Voltage drop on display panel

[8tj6]

Hi,

I have a battery which shows 12.7v at full charge.

I have hooked up a switch panel, fridge and some lights to it, but the switch panel only shows 12.6 max with nothing switched on. When I turn the fridge on, the switch panel display drops to 12.2 within a minute. When I turn the lights on, it drops to 12.1 and then 12.0 within a couple more minutes.

Is this normal or have I done something wrong? The battery was probably in its box for about a week or two, then in the van for about a month, during which time I have driven the van (yes, I see now this is a boat forum but I'm hoping you'll allow me this one) a bit and kept track of the battery voltage with a multimeter, I.e. I don't think the battery is the problem.

Thanks

 

[lumphammer]

What voltage do you measure at the battery when the switch panel is showing 12.0V

 

[V1701]

You're almost certainly correct (that the battery is ok). A fully charged, rested battery in good condition, should read 12.6v with no load on it. Bear in mind fridges are very hungry so if you only have one lead acid battery, say, it's not going to power the fridge for weeks without some charge going back in. One LA battery of 100AH gives you a useable 50AH. You can do an audit of how much power you need and work out what your charging regime needs to be to replace what you use before you ruin your batteries - google "12v battery power audit" or similar...

There's a battery charging primer that's worth reading on Canal World here...

 

[alahol2]

Posted it before but it shows the effect of current draw on battery voltage...

 

[bedouin]

The difference between 12.7 and 12.6 isn't really significant - cheap meters are not 100% accurate. I would tend to believe the readings on the switch panel meter.

You don't say what size the battery is or what the current draw of the fridge is. After running the fridge for a while you should switch off all loads on the battery and see what the voltage recovers to - that will give the best indication of the state of the battery.

The pdf posted above looks very useful - but I think it has to be for a specific size of battery (at least those at 5A and 10A loads)

 

[Buck Turgidson]

Posted it before but it shows the effect of current draw on battery voltage...

yes but that is at the battery terminals. The OP needs to measure his terminal voltage so he knows the under read (voltage drop) on his gauge.

 

[William_H]

Sounds to me like a combination of normal battery voltage demise with load and some voltage drop in wiring from battery to panel. The latter can be checked with multimeter connected between battery terminal and +ve but on panel. Should be in the region of .1 volt with all loads on. Check likewise the negative line volt drop. Battery volt drop is a function of age of battery and size of battery relative to the load applied. ol'will

 

[Stemar]

Silly thought - is it a cheap eBay voltmeter? I got some for my boat, and they only read to a precision of 0.3 amps, so they jump between 12.5v and 12.8 when they mean 12.6 or 12.7.