I have a 2018 Ram Promaster city cargo van with OEM 12v 70AH 120RC Sealed Led acid battery and a 160a alternator.

Sitting on top of the battery I have a 1200 Watt pure sine 100v inverter connected with 2 gauge wires and then have a 12 gauge run to the back of the van. I also have a single 12 gauge line running from the batteries hot to the middle of the van that gives in an always on 5v USB source.

To date, my power needs in the van are minimal. when I need 110v, it's for every short periods of time 15 minutes or less to run 500-800w appliances and when I do I am usually parked with the engine running.

When I've slept in the van overnight I run a 1a 5v fan from 10pm to 6am.

My battery has never been below 10v, but I do plan to install a 10v low voltage disconnect to the 12v hot line to be safe. My inverter already has a 10v low voltage disconnect.

However.. In the future, I would like to install a 200 Watt 18v 6a (max) solar flexible solar panel on my roof. It might be overkill, but the 32w x 42l size fits perfectly and will block a lot of sun and help with mid day interior temps. As I ponder how to benefit from this free power, NOTE: I am NOT looking to install or sleep with batteries in the passenger area. I would like to install a ceiling vent rated at 12v 3a when on high (specially a Max Air 14x14 fan 12v 900CFM fan). While I think I can easily run the fan overnight on low (12v 1a) and have no issues starting the van, I would like to run the fan on high (12v 3a) when the sun is strong during the day. Again, I have no plan to drain my 12v battery like a deep cycle. And finally, as I anticipate having more power than I need during the middle of the day even with a 12v 3a fan running, I would like to freeze the content of small 50w 12v freezer during the day (9am-9pm) and then keep it off and closed overnight. I would anticipate interior ambient temps to range from 90F midday to 80F night.

So my two questions...

(1) How can I connect the solar panels 20a charge controller (200W 18v 6a panel)to my battery so as not to impact/interfere my cars charging system and visa-versa? do need a switch or isolator? I am presuming my charge controller will have some protections like a reverse diode for night fall leak back.

(2) If later on I want to upgrade my battery to a new dual purpose 12v 100AH 200RC 830CCA battery will my 160a alternator be okay with having to work harder to recover for longer periods of time? Again, I do not anticipate ever draining my battery like a deep cycle battery. I will tell you I have experience with another automotive 160a alternator and a 90AH battery that would get close to 10v a lot and never had issues with either.


(3) also wondering about Charge controllers that have an output. Is that 12v? how different then directly from battery? possible (and seems so) they have a low battery output disconnect and output time schedule limit in that output?

  • 3
    This question may be better suited for electronics.stackexchange.com – user2451 Feb 18 '19 at 8:36
  • The sustainability angle is also not clear to me. Another stack exchange seems like a better fit. Or, reframe the question to make the sustainability context clear. – Jean-Paul Calderone Feb 18 '19 at 14:13
  • I noticed the OP has cross-posted the question here so I'm closing this one. – THelper Feb 19 '19 at 12:09
  • @Jean-PaulCalderone (and the other two commenters) a) I believe the correct answer is that decent solar panels are designed with a bypass diode and a blocking diode. b) There are a number of misconceptions in the OP's question that should be cleared up. c) Someone needs to tell him to isolate the power used for amenities. d) etc, etc, etc. – user8340 Jan 13 at 6:18