[2BirdDogs]

Hello Gurus, 
I have a question regarding my Powerline model 33-53 battery isolator (please see pictures attached). 
When I check voltage across "A" to ground; "B" to ground; "C" to ground -- I get 12.4vdc. My question is on the voltage across "B" to ground... If the diodes in the isolator are operating correctly, shouldn't the voltage be 0 between "B" and ground?
Thanks for any insights.
Paul
       

[kaptain]

Hello Gurus, 
I have a question regarding my Powerline model 33-53 battery isolator (please see pictures attached). 
When I check voltage across "A" to ground; "B" to ground; "C" to ground -- I get 12.4vdc. My question is on the voltage across "B" to ground... If the diodes in the isolator are operating correctly, shouldn't the voltage be 0 between "B" and ground?
Thanks for any insights.
Paul

Power line 33-53 the middle “B” is the INPUT terminal, which connects to your alternator’s output. The ‘A’ and “C” are the output which connect to your house and chassis batteries.

Now assuming you never disconnected any wires bolted onto the isolator when you made your measurements:

If your engine was running when you made the measurements, the “B” should has a voltage around 14 or 14.3V, and “A’ and “C” should read about 13.5V 

If your engine was not running when you made the measurements, then the “B” to ground should theoretically be 0 because alternative output was 0, but in reality, it can’t be 0 because diodes aren’t perfect, they all have small leaks, albeit small. Usually the large the rated capacity the more leak current. So your measurement readings can vary depending on the leakage and also depending on your voltmeter internal resistance, that making voltage reading here almost useless (unless you are ready to do some calculations with the entire leakage including the alternator circuitry and meters internal resistance etc), To get a more meaningful reading, add a 10 ohm or 12 ohm resistor across “B” and ground (make sure it is at least 10watt resistor just in case your isolator is bad), then measure the voltage between “B”, and ground, it should read 0 or nearly 0. Anything larger than near 0 then you have a bad isolator.

Make sense?

[2BirdDogs]

Thank you Joe. That makes sense. I just ordered a couple of 12 ohm 50w resistors from Amazon that should arrive on Wednesday. I will test again once they arrive. The Powerline website says the diodes are replaceable so IF the isolator is bad I will talk with them about possible repair vs buying a new isolator.

I will report back with test results. Thanks again.

Paul

[Richard]

Paul,

Joe gave us all an excellent tutorial on what to check and why. Thanks Joe.

Another little trick that I use when checking unknown circuits or plugging in a questionable DC component is to cobble up an inline fuse holder with the about a 5 amp fuse. That way if I am plugging into a dead short, the fuse goes pop, and nothing is harmed.

[Parisjet]

Paul,

Joe gave us all an excellent tutorial on what to check and why. Thanks Joe.

Another little trick that I use when checking unknown circuits or plugging in a questionable DC component is to cobble up an inline fuse holder with the about a 5 amp fuse. That way if I am plugging into a dead short, the fuse goes pop, and nothing is harmed.

 
I have a 6 ft jumper wire with alligator clips that i installed a auto reset circuit breaker in the middle. If you happen to hit a live wire or something that draws more than 10 amps it will trip and then reset after 15-30 seconds.

Recently i found re-setable circuit breakers on Amazon which are great if you have a circuit that gets blown often. (One for the bay lights comes to mind) They are $20 for a pack     

[kaptain]

Thanks, Richard and Paul.
Yes, I agree there are multiple ways to test the isolating diode in this case. The method Richard proposed is definitely the quickest and easiest way, without any foreseeable or potential harm here.

However, I'd be cautious about applying this method broadly. It reminds me of a mistake I made in the past: when installing a backview camera on my truck, I forgot it requires 5v DC, and I wired it to 12v through a 5 amp inline fuse that immediately fired the camera, and the fuse was intact.

Additional testing methods here, however, require you to disconnect the bolted wires or at other ends (at the batteries & alternator). Otherwise, readings can be misleading. 
Forward/Reverse function test