Dual Battery Isoloator Question

Got an another problem. I've just installed a dual battery wiring setup in my hilux to charge aux battery in camper trailer. All wired up fine with 6 B&S cable and a 50Amp auto-resent CB between main battery and isolator and works a treat, but the dual battery isolator (Matson from Battery World) appears to be draining my main battery flat overnight.

I've tested the main battery and it holds 12.8V at rest and charges at around 14.2V. Checked amp draw from isolator when not active and is about 10mA. Surely this isn't enough to drain the battery - but only have a flat battery each morning when the isolator is wired up. Total current draw without isolator wiring in is only 2mA, 12mA when wired in.

Other than when the isolator is wired in battery appears fine and is only about 2 yr old.
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Reply By: Battery Value Pty Ltd - Thursday, Jun 10, 2010 at 06:26

Thursday, Jun 10, 2010 at 06:26
Hello Mickos,

Let me check if I understand this right:
You first discovered there is a problem when you were unable to crank in the morning.
Then you figured the cranker's flat.
Then you recharged your cranker? How?
And how and when did you figure out the cranking battery holds 12.8V and gets charged by the alternator at 14.2V?

If you could post the sequence of events in chronological order, that would make things easier for us to diagnose.

Best regards, Peter
AnswerID: 420241

Follow Up By: Mickos01 - Thursday, Jun 10, 2010 at 14:37

Thursday, Jun 10, 2010 at 14:37
OK, so had flat battery.
Day 1: Clutch started in the morning - no problems for the day.
Day 2: Flat again in morning. Charged battery in the evening for about 4 hours (normal auto battery charger), replaced battery - all fine. Disconnected wiring to dual battery isolator.
Day 3: No problems starting in the morning. In evening, tested battery. Battery had 12.8V without engine running, then charged by the alt @ 14.2V on idle. After running car for say 10 min, battery returned to about 13.2 V.

Then tested current draw from pos. wiring to pos. terminal without isolator connected (2mA), and then with isolator connected (12mA).
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FollowupID: 690473

Follow Up By: Battery Value Pty Ltd - Thursday, Jun 10, 2010 at 16:10

Thursday, Jun 10, 2010 at 16:10
ok Mickos,

from your Day3-experience I gather your alternator/regulator is a two step type:
charging at 14.2V shortly after starting, and then dropping back to 13.2V after 10 mins or so.

If that's the case it'll take a verrrry long time to recharge a flattened battery from 13.2V.

Following scenario is possible:
Your cranker's on its way out (reduced capacity due to ageing).
The recently added load of the isolator solenoid coincided with a cold morning and the increase of the battery's internal resistance prevented the starter motor from spinning up. Clutch start.
Drove for some time, but battery did hardly get any charge due to the reduced 13.2V.
Thus, same problem as before the following morning.
Charging the battery for 4 hours in the evening just left enough charge to start car the next morning (note that a nearly flat battery will take 24 hours to fully recharge. And if the battery is old, it takes a full charge to be able to supply the high cranking current).

What I suggest to do:
if it's a servicable battery, check liquid electrolyte levels in all cells, top off with distilled water if needed.
Charge your cranking battery for 24 hours.
Take it to a battery shop who can load test it for you.
Or test it yourself: turn the lights on with the motor off, and check the battery voltage after 15 minutes lights still on.
While the lights are still on, you want to see at least 12V on the battery.
Don't forget to recharge after that.
If it fails, then it's shot, if not, you have to investigate further.

Hope that will reveal something.

Best regards, Peter
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FollowupID: 690481

Follow Up By: Mickos01 - Thursday, Jun 10, 2010 at 21:03

Thursday, Jun 10, 2010 at 21:03
Thanks Peter. I'll follow your suggestions tomorrow and I'll let you know how I go.
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FollowupID: 690535

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