Freaky voltage reading

[Ziggler]

Why such bizarre voltage readings on the M2 monitor on my brand new, Blue Sea Systems 360 panel? This morning it read 91.21 volts on the engine battery. Sometimes it will settle down to a realistic reading. Other times it reads 40-something volts. Battery bank #1 reads perfectly normal.

Brand new 12v system. New 2 Northstar AGMs on house side and 1 Northstar AGM on engine. 1984 Morgan 323. Thank you for any tips on how to explore this weirdness.

 

[dlochner]

Have you contacted Blue Seas? Their tech support is excellent.

My first thought is a bad volt meter.

 

[fullbore]

Agree, the meter must be faulty.

 

[Hollyberry]

If the meter reads fine on one bank, but not the other I don't think it's a meter issue... connections on the offending bank?

 

[Tedd]

There are loads of reasons that a volt meter could erroneously read low, but an erroneous high reading is pretty implausible.

My first thought was that you might have made the same mistake I've made before, where the circuit is "dead" and the volt meter is reading a floating ground voltage of, say, 91.21 mV, and I didn't notice that the meter had auto-scaled to mV instead of V.

 

[capta]

Perhaps whoever installed the unit made a mistake hooking it into the system. If it has a shunt for amperage, perhaps that is incorrectly placed on the positive terminal instead of negative?

 

[shemandr]

. ...My first thought was that you might have made the same mistake I've made before, where the circuit is "dead" and the volt meter is reading a floating ground voltage of, say, 91.21 mV, and I didn't notice that the meter had auto-scaled to mV instead of V.

I don't like the auto-scale feature. I've been fooled by it too.

 

[Head Sail]

My friend said her car's battery warning light came on so I got out the volt meter and checked the battery. I was surprised to see the battery was reading over 50 volts! I thought my meter was not working. Took the vehicle into the dealer and learned the alternator was putting out very high voltage. It's a long shot but could be your alternator.

 

[Ziggler]

Thanl you, everyone, for your kind comments and suggestions. I've transferred all ideas to a checklist which I'll work through next time I'm aboard.

 

[Ziggler]

problem with the faulty meter theory is that it is reading fine on the house battery bank and the AC Shore power.

 

[dlochner]

problem with the faulty meter theory is that it is reading fine on the house battery bank and the AC Shore power.

Faulty electronics can act wonky, it is not necessarily an all or nothing prospect.

 

[DArcy]

Is it reading the really high voltage with the engine running or with it off? If it is only while running, there is something wrong with your alternator. And maybe your battery by now too. Also check with and without your battery charger plugged in, they can go bad as well. you could try shutting of all loads and measure again.
DC meters can get fooled by stray AC voltages. Most likely culprits are the alternator (bad diodes) or the battery charger, but other devices could provide AC ripple under some failure conditions.

 

[Roland5048]

Just had this same issue with my Blue Sea panel. Volt meter for both house and start would start acting strange whenever I turned on so much as a single light. Would go all wonky when I turned the volume on the radio up. Voltmeter showed all was OK with the batts. Took a look at the back of the panel and as I lowered it, the whole systam shut down. When I put it back in place, all systems came back on. Turns out it was a loose ground on the neutral bus bar. Tightened everything up and all is well with the universe, again.