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Old 08-22-2016, 12:47 PM   #1
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Crazy idea for keeping chassis battery topped up?

I was hoping someone who has done something similar to what I'm thinking of can chime in and let me know how it worked out.....

There will be times when my AI will be sitting for a few weeks outside with no power available. I live in northern California so I'm not worried about the house batteries because I think the 100W solar panel can keep them topped up just fine. The chassis battery however is a concern. To address this, I think I can do one of two things:

- Just disconnect it. It won't lose much charge over a 30 day period so don't worry about it (manual says 1-3% at 85*F).

- Get creative (yeah, here we go.....). I was thinking of getting a small 20W solar panel and propping it up on the dash so it gets sun through the front window (I'd park facing S for max sun). Many of these come with a 12V charge controller to avoid overcharging a battery, but I'm not sure I trust it so I don't want to just direct-connect it to the chassis battery. Here's where my crazy idea comes in (and where I need some feedback): Why not use the 12V output of the solar panel to power a small inverter, then plug something like a Deltran BatteryTender into the inverter and use that to charge the battery. The reason for doing this is the BatteryTender type devices have well-proven "smarts" to reduce the chance of hurting the battery. I realize this setup will only work during the day, but I think it would run long enough to keep the chassis battery topped up, and it would be totally self-contained so there won't be any chance of it hurting the chassis electrical system. My only concern is the behavior of the solar panel's built-in 12V charge controller and how that may impact the life of the inverter, i.e. will the current output drift around enough to fry the inverter, or does the inverter have enough smarts to deal with that.....

Thoughts?
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Old 08-22-2016, 01:02 PM   #2
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Too much effort for too little gain. The reason they have that disconnect plug down by the accelerator pedal is so you can use it, so keep things simple and use it.

It doesn't disconnect everything, otherwise the remote key fob wouldn't unlock the doors, but it disconnects enough.

If after a couple of months using the disconnect plug the starting battery doesn't stay charged up enough to start the engine, THEN it's time to look at alternatives. But jumping to alternative charging methods first before trying the OEM solution is wasteful.
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Old 08-22-2016, 02:43 PM   #3
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That chassis disconnect is the easiest, simplest thing going. Can't imagine needing another method
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Old 08-22-2016, 03:01 PM   #4
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@Protagonist and @Marks71 - Yep, totally get that, and that's why I included the "use the disconnect" option in my post. If we're only talking 20-30 days, that's the smart way to go.

I'm really just curious if someone has done something similar to the small solar panel option and how it worked out (or if it worked at all). Would be cool if it did work because the parts are pretty cheap (less than $100) and they could be used for other purposes while camping.
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Old 08-22-2016, 04:10 PM   #5
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The cigarette lighter plug is live all the time in the front dash. Get a portable solar and put it in the window and plug it into that.
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Old 08-22-2016, 04:17 PM   #6
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My solar panel kept both the house batteries and the chassis battery charged. Did AS change that?
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Old 08-22-2016, 04:30 PM   #7
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A 20 watt charging panel will likely not be able to overcharge a battery. A nearly full battery probably won't take more than a quarter amp. And with only 5-6 hours of full sun per day, I don't think you would even need to check the water level more than a couple times per year.
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Old 08-22-2016, 04:30 PM   #8
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Quote:
Originally Posted by 73shark View Post
My solar panel kept both the house batteries and the chassis battery charged. Did AS change that?
Looking at my schematics it appears to me that the rooftop solar panel is only connected to the house batteries, but I'd be very happy if that weren't the case so someone please chime in if you know. Thanks!
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Old 08-22-2016, 04:50 PM   #9
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It is my understanding that the BIM will connect the chassis battery to the house batteries (so the 100 watt solar circuit) when the chassis battery drops below a certain level and there is a charge voltage available from the House battery/solar charger or Magnum.
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Old 08-22-2016, 05:19 PM   #10
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I've been using a 20 watt solar panel to maintain the chassis battery for a few years now with great results. No need for a charge controller. I plug it into the cigarette lighter after every outing and it keeps an already charged battery topped off.
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Old 08-22-2016, 05:40 PM   #11
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And with only 5-6 hours of full sun per day, I don't think you would even need to check the water level more than a couple times per year.
On an NCV3 Interstate, the starting battery is a Group 49 AGM mounted under the driver's footwell. No wet-cells anywhere in the van.
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Old 08-22-2016, 06:01 PM   #12
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Quote:
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I've been using a 20 watt solar panel to maintain the chassis battery for a few years now with great results. No need for a charge controller. I plug it into the cigarette lighter after every outing and it keeps an already charged battery topped off.
Great to hear, thank you!
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Old 08-22-2016, 06:22 PM   #13
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Quote:
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It is my understanding that the BIM will connect the chassis battery to the house batteries (so the 100 watt solar circuit) when the chassis battery drops below a certain level and there is a charge voltage available from the House battery/solar charger or Magnum.
Interesting......

So, that would only be possible if you kept the chassis battery connected and the Main Disconnect on (i.e. keep everything connected), correct? That would be awesome as it would basically keep all of the batteries topped off assuming you had fairly regular access to sunshine. The only thing that would need to be turned off would be the propane so the switch doesn't draw the batteries down faster than the solar can top them up (and I think I read that switch draws something absurd like 1Ah when on, so it would kill the batteries pretty quickly).

Just for my education, does "BIM" equate to the "Battery Separator" in the 2017 manual?

Thanks!
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Old 08-22-2016, 07:58 PM   #14
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Mcrider has it right. The
BIM (also known as a battery separator) will close the contacts on the solenoid to join both battery banks together when one bank is below the contact voltage AND there is a charging source present.

As this is a bi-directional system, it will charge a low chassis battery if a charging source is present at the house batteries and conversely will charge the low house batteries if the alternator is operational and adding charge to the engine battery.


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