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Old 07-27-2016, 09:58 PM   #1
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Question Electrical Conundrum -- Parasitic Draw

This is a simple DIY camper van on a Promaster 136". No plumbing, no heat. Just an Engel MT45 fridge, a 700W (1000W) microwave, LED lights and USB charging. SurePower 1315 separates van battery from auxiliary. TriMetric TM-2030 tells us what's going on.

One 100Ah Trojan Overdrive 31 AGM would give us about 5 days at 10Ah/day. The Engel is well insulated and even in hot weather would run only about a tenth of the time usually at 1.0-1.5A, sometimes as high as 2.0. According to Engel, max draw for this fridge is 2.5A, but we have it set at 1.5 out of 5 for an internal temp of about 37į. We ran the engine briefly when using the MW.

Notice that the usage numbers above are past tense. We were rocking along just fine until we decided to add solar and a second battery. Now after money spent, we seem no better off than when we started.

We added the second battery first. Suddenly, everything, including the fridge, seemed to be drawing twice as much as previously, so that the percent draw was the same as before. I spoke at length with Ralph at Bogart Engineering (really nice guy), and he couldn't think of any miswiring, etc., with the meter that could cause this reading. (Voltage values were consistent with amps values.)

Now we've just today added 300W of solar controlled by a TriMetric SC-2030. Ralph helped me program in the parameters for the Trojan batteries. We've not had them in full sun yet. Heavily shaded by trees they are producing ~3A.

BUT. suddenly there is an even larger parasitic draw of more than 3A, so that the net result is even worse than before we changed anything.

I'm a girl, so I can cry, but that doesn't solve anything. I'm hoping someone with more electrical smarts than we possess can help us figure this out.

(Why 300W when our needs are so small? Because we knew we will be spending a lot of time in the shade.)
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Old 07-27-2016, 11:29 PM   #2
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Keeping it simple, could the "New"battery have a dead cell? It would cause the symptoms you are having. Test the voltage of the new battery disconnected.
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Old 07-27-2016, 11:54 PM   #3
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Oh, I wish. The voltage of the new battery is the same as the old. Thanks, for the suggestion, though. We hadn't thought of that possibility.
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Old 07-28-2016, 12:50 AM   #4
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Oh, I wish. The voltage of the new battery is the same as the old. Thanks, for the suggestion, though. We hadn't thought of that possibility.
Do the batteries match? They should be identical brand, type, capacity, even the same date code if possible, or they can crosscharge and do what you are seeing.

I would just disconnect all the new stuff, and hook them up one at a time. You have a monitor, so you will see what the problem is immediately when you hook it up.
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Old 07-28-2016, 03:11 AM   #5
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.

The first debugging step I take would be:

disconnecting the house batteries from the isolator.

I mean using a wrench to physically disconnecting the cables,
not just flipping the switch.

Be careful when you are doing that; make sure you wrap any open cables immediately because they are energized.
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Old 07-28-2016, 04:50 AM   #6
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The first debugging step I take would be:

disconnecting the house batteries from the isolator.
With the Surepower 1315 you can accomplish the same thing by disconnecting the small ground wire from the GND terminal. It's normally spade lug terminated and can be easily pulled off and later reconnected without any rewiring or hot voltage potential.

You should here a 'click' when you disconnect the ground. Then you can run any isolated draw tests. When you reconnect it should click again.
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Old 07-28-2016, 12:10 PM   #7
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.


I mean using a wrench to physically disconnecting the cables,
not just flipping the switch, or unscrewing the little ground wire.

Be careful when you are doing that; make sure you wrap any open cables immediately because they are energized.

This world is full of smart people.
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Old 07-28-2016, 12:11 PM   #8
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The batteries are identical in every way except age. Before the second installation, we charged both on the 3-stage charger Trojan recommended, let them sit overnight, then checked voltage, which was within 0.1V.

We leave for a month-long trip today. Before leaving, we plan to disconnect separator and second battery, leaving just the one battery and solar.
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Old 07-28-2016, 12:23 PM   #9
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I'd check all connections and crimps etc. to make sure they're good. Each connection & crimp can add resistance. A quick check for a really bad connection would be noticeable heat. Poor connections become more noticeable as amperage increases.

The new solar input is likely enabling the house & chassis batteries to join via the Sure Power unit when the system voltage is high enough. I think the Sure Power draws 1.5A or so. Current will also be flowing through the chassis battery. The 3A solar you saw could easily be used up by those two items.
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Old 07-28-2016, 12:33 PM   #10
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::

BUT. suddenly there is an even larger parasitic draw of more than 3A, so that the net result is even worse than before we changed anything.

Sounds like one of the wires has bad isolation.

Maybe it is chafed?

When you add current to it, it goes right through.

Do you smell anything?
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