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Old 05-05-2014, 09:31 AM   #41
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Boowho
You fail to mention how you are measuring the voltage. Since only little more then 0.5 volts drop means 50% depletion! you need to measure directly at the battery terminals with a good digital voltmeter. Within your cabin's 12 volt circuit, there is current draw and minute voltage drops due to resistance of the lines. A DVM is a high input impedance device an does not produce any drop in its probe lines.

I ran two separate lines (voltage & ground) directly from the cabin batteries to a DVM called the "Volt Minder", which a settable alarm. There needs to be a fuse in the positive line right at the battery. Yes, the fuse has resistance, but if you draw no current, there is no voltage drop. The wires to the meter can be 16 or 18 gauge, since there is virtually no current draw. From my experience, the battery capacity drop from fully charged is non-linear. After getting down to around 12.27 volts, the drop slows down.

Also, when charging the batteries, the batteries acquire a surface charge. So for example, if your batteries were at 50% and then charged up to 75% when you removed shore power with no engine or generator, you would see a reading over 12 volts. This is miss-leading and does not tell you what the battery true voltage is. This surface charge will bleed off slowly and quite fast if some cabin item was on.

What voltage represents 50% is controversial. I have seen charts that go from 12.06 to 12.27 volts. You need to get the specifics from the the battery manufacturer if you can.

These batteries are deep cycle, which means that you can draw them down a lot and they can be recovered. Drawing down not more then 50% is a good idea, since you will then get more life out of the batteries. I follow this rule.

As mentioned by others, the inverter consumes current even if nothing is using it. I frequently forget and leave it on ( old age, II guess).
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Old 05-05-2014, 09:34 AM   #42
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Boohoo, before you equalize the batteries, you will want to take a gravity test to see if one or more. cells within a battery are way off from the others. Interstate Battery puts out a really nice instruction pamphlet on this topic. Craig
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Old 05-05-2014, 10:08 AM   #43
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Boohoo, is this the remote that you currently have? Click image for larger version

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ID:	51689. Craig
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Old 05-05-2014, 01:01 PM   #44
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Specific Gravity testing of the battery cells is indeed a great test. Voltage testing is good if done right at the battery with a DVM. I do not have a ME-RC, but no matter how sophisticated it is, the readings will be incorrect unless a separate voltage monitor wire was run from it to the Inverter and then to the controller.

Since I do not have a ME-RC, I admit that I might be speculating. I would suggest taking the ME-RC reading with shore power disconnected and the Inverter off. I am very curious what you get then and also curious what you get with a separate DVM.

Hank
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Old 05-05-2014, 02:34 PM   #45
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Boohoo, the reason I asked if that was the remote that you had, because there is a low cutoff setting you can program in so you house batteries don't drop below a certain level. CraigClick image for larger version

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Old 05-05-2014, 05:03 PM   #46
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Boohoo, the reason I asked if that was the remote that you had, because there is a low cutoff setting you can program in so you house batteries don't drop below a certain level. CraigAttachment 51703

Yep, I have mine set to cut out at 12.2 volts.

I'm really gratified at how many of you have jumped into this thread with info/help/suggestions. Somethings I already knew but a LOT was/is new to me. The amazing thing to me is that in less than a week, there are five pages to this thread!!

I'm beginning to think that I was expecting a lot more capacity at 220 AH; thinking (mistakenly) that things like the furnace, lights, etc (all 12 V devices) would not consume all that much current.

I do have a DVM so I'm going to take some readings under the conditions that some of you have suggested. BTW, to the person that asked, yes I was running the furnace at the time I had the problem.

I don't have a SG type tester, but I do have a load tester which I'm going check out (after allowing to batts to "settle" awhile; without charging going on).

Herk, your info on current draw for various 12 V devices is great to have. I'm going to review the entire thread to make sure that I've responded to every "potential idea" that each of you has thrown out.

Boowho??
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Old 05-05-2014, 05:04 PM   #47
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Boohoo, is this the remote that you currently have? Attachment 51689. Craig
That's it, Craig.

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Old 05-05-2014, 05:09 PM   #48
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So you have 220AH 6 volt batteries, right?
What model Trojans do you have?

Could you give me an idea of the Magnum model number?
The Magnum may not be "seeing" all the amperage being drawn from the battery bank.
There is no doubt in my mind (now) that the Magnum is only "seeing" the amperage that the Magnum itself is using (or inverting to 120V). The Magnum is "oblivious" to any other 12V devices and the current they draw.

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Old 05-05-2014, 05:11 PM   #49
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Boowho
You fail to mention how you are measuring the voltage. Since only little more then 0.5 volts drop means 50% depletion! you need to measure directly at the battery terminals with a good digital voltmeter. Within your cabin's 12 volt circuit, there is current draw and minute voltage drops due to resistance of the lines. A DVM is a high input impedance device an does not produce any drop in its probe lines.

I ran two separate lines (voltage & ground) directly from the cabin batteries to a DVM called the "Volt Minder", which a settable alarm. There needs to be a fuse in the positive line right at the battery. Yes, the fuse has resistance, but if you draw no current, there is no voltage drop. The wires to the meter can be 16 or 18 gauge, since there is virtually no current draw. From my experience, the battery capacity drop from fully charged is non-linear. After getting down to around 12.27 volts, the drop slows down.

Also, when charging the batteries, the batteries acquire a surface charge. So for example, if your batteries were at 50% and then charged up to 75% when you removed shore power with no engine or generator, you would see a reading over 12 volts. This is miss-leading and does not tell you what the battery true voltage is. This surface charge will bleed off slowly and quite fast if some cabin item was on.

What voltage represents 50% is controversial. I have seen charts that go from 12.06 to 12.27 volts. You need to get the specifics from the the battery manufacturer if you can.

These batteries are deep cycle, which means that you can draw them down a lot and they can be recovered. Drawing down not more then 50% is a good idea, since you will then get more life out of the batteries. I follow this rule.

As mentioned by others, the inverter consumes current even if nothing is using it. I frequently forget and leave it on ( old age, II guess).
You make some good points for me to ponder.

Boowho??
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Old 05-06-2014, 06:31 AM   #50
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This thread might also be helpful.

Trimetric 2025 Battery Monitor
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