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Old 05-25-2016, 04:35 PM   #1
gte
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Default Roadtrek RS Sprinter parasitic drain

I know the subject of parasitic drain has been discussed a lot on the forum. In March I installed new AGM coach and engine batteries. I have not driven it much in the past several months but weekly I check them and I have a battery disconnect switch on the coach batteries. The voltages have remained constant at around 12.8 volts or so. This week I checked and the coach batteries were fine but the engine battery was so low it would not power the engine pre-heater on the diesel. I used my generator to charge the battery, got it started and connected shore power at home for 48 hours. I had the battery load tested and it is fine. When I put the RS back in storage I disconnected the coach batteries and this time I disconnected the engine battery using the disconnect near the accelerator pedal. I also checked the current with a DVM at the disconnect and found it to be 1.4 amps. I know there is a drain on the coach circuit even with the power switch in the coach off but had no idea there was a drain on the engine battery with nothing on at the dash. Is this normal or do I have a short someplace? My old engine battery sat for months at a time and never ran down. Sorry for the long post.
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Old 05-25-2016, 07:27 PM   #2
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Default Re: Roadtrek RS Sprinter parasitic drain

The isolator relay has a significant no load draw~1 amp iirc. Hence the advice to install a positive battery disconnect in the house batteries. I have also seen those cheap relays stick, forcing the vehicle battery to try to energize the house even when the house batteries are disconnectd. I suggest changing out the isolator with a BlueSea mag latch realty that draws no current at stand by.

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Old 05-25-2016, 11:40 PM   #3
gte
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Default Re: Roadtrek RS Sprinter parasitic drain

Quote:
Originally Posted by icarus View Post
The isolator relay has a significant no load draw~1 amp iirc. Hence the advice to install a positive battery disconnect in the house batteries. I have also seen those cheap relays stick, forcing the vehicle battery to try to energize the house even when the house batteries are disconnectd. I suggest changing out the isolator with a BlueSea mag latch realty that draws no current at stand by.

Icarus
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The parasitic draw on my coach batteries is about 1.7 amps. This is why I installed the battery disconnect switch. My switch has a removable screw so it is clearly disconnected. I may have installed it incorrectly since I put it on the negative terminal of the coach batteries. Should it be on the positive terminal?

The parasitic drain that surprised me is on the engine battery. This drain was measured after the coach batteries were disconnected.

I assume the isolator you recommend does not draw any or at least much lower current but would not help with the engine battery drain
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Old 05-26-2016, 02:04 AM   #4
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Default Re: Roadtrek RS Sprinter parasitic drain

Negative terminal is proper.

I would disconnect the bwttery isolator and check the current draw on the vehicle battery.

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Old 05-26-2016, 03:26 AM   #5
gte
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Default Re: Roadtrek RS Sprinter parasitic drain

So I got about 1.4 amps on the engine battery with separator connected and the coach battery disconnected. Are you saying it might be different if I disconnect the separator? I should mention this is a brand new separator I installed a few months ago.

I will try your suggestion as it is an easy thing to do
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Old 05-26-2016, 05:28 AM   #6
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Default Re: Roadtrek RS Sprinter parasitic drain

If you are getting a 1.4 amp draw after you disconnect the relay, clearly something is wrong. The radio has a parasitic draw, and the ECU might as well. You could consider pulling each fuse one at a time and watch the ammeter and find what circuit has the draw, and then go from there.

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Old 05-26-2016, 12:30 PM   #7
gte
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Default Re: Roadtrek RS Sprinter parasitic drain

No I got 1.4 amps with the separator connected. I will try disconnecting it and measure again.

The strange thing is I had the OEM engine battery for 8 years and never had this problem before. The OEM engine battery never ran down even after 2-3 months in storage with no solar or trickle carger in place.
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Old 05-26-2016, 05:59 PM   #8
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Default Re: Roadtrek RS Sprinter parasitic drain

"this is a brand new separator I installed a few months ago" …. Hmmmmm?
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Old 05-26-2016, 06:37 PM   #9
gte
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Default Re: Roadtrek RS Sprinter parasitic drain

Quote:
Originally Posted by irvingj View Post
"this is a brand new separator I installed a few months ago" . Hmmmmm?
So how does one test the separator to know if it is working?
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Old 05-27-2016, 12:50 AM   #10
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Default Re: Roadtrek RS Sprinter parasitic drain

Google is your friend.

https://www.google.com/search?q=test...&client=safari

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