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Old 08-09-2020, 04:51 PM   #21
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So are you using a voltmeter to test voltages? Or are you relying on the inverter display?
Yep, a Voltmeter.

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Old 08-09-2020, 06:04 PM   #22
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You have to measure the battery voltage at the same time you measure the voltage at the inverter. My bet is bad batteries. They can test good voltage without a load on them.
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Old 08-09-2020, 06:12 PM   #23
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I'm not sure why you are plugging/unplugging SP to troubleshoot the inverter.

If inverter input voltage drops from 12.8 VDC to 7 VDC just by connecting the inverter I would go measure the house battery bank voltage at the same time. If the battery bank reads 7 VDC then you have bad batteries. If it reads greater than 12.0 VDC then you have a bad connection to the inverter.
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I was plugging in and out of shore power because there seemed to be a difference after each time shore power was attached when on the road. Just to be clear, connecting shore power doesn't change the voltage from the battery bank but it DOES change the voltage that is displayed across the input terminals for the inverter. When the inverter is not connected to the battery cables the voltage there is consistent.

I have pulled the batteries out, tested them and they are fine. I also checked the connections at both ends and they are good. I think there is an error inside the inverter.
How did you test them? Did you use a load tester? Did you check the battery bank voltage with a voltmeter when you had 7 VDC at the inverter?

People are trying to help you but we can't read your mind. The more complete your information is, when you answer questions, the better our information is in guiding you in your troubleshooting. Remember the phrase GIGO?
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Old 08-10-2020, 10:23 PM   #24
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How did you test them? Did you use a load tester? Did you check the battery bank voltage with a voltmeter when you had 7 VDC at the inverter?

People are trying to help you but we can't read your mind. The more complete your information is, when you answer questions, the better our information is in guiding you in your troubleshooting. Remember the phrase GIGO?

I wrote a long reply over the weekend but for some reason it didn't post as I thought. I've re-written it here - I do appreciate the help and apologize for not being clear earlier.


First step was to remove the batteries from the coach, verify the water levels were correct and fully charge the batteries. I then tested the specific gravity of each cell and they all passed. I have NOT load tested the batteries as I don't have a load tester but that's on my shopping list this week.

Anecdotally all of the 12V systems seem to work fine (other than the inverter) and I am not getting any low voltage errors when running the levelers. Slide-outs and drop down bunk are working as expected when not plugged into shore power.

I ran the tests that Judge recommended and can verify the BIM is working. I'm getting charging voltage when plugged into shore power and when the engine is running.

Batteries are now re-installed. I disconnected the inverter and measured the voltage at the cable ends that power it. When not connected to the inverter the voltage there is 12.6V. The same measurement as at the battery terminals.

I then re-connected the cables to the inverter and measured the voltage at the input terminals of the inverter. Result is 7"ish volts. I walked around to the battery bay and measured the voltage at the battery terminals as well as on the downstream side of the fuse - these all measure 12.6V. Essentially it appears that 12.6V is arriving at the inverter but once it is connected something internal is malfunctioning.

With regard to the plugging and unplugging of shore power, I did this because when I plug shore power in there is an audible "click" from the inverter and when this all started it was because the battery charge had dropped and the inverter kept clicking over and over. I did notice that after plugging and unplugging shore power something was changing as the voltage at the input terminals would bounce from 7'ish to 11'ish volts.

(edited to mention) I did notice that power to my fridge and the outlet in the passenger computer desk routes directly through the inverter. With the unit uninstalled I had to tie the AC input to the romex that comes out of the inverter to those locations. Otherwise I have no power, even on shore power.

I'm really open to coaching here - what am I missing in my steps?
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Old 08-10-2020, 10:50 PM   #25
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I wrote a long reply over the weekend but for some reason it didn't post as I thought. I've re-written it here - I do appreciate the help and apologize for not being clear earlier.


First step was to remove the batteries from the coach, verify the water levels were correct and fully charge the batteries. I then tested the specific gravity of each cell and they all passed. I have NOT load tested the batteries as I don't have a load tester but that's on my shopping list this week.

Anecdotally all of the 12V systems seem to work fine (other than the inverter) and I am not getting any low voltage errors when running the levelers. Slide-outs and drop down bunk are working as expected when not plugged into shore power.

I ran the tests that Judge recommended and can verify the BIM is working. I'm getting charging voltage when plugged into shore power and when the engine is running.

Batteries are now re-installed. I disconnected the inverter and measured the voltage at the cable ends that power it. When not connected to the inverter the voltage there is 12.6V. The same measurement as at the battery terminals.

I then re-connected the cables to the inverter and measured the voltage at the input terminals of the inverter. Result is 7"ish volts. I walked around to the battery bay and measured the voltage at the battery terminals as well as on the downstream side of the fuse - these all measure 12.6V. Essentially it appears that 12.6V is arriving at the inverter but once it is connected something internal is malfunctioning.

With regard to the plugging and unplugging of shore power, I did this because when I plug shore power in there is an audible "click" from the inverter and when this all started it was because the battery charge had dropped and the inverter kept clicking over and over. I did notice that after plugging and unplugging shore power something was changing as the voltage at the input terminals would bounce from 7'ish to 11'ish volts.

(edited to mention) I did notice that power to my fridge and the outlet in the passenger computer desk routes directly through the inverter. With the unit uninstalled I had to tie the AC input to the romex that comes out of the inverter to those locations. Otherwise I have no power, even on shore power.

I'm really open to coaching here - what am I missing in my steps?
Great write-up and I think I can say now that you definitely have a bad connection in the wiring between the battery bank and the inverter. At this point I don't think you need to load test the batteries as everything else seems to be operating normally. That also indicates the connection between the battery bank negative side and chassis ground is good.

So that leaves:
The positive cable from the battery bank, through the fusible link (or DC breaker) to the positive connection on the inverter, which you have had apart so it should be good when you put it back together.
or,
The negative side of the inverter (again, should be good) back to chassis ground.

You are dropping 5+ volts across a bad connection somewhere above. With the inverter connected and measuring 7 VDC the other 5+ VDC will be seen across the bad connection. If physically possible, with the inverter connected, measure DC volts from the positive side of the battery bank to the positive terminal on the inverter. Do that same for the negative side. Good connections will read 0 VDC on either of those tests. In your case, one should read over 5 VDC - that would be the side with the bad connection.
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Old 08-10-2020, 11:17 PM   #26
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Great write-up and I think I can say now that you definitely have a bad connection in the wiring between the battery bank and the inverter. At this point I don't think you need to load test the batteries as everything else seems to be operating normally. That also indicates the connection between the battery bank negative side and chassis ground is good.

So that leaves:
The positive cable from the battery bank, through the fusible link (or DC breaker) to the positive connection on the inverter, which you have had apart so it should be good when you put it back together.
or,
The negative side of the inverter (again, should be good) back to chassis ground.

You are dropping 5+ volts across a bad connection somewhere above. With the inverter connected and measuring 7 VDC the other 5+ VDC will be seen across the bad connection. If physically possible, with the inverter connected, measure DC volts from the positive side of the battery bank to the positive terminal on the inverter. Do that same for the negative side. Good connections will read 0 VDC on either of those tests. In your case, one should read over 5 VDC - that would be the side with the bad connection.
OK thanks for that, I can definitely run wire under the coach to the battery bank to make the test your suggest.

I am a bit confused how the reading at the cable ends is 12.6V when they aren't connected to the inverter if there is a wiring issue. Is it because my voltmeter doesn't put any load on the circuit? I'm not an electrical expert so this is baffling to me. I just assumed that if I measure 12.6v at the cables when they are not connected to the inverter that once they were connected there should still be 12.6v supplied...and the loss is coming inside the inverter, not from somewhere between the batteries and the inverter.
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Old 08-11-2020, 12:40 AM   #27
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OK thanks for that, I can definitely run wire under the coach to the battery bank to make the test your suggest.

I am a bit confused how the reading at the cable ends is 12.6V when they aren't connected to the inverter if there is a wiring issue. Is it because my voltmeter doesn't put any load on the circuit? I'm not an electrical expert so this is baffling to me. I just assumed that if I measure 12.6v at the cables when they are not connected to the inverter that once they were connected there should still be 12.6v supplied...and the loss is coming inside the inverter, not from somewhere between the batteries and the inverter.
You are exactly right - a voltmeter draws almost no current. The inverter, even in idle mode, draws much more current than the voltmeter. That current is causing the voltage drop across the high resistance connection. V=IR
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Old 08-11-2020, 01:44 AM   #28
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You are exactly right - a voltmeter draws almost no current. The inverter, even in idle mode, draws much more current than the voltmeter. That current is causing the voltage drop across the high resistance connection. V=IR
Ahhh yes, Ohm's law. It's been a while.
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Old 08-12-2020, 11:37 PM   #29
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I swear I'm not crazy but I think I might be losing my mind. I re-installed the inverter (only this time I connected the ground wires from the AC wires to the dedicated ground mounts on the unit rather than how Thor had done it by just connecting them together).

I ran a long jumper cable from the battery compartment under the rig and into the compartment where the inverter is mounted. Measuring from the negative battery terminal to the negative input on the inverter = 0 volts.

Measuring from the positive battery terminal to the positive input on the inverter = -11 volts. Huh? Let's try that again - I re-positioned the jumper cable on the battery terminal and voila, 0 volts.

OK, let's try measuring from downstream of the fusible link in the battery compartment. 0 volts on the positive side, 12.6 on the negative side.

Here's where it gets strange - I suddenly hear the inverter fans come on. Turns out it was turned on when I connected it and now it's running fine. The display panel shows input of 12.5volts. Could something have been loose in the connection to the inline fuse that I jostled when attaching the jumper cable?

Next headscratcher - after a while the voltage starts to drop because the fridge kicked on. I started the generator to make sure the batteries would charge and low-and-behold - nothing is charging from the generator.

At this point I'm sitting with a beer pouring over wiring diagrams trying to figure out where to go next. The best thing that could happen here is for lighting to strike tonight and cause a total write-off situation.

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Old 08-12-2020, 11:50 PM   #30
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Next headscratcher - after a while the voltage starts to drop because the fridge kicked on. I started the generator to make sure the batteries would charge and low-and-behold - nothing is charging from the generator.

At this point I'm sitting with a beer pouring over wiring diagrams trying to figure out where to go next. The best thing that could happen here is for lighting to strike tonight and cause a total write-off situation.

Do you have any AC power from the generator? There can be two circuit breakers on your generator. If so, maybe one of the two has tripped and it is not sending power to the Converter to charge the batteries.
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Old 08-12-2020, 11:56 PM   #31
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Do you have any AC power from the generator? There can be two circuit breakers on your generator. If so, maybe one of the two has tripped and it is not sending power to the Converter to charge the batteries.
I did not check that but will go back and do so. The fridge seemed to be causing the generator to rev a bit so I just assumed it was sending power.
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Old 08-12-2020, 11:57 PM   #32
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Here is the wiring diagram for the 12V system. According to this the cables from the battery bank to the inverter should be direct, no fuse.

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Old 08-12-2020, 11:58 PM   #33
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I swear two days ago when I had this in front of my house the batteries were charging on shore-power. According to this if the converter was not working it wouldn't work on either shore or generator power.

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Old 08-13-2020, 12:02 AM   #34
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Here is the wiring diagram for the 12V system. According to this the cables from the battery bank to the inverter should be direct, no fuse.


The Inverter should be wired directly to the battery but it should also have a fuse or breaker. On my Outlaw it had a Bussman breaker. On my Magnitude it has a battery terminal fuse block.

According to your wiring diagram, you have a 300A terminal fuse block. It should look like this and it should be on the battery post with the positive cable to the Inverter attached to it.
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Old 08-13-2020, 12:05 AM   #35
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I swear two days ago when I had this in front of my house the batteries were charging on shore-power. According to this if the converter was not working it wouldn't work on either shore or generator power.


Your Converter should work on shore power and generator power. If a circuit breaker is tripped on the generator, the Converter would not have power with the generator but it would have power with the shore power and charge your batteries.

The Converter has its own AC breaker as well. If that breaker is tripped, it would not work on shore power or generator power.

One other thing..... the Converter has a couple Reverse Polarity Fuses (usually 40A). If you accidentally crossed the battery cables when you were troubleshooting the Inverter, you could have blown the Reverse Polarity Fuses for the Converter and that would prevent it from charging the batteries.
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Old 08-13-2020, 02:17 AM   #36
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The Inverter should be wired directly to the battery but it should also have a fuse or breaker. On my Outlaw it had a Bussman breaker. On my Magnitude it has a battery terminal fuse block.

According to your wiring diagram, you have a 300A terminal fuse block. It should look like this and it should be on the battery post with the positive cable to the Inverter attached to it.
I do have one in-line but I will need to get inside the battery compartment a bit more to see what the A rating is.
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