Changing LA batteries for LIP04. Help determining if I should go 24v instead of 12v?

[Bigbillsd]

I'm considering changing my LA batteries for LIP04 this winter and trying to determine if I should go 24v instead of 12v?
If I go to 24v i would need to replace my inverter/charger. Come up with something to down-convert the 24v to 12v for all the 12v systems on the RV. Not sure about what I could start my diesel genny with if needed. That's probably a lot of 12v amps to draw thru some sort of buck converter.
The reasons I can think of to go with 24v would be that I could keep my same 50 amp MPPT controller after adding another 640 watts of panels to my roof. I am thinking that 1280 watts flat mounted would still be less than 50 amps at 24v... And the higher voltage would also not require different (thicker) battery cables to go with more AH batteries. ( 5' of 4/0 cables now between inverter and battery ) The new inverter/charger would also be a hybrid style that can supplement 20 & 30 amp shore power when needed. We really needed that a lot while traveling in Alaska and Canada for 5 months this summer. Rarely got more than a 30 amp pedestal, and quite a few were only 20 amp. Luckily it was not super hot to need AC.

Is there a compelling reason to go with 24v instead of keeping everything 12v? Something that would make the big $ changes of the inverter/charger and buck converter a little more palatable?

Thanks for your thoughts on this.

Bill

[Mike90250]

First, why are you considering change over from FLA to Li ? Are the existing batteries shot ? How long did they last you ?

My advice, rebattery with what you have, don't change to Li, don't upgrade voltage to 24V (unless you NEED it for some new loads)

There is a LOT happening in the Li battery field, and in a year or 2, there will be much better integration between chargers and BMS, and you will have a better change over.

Also, changing to Li, you get about a 20% efficiency improvement, so you may not need more PV panels.

[Ampster]

.........

There is a LOT happening in the Li battery field, and in a year or 2, there will be much better integration between chargers and BMS, and you will have a better change over.

Also, changing to Li, you get about a 20% efficiency improvement, so you may not need more PV panels.

From a few reports on SPI 2019 this may be the year of the Li self contained battery pack. Let's hope the prices find a level below $1000/kWhr in the next year or two.

For those with the skills to wire a BMS and understand the fundementals a fully functional, pack can be had for less than $500 per k/Whr using safe LFP prismatic cells. Mike points out the efficiency of Li batteries which can make charging off grid a lot less problematic because they do not have to go to 100% every charge cycle and do not self discharge the way Lead Acid batteries do. He and I have both seen situations where they can go into thermal runaway so caution has to be weighed against the other factors. The OP has already described why he is considering changing and he has some time to do the research to satisfy himself whether that is the right choice for him. It all depends on where you are standing.

[Ampster]

I might add, to address your original question, that there are fewer reasons to upgrade to a 24 volt system in an RV. It does not sound like you are adding significant loads.

Also to clarify, Lipo is a chemistry and battery type often used in remote controlled helicopters and drones. They have very high energy density but are also very volatile and account for some of the fires attributed to Lithium batteries. The safest Lithium chemistry is LFP also known as Lithium Iron Phosphate. I would only recommend LFP is much safer and still lighter per kWh than lead Acid.

[Bigbillsd]

Hi, I did mean Lithium Iron Phosphate for the battery chemistry. I am more interested in the benefits of going 24v over the 12v configuration that I am doing now. One benefit would be that I could keep the same controller (I think) I have a Victron Smart 100/50) that will do both 12 & 24v. As far as I can tell it will do 50 amp at 24v too. But changing out the inverter/charger and finding a suitable buck converter would be a lot more expensive than buying a new controller. The bi plus going with li batteries is bulk charging for all the sun prime-time hours, that should glean significantly more energy from the sun and put that into the li batteries instead of bulk till just 80%.

My current batteries are still fairly good but I would like to be able to drain them more and still have 12.5 volts. After I pull out 150 AH overnight my current batteries voltage is below 12v and things like the electric toilet don't sound very good due to the lower voltage that LA batteries produce. I also have a limited amount of battery space, I cannot get more than 4 GC2 size batteries into the RV. Hopefully li will let me stuff more AH into that space so i can keep the battery in the sweet spot of charge/discharge to up the amount of cycles they will give me.

Anyway, I want to understand the 24v vs 12v pros and cons. Thanks, Bill

[Ampster]

.......

Anyway, I want to understand the 24v vs 12v pros and cons...

If you do not need more DC power but just want the energy to last longer then there is no advantage to 24 volt. In an RV , there is more 12 volt equipment available. If you want to run a lot of AC equipment for a short period then a larger capacity 24 volt inverter would make more sense. If I understand your needs it sounds like you want more DC capacity. Do I understand your situation correctly?

One of the things that is easier to do with Lithium batteries is parallel them to make a larger pack. What you could do initially, is buy the capacity you want and run the pack at 12 volts. That would save you some expense but give you flexibility to upgrade in the future. Are you considering 3 volt prismatic cells and assembling them into a pack or are you planning on buying one of those self contained Lithium batteries with it's own BMS? That may have a bearing on the above suggestion.

[Sojourner1]

Hi, I did mean Lithium Iron Phosphate for the battery chemistry. I am more interested in the benefits of going 24v over the 12v configuration that I am doing now. One benefit would be that I could keep the same controller (I think) I have a Victron Smart 100/50) that will do both 12 & 24v. As far as I can tell it will do 50 amp at 24v too. But changing out the inverter/charger and finding a suitable buck converter would be a lot more expensive than buying a new controller. The bi plus going with li batteries is bulk charging for all the sun prime-time hours, that should glean significantly more energy from the sun and put that into the li batteries instead of bulk till just 80%.

My current batteries are still fairly good but I would like to be able to drain them more and still have 12.5 volts. After I pull out 150 AH overnight my current batteries voltage is below 12v and things like the electric toilet don't sound very good due to the lower voltage that LA batteries produce. I also have a limited amount of battery space, I cannot get more than 4 GC2 size batteries into the RV. Hopefully li will let me stuff more AH into that space so i can keep the battery in the sweet spot of charge/discharge to up the amount of cycles they will give me.

Anyway, I want to understand the 24v vs 12v pros and cons. Thanks, Bill

I can't comment on the 12 to 24v other than that seems to be the new want on rv forums.

Now with your comment on using 150ah overnight and the battery voltage at 12.5v. With my 12v 500ah lfp batteries I use 150-200ah from sundown to sunup and the batteries will be at 13.25v +/- . Just the other day after 3 weeks of bouncing between 45-95% SOC, the morning SOC was 37% (13.12v) I made 2 12 cup pots of coffee and ran the microwave for 5 minutes, SOC drop to 36% and batteries 13.06v all before 9:00am, end of day solar charged to 77% (4:45pm) good enough. Next morning 47% SOC. 45 days is the longest I've gone in a partial state of charge before solar finally topped it off.

[Ampster]

Yes, you have articulated another advantage of Lithium batteries in RVs. The flat discharge curve.

[Bigbillsd]

I can't comment on the 12 to 24v other than that seems to be the new want on rv forums. Now with your comment on using 150ah overnight and the battery voltage at 12.5v. With my 12v 500ah lfp batteries I use 150-200ah from sundown to sunup and the batteries will be at 13.25v +/- . Just the other day after 3 weeks of bouncing between 45-95% SOC, the morning SOC was 37% (13.12v) I made 2 12 cup pots of coffee and ran the microwave for 5 minutes, SOC drop to 36% and batteries 13.06v all before 9:00am, end of day solar charged to 77% (4:45pm) good enough. Next morning 47% SOC. 45 days is the longest I've gone in a partial state of charge before solar finally topped it off.

Wow, that would be awesome. I was thinking you were talking about LA batterys at first but reread it and I think you have LFP. 13v after a lot of discharging sounds like nirvana to me.

Sounds like I should stick with 12v going forward and just double my solar wattage and buy a new controller. And then if my InverterCharger ever goes kaput I will replace it with a hybrid.

Thanks Everyone!!!! -Bill

Will be home tomorrow afternoon with 10,000 more miles on the RV from our 5 month Alaska trip.

[PNW_Steve]

I went 24 volt on my RV.

1800 watts of panels, 1800 watt inverter and 4 L-16's in series.

The only DC load that I have to use a 24v-12v converter for is my Webasto. They are available in 24v but I got a rockin deal on the 12v model.

I looked at going with 12v and a 1000a/h battery bank. Battery and charge controller options were limited. I am not a fan of parallel batteries and the six 1000 a/h 2v batteries were cost prohibitive as we're charge controllers that will handle the 80+ amps that I need to keep the expensive batteries happy.