Adding Solar to a Motorhome

Johnny_Lightning · December 2021

I've been doing some reading here and this is what I have gathered regarding adding solar to a motorhome. First, what I currently have. I have a motorhome with a generator, shore power and an alternator, all of which charge the battery to my knowledge. The genny and the shore power are switched through an automatic transfer switch and presumably power the Magnum 2000 inverter charger. Since the inverter charger senses battery voltage it should not overcharge the battery if I add solar. It also has a temperature sensor for added protection. The next thing to be concerned about is the alternator charger when underway. Since the battery charging is regulated when the engine is running and even when the generator is running at the same time if I want to run the house air conditioning, there should not be any issue here if I add solar. This brings me to the issue of adding solar and what I need to be careful of. I can likely handle getting the solar to the batteries without much issue, there's plenty of schematics on the Internet on how to do that. My question is will anything in the solar system be adversely affected by the other charging source as they will all be charging the batteries simultaneously at some time or another. I realize that only the genny or the shore power will be charging at one time but there are absolutely times when the alternator, genny and solar will be charging at the same time. Any help will be appreciated. BTW I have and will keep for the time being 2 12V AGM batteries.

littleharbor2 · December 2021

So, say you're underway, cruising down the highway and running your A/C. Does this require the genny to be running? If so I see the issue. While all charging systems are presumably set to taper off around 14.4 - 14.8 volts the problem I see is the amount of current the batteries are going to see while bulk charging. Two, lets say, 100 Ah. AGM batteries in parallel = 200 Ah. AGM batteries can take up to 20% of their Ah. rating in charging current. Anything over 40 amps could become a problem. If you know the total amount of current you'll ever see in this scenario you may be able to add another battery to buffer any excess current. Thing is, adding more batteries, in parallel, especially AGM batteries become difficult to maintain balanced charging between batteries. You may be able to simply use higher capacity batteries next time you replace them or change chemistries to LiFePo4

Johnny_Lightning · December 2021

Yes, you are correct, I may, at times, be running my genny, solar charging, and the alternator will be charging the batteries, in this case 2 100 AH AGM batteries, at the same time.These batteries can apparently be charged at .3C or 30 amps each. Does this mean I can charge the bank of 2 at 60 amps, 30 amps or something in between? I'm thinking that an overcharging situation will overheat the batteries, but I don't know. I also don't know what the overcharging situation would cause the inverter/charger and the charge controller to do. From reading the literature it seems that if the batteries are overheating the inverter/charger and the charge controller simply reduce voltage, presumably leaving the amperage the same, but I don't know. The inverter/charger has a temp sensor on the batteries and any solar system will also, I'll most likely be using Victron control equipment with yet-to-be determined PV panels. I'm wondering if the temperature sensors will alleviate any overcharging situation. Again, I simply don't know.

Ralph Day · December 2021

Solar needs a charge controller to control how much power it puts into the batteries, along with all the other sources. Wiring a solar panel direct to battery only works when the panel is small (5-10 watts) just for overcoming self discharge (like for a seldom used tractor). Any more solar needs a charge controller.

Johnny_Lightning · December 2021

I know I need a charge controller, I left that out in the above comments, sorry. If that was the only thing I was charging the batteries with I wouldn't be asking this question. My question revolves around having 3 potential sources of charging, inverter/charger, engine and solar all charging the batteries simultaneously and interactions between the 3. This is where I'm not sure how things are going to work.

mike95490 · December 2021

If all sources are regulated to the desired battery voltage, you should have no trouble. The issue is to change the solar charge controller setting from "One size fits none" to the voltage your battery needs. 13.8V or 14.4v ??

Johnny_Lightning · December 2021

All sources will be regulated to the correct voltage, so maybe I'm OK. Littleharbor2 above was concerned about too much amperage during bulk charge. I'll have plenty available so I can see where this might be an issue, but I don't know.

littleharbor2 · December 2021

Separate charging sources aren't necessarily a problem . Again you need to be sure all sources combined don't send too much current to your batteries. Do you have a ac/dc clamp meter? You should easily be able to figure out how much total and individual current you're getting from your 3 sources.
Temp sensors will tell the inverter or CC whether to increase or decrease voltage. More voltage when cold, less when hot. As far as I know the current isn't affected. Keep in mind, when your batteries are in a low state of charge your charging sources should be "bulk" charging, allowing all available current into your batteries. As the batteries state of charge increases the current they will accept decreases. If you are using the clamp meter you should ensure you are bulk charging so that you see ALL available current.

Johnny_Lightning · December 2021

I do have a AC/DC clamp meter. It looks like I've got plenty, probably too much current available. The inverter charger I have, a Magnum MS2000 can, and probably will, supply 100 amps, or so their literature says, the solar charger I'm looking at, a Victron 100/50, can supply 50 amps, but I can regulate it. I don't know how much current the alternator will supply so that's still an unknown. It may be limited by the BIRD, but I don't know. The batteries are 2 Universal UB121000 with a charge rate of .3C per the data sheet. If I understand C rates correctly, and I might not, I can charge the pair in parallel at 60 amps. This being the case it looks like my best bet is to find a way to cut the inverter/charger out of the loop when I'm driving. I don't know if I can so this with the charger controls but I can figure it out. Thanks to everyone for their help.

littleharbor2 · December 2021

My old Trace SW40234 has adjustable charging current. Look into your inverter. They do this so as to not overload small generators. Hopefully you can dial down the current to a minimal amount for these times you are charging with all three sources.

WebPower · January 2022

You're looking to do what i did. Everything adjusts automatically to the charge currents needed by the system. My 2012 Coachman didn't charge the house batteries from the alternator. That's one of the reasons i installed the Renogy battery to battery charger. I went with renogy because it had an app with bluetooth and seemed cheaper than the Victron and had the features i wanted. My AC is too much in rush for the MS-2000 inverter. I'm going to get a 3000W to handle the turn on surge. You should take advantage of the solar if you store you RV at all while not connected to shore power. Mine tops off the engine battery and keeps it fully charged once the house is fully charged. My stock power panel doesn't have a smart charger for the house batteries so i turn it off and the MS-2000 does the charging in parallel with the Renogy's. AC excepted, i almost never use the generator unless totally off grid for an extended time. And never while driving down the road as i get over 60 amps combined from solar and alternator during the day. If you don't have an ARC-50 controller installed on the magnum you should get it as you can see charge states and set the max charge current. Look at my RV power plant installation post for parts details.
Pat

Adding Solar to a Motorhome

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