adapting my second hand speed pedelec to my needs?

[meesterkweepeer]

Hello,

Any hints on the best way to adapt my newy-bought second hand speed pedelec to my needs?

Specs:
• battery: 48V removable in-frame, 2 pcs, nominally 500 Wh each, old so presumably little capacity left
• motor: 48V 500W Bafang/8FUN rear hub motor (uart)
• display: Kingmeter SW-LCD
• controller: no idea. Probably lishui or kunteng, but could be anything decent really.

Use case. I need to bridge a 70 km distance one way twice a week. I figure about 2 kWh of battery capacity would be ideal: 0.02 kWh/km* 70km = 1.4 kWh +0.6 kWh optimal charge/discharge range 15-85%.

Battery options. Please shine your light on these. Which one would you go for, and why?
• option 1. keep the two existing batteries as they are. connect one ~1kWh new generic battery each in parallel to each old frame battery. something like https://enerprof.de/fahrradakkus/rahmengestell-akkus/akkus-48v-13s/1357/enerpower-rahmenakku-hebron-48v-25ah-bms-20a-1200wh?c=9 . switch mid-way. Once the frame batteries die, keep only the hull and try to connect these directly. the least intrusive/expensive, most incremental way. fast charging.
• option 2. get the two existing batteries recelled (600Wh capacity) if that can be done. connect one ~ 0.4 kWh generic battery in parallel to each recelled frame battery. mid-way switch required. aesthetically pleasing. lowes point of gravity. Leaves me dependent on both old batteries functioning after recelling.
• option 3. get one new >=2 kWh softpack battery in a case on the luggage rack. try to get it to work with the controller and lcd or replace those. no mid-way switch required. slow charging.
• option 4. gut the frame batteries. add a 1kWh hard case battery on top of the frame battery holder. add another on the luggage rack.

Speed. A nice to have feature would be to be able to ride the bike at the EU speed limit of 45km/h. It is currently limited to about 40-42km/h. Not the motor. Just firmware. Changing that would probably require fiddling with the controller and/or lcd or replacing them. That pleads in favour of option 3.

Motor replacement. The motor might be perfectly healthy or it might be close to dying. Is a replacement uart bafang 500w rear hub motor still easy to source, or are the newly produced ones all can bus based? Any hints on that?

Free and open source software/firmware. I love this. Any hints on how to open up my speed pedelec as much as possible?

Kind regards,

Meester Kweepeer

 

[From-A-To-B]

Hello, Kweeleer— welcome to the forum and Land of the Posters.

Hope you’re having fun with your new-to-you bike. I can only comment on some of your questions.

Re: the motor— motors tend to either work, or die. If the 500W motor was used at or around 500W (or under 1000W, really), and doesn’t have water ingress issues, it’s likely fine and will continue to be fine for a long time! Some ES members have put tens of thousands of miles on rear hub motors— if they’ve made it a thousand miles, they’ll live a long time.

About your battery situation: 70KM is about 44miles. On my personal bicycle, 1KWH of battery will get me 70 miles (112KM) at a speed of 20MPH/33kph but I enioy peddling and don’t mind riding in a tucked position along flat stretches of road. 2KWH sounds like a good about of battery for your goal of 140km without recharging. However, that’s a lot of battery, and will weigh a lot! If you can reliably charge midway before turning around, it will do a lot to reduce weight. A charger weighs much less than 1KWH of battery.

Re: how to extend your pack— while mixing new cells with old cells is possible and all 4 of your options may be serviceable, I personally would start from the beginning with new cells. This way, I’d be able to have matched batteries with matched performance that may be easier to maintain over the long term. I personally would look at how to build 1 big battery or two new packs connected together to meet my battery requirement. (I also don’t care for switches — it’s more complication and I’d rather monitor one battery than monitor multiple packs that I am switching back and forth between.)

The two packs connected together could be 13S5P + 13S5P in parallel, OR 6s10P + 7s10P in series. It’s the same battery capacity, but the second option is one big battery with one BMS, that charges and discharges as a single pack, instead of two separate packs. Neither is necessarily better — depends on your use case.

Speed: if you don’t have a 3-speed switch or something of the like, changing max speed may be difficult. You could go to a 52v (14s) battery, which is likely compatible with your controller, but swapping voltages in any system has its risks (blown parts). KT controllers are great as far as budget ebike controllers go, and have customizable max speeds, up to the system max (which is your motor’s KV and available battery voltage). Is it worth spending USD$70-90 to get a new KT controller, and the work to rewire, just for an additional 3-5kph? That’s up to you!

Good luck and keep on it! Share updates and questions as you go, including pictures! Love seeing pictures.

 

[E-HP]

Is a replacement uart bafang 500w rear hub motor still easy to source, or are the newly produced ones all can bus based?

What is a uart motor?

 

[docw009]

.02KWh/km = 20 Wh/km = 32 Wh/mile, I guess people ride fast in Germany? Reasonable if I were to go 40 km.hour.

I would not buy a new battery and hook it in parallel with older packs of unknown quality, Normally, ebike packs in parallel work OK when both are similar in discharge characteristics, and if they differ a little, you can predict how the current pro-rates between them by their Ah ratings. But If one is powerful/new and the others are old/weak, you cannot predict what happens til you try it, and sometimes you get seemingly strange results, mainly the parallel combination is hardly any better than the new battery alone.

It's like conservation of mass or energy. If you have one battery that hardly runs the bike, how is it any better when paired up with a new one? A little different if both are capable, Then you will have a cases where the losses are offset by having two packs.

You could use diodes in the y-connector to prevent one from charging the other and also guard against user errors in combining packs at different voltages. It just seems better to minimize the load and stay with as few packs as needed.

 

[meesterkweepeer]

Hello, Kweeleer— welcome to the forum and Land of the Posters.

Hope you’re having fun with your new-to-you bike. I can only comment on some of your questions.

Thank you for your hints. The purchase fell through at the last moment :-( I'm now looking for something else. See my other post.