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

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deek asked Dec 7, '20

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 Monitor Relay

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Paul B commented · Dec 08, 2020 at 05:34 AM

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

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deek Paul B commented · Dec 10, 2020 at 01:50 PM

sorry 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?

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20201209-1551361.jpg (3.3 MiB)

Modifications Space

Node Red Space

Answer 1 · 2020-12-10T17:14:46Z

deek answered · Dec 10, 2020 at 05:14 PM

and here are screenshots of the alarm and relay settings

screenshot-20201210-1004101.jpg (184.2 KiB)

screenshot-20201210-1004301.jpg (270.4 KiB)

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Answer 2 · 2020-12-10T17:34:58Z

Matthias Lange - DE answered · Dec 10, 2020 at 05:34 PM

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?

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deek commented · Dec 10, 2020 at 07:33 PM

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.

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Answer 3 · 2021-10-27T16:19:42Z

evofxdwg answered · Oct 27, 2021 at 04:19 PM

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.

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