question

deek avatar image
deek asked

BMV-712 running contactor - what am i doing wrong?

I've reviewed all the related posts here I can find but I still cannot figure out what I am doing wrong.
I want the BMV to operate a 12V relay as a low voltage cutoff. I want the relay to be normally open and only close and allow power to pass when the voltage is above cutoff value.
The contactor pulls just shy of 1A when it's closed.
I have a 48 to 12v dc-to-dc converter that i am using to power the contactor. I took the 12V positive with in-line 2A fuse and ran it to the "C" port of the BMV. I ran a wire out of the "NO" port to the plus side of the contactor. Ran a wire from the negative side of the contactor back to the negative bus.
I have also tried using the "NC" port instead.
I can get no response from the BMV. I have it set for Default mode and have toggled between the two "Invert" modes. I can hear something happen in the BMV but the contactor never actuates.
Anybody have an idea what I am doing wrong?

BMV Battery MonitorRelay
2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Paul B avatar image Paul B commented ·

please do a hand sketch of the wiring diagram and attach also send a screen shot of the BMV settings when in victron connect app

of the alarm settings page and the relay settings page


you are setting up the relay settings page ????? as this is separate to the alarm page

0 Likes 0 ·
deek avatar image deek Paul B commented ·

20201209-1551361.jpgsorry Paul, I hadn't checked in a couple days. i'll attach a hand sketch here and get pix of the BMV settings. i have only been working on the "Relay" settings, haven't looked at the alarms. Is that the problem, i.e. do i need to set the Alarms to activate the relays?

0 Likes 0 ·
20201209-1551361.jpg (3.3 MiB)
3 Answers
deek avatar image
deek answered ·

screenshot-20201210-1004301.jpgand here are screenshots of the alarm and relay settingsscreenshot-20201210-1004101.jpg


screenshot-20201210-1004101.jpg (184.2 KiB)
screenshot-20201210-1004301.jpg (270.4 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

1. Disconnect the contactor and try to measure the continuity BVM relay and use "invert relay" to switch it. Is it switching?

2. Try to connect the contactor directly to the 12V. Does it engage?

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

deek avatar image deek commented ·

good ideas. i did try to measure at the C and NC and NO outputs of the 712 but the probes on my meter seemed to be too fat to get down in there, i could set some wires in there and go from them but haven't yet. i can however hear it switching as i toggle in and out of inverter mode.

and, yes, the contactor does operate with a standalone 12V source.

0 Likes 0 ·
evofxdwg avatar image
evofxdwg answered ·

1. To troubleshoot, you need to measure if the BMV-712 relay is opening and closing. Find some sockets of the correct size to go on the pins and connect your meter to them. Do as Matthias Lange suggests.

2. The manual says the internal relay is rated for 1A max. Have you burned out the contacts? I always derate components from 30% to 50% of thier rated usage. You may need another relay between the BMV 712 relay and the contactor to handle its necessary current.

3. Contactors typically generate a high voltage pulse upon opening the coil path due to the magnetic field collapse. This can also open or weld you BMV-712 relay contacts. A shunt capacitor, zener diodes, or MOV (surge protector) across the coil terminals will help. But I would tend to isolate it with another, smaller relay as described above.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

Additional resources still need to be added for this topic