nukezero
10 kW
riba2233 said:
I think 3A is indicative of a normal sized pack. For example, most home-built packs are now alteast average 6P paired with a common Bafang mid-drive at 18Amp. 18Amp max / 6p = 3A max draw per cell.
Samsung 25R/LG 18650HE2/ Sony VTC5 high power 18650 battery
- Thread starter Ebikebert
- Start date
I think 3A is indicative of a normal sized pack. For example, most home-built packs are now alteast average 6P paired with a common Bafang mid-drive at 18Amp. 18Amp max / 6p = 3A max draw per cell.
Yeah, if you are going to use 3 A per cell (which is great for cells), no need for buying high rate cells, buy cells like 29E or PF, they are very cheap and have more capacity. Or even something like 32E which costs similar but has almost 30% more capacity 
nukezero
10 kW
riba2233 said:Yeah, if you are going to use 3 A per cell (which is great for cells), no need for buying high rate cells, buy cells like 29E or PF, they are very cheap and have more capacity. Or even something like 32E which costs similar but has almost 30% more capacity
oh yeah that's right, 32E !
robocam
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Let's say I have a device that presents a 5A load. Is there any advantage to using a 25r (20A maximum discharge rating) over a 26f (5.2A maximum discharge rating)? Would the 25r be able to hold a higher voltage under that 5A load, last longer (more usable amp hours), and/or have a greater cycle life since it is not worked as hard?
If there are advantages, do they still hold true under a 2.75A load, or do the advantages lower in magnitude?
The scenario is an ebike that presents a either a 22A or a 40A load to a pack that has 8 groups in parallel (14 in series for 51.8V). I'm trying to determine if it is worth paying more for a pack made with 25r cells vs 26f cells.
If there are advantages, do they still hold true under a 2.75A load, or do the advantages lower in magnitude?
The scenario is an ebike that presents a either a 22A or a 40A load to a pack that has 8 groups in parallel (14 in series for 51.8V). I'm trying to determine if it is worth paying more for a pack made with 25r cells vs 26f cells.
riba2233 said:Yeah, if you are going to use 3 A per cell (which is great for cells), no need for buying high rate cells, buy cells like 29E or PF, they are very cheap and have more capacity. Or even something like 32E which costs similar but has almost 30% more capacity
Ohbse
10 kW
robocam said:Let's say I have a device that presents a 5A load. Is there any advantage to using a 25r (20A maximum discharge rating) over a 26f (5.2A maximum discharge rating)? Would the 25r be able to hold a higher voltage under that 5A load, last longer (more usable amp hours), and/or have a greater cycle life since it is not worked as hard?
If there are advantages, do they still hold true under a 2.75A load, or do the advantages lower in magnitude?
The scenario is an ebike that presents a either a 22A or a 40A load to a pack that has 8 groups in parallel (14 in series for 51.8V). I'm trying to determine if it is worth paying more for a pack made with 25r cells vs 26f cells.
riba2233 said:Yeah, if you are going to use 3 A per cell (which is great for cells), no need for buying high rate cells, buy cells like 29E or PF, they are very cheap and have more capacity. Or even something like 32E which costs similar but has almost 30% more capacity
Yes to all of the above. A cell with lower ir will have less voltage drop, less heat generated, more energy delivered at that amp limit, longer cycle life etc.
robocam
10 kW
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Thanks. Other than price, is there any situation where it would be advantageous to have the 26f over the 25r? Would the 26f be safer if the cell was damaged by impact? That might be a stretch =). I'll be sure to pad the pack in a plywood enclosure.
Ohbse said:robocam said:Let's say I have a device that presents a 5A load. Is there any advantage to using a 25r (20A maximum discharge rating) over a 26f (5.2A maximum discharge rating)? Would the 25r be able to hold a higher voltage under that 5A load, last longer (more usable amp hours), and/or have a greater cycle life since it is not worked as hard?
If there are advantages, do they still hold true under a 2.75A load, or do the advantages lower in magnitude?
The scenario is an ebike that presents a either a 22A or a 40A load to a pack that has 8 groups in parallel (14 in series for 51.8V). I'm trying to determine if it is worth paying more for a pack made with 25r cells vs 26f cells.
riba2233 said:Yeah, if you are going to use 3 A per cell (which is great for cells), no need for buying high rate cells, buy cells like 29E or PF, they are very cheap and have more capacity. Or even something like 32E which costs similar but has almost 30% more capacity
Yes to all of the above. A cell with lower ir will have less voltage drop, less heat generated, more energy delivered at that amp limit, longer cycle life etc.
parabellum
1 MW
There are no (any) advantages, including price (long term) of 26f to 25r unless you want to listen your grandpa radio for weeks until recherche.
Ohbse
10 kW
robocam said:
Nope, it's just a cheaper/worse cell.
robocam
10 kW
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And here's some data from their spec sheets to confirm those claims.
25r:
0.2C capacity 2.560 Ah, 9.38 Wh
10A capacity 2.539 Ah, 8.74 Wh
26f:
0.2C capacity 2.550 Ah
0.5C capacity 2.423 Ah
1.0C capacity 2.295 Ah
2.0C capacity 2.040 Ah
So this means if I pull a continuous 5.4 A load from a 26f, it will only deliver 80% of its rated capacity, making a 20.4 Ah pack turn into a 16.32 Ah pack.
If I pull a continuous 10 A load from a 25r, it will still deliver 99% of its 0.2C capacity (although the Wh delivered is slightly less at 93%). A 20 Ah 25r pack would still be a 20 Ah battery.
However, I probably won't be pulling 40 A continuously, reducing those disparities. I wish I had Wh information on the 26f.
25r:
0.2C capacity 2.560 Ah, 9.38 Wh
10A capacity 2.539 Ah, 8.74 Wh
26f:
0.2C capacity 2.550 Ah
0.5C capacity 2.423 Ah
1.0C capacity 2.295 Ah
2.0C capacity 2.040 Ah
So this means if I pull a continuous 5.4 A load from a 26f, it will only deliver 80% of its rated capacity, making a 20.4 Ah pack turn into a 16.32 Ah pack.
If I pull a continuous 10 A load from a 25r, it will still deliver 99% of its 0.2C capacity (although the Wh delivered is slightly less at 93%). A 20 Ah 25r pack would still be a 20 Ah battery.
However, I probably won't be pulling 40 A continuously, reducing those disparities. I wish I had Wh information on the 26f.
Allex
100 MW
25r is old, buy 30q instead unless 25r are much cheaper. with 30q you can reduce the number of cells to loose weight or gain Ah
The 30Q might be a good replacement since it appears to deliver over its rated spec, making it perform similarly to the 25R:
https://www.e-cigarette-forum.com/forum/attachments/image-jpeg.530587/
It's be nice to see a full discharge curve for each at something like 20/25/30A though.
https://www.e-cigarette-forum.com/forum/attachments/image-jpeg.530587/
It's be nice to see a full discharge curve for each at something like 20/25/30A though.
Ohbse
10 kW
30q's are fantastic by all accounts, but they are more expensive - even by capacity/$. The latest/greatest are usually more expensive in every product category, these are no different.
I see this a lot, but in reality you should never be specifying this cell if your use case is >8c constant discharges. They're going to get hot, cycle life will be bad and in reality a pack that lasts for ~7 minutes is not that useful on an ebike or other lightweight electric vehicle. Extrapolating real world performance which is closer to pulse discharge and shallow cycling is difficult and sometimes misleading.
Punx0r said:
I see this a lot, but in reality you should never be specifying this cell if your use case is >8c constant discharges. They're going to get hot, cycle life will be bad and in reality a pack that lasts for ~7 minutes is not that useful on an ebike or other lightweight electric vehicle. Extrapolating real world performance which is closer to pulse discharge and shallow cycling is difficult and sometimes misleading.
Hillhater
100 TW
^^^+1...
I know from personal experience with a 15Ahr pack, I easily get over 2 hours riding. That tells me I am likely averaging 5-6Amps (0.3C) , but with short periods of 30A on hills or accelerating ( from wattmeter) , and other periods of 0Amps. ( downhill / coasting).
I would guess the % of time at max amps is less than 5% total..( 20 bursts of 20 sec at a time ?), but of course the pack needs to be able to run at that level when needed.
So a discharge curve of that would be a very mild 0.3C discharge with intermittent 2C spikes and similar intermittent "resting" periods........and very rarely discharging below 3.7 volts !
Which explains why my Turnigy 20C Lipo has lasted over 6 years so far ! :lol:
I know from personal experience with a 15Ahr pack, I easily get over 2 hours riding. That tells me I am likely averaging 5-6Amps (0.3C) , but with short periods of 30A on hills or accelerating ( from wattmeter) , and other periods of 0Amps. ( downhill / coasting).
I would guess the % of time at max amps is less than 5% total..( 20 bursts of 20 sec at a time ?), but of course the pack needs to be able to run at that level when needed.
So a discharge curve of that would be a very mild 0.3C discharge with intermittent 2C spikes and similar intermittent "resting" periods........and very rarely discharging below 3.7 volts !
Which explains why my Turnigy 20C Lipo has lasted over 6 years so far ! :lol:
Ohbse said:
This is really what I'm trying to do... I figure a cell capable of high continuous discharge will have a lower IR, which for pulse discharge will mean less voltage sag and ohmic heating (also less capacity loss).
The 30Q is about 50% more expensive, by NKON's prices. I see they've uploaded the Samsung datasheet for the cell and it makes interesting reading
http://eu.nkon.nl/sk/k/30q.pdf
Discharge curves for 5/10/15/20A (the latter being 3.2V Av. 2.88Ah and 99°C)
Short-circuit current (130A)
Cycle life (@ 22A: 83% @ 100 cycles, 72% @ 250 cycles)
I like the 20V/20A over-charge test
tomjasz
1 GW
I'm curious, how many of you are arm chair users as apposed to actual users? All this theretical use as apposed to realtime use? There's always a better cell, but can you buy it?
Having picked through the datasheet for the 25R the discharge performance is more similar to the 30Q than I thought. Nkon have also dropped their prices so now the 30Q is only ~10% more expensive. Decision made in favour of the 30Q
Yes, I think it is time to move away from RC lipo. The 18650 pack will be about 1/3rd smaller and lighter than the lipo pack it replaces. As well as hopefully living longer, being safer and letting me use more of its capacity (rather than 4.1-3.6V range on the lipo).
I was set to buy a spot welder but then saw nkon will also spot-weld tags for .40 euros per cell which will allow them to be soldered to bus wires. Just need to check ampacity of the nickel strip they use.
I was set to buy a spot welder but then saw nkon will also spot-weld tags for .40 euros per cell which will allow them to be soldered to bus wires. Just need to check ampacity of the nickel strip they use.
Hillhater
100 TW
Punxor
Have you compared the discharge voltage curves from Lipo and a similar capacity 18650 pack ?
...(or even similar amp draw from what ever pack size you think you will use )
The useable voltage/capacity range is not the same on 18650's as Lipo.
I suspect you will find that for similar capacity packs and current draw, you will be running with significantly more voltage sag. ('unless you find some 30C 18650 cells !). And in order to use all that capacity , you will be running those 18650's way down below 3 volts/cell.
Have you compared the discharge voltage curves from Lipo and a similar capacity 18650 pack ?
...(or even similar amp draw from what ever pack size you think you will use )
The useable voltage/capacity range is not the same on 18650's as Lipo.
I suspect you will find that for similar capacity packs and current draw, you will be running with significantly more voltage sag. ('unless you find some 30C 18650 cells !). And in order to use all that capacity , you will be running those 18650's way down below 3 volts/cell.
It's a fair point and I do get that RC lipo has advantages in that regard. However, I'm going from 12S 10Ah 25-35C lipo to 18S 12Ah 18650. A lot of my riding will be assisted at a steady 20-30mph, so maybe 10-15A draw. For occasional acceleration and offroading I may pull peaks of maybe 100A. Yes, there will be considerable sag, but it will be at relatively low speeds, so hopefully not an issue.
30Q DC IR is 20 mohm, or 5 mohm for 4P. With 18S that's 90mohm (plus tabs/solder joints). At 100A that'd be 9V of sag. Admitedly, that's about 3 times what it would be for the lipo.
30Q DC IR is 20 mohm, or 5 mohm for 4P. With 18S that's 90mohm (plus tabs/solder joints). At 100A that'd be 9V of sag. Admitedly, that's about 3 times what it would be for the lipo.
Hillhater
100 TW
Ah, so it's a very different pack, voltage etc.
But estimating sag is tricky from spec data.....
IE... From this pulse discharge test below on similar cells (25R). the sag at 20 amps is more like 0.75 volts/cell which on your 18S , 4P pack @ 80amps, would be 13.5 volts ( and you could extrapolate that to 16+ amps at 100 amps !)
But estimating sag is tricky from spec data.....
IE... From this pulse discharge test below on similar cells (25R). the sag at 20 amps is more like 0.75 volts/cell which on your 18S , 4P pack @ 80amps, would be 13.5 volts ( and you could extrapolate that to 16+ amps at 100 amps !)
It's a good point, bud and I thank you for the warnings. I think if I was replacing 12S lipo with 12S 18650 I'd be in for an unpleasant surprise... I see why 12S is normal for lipo to approximate 48V but 18650 packs tend to be 13 or 14S for the same.
18650s are getting better and better and I think it's time to dip my toe. The 100A peak is a worst-case scenario I might not need (doesn't hurt to over-spec) and if this 30Q turns out to be not all that, there will probably be newer, better cells come along in the meantime. Also, I'm tight on space in the frame.
It will be interesting and educational to see how heat and usable capacity I get with the 18650s.
18650s are getting better and better and I think it's time to dip my toe. The 100A peak is a worst-case scenario I might not need (doesn't hurt to over-spec) and if this 30Q turns out to be not all that, there will probably be newer, better cells come along in the meantime. Also, I'm tight on space in the frame.
It will be interesting and educational to see how heat and usable capacity I get with the 18650s.
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