New RV, battery advice please.

[Norm01]

Hi all, new here, first post. Been watching a lot of youtube videos about batteries/solar and trying to learn as much as possible. We recently ordered an LTV U24TB RV. Won’t get it for at least another year as there’s huge backlogs in the RV world. I ordered the 400w solar panels, it will have a 2000w inverter and a 3600w generator. House batteries can be charged by solar, generator, shore power or alternator.

Situation, at first I chose the AGM batteries (2 x 100A) which was included in the cost of the RV. After much research on the net I came to the conclusion that I needed lithium’s so I upgraded my purchase order. The upgrade cost for 2 Battle Born 100A batteries is $4500 CDN (I’m in Montréal). Watched many of Will’s videos and I can get the Aliexpress 280ah kit delivered to my house for $650CDN. Two kits @ $1300 would supply me nearly 7.2kw of power versus the LTV upgrade of 2.5kw‘s for $4500. I already validated that the solar controller, dc to dc charger and house charger are all lithium compatible, just need to program them.

Assumptions, if I reverse my upgrade and go back to AGM I will have two new batteries to sell. The batteries are side by side in the footwell and I am sure all wiring can support the inverters 2000W draw.

Question, so is the proper approach to build two 12.8v, 280Ah batteries. I believe I would need two BMS’s, one for each battery. I believe once these are built it would be a simple question of removing the AGM and installing the 2 LiFeP04’s. I need BMS’s with low temp charge protection, does Daly make this yet. Also another question is, will a 100A BMS per battery suffice as once they are paralleled I would have 2,560W to power my 2000W inverter or does each battery need a 200A BMS to take the whole load.

Appreciate comments and opinions on what to do and how.

Thanks, Norm

 

[snoobler]

NORM!

Welcome to the forum.

8 cells total.

4 cells in series per battery.

1 BMS per battery.

Having two batteries with their own BMS offers some redundancy should you have an issue with one.

Overkillsolar 4S BMS is 120A and has low temp protection.

DALY SmartBMS have low temp protection.

You add the current ratings of the two BMS to get your total assuming the loads are perfectly balanced between the batteries. Assume you only get 80-90% of that for safety unless you verify the balance by measurements. If you have to take one battery out of service, you are then of course limited to the single BMS.

 

[chrisski]

Just to gauge what 2000 watt hours of power means to me.

For my 35 foot RV, I use up to 2000 watt hours of energy a night. Most of that is from the 8 amp DC propane blower motor, followed by a close second of charging a laptop computer, 125 watts when charging, being left on. Compared to thone two things, I can watch all the TV I want and charge any number of phones and tablets and not even blink at what‘s used. That high power draw is not on cold nights. If it‘s a warm night and no laptop, I can use 300 watt hours. My four golf cart batteries would last 5 days with that, or two days worst case scenario. So my energy usage swings wildly.

If your generator will auto kick on before the battery gets to 50%, it will be fine. I honestly don’t know how the auto transfer switches work.

You mention 400 watt panels? How many total? If it comes with more than 600 watts from the factory, for my use that’s great.

 

[Norm01]

It’s 400W total, 4 x 100W roof mounted panels. My Onan 3600W LP generator is auto start and can start on interior temp to cool the RV and can start on low batteries to charge. All these settings are user adjustable. The RV is a Class B+, 24ft. I know with the systems I have that the two Battle Bornes would do the job well. My post is more about value for the money. Two BB at $4500 for 2,560W is $1.75/W compared to DIY of +/- $2000 for 7,168W works out to $0.28/W that’s a factor of 6.25.

 

[Norm01]

Oh, BTW. Since my RV will have a Diesel engine I may invest in an Espar or Webasto diesel heater. Compared to the RV heater that draws 8A, these run on less than 1A and would draw diesel from my main tank. These heaters are about $1,000 now and put out 25,000btu’s. You can also do a Chinese knock off for $150 but I don’t think I would chance that in a new RV.

 

[mkaye]

don't forget about the alternator, SCC & charger - they must have an LFP profile
they should have since they offered you BB, but make sure you change them

if you have the knowledge to handle DIY LFP, then it is the better way to go, but i wouldn't recommend it if you are just trying to follow Will or any other youtube videos

 

[chrisski]

ompared to the RV heater that draws 8A, these run on less than 1A and would draw diesel from my main tank.

I'll look at that. I think the reason mine draws the 8 amps is the large central heating for the 35 foot RV with multiple rooms. The few diesel heaters I've looked at on Amazon do not have the forced air portion. I have heard that the diesel heaters are toasty warm compared to the propane.

It’s 400W total, 4 x 100W roof mounted panels. My Onan 3600W LP generator is auto start and can start on interior temp to cool the RV and can start on low batteries to charge. All these settings are user adjustable. The RV is a Class B+

I looked up the Class B you have and seems nice. Took me a long time to put the solar system together for my 35' fifth wheel and I certainly do not have the auto transfer switch for the generator. Would have been nice to have an option complete from the factory like your travel van has.

 

[pheidingsfelder]

You add the current ratings of the two BMS to get your total assuming the loads are perfectly balanced between the batteries.

Hey @snoobler , thanks for all of your insight on the forum. I have a question on this. What's the best way to make sure the loads are balanced? I'm assuming same length main positive and negative cables running to a bus bar such as the lynx distributor?
I was planning to run 24v setup until the new Multiplus II came out in 12v only. Now I'm trying to readjust my plan with 12V and the overkill 120am BMS

 

[snoobler]

Connect with best practices ("Wiring" in link #2 in my signature).

Clamp ammeter to measure current through each battery under high current charge and discharge situations.

Not a lot you can do about imbalance, but it's important to establish the currents are within ratings.

 

[TexasFan]

Once my order arrives I will be upgrading by Class B RV from 400AH AGM to 4 272AH = 1088AH of Lifepo4. I have no generator but my rig came with 2nd dedicated 270 amp alternator and a 3000w inverter. I will have to convert from built in internal regulator to a external one capable of charging Lifepo4 batteries.

My end goal of this project is be able to run the AC when and if I decide to take a nap on road trips as I like to travel in the summer.

 

[TexasFan]

RV propane heaters draw a lot of watts due to the blower fan.

 

[snoobler]

Once my order arrives I will be upgrading by Class B RV from 400AH AGM to 4 272AH = 1088AH of Lifepo4. I have no generator but my rig came with 2nd dedicated 270 amp alternator and a 3000w inverter. I will have to convert from built in internal regulator to a external one capable of charging Lifepo4 batteries.

My end goal of this project is be able to run the AC when and if I decide to take a nap on road trips as I like to travel in the summer.

Assuming a ~13500 BTU/h rooftop AC, you need to plan for a run of about 1500W, You'll need at least 4500W to start it, so if that 3000W inverter is a high frequency inverter, good luck. You can likely make it work with a micro-air soft starter installed on the A/C. From a full charge, you should get 8 hours of A/C run time with nothing else going.

RV propane heaters draw a lot of watts due to the blower fan.

My 33 and 37 ft 5th wheel propane furnaces use right around 125W each. I wouldn't call that a lot.

 

[TexasFan]

Assuming a ~13500 BTU/h rooftop AC, you need to plan for a run of about 1500W, You'll need at least 4500W to start it, so if that 3000W inverter is a high frequency inverter, good luck. You can likely make it work with a micro-air soft starter installed on the A/C. From a full charge, you should get 8 hours of A/C run time with nothing else going.



My 33 and 37 ft 5th wheel propane furnaces use right around 125W each. I wouldn't call that a lot.

My 2015 Roadtrek 190 Anniversary edition came with features not available on other 190 models. My 10000 btu AC heat pump starts fine and runs off my 4 100 AGM's but only for 1 1/2 hour. My rig with the 2nd dedicated 270 amp alternator runs the AC anytime I want while engine is running and also has Alde hydronic heater that runs on electric or propane and never gets cold inside even in below freezing temps. My rig is rated for 4 season by Roadtrek which came with every water and waste tank encased in spray on foam then covered by alum case. Only thing I could want for is more battery power for when I am stopped.

 

[mkaye]

install softstart to control the initial current draw on the batteries from the AC

 

[Epfd217]

My 33 and 37 ft 5th wheel propane furnaces use right around 125W each. I wouldn't call that a lot.

125 watts at 12.8v = 9.76 amps. That's ALOT for a furnace which makes sense for a large 5'r. Low power usage compared to electric heat, but still large draw if you're on battery only.

So if your furnace runs twice an hour for 15 mins each, every hour for 10 hours overnight....That's 48.8 amp/hours of battery just to keep your rig warm for ONE night. Hence the reason most new dry campers find out why one FLA battery doesn't last a cold weekend.

 

[snoobler]

125 watts at 12.8v = 9.76 amps. That's ALOT for a furnace which makes sense for a large 5'r. Low power usage compared to electric heat, but still large draw if you're on battery only.

So if your furnace runs twice an hour for 15 mins each, every hour for 10 hours overnight....That's 48.8 amp/hours of battery just to keep your rig warm for ONE night. Hence the reason most new dry campers find out why one FLA battery doesn't last a cold weekend.

Yep. I wish my furnaces ran that little. When it's below freezing, they run almost continuously. I have 12kWh of T-1275 and 3kW solar to get them charged back up...

 

[Epfd217]

Yep. I wish my furnaces ran that little. When it's below freezing, they run almost continuously. I have 12kWh of T-1275 and 3kW solar to get them charged back up...

Im jealous of the setup. I live in MN and frequently hunt and camp in the spring and fall. Adding a 150w solar panel to my dual 6v FLA setup made a huge difference.

To the OP, switching to a diesel heater would definitely reduce power usage compared to a forced air propane furnace. Having a genset backup is a great advantage for high draw usage like AC, microwave etc.

I think a weak point is the flexible panels glued to the roof. I would consider adding glass panels, but thats just me.

 

[Epfd217]

@snoobler , Does the Daly have low-temp protection? I thought it only had high temp cutoff. Everything I found, including Will's page, shows the Daly is high temp only.

 

[snoobler]

It's unclear to me. The only one that seems to have low temp charge protection is the Daly Smart BMS.

 

[Epfd217]

It's unclear to me. The only one that seems to have low temp charge protection is the Daly Smart BMS.

Thats what I was asking about. I dont think the Daly smart has low-temp.
Only the Overkill solar BMS has the low temp that works.