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Old 04-17-2017, 06:59 PM   #1
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2 amp battery draw with main disconnect off

Mercedes mechanic says I have a 2 amp draw on the engine battery coming from the coach when the main disconnect is off. 2016 Dynamax Isata 3. After 1 week I can't start the engine unless I use the bypass (engine battery dead). Any idea what would draw that I could disconnect from any of the Mercedes fuse panels or the coach fuse panels? I afraid Dynamax tech would send me back to Mercedes tech. I just bought it used from private party and think he may have forgot to tell me about the issue? Thanks!
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Old 04-17-2017, 07:01 PM   #2
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Install a battery isolator between the starting battery and the coach batteries that will keep the starting battery from being drawn down by the coach
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Old 04-17-2017, 07:03 PM   #3
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Put a clamp meter on the battery cable and start pulling fuses would probably be where I'd start if there's nothing obvious. 2A @ 12V is only 24 watts so that's not a ton, but still pretty parasitic as you've outlined. Could always just install (rewire?) your own disconnect to really shut it down. Or a tiny solar panel could probably keep up with it.

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Old 04-17-2017, 07:05 PM   #4
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i think 2amps is acceptable, if it was me i would put another body to chassie ground wire on,

you will always have some kind of parasitic draw
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Old 04-17-2017, 07:54 PM   #5
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2 amp draw on engine battery sounds awful high. I would track down what's drawing on that battery.
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Old 04-18-2017, 06:16 AM   #6
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"2 amp draw on engine battery sounds awful high. I would track down what's drawing on that battery."

Agree, totally unacceptable, and MUST be corrected.
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Old 04-18-2017, 08:59 AM   #7
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It is likely one of two things...
1. electric step. That gets connected to chassis battery..only reason it would pull that much is bad ground maybe?
2. Slide out brain. Pull the power wire to the Power Gear Slide control module, retest for draw. They say that thing doesn't draw much power, but who knows what they think is "not much".

If I am not mistaken, those are the only two items that get connected to the chassis battery. Unless the original owner added something.
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Old 04-18-2017, 12:01 PM   #8
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Quote:
Originally Posted by toslow View Post
i think 2amps is acceptable, if it was me i would put another body to chassie ground wire on,

you will always have some kind of parasitic draw
Exactly. Install an isolator for the engine battery.

Every electronic device in the coach has an idle current draw, the fridge, the CO detector, anything electronic. Like when you turn off your computer, it still draws idle current.
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Old 04-18-2017, 12:15 PM   #9
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But there already is an isolator on the engine battery! The problem is that there are some additional loads that go directly to that battery. Unless you are referring to a battery cutout switch on the chassis battery to ground. Of course, that would do it, but then you would lose clocks and you would be always resetting all of the engine computers and actuators. Probably not a good idea since this an a Mercedes chassis and they are really finicky about this stuff.

The problem is that 2 amps is too much for a starting battery.
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Old 04-18-2017, 02:29 PM   #10
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I'd put a disconnect knob on the engine batt negative terminal and end the problem. 2 amps as SUPER high. Even 1/2 amp will cost you 12amp/hours a day and that ain't good.
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