Precharge resistor guidance Topic is solved

[maiks]

Hello,
In my EV conversion project using a Zombieverter, Nissan Leaf drivetrain, and a 400V battery pack, I’ve been using a 50W 35ΩJ resistor as part of the pre-charge circuit. However, the resistor works for a few days before failing—I’ve already replaced it three times.
I would appreciate your help in determining the correct type and rating of resistor to use for reliable and safe operation.
Thank you in advance!

[tom91]

I tend to just use an oversized 100watt 100 ohm resistor. Most builds do not need a low resistance precharge.

[jrbe]

The resistor in your image is 35 ohm, not 350 ohm. At 400v there is 4500 watts acting on it initially.

Tom's recommendation has 1600 watts as the initial hit.
These both sound huge but are short duration.

These both have wattage taper down as the voltage delta drops over time. You can use https://www.digikey.com/en/resources/co ... e-constant
To see the current and voltage over time if you know the voltage, resistance, and capacitor values of your build. This will show the time to charge as well. Something like this,

This gives you the charge time, take the joules divided by time to charge to give you the average resistor watts for this charge time.

[maiks]

I tend to just use an oversized 100watt 100 ohm resistor. Most builds do not need a low resistance precharge.

Thank you tom91 . I tried 100W 40 ohms and that didn't even last for 10 minutes

[maiks]

The resistor in your image is 35 ohm, not 350 ohm. At 400v there is 4500 watts acting on it initially.

Tom's recommendation has 1600 watts as the initial hit.
These both sound huge but are short duration.

These both have wattage taper down as the voltage delta drops over time. You can use https://www.digikey.com/en/resources/co ... e-constant
To see the current and voltage over time if you know the voltage, resistance, and capacitor values of your build. This will show the time to charge as well. Something like this,
Screenshot_20250502_063444_Samsung Internet.jpg

This gives you the charge time, take the joules divided by time to charge to give you the average resistor watts for this charge time.

Thank u . Have got 2 50W 30 ohms and l want to connect them in series to make 100W 60 ohms . Is this a good idea?

[tom91]

Is this a good idea?

Yes its better(lower peak power) then any other resistor you tried so far.

[maiks]

Yes its better(lower peak power) then any other resistor you tried so far.

Thank you . Have tried it and it has worked

[mattes]

thanks for that info. I just blew the precharge resistor in my ev build with a leaf 2020. I am in the process replacing it. I ordered some 100w 33ohm from amazon to replace the oem 30ohm 40watt. Curious how they are gonna work.

one thing i came to notice is that the zombiverter leaves the precharge relay engaged and never turns off after the main contactor is active. Was surprised to see that.

This is a different behavior compared to the original leaf VCU. This turns precharge off, some seconds after the main contactor is engaged. My guess is I blew my resistor because I had some cabling issues. and the main contactor wasn't engaged and once i applied power it blew the resistor. not 100%, but i think thats a solid guess.

Is there a reason why zombie leave the pre-charge relay enabled?
in case there are some issue with the main relay, I think it is a given to blew the precharge side, due to the overload