Basic 12v testing advice needed

[starman]

I'm pretty sure my 3 leisure batteries are knackered - they are ageing and discharging down to below 50 % in less than a day with basically just the fridge in use.

But recently I came back to the boat after a week away and found them all but flattened. The fridge had been switched off but the master switch left on. No obvious lights left on either.

So is there a hidden drain? I've done a basic check of connecting voltmeter between battery + and cable. It reads 0.2v with master switch on or off. Also taken fuse out of bilge pump circuit - no change. The only thing left connected was Smartgauge.

Have I a problem or is this an insignificant result?

[MoominPapa]

I would recommend disconecting the batteries from each other and doing voltage tests on each one separately. The symptoms you are seeing are consistent with a shorted cell in one battery, causing the others to discharge through it when the bank is at rest.

 

 

MP.

[Phil Ambrose]

A hydrometer will show you a dead cell, useful bit of inexpensive kit, you need to check each cell.

Phil

[Genn]

Hi Starman

 

To find out if you have a current draw from the baterries with just the master switch on disconnect the main live and put your multimeter in circuit to measure current draw, or if you have one use a clamp meter. Once you have done this you can make a more informed decision on wether your baterries are US.

 

Glenn

[starman]

I would recommend disconecting the batteries from each other and doing voltage tests on each one separately. The symptoms you are seeing are consistent with a shorted cell in one battery, causing the others to discharge through it when the bank is at rest.

 

 

MP.

Spot on - one v down battery. Thanks.

[MoominPapa]

Spot on - one v down battery. Thanks.

Good stuff. With luck, you'll be able to wring a bit more life out of the other two.

 

MP.

[smileypete]

DC clamp ammeter can be helpful for this sort of thing, the duff batt will draw more current under charge, plus there will be some flow as it flattens the others.

 

cheers, Pete.

~smpt~

[Bright Angel]

Can anyone recommend a good AC/DC clamp meter that doesn't cost the earth ? E bay have them from £3.99 to over £500...help

[smileypete]

Can anyone recommend a good AC/DC clamp meter that doesn't cost the earth ? E bay have them from £3.99 to over £500...help

 

There's a some mentioned in this post:

 

http://www.canalworld.net/forums/index.php?showtopic=67670&p=1339171

 

Also CPC do one:

 

http://cpc.farnell.com/tenma/72-7224/clamp-meter-with-frequency/dp/IN0511005

 

Seem to be much of a muchness, differences being the battery type, layout of controls, backlight etc.

 

The Mastech MS2108a looks to be a bit better for mains work and takes AAA batts, though the controls look a little more fiddly.

 

cheers, Pete.

~smpt~

Edited July 26, 2014 by smileypete

[Arthur Brown]

Read the spec on your proposed camp meter! all measure AC but only some measure DC as well. Don't expect too much accuracy either. My meter is one scale 400A AC or DC so it's poor to look for currents below an amp.