Strange Electrical Voltage Drop

Maine Sail · Aug 31, 2012

Jim,

A 17' one way run, 34' round trip, with 8GA at 15A is a 2.74% volt drop at 12V. You likely have some termination or corrosion problems...

heritage · Aug 31, 2012

When you checked for voltage drop did you eliminate the negative side of the circuit? That is, touch the negative multimeter terminal directly to the negative battery lug. If the drop is being caused by a problem in the negative side, I would run a new negative wire directly to the battery negative bus. If the drop is in the positive side and you can't find the source of the resistance, a new direct run to the battery with a fuse and on/off switch would work or rewire the old positive wiring.

My PO installed an on/off switch that stays lit when it is on.... works for us.

Dan Johnson · Aug 31, 2012

Jim...

Try doing a resistance check on both the positive and negative wiring runs, moving from point to point of each connection and looking for resistance in each section. Suspect connector corrossion as did Maine Sail...

Benny17441 · Aug 31, 2012

Sometimes it is easier to lay new wiring than to try and find the cause of the voltage drop in the old circuit. I like the idea of a shorter run as it allows for reduced wire gauge.

Don12364 · Aug 31, 2012

Measure both Pos feed drop and Neg return drop independently

Measure both positive feed drop and neg return drop independently.

With the unit running put the meter + lead on the battery positive lug and the meter - on the pos connection to the fridge. You may need to extend the meter leads.
Volt drop should read not more than 1/2 volt.

Then put meter + lead on negative connection to fridge and meter - on the negative battery lug.
Again this should not exceed 1/2 volt and the lower the better. (i.e. less than 5% of the supply voltage).

Both volt drop measurements should read about the same and if either is too high then your wiring is too light or your connections are bad.

onecoolair · Aug 31, 2012

Jim Seamans said:
I have a factory installed refrigeration on H356. Wires from the DC panel to the refrig is 8 awg. I'm the process of installing a new compressor after the 10yr old died. Was checking the voltage and found I had a 1.6v drop from the panel to the install location 13.4v to 11.8. The line run appears to be about 17ft. Positive connections on both ends look good. Have to trace the ground side to check it. Very Strange drop.

Looking at installing a new power source directly from the batteries which are only 6ft, fused for 15amps and a new on/off switch push button.

Anyone have any ideas?

Check for a 12v light bulb that may have power to it full time and is switched on by giving it ground. Also some of the new electronic bilge pump sensors may also get triggered the same way. ??

Bill Roosa · Sep 1, 2012

I'd be cautious installing new grounds directly to the batteries. This adds yet another connection to the battery terminals which gets cumbersome if the number is too high and the max number for a connection to the batts is 4 wires per terminal if memory serves. It also opens up the possibility for a ground loop which can lead to corrosion problems. Also, and of much lesser concern unless you have a ham/marine HF radio, is the running of power wires in anything other than parallel sets. The magnetic fields of parallel wires with current going in both directions (one out and one back) cancel. If you run them other than parallel you get pops and snaps as the unit cycles on and off. Also can effect the compass if the wire runs close by.