Twin Battery Split Charge weird problems....

[auf_wiedersehen_pet]

This one has had had me stumped for ages..............

I've got a twin battery set up with a split charge similar to this http://www.wizardbilt.com/Split%20charge%20circuit.htm

The charging works fine. The 2nd battery is new (2 months) as is the 1st battery (4 months). Both batteries have gauges to show voltage. The 2nd battery feeds an amp, an internal auxilliary fuse box and an engine bay auxilliary fuse box.

The problem is, when the engine is switched off (and the link between the two batteries is broken) the 2nd battery will either,

(A) Remain at a decent voltage 12-13v indefinately.

(B) Drop instantly to less than 1v. When checked the battery is still 12-13v but the feed into the interior auxilliary fuse box is less than 1v.

© Drop instantly for an unspecified period of time and the rise to 12-13v, then drop, etc.

Any suggestions before I rip it all out and rewire it.

[ChrisB]

Ok Rob. Where exactly is the aux voltmeter connected to (both wires), and what type is is it please (analogue/digital etc).

It sounds to me like there could be a dodgy connection on the feed to the voltmeter somewhere. Have you been able to verifiy any of the readings with a separate multimeter or similar?

Batteries don't drop to <1v, so there must be a wiring/connection problem *somewhere*.

Chris

[auf_wiedersehen_pet]

Hi Chris,

The voltmeter takes its feed from the internal auxilliary fuse box. It's not a problem with the voltmeter as the feed into the aux fuse box drops aswell.

I've checked every thing with a digital multimeter.

When it "dropped" this morning the feed into the int aux fuse box read 1.14v (the voltmeter was off the bottom of its 8v minimum) but the battery was 12.74v.

Both gauges are analogue and I can confirm they are functioning and accurate with multimeter readings.

Still confused?

[ChrisB]

What is the voltmeter earthed to? how is the int fuse box connected to the battery?

Chris

[gripper]

does the 2nd battery feed the aux box through the split charger? if so there may be a connection problem in there. can you wire the battery direct to the fuse box and only have the split charger connected to charge it?

[fozsug]

Have you checked the condition of the battery,load tested it, ie its CCA etc? Could be showing 12volts but have a low output due to a dead cell? Just pop down to youre local car spares shop and they will put a tester on it .

[auf_wiedersehen_pet]

What is the voltmeter earthed to? how is the int fuse box connected to the battery?

The voltmeter is earthed to the passenger seat base. The int aux fuse box is connected directly to the 2nd battery using (60 amp cable) via a 40 amp fuse.

does the 2nd battery feed the aux box through the split charger? if so there may be a connection problem in there. can you wire the battery direct to the fuse box and only have the split charger connected to charge it?

No. The int aux fuse box is connected directly to the 2nd battery using (60 amp cable) via a 40 amp fuse. The split charge relay sits between the two batteries and "switches" with the ignition.

Have you checked the condition of the battery,load tested it, ie its CCA etc? Could be showing 12volts but have a low output due to a dead cell? Just pop down to youre local car spares shop and they will put a tester on it .

The same thing has happened on two previous different batteries which I had knocking about. I thought they were both tired, hence the purchase of the new battery.

http://www.tayna.co.uk/Numax-CXV-X-1000-Amp-P7632.html

Thanks for all of the help so far.

[MrKev]

Does sound like the aux battery is not grounded properly. Have you tried putting a volt meter directly across the battery terminals?

[pinny]

i had a similar problem and found it to be a bad earth connection cleaned all connections been ok so far,chris.

[auf_wiedersehen_pet]

Does sound like the aux battery is not grounded properly. Have you tried putting a volt meter directly across the battery terminals?

i had a similar problem and found it to be a bad earth connection cleaned all connections been ok so far,chris.

Sounds like the battery earth is the next place to check then.

Thanks for the replies again.

[auf_wiedersehen_pet]

Sounds like the battery earth is the next place to check then.

Stripped down the earth connector this morning - taken it back to bare metal again. Cleaned the terminals, etc.

Seems okay so far but the old fault sometimes took days before it happened.

Fingers crossed.

[auf_wiedersehen_pet]

Stripped down the earth connector this morning - taken it back to bare metal again. Cleaned the terminals, etc.

Seems okay so far but the old fault sometimes took days before it happened.

Fingers crossed.

Well - after 10 days it's perfect.

Many, many thanks to everyone and in particular to MrKev and Pinny.

[MrKev]

Glad to hear it.

Kev

[pinny]

not trying to tell you how to suck eggs but give them a covering of grease/vaseline will keep out the water and slow down the rusting,chris.

[auf_wiedersehen_pet]

not trying to tell you how to suck eggs but give them a covering of grease/vaseline will keep out the water and slow down the rusting,chris.

I do like a good dollop of vaseline

Coated the connection when I re did it - and my battery terminals too.