(another) electrical problem - tracking down battery drain (1 Viewer)

[YukonCruisers]

The '78 has been on the back burner for the last few months, but I have finally gotten through most of the remaining issues - except the electrical.
I think I have have some sort of battery drain and I am struggling to locate it.

Things that are not stock in the systems are:
Light switches for fog/day running etc - positive straight off battery, isolation switch and fuse in line
Radio - switched power supply as well as constant for clock
Early series ARB bumper on the front with led lights, newer led friendly flasher (was buzzing at low batt voltage at one point).

When I charge my battery, the self diagnosing charger says the battery is fine. I could try dropping in another battery, but I really don't think this is the issue - especially since when the truck is disconnected, it holds charge fine.

While charging with the key in the off or ACC position, the charger shows a 90% charge, turn to the Start position and the charger drops to low and my voltmeter immediately starts dropping off.

I tried to isolate which circuit it might be by pulling fuses one by one... all pulled and still have the battery drain issue.

So - do you think the ACC and Start changes in voltage are significant? If so, what does that point to when you consider all the fuses are pulled?

 

[Phrog]

With the key out and everything off, put your multimeter in line between a battery cable and the battery. (Make sure your multimeter is set to its highest amp setting/range). This will give you a definitive answer to whether you have a drain. If you do, try disconnecting the non-stock system components, one at a time, and see if you can isolate the drain.

For more details on how to use your multimeter to measure current, see How to Measure Amperage .

-Phrog

 

[DougAustinTx]

I am not sure I understand your problem. A "drain" is when your otherwise good battery goes dead over a few day's time. Usually caused by a light left on in a glove box, bad diodes in the alternator etc. However, what I think you described is a reduction in available amperage/voltage when you put the electrical system under a heavy load, such as cranking the engine. If the latter, then your symptoms would lead me to believe that you have high resistance between the load and the battery. Possibly a corroded battery terminal, bad connection at the switch, shorted coil in the starter etc., or maybe your battery is about to croak.

 

[YukonCruisers]

Thx Phrog/Doug - I tested the battery after an afternoon of charging and it sits at 12.8v and 2.8a... thinking its just a dead battery. Will grab a new one tomorrow and try it out. I guess i shouldn't have been trying to diagnose with the charger.

Edit: It was the battery, I feel dumb. I thought it improbable that the charger would read ok and that it could die so suddenly - anyway, just waiting on replacement mirrors and another 40 should be on the road.

 

[B y r o n]

Over time the plates in a battery build up a coating that makes them less efficient. There are chargers on the market that can reverse the buildup on the plates so that the battery operates at peak performance. Take a look at the CTEK MUS 4.3. For less than the cost of a new battery you can often revive an older battery, as long as it is not too far gone. Sounds like you've already spent the money on a new battery but pick up one of these chargers/maintainers and you might be surprised at how long your battery will last.

 

[YukonCruisers]

Thx Byron, yup, already bought a new one - but my charger did have the capacity to do the reconditioning, I think it was too far gone. I wanted to go grab a new one anyway as I wanted to get a batt with the side posts for the winch - cheers!