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18650 vs 21700 battery packs.

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  • AZguy
    commented on 's reply
    Hardly voodoo

    Dividing the sum of the initial voltage and the final voltage by two gets the average of the two so is a suitable approach to calculating energy capacity - and as explained if the discharge voltage was linear, entirely accurate

    OTOH the accepted approach is to use the nominal cell voltage (3.7V) as I did in the latter example

    The difference between the two methods for a 52V 20Ah battery would give the 974Wh as explained and if using the nominal cell voltage (optimistic since it would require running the battery to 0% which nobody does) would give 1036Wh - very close and higher as expected



    But again, the *only* way to know what the capacity is (usable or total), is to measure it with a Wh/Ah coulomb counting meter

  • stts
    commented on 's reply
    waste of time
    Last edited by stts; 03-24-2023, 05:23 PM.

  • AZguy
    commented on 's reply
    FWIW, my comment "The math is flawed" is directed at jyouellette

  • Retrorockit
    commented on 's reply
    My battery was sold as 40A continuous.Since my motor is limited to 30A I use that figure. 50V x30A=1500W.That's how everyone advertises the BBSHD. Not sure why the 20A figure keeps coming up? So it should make 2000W which means absolutely nothing in the real world. When the battery is low I'm sure it doesn't make 1500W anymore. I can feel it. But it can take full throttle and run over 30mph at the end of a 40 mile ride. Is it 1200W? 1100W? I don't really care.

  • stts
    commented on 's reply
    waste of time
    Last edited by stts; 03-24-2023, 05:23 PM.

  • Retrorockit
    commented on 's reply
    The math is correct. 48V. 13s,5p has 65-21700 cells.
    52V. 14s,4P has 56- 21700 cells.
    21700 cells can have up to 5000mAh, 18650 tops out at 3500mAh.
    Of course measured net power will be less than calculated gross power. You are "measuring" inefficiency, not "disproving" the math.
    But when buying new batteries the number of cells and the capacity of each cell is valid for comparison.
    I don't care how many Watts are on a meter. I care how far I can ride before I have to push the bike, and if I can go fast when I need to, or ride into a heavy headwind all the way to where I'm going. This battery does all of that, often in the same ride.

    The 52V. battery will allow you to run at 1800 theoretical watts at 30A.. This will not increase range compared to 48V@1500W. (Fully charges V. is higher than advertised V.). Range will be quite a bit less if you actually use the 1800W setting. I see no use for it myself. The 52V. will only have more range if the battery has more cells (they often do). That is not the case with this particular battery.
    The extra cells will allow longer range. The Voltage of each cell runs from the same Voltage full to empty. 48V has banks of 13 Cells, 52V. has banks of 14 cells to produce 4 more total Volts. It will shut down 4 Volts soonerto protect the cells.

    AZ-measuring your bike tells absolutely nothing about my bike.

    I can assure you that a 45mile ride @ 20mph is not a problem for my bike. Unless there is a 20mph headwind which is like going up a hill that never ends.
    This is normal weather much of the time where I ride. Occasional sprints to 30mph come with the territory.
    Sorry guys I won't be staring at a Watt Watcher in urban South FL traffic.I buy more Watt/hours at the start and work from there.
    Does it cost more? Yes, Does it weigh more? Yes. Does it do everything I ask of it? Yes.
    Last edited by Retrorockit; 11-02-2022, 10:58 AM.

  • AZguy
    commented on 's reply
    The math is flawed

    If the discharge voltage was linear (it's not, but close enough for very rough estimating) then the usable power would be roughly computed by multiplying Ah * (Vinitial + Vfinal) / 2, or in your example 20Ah * (58.4V + 39V) / 2 = 20Ah * 48.7V = 974Wh

    There are variables that will effect the actual usable Wh, including but not limited to the current/power draw, temperature, battery age, etc.

    The only way to really know the usable capacity is to install a Wh/Ah meter and measure it on the bike... I've got a well calibrated meter on my bike so have a very good idea of the usable capacities on my several batteries and it's always less than the Ah * Vnominal but generally only about 10%... so if a battery is a 14s4p with 3Ah cells the total "nominal" capacity is 4 x 14 x 3Ah x 3.7V = ~622Wh - with a new battery like this the usable is going to be closer to ~560Wh and will obviously go down with age

  • jyouellette
    commented on 's reply
    I agree ur doubling the power but let not forget let not forget usable power is not 1152 nor 998 wh. Ur ebike controllers limit the usable power from say (52v bat) @ 58.4v to 39v leaving u with a usable 19.6v of battery range before ur controller cuts out. Effectively u only have 19.6v x 20ah= 392wh of usable power, hardly adequate for a 45 mile ride on a 26" bike. Am i right or missing the point all together
    Last edited by jyouellette; 11-02-2022, 07:24 AM.

  • Retrorockit
    replied
    I found this seller listing a few 21700 battery packs that specify Panasonic 21700 cells from a US warehouse. I have no experience or connection with this seller.
    They show 5000mAh for each Panasonic 21700 cell.

    TRIANGLE
    48V 20Ah 40A triangle pack, and 52V 20Ah 40A triangle pack. Both are in the drop down menu.


    SHARK
    This one looks like the battery I have with the funky bracket in 52V 20Ah instead of my 48V 24Ah (which I much prefer).
    H HAILONG 48V 20Ah ebike battery lithium Li-ion Battery for 200W-1200W E Bike. H HAILONG 52V 48V 36V 15Ah 20Ah Lithium Battery for 750 1000W Ebike Motor EBike. H HAILONG 48V 20Ah battery for 1200W Power Ebike motor lithium Li-ion Batterry.


    It may be that 21700 cells are new enough the copycats haven't tooled up for them yet. Just a guess on my part. I'm sure it won't be long.

    BRICK
    There are some 21700 brick batteries on this page up to 30Ah. The sizes vary quite a bit with capacity and the 21700 are thicker.
    12V 12AH Deep Cycle LiFePO4 Lithium Iron Phosphate Battery for RV car electric. Capacity (amp hours) : 12Ah. Usable Capacity (AH): 12AH. Applicable to electric bicycle: 48V 100W 200W 350W 500W 750W 1000W 1200W 1500W 2000W motor.





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  • Retrorockit
    replied
    I ran this battery all the way down again. I took a longer than normal ride. Davie to Ft. Lauderdale for brunch, a ride to Dania Beach pier (26mph into 10-15mph headwind (riding faster than before due to Tannus tire liner in the rear on the HT), back to N.E. FTL, then back to Davie, They've installed a small traffic circle on my return route which requires a full throttle blast so cars aren't trying to pass me going into it. This is where I find out how much battery I have left. It didn't shut off, but PAS1 the rest of the way home. Done riding for the day since it takes 12 hours to charge this back up. I my need to invest in the 4A charger. The only place i tried to conserve the battery was running PAS2/5 instead of 3/5 for about a mile. Due to a tailwind I was still running 24mph.
    I could have ridden to all these places if I had gone straight to Dania from Davie and made a single loop. But Sunday brunch had to happen first. I could have done the visit to N.E. FTL any time, but they're open Sunday so I added some miles to this already long ride. The Davie to Dania direct run is on a road that's know for motorcycle accidents. Mostly head on left turn stuff. I prefer to take the long way around the airport..
    I could have done the Brunch, N.E. FTL visit and then Dania Beach in that order and come straight home. The MC crashes are mostly weekday rush hour stuff.
    I'd say the BBSHD and 24Ah battery are about an even match. The whole run east into FTL and Dania was at PAS 3/5 due to headwinds off the ocean..
    Last edited by Retrorockit; 08-22-2022, 07:10 AM.

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  • Retrorockit
    replied
    I saw this listing for you battery geeks. Samsung 40T3 21700 4000mAh 35A batteiry for $3.99 (was $ 5.99).
    Discover the Samsung 40T 21700 4000mAh Battery. With a high capacity and ultra-high discharging capabilities, this battery is perfect for demanding needs. Buy now!

    The price breaks on the quantity discount list are still based on the $5.99 price. So IDK what you will get if you order a bunch of them?

    Leave a comment:


  • Retrorockit
    commented on 's reply
    With the Tannus in the rear tire cruising comfortably in the 26mph range is now possible. With the headwinds 900W 3/5 assist is now commonly used. I'm finding the 24Ah battery is just the right size. I also discovered that 5/5 PAS is not= full throttle. 32mph 5/5, 35mph @ full throttle.

  • Retrorockit
    replied
    I finally found the bottom on this battery. It took a 40 mile ride with no regard for range to do it. It was fun too. Lots of full speed runs on the throttle. Good weather, almost no traffic. The usual 20mph headwind on the way into town. Pretty much street slalom all the way home after a couple stiff drinks.I had to pedal it the last mile. My old battery would recover some if I gave it a few minutes rest. This one when it's over it's over.

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  • Retrorockit
    commented on 's reply
    I'm very happy with this battery. I installed a Tannus Armour tire liner in the rear. The damping effect allows my hardtail to cruise comfortably at higher speeds than it did before. That combined with the seasonal winds off the ocean here means I'm using a lot more power to get around. If the Tannus has increased rolling resistance it's not obvious. On a 36 mile ride with 20mph headwinds on the way out, and trying to outrun a thunder storm on the way back with it's own higher headwinds I managed to pull it down into the 25% range. The acceleration wasn't as sharp as with a full charge, but fast running without any low Voltage cutout was possible all the way home. My old 17.5Ah batttery would have thrown in the towel a long time ago.

  • Retrorockit
    replied
    After R&R the battery a few dozen times the point of interference became obvious due to the scratched plastic there. I filed it down a bit and the effort to remove the battery is now within the normal range. Whether it's poor fit of the bracket, or lack of precision in my mounting technique, it wasn't too hard to solve. This is the Hailong Mega Shark 21700 bracket. Others have had the same issue.

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