Testing Voltage Drop

[superg]

Hi guys ive just hooked up some wiring for my 3way fridge just while im in transit.

At the moment i have it connected 8GA wire from a red arc isolator, not being used for a dual battery yet so ive hooked it up to that so if i stop for a break for a few mins it wont run my battery flat. Ive got the 8Ga from the isolator to a 20A breaker then 8GA to an anderson plug then to the fridge and then negative 8GA back to the battery.

SO how do I test if there is any voltage drop?

If i do it while the car is started do i hook the fridge up or just test at the anderson plug? do i test it with the car started or not?

Whatever way it is meant to be done what is the acceptable voltage drop? thanks guys.

[-Scott-]

See if you can get your multimeter probes into the back of the anderson plug - that's probably the most convenient place to measure the voltage at the fridge.

Without the fridge connected, you have no current draw to create a voltage drop, so the voltage at the anderson plug should be the same as at the battery.

Then connect the fridge, make sure it's actually "running" and measure the voltage at the anderson plug and at the battery. You could try again with the engine running, and both voltages should be higher, but the difference between battery and plug should be basically the same.

[MART]

Scott , I might be wrong but if you use an isolater they have diodes which allow power in one direction only , so would their be any power when the car is stopped as he said he hooked it up directly to the isolater , and is it safe to run the fridge on the alternator only as the voltage would fluctuate as revs change , just curious , Cheers Paul.

[-Scott-]

Scott , I might be wrong but if you use an isolater they have diodes which allow power in one direction only , so would their be any power when the car is stopped as he said he hooked it up directly to the isolater , and is it safe to run the fridge on the alternator only as the voltage would fluctuate as revs change , just curious , Cheers Paul.

Good point - I missed that bit.

I don't know how the Redarc isolator works. If it's a simple isolator switch, which effectively connects the second battery to the first (either electronic or mechanical switch) there shouldn't be a problem.

If it's a fancier unit which switches between charging either the main battery or the second battery, then I'm not sure how well the voltage regulation will work WITHOUT a battery there - but I would guess "not well."

If it's a simple diode isolator (I don't think Redarc make them) then the fridge should receive power OK, but it will be down about 0.7V from the diode alone. No load, I would expect full battery voltage to be measurable at the anderson plug - a diode also needs forward current to create a voltage drop.

Or I could be completely wrong - again.

[MART]

Sounds good Scott , Cheers Paul.