Do I need to compress these batteries?

[Number21]

I'm building a 4s 2p starting battery out of some of the used SPIM08HP pouch cells from Battery Hookup. I'm trying to get rid of my giant lead acid starting batteries in my truck.

I have made 2 separate packs of 4 cells each. Each one is not going to be charged past 4.0 volts per cell (16.0 total). These batteries can handle starting my truck easily with 1p, let alone 2p! (It's also got 2 separate chargers, 2 protection boards, and a lot of other things that aren't worth going into here)

I am essentially using these batteries like capacitors. The starter will pull less than 100A per battery, and then be charged back to 16.0v. Obviously I only need to use the starter for a few seconds. They will not be fully cycled.

Given this super low stress lifestyle, do I still need to compress these pouch cells? If so, everybody says you can just put 4 long bolts through each corner, since they have a nice little plastic protector around them. What about the top and bottom, do I need some kind of plate there? They seem kind of flimsy at both ends if you bolt them together.

 

[Daddy Tanuki]

I cannot comment on if you need to or not, but what I will say is that compression discussions on this forum, are like oil discussions on any car forum.... deep deep rabbit hole. good luck.

 

[Number21]

I cannot comment on if you need to or not, but what I will say is that compression discussions on this forum, are like oil discussions on any car forum.... deep deep rabbit hole. good luck.

Understood. The main thing I wonder is if I'm only using for a 3 sec pulse, does that make it less likely to need compression than a cycled battery? I'm probably just nit picking.

Definitely each stack of 4 will be compressed, only the ends are open. (Though they do have some plastic straps across the battery ends, but they're pretty small and loose)

And just to be clear I spent little money on these and I do not need them to last forever.

 

[Daddy Tanuki]

i would go with a restraint system that offers little to no compression at 75% and only start to offer compression above 75% of discharge. I built mine with springs calibrated to give 12 PSI across the face at 75% of full charge. at full charge the springs are fully compressed and the batteries see 15 PSI Across the face.

this is the accepted (by most if not all of the threads i could find for EVE, CATL and other aluminum cased prismatic's. For Nylon(plastic) cased cells like Calb, Sinopoly and Winston they simply recommend a banded fixture with no possibility of expansion that is essentially 0 PSI at low levels of charge and ramps up as the cell charges. (to what nobody can tell me.) however Winston, Sinopoly and CALB have all been in the game for over 20 years so there is surly some method to their madness???

 

[Number21]

Interesting, little more complicated than I thought for some of the big stuff! This battery should stay close to 75% most of the time. They will immediately be recharged to 16.0v after a start. (It will always be hooked up to a much larger 48v battery) Might have to adjust the charging voltage a bit, I'm hoping to see 15v at the starter, after all the various connections and voltage drops.

It's funny how we think of cranking batteries as having so much power, but in reality it only takes like 3 watts to start a big engine! LOL

 

[Brucey]

Batteryhookup sells the compression rods for those.

 

[Number21]

Batteryhookup sells the compression rods for those.

Did you even read the question?

The question concerns the two open ends of the battery pack when bolted together. Battery hookup does not say. If you look at the batteries they were originally removed from, they do indeed have a steel plate on each end, but they were also meant for a different purpose.

 

[Brucey]

Did you even read the question?

The question concerns the two open ends of the battery pack when bolted together. Battery hookup does not say. If you look at the batteries they were originally removed from, they do indeed have a steel plate on each end, but they were also meant for a different purpose.

Not sure what your budget is:

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[Number21]

Not sure what your budget is:

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Looking for the best Spim End Plates in the US? Sriko Batteries is the perfect choice; we are the top online electronics store for electronics. We deliver the lithium-ion battery in US. We have the best BMS for lithium-ion batteries.

srikobatteries.com

That is very nice, I was thinking of using a plastic cutting board like that, but not so sure if it was stiff enough. I already need to make some plastic covers for the ends over all the terminals, these giant things scare me!

 

[OffGridForGood]

It's funny how we think of cranking batteries as having so much power, but in reality it only takes like 3 watts to start a big engine! LOL

3W?
Let's see,
I put a DMM on my 5.7Hemi and it took about 300 A at 14 volts to start it up.
300 x 14 = 4200W

this only took 3 seconds though,
3 seconds x 4200W/3600seconds per hour = 3.5Wh

 

[Number21]

3W?
Let's see,
I put a DMM on my 5.7Hemi and it took about 300 A at 14 volts to start it up.
300 x 14 = 4200W

this only took 3 seconds though,
3 seconds x 4200W/3600seconds per hour = 3.5Wh

What's your point? Wow, you can do math. And no, a 5.7L engine on a lead acid battery does not see 300 amps. More like 120. If it's using 300 amps you need a new starter or you must have 15:1 compression...

My 5.7L Chevy starter is rated at 1.4kw, or 120 amps. Yours is the same unless you're building a diesel out of it. Even all the fancy high torque/gear reduction aftermarket starters use in the low hundreds.

Also if it takes a full 3 seconds of cranking something is broken.

 

[OffGridForGood]

What's your point?

3Wh not 3W

 

[hwy17]

What's your point? Wow, you can do math. And no, a 5.7L engine on a lead acid battery does not see 300 amps. More like 120. If it's using 300 amps you need a new starter or you must have 15:1 compression...

My 5.7L Chevy starter is rated at 1.4kw, or 120 amps. Yours is the same unless you're building a diesel out of it. Even all the fancy high torque/gear reduction aftermarket starters use in the low hundreds.

Also if it takes a full 3 seconds of cranking something is broken.

Motors draw startup surges. A starter motor especially is not gonna have a clean amperage number, it's gonna jump all around and could easily be double it's rating in the first split second.

 

[Daddy Tanuki]

please folks stop splitting hairs.. which is what you are all doing. better things to argue about.

 

[Zwy]

Interesting, little more complicated than I thought for some of the big stuff! This battery should stay close to 75% most of the time. They will immediately be recharged to 16.0v after a start.

4S LFP at 16.0V is 4V per cell. Better rethink that.

(It will always be hooked up to a much larger 48v battery) Might have to adjust the charging voltage a bit, I'm hoping to see 15v at the starter, after all the various connections and voltage drops.

Don't count on system resistance, use a voltage regulator such as a DC to DC charger that can limit the voltage to 3.65V max per cell.

It's funny how we think of cranking batteries as having so much power, but in reality it only takes like 3 watts to start a big engine! LOL

600A x 12V = 7200W

400A x 12V = 4800W

I have yet to find a starter drawing 3 watts when cranking over an engine. Not even on a lawnmower.

 

[MattiFin]

LFP at 16.0V is 4V per cell. Better rethink that.


Don't count on system resistance, use a voltage regulator such as a DC to DC charger that can limit the voltage to 3.65V max per cell.


600A x 12V = 7200W

400A x 12V = 4800W

I have yet to find a starter drawing 3 watts when cranking over an engine. Not even on a lawnmower.

Everyone is so fixated on lifepo4 but these cells appear to be 4.2v li-ion variety.

I’d compress the cells if your target is more than 1-2year lifetime, lithium-polymer pouch cells are notorious for swelling. As well as catching on fire.

Depending on where you live I’d also include ample headroom for cold starts.
Gasoline guzzers are not that bad, but even small 2l diesel is easily 800A in -20C weather if your battery supports it. Might start with less. Or not.

 

[Zwy]

Everyone is so fixated on lifepo4 but these cells appear to be 4.2v li-ion variety.

I see now that you corrected me.

I’d compress the cells if your target is more than 1-2year lifetime, lithium-polymer pouch cells are notorious for swelling. As well as catching on fire.

I only buy lead acid starting batteries and only those the caps can be removed. Actually I get free ones all the time.

I use a DC welder to blow sulfation off the plates and use those for starting batteries. Those that don't come back to life get scrapped.

I charge the li-ion batteries for the ebikes outside and off the bike. I don't need to burn down the nice shed or shop. Eventually these will be LFP.

Sometimes a deal isn't such a great deal.

Depending on where you live I’d also include ample headroom for cold starts.
Gasoline guzzers are not that bad, but even small 2l diesel is easily 800A in -20C weather if your battery supports it. Might start with less. Or not.

The starter surge after the glow plugs cycle is the big killer of batteries on diesels.

Modern gassers with fuel injection need power for fuel pump, ecm, ignition, fuel injectors. Not a small amount of power, one doesn't get far when the alternator goes out.