[rov_foel]

Apologies if my ignorance borders on being offensive.

I'm looking to build a battery using Outlander modules with their bms'es on them. And i gather Simp BMS would be nice for cell balancing and more.

And I have made use of this community's search function, I only found this:

Paralleling Outlander LEV40 modules

What are the options to parallel the LEV40 cells coming from an Outlander ? Each 8S1P module contains 8 cells and internal 8 channel BMS unit. Using them as is would be easiest but i need/want a lower Voltage and higher Ah from the modules. I'd prefer to parallel at cell level than at module...

www.diyelectriccar.com

Which is about paralleling but without using the pack's original bms'es

I want to "parallel" this battery as: 5 in parallel and 2 in series, as this seems to be the easiest way to hit a common voltage level (29,6*2 = 60), because I want to use it with an inverter to get 220v. So, 24v, 36v, 48v or 60v right?
The reason I want to go the easy way is that I'm not proficient with the soldering iron.
End result is supposed to be powering the appliances and heat in an RV.

Also, if this is a damn stupid noob question, maybe you could point me towards some good resource for learning this art.

 

[john61ct]

I would only use LFP, or maybe LTO chemistry for that use case.

No matter how expert and careful you are, those high-voltage Li-ion chemistries IMO are far too susceptible to "thermal runaway" (boom bad!)

for use in or attached to a small mobile living space with humans inside.

 

[reiderM]

I would only use LFP, or maybe LTO chemistry for that use case.

No matter how expert and careful you are, those high-voltage Li-ion chemistries IMO are far too susceptible to "thermal runaway" (boom bad!)

for use in or attached to a small mobile living space with humans inside.

With a good BMS this isn't an issue.

 

[reiderM]

Apologies if my ignorance borders on being offensive.

I'm looking to build a battery using Outlander modules with their bms'es on them. And i gather Simp BMS would be nice for cell balancing and more.

And I have made use of this community's search function, I only found this:

Paralleling Outlander LEV40 modules

What are the options to parallel the LEV40 cells coming from an Outlander ? Each 8S1P module contains 8 cells and internal 8 channel BMS unit. Using them as is would be easiest but i need/want a lower Voltage and higher Ah from the modules. I'd prefer to parallel at cell level than at module...

www.diyelectriccar.com

Which is about paralleling but without using the pack's original bms'es

I want to "parallel" this battery as: 5 in parallel and 2 in series, as this seems to be the easiest way to hit a common voltage level (29,6*2 = 60), because I want to use it with an inverter to get 220v. So, 24v, 36v, 48v or 60v right?
The reason I want to go the easy way is that I'm not proficient with the soldering iron.
End result is supposed to be powering the appliances and heat in an RV.

Also, if this is a damn stupid noob question, maybe you could point me towards some good resource for learning this art.

The advice I've gotten is to have a separate BMS for each parallel string. Otherwise, the modules can become unbalanced and that's when it can get dangerous.

 

[lj516]

The more BMS the better, if you parallel modules you are increasing the risk of a cell failure going unnoticed. Having an additional BMS to watch your cells is wise, yet expensive.

 

[john61ct]

BMS failure is often the cause of packs getting murdered.

And even those costing thousands can fail.

For that use case, starting with a cell chemistry that is very difficult to ignite

is much much safer than those used for consumer EV propulsion these days.

 

[OR-Carl]

BMS failure is often the cause of packs getting murdered.

This may have once been true, but I dont think it is the case with a modern CAN enabled BMS and charger. I just finished setting up a thunderstruck motors charger and BMS, and it makes for a very safe setup. If the BMS fails to report in, the charger will shut itself off in about 500ms. I inadvertently tested this by asking the BMS to print the Help menu while charging, and it must have distracted the BMS long enough for the charge cycle to end, and log it as a BMS Timeout in the charge history. The BMS also runs a warning buzzer at Low Voltage Cutoff, but for complete safety, you would need to make sure whatever is drawing a load from the batteries also has a voltage cut-off. Most inverters have such a function, but you would have to check if the threshold is configurable, as most of them are probably set up for lead acid voltage levels.

A good BMS I would say is a must for any lithium system, regardless of the risk of thermal runaway. You dont want to destroy the bank with over/under discharge. It should also be monitoring the temperature probes, as thermal runaway does not start until you start getting up over 300 degrees F, which is way outside the safe charging/discharging range.

I have not read through the SimpBMS documentation, but it looks like it might be ideal for this situation. It will communicate over CAN with the boards already on each module, which means it should not really matter how many cells you have, or how you arrange them. The important thing is that the BMS can see every cell. Read over the installation info and do a little reading about CAN and BMSes in general, and then come back here with more specific questions. I have an interest in this topic, and will try and help answer questions if I can.

 

[john61ct]

Sorry, but relying on circuitry to prevent problems is all fine and good

but the only technical benefit of using the riskier chemistries is higher energy density.

So even if an expensive BMS is "proven" 100% reliable for decades of daily use

for this use case I will continue to reco just using an LI chemistry that is inherently safer, by at least a couple orders of magnitude.

The fact that they also can have a cycle lifespan 10x to 50x longer,

bringing the per-Ah per-year cost down cheaper than the cheapest Pb FLA

at ~$1/Ah @12V

is just icing on the cake

 

[OR-Carl]

but the only technical benefit of using the riskier chemistries is higher energy density.

I think you are forgetting about price

It is hard to beat the upfront cost of used traction batteries. I will grant you that on paper, LFP cells should outlast the other chemistries, and I do not have the experience yet to say any different. However, those are very robust batteries that are designed to handle very high loads for at least the life of a vehicle (what, around 7 years?) I suspect they will wind up being a good deal in the long run.

My next off-grid battery is going to be a repurposed traction pack. I could buy a running leaf with 40kwh of (granted, worn down) batteries for less than the cost of a 6kwh LFP bank I bought last year. Id also get a solid drive motor, a bunch of electronics, a handful of re-sellable leaf parts, and a chassis to scrap.

 

[john61ct]

OK if you are saving money

then fine if the only life you're risking is your own.

But family members coming along

No, not worth it.