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Old 07-19-2021, 02:34 PM   #1
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Brand: Thor Motor Coach
State: North Carolina
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THOR #19843
Parasite draw

Having problem with coach battery going dead when plugged into shore power. Most of the time it will not crank after about two days. Did jump the other day, drove 25 miles and engine wouldn't crank. Normally if I run generator, coach will crank.

My question is this. Have looked at you tube on finding parasitic draw. They are hooking amp multimeter between NEG battery post and frame to check any draw. The neg battery post is almost impossible to get to. Can I do the same test on the positive side. Know I may get some sparks. I can easily get to the POS post wire on the Thrombetta and disconnect. Is there anything between POS post and thrombetta.

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Old 07-19-2021, 03:18 PM   #2
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Model: Axis 24.1
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THOR #20289
Your post is really confusing. You say the coach batteries won't crank. Coach batteries don't crank the driving engine, chassis batteries do. But ignoring that for a minute.

The other confusing part is "hooking the ammeter between the negative battery post and the frame". Do you first disconnect the cable to the battery post. I suspect not because you say the negative battery post is almost impossible to get to. When you measure current between the negative battery post and the frame with a heavy cable in place from the negative post to the coach's frame negative point, you will measure nothing.

So.... You can do something similar by removing all terminals from the positive battery post. Well, don't remove and cable terminals that connect the other battery. Then put your ammeter between the battery post and separately connect and measure the current from the battery post to each terminal you removed. When you find one that is consuming significant parasitic current, then you can investigate where it goes and what it does.

Measuring at the Trombetta terminal will only give you current to that device. There are probably other DC circuits going to the converter and the generator starter as well.

FWIW a DC clamp on ammeter is more useful if you can get to the battery terminals. You don't have to remove anything, you clamp on the wire that you want to measure its current. But in my experience <$100 DC clamp on ammeters aren't accurate enough to measure fractions of an amp very well. It takes a >$100 Fluke or similar high quality clamp on DC meter to do that.

David
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Old 07-19-2021, 03:37 PM   #3
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Sorry got wrong battery, Having problem with chassis battery.

On the you tube They are removing the wire going the the NEG post and hooking the amp meter to the battery post and battery wire, completing the circuit.

I don't have a wiring diagram, but I think the POS battery wire goes directly to the trombetta, so it should be the same. Disconnect wire, put amp meter in circuit between battery post wire and trombetta post. Like I said , may get some sparks.

I plan to check out the chassis alternator to day, and make sure it is charging, Chassis battery was replaced less than 6 months ago.
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Old 07-19-2021, 04:28 PM   #4
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Originally Posted by exit55 View Post
Sorry got wrong battery, Having problem with chassis battery.

On the you tube They are removing the wire going the the NEG post and hooking the amp meter to the battery post and battery wire, completing the circuit.

I don't have a wiring diagram, but I think the POS battery wire goes directly to the trombetta, so it should be the same. Disconnect wire, put amp meter in circuit between battery post wire and trombetta post. Like I said , may get some sparks.

I plan to check out the chassis alternator to day, and make sure it is charging, Chassis battery was replaced less than 6 months ago.
Never remove the chassis battery connections when the engine's alternator is running. The alternator uses the battery as ballast. The spark you see is probably the alternator drying to balance the load and regulate the output voltage. The best thing is you will only burn out the regulator and not damage the alternator, but the unlucky will also takeout the rectifier module.
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Old 07-19-2021, 04:31 PM   #5
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The chassis battery positive goes to more places than just the Trombetta: the chassis engine starter, the chassis alternator and the chassis electrical system. You need to measure the current in all of these circuits if you can't get to the negative terminal.

The reason they say use the negative terminal is that it often is just one cable so it is easy to disconnect and measure.

David
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Old 07-19-2021, 05:03 PM   #6
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Agree with Beau388 above. Also since you seem to be focused on the Trombetta relay, maybe you think it is stuck in the closed position so that the coach loads are drawing the chassis battery down. There is an easier way to check this:

Measure the coach battery voltage and the chassis battery voltage. If they are different within the accuracy of your meter then the Trombetta is not stuck. Then start the engine. The chassis voltage should immediately jump to about 14 V but the coach voltage should stay the same. If they both immediately jump to 14V then the relay is probably stuck.

The foregoing test works with the Precision Circuits BIM 160 on my Axis as it takes at least a minute or two for the BIM to connect so if you measure quickly you can determine if it is already connected because it is stuck. Maybe the Intellitec Trombetta relay system doesn't work the same way.

David
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Old 07-20-2021, 12:34 PM   #7
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What year is your rig?
Possibly the battery is at end of life
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Old 07-21-2021, 12:19 AM   #8
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Originally Posted by Trkyte@msn.com View Post
What year is your rig?
Possibly the battery is at end of life
Well did some more work on it today. When I checked, the chassis battery was at 1.4 volts. Of course would not crank. Checked voltage on coach batteries at trombetta. Was 13.4 volts so batteries are separating.

Put charger on chassis and it imediately went to 10.4 volts, then higher to 12.4 volts. Tried to crank but not enough. voltage at trombetta coach post was still over 13 volts. Had to leave so removed charger. will try again tomorrow.

Was finally able to get into fuse box. Will remove one fuse at a time to determine where my parasite. is. main wires are easily disconnected at fuse box. Was also able to get wiring schematic from Thor. Wires from the POS post on Chassis battery go to trombetta and fuse box.

Didn't get it cranked so still have to check ouput of alternator.
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Old 07-21-2021, 12:45 AM   #9
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Quote:
Originally Posted by exit55 View Post
Well did some more work on it today. When I checked, the chassis battery was at 1.4 volts. Of course would not crank. Checked voltage on coach batteries at trombetta. Was 13.4 volts so batteries are separating.

Put charger on chassis and it imediately went to 10.4 volts, then higher to 12.4 volts. Tried to crank but not enough. voltage at trombetta coach post was still over 13 volts. Had to leave so removed charger. will try again tomorrow.

Was finally able to get into fuse box. Will remove one fuse at a time to determine where my parasite. is. main wires are easily disconnected at fuse box. Was also able to get wiring schematic from Thor. Wires from the POS post on Chassis battery go to trombetta and fuse box.

Didn't get it cranked so still have to check ouput of alternator.
1.4 volts after 2 days sounds like a bad battery to me. Especially if only at 12.4 volts with a charger connected.
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Old 07-21-2021, 04:58 AM   #10
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Originally Posted by 16ACE27 View Post
1.4 volts after 2 days sounds like a bad battery to me. Especially if only at 12.4 volts with a charger connected.
It sounds like you have a volt meter. Charge your battery on a charger and you should get it up to the 12.4 or above. Connect your volt meter across the battery, red to positive and black to negative. With your engine off, turn on the headlights and see what happens to the voltage. if it falls off quickly, you have a bad battery. If, after two minutes, your still in the >12v range on the meter reading, have somebody start the engine for you and watch the volts. It will drop rapidly and then bounce up to the 13+ range as the alternator kicks in. If the drop goes below 10V you likely have a battery problem. Below 8V you defiantly have a battery problem and that problem is the battery cant supply the cranking amps.
If you are looking for parasitic loads, you can use a clamp meter. Its not perfect but it will give you some directionally correct info. They are not expensive and a useful tool to have!
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