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REC and WS500 User Forum

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Help: cannot energize Contactor via BMS pin 4

As the subject notes,  I cannot seem to get the BMS to send out any voltage to close my main contactor.  I am using a Pre Charge module and I have the lead going to Pin 4 wired to "BMS INPUT" on the module.  I've tested every single lead coming from the harness, and there is no voltage on any of them.  I've looked into any settings that might activate the internal relay, and I haven't found any that solve this issue.  As I understand it, the relay is supposed to close when the BMS is started up, thus supplying 12v from pin 4, so as to close a NO contactor.  I have emailed REC and not received any response... so maybe I someone can point me in the right direction.

Here are some good troubleshooting tips for no voltage to contactor.

(Re-posted from Tine Email:)

Is the Discharge relay fused input connected to battery 12V and NO to the pre-charge BMS input?

Is the pre-charge System- connected to system negative after the shunt?

Do you get the battery pack voltage on the pre-charge BMS input when the relay inside the ABMS clicks?

If not you could have burned the relay fuse inside ABMS. There were 2 spare in the delivered system.

What kind of Gigavac contactor are you using?



Listen to the boot up of the BMS. When I do I hear 2 separate clicks indicating the relays are functioning. If that is working, Using the wires from the main connector, Tie pin 5  (fused input to relay contact) to the 12 v bus. Take pin 4  (normally open) to one side of the coil for the relay or contactor, take the other side of that coil to the negative side of the battery. Note...the fuses are 3 amp (I think that was the rating)  I used a smaller signal relay to trigger the higher current contactor. My contactor indicated the inrush current could be as high as 7 amps for 20 milisecs. I didnt want to risk things and have to open up the bms.



Rick-admin has reacted to this post.

Thanks, yes if didn't connect pin 5 to 12v.  I had assumed that the 12v going to the BMS would handle that, but it only opens and closes the relay.  And yes Patrick, I was hearing the relay close upon startup, and that was confusing me.