DC motor control

[The EE student. No.288990]

Ask a guy how just started a special course on building a 250A motor controller anything,

Specs:
Vin: 30-60V
Imax: 250A (continuous)
Load: ~10kW
Swich Frequency: ~25KHz
Semiconductor: 6-10 N-Channel Mosfets
Estimated mosfet loss: ~ 70-140Watt
Topology: Chopper

[Anonymous No.288992]

1. purpose?
2. schematic?

[The EE student. No.289005]

>>288992
1: Learning the complete process of designing a high power circuit involving:
- EMC and circuit theory./design
- HF Pulsed Mosfet operation and paralleling.
- SMPS (for supplying control boards)
- Dimensioning thermal design
- Finding the "right" components
- Building high power / HF circuits

And also for the fun of controlling a big DC motor that is going to drive a gokart.

2. I currently don't have a complete schematic, as it is something that I'm going to do myself during the semester.

although if a had one i probably wouldn't share all of it, due to the fact that I might be able to sell it.

[Anonymous No.289048]

Good on you for learning all that OP.
Any good textbooks you can recommend that you've used in your studies?
(Anything at all, I'll read it: From beginner to graduate level to professional engineering level books)

[The EE student. No.289063]

>>289048
Woohh, cant recall the exact names of them, and some of them were to no use at all.

But I'll get back to you with names of the ones that I thought were decent, it will have to wait for tomorrow.

You can find some great online lectures, perhaps take a look at some from http://www.youtube.com/user/nptelhrd

Have used their lectures on Electric motors to refresh a course names "Electrical Machines", they do a very good job.

Pic: Grinding ??? the front wheel so a bigger barring would fit.

[The EE student. No.289452]

Used:
- for sensor theory, some of the chapters states a lot that i think is common school material from "High school" (what we call Gymnasium).

Jacob Fraden
Handbook of Modern Sensors
Physics, Designs, and Applications
Fourth Edition

ISBN 978-1-4419-6465-6

- Used for Electrical Machine Theory
Electric Machinery 6. ed
ISBN: 0-07-366009-4

- Electro magnetism and transmission lines
Fundamentals of applied electromagnetic
ISBN: 0-13-241326-4

- Using Basic Electronic knowledge
Microelectronic Circuits
ISBN: 0-19-514252-7
Picture:
my lab, not used that much any longer as i have access to better equipment at school.

[Anonymous No.289474]

I need to step down a 12v DC power supply by 20% (9.6v) and 40%(7.2v), respectively, to power a couple of DC motors. One power supply but two different voltage converters. Each unit will need to handle up to 10 amps, so I have been told that just using resistors would produce a fuckton of heat. As these controllers will be mounted in a confined space for long periods without ventilation I was pointed towards PWM as a solution. Problem is I have zero working knowledge of this kind of stuff so I can't design what I need myself. Assembly isn't a problem as I can solder well enough. Wut do?

[The EE student. No.289561]

>>289474
You could buy some ready made SMPS or pwm motor controller.

go search google to get an idea of how they work. when you have got an idea of what you need and how they work, you can look for one in dx.com or goodluckbuy.com

Why is the voltage of the motor so important?

[Anonymous No.289586]

>>289561

Good question, no clue. They are drill motors and thats the voltage they run at. If I could run them on 12v it would make my life a whole lot easier but I have no way to tell if they can handle 12v or not without possibly blowing them.

They story is I acquired a bunch of older Makita cordless power tools that run at 9.6 and 7.2 volts. They are solid tools but most of the batteries they came with were worn out. Replacement batteries cost 40-60 bucks each and for that price I could hack something together myself instead. 12v DC power supplies for LED can output plenty of amps and are cheaper than one battery, so all I'd need is something to downstep the voltage.

[Anonymous No.289602]

>>289586

9.6V NiMH battery has a maximum voltage of 11.6V, so you can expect that at least they won't blow up immediately, if you give them 12V. You might have problems if you run them at that voltage for extended periods of time.
If you have a "bunch" of them and they don't have any other use, why don't you just give it a try?

[Anonymous No.289615]

Hmmm. Interesting application -- but im thinking there's more to the story.

I question the value of a 60V 250A controller though. I mean, why 60V? Do you have a shitload of 0000AWG wire laying around or something?

Also, I'm not sure i've ever seen a 10KW DC motor rated for an input voltage of 60V. Is this normal? Like, if it application specific to electric vehicles or something? Now, im just assuming your output voltage is identical to your input. Because, adding a 250A boost converter to the mix seems like a pain in the ass.

Personally, i'd rather have a 250V 40A controller -- but, it's a noble pursuit nonetheless.

[Anonymous No.289620]

>>289586

They should be fine, as >>289602 said the rating of a NiMH is there nominal voltage which is 1.2V per cell but there max voltage can be as high as 1.4V. So when you consider that the motors themselves can tolerate some voltage variation, so long as you don't go too much past 12V you should be OK. Plus it would probably be easier and more efficient to rewind the motors than fuck around trying to step down the voltage.

[Anonymous No.289622]

>>289620
*their

[Anonymous No.289629]

>>289602

Most of the tools are 7.2 volts and are of different types. Flashlight, 3 drills (different types and vintages), and a grinder. The 9.6 volt tools are a flashlight and a drill. So I'd still need to step down the voltage if I wanted to use most of them. I have no clue what kind of amps they pull so I figured I'd be on the safe side and get a 10 amp PSU, its only like $10 more than the lesser ones anyway. Replacement motors, on the other hand, run about $40.

[The EE student. No.289642]

>>289586
You could take apart the battery pack, and change the cells, that is what i would do.

Otherwise just power the devices by 12V but i think that 10A is a bit underrated for a power drill, perhaps more like 20A peak..

>>289615
I we why you do question it, it is a motor designed for 28V 120A continuous load at 70celcius, so at ambient at 30celcius, the power can easily be cranked up.
Not sure if the current motor would handle all 250A, otherwise i will rewind it, or get hold of another one.

the 250A at 60V is not unheard of, look at electric forklifts.

If i had the possibility of doing something like 110V 100A i rather do that, but it is not possible.

at 100% duty Vin = Vout yes, but this here is current controlled, so not interested in Vout.

[Anonymous No.289650]

>>289620

The batteries these came with are NiCads, that change anything at all? Also, like I said in >>289629 the majority of my tools are 7.2v. I only have 1 drill that is 9.6v.

>>289642

I took apart one pack to see what I would be working with. I even used an old school one that has a couple of tabs holding the base together and it was still a serious PITA. The tabs were so strong I couldn't budge them even with my full weight on them! I have to drill them out. The newer ones have no external tabs at all so I have no clue whats holding them together. Might be glued for all I know. I'll give Makita props for having some serious fucking battery cases.

The cells are also kind of weird looking. Short, tubby little things. Much fatter than a AA but only about 2/3rds as tall. I have no clue where to buy them and they were completely unmarked.

Pic related, its the older style ones with tabs. The new ones are completely smooth.

[Anonymous No.291215]

>>289650

Most places that refresh batteries have a special tool for getting the bottoms off of old Makitas, if they still service that kind of battery regularly. The ones without tabs they cut off and epoxy back on.

[None !!b1y795nhfDZ No.291790]

What university is this at?. At the bare minimum I'd imagine you'd include current sensing, variable PWM generation and ADC for throttle in an MCU. Beyond that its pretty much just gate drives and suitably heatsinked mosfet bridge. You don't even need to make a floating PSU for the bridge high side with most IC gate drives. I feel bad for your traces though.........you will need to use to-247 packaged fets just so you can get enough track width to handle the current.

>although if a had one i probably wouldn't share all of it, due to the fact that I might be able to sell it

if it were a servomotor system, probably, but that's about 3 orders of magnitude difference in complexity.