Simple EV bike build with no controller?

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neptronix
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Simple EV bike build with no controller?

Hey there.

I'm interested in rolling my own simple setup.
I have a hybrid style bike with an aluminum frame. I figure this is the least desirable bike... But i do not want a lot of power. Just 200-300 watts to assist up some hills.
Not interested in regen, cruise control, or anything fancy.

I am wondering if i can run batteries direct to a hub motor without a controller. I am thinking of using two 18v batteries, with one switch per battery to activate it, so that there are two speeds, 18v and 36v.

I'd like to use DeWalt batteries. The BMS in them seems adequate. I assume the BMS on those prevents them from going under the charge level that lithium batteries like.

Is this feasable?

Thank you.
-David

Spaceangel
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Re: Simple EV bike build with no controller?

What is the brand of motor you are desiring to use? Most Hub Motors are BLDC type as in three phases and some call them AC motors but anyway it does require a controller of the Variable frequency drive type to work. Pure DC from a battery pack won't spin the motor. There are Hub Motors with brushes but brush life if very short lived. Now for a real kick in the @zz. Controllers add a very significant amount of energy back to motor via the use of recovery diodes or flyback diodes. Well that is for the brushed type of motor you speak of. You can get increased range on BLDC motor controllers via reduced frequency meaning slower speed and less current drawn. Let us know the brand of motor and type of design and see if it is possible to use without controller. On eBay there is a wheel assembly for rear wheel for under $400.00 listed as of today's date with a controller. The more power of the motor the more the it will need from battery pack and I find 1000 Watt comfortable for my 6 foot body is fine. But it requires 48 volts so maybe a 36 volt motor might be able to use DeWalt battery packs. Usually the less voltage the lower the current draw and power to motor. DeWalt batteries do well in 300 Watt grinder,18 volt Nano battery pack. Another useful part of using a controller is low voltage cut off. Go with a controller. Most can be programmed for useful stuff like current draw and low voltage.

KB1UKU

neptronix
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Re: Simple EV bike build with no controller?

Well, for the motor i wanted to use a brushless, but i heard it required more complicated controls than i understood. So i could settle for a brushed, considering the low mileage i plan on putting on the motor.

I heard there is power loss when doing PWM controlling. That's why i was thinking maybe i can ditch the controller, even if it requires using a less sophisticated motor.
I guess there is no way around the controller then. I had no idea.

Another reason is that there seems to be little information on these controllers, none of them are ready for someone like me with very limited electronics knowledge; at least from what i've read..
Am i wrong? or missing a thread? i've been searching for a while now. This stuff does not seem plug and play at all.

Another idea i had was to buy 3-4 DeWalt cordless drills and use them with some sort of chain drive setup.. please let me know if this is a stupid idea or not.. ha ha :)

colin9876
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Re: Simple EV bike build with no controller?

Well you can do it but I would like to offer a word of warning from my past experience.

I hate overcomplicating things, so like you, wanted to make my first bike without a controller!

1) If you do the one bat / 2 batts thing, make sure your switch works so that when ur only on 18v it pulls off both batteries in parallel, otherwise they will run down unevenly.

2) The problem I faced was the switch. With out a controller at start up the motor can pull 100amps. It welded my (20 amp rated) switch together.
...Full speed into a bus - luckily no injury!

NB. If u do go with a brushless hub I prefer 'sensorless' controllers - avoids the big hassle of hall sensors.

Spaceangel
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Re: Simple EV bike build with no controller?

I heard there is power loss when doing PWM controlling. That's why i was
thinking maybe i can ditch the controller, even if it requires using a less
sophisticated motor.
I guess there is no way around the controller then. I had no idea.

Quite the opposite. You gain so much because of flyback diodes on a PWM controller otherwise known as a chopper. It controls via turning signal as in the "Battery" on then off then on etc 15 to 35,000 times a second and fast switching diodes turn that off time into free electricity to run motor like a flywheel or capacitor effect. So in that respect there is NET gain and NO losses.

The other thing is just like colin said, is a motor will try to draw full current at start up and that means welding of contacts of switch or contactor. Controllers are just that. A Controller. They limit current flow to a safe and reasonable level. A simple and easy way to go and not complicated. Try to bench test "mock up" and use one for a light dimmer first. Then remove lamp and use a motor. It starts off smooth all the way up to full speed. Just so easy.

KB1UKU

bnorthup
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Re: Simple EV bike build with no controller?

I built 3 EV bikes with no controller. They work great for me. Other people seem to have problems with them. I never flip the switch to "on" from a complete stop. I always pedal the bike up to about 5 miles per hour or so and then I flip the switch on. At 5 MPH the bike will draw about 40 amps as it pulls you up to speed. At about 12 mph the current draw will fall to a normal 15 amps or so. The problem has become finding the brushed hub motor. Mine say Aotema on the hub motor. Evidently no one wants to buy a hub motor that is brushed anymore. This causes the electric bike to cost as much as a used car. ... In the old days (5 years ago) you could buy brushed hub motors from Wilderness Energy but I don't know if they still have them. Or, I am sure that if you wanted to buy a whole container full of brushed hub motors from China (Aotema) then you could still get them.... I have mine and I put a LiFePO4 battery on it and I am very happy with it.... They say that the brushes will last for 5,000 miles.

reikiman
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Re: Simple EV bike build with no controller?

If you really insist on going this way - use a contactor. (aka Relay) Make sure the relay/contactor is rated for high amps. Use of the contactor/relay means you're not running full motor current through the switch on the handlebar.

Contactor/relay's work by having a high amp rated switch operated by a solenoid that can be energized at low amps. The switch on the handlebar thence only has to handle the low amps required to operate the solenoid. The solenoid/contactor/relay/thingymajig is then your controller. Of course the contacts inside that can become welded shut if they aren't rated for the current your motor requires. I've done that to at least one contactor.

But - PWM controllers do not have (significant) energy loss. Earlier controllers (SCR and resistors) do have energy loss. At least thats as far as I understand/remember having carefully read Radio Shacks Op-Amp Cookbook about 30 yrs ago. Every electric circuit has efficiency factors and any efficiency less than 100% does mean energy loss. But I believe PWM controllers have an efficiency factor in the 95% range which is high that I wouldn't worry about it. Again it's been 30 yrs since I read the Op-Amp Cookbook so of course take this with an appropriately sized chunk of salt.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

neptronix
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Re: Simple EV bike build with no controller?

Thank you guys for your advice. I've been reading some other forums and have decided to go the way of the brushless geared hub. It seems like the most efficient setup; i'm thinking the ampedbikes kit and dewalts will do.

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