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Old 09-04-2020, 06:46 PM   #1
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THOR #10522
Parasitic Draw

Here is my issue, and I am at a total loss. First the background:

I have a 2017 Chateau 31w (Class C) with two 110ah batteries (Total 220ah). Six weeks ago I put the motorhome in temporary storage. I turned off the battery disconnect switch, but forgot to turn off the inverter. When I came back to the motorhome three weeks later the inverter was beeping. I did not notice if the display showed an error code. I went on a trip and was plugged into the pedestal the entire time. I parked the motorhome after that trip at the storage lot. I made sure the battery disconnect switch was off, and the inverter was off. The batteries were fully charged when I parked it. When I returned three days later the batteries were at 12.0 volts (only 50% capacity). I charged the batteries with the generator for a couple of hours. Over the next few days I returned daily to the RV checking the voltage, and I would lose about 20% capacity each day or two with the inverter off and the battery disconnect switch off. I thought maybe the batteries went bad from getting too discharged for too long as noted previously when I left the inverter on. I pulled the two coach batteries, charged them fully, and left them disconnected for about five days. The lowest voltage shown on day five was 13.2 volts. The batteries are good.

I then checked for a parasitic draw with a multimeter. It shows .5 - .6 amps drawing with the battery disconnect switch in the off position. (Still not as much draw that was required to reduce fully charged batteries by 20% each day or so, but a draw nonetheless. I pulled every fuse in the coach and the chassis one by one, and switched off all breakers, and the parasitic draw remained the same. The multimeter was hooked up correctly.

I apologize for the long post, but I thought it was necessary to note the background information. Have I missed something? There are no fuses left in the coach or the chassis. I am at a total loss. Any help that can be provided would be appreciated.

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Old 09-04-2020, 07:12 PM   #2
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THOR #13932
Excellent post.

A few things I can think of, but it might not be any of them:

Thermostat draws a bit. Again, not enough to mess you up the way you were messed up.

My inverter does some odd 'tap' at preset occasions to check out the system.

I think my bird or whatever that thing is often 'taps' to see where and why with the 12v.

Some radios have an always hot which might not have a fuse anywhere but in line.

You didn't tell us the status of your fridge. It uses 12v even when on propane.

The o2 co2 gas monitor uses 12v and I don't know that it's fused.

My bins have the stupidest lights in them. On off switch right on the light, and I don't think they're fused. If I left one on, they'd not draw much but they'd kill a battery.

My overhead bed ALWAYS has the nine blink, bad ground display. That has to use some 12v.

My outside TV always has a little light on. Even when it's off, there's a light on.
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Old 09-04-2020, 07:15 PM   #3
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Originally Posted by ducksface View Post
Excellent post.

A few things I can think of, but it might not be any of them:

Thermostat draws a bit. Again, not enough to mess you up the way you were messed up.

My inverter does some odd 'tap' at preset occasions to check out the system.

I think my bird or whatever that thing is often 'taps' to see where and why with the 12v.

Some radios have an always hot which might not have a fuse anywhere but in line.

You didn't tell us the status of your fridge. It uses 12v even when on propane.

The o2 co2 gas monitor uses 12v and I don't know that it's fused.
My fridge is a residential unit. After I checked every fuse, I opened and closed the fridge doors - no change to the reading. My co2 detector shuts off when I turn off the battery disconnect switch.
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Old 09-04-2020, 08:29 PM   #4
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THOR #3610
The LP/CO (not O2 or CO2) detector is hardwired directly to the battery & will have a small amount of draw.
Some electric slide motors are also always connected, the theory is if not connected they could idle & slides may move during travel.
The only total battery disconnect is to disconnect the negative cable from the battery that goes directly to ground, no ground no power, or add another disconnect to that cable.
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Old 09-04-2020, 09:08 PM   #5
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I think that the terminal voltage (13.2V) on a disconnected battery is not a good sign it's good? One may have a bad cell and deplete both when hooked up. Of course you may have some other load like the propane detector.
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Old 09-04-2020, 09:10 PM   #6
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I think that the terminal voltage (13.2V) on a disconnected battery is not a good sign it's good? One may have a bad cell and deplete both when hooked up. Of course you may have some other load like the propane detector. So how old are the batteries?
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Old 09-04-2020, 10:25 PM   #7
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Originally Posted by camperguy99 View Post
I think that the terminal voltage (13.2V) on a disconnected battery is not a good sign it's good? One may have a bad cell and deplete both when hooked up. Of course you may have some other load like the propane detector.
When I first disconnected my batteries from the charger they were at 13.4 volts. Over five days they only dropped to 13.2 volts. It seemed they were still good to me as 12.6 is still a full charge. They will go down over time, but seem to be holding a full charge OK. I think??
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Old 09-04-2020, 10:35 PM   #8
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[QUOTE=camperguy99;253114]I think that the terminal voltage (13.2V) on a disconnected battery is not a good sign it's good? One may have a bad cell and deplete both when hooked up. Of course you may have some other load like the propane detector. So how old are the batteries?[/QUOTE ]


Every time you discharge a lead acid battery you loos some of the amp-h capacity. The more you discharge it, the more capability you loose as the chemical reaction is not totally reversible. The amount of degradation is also dependent on the amount of time the battery remains partially discharged. The only way to test a battery's true state is to load test it or with a hydrometer. You can buy a cheap battery load test meter or you can take to a FLAPS (Autozone) and have it load tested. Remember the 50% discharge suggestion is only a way to extend the flooded batteries nominal life to 400 cycles. After that the battery still works, but only has about 25% of its original amp-h capacity. Even you think the batteries are still good, I would recommend you start with a load test before you start trouble shooting.
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Old 09-04-2020, 10:38 PM   #9
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THOR #13932
We call that a
Surface charge.
Seems right, numbers are right
But
A slight load and it crashes.
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Old 09-04-2020, 10:55 PM   #10
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Buy,borrow or go to auto zone and load test the batteries. Like another said,you might be seeing just a surface charge.
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Old 09-04-2020, 11:35 PM   #11
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Interesting! I did not know the batteries would need to be load tested. I thought just checking to see if it holds a charge (with no load) would be sufficient. Off to Autozone I go tomorrow. Thank you all for your help!!!
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Old 09-05-2020, 12:11 AM   #12
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When you're putting them back in: add battery disconnects to the ground line coming out of them into the coach system.
That ought to kill off the parasites!
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Old 09-05-2020, 06:52 PM   #13
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Quote:
Originally Posted by Bob Denman View Post
When you're putting them back in: add battery disconnects to the ground line coming out of them into the coach system.

That ought to kill off the parasites!


Suggest a rotary one in a nearby compartment so you can disconnect from outside without going under the steps - if yours is a coach that keeps its batteries in that inconvenient location.
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Old 09-10-2020, 08:09 PM   #14
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Quote:
Originally Posted by ducksface View Post
We call that a
Surface charge.
Seems right, numbers are right
But
A slight load and it crashes.



As Beau388 said, a hydrometer or a load test will tell you the condition of the battery itself. The voltage reading is easily confounded by surface charge. In my schoold days as a part time service station employee the hydrometer test (properly adjusted for temperature) was the definitive test of a battery's electrochemical charge. They're still around; you can pick up a hydrometer for around $15.
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Old 09-10-2020, 08:16 PM   #15
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I did a load test on both batteries with a battery load tester, and they showed good. Also, the batteries are AGM, so I'm unable to do a hydrometer test.
Quote:
Originally Posted by CHRIS1u View Post
As Beau388 said, a hydrometer or a load test will tell you the condition of the battery itself. The voltage reading is easily confounded by surface charge. In my schoold days as a part time service station employee the hydrometer test (properly adjusted for temperature) was the definitive test of a battery's electrochemical charge. They're still around; you can pick up a hydrometer for around $15.
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Old 09-10-2020, 08:16 PM   #16
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5 days. I wonder how far away Autozone is
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Old 09-10-2020, 08:19 PM   #17
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I have an RV mechanic coming out Monday to look at it.
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