Add cheap current limiter to Ebike

[jmamcarson]

I'm building up an e-bike based on an SW900 display, generic cheap Chinese controller and a 350w 36v motor overvolted to 48v.
In my various dealings with this controller/display I have fried the headlight transistor and I think either I have broken the current limiting of the controller or it never worked in the first place. Adjusting the P14 setting does nothing for the current limiting.
The motor draws high peaks of up to 1100w (instantaneous) when accelerating hard. I'm looking to find a cheap current limiter in order to bring the motor down to instant peaks of 350w-700w.
With my bike I am aiming for high efficiency as it will have to travel 35km everyday on a 48v 10ah battery. completing each leg of the journey in around 45min so average speed of only 23km/hr but including stops its closer to 30km/hr. I am also aiming to be able to make the trip without pedaling, I will pedal but I just want the option (in case I'm feeling lazy). So the high peaks are obviously not in line with a high efficiency hence why I am looking for a current limiter. If anyone has any other tips for increasing efficiency let me know
A quick search of eBay and I found cheap DC motor drivers. Could I put a properly rated DC motor driver in series with the battery and successfully limit the current? would the PWM signal mess with the controller? How would limiting the current affect the voltage to the controller? As this circuit would introduce extra losses would it be worth being able to switch it inline/out of line whilst riding so it can only be active when needed?

 

[Chalo]

Easiest would be to get a 350W rated controller, and use that.

Second easiest would be to get a controller and display of about the same power as what you've got, but which allow you to set different assist levels/throttle levels to economize on power.

 

[jmamcarson]

thanks but I forgot to mention I'm both trying to do this on a budget / with parts already on hand and also looking for oddly enough the less simple solution as it lets me tinker

 

[ColinB]

I wonder if it is possible at all? If you have some device in front of the controller limiting the current to the controller, what happens when the controller sees full throttle? Would it be starved for voltage/power, and suffer a brown out? I know that it is recommended to supply your devices with adequate power (ie: you don't run your table saw on a cheap thin extension cord) because it is bad for them.

How about other methods? Can you program any other controller settings?

How about your riding style? Don't use the throttle at all until you get your bike up to speed. Go easy on the throttle.

It sounds like a fun project, but may not be reliable for long term commuting?

 

[pullin-gs]

Here ya go...20 amp fuse....costs about .20 cents for each fuse, and about $1 for a holder

 

[markz]

Free - Limit the throttle usage, or epoxy a throttle stop.

 

[Chalo]

thanks but I forgot to mention I'm both trying to do this on a budget / with parts already on hand and also looking for oddly enough the less simple solution as it lets me tinker

Well, if you get stuck, a 350W controller is $12 shipped. Not a budget buster.

https://www.ebay.com/itm/36V-48V-350W-Electric-Bicycle-E-bike-Scooter-Brushless-DC-Motor-Speed-Controller/113967106563

 

[markz]

thanks but I forgot to mention I'm both trying to do this on a budget / with parts already on hand and also looking for oddly enough the less simple solution as it lets me tinker

Less simple way is to shave some metal off the shunts.
Cost is free.

 

[docw009]

If it's a goalpost type shunt, with high enough legs, snip the shunt at one leg. Then solder a thin wire across the legs. This allows you to repair it if you want in the future.