22a/45a sinewave or 30a/60a square for my build

[Johncioni]

Hi everyone,

Coming down home stretch on a scrambler style 20x4 rear hub build and having last minute thoughts about upgrading the controller.

I purchased a 1500w 48v kentung kit from Ali. Initially it came with 12 fet 20a continuous controller with max of 40a I believe. I had a battery pack built at 48v with 20700b cells (genuine and high quality). Total capacity is approximately 21 ah. I had the BMS bypassed for discharge simply because it could only supply 30a, however it is still used on charging. I believe this pack is capable of somewhere between 75a to 95a discharge capability. I plan on relying on the LVC set at 42v on the controller for some rough discharge protection.

I purchased a sinewave KT controller with 18 fet rated for 22a continuous, 45a peak. Today I've come across another KT controller which appears to be square rated for 30a cont. and 60a peak.

Question is: is it worth replacing the sinewave with a stronger square in this case? Should I stick with the one I have and add a little solder to one of the shunt bridges? Or should I not touch anything at all and be happy that the sinewave 22a is working as intended?

This is my first build and a lot of this is very new to me. I'd prefer to stick with a KT controller for simplicity sake in not needing to build a harness and as well as the fact that they're cheap enough if I end up burning it out. Thanks in advance for any advice and thoughts.

 

[amberwolf]

Should I stick with the one I have and add a little solder to one of the shunt bridges?

Doing this removes the controller's ability to protect itself, as it can no longer determine or limit current as it was designed. Sometimes it works ok this way, and sometimes it does not (letting the smoke out).

I've modified the shunt on a controller successfully by adding one extra shunt (out of a dead controller) in parallel to the existing ones, to get a percentage more out of it...but it did eventually fail.

If you need it to be reliable, keeping in mind that enough of this equipment is a crapshoot in quality anyway :/ I'd recommend leaving it the way the factory built it.

If you don't mind experimentation and replacing it when things go wrong, you can try it out.

If you *are* going to use higher power, *and* intend to use the pack down to it's "empty" range very much, I do recommend having some form of cell-level monitoring, so you don't accidentally overdischarge any cells and damage your new pack. Controller-level LVC is ok, but if the cells are driven low often they can become unbalanced. If charging rebalances them, it's not a big deal, but if it doesn't, then they can get unbalanced enough over time to let some cells go below a safe low voltage, even though the controller LVC hasn't shutoff yet. If all the cells are well-matched in all their properties, this generally won't happen, at least until they age enough to be no longer matched. But it's rare for this to be the case, even with "good quality" cells.

As for the extra power...depends on what you need it to do for you whether the power will be useful or not.


Regarding sine vs trap: sine is quieter, usualy virtually silent. If that matters to you, stick with a sine controller. If not, go with whichever one does the job you need it to. Trap controllers vary in noise level both based on the controller itself, *and* the motor; some of the combinations I've used have been very quiet but not silent, and some are so noisy it sounds like a garbage disposal inside. :lol:

 

[Johncioni]

Thank you, I figured at this level of power that since vs trap wouldn't make all that much difference. When you added your additional shunt, did you have a tool on hand to measure the increase in continuous amps running through it before it eventually failed? I do not plan on running this battery down to 0 however I doubt my cheap BMS does cell balancing on charge. Maybe time to invest in a decent balance charger.

 

[E-HP]

I'd use the 22A/45A KT as-is. If it's your first ebike, you'll ride it around for a while and over time figure out what works and what you need more of. I used the same controller for about a year, and it worked great. It never got warm; I could climb 1/2-3/4 miles at 15% (with pedaling), and the controller would be cool (the motor would warm up), at something over 2kW (display maxed out). If you have a compatible display, you can flash the firmware with open source and have FOC and other features too.

Sure you'll outgrow it, but the next upgrade will be a much more informed purchase, and matching your own riding style and conditions, much more that if you attempt to describe them here without having the riding experience.

 

[amberwolf]

Thank you, I figured at this level of power that since vs trap wouldn't make all that much difference. When you added your additional shunt, did you have a tool on hand to measure the increase in continuous amps running through it before it eventually failed?

Yes, I use the Cycle Analyst v3, monitoring both the controllers on the trike at the same time, thru a common measuring shunt (separate from those the ocntrollers have in them). IIRC, originally the controller was about a 33A continuous & peak, and adding the (third?) shunt moved that up to about 40A+ continuous, with very short 80A peaks at startups from a stop. Even getting those peaks indicated the controller was not able to regulate "normally" with the extra shunt; I expect it was insufficiently protected that if I had done the solder-on-the-shunt modification instead it would've probably kapow-eed the first time I started up. :lol:

It was a wierd controller anyway, supposedly was sensored and had sensor wires, but it never used them (ran exactly the same with as without), and all phase and hall signal wires were green. Strongest regen braking I ever had, though, even before the added shunt. I miss that part. :/ I have a thread about it here somewhere, though it's incomplete. Most of the stuff about it is buried inside the SB Cruiser thread over the last few years.

I found a pic of the added shunt:

I do not plan on running this battery down to 0 however I doubt my cheap BMS does cell balancing on charge. Maybe time to invest in a decent balance charger.

It probably does balance (even the cheapest ones usually do), but probably only at full charge levels (4.2v/cell or thereabouts). If it looks like it has a bunch of "channels" on it with sets of identical components equal to the number of series cells in the pack, that's probably balancing circuitry.