I'm developing a battery problem...

AlexLTDLX

AlexLTDLX

Administrator
Staff member
So I know in several posts I've reiterated the idea that, when it comes to almost all things e-boost, "Nobody knows yet." My first packs were LiPo. I'm about 99% done with my new massive LTO packs. And this morning I made an impulse purchase of 160 of these:

www.ebay.com

Lot of 80 cells) Used A123 ANR26650M1B LiFeP04 3.3v 2500mAh in 10 EMC Packs | eBay

Cell Type: 26650 Lithium Ion Power Cylindrical Cell. Cycle Life at 1C/1C, 100% DOD: > 4000 cycles. Energy: 8.25 Wh. Capacity: 2.5 Ah.
www.ebay.com

I've also got everything I need to make a massive load tester - and assembly should be fairly quick, since I've taken advantage of all the cheap parts available for 3d printers - extrusions, lead screws, etc. So very soon I should be able to do a LiPo vs LTO vs LiFePo4 load test. BTW, those little LiFePo cells have a 50 amp continuous, 120 amp peak discharge... should be interesting...
 
I think it would be really useful to start a E-boost battery post for TESTED batteries.

Batteries would need to be tested for Capacity and IR since those two things are most important to us and frankly seem to be made up numbers in adds .. We need to know the real numbers.

We only need a few of each for testing. Ideally we'd use the same Testing method so results from different people would be comparable.
I just bought one of these it would be really useful if you bought the same one .. I mean you've going to have to test every cell you buy New or Old so it could be good for that.

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www.banggood.com

180W DL24P 2.4 Inch DC USB Tester Electronic Load APP 18650 Battery Capacity Monitor Discharge Charge Power Meter Supply Checker with Color Display 4-wires System

Only US$59.99, buy best 180W DL24P 2.4 Inch DC USB Tester Electronic Load APP 18650 Battery Capacity Monitor Discharge Charge Power Meter Supply Checker with Color Display 4-wires System sale online store at wholesale price.
www.banggood.com www.banggood.com

As for the specific batteries you ordered i found this rather useful. they are the smaller brother of the "AHR32113M1 Ultra-B" i just ordered

contrel.com

Contrel

contrel.com contrel.com


Im still not sure why you down graded to LTO's from lipos? Lipos have better IR and Capacity for their weight. Not that i would use Lipos cos of their many issues, but in a drag car their short comings dont matter.
 
Headway 38120HP are the other obvious contenders in the lifepo4 chemistry they are clamed to be 8ah and <2.5mohms but on you turbe the have be reviewed at less capacity and higher IR , which is why id love for them to be tested in the same manner so the results are comparable.
 
I'm switching to LTOs for a few of reasons - temperature stability, safety and incredibly low internal resistance. The biggest "strike" against LTO cells is their lack of power density. But that's not a con in this case - that allows for tremendous internal surface area. Sort of like the old adage, "There's no replacement for displacement." (that's why I crammed the biggest engine I reasonably could under my stock hood - 365 cubic inches) Plus, someone's got to do it and right now there's literally no one else - though I hope that changes soon. The specs all listed the Lishen 18ah cells at a 50c continuous discharge rate (i.e. 900 amps continuous!), and an internal resistance of less than 1 milliohm. The whole point is to minimize voltage drop under load, since I'm limited to 70 volts to the ESC. Add in the 8mm stud terminals (as opposed to the 10 gauge wire on the Lipos), and you have a recipe for (theoretical) success.

A few days ago I found a guy who actually measured the internal resistance of these cells:

He got an average of .3 milliohms. Wow. We're talking about cells that have peak burst discharge rates in the several thousands of amps. Now all this is true "in theory," but practice will tell if that holds true or not.

The LiFePo4 cells were more of an impulse buy because the were rather cheap and even at 80% capacity still should have enough juice to do the deed. But on paper not as well as the Lishen LTO cells.
 
I have never considered batteries without screw terminals because then you have to invest in a spot welder.. Also what happens when a cell dies ?? Also the welded strips are tiny... we'd need to parallel them across different cells and collect them all up into a single large gauge wire.

They still might be best once these issues are overcome... who knows we'd need to get some and test them and run the numbers. based on space, weight and cost,
 
Yeah, the spot welding is a bit of a downside. I'm not sure what I'm going to do with those 123 cells I just ordered. They do come in a holder, maybe there's something I can do to use the holders. You can make your own spot welder for a few bucks:


I've discovered using one of Lishen cells (remember I bought 60 of them) makes an excellent spot welder. That giant car-battery super cap I have just vaporizes everything. There is, however a pretty significant advantage to having multiple cells in parallel - weak cells are "averaged out." And you can get nickel strip in various widths and thicknesses. I saw a video where one guy made a high-current battery pack by using ton of nickel strips. He kind of went nuts. The other advantage of using smaller, commonly available cells is that holders for them are cheap and ubiquitous. There is the spot welded downside - taking them apart is a PITA, but there are down sides with everything. I even though about just slipping them into a tube like AA cells or something. But running the balancing wiring is difficult, unless you mill off say 1/3 of the tube length wise.
 
Those a123 cells showed up today; I pulled one out of a pack, charged it up (it was almost charged), and even discharging down to only 2.9 volts, I still got 2,350 mah. So those cells seem to be quite good. This was at a 1.5 a discharge rate. If I had taken it down to 2 instead of 2.9, we would've easily exceeded the 2.4 ah rated capacity. Just wanted to update you all.
 
I was hoping my high-zoot RC charger would tell me the internal resistance on the discharge test. Turns out it's pretty limited - not only no internal resistance results, but it also cuts off LiFePo4 cells at 2.9 volts. There's still some capacity all the way down to 2 volts... I'll have to check out my other charger and see if it will tell me.
 
AlexLTDLX said:
Yeah, the spot welding is a bit of a downside. I'm not sure what I'm going to do with those 123 cells I just ordered. They do come in a holder, maybe there's something I can do to use the holders. You can make your own spot welder for a few bucks:


I've discovered using one of Lishen cells (remember I bought 60 of them) makes an excellent spot welder. That giant car-battery super cap I have just vaporizes everything. There is, however a pretty significant advantage to having multiple cells in parallel - weak cells are "averaged out." And you can get nickel strip in various widths and thicknesses. I saw a video where one guy made a high-current battery pack by using ton of nickel strips. He kind of went nuts. The other advantage of using smaller, commonly available cells is that holders for them are cheap and ubiquitous. There is the spot welded downside - taking them apart is a PITA, but there are down sides with everything. I even though about just slipping them into a tube like AA cells or something. But running the balancing wiring is difficult, unless you mill off say 1/3 of the tube length wise.
Click to expand...
remember you know a machiniste 💁‍♂️🙋‍♂️
 
Lol. Yes indeed. Actually, I'll send you a private message later on today (I'm actually am trying to get out to the garage right now to do a little machining of my own - my load tester's almost done), but I don't have the stuff you do. I have some ideas on things we could offer to help people put together their own units.
 
AlexLTDLX said:
Lol. Yes indeed. Actually, I'll send you a private message later on today (I'm actually am trying to get out to the garage right now to do a little machining of my own - my load tester's almost done), but I don't have the stuff you do. I have some ideas on things we could offer to help people put together their own units.
Click to expand...
Im at work right now and I have a little production to make, so I have the rest of the day pretty much "off". so I can check your project and talk with you !
 
As for cylindrical cells, battery hookup has the 3800 mah k2 energy cells at $220 for a box of 120. Each cell can do 27a continuous
 
First off, welcome Nwhittredge. Our little group is growing slowly! and thanks for the links.

To be honest, the largest attraction to the Lishen LTO cells I bought is their insane continuous discharge rate and super low internal resistance. I got them from battery hookup and the cells were neither new or tested - I got a bunch of dead cells. He gave me a discount after I posted an unlisted video, but not sure I'd order from them again, even though they are relatively close. And I'm not the only one - there's a young couple converting a school bus for some other purpose, and they bought the same cells from the same supplier. They also got a few cells that had a very high self discharge - they were losing about 2-3 volts a week (!) on a 6s pack.

The reason for the massive continuous discharge and low internal resistance is that voltage drop is a big issue under load. Unless you throw down for a high voltage ESC like APD's $1,800 unit, there's not much room for voltage drop - it'll cost you boost. I'll be confirming this theory pretty soon, but it certainly does appear to hold true based on our first drag strip tests - what appears to be happening is that with more voltage drop you pull more current and the motor duty cycle drops, as does boost. More voltage gives you higher motor duty cycle and less current draw at the same time.

If I was starting from scratch and I wanted to save as much money as possible, I'd be looking for hyrbid or electric car battery modules on ebay. I found some really good deals on battery modules that would easily cost several times more than if I just bought the cells individually.
 
By the way @Alex i think i like those A123 26650 cells because of their size and how they'd fit on my tight confinements.

V Headway 38120, They are pretty much 1/2 the length so you can get 2 for the same length .. and because they are about 1/3 smaller diameter for every 3ish 38mm cell i can have one more 26 cell which actually means 2 more.

So for my enclosure i can have 14S1p of 38120 OR 14s4p 26650 ! this should result in more MAH for the space and i would expect a lower resistance too.. But i still need to order some headways and these 26650's for testing..

@Nwhittredge . you could be right. you'd have to buy some and test their real capacity and IR then you could work out have many you'd need for a similar IR...

Like Alex said and i keep banging on about too.. IR is more important than anything else (dont suggest CAPs :p)
 
MkngStffAwesome said:
By the way @Alex i think i like those A123 26650 cells because of their size and how they'd fit on my tight confinements.

V Headway 38120, They are pretty much 1/2 the length so you can get 2 for the same length .. and because they are about 1/3 smaller diameter for every 3ish 38mm cell i can have one more 26 cell which actually means 2 more.

So for my enclosure i can have 14S1p of 38120 OR 14s4p 26650 ! this should result in more MAH for the space and i would expect a lower resistance too.. But i still need to order some headways and these 26650's for testing..

@Nwhittredge . you could be right. you'd have to buy some and test their real capacity and IR then you could work out have many you'd need for a similar IR...

Like Alex said and i keep banging on about too.. IR is more important than anything else (dont suggest CAPs :p)
Click to expand...
tesla first use 18650 for there batterys and now use 26650. it supposed to be the perfect size/power for a battery. nothing wrong to use it
 
I can personally vouch for the K2 lifepo4 cells that they can push an insane amount of current but I haven't bought a good internal resistance meter. Of course LiFePO4 can't charge nearly as fast, but you can also fit more Amps and Ah in a smaller space and weight. Then again, building 26650 packs with spot welder isn't fun, even if you have a spot welder. I've been using conductive adhesive copper tape on top of my nickel strip welds to increase the current capacity in my smaller packs. Still, it's lots of work when the cells are only ~4ah each

Greentechhybridbatteries on eBay has some amazing deals on A123 pouch packs right now. Also some good deals on other OEM hybrid packs. I've been pestering them to see if they've done any capacity testing and haven't heard back. But, they do come with 30 day warranty so I suppose you could just buy one and if it fails capacity just get a refund.

I've also been chatting with Shenzen Hong Sen Feida on AliBaba for their Prismatic 33ah LTO cells rated at less than or equal to 0.38milliohms. He quoted me at roughly $1400 for 48 brand new cells shipped to MA. The form factor would certainly make it easier for the 115v pack. Only rated at 10c discharge but that would need to be verified with testing. One would expect that prismatic cells would have lower power than cylindrical.
 
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