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560ah 12v Bank for Sprinter RV

Indolent58

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Sep 14, 2020
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Since I have learned so much from this forum I thought I would share my approach to upgrading my Sprinter RV's battery bank. When I bought my Winnebago ERA it had two undercarriage mounted 100Ah AGMs and no inverter. Some years ago I added a 300 watt Renogy solar array, a 20 amp MPPT charge controller and a 2000W Kisae-Abso charger/inverter. That worked fine for coffee machine and microwave use while boondocking until the LP refrigerator failed and I replaced it with a 12v Marine refrigerator. With the additional load the system could keep up most of the time but only just, and the AGMs were suffering from deep discharges. Occasionally we didn't have enough power to make coffee in the morning. Lack of coffee is unacceptable so I embarked on this upgrade. I started with the intention of just using drop in 12v replacement LIFEPO4s but learned that the exposed location of the battery holders was just bad news for Lithiums even with temperature protection. That, and the price/kwh of DIY LIFEPO4 banks made me look for ways to build a bank that would live inside the van where temperature extremes can be mitigated. Sprinter RVs have very limited interior space for new stuff and we wanted to minimize lost storage. I built a 16 gauge steel case to fit 8 280ah EVE cells that goes on the side of the rear convertible bed. The cells are managed by two Overkill Solar 4S BMS. The cells are protected from contact with the case by a combination of FR4 and heavy polypropylene sheets. To constrain the cells they are held in place by a steel plate clamped against steel angle brackets and bolts. The system is not as rigid as a threaded rod apparatus would be so the cells can't be as tightly compressed but I expect that it will be sufficient to keep them from moving much if at all. I made cell busbars out of multiple layers of 12 oz copper sheet tinned where they make contact with the cells and fabricated terminal busbars out of tinned copper bar stock, stainless steel bolts and epoxied FR4. The lid of the battery box is FR4 sheet partly for insulation and partly to make sure signals from the BMS bluetooth modules aren't blocked. As part of the project I added a Renogy 60 amp DC-DC charger to manage alternator charging. Haven't had a chance for a real world test yet but I expect that this will more than sufficient for extended boondocking.
 

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Nice box. you seem to have the same approach as I. 2 - 280ah 12v banks in parallel. Using the smaller 120ah BMS we need to watch the draw. the max is 240 on paper.
 
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Nice box. you seem to have the same approach as I. 2 - 280ah 12v banks in parallel. Using the smaller 12ah BMS we need to watch the draw. the max is 240 on paper.
Right. In my application with a 2000w inverter I would be hard pressed to exceed that.
 
How are you doing charging the 560ah with 300watts of solar? My sprinter will have the same battery bank but I am bumping my solar allowance from 400watts to 500watts based on figures to charge the bank, so hoping you can provide real life datum
 
Great job! I'm looking to do something quite similar for my Promaster. Could you tell me more about the fuse you have on the side, there? Type and capacity.
 
How are you doing charging the 560ah with 300watts of solar? My sprinter will have the same battery bank but I am bumping my solar allowance from 400watts to 500watts based on figures to charge the bank, so hoping you can provide real life datum
You're right that 300 watts of solar isn't sufficient to charge the bank by itself. But when we are on the road we rarely stay in one place for more than a few days and so far it appears that only makes a minor dent in the battery bank's SOC. Driving brings the 60 amp DC-DC charger into play which tops off the bank pretty quickly. Based on what I am seeing I don't think we will ever get under 50% SOC.
 
Great job! I'm looking to do something quite similar for my Promaster. Could you tell me more about the fuse you have on the side, there? Type and capacity.
It's a 300 amp T-class fuse. I learned from this forum that T-class fuses are needed for large lithium banks because they have a high inrush current rating. In the case of a hard short circuit a conventional fuse or breaker could blow but still pass current via arcing. The 300 amp rating was based on recommended fusing for my inverter. I put the fuse on the outside of the case because the case is pretty inaccessible can only be opened by removing the rear bed.
 
We have a NovaKool R3800. It's rated at 2.1amps @ 12v. It seems to draw more than that in real life but I haven't measured it precisely.
cool I want a 12v option. I have the original gas/electric and 2nd 4.5 Cu Ft mini fridge ran off my inverter, 200AH AGN, 710w PV. never drops much. I am going to 560AH Lifepo
 

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It's a 300 amp T-class fuse. I learned from this forum that T-class fuses are needed for large lithium banks because they have a high inrush current rating. In the case of a hard short circuit a conventional fuse or breaker could blow but still pass current via arcing. The 300 amp rating was based on recommended fusing for my inverter. I put the fuse on the outside of the case because the case is pretty inaccessible can only be opened by removing the rear bed.
I had already bought a 300A MRBF fuse for my inverter (Samlex 2000W). I wonder if this is adequate for my 560Ah battery setup...
 
I had already bought a 300A MRBF fuse for my inverter (Samlex 2000W). I wonder if this is adequate for my 560Ah battery setup...
The fuse is for the wiring. What gauge wire are your battery cables made out of?
 
did you apply any clamping force to the batteries?
looks good.. my 8 batteries are on the way
If you look at the pics the cells are clamped in place with threaded angle brackets and bolts pressing on a steel plate. I didn't have room to put threaded rods on either side of the cells. The clamping force is not as strong as it could be with threaded rod but it keeps things from moving.
 
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