2 amp battery draw with main disconnect off

[jk6164]

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!

[SeaDog]

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

[FOURWHL]

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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[toslow]

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

[sgtlm17]

2 amp draw on engine battery sounds awful high. I would track down what's drawing on that battery.

[FFred]

"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.

[bclemens]

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.

[SidecarFlip]

Originally Posted by toslow

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.

[ScottBrownstein]

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.

[camaraderie]

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.

[ScottBrownstein]

You could do that but as I said, the MB guys will probably will flip. Better solution is to move those two loads over the the house batteries and wire them directly to the battery or through the battery disconnect switch. 2 amps is way too much for the starting battery but it is still significant for the house as well. Of course don't walk out the door with the main disconnect turned off or "mind the first step" and nobody is going to expect to use the slides with the disconnect turned off.

[jk6164]

Originally Posted by ScottBrownstein

You could do that but as I said, the MB guys will probably will flip. Better solution is to move those two loads over the the house batteries and wire them directly to the battery or through the battery disconnect switch. 2 amps is way too much for the starting battery but it is still significant for the house as well. Of course don't walk out the door with the main disconnect turned off or "mind the first step" and nobody is going to expect to use the slides with the disconnect turned off.

I was wondering what could be drawing power when everything was off. I will check those two items next time I get it out of storage. It doesn't make sense that the house and engine batteries are connected as there is the bypass button I use when the engine battery is dead and use the house batteries to start it. Thanks for the advise. Would be nice to have the drawing of the electric system.

[ScottBrownstein]

Remember the MB mechanic said you "have a 2 amp draw on the engine battery coming from the coach when the main disconnect is off." What he means is that it is not coming from HIS engine or chassis. B Clemens indicated that you have the steps and the slide controller connected to the chassis battery. You already have a battery isolator and that is why you have to depress the boost switch to start when the chassis battery is dead! Your problem is undoubtedly the two loads that he indicated are drawing from the chassis. Move them and put them through the main switch and your problem is solved. On my 1997 Bounder I could shut off either the chassis or the house or both. If I didn't remember to leave the steps out, I would have to jump down or back up as the switches weren't close to the door.

From what I see in storage lots, a lot of coaches allow this since there is no way to leave a coach with the steps extended unless the controller goes through a shutoff.

[270S]

Originally Posted by ScottBrownstein

From what I see in storage lots, a lot of coaches allow this since there is no way to leave a coach with the steps extended unless the controller goes through a shutoff.

There is a switch installed on my GT 270 allowing me to leave the steps extended or extend/retract with the door open/close. Another cool feature is that if I left the switch there and go inside and start to drive, the steps will retract automatically compensating for any stupidity (forgetfulness) on my part.


BTW, I removed ALL Parasitic loads wired directly to the battery. They are on the coach side of the disconnect switch, not the battery. I installed a covered bus bar to connect them all (?8)

[ScottBrownstein]

You are right, never thought about it that way. Mine too. The point was, if your step controller is a parasitic load and you put it on the disconnected side of the switch, when you open the door the steps won't extend...unless you already left them that way before your flipped the switch. Frankly I don't know why they put these loads directly to the battery. Perhaps there is a RIVA code on some of the "safety" units.

[bclemens]

I doubt it is the step, because that is pretty common....I think we wire direct on that one due to the lock-out set up to prevent driving away with the steps out.

As for the slide...I believe that is recommended by the slide mfg. I think that was a result of 99% of slide issues being low voltage. By wiring to the chassis battery, chassis running and E-brake on, they ensure proper voltage for the slide out equipment. It's the easiest way to get the voltage they want.

[ScottBrownstein]

Sounds reasonable, if the chassis is dead you can't drive away without starting and that will power the steps!

[jk6164]

Originally Posted by bclemens

I doubt it is the step, because that is pretty common....I think we wire direct on that one due to the lock-out set up to prevent driving away with the steps out.

As for the slide...I believe that is recommended by the slide mfg. I think that was a result of 99% of slide issues being low voltage. By wiring to the chassis battery, chassis running and E-brake on, they ensure proper voltage for the slide out equipment. It's the easiest way to get the voltage they want.

. That is interesting as the slide will not work with the engine running as we found out trying to defrost the window early one morning this spring returning from FL.

[jk6164]

Originally Posted by jk6164

. That is interesting as the slide will not work with the engine running as we found out trying to defrost the window early one morning this spring returning from FL.

Question: does the chassis battery charge when the generator is running?

[270S]

Originally Posted by bclemens

I doubt it is the step, because that is pretty common....I think we wire direct on that one due to the lock-out set up to prevent driving away with the steps out.

As for the slide...I believe that is recommended by the slide mfg. I think that was a result of 99% of slide issues being low voltage. By wiring to the chassis battery, chassis running and E-brake on, they ensure proper voltage for the slide out equipment. It's the easiest way to get the voltage they want.

Too many years flying - Do it right the first time, NO Inside Diamond, follow procedures,.... Before I leave or Start engine, .... Turn on Battery Disconnect switch, remove power cord, check all DC & AC Remote Control Displays (ensures all is well with all power sources), check cabinets locked, propane locker, ... Yes a checklist, no exceptions!

So my steps won't be affected by "forgetting". Call me OCD, that is why a checklist. Military manuals include lessons learned based on mistakes made in the past. Checklists are an aid to assist in eliminating that.