Overvolting/amping 9c clone, maybe with booster batteries

[Haien]

I recently built an ebike from one of those cheap kits on amazon, and it is really fun, though quickly felt lacking in both speed and acceleration.

Apart from the controller already connected I have got another one rated for 48 to 72V and 50A, though the capacitors inside it were 100V ones. My battery is a downtube 52v 14s5p 40A BMS by Unit Pack Power. Would it work (and give me better torque) if I simply swapped controller to this higher amperage one, or would I risk blowing the BMS or batteries? Is trimming the shunts the only way of slightly lowering the amperage draw on these cheap controllers?

As this controller is rated up to 72V, and the known cheap and dirty way of getting to 40 mph is feeding these 9c clones with 72V 40A, could I connect a booster battery of about 20-24V in series with the 14s5p whenever I want to try that? Would two SLA 12V 12Ah in series work if I carefully monitor the voltage and don't let them drop below 11.80V each (empty voltage). If I use Andreson conncetors I would be able to connect the booster when I want it and disconnect it when I don't or it goes out of power. Or would it be better to use a few 20V cordless drill batteries in parallel? I would prefer this, but I already have those two 12Ah SLA:s, and I would still need to check voltage as it would be hard to get 17.5Ah.

Thanks in advance!

 

[E-HP]

As this controller is rated up to 72V, and the known cheap and dirty way of getting to 40 mph is feeding these 9c clones with 72V 40A, could I connect a booster battery of about 20-24V in series with the 14s5p whenever I want to try that?

Since you didn't provide many details about your existing or new controller, can't provide help on your other questions, but for the one above, it would be yes. The maximum current should be limited to the lower of your pack's capability and the additional batteries you're connecting in series.

 

[Haien]

Thank you, Then I will probably try that sometime.

What would you like to know about the controllers? The current one is 48v rated at 1000W which would give about 21A, but I have seen others getting 30A drawn whith these kits. The bigger controller is rated 48 to 72V, and maximum 50A. It is chinese and really cheap, no brand or such.

Though my pack is rated 40A (5P Samsung 35E, 8A max continous), so drawing 50A doesn't seem like a good idea, or would it work in short bursts, cruising at a lower 15-30A?

 

[E-HP]

Since it's a 9C clone, you could use the Grin motor simulator to see what the expected performance would be when modifying your components (controller, battery, etc.). If you know the current top speed and add in the parameters for your battery and controller, then you can choose from the various 9C motors to find one with a similar KV rating (same speed). Then you can change the controller or battery parameters to see what the performance results are. In the example below, you can see that the controller itself is not limiting the speed, since the 21A controller on the left, and the 40A controller on the right result in the same speed (however there's a notable torque difference)

https://www.ebikes.ca/tools/simulator.html?motor=9C212_7.5T&batt=B5220_GA&hp=0&axis=mph&cont=cust_21_42_0.03_V&cont_b=C40&motor_b=9C212_7.5T&batt_b=B5220_GA&hp_b=0&bopen=true

 

[John in CR]

"9C clone" cracks me up every time I read it. How can a generic hubmotor for which anyone can go buy the parts at giant ebike parts shopping areas in China and assemble themselves be cloned?

 

[Haien]

Since it's a 9C clone, you could use the Grin motor simulator to see what the expected performance would be when modifying your components (controller, battery, etc.). If you know the current top speed and add in the parameters for your battery and controller, then you can choose from the various 9C motors to find one with a similar KV rating (same speed). Then you can change the controller or battery parameters to see what the performance results are. In the example below, you can see that the controller itself is not limiting the speed, since the 21A controller on the left, and the 40A controller on the right result in the same speed (however there's a notable torque difference)

https://www.ebikes.ca/tools/simulator.html?motor=9C212_7.5T&batt=B5220_GA&hp=0&axis=mph&cont=cust_21_42_0.03_V&cont_b=C40&motor_b=9C212_7.5T&batt_b=B5220_GA&hp_b=0&bopen=true

Yes I have done that (though didn't know you could compare two setups in the same graph, thanks), I am not particularly looking for more speed with the higher amperage, the 30mph I get currently is enough, torque is just what I want. Connecting the two SLA:s though, that would be for speed.

What I am worried about is stressing my battery too much if drawing 40-50A occasionally. Some say it should be ok with 50A for a brief moment while others say 40A occasionally is stressing it looking for problems. Looking at the simulator, coasting at 30mph will use just over 20A, which is what I at most will use constantly. Setting the throttle to 65% gets me 20mph at around 10A, which will be fine riding at in town.