Adding solar to a motorhome, any conflicts?

[Johnny Lightning]

Ok guys, here's the deal. I have a motorhome with a Magnum MS2000 inverter/charger and alternator charging. I want to add solar but I'm somewhat concerned about supplying too much amperage to my 2 100AH AGM batteries with a charging limit of .3C or 30 amps. I can see situations when I will be charging the batteries from all three sources at one time if I'm running the generator to cool the coach when I'm driving. I have a couple of question>
1. Does the C rate double when I have 2 batteries or not?
2. Do I run a risk of providing too much amperage to the batteries if all three systems are charging the batteries at the same time? The inverter/charger and the solar charge controller will have temperature sensor.

I know I should upgrade to lithium batteries but that's not in the cards right now, maybe in a year or two. Any help would be appreciated.

 

[John Frum]

Ok guys, here's the deal. I have a motorhome with a Magnum MS2000 inverter/charger and alternator charging. I want to add solar but I'm somewhat concerned about supplying too much amperage to my 2 100AH AGM batteries with a charging limit of .3C or 30 amps. I can see situations when I will be charging the batteries from all three sources at one time if I'm running the generator to cool the coach when I'm driving. I have a couple of question>
1. Does the C rate double when I have 2 batteries or not?
2. Do I run a risk of providing too much amperage to the batteries if all three systems are charging the batteries at the same time? The inverter/charger and the solar charge controller will have temperature sensor.

I know I should upgrade to lithium batteries but that's not in the cards right now, maybe in a year or two. Any help would be appreciated.

With a modicum of care the inverter/charger and the alternator should not be providing charge current at the same time.
If the batteries are in parallel the charge current is split between the batteries.
So if one can take 30 amps, two can take 60 amps.
You don't mention how much charge current the alternator or solar charge controller can deliver.

 

[John Frum]

To be clear its unlikely that you will be plugged into shore power while you are driving.

 

[Johnny Lightning]

I don't know how much charge current the alternator or the solar charge controller can provide but I will likely buy a Victron 100/50 so I can control the charge current. I also don't know the charge current of the inverter/charger and it doesn't seem to be in the specs, but I've only looked once. I should probably look again. As to the inverter/charge and the alternator providing charging at the same time this is actually fairly likely as in hot climates I will have to run the genny to cool the coach when I am driving, the dash A/C won't be able to keep up. I'm trying to make this idiot proof because I can be an idiot at times. With all of that said, it's good to know that I really have 60 amps of charge current to work with instead of 30, it makes things easier.

Edit: I have found out that the maximum charge current from the inverter'/charger is 100 A, so that's quite a bit. My AGM batteries can accept a charge rate of .3C or 30 amps giving me a total charge amperage maximum of 60 for two batteries if I understand parallel wiring correctly.

 

[John Frum]

I don't know how much charge current the alternator or the solar charge controller can provide but I will likely buy a Victron 100/50 so I can control the charge current. I also don't know the charge current of the inverter/charger and it doesn't seem to be in the specs, but I've only looked once. I should probably look again. As to the inverter/charge and the alternator providing charging at the same time this is actually fairly likely as in hot climates I will have to run the genny to cool the coach when I am driving, the dash A/C won't be able to keep up. I'm trying to make this idiot proof because I can be an idiot at times. With all of that said, it's good to know that I really have 60 amps of charge current to work with instead of 30, it makes things easier.

Suggest you add a shunt based battery monitor to your system.
That will answer your questions about charge current.

 

[McCarthy]

The Victron 100/50 comes with Bluetooth / data logging / charge current reading.

 

[Cajunwolf]

I don't understand the confusion here. Any charger designed to charge your type of battery will do it correctly no matter the supply current; the charger controls what goes into the battery depending on its state of charge. If the battery is fully charged, the charger(s) should stop charging and maintain. If you're running your generator, you have an AC charger, and if driving at the same time, you have a DC to DC charger running. Both should shut down if the batteries are charged. If it were me, I'd add a switch/relay where the generator is running while driving the charger it supplies is turned off. The only time the alternator supplied DC to DC charger is needed while driving. Boondocking, you use solar or generator, and as I said, you can use both; the chargers are supposed to be in charge. (pun intended)

 

[Johnny Lightning]

To be clear its unlikely that you will be plugged into shore power while you are driving.

You are right I won't be plugged into shore power when I'm driving but I will likely at times have the genny running while driving down the road which is functionally the same thing.

 

[Johnny Lightning]

I don't understand the confusion here. Any charger designed to charge your type of battery will do it correctly no matter the supply current; the charger controls what goes into the battery depending on its state of charge. If the battery is fully charged, the charger(s) should stop charging and maintain. If you're running your generator, you have an AC charger, and if driving at the same time, you have a DC to DC charger running. Both should shut down if the batteries are charged. If it were me, I'd add a switch/relay where the generator is running while driving the charger it supplies is turned off. The only time the alternator supplied DC to DC charger is needed while driving. Boondocking, you use solar or generator, and as I said, you can use both; the chargers are supposed to be in charge. (pun intended)

I understand that the chargers will supply the correct voltage, and will stop when full charge is reached, all of them. I'm not so sure about the amperage. The inverter/charger can supply 100 amps, the solar charger can supply up to 50 amps, but I can regulate that but I'd rather not and I have no idea what the alternator can supply but I'm assuming at least 10 amps. I have two 12V AGM batteries that can be charged at .3C or 30 amps each. Combined they can absorb 60 amps and I will have 150 amps + trying to feed the batteries. What I don't know, and can't seem to find out, is do these various charging methods sense the amperage charging the batteries and adjust accordingly or simply supply what they supply with no regulation. It can't be good to supply batteries with 2.5 times the amperage they can absorb. Me thinks the results will be very short battery life. In short, voltage, which is what everyone wants to seem to talk about, isn't the issue, amperage is.

 

[Cajunwolf]

Like I said above, the charger(s) control the current, not the source(s).

 

[Cajunwolf]

If you have a 10amp charger, that's all it's going to supply, no matter the "potential" feeding it. If the battery is fully charged, the charger will not keep trying to charge it.

 

[Cajunwolf]

By the way, an alternator will put out what the load demands up to its limit; its voltage regulator controls this to a large degree. In other words, if the batteries are charged, there is no potential to attract a charging current from the alternator via the charger.

 

[Johnny Lightning]

So I see said the blind man, the various charge controllers control the current and the voltage. Is this correct?

 

[Cajunwolf]

So I see said the blind man, the various charge controllers control the current and the voltage. Is this correct?

Yeah, but terminology is important; else, folks get confused. A charger charges a battery. A solar charger is called a charge controller because it controls the charge to the batteries from the solar panels where the voltage is always varying. You can have multiple chargers working simultaneously; in your case, that's not a benefit because of the LA batteries, which is a weak point. I know you need each charger put on a separate cable to the battery. I understand you can get noise into the system if you don't, but that's not my expertise. On my RV, I'll have both the solar and alternator charging the batteries if need be when running the rooftop A/C, not for the window unit. I run my generator only when necessary.

 

[caymaanedge]

With 200ah of AGM it won’t take much to charge them and they won’t last very long with much of a load.
A 100/50 controller can handle a sizable amount of solar, probably lose to 800watts, which is way more than you can use with 200ah of AGM.
I would step back, analyze your power requirements and then build the system. A good controller will manage the battery charge. If you upgrade to LifePo4 you will need a new Magnum controller to set proper charge voltage too.

 

[Cajunwolf]

What size of motor home are we talking about? Is it a class A or C? It sounds to me like your batteries are your limitations, and you're trying to make something work around an inadequate battery bank instead of something more powerful and efficient. That's why you have to run your generator while driving, and this doesn't make sense because your alternator should be able to maintain that battery bank with no problems. I just bought four 12-volt 200ah LiFePO4 batteries configured into 24-volts at 400ah for $2400. I'm not rich, far from it, and even though I'll have to pay it off over three months, it was too good of a deal to pass up. They're going to be shoehorned into my 28-foot Class C RV. I'll be living in it shortly, and I won't have to run the generator while driving. Still, I will have an extra alternator exclusively to charge my battery bank via a 12/24-volt charger while driving if I run an air conditioner. During the day, I have 1400 watts of panels on the roof that can take care of what the alternator cannot.

 

[McCarthy]

The battery takes what it needs in terms of amps. Just because a charger can supply 2000 amps doesn't mean the battery will absorb 2000 amps. The chargers don't have to control the amount of amps and they don't, the battery does. The chargers only cut off at a certain voltage, not at a certain amperage.

The only problem you may have with a strong DC to DC charger is your alternator. If your battery can take in a 100 amp charge and you have a DC to DC charger that can convert 100 amps, your average alternator will take a shit eventually due to overheating and melting / shorting its windings.

Most car alternators can handle an extra 30 amp draw on a regular basis. But if you would pull 60 amps while idling, it may not live all that long. I got a 30 amp DC to DC charger for my minivan camper and its doing fine so far. If you have a heavy duty 280 amp alternator in a pickup truck, that thing will do fine with a 60 amp charger at idle. Not sure what your motor home alternator is rated for. If its a rather weak car style alternator and you want to charge with more than 40 amps, at idle, I'd get an aftermarket alternator with a higher rating. The issue with charging at idle is the fact that the alternator doesn't get enough cooling.

 

[Johnny Lightning]

The motorhome is a Super C with a 160 Amp alternator, or so says the build sheet I have. If you want to think of it as a Class A for this purpose you wouldn't be wrong. I realize that the batteries are a weak link in the system but I'm trying to build out the system piecemeal, thus the small batteries and a large charge controller. I already have the generator and the inverter installed on the coach and I'm not going to change them, they're what came standard on the rig and they're not broke so I'm not going to fix them. As for LiFePo batteries I'm aware of them and they're advantages but right not they're not in the cards and even if they were they wouldn't support my rooftop A/C. The only thing on the coach that is able to support the A/Cs is the generator, thus the reason I'm asking the questions here. I realize that the A/Cs will consume a great deal of the power provided by the generator but they will cycle on and off during the day. When the A/Cs are cycled off the entire output of the generator will be converted to charging current for the batteries. I guess I need to figure out if I can disable the charging function on the inverter/charger while I'm driving. But then again, it charges the batteries, presumably with 100 amps whenever I start the genny and don't run the A/C, so I'm not sure the inverter/charger is not current limiting in some fashion. I think I have more research to do. Thanks to everyone for their help.

 

[Cajunwolf]

I suppose if you're going to be on shore power or generator and an alternator while driving. In that case, the only reason to have solar is to maintain a charge on your batteries while parked, and that's very inexpensive.

 

[McCarthy]

I've got 3 Victron chargers hooked up to one battery bank. They all can charge at the same time. They all use the same cut off voltage.

It's like a big water bucket, you can fill it with one or 3 hoses.