Weird electrical issue

bruceh · 02-04-2012, 01:00 PM

Hi All,

I have been beating my brain for a while now with no success.

Situation: not plugged into shore power running stricly on batteries (4 6 volt), turn on lots of lights etc.

The voltage meter that came with the coach reads about .5 to .7 volts lower than the battery when a lot of electrical stuff is turned on. I dug a little deeper and it seems that the #6 cable from the battery to the converter is dropping this voltage only under load. I measured with a good DVM from point A to point B on the simplified diagram, and measured the voltage drop, essentially from one end of the wire to the other. That is a lot of voltage drop for a simple piece of wire.

I measured the ground connections and saw no appreciable voltage drop from frame ground to the negative battery cable.

How do I solve this? I could go to a fatter wire, 4 gauge perhaps? Replace the existing wire? Any other ideas.

Sorry about the way that the picture appears, I had hoped that it would be bigger.

wa8yxm · 02-04-2012, 02:29 PM

Very common.. TWO causes... As is often noted fuel gauges are the worst, accuracy wie, made, and the coach's voltmeter is, after all, a fuel guage.

But I don't think that's it, You said this only happens with "lots of lights on"

In my coach from the batteries to the main 12 volt fuse block is around 40=50 feet (my best estimate) and ... Well... that's what is called "Line loss" You have that much wire one way, and then you have wire running back as well, so that's around 100' of wire, and there is simply loss in the line.

Pusherman · 02-04-2012, 03:16 PM

Forgive me for this one, as it's pretty obvious -- possibly dirty or corroded terminal connections either at the battery or the distribution end.

Cheap fix if this is the problem.

bruceh · 02-04-2012, 04:18 PM

I will pull the wires on the inside and check for a dirty connection. I have already checked the outside and measured on the wire itself, not just the connector.

My wire run is rather short (about 10 feet) so there really shouldn't be all that much line loss.

Thanks for paying attention.

I do my measurements with an external DVM, I don't trust the bujilt in on e either.

EngineerMike · 02-04-2012, 04:49 PM

If connections don't resolve it, I'd suspect too small wire. #6 is teeny for a main cable (I can't read the diagram so I'm assuming that the main run). Voltage drop is proportional to length of run & inversely proportional to copper cross section area (i.e. fatter wire-> less loss). Also, if there are any stainless washers (or split washers) in the stack at connections, replace those w/brass or galv type; stainless is a lousy conductor. Stainless wing nuts on top are fine, but from cable connector to battery lead should be all brass or steel mashed together, no stainless in between.

JimM68 · 02-04-2012, 05:10 PM

It's always worth taking all the connections apart and "cleaning" them with an abrasive, a file or a wire brush.

There should be nothing at all between the cable terminal and the top of the battery, never. Terminal goes on, second terminal if needed, washer only if you must, then a nut. I stay away from wingnuts, too.

Cleaning the tops of the batteries with baking soda paste, then flushing with lots of water is a good thing.

6 gauge wire is tiny for this use...

wa8yxm · 02-04-2012, 06:31 PM

I can not tell you what size lamps you have but the 1156 size (Be it a real 1156 or a blade type equivlent) are, as I recall, 26 watts each, that's over 2 amps per lamp.

10 lamps = 20 amps, NOTE a fixture may have 2, or more, lamps.

Interesting thing: I sometimes tell of low-power ac/dc refrigerators made by both Norcold and Dometic... They draw LESS power than a 2-lamp 1156 Fixture!!! (Door closed that is, power consumption goes WAY UP when you open the door, turning on the light)