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Old 03-18-2016, 07:21 PM   #1
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Electrical problem

I have a 2002 Safari Sahara with Cummins ISC engine in rear, 39 ft coach.

I'm having an electrical problem. When disconnected from outside electric, such as spending the night at Walmart, the panel states the house batteries are at 9.8 to 10V and won't let the inverter run, so we have no 110 power.

If I go outside and put a meter across the house batteries I get 12.65 V (fully charged). If I turn on the generator the panel shows 13.5 - 14 V and we have 110 V no problem. Generator off and again inside control panel drops to around 10V and inverter says "fault" and shuts down. Outside house batteries again still show fully charged with portable meter.

110 V works fine when plugged in at campground.

House batteries are 4 marine batteries < 6 months old. I disconnected them and voltage was even when tested individually again at 12.65 V.

Any ideas? I can't intuitively figure this out.

Thanks,

Chuck
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Old 03-18-2016, 07:32 PM   #2
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Do your 12v lights work ok?
For some reason, the inverter thinks the voltage is low, that is why the panel shows low.

Check the DC connections from the batteries to the inverter.
Do you have a battery disconnet? Turn it off/on several time to clean the contacts.

Finally your inverter might be bad.

Dan
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Old 03-18-2016, 08:17 PM   #3
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Have you checked the voltage at the inverter input?

It sounds like a bad connection. Start working down the connection chain between the inverter and the battery. Do not forget to check the voltage from the negative inverter terminal to chassis.
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Old 03-18-2016, 08:17 PM   #4
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Check all the connections from the battery to the inverter. Loose or corroded connections could cause voltage drop.
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Old 03-18-2016, 08:45 PM   #5
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There are also sensors used in conjunction with some inverters. You may find a battery temperature sensor attached to a battery terminal or taped to the side of a battery. Sometimes they go bad and make inverters act crazy. There are also a circuit called a DC shunt connected to some systems. That will be connected to the bank main 12 + terminal on one side and the bank - terminal on the other side. It is essentially a resister that is calibrated to show what the actual current flow is to your inverter/MH (control panel.) It may be bad and giving your inverter bad info.
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Old 03-19-2016, 07:22 AM   #6
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FWIW the shunt is for measuring current, not voltage. Typically they designed to drop something in the millivolt range. Measure the voltage between the chassis and negative battery terminal and it will include the shunt drop. It should be well under a volt but he is looking for a couple of volts.
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Old 03-19-2016, 09:19 AM   #7
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Quote:
Originally Posted by nothermark View Post
FWIW the shunt is for measuring current, not voltage. Typically they designed to drop something in the millivolt range. Measure the voltage between the chassis and negative battery terminal and it will include the shunt drop. It should be well under a volt but he is looking for a couple of volts.
The point Jerry was trying to make is that the shunt introduces two adfitional connection points that could be bad.

Dan
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Old 03-19-2016, 09:42 AM   #8
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Volts

The 12 volt lights are working fine. Voltage into inverter matches inside panel as being low but is normal at batteries. I'll poke around the connections and see what I can turn up. Thanks so far.
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Old 03-19-2016, 09:56 PM   #9
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I had the same problem with my Xantrex rs 3000, Xantrex wont repair it, the problem is the main power relays not passing the voltage to the rest of the inverter. disconnecting all power, 110 and 12v letting it reset worked for a couple years, then even that didn't work anymore
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Old 03-20-2016, 10:38 AM   #10
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Quote:
Originally Posted by genopower View Post
The 12 volt lights are working fine. Voltage into inverter matches inside panel as being low but is normal at batteries. I'll poke around the connections and see what I can turn up. Thanks so far.
Great, that says your inverter is fine.
We should be talking about two cables between batteries and inverter.
EITHER gnd or pos could have a poor connection to cause this.
Unless you have a disconnect switch wired in.....remember to check the shunt connections

Regards,

Dan
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Old 03-21-2016, 05:46 PM   #11
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update

I'm still perplexed.

I can't find any bad connections or grounds, they all appear sound to me. Do the batteries go straight to the inverter or is there an intermediary? The reason I ask is the voltage at the two big terminals on the inverter is low (outside and on panel inside) but at the batteries normal. 12.46 at batteries and around 10 V at inverter.

I tried this: campground circuit breaker off, then RV's inside circuit breaker off followed by on and for about a half an hour there was no voltage at the inverter but still 12.46 at batteries (I admit it freaked me out).

I turned the main power at campground back on and let things sit for about an hour and when I killed the campground breaker, voltage at the inverter went back up but still low at 10V.

At least I know we have the 12V system back when not in a campground.

I'm starting to suspect the inverter. Is there an easy way to test it?

Thanks again,

Chuck
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Old 03-21-2016, 06:17 PM   #12
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Quote:
Originally Posted by genopower View Post
I'm still perplexed.

I can't find any bad connections or grounds, they all appear sound to me. Do the batteries go straight to the inverter or is there an intermediary? The reason I ask is the voltage at the two big terminals on the inverter is low (outside and on panel inside) but at the batteries normal. 12.46 at batteries and around 10 V at inverter.

I tried this: campground circuit breaker off, then RV's inside circuit breaker off followed by on and for about a half an hour there was no voltage at the inverter but still 12.46 at batteries (I admit it freaked me out).

I turned the main power at campground back on and let things sit for about an hour and when I killed the campground breaker, voltage at the inverter went back up but still low at 10V.

At least I know we have the 12V system back when not in a campground.

I'm starting to suspect the inverter. Is there an easy way to test it?

Thanks again,

Chuck
There will be a fuse somewhere in the circuit. Should be on the positive side. They don't look like the normal plastic or even glass fuses. They look more like a solid copper piece of metal between two cables. It will look something like this. Not exactly but should give you something to look for. Good luck.
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Old 03-21-2016, 08:44 PM   #13
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Here is what you need to remember.
if you measure a battery, and it is 12,5v, and then if you connect two long battery cables (1 pos ,1 neg), and then measureat the ends of the cables, you will measure the exaxt same voltage.

Now if the cables are the proper size, and you connect a load, you mightt see a slightly lower voltage. BUT.... if one of the connections is bad, there will be a voltage drop across that bad connection.

So now lets determine who is driving what
By that I mean if you are plugged into shore power, your inverter is driving by supplying a charge voltage. So you should measure 13.8v or higher at the inverter, and also at the batteries.

Disconnect shore power, and the batteries are now driving, and providing 12.5v if fully charged.

So you should start measuring at the voltage source.
Find each cable, and trace it.....both ends should have very close to the same voltage.

Thd last thing to remember is that the ground cable should be 0v everywhere.
a bad conndction in the ground circuit will show 1 or 2v.

Hope this makes sense.
With what you have said, no reason to suspect the inverter yet...

Dan
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Old 03-21-2016, 09:09 PM   #14
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Cables can go bad. If you flex the cable and you hear crunch it's done for. Most likely spot would be near the batteries.


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