question

crawfosj avatar image
crawfosj asked

CTEK D250SA & BMV712

Hey all,

Will be installing a BMV712 into an existing canopy set-up once it arrives. Aux battery is under the tray, wired through to a D250sa within the canopy. Basic question is - the 712 asks for a pos. supply cable to go from B1 on the shunt through to the pos. on the battery. Now, I've already ran cables through the base of the tray and thoroughly sealed them, so to install another cable to the pos. on the battery would mean more holes which I'm keen to avoid. Can I simply take the pos.supply it's wanting from the "Batt. out" terminal on the CTEK? It's connected to the pos.on the aux. battery and it's where I get my pos. feed for the whole canopy. Voltage is obviously the same - can't see why this wouldn't be OK but thought I'd better ask.

Cheers, Stu.

BMV Battery Monitor
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3 Answers
wkirby avatar image
wkirby answered ·

You'll get inaccurate readings if you don't connect the B1 terminal directly to the battery positive terminal.
The only time that the Voltage at the CTEK "Batt out" terminal will be the same at the battery positive terminal is when there is 0A going through the cable. Once the CTEK starts charging, the Voltage at its output terminal will be higher than the battery positive terminal, that is what needs to happen to cause a charging current to flow towards the battery.

There will always be a differential of Voltage from one end of a cable to the other end when a current is flowing through it, that is down to Ohms law.

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harold avatar image
harold answered ·

However, Amps in and out are the most important to follow, esspecially if you use the BMV only for monitoring SOC. And don't use is for steering systems.

If the cable dimentions are Ok and there are no splits between the terminal and the shunt.

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crawfosj avatar image
crawfosj answered ·

Thanks fellas,

I reckon I'll just do it the right way and go straight to the pos on the battery, although if I understand it correctly it wouldn't actually make much difference if I'm just looking for amps used/SoC?

Though this raises another question - should loads be run directly from the pos on the supply battery rather than running everything from the "battery out" terminal on the CTEK? There's 8 B&S from the battery to the CTEK so that's fine - and I run some 25A cable from the CTEK to the switch box for the fridge/lights. Got me wondering now.

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