hub motor as a electromagnetic brake

[bzhwindtalker]

hello all!
I just finished to route the chain of my new velomobile chassis, and to test its behavior under load I wired an unlaced hub motor in short circuit to provide a constant load. However, this made too much load for me to actually pedal it, so I tried to wire another motor phase to phase with the hub, to increase phase resistance and decrease the load. The motor I used is an inruner from a fiat car steering system, intended to run on 12v. This worked, but the load was still too high, seemed like starting with the smallest cog on a 10% grade! A fun thing with this set-up was the synchronous operation of the two motors, the hub was driving the smaller inruner, electric chain anyone?
Now I guess the best way to have a variable constant load would be to find 3 big potentiometers? Another idea could be to use a controller with a variable regen brake, I don't know if most controllers do that?

 

[lifepo4ever]

infineon can regen to slow down but not for emergency stop

 

[amberwolf]

Now I guess the best way to have a variable constant load would be to find 3 big potentiometers? Another idea could be to use a controller with a variable regen brake, I don't know if most controllers do that?

For pots, you'd probably have to use stage-lighting dimmers like the ones I have here, which themselves are larger and heavier than my 9C.

There are a few controllers that can do variable-regen braking; ebikes.ca used to carry some so they are probably still on their pages, or you could email or call them to ask which one(s) they were and if they might still be avaiable. The variability worked (AFAICR) by engaging the brake and then changing throttle position to get more or less braking.

Alternately, you could modify a controller to short the phases with the regular throttle PWM instead of providing power to them. You'd need to cut all the B+ power traces to the FETs so that they only get gate and B-, and then wire B+ to the positive of a much lower-voltage supply like a partially-charged LiPo, or 12V FLA or something, to use as a load. Whatever kind of battery, just something that can take a fair bit of fast charge current for a while, and has enough Wh capacity to hold whatever you are going to generate while testing. Or use a barely-charged FLA/SLA and a bunch of 12V headlamps or something to give a nice hefty load. B- would of course still go to the battery negative. You'd also need to have a separate (higher voltage, fully charged) battery supplying the controller's normal power to it's low-voltage regulator and stuff. It's probable that the gate transistors are powered off the main B+ via some voltage dividers, so you would need to try cutting *only* the FETs off the B+, rather than anything else.


Also, if you only short one phase you'll only have 1/3 as much load, and two phases 2/3 as much, as if you short all three, I think.

 

[bzhwindtalker]

Thanks for the advice on the Ebike.ca controller, I will look at those if they are cheap enougth
I tested the load with two phases shorted, reduced load to an acceptable level, but it was really not a smooth constant load anymore, it had like steps.... I'll try to find some magnet wire to wrap into coils, this should work okay if they have a big enough resistance

 

[vanilla ice]

Use a few cheap halogen 120v light bulbs as a load, those are pretty skinny. Here's a couple:

1500w $1.82
https://www.1000bulbs.com/product/1294/Q-J10395.html
500w $0.85
https://www.1000bulbs.com/product/5108/Q-J0500120.html

You can paint them red and put them out back as a brake light!

 

[vanilla ice]

Or maybe you could attach wires at different points to a heating element from a scrapped electric heater.

 

[bzhwindtalker]

Thanks for the idea of halogen lights, I even have some on hand to test this out! I have a couple of 12v ones too, but those will probably die with the high voltage back emf of the motor?

 

[fechter]

If you use light bulbs or electric heating elements, you can probably place a light dimmer in series with the load to make it variable. Since the ouput of the hub motor will be AC, the triac circuit should work if the voltage is about right.

 

[lifepo4ever]

i hope we can see i video of your work

 

[bzhwindtalker]

hello!
I tested the set-up with 3 12v 20w halogen bulbs, it worked really nicely and was fun to watch too, but quickly I burned one of the flashbulbs, so I found another idea : I had a bunch of 10w resistors left from a non-working electronic (I'm no good at electronics ) project, I wired 3 of them between the coils, worked nicely but the resistors could not dissipate the power in. So I had the Idea to put the resistors in a glass of water, to help to dissipate the heat. so I had another idea based on that : A thermometer, a calibrated amount of water, and some calculations... This set-up will be used as my training bench for my road trip this summer, I may see some of you Americans on the road :wink: http://www.triketrek11.com

 

[amberwolf]

Interesting trip project; I wish you were coming thru Phoenix.

BTW, the link in your sig:
http://www.electricgarage.weebly.com/la-machine.html
gives the following error:

Site not published
The site you are looking for has not been published.
If you are the owner of the site, you can fix this message by republishing your site.

 

[bzhwindtalker]

aWW Thanks Amberwolf I'll fix that
I'm training 30min a day, will soon increase that to about one hour per day, I need to rework my idler or machine a new one, cause the current one is making such a horrible noise