Buck-Boost 26v at input terminal

[MarCorpsMustang]

I set up a new 50A Victron Buck-Boost in my MB Sprinter RV to charge 12v LFP batteries from the alternator. If I test the line-in cable at the alternator/starter battery end, it reads 13.1v. When I test it at the Buck-Boost input terminal, it reads 26v. Can someone help me understand why this is happening and what's wrong with my installation?

[markopolo]

Originally Posted by MarCorpsMustang

...... When I test it at the Buck-Boost input terminal,..........

Is that the output terminal?

If so, seems like it is set for 12V to 24V conversion. It's programmable via Windows PC so take a look at the settings.

[MarCorpsMustang]

No. It's the other end of the cable running from the starter battery/alternator. 13v at the alternator end; 26v at the buck-boost end when connected to the buck-boost input terminal. How is that even possible?

[avanti]

Where are you getting your ground reference?

[MarCorpsMustang]

Off the BMV-712 shunt

[MarCorpsMustang]

Originally Posted by MarCorpsMustang

Off the BMV-712 shunt

Sorry; that wasn't much of answer. Yes, tapping into the BMV-712 shunt, which in turn is grounded at the Xantrex Freedom SW 3000W inverter/charger that charges the same set of LFP batteries I want the buck-boost to charge..

[booster]

What does that voltage read when it is not connected to the buck boost but just open. If it reads OK, you must have a bad unit or ground on it. The odd part is it should back bleed out of the input unless it just goes to the alternator where the diodes would hold it up.

[MarCorpsMustang]

When not connected to the buck-boost the voltage reads zero.

[booster]

Originally Posted by MarCorpsMustang

When not connected to the buck-boost the voltage reads zero.

If it reads 13+v at the other end of the cable and zero at the buck boost end when disconnected, it would be very odd and a bad cable or breaker, I think.

[MarCorpsMustang]

Thanks, Booster. I was afraid of that. I sincerely do not wish to run another cable, but that may be what I'm faced with.

[booster]

Originally Posted by MarCorpsMustang

Thanks, Booster. I was afraid of that. I sincerely do not wish to run another cable, but that may be what I'm faced with.

Before you consider running a new cable be sure to look for breakers and fuses in the line. Most OEM setups will have a breaker on each end of the cable because of the two direction current they carry.

[MarCorpsMustang]

I sure will; thanks. I put fuses on both ends of the cable I ran and will check them again.

[MarCorpsMustang]

Issue resolved! It was a bad ground, something wise forum members tried to tell me, but this gnarly old Gyrene wouldn't listen. Thanks for your patience and assistance!

[markopolo]

Thanks for posting the solution.