diy 500Ah best config

[PaulStafford]

I currently have 3 x 100Ah AGMs on my trailer. I'd like to upgrade to 500Ah.
There's a commercial battery from Cyclenpo with this capacity, and it would drop right in, but I'm really nervous about ordering direct from an unknown Chinese supplier- if there's any problems, I'm probably SOL.

The alternative is to DIY out of individual cells and a BMS as many on this forum have done. I've never done it, but this forum (along with Will's many YouTube videos) makes it look relatively straightforward.
This needs to be a 12V system to be compatible with the trailer system and existing MPPT, and with at least 300A max discharge current to supply my Multiplus 3kW inverter. I've gotten as far as selecting the Fortune 100Ah (4S 5P). They would fit neatly in the current battery space, and a threaded rod will hold them together just fine.

My question is - whats the best BMS and configuration to use? I haven't found anything that's directly usable in this config. Most BMS seem to have a maximum of 200A. I'm really hoping not to have to parallel multiple BMS...very expensive.

Another question is environmental. My current 3 AGMs are IP67, and I don't have a battery box (the terminals are well protected against shorts). Can these cells and/or BMS live in the Wx or do they need a box?

 

[Al D]

While your inverter can handle 3kW output, it's best not to do that from your batteries. You would be drawing more current than most wires can handle. Not to mention the C rating on your batteries is probably not even close to that. To put it into perspective, your house breakers are designed to trip around 1.8kW, almost half of what you are supposing you'll need.

Most people who have a 3kW inverter have either oversized it for longevity purposes, or are running 24V+ systems. It is not advisable to draw 300A for extended periods of times, and certainly not with your proposed batteries. Maybe if you had some 300Ah+ with a 1C rating (and even then, you'd probably be limiting the battery's lifespan a bit)...

Edit: just realized you meant to have 500Ah at 12V. So if the Fortune cells have a 1C rating, you'd be fine on that account, but you'd still need very thick wires.

 

[BentleyJ]

I'm using Cyclenpo brand automotive starting batteries in my Dodge-Cummins diesel. After a couple of years, so far so good. I ordered directly from China, shipping and delivery was relatively fast considering they had to customize both batteries by swapping the + and - terminals to fit the existing cables in the truck. Based on my experience, Cyclenpo seems to be reputable.

300A is a lot of current but a 500Ah LFP battery should be able to handle it since 300A would be well below 1C discharge rate. In this situation you would need to use a BMS that has an output designed to operate an external high current contactor. Batrium is one choice or QUCC. Even some of the popular FET based BMS products do have an aux output for operating a big contactor so the high current bypasses the BMS completely.

 

[PaulStafford]

Laserguy - my current setup uses 4/0 cables (.460" in diameter!), which according to the ABYC tables are good for 360A. I typically am never drawing more than 100A for longer periods, but have seen loads up to 200A for a few minutes, which would be .67 C on the present batteries, and .4C on the new one.

BentlyJ, really interesting you have experience with Cyclenpo. Their package is compact and cheap at $1080 for 500Ah + heater. I may reconsider, given the BMS challenges of DIY.

Still interested to know if cells are IP67 or not.

 

[Al D]

Laserguy - my current setup uses 4/0 cables (.460" in diameter!), which according to the ABYC tables are good for 360A. I typically am never drawing more than 100A for longer periods, but have seen loads up to 200A for a few minutes, which would be .67 C on the present batteries, and .4C on the new one.

BentlyJ, really interesting you have experience with Cyclenpo. Their package is compact and cheap at $1080 for 500Ah + heater. I may reconsider, given the BMS challenges of DIY.

Still interested to know if cells are IP67 or not.

4/0 wires are very thick. There's not much bend to them. On a constantly vibrating vehicle, you might want to check your connection periodically. Good job having appropraitely sized wires! I know they weren't inexpensive.

It's too bad you're really set on having a 12v system. A 24v system would decrease your current draws from the battery by half. There are 24V to 12V DC converters out there in case you want to go that route and still have 12VDC available.

As for weather resistance, remember that the Ingress Protection rating (you mentioned IP67) only applies to the device's ability to keep physical particles out. It has nothing to do with the short circuit effect caused by pooling water around the electrodes (though you mentioned your terminals are well protected, so you seem to ok there). It also doesn't include protection from UV rays, hail, bird poop, animals, or children.

 

[HRTKD]

Paul, I have the Multiplus 12/3000, powered by 560 Ah of LiFePO4. My batteries are 4s2p, two distinct batteries, each with its own BMS. My system works very well. I've stress tested it and I'm quite satisfied.

The Multiplus 12/3000 is actually 2400 watts, not 3000 watts. It works just fine with my 12 volt system. I am using 2/0 cables.

To say that using parallel BMS is very expensive is a matter of context. Compared to the cost of cells, the second BMS isn't that much. I am using the Overkill Solar 120 amp BMS for a total of 240 amps of maximum current draw. I have yet to exceed 200 amps.

With regard to placement of the LiFePO4 battery bank, I would NOT put it out in the weather. Most BMS are not sealed and would allow dirt/dust/whatever to accumulate on the internal parts. I found a "hidden" compartment in my trailer that was not used and repurposed that for my batteries and other components. LiFePO4 does not like being charged below 32°F. I put a warming system on my batteries and then insulated them. It doesn't take much energy to keep them between 35°F and 45°F. I leave my batteries in the trailer year round here in Colorado.

 

[Rocketman]

I am running a 544ah 12v battery in my MotorHome (full timer). I used a Batrium bms and eight Lishen 272ah cells. Here is a long writeup on installing it:

Batrium Watchmon Install

Hello everyone, I have a 2000 Monaco MotorHome, I will be installing eight 272ah Lishen LiFePo4 cells making a 2p4s 12v 500Ah (useable) battery. My two largest loads are a Victron MultiPlus 12/3000 inverter/charger and the engine "Boost" if my chassis battery gets low. For the BMS I chose a...

diysolarforum.com

I Love those Fortune cells and I could have gotten a larger battery using them - but the cost was a LOT more. See if you can get eight of the Eve280K cells in the spot or twelve of the 210ah (or so) cells.

I needed to stay with 12v to be able to “boost” my chassis (starting) battery if needed. If I had a non- MotorHome, I would look at 24v or 48v and run a converter back to 12v- much better on the wires, inverter, and fewer solar charge controllers. (It can actually be cheaper and the wires are easier to deal with).

On the bms’s- a Batrium is expensive, then you need everything else around it - three or four Overkill 120a 12v bms’s would be cheaper than one complete Batrium. But I do like the Batrium.

Make sure you have low temperature charging figured out. You NEVER want to charge cells below 32F or you ruin those pretty cells. ?

Good Luck!

 

[chrisski]

I currently have 3 x 100Ah AGMs on my trailer. I'd like to upgrade to 500Ah.
There's a commercial battery from Cyclenpo with this capacity, and it would drop right in, but I'm really nervous about ordering direct from an unknown Chinese supplier- if there's any problems, I'm probably SOL.

Does your trailer have a built in generator? If so lithiums may not be able to start it.

For 500+ ah of capacity, I would consider getting two cases to hold 4 X 280 ah cells each. With the L x W x H of this case, I’d see if there’s space. These cases are pricey. Can be $100 real dollars each with tax and shipping.

Reason I bring these two things up is I’m helping someone with a solar build that has a built in generator with an unknown starting amperage and the batteries are mounted below the RVs floor, on the vehicle frame.

 

[HRTKD]

The starting amperage for generators has been posted a while back. As I recall, an Onan 5500 generator was about 200 amps.

 

[chrisski]

The starting amperage for generators has been posted a while back. As I recall, an Onan 5500 generator was about 200 amps.

Thanks. The build I’m helping with has a 2400 watt Onan generator. Was considering 200 ah of 12 volt batteries. What I remembered from the thread was 100 ah of lithium would not start it, but 200 ah may.

 

[HRTKD]

Thanks. The build I’m helping with has a 2400 watt Onan generator. Was considering 200 ah of 12 volt batteries. What I remembered from the thread was 100 ah of lithium would not start it, but 200 ah may.

Depends on the BMS. A 100 Ah battery may have only a 50 amp BMS.

The reported results also involved the Overkill Solar/JBD BMS as I recall. That BMS is known for punching above its weight.