Home -made electric bike speed controller

[Jules]

I am making an electric bicycle using a Sinclair 12 volt motor, gearbox and 12 volt battery. I have found several PWM speed controllers around, but none to control the high currents involved. Has anyone a schematic or helpful link ? Thanks

 

[Nigel Goodwin]

I am making an electric bicycle using a Sinclair 12 volt motor, gearbox and 12 volt battery. I have found several PWM speed controllers around, but none to control the high currents involved. Has anyone a schematic or helpful link ? Thanks

There's quite a lot of useful info at 4QD, have a look here https://www.4qdtec.com/pwm-01.html#soph.

You could also try looking up 'Robot Wars' sites, a number of those have used the old Sinclair motors over the years.

 

[ante]

Jules,

How much power are we talking about here? The motor ratings?

Ante :roll:

 

[Jules]

Hi, the 4QD site has some ideas, but they are early prototypes, all with various problems such as MOSFET overheating! You have to pay to join that site. The motor I am using is a Sinclair C5, 29Amps, 250 Watts, 3000RPM. It has a reduction drive gearbox fitted. I guess I need some sort of high current controller (power MOSFETS?) I want to power an electric go-kart or a bike. Any ideas?

 

[Klaus]

Jules, have a look at :www.sevcon.com
and look up their Millipak 4Q controllers
They make controllers good for well over one hundred amps as would be used on electric boat motors or go cart motors like the Etek.

Building such a controller yourself would be a real challenge and I doubt you'd get one as good as the commercial ones, even if they are rather expensive.
Klaus

 

[ante]

Jules,

It,s not to hard to build one yourself but here is a good alternative: **broken link removed**

Ante :roll:

 

[chemelec]

Numerous guys have used the "PWM" control that I designed for that purpose. There are two versions shown, one is very high current capability.

**broken link removed**

Take care........Gary

 

[ante]

Gary,

First I must say it is a very nice site you have put together. It’s has a nice blend of well-explained circuits. I like it, keep up the good work! About the PWM circuit; this will do the job if modified slightly, a big diode across the motor (freewheeling diode) is necessary. And depending on the mosfets used you have to make sure that these are switched completely on as well as of to get as little heat as possible. A safety relay would be a good thing too.

Ante :roll:

 

[chemelec]

Ante, Thank for the Compliment on my site.

Yes a diode may be needed, or a good Movistor. [a big diode across the motor (freewheeling diode) is necessary] but I designed this a a general purpose device and the diode is only needed on Inductive Loads, not resistive loads. Definately use a Good Heatsink, possibly a Fan on it.

As to the Safety Relay, Not sure what you mean, But a Fuse or a Fuseable Link might be Useful as well as a Master On/Off Switch.

Take care.......Gary

 

[Jules]

High power PWM motor control

Thanks for the ideas. I'll try them out, adding lots of over current protection! I'm not sure why the MOSFET ground leads are all run separately back to the battery. The motor I have is from a Sinclair C5 (a lot were available for DIY about 10 years ago. Difficult to get now). it is rated at 29 Amps. I don't know what the stall current would be. I'm using a regular car battery to power it. Why are N-channel MOSFETS used in preference to P-channel ones?

 

[chemelec]

Hi Jules, You may want to use more than one car battery, but one will do for a start.

1) N-Mos Fets tend to be More Relialable than P-Mos, same goes for NPN and PNP Transistors, NPN are Better with Much Lower Leakage. (Very Simply Put, Mainly due to internal Construction.) And Current Sinking is almost always More Efficient than Current Sourcing.

2) Also, N-Mos Fets have the Tabs as the Anode, therefore in this circuit, all can be placed on a common heatsink and the Anodes are typically connected together via the heat tab.

3) Stall currents: probably at least double. (60 amps? or so) Because of this, and/or the possibility of Mos-Fet Failure, A fuseable link is highly recommended and it can be easily made using a 1 inch long piece of a smaller copper wire, (maybe a 20 AWG) inserted into the Anode lead coming from the battery positive.

4) Seperate ground returns help Equil out small differences in the Anode to Source between each of the mosfets.

5) A direct Return of the Source's to the batterys negative is necessary to prevent voltage drops being created that can affect the 555.

Need more help Jules, just e-mail me direct.

Take care.........Gary

 

[ante]

Gary,

I did not mean that your circuit was in any way wrong, but as you say with a inductive load a diode is needed. A safety relay is meant to switch in the motor at the beginning of the throttle movement, this way if the circuit have a short the motor shuts off when the throttle is released. Then it is also possible to add a bypass relay, this will reduce the heat by bypassing the transistors at full speed. This will need an extra circuit that measures the motor current and allow the relay to pull when the current drops to a preset level and the throttle is at max.

Ante :roll:

 

[Nigel Goodwin]

3) Stall currents: probably at least double. (60 amps? or so) Because of this, and/or the possibility of Mos-Fet Failure, A fuseable link is highly recommended and it can be easily made using a 1 inch long piece of a smaller copper wire, (maybe a 20 AWG) inserted into the Anode lead coming from the battery positive.

I would expect the stall current to be a great deal more than that, it's certainly likely to be more than 100A, and could be much more - it really depends if the motor was designed to be self limiting or not.