Is two separate battery banks a bad idea?

[FTRVR]

I am finally looking to finish my solar and Lifepoe4 install on my 5th wheel. I have already installed 1380 watts of solar and a Midnite Solar Classic 250v SCC. I My plan is to use a Samlex EVO-4024 with Lifepoe4 24v bank, and have a separate 12v Lifepoe4 bank for my 12v Hydraulic jacks, electric cord reel, furnace fan and lighting. The jacks and cord reel draw about 115 amps when setting up and breaking down camp. I originally planed on using a step down converter, but I am thinking a separate system might offer a little better way to make sure I always have power to the essentials. Everything is basically already there except the new 12v batteries. Is this a bad idea?

 

[Supervstech]

Only issue I have is, how are you charging the separate banks?

 

[FTRVR]

I am thinking of using the existing 60 amp charger/converter for the 12v bank.

 

[chrisski]

I think you are going into uncharted waters with a 24 Volt install in a fifth wheel.

I have a fifth wheel and want to upgrade to 24 VDC, but that will be in a few months at the soonest. I have no idea how many amps my converter does, but it is fused for 10 amps and can charge my single interstate battery. I am considering keeping that installed so I can run the equipment you mentioned and the breakaway brake.

What I am looking more at doing is using a VIctron 24 VDC to 12 VDC Charger. They have a converter model, but that is for supplying electricity for appliances but not for charging batteries. I am thinking of going this route because I think this will draw a lot less energy than my converter does, and if I keep the RV converter, I would need to have AC plugged in to use it. With the VIctron Charger, that would be hard wired from the 24 VDC solar battery bus bar to the 24 VDC —> 12 VDC charger to the RV 12 volt battery. This would allow it to charge while driving.

If you have a 60 amp Charge Converter, my guess its oversized for the battery, which could be fine, I would include whatever it draws.

So when my 12 volt build is finished in a couple of weeks, I am going to look at things like how much energy my converter draws. I looked at it and its connected to a regular AC plug, so I could just use a killawatt meter. I’d also take a look at the VICTRON Charger to see what sized wiring it can take. I need to be sure DC loss is not an issue if I use it and there’s max wire size. The RV Converter has been working fine for years, so if I keep that route I’d not need to worry about wiring.

Also curious why for the 12 volt battery you switched to LIthium Phospate and did not keep the lead acid? This never crossed my mind, probably because my RV charger/converter only has a lead acid profile.

If I do go 24 volts, I will be going from 1000 watts of panels to 1300 watts of panels.

 

[Jim Burrow]

I am finally looking to finish my solar and Lifepoe4 install on my 5th wheel. I have already installed 1380 watts of solar and a Midnite Solar Classic 250v SCC. I My plan is to use a Samlex EVO-4024 with Lifepoe4 24v bank, and have a separate 12v Lifepoe4 bank for my 12v Hydraulic jacks, electric cord reel, furnace fan and lighting. The jacks and cord reel draw about 115 amps when setting up and breaking down camp. I originally planed on using a step down converter, but I am thinking a separate system might offer a little better way to make sure I always have power to the essentials. Everything is basically already there except the new 12v batteries. Is this a bad idea?

As I understand it, you want to connect a 24-volt battery to a 12-volt battery in parallel. That's a bad idea as the 24-volt battery will try and charge the 12-volt battery to the same voltage potential as itself. Then when charging, the 12-volt battery will overcharge, overheat, and could explode.

Also once the two batteries are at the same voltage level, you will have a voltage level somewhere between the 12v and 24v. probably around 18v. Again that is assuming the 12v battery doesn't get destroyed.

But note, I have no experience with Lithium batteries. only 15 years with Ni-Cds, fuel cells, and lead-acid with the company I retired from in the space industry. So I could be all wet behind the ears on what I just posted. So follow the posts from the experts in this group.

 

[FTRVR]

If I was going to do it again I would go with a inverter that could power both legs of my 50amp panel. I installed a sub panel to power half the circuits but it isn't ideal.

 

[FTRVR]

As I understand it, you want to connect a 24-volt battery to a 12-volt battery in parallel. That's a bad idea as the 24-volt battery will try and charge the 12-volt battery to the same voltage potential as itself. Then when charging, the 12-volt battery will overcharge, overheat, and could explode.

Also once the two batteries are at the same voltage level, you will have a voltage level somewhere between the 12v and 24v. probably around 18v. Again that is assuming the 12v battery doesn't get destroyed.

But note, I have no experience with Lithium batteries. only 15 years with Ni-Cds, fuel cells, and lead-acid with the company I retired from in the space industry. So I could be all wet behind the ears on what I just posted. So follow the posts from the experts in this group.

The batteries will be completely separate. The 24v will only be to power AC circuits through the inverter. The 12v will only be used to power 12v loads.

 

[schmism]

The batteries will be completely separate. The 24v will only be to power AC circuits through the inverter. The 12v will only be used to power 12v loads.

Fairly typical setup for 24v solar on an RV.

Only change would likely be a buck converter to step the 24v down to 12v to charge the 12v instead of
24vDC-->120vAC -->12vDC (via existing RV charger)

 

[FTRVR]

Fairly typical setup for 24v solar on an RV.

Only change would likely be a buck converter to step the 24v down to 12v to charge the 12v instead of
24vDC-->120vAC -->12vDC (via existing RV charger

Buck converter sounds like a great idea. My existing charger/converter isn't a lifepo4 charger.

 

[schmism]

Buck converter sounds like a great idea. My existing charger/converter isn't a lifepo4 charger.

You'll still need a BMS for the LFP which will manage the battery.

 

[FTRVR]

You'll still need a BMS for the LFP which will manage the battery.

I am thinking about using 8 of the Battery Hookup 12.8v 32ah LifePo4 modules with a medical grade BMS.

 

[Hovanic]

The Victron Multiplus had an additional 4A Starter Battery Charger. After a quick read I could not see that it was 12v but I do not know why it would not be 12v. If going with a multiplus this may solve your 12v charging needs and you can get rid of the existing converter/charger.
From the manual:

Two DC outputs for charging two batteries The main DC terminal can supply the full output current. The second output, intended for charging a starter battery, is limited to 4A and has a slightly lower output voltage.

I have been bouncing back and forth from 12v to 24v for my motorhome.

The only 12v draw that I am worried about is my leveling Jacks. It is currently protected by a 100amp circuit breaker. (I have not measured how many amps it actually is drawing). With That heavy of a draw the Victron 24v-12v (orion DC-DC Converter) gets pretty expensive.

The other feature on my motorhome that would be nice to keep is the alternator charging and jump start switch. This can be solved for 12v with the LI-BIM225. If i went 24v I could use an isolated Orion 12v-24v from the alternator and buy a jump starter pack from Costco and just keep it charged in the coach. Likely costs would be close to the same.

I have not done the math on all the components to see which is more cost effective. Probably leaning towards 24v. I can leave the existing 12v lead acid battery to run the jacks and jump start circuits. I could even disconnect the existing converter/charger and just charge the 12v off the alternator. This would let me separate out the parts of the project which I can tackle at different times.

 

[chrisski]

The only 12v draw that I am worried about is my leveling Jacks. It is currently protected by a 100amp circuit breaker.

The leveling jacks on mine I am worried about also. I do have an unused clamp amp meter I will take out of the box next time I use the jacks to measure.

I do not know the specs on the jacks and the leveling system is wired directly from the battery, skipping over the self-resettable circuit breakers. If these jacks are drawing that much power, I think using a DC-DC converter would be a bad idea. Perhaps the DC to DC converter could run a breakaway, but with hydraulic jacks drawing that much power, I'd need a battery in the system and would have togo with the Victron Dc to DC charger.

 

[GSXR1000]

i would run victron DC-DC 24-12 converters they run 70 amps continuous and can be paralleled up 5 so 350 amps.. be much simpler and less loss

https://www.victronenergy.com/upload/documents/Datasheet-Orion-DC-DC-converters-high-power,-non-isolated-EN.pdf

 

[HRTKD]

I sort of threw up my hands on if my 560ah 12v LiFePO4 battery bank would be happy starting my on-board generator. The Onan service manual was useless for telling me how many amps it would pull. All it said is that a 440 CCA battery was necessary. I retained a small 12v starter battery on the tongue for the generator. It's charged by a 150w solar panel as well as the 7-pin connection to the truck. The LiFePO4 batteries are completely separate from the truck's charge circuit, they don't need a charge from the truck at all. The solar takes care of that nicely.

My ammeter at the time didn't have the ability to track the max amp draw. My new one does, so I hope to get a reading on it soon.

I've read that those hydraulic jacks can be real power hogs. I would lean towards a semi-isolated 12v battery to power it. However, getting the wiring changed over could be interesting.

 

[GSXR1000]

I sort of threw up my hands on if my 560ah 12v LiFePO4 battery bank would be happy starting my on-board generator. The Onan service manual was useless for telling me how many amps it would pull. All it said is that a 440 CCA battery was necessary. I retained a small 12v starter battery on the tongue for the generator. It's charged by a 150w solar panel as well as the 7-pin connection to the truck. The LiFePO4 batteries are completely separate from the truck's charge circuit, they don't need a charge from the truck at all. The solar takes care of that nicely.

My ammeter at the time didn't have the ability to track the max amp draw. My new one does, so I hope to get a reading on it soon.

I've read that those hydraulic jacks can be real power hogs. I would lean towards a semi-isolated 12v battery to power it. However, getting the wiring changed over could be interesting.

so I measured my Onan 4k it was inrush=115A starter running 70ishA and did max at 235A

 

[HRTKD]

so I measured my Onan 4k it was inrush=115A starter running 70ishA and did max at 235A

Thanks for posting that info!

That max measurement would be close to the rated limit of my combined BMS's. I know it's a short term draw, but I'm going to stick with the separate starter battery for now.