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Old 08-23-2009, 10:44 PM   #1
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Re: Electrical Drama--Help!

First, be sure the batteries are actually fully charged. Checking the voltages at the inverter connections with a digital volt-meter, you should read 13.5-13.8 volts. If this checks properly, then use the DC amp function on the DVM to check the current draw of the inverter. When hooked in series with the inverter, the current should show no higher than 60-70 amps for the lowest normal draw of the inverter (800 watts). If both of these checks return normal results, you probably have a faulty inverter.
Best of Luck
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Old 08-24-2009, 12:22 AM   #2
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Re: Electrical Drama--Help!

Quote:
Originally Posted by Nachtwulf
First, be sure the batteries are actually fully charged. Checking the voltages at the inverter connections with a digital volt-meter, you should read 13.5-13.8 volts. If this checks properly, then use the DC amp function on the DVM to check the current draw of the inverter. When hooked in series with the inverter, the current should show no higher than 60-70 amps for the lowest normal draw of the inverter (800 watts). If both of these checks return normal results, you probably have a faulty inverter.
Best of Luck
Lee
With the bus running and the alternator spinning. My inverters will do the same thing with a bad ground. Lower voltage due to bad connections means that higher current is required to get the same power and the inverters will shut down from overcurrenting. A similar test that will show just exactly where your loses are is to do a voltage drop test. Put one lead of the meter on the positive battery post. Put the other lead on the positive post of the inverter. This will create a second, high resistance path for electricity in parallel with the first. If the meter reads any more than about .25 volts I would say you have poor connections though it shouldn't cause the issue you're describing. 1 volt might though. Do the same test on the ground side with one lead on the negative battery post and the other on the negative terminal of the inverter and see what you get. I should mention that the inverter needs to be on and running, preferably with the biggest load you can put on it at the time you're doing these tests.
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Old 08-24-2009, 06:33 AM   #3
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Re: Electrical Drama--Help!

Other hints:
Keep the distance between your batteries and the inverter to a minimum, without being in the same compartment. Batteries emit explosive gasses, and corrosive gasses.

Shorter distance of the 12VDC cables means less line loss.

Cables should appear to be "overkill" sized. Large cables reduce line loss and can handle the loads without heating up. Best place I have found is a welder's supply shop, get arc welding ground cable. It can handle the load, is made with great insulation, and is very supple. Solder lugs on the ends for connections.

install a fuse on the + cable close to the battery. Car stereo shops carry nice high amperage fuses that are friendly for RV use {but generally not cheap}
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Old 08-25-2009, 10:10 PM   #4
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Re: Electrical Drama--Help!

The surest easy way to measure the battery charge with wet cells is testing the cells with a hydrometer. There are electronic meters available that remain connected to the battery, and count amps in and amps out. After calibration they calculate percent of charge, but they are for upper budgets.

Otherwise, a full battery bank will measure about 12.7 volts after 24 hours with no charge and no load. Batteries will read a "surface" or "face" charge of 13+ volts right after coming off of a charger, even if the capacity has not been fully refilled.

Also, deep-cycle batteries are usually rated at C/20 - constant discharge at 1/20 of the rating for 20 hours. So a pair of 200 AH 6-volt batteries will give 10 amps at 12 volts for 20 hours. They will usually not last a full 60 minutes at a 200 amp draw.

It needs to be said over and over and over - clean and tighten all your connections. You would be surprised at the number of starters, alternators, and batteries that have been replaced unnecessarily because of a spot of corrosion on a connection.
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