Please Help Suggest a Cell for my eBike Business

Marlz

1 mW
Joined
Apr 2, 2015
Messages
17
I own an ebike tour company in a developing country. I have been doing this for a few years now and have always used batteries built from 18650PF cells. They have been doing fine but I wonder if I might be missing an opportunity to use a more appropriate cell type.

So I hope some of the generous people of this forum might make a suggestion based on my use case and goals. This is how my batteries are used:

Motor: magic pie edge 500W motor at 48V
Batteries: HL1 case, Panasonic 18650PF 48V 10.8Ah
Charger: 2A

Usage:

Bikes do 2 tours a day. Each tour uses about 30% of the battery's capacity. When the morning our comes back (battery at 70%) we charge them for about 2 hours with the 2A charger so they are ready for the afternoon tour. I estimate that we get close to 100% charge from that. The bikes go on another tour and come back around 70%. They are then charged to 100% for the next day's morning tour.

So as you can see this is not strenuous usage (at least I don't think so). I don't need the best of the best and price is important to me. What I'm hoping for is a cell that might have an even longer cycling life.

Over the years I have lost a handful of batteries due to individual cells failing but the attrition rate is not drastic considering some of my batteries have had around 2000 cycles. But I am always looking to improve.

I have to buy 7 new batteries and I am wondering if I might do even better with a different cell. I wonder if based on my usage, someone might have a recommendation.

Any and all advice is welcome. Thank you!
 
Since you only use 30% of each charge a suggestion would be to only charge to 80% thus getting the bikes back still with 45-50% charge. Charging to only 80% will double or even triple the life of your battery packs no matter which cells you go with
 
Diggs said:
Since you only use 30% of each charge a suggestion would be to only charge to 80% thus getting the bikes back still with 45-50% charge. Charging to only 80% will double or even triple the life of your battery packs no matter which cells you go with

Thank you, I did not know that.
 
I should have given a bit more info. This graph shows how the number of charge cycles can be drastically increased by keeping the pack in it's "sweet spot" which is generally recognized to be 20-80% state of charge (SOC). You can see that anything getting 100% charge has the shortest lifespan.

DST-cycles-web2.jpg
 
Diggs said:
I should have given a bit more info. This graph shows how the number of charge cycles can be drastically increased by keeping the pack in it's "sweet spot" which is generally recognized to be 20-80% state of charge (SOC). You can see that anything getting 100% charge has the shortest lifespan.

Yes looks like I should be able to hit the pink line.
 
I have an additional question regarding your suggestion....

If my target were to max charge to 75% every cycle would my batteries not have the opportunity to top balance and therefore suffer for that?
 
Marlz said:
I have an additional question regarding your suggestion....

If my target were to max charge to 75% every cycle would my batteries not have the opportunity to top balance and therefore suffer for that?

True, but packs do not need to be balanced every charge. The actual need for balancing depends on how matched the cells were from the maker which isn't really known on most packs. I don't know how often to recommend to charge your packs to 100% for balancing. I've seen mention of every 15-20 cycles but it seems to vary by different sources. Maybe someone here has a more complete answer.
 
It's nice to be able to see the individual cell groups parallel groups their voltage. I have a BT bms and can see each parallel groups voltage and more. This would be over kill for a rental business. All my earlier batteries have just balance wire and no bms . No good for rental business . But could read cell voltage and monitor.
Meaning it would be nice to know cell voltage and balance
Yes you would only need to full charge every 3 months or so to balance for bms, but you would to leave on for 24hrs for balancing.
You see it just gets more complicated.
If you are getting 2,000 cycles you are great

.
 
Marlz said:
Bikes do 2 tours a day. Each tour uses about 30% of the battery's capacity. When the morning our comes back (battery at 70%) we charge them for about 2 hours with the 2A charger so they are ready for the afternoon tour. I estimate that we get close to 100% charge from that. The bikes go on another tour and come back around 70%. They are then charged to 100% for the next day's morning tour.
As long as a fully charged battery is used within an hour or two of charging it's possibly best to leave well-enuf alone. Any fully charged batteries that weren't used on the first tour should be the first ones put to use on the next tour.

Another suggestion is after fully charging you and your assistant take the bikes scheduled for the next tour for a short ride just to make sure everything is OK. That way the battery will no longer be fully charged, but still at least 90% SoC. ... Also in case a couple sheduled riders are no shows and their bike(s) won't be used until the next tour.
Marlz said:
Over the years I have lost a handful of batteries due to individual cells failing but the attrition rate is not drastic considering some of my batteries have had around 2000 cycles.
The only way to increase cycle life (other than casual use) is charging to a lower voltage, say from 54.6V to 53.0V (4.08V/p-group) or whatever you believe is best (90%, 85%). But doing so means you have to open up all your 2amp chargers and adjust its trim pot to voltage you decide is best. That is assuming your chargers have a trim pot for adjusting voltage output. Probably best to just leave well-enuf along (IMO) if your chargers' voltage isn't adjustable.
Marlz said:
I have to buy 7 new batteries and I am wondering if I might do even better with a different cell. I wonder if based on my usage, someone might have a recommendation.
No matter what battery with name brand 'Grade A' cells (10amp rating) you decide to purchase you may experience similar results. A few possibly achieving 2000 cycles and a few failing due to individual cells taking down a battery ... (possbly due in part to a faulty BMS or rider abuse).

As far as fully charging once a month and leaving plugged in for a few hours after greenlight comes on (BMS balancing p-groups within 30mV) is debateable whether doing so is worth the effort. Although some have suggested so ... don't believe i've ever heard of anyone at ES doing it as a scheduled monthly routine with result being increased cycle life.

Have you checked the voltage output of all your 2amp chargers to make sure none are putting out more than 54.6V ?
 
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