samsung 40t 21700

[goatman]

I asked my battery guy to recommend a battery he had in stock for 17s4p that can handle 50 amp burst. a 25r is 10ah 80 amp and 68 cells
he came back with the Samsung 40t 21700, at 17s3p that's 12ah and 90amps. mooch rated it as good but really a 25amp cell so 75 amp burst and only 51 cells. and they 67g a piece

anyone using these?

 

[electric_nz]

I’m using the US21700 VTC6A which is similar in a 4P configuration- no trouble putting out 50A peaks. 3P would be enough but that’s only going to be 12Ah - not a huge range potentially. Also any cell used at high C rate 3C+ might have a reduced cycle life

 

[goatman]

I’m using the US21700 VTC6A which is similar in a 4P configuration- no trouble putting out 50A peaks. 3P would be enough but that’s only going to be 12Ah - not a huge range potentially. Also any cell used at high C rate 3C+ might have a reduced cycle life

im just building this bike for quick little trips like 20km range. nice and light to throw on a bus rack or carry up the stairs.
17s3p at 40 amps means my batteries dead at 51v and 40amps= 2000 watts so im still doing 30mph

with these batteries at 25/30 amp rating I tend to think 10 amp continuous wouldn't be an issue, theyre not a typical 10amp 18650.

in your 4p what kind of volt sag are you getting? 50amp peaks at what voltage?

 

[Tommm]

For 12.5A per cell peak you don't need high drainage cells, you would be fine with high energy cells too, like 50e. The 40t can do 25a cont and a bit above it peak.

 

[electric_nz]

in your 4p what kind of volt sag are you getting? 50amp peaks at what voltage?

about 4 or 5V sag at 52 A according to my watt meter. (14S pack going from 56.5V starting voltage to approx 51.5V at peak current)

Also note that 20km at say 40km/h is 1/2 hour. estimating you use 25A continuous (1/2 peak current of 50A) to maintain that speed this will require 12.5aH minimum battery and will require recharge at your destination. that's a pessimistic estimate though, depends on terrain.

 

[goatman]

in your 4p what kind of volt sag are you getting? 50amp peaks at what voltage?

about 4 or 5V sag at 52 A according to my watt meter. (14S pack going from 56.5V starting voltage to approx 51.5V at peak current)

Also note that 20km at say 40km/h is 1/2 hour. estimating you use 25A continuous (1/2 peak current of 50A) to maintain that speed this will require 12.5aH minimum battery and will require recharge at your destination. that's a pessimistic estimate though, depends on terrain.

if your getting 4 or 5 volt sag with 56v 4p at 50 amp burst I have room to fit 4p of the 21700.

im normally running at 25/30 amps. my battery dead voltage is 51v with a charged voltage of 70v. so with 3p if I cracked the throttle at 58v it would sag to 51v. I have to go 4p

thanks

 

[goatman]

For 12.5A per cell peak you don't need high drainage cells, you would be fine with high energy cells too, like 50e. The 40t can do 25a cont and a bit above it peak.

I just don't like 10 amp cells, ill take amps over ah. im weird that way less volt sag. I like dd motors but if I was running geared motors I would use 10 amp cells.