An Even Better Way to Charge the RV’s Chassis Battery with Solar!

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It seems like just a couple weeks ago I made a video about keeping your RV’s vehicle starting battery charged with solar… because it was!

But on our current road trip, we found ourselves in Bend, Oregon, which is the home of Zamp Solar.  We stopped in, and not only had they seen our video, but they had some ideas on how we could accomplish the same thing – but better and easier!  Have a look at the video to see what we did.


Basically, we replaced our existing solar charge controller with another model, the ZS-30AD.  This is a charge controller that is capable of charging two batteries (chassis and house, in our case).  The important thing to us about this controller is that the two batteries charged can have different chemistries, since we have a lithium-ion house battery, and an AGM chassis battery.  Beyond that, you can direct the proportion of the charge that goes to each battery with a simple programming step.  You’ll actually see me carry out all the programming in the video.

Besides simply swapping the panel, the only change we had to make was to run the included wiring harness from the solar charge controller to the vehicle starting battery.  That was actually the hardest part of the whole install, since it had us pulling wires.  Once we got that done, it was hooking up four electrical connections and we were done.

The charge controller we used was the ZS-30AD, which you can find toward the bottom of this page on the Zamp site:

You can find the same controller on Amazon, at this link:  Zamp ZS-30AD Solar Charge Controller

So now, I have a way to keep the chassis battery charged that doesn’t require me to do anything at all.  AND, I have the setup I came up with in the first video as a spare… Hmmmmm…..

James is a former rocket scientist, a USA Cycling coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.

    25 thoughts on “An Even Better Way to Charge the RV’s Chassis Battery with Solar!

    1. John

      How do you keep from overcharging the batteries? Does the controller have an auto shutoff? Sorry, new to this stuff.

      1. James - Post author

        Yes, exactly.
        The controller has a different programs for different types of batteries. When the battery is fully charged, it will go into “float” mode, and keep the battery just topped off without overcharging.

    2. Ted

      We actually drove through Bend a few weeks after you guys. It wasn’t till we got back that I stumbled across this event: “Descend on Bend” every September.

      I had no idea this was going on…. but then again I don’t feel “Shaggy” enough to fit in. I’m sure James is watching this aghast at all the dust flying around.

    3. Koert

      We just replaced our absorption refrigerator with an electric one and I’d love to figure out a way to keep our lead-acid batteries while installing an additional lithium battery dedicated to the refrigerator.

      This solar charge controller looks like it might be just what we need. But I’m surprised that it’s a PWM controller and not an MPPT, which is more efficient with higher voltages.

      1. James - Post author

        At the wattages, voltages and distances we’re talking about, a MPPT controller doesn’t get you a whole lot (except lighter pockets…).

        1. Martine

          I had the same concern about PWM vs MPPT. I’m not a battery expert and a complete amateur at anything electrical. However, it does not seem logical.
          1. Distance from your van Lance’s chassis battery to Zamp Dual PWM Charge Controller was only about 5-6 ft. Not a great distance.
          2. Not sure how voltage and wattage play into PWM vs MPPT.

          If MPPT is more efficient, and distance is only 6 ft, it will be more efficient in charging up the chassis battery as well as the Lithium house battery bank. Even if the chassis battery needs are small, and efficiency is not important, certainly the Lithium bank needs are great and efficiency counts here.

          I’m confused as to why you think this Zamp PWM Dual Charge Controller is better than an MPPT Charge Controller, apart from the dual function. You could have simply added a PWM single Charge Controller for the chassis battery and not affected existing efficiency of the MPPT controller for the Lithium bank. Knowing you James, you probably picked the best solution, but its not clear to me why.

        2. James - Post author

          Understand – Lance has a 7000 Watt-hour battery. The solar panels on Lance have a nominal voltage of only 18-21 volts or so (I don’t remember exactly, but that’s the range). So the extra efficiency we’re talking about here is somewhere in the neighborhood of (I’m guessing) 20-50 watt hours per day. That’s less than 1% of my total battery capacity. I’m not interested in chasing less than 1% if it costs me any money at all. Particularly since I’ll most likely be driving while I’m using the rig anyway, which provides thousands of watt-hours of charging.
          Eventually, folks will realize that solar is a very small contribution when compared to the capacity of these lithium systems.
          At least, until solar technology makes a big leap forward. And I’m sure it will one day.

          But back to Lance. The previous controler was a PWM controler anyway. So it’s not like I gave anything up.
          The main reason for this modification was to add the capability to charge the second battery (because that needs charging the most when Lance is sitting un-used). We accomplished that perfectly.

    4. Robin

      Another interesting videoJames! Wondering if your coach battery negative is floating? I was puzzled that the installer had to splice in the negative wire from the chassis battery at the controller. Figured both the chassis battery and the coach battery already had their negative sides tied to the chassis. If so wouldn’t that path suffice for the fairly low chassis battery charging current return?

    5. Robert Seidl

      James – I like this approach ! Out of curiosity – do you remember how long the cable harness needed to be for the G and what gauge Mr. Zamp used ? Also, is it really necessary to wire the ground as well ? Aren’t all the grounds of all the batteries already joined by being wired to chassis ?

      1. James - Post author

        It is true that all of the grounds are wired together…
        However, on our rig, the solar is wired directly to the battery, and I sometimes (in the winter) shut the battery completely off. Not sure if that would have induced any weirdness with the dual-battery controller (which I would like to charge the chassis battery, even if the house battery is AWOL).
        In this case, we were following the install recommendations, and basically removing any doubt about the connections. I don’t like doubt.

    6. Ray Jones

      I’m still glad you posted the first video. My fishing buddy has a pontoon boat and he is / was looking for a re-charging solution for his battery. We had seen other parked boats (on the lake) with solar cells on the rear. So when I saw your 1st video I sent him a link to it for his future reference.

      I can certainly see where the dual charge system for the house and chassis battery will come in handy! Thanks for sharing with us.

      1. James - Post author

        The first solution would definitely work well for a boat battery – particularly one that is used infrequently.

    7. Phil

      Good job!

      Does you ah battery sizing still seem appropriate in hindsight – about 430ah if I remember correctly?

      I have decided on CALB (Chinese airline battery) and there are 2 Sprinter packages available: 400 and 800ah. But for alternator charging, they only advertise the 400ah battery package; and just give a disclaimer for $$$ per additional 100ah batteries each.

      **. SO… would you bump it up to perhaps 600ah or any other optimum size given your engineering review of the accumulated empirical evidence since then? (any sweat on the eyebrows? 🙂

      Thanks Greatly for Your Expertise!

      1. James - Post author

        Our battery went through an upgrade, and is now about 7000 Watt-hours. It’s been good about 90 % of the time.
        Only once have we thought about idling the engine so we could run the air conditioner. Most of the time, we just do what we want without thinking about it too much.
        But some times, we have refrained from running the AC at night – because of the juice and/or the noise.

        Bigger is always better. I suppose if we doubled the size, we could run the AC all night. Then, even in a stagnant Wal-Mart parking lot, we’d be pretty comfortable.
        Except I’d have to argue with Stef about the noise.
        But in any case, 14,000 Watt Hours should be all you’d ever need.

        1. Phil

          Thanks for replying!

          With pretty much your same components and calculations, I got 1044ah/80% efficiency = 1300ah for 8hr night with AC (dead on with your estimate – I live in muggy SE US!) I don’t know if US can get the new Calb 400ah modules yet, but I’ll find out.

          I am going to do Exactly as you did with the same company’s Inverter Consultant, and then just specify the large Calb unit battery modules (a modest yearly replacement cost present value-wise.) I’ll work on ‘fitting’ a discrete number of 400ah battery modules to keep it simple(r.) I already have the Nation’s 2nd alternator/rectifier installed on top of my engine under the hood (but you have 5′ more linear interior floor space, less weight, and better mpg’s!)

          And by charging at 70%, I go from 2000 to 3000 charge cycles modestly estimated. I also found out the optimum storage temps are 69 to 80F temp, so I’ll blast my van’s ac until 80F is reached, where lithium battery degradation begins.

          Thanks for all of your brilliant expertise and being a guiding light for van dwellers!

      1. James - Post author

        That’s an interesting idea. I don’t know how much of an upcharge it would be for the upgraded controller, but it’s pretty darn useful!

        1. Bill Phillip

          I knew about line loss but hadn’t put 2 and 2 together as far as how that affected battery charging. Also the need to keep solar panels out of the shade as much as possible. Hope you find it interesting.

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