KU90 Controller (BmsBattery) Solder Shunt Mod

[Scottyf]

Morning All,
I got a bit bored last night and took apart the controller again...

I thought i'd have a go at the solder shunt modification that so may people have done on exisiting controllers to basically ramp up the amp's.

Now this really is a super easy way to modify most controllers.

The controller I have is the KU90 model from BMS battery.
This is a brushless 36v 48v sensorless controller, There pretty cheap from BMS battery so I thought if i do bugger it up i'll buy another one.

First of the controller is rated at 10amp with peaks of 20amp.
Now on the watts up meter I measure peaks of 20.4amp and peaks using lipo of around 960watt (@44v nominal)

The caps in the controller are 63v whiles the mosfets are model RU7088r MOSFETS
Specs listed on the link. So the mosfets should be good for 80v and allow some headroom on the peak amps.

I've soldered up the legs on the shunt, effectivly decreasing the resistance.

Now there are formulars to work on the resistance you'd need to get the correct peak amps you'd like. But when soldering the legs its hard to get the right build up to what you'd like anyway.

Long story short I fired it up this morning on the bike. Twist the throttle and it works which is great...

I might have gone a bit mental on the soldering as I've now changed the peak amps from 20amp to 27.3amp.

Which is quite a considerable leap. So now pushing 1344watt peak.
Which is a good +40% increase.

Acceleration is quite a bit quicker as expected however becasue top speed is no affected my total amp hr used for the same 10.5 mile journey hasn't actually increased. I still used 3.5amp hrs even with the increase in peak amps.

Which is a little surprising as I would have thought it would have chewed up an extra amp with the extra stop starts.
Controller still stays cool and motor is still cool even though the increase in 40% torque (Which is linear to amps) should increase heat by 160%.

Looks like as long as I pedal and keep the bike speed up and not just do full on hill climbs I shouldn't see any adverse affects.

Not sure if the BPM is made for those peaks though :-(

 

[NRG]

....or the battery, the limit imposed by the controller achieved by measuring the drop across the shunt is there primarily to protect the battery.



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[Scottyf]

The batteries / cells are rated @ 20c with peaks of 30c (Standard lipo Turnigy packs)
So the cells themselves should handle the additional discharge draw?

I probably should take some solder off just to make sure I don't ruin anything really.
Its just I got bored and thought i'd have a go since there is lots of info on the Intarwebs!

 

[Deleted member 4366]

Thanks for a good demonstration of the mod, which I also think is an excellent way to get a useful gain in power for no cost.

I've experimented a lot with different currents and volts and have come to the conclusion that about 22 amps is enough for normal road use and it'll get you up virtually any hill. Maybe 25 amps would be an absolute maximum. After that, the torque can be a bit fierce and the bike starts to become less safe when you start to lose grip in the rain , or on gravel, leaves and other bad surfaces, and then the ride starts to become less enjoyable as you have to concentrate more. If you want to do this mod on anything other than a 250w controller, it's best to add a little bit of solder at a time and then check the amps with a meter so that you know how far you've gone. It's easy to go way over the top and then have a bike that's too fierce and unenjoyable with no way back (unless you want to get a new controller).

If you have a 250w controller, it's quite easy to get an increase from the basic 12 to 15amps up to 20amps. To go further, you risk cooking your FETS, so without a meter, I wouldn't solder much more than 1/3 of the shunt. Don't be greedy and go for the lot: It'll only end in smoke and tears. Most bikes have a 10aH battery that can manage 20amps for very short periods, so again, if you do the mod, don't go full power all the time: You won't see any immediate effect, but your battery will need replacing much sooner. It's worse for an 8aH battery.. Not a problem at all if you have lips, which can give 200 amps plus.

 

[Scottyf]

I agree with the 20amp current draw being good for road needs.
I think I'll be removing the solder off but it was a good way to review how much additional power acceleration it would actually give me without the need to purchase an additional controller.

The 250w Controllers with 12/13 amp max would be a good useful modification for pennies yet offer quite a large gain without cropping up legalities of the motor in question.

So even as the MOSFETs can handle 80v what are the chances of me getting new caps and running at 72v

 

[wurly]

Something i would like to know. I see you have a 9 FET controller (mine is 6) and i know that controllers that can handle lots of current have 12. How do they work on 3 phases? are they connected in parallel to share the total output per phase or are they connected and working in some other way?

 

[NRG]

Mel, in a 6 Fet controller you will have FETs working in pairs, current will flow via the 'top FET' though one Phase wire and out of a second into the 'bottom FET'. I cant recall which FET takes the most hammering but in the 9 FET controller the overworked one gets a partner paralleled with it to handle more current. In a 12 FET controller both top and bottom FETs are paralleled.

 

[wurly]

Ok, so they are parralleled up. This i understand.
Sorry, more questions. I don't understand why you need a pair per phase, If the windings are wired in Y , 1 FET will send current through phase wire A and back through phase wire B and i presume the 2nd FET is flowing curent in the opposite direction (working in pairs?). Why is that? wouldn't 3 FETs flowing current to a negative side of ther windings do the same job?
Got any good links?i need to do some swatting up