450amp H-Bridge ?

hey all

I have a large motor that I stole from a boat winch that I calculate will be capable under max load of pulling roughly 450amps.

I'll need to drive it with pwm so solenoids are out, but some pwm cycles will approach of not get to 100% duty. I was planning on mosfets of course but I wasn't sure if they made special packages and fets just for stuff like this ?

I know heat will be an issue but its taken care of (own a CNC Mill and large blocks of stock). This should only be running for 30 seconds max with at least 2 min between uses.

The largest mosfet I can find is 80A (D2Pak). I'm not 100% sure but I should be able to put say 6 to each side of the H no? Thus split the load and rON values ?

Anyone have any thoughts or practical examples of something this large.

Thanks!

Look at the HEXFET >>>MODULES<<< from www.irf.com. They are massive but 450A is more massive. You will need to parallel two of them together. Also, you will need to get some driver ICs like the IR2010 and not use very high switching frequencies since large MOSFETs have high capacitances and slower switching speeds. All you need to do with the modules is bolt them to a metal plate as a heatsink (maybe watercooled would be even better). THey also screw terminal attachments so no PCBs to deal with for the power path (just the drivers).

450 A is pretty huge - what kind of wire is in this thing? It should have around .55" diameter wiring to carry that much current.

Also, I think at that current level you are going to see skin effect so you better use standed wire and pwm at a pretty low frequency.

You might also want to look at IGBTs at that current level, as well as MOSFETs. THe voltage drop across the FET on resistance at those currents might exceed the voltage drop of a diode (which is what the IGBT does).

Thanks, I'll check out www.irf.com, but so far they seem a little expensive. Plus I only found a 180 max unit. So I'd need 3 on each side, 12 total, * $18 is $216. Ouch. I found those 80A D2Paks for $4.5 but which comes out to $108, thats a lot more reasonable but still no where I want to be.

It should have around .55" diameter wiring - yea, thanks about right Its 2ga I think.

I don't imagine the pwm would be over 100Hz or such. Probably somewhere around there if not way less. What did you guys think would be an appropriate freq ?

I don't know much about motor controllers or power mosfets (yet). But it doesn't seem that using a few in parallel will be a problem.

I'll keep looking,

ESC's for large motors are big, expensive, and easily destroyed! - you might have a look at https://www.4qd.co.uk/faq/index.html which has a lot of information about them.

Oh. Well if you don't know a lot about motor controllers, I wouldn't suggest your first one be a 450A driver! Just buy it? Save yourself frustration, work, and broken parts. Isn't 100Hz too slow for the motor to not pulsate? The best frequency would be the highest one possible (for the motor to not pulsate) that doesn't overheat the drivers. 450A is huge...I dunno...2kHz at least? WIth so many large parallel FETs, you might even need to parallel FET gate driver ICs. Just buy a driver.

Another thing you might want to check into is the duty cycle of the motor.
A hoist is not generally continous duty, and if you plan on using it for long periods you might have a overheating problem...

Is this a DC motor with brushes?

What voltage does this thing run at?

Just buying it is not an option. Too many custom requirements. (Misc Input/Outputs, rpm and torque monitoring, etc etc). Its going to be made,

One note, the 450A is only when this thing is maxed out (10,000lbs). I expect most loads to be 300-375A.

What voltage does this thing run at?

Click to expand...

Its hooked to a generator and auto/marine battery so I'd say 12V, but in reality I know when used on the boat it dropped the system down to 10, figure 14V max.

Is this a DC motor with brushes?

Click to expand...

Yes of course. Otherwise I wouldn't be looking at an H-Bridge setup.

A hoist is not generally continuous duty, and if you plan on using it for long periods you might have a overheating problem...

Click to expand...

Right, 30s max expected use, but I want the option of continuous use for 1 min.

Isn't 100Hz too slow

Click to expand...

Yes, I just threw number that out there without any regard for proper design 2kHz sounds like it would be fine but I don't see any problem with a little pulsing if it were lower.

I think my numbers may be off but... Something did just catch my eye though. I found a similar company called warn that sell winches. They have a chart on their site that has a 9500lb winch that they say draws 425A but I checked an AWG guide an it says 2ga is conservatively for 181A. I wonder if my math is right, but it does match this companies ratings so I guess it must.

WIth so many large parallel FETs, you might even need to parallel FET gate driver ICs

Click to expand...

Just out of curiosity why is this ? The fet gate draws almost nothing. You should be able to drive an infinite number of fet gates with one output no ?

Thanks!

FET gates draw nothing...once they're on. They are a high resistance with a moderate capacitance in series. So once the capacitance is charged and the FET is in steady state (DC), sure there is very little current. So you can keep a huge number of gates on with one output...

But during switching, the capacitance allows the AC to pass, drawing current. Only when this capacitance is charged does the FET turn on and begin to draw very little current. The more FETs, the more capacitance, the longer it takes for them all to turn on, and the longer the FETs spend in the inefficient middle-regions between off and on. THe result is huge amounts of heating.

You could try turning on 1000 transistors from one output. It would work and you'd have no trouble once the FETs are on. You'd just have to wait forever for the FETs to actually turn on, and PWM requires fast switching.

Sooooo..... Assuming I have enough parallel fets and enough drivers the only thing I have to really be concerned about is heat correct ?

iso9001 said:

Sooooo..... Assuming I have enough parallel fets and enough drivers the only thing I have to really be concerned about is heat correct ?

Click to expand...

Did you try reading the website I posted?.

Nigel,

Yes, It has some really good info. But, I found nothing about parallel mosfets. They have a ton of info about their own controllers (of course) but little for the do it yourself types.

I found something very similar to what I want to make, its from that same winch company. Here is the link: https://warn.com/truck/accessories/mosfet_control.shtml And no this unit will not work for me, but its very close. They seem to have no problem with this even at 12V.

I would just crack one of these and modify it but it seems they are VERY expensive, that wouldn't be much fun anyhow.

I don't need very fast pwm, I have lots of room for caps and drivers, its low use, have complete design freedom, I'm just not sure where the next difficult design step is.... ideas?

The motor inductance is what determines how fast the PWM has to be- not the number of drivers you have or the caps. How well the motor's inductance sustains current flow determines how slow you can PWM. What voltage is the motor anyways? 450A is huge. Usually such a motor is higher voltage, lower current since that runs more efficiently and is also easier to build drivers for. If it's only limited duty cycle...*maybe* overvolt the motors so you have to deal with less current.

Do you really need PWM for a winch? It's not really motion control. It'd be so much simpler just to have one MOSFET (for unidirectional) that just goes on/off. Or if you need bidirectional, to just have a H-bridge that goes on/off.

Do you really need PWM for a winch? It's not really motion control. It'd be so much simpler just to have one MOSFET (for unidirectional) that just goes on/off. Or if you need bidirectional, to just have a H-bridge that goes on/off.

Click to expand...

Do I 'need' pwm ? No... Not really, but I would like to control the speed. The micro will be required for RPM and Torque, so why not drive the fets via pwm is possible ?

just to have one MOSFET

Click to expand...

Trust me, if I could find a mosfet large enough then this wouldn't be a problem at all

Well, when I meant one MOSFET I meant one switch, whether it's just one device or many parallel devices. A reason to it's hard to switch something(s) big enough to pass 450A at PWM speeds.

THen again...if you want torque and RPM control, you need PWM. BUt it's very unusual to run something a 5.4kW motor at 12V. It's just bad practice because it's hard to deal with such large currents. Usually the voltage is increased so the current is reduced- this also increases efficiency and decreases heating.

If you are running it on limited duty cycle...maybe the FETs don't have to be as big? Depends on how fast the FETs heat up. You just gotta be able to remove the heat fast enough so the duty period ends before the FET exceeds it's max temperature.

If you are not changing directions fast you might consider using solenoids on the high side and send your PWM to FETs on the ground side.