diy solar

diy solar

Looking for input on an unusual RV installation

Big Eats

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Mar 23, 2021
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Greeting all!

I own a Safari Trek motorhome which currently has 50A service and uses a 2000w Xantrex modified sine wave inverter along with two FLA 12v batteries. The inverter feeds one leg of the panel which, with no surprise, does not feed the microwave or single AC unit. 50A service is clearly overkill for this coach - but that's how they built it.

I am planning on doing an unconventional upgrade to the coach - I'm going to add ~11kW of LiFePo4 batteries in a 8s2p configuration; a Samlex EVO-4024 inverter; and two separate converters (likely the AIMS Power CON120AC1224DC)... and none of this is to be permanently installed or replace my existing system - it will simply augment what I have with the existing system as a backup as I need to make sure some medical devices can always be powered.

The idea is to have sufficient ability and capacity to run the AC in the evening without being connected to shore power nor running the generator - and when I am connected to shore power (almost exclusively at friends and relatives homes) I can be recharging the LiFePo4 bank with a predictable (and controllable) amount of power while the coach can use whatever it needs at any given time. Think of it like a hybrid electric car that uses a small ICE to charge the batteries while the batteries supply the necessary power needed to run the vehicle at meet any demand asked of it.

I plan to come out of the inverter into a 30A receptacle - and then using a dog bone adapter to connect to my 50A shore cord. This way - the legs get connected together and everything gets power from the inverter until the generator is started... at that point the transfer switch will disconnect the inverter - and one of the converters will charge the battery bank. When I want to rapid charge the bank while connected to shore - I can run the generator to power one converter while using the shore power to power the other. For a small price - I get redundancy on the converter (which I need with only one 300w solar panel) and faster charging of this relatively large battery bank when I need it.

Because of my health, I probably won't be able to keep my RV for more than another two years... so I wanted to design a system that I could remove and use in a backup system at the next home of which is yet to be determined - or I could sell it with the RV if the buyer was willing to pony up the cash to buy it.

I'm open to questions and opinions on this setup, as I've just ordered my batteries through Michael Caro (16 x 270ah Lishen cells) and need to finalize my component acquisition prior to their arrival in a few months. Overkill is the intended 24v BMS. I'm also open to any suggestions regarding preparing for readying the cells for their installation.

Thanks in advance for your suggestions and comments!
 
Welcome to the forum.

Sorry to hear you're dealing with health issues.

11kWh of LFP should allow 11000*.8/1500 = 5.9 hours of A/C operation.

So you will have a self contained inverter + 24V battery bank with a 30A RV socket on it. You'll plug the RV power cord and the system will power the RV as though you were plugged into 30A shore power. This system will also power the on-board converter and float the existing 12V batteries/provide 12V power. Do I have that part?

How will the converters be wired in?

How will you charge from shore and generator when the ATS will choose one or the other?

A single 24V Overkill will only allow 2400W output. Do you intend to have 2X 8S 24V batteries, each with their own overkill with the batteries wired in parallel? You might also want to consider a Micro-air soft starter on the A/C.
 
Welcome to the forum.

Sorry to hear you're dealing with health issues.

11kWh of LFP should allow 11000*.8/1500 = 5.9 hours of A/C operation.

So you will have a self contained inverter + 24V battery bank with a 30A RV socket on it. You'll plug the RV power cord and the system will power the RV as though you were plugged into 30A shore power. This system will also power the on-board converter and float the existing 12V batteries/provide 12V power. Do I have that part?

How will the converters be wired in?

How will you charge from shore and generator when the ATS will choose one or the other?

A single 24V Overkill will only allow 2400W output. Do you intend to have 2X 8S 24V batteries, each with their own overkill with the batteries wired in parallel? You might also want to consider a Micro-air soft starter on the A/C.
Thank you.

Luckily, AC units don't require a constant 1500 watts, as they cycle on an off... and the need for AC declines when the sun goes down. :)

Yes the new system would keep the 12v batts topped off... along with the existing 300w solar panel and charge controller.

Converters would be wired directly to the battery bank... inputs would be through standard 120v plugs - one would be manually plugged in when at a shore power location and the other would be plugged in manually when I want to charge the bank off the generator.

When running on the generator, the converter plugged into the coach will charge from the generator. When I'm finished charging I will pull the plug and shut the generator down (or else the converter would try to charge the bank from the bank... which would make no sense).

When connected to shore - the other converter would charge the bank.

When connected to shore with the generator running - both converters can be used to charge the bank at twice the rate.

There will be two Overkill BMSs; one for each 24v bank in parallel.

I think the previous owner of my coach may have already installed a soft start, as I've never had any problem using a 50A to 20A adapter and running the AC while mooch-docking. That even surprised my brother in law, as he can't do that with any of his RVs.
 
Thank you.

Luckily, AC units don't require a constant 1500 watts, as they cycle on an off... and the need for AC declines when the sun goes down. :)

I'm in AZ. We have different perspectives... :)

Mine don't cycle off. Ever.

Yes the new system would keep the 12v batts topped off... along with the existing 300w solar panel and charge controller.

Cool.

Converters would be wired directly to the battery bank... inputs would be through standard 120v plugs - one would be manually plugged in when at a shore power location and the other would be plugged in manually when I want to charge the bank off the generator.

  1. So the first would be plugged into a 15A/120VAC socket at shore power - no where onboard the RV.
  2. Second would be plugged into the RV 120VAC. Inverter output would be isolated from RV AC via ATS.

When running on the generator, the converter plugged into the coach will charge from the generator. When I'm finished charging I will pull the plug and shut the generator down (or else the converter would try to charge the bank from the bank... which would make no sense).

When connected to shore - the other converter would charge the bank.

When connected to shore with the generator running - both converters can be used to charge the bank at twice the rate.

Sounds good as long as it's as 1 and 2 above.

There will be two Overkill BMSs; one for each 24v bank in parallel.

Win.

I think the previous owner of my coach may have already installed a soft start, as I've never had any problem using a 50A to 20A adapter and running the AC while mooch-docking. That even surprised my brother in law, as he can't do that with any of his RVs.

Excellent.

My only remaining concern is that you have purchased an inverter/charger, and you're not using the charger feature. You've purchased two separate converters. Consider using only 1 for generator charging.

IMHO, if this RV can reliably operate off 30A without concern, consider lightly and temporarily modifying it by connecting the Rv power cable to the inverter AC in instead of the ATS. Connect the output of the inverter to the ATS. You would need to ensure that plugging into 50A power only picks up L1, and the inverter L1 output would be jumpered to L2 as well.

This way, you plug in the RV umbilical to 15, 30 or 50A shore power, and you're using the inverter's built-in charger as well as powering loads.

RV power cord -------> L1, N G only to Samlex AC in -------> ATS in (L1 jumpered to L2, where power cord was) -------> AC panel

Once the "mobile shore power" unit is installed, this modification could be done and undone in an hour or two.

It would have an additional advantage of acting as a UPS in the event that you lost shore power.

Lastly, if you want to avoid the "manual" aspect of genny converter charging, You could run the genny L1, N, G to a MOES ATS and have it automatically engage the 24V converter for genny charging.

Genny -------> ATS1 -------> AC panel
|-->ATS2 -------> 24V converter -------> LFP battery

The only disadvantage I see is that you wouldn't get dual charging from shore and genny, but you get automatic charging from either.
 
Only thing I might add is a DC-DC converter to keep the pair of FLA batteries charged from the large LFP.
 
I'm in AZ. We have different perspectives... :)

Mine don't cycle off. Ever.

LOL - yes I can see how that works!

Excellent.

My only remaining concern is that you have purchased an inverter/charger, and you're not using the charger feature. You've purchased two separate converters. Consider using only 1 for generator charging.

IMHO, if this RV can reliably operate off 30A without concern, consider lightly and temporarily modifying it by connecting the Rv power cable to the inverter AC in instead of the ATS. Connect the output of the inverter to the ATS. You would need to ensure that plugging into 50A power only picks up L1, and the inverter L1 output would be jumpered to L2 as well.

This way, you plug in the RV umbilical to 15, 30 or 50A shore power, and you're using the inverter's built-in charger as well as powering loads.

RV power cord -------> L1, N G only to Samlex AC in -------> ATS in (L1 jumpered to L2, where power cord was) -------> AC panel

Once the "mobile shore power" unit is installed, this modification could be done and undone in an hour or two.

It would have an additional advantage of acting as a UPS in the event that you lost shore power.

Lastly, if you want to avoid the "manual" aspect of genny converter charging, You could run the genny L1, N, G to a MOES ATS and have it automatically engage the 24V converter for genny charging.

Genny -------> ATS1 -------> AC panel
|-->ATS2 -------> 24V converter -------> LFP battery

The only disadvantage I see is that you wouldn't get dual charging from shore and genny, but you get automatic charging from either.

Yes I agree... it's a shame to buy an inverter that has a decent charger in it - and then not use the charger. According to the manual - if the inverter is in use - the charger won't charge.

My understanding is that if I wire it up to feed the shore power directly into the inverter (it also allows separate input from the genny) it will pass the power through using the inverters internal ATS... but it's not a hybrid that will assist - so feeding 15A shore power will limit the system... but while it passes the power through it will charge the bank. Maybe I'm reading it wrong... anyway I shelved the idea because of the next point.

By using the inverter all the time - it's acting like a UPS. If I lose shore power - I'd never know it. Life would go on without a flicker.

I did think about a possible installation of some sort of a transfer switch that could be activated whenever the genny is started - but I haven't given it much thought. The chargers and batteries are going to be inside the coach in a closet - the inverter in the basement. I've got a few months to noodle out the details.

I like your take on it, though. I seriously considered just pulling out the existing inverter (it's only a year old - and works great) but frankly I like the idea of redundancy. Even then I would have added another converter to handle delivering faster recharge times. Thanks again. :cool:
 
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Only thing I might add is a DC-DC converter to keep the pair of FLA batteries charged from the large LFP.

In a roundabout way - it's getting charged. The new inverter would feed the existing inverter which has a built-in charger that I can turn on when the solar panel doesn't maintain a proper SOC. The motorhome also charges the house batteries when the engine is running. You make a interesting observation, though... a DC-DC converter would allow me to completely shut down the existing inverter and charger and only turn them on in an emergency... hmm...

Thank you.
 
LOL - yes I can see how that works!



Yes I agree... it's a shame to buy an inverter that has a decent charger in it - and then not use the charger. According to the manual - if the inverter is in use - the charger won't charge.

My understanding is that if I wire it up to feed the shore power directly into the inverter (it also allows separate input from the genny) it will pass the power through using the inverters internal ATS... but it's not a hybrid that will assist - so feeding 15A shore power will limit the system... but while it passes the power through it will charge the bank. Maybe I'm reading it wrong... anyway I shelved the idea because of the next point.

Correct. Very few inverters provide power assist. The Victron Multiplus and Quattro do.

Got it. You want the full 4kW available with separate charging. I see that now. A 15A shore connection would limit you. I wasn't considering that 15A shore power might be the the more common option. The separate converter allows for a continuous 15A feed while you can run 4kW as needed.

By using the inverter all the time - it's acting like a UPS. If I lose shore power - I'd never know it. Life would go on without a flicker.

I did think about a possible installation of some sort of a transfer switch that could be activated whenever the genny is started - but I haven't given it much thought. The chargers and batteries are going to be inside the coach in a closet - the inverter in the basement. I've got a few months to noodle out the details.

I like your take on it, though. I seriously considered just pulling out the existing inverter (it's only a year old - and works great) but frankly I like the idea of redundancy. Even then I would have added another converter to handle delivering faster recharge times. Thanks again. :cool:
 
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