Frey M600 V2, 21700 battery pack

[tsellers]

I recently received shipment of a Frey M600 V2 eBike. Instead of buying the 18650 OEM battery, which requires separate shipping via UPS for an additional $150.00, I decided to make my own. Frey facilitated my ability to do this by selling me three empty battery cases for the bike that I bought. This would allow me to take advantage of using the newer 21700 cells, and as well, make both 48 and 52V battery packs. For this project I used LG M50 21700 Li_ion cells in a 13S2P configuration that resulted in a 48V 10AH capacity pack.

The first part of this video outlines some of the considerations you need to take into account if you plan to make your own battery pack for this bike.

It should be noted that the internal volume of the empty battery case is not compatible with assembling a 52V battery using 21700 cells unless you are happy with a 14S 1P configuration that will result in a capacity of only 5AH. So for the 52V pack I used one of the empty battery cases as an interface to connect a 14S2P external battery to the motor (picture is at end of this video). Because this video ended up being so long, the external pack will have to be featured in a subsequent demonstration.

[youtube]c-x3YC2Fv2g[/youtube]
https://youtu.be/c-x3YC2Fv2g

 

[waxed]

hey what was the reasoning for using the LG M50 21700 cell?

the LG specification sheet for the M50 has the maximum continuous discharge at only 7.25A/cell
with the M600 the full load current draw is 18A
given that you are using 13S2p you are going to run up to 9 amps per cell!

I am sure the LG M50 cell will deliver 9A but they will get very hot, quickly

for ebikes I don't believe we should be running any cell near its max continuous rating
Mainly because the cells are in Series/Parallel arrangement in an enclosed space
The cells /battery pack has inadequate cooling....

 

[tsellers]

Due to having the '2P' configuration, your maximum nominal current capacity for those cells would be around 14.5A. The M600 in real world use under a max load condition that I have been able to apply (steep mountain road, power level '9' and full throttle), is around 9 amps for the 52V pack, and can flirt with 9.7 for the 48V pack. The battery is warm at the completion of that interval, (not even close to 60C). That 52V pack now has about 1000km on it, and the 2P 48V pack has about 500km. As the Frey controller does not like to power up above 58V, I have adjusted the POTs in the charger to cutoff at 57.3V.

Edit: After I wrote the above, I was able to ride that same mountain road, but this time squinted at the barely readable current display on the M600 (which is impossible to see in daylight with polarized sunglasses on BTW). Indeed it turns out that the 9.7A is my average draw, but if I choose power level '9' on the steep hills I can draw as much as 14A pedal assist for awhile, which seems to average out in the 10-13 range. Then if I pin the throttle as well on one of those hills, while drawing 14, I can indeed spike it to 18A.

So perhaps the take-away would be, if you plan to ride mountain roads, and you want to use these cells, and you plan to throttle all the way to the top like you are on a scooter, then you better consider a '3P' configuration. Otherwise, the 2P form factor (with a 20A BMS) is working well for my style of riding. I checked my (external) battery after climbing 250 vertical meters and it was just warm to the touch. Next week I'll place a temperature probe in it and get a more accurate reading.

 

[goatman]

how are those batteries holding up?

 

[tsellers]

I find that the 10aH packs will allow for about 45-50km of range on a ride with 200m of elevation gain as long as you are never on the throttle, and keep the assist levels conservative (never higher than 4, and often on 1). That would be for a 200lb person on the Frey M600. On the same ride with She Who Must Be Obeyed @110lbs on a much lighter Giant Full-e with Yamaha motor and stock 36V battery pack, she returned with almost 70% power left on the guage.

One problem I have when riding the M600 is trying to see the Amp draw. The display is so tiny it is hard to read at the best of times, then with polarized sunglasses on, you cannot read any part of the display whatsoever. So to get an idea of how many amps you're drawing I have to remove my sunglasses, and bend over and try and get my face as close to the display as possible. That's a contortion I do not find particularly easy to perform.