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Terrible Idea Boost Converter To Be Tested On Gocart

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i_am_fubar:
I got an 1800W treadmill motor a while ago and decided to make a go cart with it.

It's a 180v motor.

I've run it off 4 SLA's, but at 48v, the speed is less that impressive. Plus, I think the batteries are almost dead, so really not as fun as I hoped.

Sooooooooooo, I've decided to build a boost converter / motor driver to run treadmill motors (upto 200v) from not 4, not 3, not 2 but 1 SLA battery (probably a big ol' leasure battery).... Just dealing with the fact it'll pull 150A. It's freaking me out a bit :)

Have got prototype working on the bench without load, but wondering if there are any other similar designs out there I could get inspired from?  :-+

richard.cs:
Boosting a 12 V battery up to 180 V for a motor can probably be made to work but for that sort of power levels will almost certainly cost more than buying a lower voltage motor or a higher voltage battery pack. A 150 A input boost converter just isn't that sensible but if you really wanted to then you should look at schematics for a 2 kW inverter minus the output chopper (or just buy one and modify it).

I have a kart project at the moment using a car dynamo as the motor (in seperately excited mode) with a 48 or 60 V battery (not settled yet). This is a very cheap way of getting a brushed motor capable of around a kilowatt.

T3sl4co1l:
Just one?  It's not going to run long, that's for sure; that's typical current draw for a starter motor!

Consider using several channels in parallel, and using push-pull forward converters.  This reduces the amount of reactive power required, so you can use smaller inductor, capacitors and transistors, and layout is easier and efficiency is better.

Transformers can be scrapped from car audio amps, rewinding the secondary for the desired output voltage.  The power transistors and controller (usually a TL494) can be reused.  You will need to add an output filter choke, current sensor (can be a shunt resistor or Hall effect sensor), gate drivers and rectifiers; snubbers are a likely addition as well.

The channels can be phase-shifted between each other, to help cancel out some ripple, so you don't need as large capacitors at the input and output.  (The caps from the audio amps would be fine for input, and caps from off-line PSUs would be fine for output.)  You then need one TL494 controller per channel, and a phase shift / clock oscillator to run them all (which I haven't figured out a minimal method for TL494s just yet, but there are some straightforward options to start with).

It's no harder than doing just one channel, it's just more bother, repetition.  Indeed you'll have a higher chance of success with the smaller channels, than with one big one.

Tim

i_am_fubar:
Yea, the prototype doesn't have a choke or any filtering other than the caps (all elec, no ceramics so RF will be a pig). Will need to add some external filter to the actual switcher. Thankfully I'm not going for EMC tests, but how hard could they be....  :-DD

I've got 1 phase made up at the moment. Another I can make up, buy provision for 4. Using a PIC to generate PWM, won't be smooth as far as far as PSUs go, but it's driving a motor, so not too worried. Plus I can adjust motor speed with finer resolution from the drive PWM.

Have got current and voltage monitoring on input and output. At the moment streams results to PUtty, but got a phone app that will give me a proper dash board in time.

Going to try and attach a picture now.... Seems to be working  :)

Resistors give me 200ohm, so it's enough to mad a 10A bench supply out for now. Once I'm happy with control loops and voltage rating, I'll swap over to a (fused) battery.

Have designed to take up to 36v input, so could knock it down to 50A input which is a much happier current.

Also, I know this isn't an ideal way of doing it....bits just fun :p

Also, proof of concept... On verovoard... That blew up...  :-//
https://youtu.be/SDAV5vs-Nlo

Zero999:
Your best bet is to scrap the boost converter and use more batteries in series to give 180V. Failing that go with a lower battery voltage, but still higher than 12V, such as 48V or  60V, to keep the current low. It will be easier to construct an efficient boost converter to go from 60V to 180V, than 12V to 180V.

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