I'm working on building an electric bike... well, doing the research for it anyway.
Right now I'm thinking about motor controllers - which are pretty expensive to buy already built.
My thought is that I could just build my own. I'm just not sure if I could use the same schematics for an h-bridge, but just upgrade the components to ones rated for higher voltages.
I'll be working in the 24V to 36V range if that helps at all.
In my head there's no problem with it... but then again I'm still pretty new to the electronics bit.
From what I read, they From what I read, they generally have quite a bit of pull, but I don’t know specifics yet because I don’t know what motors I’ll be getting.
Get a nice, hefty IGBT (Insulated Gate Bipolar Transistor) to drive your motor. They can take large voltages and amperages, and are very tolerant of high frequency PWM. I presume you’re going to use a microcontroller to interface the pot/etc with the motor drive?
I’m not sure if this makes sense… but I’ll try to be clear.
What would be nice is to have a transistor that allows high voltages, like you said, but the base would take a low voltage, such as turning one of my Arduino pins HIGH.
I could then use a piece of equipment that I already have and know how to use… I just don’t know anything about the IGBT’s yet, so I’ll have to do some searching.
Here’s one I’ve used before: Here’s one I’ve used before: 16A, 600V, only requires 3-6V to turn on =) If you need more current, but the transistors you’re looking at are starting to become expensive, you can always use a few cheaper ones in parallel and share the load.
Yep, 600V blocking capability, even I haven’t been able to kill one of these yet =D
Although 600V is total overkill, you will want a solid overhead relative to your 24V supply. As you may already know, stopping or rapidly decelerating a DC motor will cause it to dump the magnetic field energy back into your circuit, which is seen as a large voltage spike aimed directly at your motor driver in most cases. Will the ability to take 600V you have little to worry about.
Also these guys only cost ~US$2.50, so it’s not like that high voltage ability is costing you anything extra.
Are you saying I can simply send this transistor a PWM signal to its base (gate) and thus drive 16amps? No mosfet driver or the like? This can’t be as easy as a shared ground, 5v data line, and a ground going in and a ground going out, could it? What about failure? Do they fail like mosfets and slam your motors to full on? Seems too good to be true.
Oh, what about diodes? Are they called “anti-flyback”?
• This type of IGBT is • This type of IGBT is designed to be driven with PWM. • 16Amps is the minimum current cap, check out the datasheet, it’s quite a beast with proper cooling. • Ideally you’d drive the gate with 6V, but 5V will do the job in almost all circumstances. • Virtually all transistor devices can burn out and cause a short circuit, but you’d really really have to punish one of these guys to cause such a meltdown. In any case, a relay or direct ‘kill-switch’ is always advisable for moderate to high power projects. • There’s a ‘body diode’ built into this IGBT, which is pretty common in power transistors. It can handle at least 12A reverse current, so there’s no real need to add anything extra. This guy was born to drive motors.
Depends on the current you need - if you use the IRG4BC30KD you can get 16A at up to 100°C, or up to 28A at up to 25°C. Naturally the harder you push the IGBT the more likely you’ll need a better heatsink. Below 16A I wouldn’t bother with one, just try to not crowd the big guy too much.
The motor I think I’ll be The motor I think I’ll be getting will be somewhere around 16.5A, so I shouldn’t need one… I’ll probably end up using one just in case I end up needing more punch, thus more amperage. They’re cheap, so it’s not a huge deal - I could even just mooch one off a dead PC.
I wanna! Man, one $2.50 transistor, a pot and a pic… Not to mention, it would be about 6 lines of code! I want to make an electric bike! Damn, now I have to go google for parts…
The most expensive piece is going to be the batteries.
I’d love to get Lithium, the amp hours are a lot lower, so you get a lot longer charge out of them - but they’re so damn expensive.
I found a motor on Craigslist that’s just what I need, and at only $20. I just need to go pick it up. And the gearing can be done REALLY simply, so that’s nice for me as I’m not much with the building things just yet.
Go with ebay for the motors I was doing a bunch of looking for batteries when I needed one for Walter. The best prices are on ebay and you can get great deals on packs of 4. Do an ebay search for 12v 12ah SLA.
