# Precharge resistor and coil suppression diode



## rtwelder (Aug 11, 2010)

Hi!
I got with me a PM Motor controller, a Mars ME0709 and a 400amp main contactor and also a reverse contactor.


For the main contactor (as well as the reverse contactor), there should be pre-charge resistor and also a coil suppression diode, right?

Problem is I am not sure if we have those available here. I can probably order online from the US but I live here in Asia and I think I would try to find some other source first before ordering from the US.


Question.

For the pre-charge resistor,
is it just an ordinary resistor with the correct AMP rating and the correct resistance (OHMS)?


For the coil suppression diode,
how does it differ from an ordinary diode? Is there anything unique or special about it?


for my ME0709 motor which can do 300amps (some say it can go over that for a few seconds) and run at 72volts DC, what resistor and diode would you recommend?


----------



## dhrivnak (Sep 25, 2008)

Just my $.02 but the resistor is a high wattage resistor, normally 750 ohm and 25W. I used a 5W standard diode I found at Radio Shack.


----------



## rtwelder (Aug 11, 2010)

So all I have to do is look for a resistor with the correct values (OHMs and AMP/WATTs)

My original question, is a pre-charge resistor any different from an ordinary resistor? ANything special or unique about it?

I hope you don't find this question dumb but I just new to this. Thank you


----------



## nogas1 (Aug 25, 2010)

just an ordinary resistor and it dont hav to be vary high watts,. Where i live part are hard to come by, i recycle.


----------



## rtwelder (Aug 11, 2010)

okay cool! thanks.

what about the coil suppression diode?

would any diode work as a coil suppression diode (as long as it can handle the current that passes through it)??


----------



## JRP3 (Mar 7, 2008)

No. A regular diode will actually delay the contactor release and possibly cause arcing. All you want to know about the diode, and more:
http://www.diyelectriccar.com/forum...ression-diode-damaging-contactorsi-42544.html


----------



## CrunchTime (Feb 13, 2009)

Another useful site: http://zeva.com.au/tech/contactor_jewelry/


----------



## rtwelder (Aug 11, 2010)

so for your EVs, do you need both a coil suppression diode and a pre-charge resistor?

some people say that a coil suppression does not only good but also bad to the controller or contactor.


----------



## rtwelder (Aug 11, 2010)

CrunchTime, thank you for that link. I like what I read.

I guess the coil suppression diode is for the relay/contactor coil.

and the pre-charge resistor is for the main contacts which open and close the connection to the motor controller. Thank you

Now to go shopping for the zener diodes and the resistors.


----------



## JRP3 (Mar 7, 2008)

Or get the manufacturer recommended silicon transient suppressor diode.


----------



## rtwelder (Aug 11, 2010)

thanks! I will look that up. Though I hope we have it here in the Philippines


----------

