Adding solar to a motorhome

[nairbg]

Given the complex charging system in a large old RV which charges the house batteries and the chassis battery from the engine alternator, from an onboard genset, and from a shore-power plug-in, and which includes one or more automatic "interruptors":

Is adding a 300-500W solar system simply a matter connecting the system to the batteries, or is there some controller interface with the existing system to prevent electrical conflict between the existing RV system and the solar addition?

[Mike90250]

It all depends on how the existing system is designed.

The main principle is to reserve the vehicle starting battery as absolutely top priority, so you can always start and go. With contactors and voltage sensitive relays, there are a dozen ways to cobble it together, and you have to reverse engineer it all, when you want to add another charge source.

[NCmountainsOffgrid]

RVs are wired to go directly from the Solar Panels to the Solar Controller to the HOUSE BATTERY bank.... nothing in between. The solar is simply to CHARGE the house battery bank.

Most motorhomes also make use of an INVERTER, which gives the house 120v power from the batteries when no generator is running or no 120v shore power is available.[edit: the Inverter is typically only to power low-draw amperage appliances, or basically OUTLETS, where things plug in, though it's not for anything with a high-draw, such as heaters, air conditioners, etc. - those are left to the generator or shore power only.]

I own one with all of the above.

[nairbg]

Having researched my MH's Battery Control Center (BCC) unit (F73-1020) I have discovered that there is a dynamic battery-charging priority logic built into the BCC. This logic provides that the system gives charge priority to the chassis (starter) battery when the engine alternator is feeding the system and once it reaches full charge the BCC switches charge current to the house batteries.
In the alternative, the BCC feeds shore power and the generator charge current through the converter to the house batteries first and to the chassis battery when the house batteries are fully charged.

If I convert the house battery bank to LiFePO4 batteries...
With the solar system's Charge Controller feeding directly to the house batteries I am afraid that there will be a conflict because the house/chassis batteries are mismatched and their respective charge cycle parameters are different.

I know that the Pb-acid type battery charge profile (that the converter will have resident) cannot hurt the LiFePO4 house batteries. I wonder if the Solar Charge Controller's LiFePO4 charge profile will damage the Pb-acid chassis battery? More research to follow.

[Sunking]

I know that the Pb-acid type battery charge profile (that the converter will have resident) cannot hurt the LiFePO4 house batteries. I wonder if the Solar Charge Controller's LiFePO4 charge profile will damage the Pb-acid chassis battery? More research to follow.

Huh? There is no difference between a PB Charger and LFP. They both use the exact same voltage and algorithm.

[Ampster]

Huh? There is no difference between a PB Charger and LFP. They both use the exact same voltage and algorithm.

I think what you mean is constant current and constant voltage are the same algorithms. Just my personal preference, but I prefer different voltage settings for longer life of LFPs. I do think you would agree that putting a LFP on Float or EQ would not be a good thing?

[Sunking]

I do think you would agree that putting a LFP on Float or EQ would not be a good thing?

I am not stupid. I know both Float and EQ are the exact same thing (algorithm). Like calling black ebony.

[Ampster]

I am not stupid. I know both Float and EQ are the exact same thing (algorithm). Like calling black ebony.

No, I know you are stupid, but if you assume the person asking the question is stupid they could take you literally and keep the same Pb settings for their LFPs and ruin them by keeping them at high SOC for extended periods of time. Or worse, no Float on a Pb battery so it self discharges when the motor home is parked. Maybe that is not a problem for you.

[nairbg]

Somebody here that seems to know everything apparently needs to see this:

https://www.power-sonic.com/blog/how...po4-batteries/

[Ampster]

Good post explains it better than the expert did.

[Sunking]

Somebody here that seems to know everything apparently needs to see this:

https://www.power-sonic.com/blog/how...po4-batteries/

You need to learn about batteries and chargers.You have it in your mind because the profile is different has something to do with the chargers. You see that word 3-Stage for Pb and think there is something different, there is not. It is simple Ohms Law.

If you stop and think about it, something might occur to you. Right now today if you can afford it , you can buy a LFP battery. Requires absolutely no modifications to the vehicle's electric system because LFP is directly compatible with PB at 6-volt intervals. Both Pb and LFP can be charged anywhere from 13.2 to 14.4 volts. Your vehicle is 14.2 to 14.4 volts. How can that be with your analogy?

The only reason they use 3-stage charging for Pb is TIME, something you do not have any using solar. They are made to charge as fast as possible A three stage charger just turns up the voltage during the first stage called Bulk. Typically set to 14.4 volts, same as LFP if you are going to 100%, then backs off to 13.6 to 13.8 for Float. Automobiles, telecom, data, military, and critical mission operations do not use 3-stage algorithms because it is too hard on batteries. They do not cycle batteries daily. They use Float which means nothing more than a Constant Voltage set to gentle 13.2 to 13.8 volts depending on battery type.

You just have to know something about batteries and how they charge. Any Pb charger and be used to charge a like voltage and capacity LFP. You just have to know what you are doing. Every single charge controller can be set to LFP. Stupid simple to do any 6-year old can do. Otherwise John Consumer just pays up, does not ask questions, buys something that says SMART on it to make up for their ignorance. Good marketing.

Let me know when you turn 6 and I will teach you.

[Sunking]

Good post explains it better than the expert did.

Why do I have to repeat myself? Did that years ago. It is in the STICKIES already. You just keep exposing yourself as not really knowing anything about the subject.That is what Green Mafia and Pretenders do.

FWIW smart guy, you can buy 5-stage Lithium Battery Chargers. Bulk, Absorb, Float, Restore, Rebulk. Do you need a Link. Nah you already know who it is and don't understand it.

I got a 6-stage Algorithm for Lithium and PB. Programmed it myself. Me and a couple of Peers at C&D battery came up with it. We even Patetened it. Want one? It is for sale to John Consumer.

[SunEagle]

To Ampster and Sunking. Please stop bickering with each other or I may have to give both a vacation.

[Mike90250]

Somebody here that seems to know everything apparently needs to see this:

https://www.power-sonic.com/blog/how...po4-batteries/

I like their simplified how to connect in series/parallel
https://www.power-sonic.com/blog/how...-and-parallel/
where in series, you should use a separate charger for each battery, but don't address the specifics of the right way and wrong way. But they are around to sell you batteries.

I also think that sunking made a error or typo with the battery charge profile comparisons, since I recall him having explained it differently another time. But end result, you always go with the battery mfg's recommended charging regimen. Lead acid is usually much more forgiving and fails more gracefully than Li batteries.

[Ampster]

That was all that @nairbg was trying to say. We all make mistakes in wording that can be interpreted by others not as we intended. The irony is it is all very clear in the stickies.