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Newcomer RV solar help

WV Camper

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Nov 8, 2021
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Hi, I'm brand new here and haven't been able to find a couple of probably stupidly basic answers. We have a 5th wheel RV with an Onan 5500 watt generator. We'd like to start doing more off grid camping so I am looking to upgrade the cheap battery that came with the camper with maybe 2 AGM 100AH batteries or a single lithium battery. We will user the battery to run 12V systems only as we do not have an inverter- If we want to run the AC or microwave, we can use the generator.
My questions are:
  • Do I need solar to begin with? If I can charge the batteries with the generator running a couple hours a day (assuming AGM at 50% or Lithium at 80% discharge) then I'm all set. I'd like to not have to run the generator more than that.
  • If I do need solar to help charging, then what batteries? It will need to run the 12V systems and start the generator
    • I guess we could have a different battery for starting the generator but that seems like a lot of complexity?
I have read that Lithium are not good for staring an engine but I can't find if they are just not "ideal" or just won't work at all.

Thanks to anyone that can off guidance.
 
Hi, I'm brand new here and haven't been able to find a couple of probably stupidly basic answers. We have a 5th wheel RV with an Onan 5500 watt generator. We'd like to start doing more off grid camping so I am looking to upgrade the cheap battery that came with the camper with maybe 2 AGM 100AH batteries or a single lithium battery. We will user the battery to run 12V systems only as we do not have an inverter- If we want to run the AC or microwave, we can use the generator.
My questions are:
  • Do I need solar to begin with? If I can charge the batteries with the generator running a couple hours a day (assuming AGM at 50% or Lithium at 80% discharge) then I'm all set. I'd like to not have to run the generator more than that.

No, but it could possibly eliminate the need for running the generator except for the devices that need it. A 2000W inverter could run the microwave, so the only reason you need to run the gen is for A/C.

  • If I do need solar to help charging, then what batteries? It will need to run the 12V systems and start the generator

Whether you need solar or not, you need to size your batteries based on your loads/desired run time..

    • I guess we could have a different battery for starting the generator but that seems like a lot of complexity?

Would be pretty trivial. Generator connected only to lead-acid. Lead-acid connected to $40 13.8V converter trickle charged by the 12V system.

I have read that Lithium are not good for staring an engine but I can't find if they are just not "ideal" or just won't work at all.

Lead is unmanaged. You can pull almost whatever you want from them, and they just give it and drop their voltage accordingly (often substantially).

Lithium is much lower resistance and has the potential to deliver high current, but it has a BMS that has a current limit. Surge and crank from starters often exceed those current limits. Starting a gen is way less of an issue than a vehicle. Get a clamp DC ammeter and measure the peak current the generator pulls while starting.

If you consider lithium, you need to know the charge specs of your 5er's converter. If it charges below 14.6V and floats below 13.6V, it should work fine. 14.4V boost/bulk, 13.8V absorption and 13.2V float are very common parameters for RV AC-DC converters. That works fine for LFP in most cases.
 
Lithiums may not start an engine when compared to a similarly sized battery. The BMS limits amerage output.

Do not need solar. It may come down to how much is the peace and quiet worth to you for the generator cycling on and off, or the campgrounds that may limit generator usage to certain hours.

A couple of AGM batteries like you mentioned could be charged in a few hours on the generator. AGMs have a limited charge current. Check your. Battery, but could be 33%, so two hours to charge with the correct charger considering they will not be discharged to nothing. My FLA batteries are limited to 13% AH rating charge. Lithium has a quicker charge rate. Usually 50% or greater.

A rule of thumb for boondocking is 2 golf cart batteries and 400 watts of panels. With that, keep in mind you will not be able to run nearly as much as that 5500 watt generator. With just the solar, all the lights and TV you want to watch, and a little but of heating overnight, but not a cold night where that propane blower heater blower motor is going all night long. Those cold nights would kill a battery. TO do that, I need 4 golf cart batteries.
 
There have been different reports. Some reports are that a single lifepo4 could start a generator, others are that with cheap lifepo4 batteries you may need two. The BMS will determine what surge the batteries can handle, but because lifepo4 runs at a higher voltage engines tend to start a little easier. I'd be tempted to buy two cheaper batteries with low temp charging or a single 200ah battery with a higher amp BMS and skip the lead acid altogether. SOK, HQST, and possibly ampere time (look at plus models and read specs closely as some do not have low temp charging protection). Why have to mess with maintaining a lead acid? It will still take space.
 
Also keep in mind BMSes have a continuous and a max amp rating. They vary quite a bit depending on what you buy. The max may be what you are interested in for starting a generator.
 
The 400Watts of panels suggested and a couple AGMs with an inverter will pretty much eliminate the generator running most of the time and probably be well under $1000 and work very well. Just kill the converter when on solar and plug the 30A cord into the inverter with a 15/20A adapter.
 
Besides the weak link being your battery, the next issue is your stock converter in the RV. If you replace that single lead acid battery with a couple of AGM’s, golf cart or a LiFePo4 battery, expect to run that generator a minimum of 5 hours with the stock converter(probably closer to 8). You can easily upgrade the converter for a couple hundred which will need to be done even if you do decide to go the solar route because of the predictability of the weather.
I agree with the above posters about getting an inverter. You will need two batteries if you purchase a 1500 Watt inverter or more. 1000 Watts will be fine for a single battery but you won’t likely be running your microwave or coffee machine. Outlets and TV are about it but that will certainly open up a whole new world to camping possibilities. Two 200 Watt panels are what I would look into as well. You will be able to charge a 200Ah battery easily on a nice sunny day at around 30Amps with a good Mppt controller.
 
1000 Watts will be fine for a single battery but you won’t likely be running your microwave or coffee machine
I went with a 1200W pure sine 3 years ago

800W was “enough” but my vacuum cleaner (I thought) was 750W. Vacuum is more like 900W and the ‘headroom’ of 1200 worked out nicely. I run a 5-cup coffeemaker (580-600W) simultaneously with a 5CF fridge (60-80W) and I haven’t outgrown it (I do have a ‘ spare’ new in box 1500W but I don’t need it).
Entertaining on coffee: https://diysolarforum.com/threads/coffee-maker.10201/
The 1200W ran ok on two deep cycles with 200W but when I went 120V fridge and the inverter 24/7, 400W 2S2P, 6 batteries, and mppt SCC made overnight with the fridge a non-issue.
With many 800W microwaves the 1200 would work; a lot of microwaves won’t work on that size inverter. I don’t have a microwave installed but I’ve tested an older 1000W and if the batteries are not over 12.8 it’s not a very good use. But it ran
 
1. No, you do not need solar, and if you imagine that you will regularly be running the generator anyway there is no reason to have it at all. BUT - you might pause and consider the joy of leaving the generator at home when you don't need AC. The good news: solar is just as easy to add after the fact.

2. Since Lifepo4 can accept higher charge rates, it will be MUCH better suited to generator charging. But the truth is Lifepo4 is superior in almost every way at this point and I would recommend you use it regardless. AGM is pretty much obsolete for deep cycle energy storage.

As far as engine starting, I've seen reports of people using them no problem and seen reports that they don't work. Regardless of what the internet tells you, your BMS and generator will have specific performance curves that won't be documented on a datasheet. Real world testing is king.

So I would go ahead and purchase the Lifepo4 that best suits your needs and try it. If it doesn't work, a cheap lawnmower lead acid will likely provide the needed oomph for not much penalty. A big audio capacitor is another option to support high surge currents in starting applications, but I have not tested the solution and it's a bit niche. Either way, remember that if you're running off your starting battery there's the risk of not being able to start the generator when you need it most. Having a backup plan like jumping it from the truck is essential.

Finally, if you're going to be generator charging pay close attention to the charger current specification. If you get a charger and battery that can charge at 1C, then you can limit your generator usage to one hour at a time. But if you have a 20A charger and a 100AH battery, you're going to be charging for up to 5 hours. But I'm afraid that once you start looking into the price of 100A chargers the solar will start to look mighty interesting.

Good luck!
 
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