Just in the planning stage

[DocRobbs]

I am planning replacing bad Trojan T105 batteries in my RV. I am starting with 8 GC2 Trojans with 2 Magnasine MS2812 inverters. If I was starting from scratch I would go to higher than the 12V system but that would not fit with everything allready built for 12V.

The MS2812 inverters and handle quite a bit of amperage and that is my dilemma. Continous it will take 234 Amps and up to 325 Amps on a surge. I'm on a budget and it's getting streched. Building my own I would go with the group buy 280Ah cells. If I use a 2P4S configuration that would give me 12V 560Ah but what do I use as a BMS. Daly has one that goes to 200-300Amps but no temp sensors. I like the ones at Overkill Solar but they are 120 Amps. I could go with 2 4S configuration with the BMS and then put these in parallel.

I'm looking for suggestions and recs on what else I'd need. If I go with the overkill BMS can I get away with using the bluetooth app or do I need to build in a monitoring system?

My wife wants me to get a plug and play set up and I like the BigBattery 12V 170Ah powervault as it is essentially the same size as the T105's but 4 of them is over budget and 2 of them isn't enough.

 

[Steve_S]

MS2812 (MS2812-G, MS2812-U)​

The MS Series Inverter/Charger – a pure sine wave inverter designed specifically for the most demanding mobile, backup, and off-grid applications. The MS Series Inverter/Charger is powerful, easy-to-use, and best of all, cost effective.
Battery Profile Presets: Using the ME-RC, ME-ARC, or ME-MR Remote Controls, easily choose from and set standard battery profiles, including Lithium Iron Phosphate (LFP) – only available via the ME-RC and ME-MR, Gel, Flooded, AGM1, and AGM2.

Source: https://www.magnum-dimensions.com/product-inverter/2800w-12vdc-pure-sine-inverter-charger-ms-series

The Inverter will support LFP so you have an immediate advantage for using it. Choosing DIY or Prebuilt really comes down to budget & how much your willing to have faith in what your assembling with DIY. It is a leap of faith for a lot of folks... Anyone who is reasonably "handy" and has healthy respect & knowledge of electrical in general can assemble a very good, long-lasting battery system. Will's videos certainly help in that line, in so much as the assembly and making it all work.

Plug & Play can be good and can be awful as well. Battleborn, SimpliPhi, Relion and other "Big Commercial" companies you know what your getting, the backing & warranty behind the products. Smaller more aggressive prebuilder's can be really good, BigBattery has learned several valuable lessons and has made every effort to improve and is making good progress... That is in large part to Will's Videos and evals, again doing a Good Service to Solay & DIY Enthusiasts and even the Company to improve itself... Will also discovered some pretty shoddy prebuilts, as well as some of the membership here, myself included.

At present the 280AH cells are the "going thing" due to price & capacity but as they became popular the pressure is on for the pricing due to availability. Other similar capacity cells are hitting the market which are of good quality at good prices. These are of course "commodity cells" which means they pass manufacturing specs & standards but are not Matched and Batched together with thorough testing.

My personal suggestion would be to build two battery packs of 4 cells in series (4S), each with BMS & Fused, placed in parallel. A 4S 250A+ BMS is not so easy to come by. The Battleborn, Big Battery etc, none of them have that kind of amp support. Two packs sharing the load & charge capacity in parallel is more workable, and with 150A+ BMS' it's fairly straight forward. Higher amp capacity BMS' are better, just to ensure you can take the surges & loads when they happen. That and most FET BMS' are "optimistic" with their capacities, so best to have elbow room. Hi & Lo Temp sensing depends on your location & conditions but having both in a mobile environment is wise, especially with the weird freaky weather in many places. Many like the BlueTooth option for monitoring & configuring, it is a very convenient option and can save stresses.

Hope it helps, Good Luck

 

[HRTKD]

I went with 4s2p. Each battery has its own 120 amp OverKillSolar BMS. I haven't pushed it hard, only a 90 amp draw at most so far. This is limited because I have only a 1000 watt inverter.

Plug-and-play is nice, Fewer wires, a less complicated system. More expensive. If I had gone with Battleborn, the batteries alone would have been around $5k. DIY from China, I spent just over $900, plus the cost of the BMS. I'm very satisfied with my system.

When I was running the Trojan T-105's I never would have run my vacuum off of the inverter. Now, I hardly think twice about it. Sometimes I even leave the lights on when I'm not using them!

 

[DocRobbs]

Thanks, that's what I'm looking at. We seem to "Boondock" quite a bit and my wife likes it be just like home! Clearly when we need the A/C we'll run the generator but for lights and some other conveniences (I can't go without my coffee) I'd like to on batteries. The trojans died when we had a power failure and we were away from the rig and that bottomed them out just from a refrigerator. I thought we were safe since we were on shore power and didn't know about the PF until we returned.

 

[DocRobbs]

I've thought about a few more questions I hope you guys can help with. Will expresses concern about the vibration and the busbars and terminal connection. I'm trying to mitigate that and I don't know if having the cells tight together in a case would be better or slightly spaced with a dampening i.e. thin layer of rubber sheeting. I also thought about using cables in a C shape instead of bars to act as a shock absorber/dampener. Cables would be a lot of components, crimps ect and therefore maybe more things to fail. I was also thinking of some kind of dampening of the case mounting.


Has anyone had trouble with vibration damage to their terminals? Am I overly concerned?

 

[HRTKD]

I'm upgrading my RV in steps. I conceded that I couldn't afford a new inverter, so to run the microwave and air conditioning I run the on-board generator.

I have four 320w panels. Two on the roof and two portable panels deployed on the ground. With all four panels and full sun, I think I will be able to run the air conditioner with minimal to no draw on the battery. When I get to the point of upgrading the inverter I'll also install a soft start module on the air conditioner.

 

[HRTKD]

I've thought about a few more questions I hope you guys can help with. Will expresses concern about the vibration and the busbars and terminal connection. I'm trying to mitigate that and I don't know if having the cells tight together in a case would be better or slightly spaced with a dampening i.e. thin layer of rubber sheeting. I also thought about using cables in a C shape instead of bars to act as a shock absorber/dampener. Cables would be a lot of components, crimps ect and therefore maybe more things to fail. I was also thinking of some kind of dampening of the case mounting.


Has anyone had trouble with vibration damage to their terminals? Am I overly concerned?

The road out of camp last week was really rough due to 15" of snow and repeated freeze/thaw cycles. Plus I was moving fast to keep up my speed for the hills. I was working on my batteries yesterday and saw no ill effects. My batteries are compressed with threaded rod and 3/4" plywood. I have no spacers between the cells. If you use spacers, the standard bus bars may not fit well. The plywood ends of my compressed pack are attached to the "floor" using 1" angle aluminum.

Unless a battery pack is poorly secured and not well compressed, I don't think vibration and the bus bars is an issue.

 

[DocRobbs]

Thanks, I like the idea of compression between plywood casing. That would mimic what benefit the Fortune cells have. Back to the drawing board!

 

[HRTKD]

You don't need much force on the threaded rod. As I recall, I torqued each nut to 21 inch lbs. I was able to pick up the entire 4 cell battery pack using the threaded rod.