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Hazza

Strange battery charging

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Hi all,

I've got a strange issue on the 110, but as it's battery/electrics related it likely crosses all models.

I've got 2 batteries fitted, linked by negative terminals to a chassis earth. Positive terminals are linked by either a voltage sensing split charge relay (currently disconnected to rule it out) or by a large isolator switch.

The main starter battery is currently only showing about 13.6v when the engine is running, it's not charging properly as a result and the 200tdi struggles to start unless jumped off the leisure battery using the isolator switch.

I suspected the issue might be the alternator but when the isolator switch linking the batteries together is closed, the leisure battery charges normally, getting up to 14.3v from the alternator while the starter hovers around the 13.6v mark.

Would I be right to assume that the starter battery is due for replacement?

Thanks in advance!

Harry

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Something's odd - if the two are linked they should be at the same voltage, give or take. If you've got >1v across your isolator switch I'd suggest it's got a problem, or your wiring has.

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Both the isolator and the split charge show a similar voltage difference which I think rules out a fault in these.

Also when the alternator is just charging the main battery (i.e. no split charge and batteries not linked through the isolator) the voltage still remains at 13.6ish volts.

Surely this rules out the wiring?

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Could you swap the two batteries to see if the problem moves with the battery or stays where is was. 

When they're linked I would expect the voltages to be the same as they're linked. What are you using for your ground on the meter? 

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30 minutes ago, Hazza said:

Surely this rules out the wiring?

Nope, something's bad. Are you measuring the battery voltage against the same ground point or across the terminals?

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Thanks for all of your replies so far.

I've done some more digging and it seems that the voltmeter I have for the main battery is under reading by about 0.5v, having checked with a multimeter both batteries are getting approx the same voltage from the alternator, sorry! That'll teach me not to double check the guages with a proper meter!

It does seem that the alternator is struggling a little though - is a 45A alternator powerful enough to charge 2 batteries? 

The 110 is seeing more short distance use (15-30min drives) than it has before and I'm wondering if it might be that the alternator isn't capable of topping both batteries up with such short trips?

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45 minutes ago, Hazza said:

 is a 45A alternator powerful enough to charge 2 batteries? 

no. :)

 

i wouldnt run less than a 90a alternator with a split charge.

 

but it doesnt rule out a battery issue.

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59 minutes ago, Hazza said:

It does seem that the alternator is struggling a little though - is a 45A alternator powerful enough to charge 2 batteries?

It's at the low end, depends what you're doing though - short trips with lights & heater etc. will give it far less opportunity to replace what's used. After a minute or two running you won't be putting much more than 10A into a battery anyway. If the charge light doesn't glow then in theory you're not exceeding the capacity of the alternator to hold the volts up.

What happens if you leave the battery on charge overnight and leave the 2nd battery disconnected / out of use for a week?

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16 hours ago, FridgeFreezer said:

What happens if you leave the battery on charge overnight and leave the 2nd battery disconnected / out of use for a week?

Thanks for the replies. I'll try this and see how I get on. If the battery stays charged then I'm guessing it would prove that the alternator can't deal with 2 batteries?

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Ok - so further investigations suggest that I had a raft of issues. The main ones being one of the voltmeters reading incorrectly as mentioned above, and another issue of a rather (very) loose alternator belt! 

Re-tensioning the belt has given me increased charging, with 14.2-14.3 across both batteries (when checked with a multimeter on the terminals). So success there!

I now need to check over all of the dash and chassis earths as I believe these may be causing a number of issues I'm experiencing, namely: incorrectly reading aftermarket voltmeter (and the standard LR battery charge indicator gauge), poor radio reception, dimly glowing interior lights with doors closed, a non-functioning oil pressure light, and a started which is reluctant to turn over. 

I'm going to check for voltage drops across various parts of the loom and see what I find. But ultimately I think this problem is solved...

Thanks to everyone for your help!

 
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