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Old 07-27-2016, 10:58 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 37. 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 07-28-2016, 12:29 AM   #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 07-28-2016, 12:54 AM   #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, 01:50 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, 04:11 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, 05:50 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, 01:10 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, 01:11 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, 01:23 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, 01:33 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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Old 07-28-2016, 01:35 PM   #11
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.

The SECOND debugging step I take would be:

disconnecting the appliances one by one to see which is causing the draw.


if you have disconnected ALL the lights and appliances (including inverters),
and the draw is still there,

that means.... ???
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Old 07-28-2016, 02:16 PM   #12
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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.
Marko wins the prize, I think.

Very good call on this, I think this could be a big part of it! We experienced this ourselves, and the solar can all be wasted by the separator and van electronics and starting battery, especially in low sun conditions.

I would start with this, as it is nearly certainly and issue. The solution is to get a separator that has a manual override, or is strictly manual operation. We use a Blue Sea manual unit with a switch on the dash.
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Old 07-28-2016, 03:13 PM   #13
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.................................
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.)....................................
That part is puzzling. Did you increase the battery capacity setting in the Trimetric when you added the second battery?
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Old 07-28-2016, 06:10 PM   #14
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Yes, from 100 to 200.

Marco, you may indeed have found the second draw. Just before that, my husband hooked up a small light--irrelevant, except that while doing so, he noticed a loose wire and plugged it back in. That wire was the separator ground. So the separator appears to have been eating up the meager solar output. This is disappointing because we were looking forward to the solar keeping the van battery charged when the van sits for long periods.
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Old 07-28-2016, 06:13 PM   #15
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Yes, from 100 to 200.

Marco, you may indeed have found the second draw. Just before that, my husband hooked up a small light--irrelevant, except that while doing so, he noticed a loose wire and plugged it back in. That wire was the separator ground. So the separator appears to have been eating up the meager solar output. This is disappointing because we were looking forward to the solar keeping the van battery charged when the van sits for long periods.
Just replace the separator with a manual switch or bistable relay, and you will get rid of the 1.5 amps to the separator. The solar may then be able to keep up with keeping all the batteries full in storage.
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Old 07-29-2016, 01:54 AM   #16
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After weeks of living on backpacking food, to return "home" at the trailhead to a cold Mountain Dew will be worth all the sweat that has gone into this build.
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Old 07-29-2016, 03:17 PM   #17
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... he noticed a loose wire and plugged it back in. That wire was the separator ground. So the separator appears to have been eating up the meager solar output. This is disappointing because we were looking forward to the solar keeping the van battery charged when the van sits for long periods.
When our Sportsmobile was built solar was relatively uncommon so Surepower 1315 was the standard separator. The 1.5 amp solenoid draw wasn't considered problematic when shore power or highway driving did most of the charging at 35 amps or more.

Newer SMB builds usually incorporate solar and have switched to the BlueSea 7622 magnetic latching charging relay. It uses only 13 milliamps parasitic draw, about one hundredth of the Surepower, and is well suited for the lengthy but low amperage charging rate of solar.

The BlueSea 7622 is more expensive than Surepower's 1315 model, but probably worth the investment when you have solar.
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Old 07-29-2016, 03:52 PM   #18
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The 7722 would be my first choice for anyone who was looking to replace the Surepower separator, and wanted to keep it automatic connect like the Surepower. Very nice because it also has the remote shutoff/on switch for override, as well as the mechanical lockout for safety.

We didn't have a need for the autoconnect as we run our engine charging manually when we drive to control charging better, and normally want all the solar to go to the coach (can still manually connect the starting battery, though), so we got the manual only version of the same relay Blue Sea number 7700. It is a bit less expensive and uses no power except when switching.

Both are bistable relays and of very high quality.
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Old 09-01-2016, 10:02 PM   #19
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Mystery solved and the fix took about one second once it was found.

At the same time MrNomer added the second battery, he also switched from solid to stranded wires between meter and shunt. At the meter, one strand of the "G2" wire escaped and wandered over to touch the "G1" wire intermittently, thus causing a short which caused the meter to read incorrectly and erratically.

My hat is off to Ralph at Bogart Engineering. He answers his phone personally and promptly. He has the patience of Job and went to great lengths to help me figure this out.

A telling symptom was when the AC charger thought the batteries were almost charged while the meter was saying 61% charged.

In spite of the meter, our trip was a total success and that was the best Mountain Dew I've ever tasted.
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Old 09-01-2016, 10:14 PM   #20
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Thanks for giving us the update.
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