charge lithium batteries ONLY from RV Generator

Firstascent

Solar Enthusiast
Hey all,

I'd like to do some boondocking in my toy hauler trailer next month for a trip to Utah I have planned already, but I've still got a ways to go on my solar build.
So here's what I'm thinking so I don't have to be running off of my generator 24/7.

My toy hauler came with a factory installed ONAN QG 5500 generator and 2 lead-acid batteries. Obviously these batteries wouldn't last long under load (laptop's, my internet setup, residential fridge).

I already have 16 280-Ah LiFePo4 batteries (14.3kwh total) that would help immensely. So I would remove the current lead-acid batteries, install my LiFePo4 batteries, only use the generator to charge up the batteries, and then I would only need to run the generator when the batteries became too low to charge it back up again. I can even set the generator to auto start when the batteries reach specific (somewhat user selectable) voltages.

I already have a Batrium BMS, the toy hauler already has some type of converter since I can currently charge the factory lead-acid batteries with the generator.

Am I missing anything or is this really as simple as installing my batteries and BMS and removing the lead-acid batteries? (of course configuring the BMS etc)
I shouldn't need to buy anything extra at this time and would make this trip MUCH better.
The boondocking portion of the trip would probably only be about 5-7 days.
 

snoobler

Solar Honey Badger
The only concern is the charge voltage of the RV converter. If it follows a 3 phase, 14.4 bulk, 13.6-13.8 absorp and 13.2V float, should be fine.

Hopefully, you have top balanced your cells, or the BMS might trip off as the slightly higher ones go over-volt. If you can adjust the charge voltage down a bit, that can help. Batrium balancing can also help too, but don't be surprised if the BMS trips off before charging is complete the first few (several) times.
 

Firstascent

Solar Enthusiast
thanks @snoobler , I'll need to verify which converter they installed from the factory to verify. and thanks for the info/tips on the BMS as well. appreciate it!
 

HRTKD

Boondocker
What configuration are you going to use for those 16 cells?

I started with the same setup you did. Toy hauler, Onan 5500w generator and batteries on the tongue. There is a LOT to consider when replacing lead acid batteries with LiFePO4.

The converter issue that snoobler brought up is one of the top three design considerations. You also need to figure out what you're going to do about the 12v feed from the 7-pin cable. I added solar to my trailer, so that made the design a bit more complicated.
 

Firstascent

Solar Enthusiast
What configuration are you going to use for those 16 cells?

I started with the same setup you did. Toy hauler, Onan 5500w generator and batteries on the tongue. There is a LOT to consider when replacing lead acid batteries with LiFePO4.

The converter issue that snoobler brought up is one of the top three design considerations. You also need to figure out what you're going to do about the 12v feed from the 7-pin cable. I added solar to my trailer, so that made the design a bit more complicated.
Probably 4S4P

Ah yes, didn't think about the power from the 7-pin, thanks for mentioning it. How did you handle that? Since depending on how it's currently setup I don't think the BMS could turn that off.
 

HRTKD

Boondocker
Probably 4S4P

Ah yes, didn't think about the power from the 7-pin, thanks for mentioning it. How did you handle that? Since depending on how it's currently setup I don't think the BMS could turn that off.

I disconnected the 7-pin circuit from most of the trailer. I now have the 7-pin connected to an isolated circuit that contains a 12v FLA battery on the tongue, the generator, trailer breakaway brakes and tongue jack. The existing converter needs to be wired into this isolated circuit so it can keep the tongue battery charged while the generator is running.

I have 560Ah of battery in a 4s2p configuration, using a 120 amp BMS on each battery. The max amp draw of the generator is slightly higher than what my two BMS together are rated for. At this time, the isolated circuit was the easiest way to deal with that.

With your four batteries, you'll have enough amps to start the generator, even with just three batteries. With that in mind, a DC-DC charger between the 7-pin and your LiFePO4 battery bank is easier than the way I did it.
 

Firstascent

Solar Enthusiast
I disconnected the 7-pin circuit from most of the trailer. I now have the 7-pin connected to an isolated circuit that contains a 12v FLA battery on the tongue, the generator, trailer breakaway brakes and tongue jack. The existing converter needs to be wired into this isolated circuit so it can keep the tongue battery charged while the generator is running.

I have 560Ah of battery in a 4s2p configuration, using a 120 amp BMS on each battery. The max amp draw of the generator is slightly higher than what my two BMS together are rated for. At this time, the isolated circuit was the easiest way to deal with that.

With your four batteries, you'll have enough amps to start the generator, even with just three batteries. With that in mind, a DC-DC charger between the 7-pin and your LiFePO4 battery bank is easier than the way I did it.
great, and nice ideas! I may opt for a dc-dc charger as a quick solution during this temporary phase. This is going to be so nice once the solar is complete :)
 

HRTKD

Boondocker
great, and nice ideas! I may opt for a dc-dc charger as a quick solution during this temporary phase. This is going to be so nice once the solar is complete :)

I have enough solar that I don't need the charge from the tow vehicle. Or, I fire up the on-board generator. But I haven't needed that yet either, except to run the microwave.

Don't forget that LiFePO4 batteries do not like to be charged when they are under 32° F.
 

chrisski

Photon Sorcerer
When I upgrade my RV converter to handle charging my solar battery bank, I plan on going with an Iota Converter. They come in various amps. I'm looking at a 40 amp or 45 amp for the battery bank I have now.

What has sold me on this is you can buy a chip to put in the back of it based off your battery. Mine is FLA, and I'd get a chip for that, but there is also a Lithium chip available. I don't like the fact you need to buy a chip for what I do with bluetooth on my Victron Charge controller, but I found no other option. Perhaps connecting a DC power supply to the Charge controller set to 18 VDC....

This is the only RV converter I found that will deliver the amperage for my batteries and has tailorable settings (via the chip). You may not "need" this 10% amperage to charge, but that many amps will deliver a good deep charge inside the RV without a need for me to pull these batteries out, lug them back to my house, and then place on my charger, and reverse that when I put them back in.

I've got a couple of more points to research before buying, and this is mostly finding if it will work with my existing charging wire or not. Since I have 10 amps for a converter now, I think I will need to upgrade the installed 6 AWG to match the new higher amperage output, so its not just plug and play.
 

HRTKD

Boondocker
I've got a couple of more points to research before buying, and this is mostly finding if it will work with my existing charging wire or not. Since I have 10 amps for a converter now, I think I will need to upgrade the installed 6 AWG to match the new higher amperage output, so its not just plug and play.

I run 6 AWG from my 55 amp converter to my LiFePO4 battery bank, a distance of around 24". One of the voltage calculators I use says that I'll see a drop of .09v. I'm good with that.
party.gif


The specs for the IOTA Engineering IQ4 LiFePO4 plug-in module says that it charges in bulk stage at 14.7 volts. If that's true, I think my BMS would have registered a complaint as it has an over voltage protection ceiling of 14.6v. I have used my IOTA Engineering DLS-55 with IQ4 module for maybe eight hours total, not all at once. My BMS tracks over voltage triggers and so far I don't see any in the log. So I wonder if the specs in the document below are really correct with that 14.7v number. However, I haven't put my voltmeter on the wires to see what voltage is really being produced. It does say the high trigger is 14.6v which is when it switches to float mode 15 minutes later.

I sent a few questions to IOTA Tech Support tonight. I'll let you know what they say. I suspect that the criticism of the IQ4 LiFePO4 module is unfounded. Some of the blame resides with the way that IOTA worded the description of their bulk stage.

 

chrisski

Photon Sorcerer
I run 6 AWG from my 55 amp converter to my LiFePO4 battery bank, a distance of around 24". One of the voltage calculators I use says that I'll see a drop of .09v. I'm good with that.
How big is this Battery Bank?

Running numbers for me, I think its 5 foot one way and I’d use 40 to 45 amps to charge my FLA 458 AH battery bank and get between 1.5 and 3% loss with 6 AWG wire so I should be fine with that wire size. Turns out my new Battery bank is about half the distance to the converter from where the factory installed battery bank is, so that does make a difference.

Now, I would need to figure if the AC fuse size changes from an 10 amp converter to a 45 amp converter.
 

HRTKD

Boondocker
How big is this Battery Bank?

Running numbers for me, I think its 5 foot one way and I’d use 40 to 45 amps to charge my FLA 458 AH battery bank and get between 1.5 and 3% loss with 6 AWG wire so I should be fine with that wire size. Turns out my new Battery bank is about half the distance to the converter from where the factory installed battery bank is, so that does make a difference.

Now, I would need to figure if the AC fuse size changes from an 10 amp converter to a 45 amp converter.

560 Ah battery bank. 4s2p. There is a 15 amp AC breaker upstream of the converter.

I don't end up with a high C charge rate. Not even close. The converter is not my main source of charging. The solar gets that honor.
 

chrisski

Photon Sorcerer
With a bigger converter, the lead acid batteries would get the deep charge and equalization that solar just can’t get them to get the FLA years more life
 

Firstascent

Solar Enthusiast
well dang, I looked into my current configuration in the RV a little more. I thought there was an inverter from the factory but there isn't. So that changes my plan drastically.

Originally I wanted to use the generator to charge up the batteries, then run off the batteries, and recharge as needed. There is only a converter though, so I can charge the batteries, just can't run off them unless it's 12vdc. but I would need 120vac in order to work.

So this puts me back to the beginning and will need to run solely off the generator :( darn.
 

snoobler

Solar Honey Badger
I think you're only a couple components and less than $1K away from getting there.

30 or 50A service?
Do you have a transfer switch for shore/generator selection, or do you plug your umbilical into either a socket powered by the generator or shore power as needed?
 

Firstascent

Solar Enthusiast
I think you're only a couple components and less than $1K away from getting there.

30 or 50A service?
Do you have a transfer switch for shore/generator selection, or do you plug your umbilical into either a socket powered by the generator or shore power as needed?
Agreed, I'm not far off.

50A, and yes I have a ATS already from the factory for shore/generator.

I'm definitely getting a Victron inverter, and part of the problem is the end game is a 24v setup. So I don't want to purchase another inverter just for this trip to run off of 12vdc. :)
 

Samsonite801

Solar Addict
I run 6 AWG from my 55 amp converter to my LiFePO4 battery bank, a distance of around 24". One of the voltage calculators I use says that I'll see a drop of .09v. I'm good with that.
party.gif


The specs for the IOTA Engineering IQ4 LiFePO4 plug-in module says that it charges in bulk stage at 14.7 volts. If that's true, I think my BMS would have registered a complaint as it has an over voltage protection ceiling of 14.6v. I have used my IOTA Engineering DLS-55 with IQ4 module for maybe eight hours total, not all at once. My BMS tracks over voltage triggers and so far I don't see any in the log. So I wonder if the specs in the document below are really correct with that 14.7v number. However, I haven't put my voltmeter on the wires to see what voltage is really being produced. It does say the high trigger is 14.6v which is when it switches to float mode 15 minutes later.

I sent a few questions to IOTA Tech Support tonight. I'll let you know what they say. I suspect that the criticism of the IQ4 LiFePO4 module is unfounded. Some of the blame resides with the way that IOTA worded the description of their bulk stage.


I had no idea IOTA had a LiFePo4 IQ4 module for these. I've had one of the 55a chargers for many years I used for charging stuff in my shop, and I have the IQ4 module for lead-acid multi-stage... This is cool, I can repurpose this charger and use it for charging LiFePO4 bank now.

THANKS for that tidbit of useful information!
 

HRTKD

Boondocker
I had no idea IOTA had a LiFePo4 IQ4 module for these. I've had one of the 55a chargers for many years I used for charging stuff in my shop, and I have the IQ4 module for lead-acid multi-stage... This is cool, I can repurpose this charger and use it for charging LiFePO4 bank now.

THANKS for that tidbit of useful information!

I have a few questions into IOTA Tech Support on their converter and module.
 

snoobler

Solar Honey Badger
What's it worth for you to just run your generator 1-2 days in 5-7?


I have the 24V version of that I used as my "starter" system.

Power via onboard 12V.
Attach a 30A plug to the AC out and use a 30-50A adapter on your umbilical.

Disconnect IOTA from AC power while powering from the inverter.
Disconnect umbilical from inverter and connect IOTA to AC power while charging with generator.

Maybe $350 when you're done. :)

Your batteries in 4P4S config will power a full sized residential fridge for 7 days.
 

Firstascent

Solar Enthusiast
What's it worth for you to just run your generator 1-2 days in 5-7?


I have the 24V version of that I used as my "starter" system.

Power via onboard 12V.
Attach a 30A plug to the AC out and use a 30-50A adapter on your umbilical.

Disconnect IOTA from AC power while powering from the inverter.
Disconnect umbilical from inverter and connect IOTA to AC power while charging with generator.

Maybe $350 when you're done. :)

Your batteries in 4P4S config will power a full sized residential fridge for 7 days.
That's not bad at all, comparitively. I've been looking into all options more, for the area I'll be in (that has a lot of amazing boon docking spots) there is an state park with full hookups (Sand Hollow State Park) and you can even directly access all the off road trails.

$350 would get me about 2 weeks there with a 3 day break in the middle that isn't available. Unfortunately those 3 days are week days which means I'd definitely need to work and need internet, so generator running most of the "day" at minimum. This would be the cheapest option. buuuuut for $300 for a temp inverter, it's almost worth it as well. I'll have to think about this one, but I need to decide quick, I'm hitting the road on 12/18 and will be gone for 6 weeks (Southern Utah and then Sedona!)
 
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