it affect our controller??


Hi nikita,

You don't say which controller it is, or what voltage, or show the wiring diagram in question. That would help. Also, please go the the user CP and fill in your location. You don't sound like you're from these parts and I think it is beneficial to us attempting to help to know where you're from 

First off, Kelly isn't the best of motor control companies or the most technically helpful. I was able to find a manual for their KDC series which had wiring diagrams. Those specified a 1KΩ precharge resistor.

You do realize the function of the precharge resistor, don't you? Once you close the contactor, it is shorted (by-passed) and out of the picture. So it has no influence on the operation of the controller.

The Kelly wiring diagrams which I saw have no other contactor or switch in the main power circuit or precharge circuit. So once you have wired your battery/controller/motor circuit, it precharges initially once and the controller stays charged for life. So you would not need to wait at all when turning on the key in your EVcar. The controller is always charged and ready to go.

If you have altered that wiring diagram and used a second contactor in the battery circuit, or use a disconnect, or have a switch in the precharge circuit, then the controller will need to precharge when you enable the battery or precharge circuit.

Here is a good white paper on the subject: http://liionbms.com/php/precharge.php


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## nikita (Aug 24, 2013)

major said:


> Hi nikita,
> 
> You don't say which controller it is, or what voltage, or show the wiring diagram in question. That would help. Also, please go the the user CP and fill in your location. You don't sound like you're from these parts and I think it is beneficial to us attempting to help to know where you're from
> 
> ...




this is the wiring diagram which we are using.
and according to u,we will not use a discharge circuit..as our capacitors will remain charge for the whole lifetime!


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## major (Apr 4, 2008)

nikita said:


> this is the wiring diagram which we are using.
> and according to u,we will not use a discharge circuit..as our capacitors will remain charge for the whole lifetime!


Correct. The controller will remain energized through the precharge resistor even with the contactor off until you disconnect the battery. Are you sure that is what you want?

You didn't like my suggestion of indicating which part of the world you are in? That's o.k.


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