AC speed control for 24VDC system

[Clayts]

Hello there.

 

A few things have dawned on me lately!. I'm thinking that maybe I can grab a normal variable speed AC controller...rip out the full wave bridge rectifier, rewind a 400VAC to say a 24VAC 3 phase and worry about the current later...what do you think?. Is there any controller out there where the IGBTs or MOSFETS (entire Cct in general) is able to withstand say 100+ amps. I'm getting very desperate here.

 

Anybody want to bring some expertise to this, because quite fankly I'm legging this in a big way!!

 

Best Regards

 

C M

 

ps a little knowledge is dangerous but a whole lot of fun. )

 

 

 

[marke]

Hello Clayts

 

There are many VSDs out there that can supply more than 100 amps but it would be a very expensive exercise to buy one and modify it for use on 24VDC. The power devices are rated at 1200V and are very expensive compared to low voltage devices of the same current rating.

 

I do not believe that your proposal is a truely practical solution. There will be too many complications such as the power supply is designed to operate from the high voltage DC. At 24V DC, there is no way that the switch mode supply will work.

 

You would probably be better off getting a small drive and using the control pcb as the waveform gnerator to drive your own power stage designed to operate on 24VDC. You would need to have a lot of information on the control pcb to make this work, and I suspect that will be a tall order also.

 

Good luck with your endeavours!!

 

I think that if you are serious, you could start from scratch and use a micro to create the waveforms, there are many kits around to demonstrate this, and build your own power stage.

Try looking at the Atmel AVR site, I am sure that they have an app note on using an AVR for motor control.

 

Best regards,

[mariomaggi]

Hallo!

Today I've received a serious inquiry for a certain quantity of 24 VAC motors to be powered by 36 VDC batteries. The biggest one has an output power of 2500 W.

I've already found some potential suppliers, this voltage in this case is necessary for safety reasons.

 

I'm convinced that these drives will have a future in some special applications.

 

Regards

Mario

 

[Clayts]

Hallo!

Today I've received a serious inquiry for a certain quantity of 24 VAC motors to be powered by 36 VDC batteries. The biggest one has an output power of 2500 W.

I've already found some potential suppliers, this voltage in this case is necessary for safety reasons.

 

I'm convinced that these drives will have a future in some special applications.

 

Regards

Mario

 

 

Thank you Marke and Mario for your replies to my post. Looks like I may have to sit level 5 simply for power electronics!. You would think that my request would be a common one, particularly when it comes to EV applications in general and the obvious benefits of 3phase AC induction motors. If anybody else happens upon this post and can come up with a product..pref with regenerative braking. I would be more than happy to wheel and deal. I can offer my time and labour minus copper costs in exchange.

 

I'm open to suggestions and I will check back here often.

Cheers

 

Clayts

[mariomaggi]

Dear Clayts,

pref with regenerative braking.

 

Almost all variable-frequency inverter drives for low-voltage DC power supplies are regenerative.

Braking is possible if the generator (battery?) is not fully charged. Otherwise you have to dissipate energy on a power resistor (this action is not "regenerative") or to inject DC current into motor windings.

 

First of all you have to explain better your application and what you have in mind, further info could follow.

 

Regards

Mario

[Clayts]

"First of all you have to explain better your application"

 

The inverter/VFD is to control a 4 pole 1.5kw series wound 3 phase motor (the motors voltage I can vary, depending on properties of supply and controller) for a road bike conversion. The DC supply I can vary from 24VDC to 48VDC. I would prefer 24V on account of potentially uneven charging with batteries in series and other reasons, however I could use a PLC to switch charge sequence (which I intend to incorporate anyway) . By saying this, having a larger voltage say 48V will reduce the current and possibly improve my chances of finding a dedicated, compatible or less likely (as Marks pointed out) convertible drive!.

 

I have had a look at your web page and don’t think you require any help with specialized motors. If you know of anything out there suitable to my application, I would be eager for any quotes.

 

 

 

 

 

 

 

[mariomaggi]

Dear Clayts,

I've few time now, sorry!

 

Do you abandoned the possibility to use a brushless instead of an asynchron motor? A brushless motor is more efficient, is lighter and smaller than an asyncron, generally speaking.

 

If you need absolutely an asynchron motor - for some prototypes - you can look to some special asynchron motor, costly. Otherwise you have many standard solutions with standard brushless motors and related drives.

Another important point is the selected motor speed (nominal sped at nominal power and maximum speed). Do you have already selected the mechanical transmission?

 

Let me know

Mario

[Clayts]

Hi Mario

 

I have not abandoned the brushless idea. The guts of it, is that a squirrel-cage type 3 phase asynchronous special for me is not costly. I can wind myself one for minimal cost, which is why I’m complicating this out of all proportion and was considering butchering standard AC drives to work direct from DC with a smaller voltageAC output . I was also hoping for lower voltsDC input to drive, as I do not require so many batteries in series, which for me would have many disadvantages. I am going to have to do a massive rethink. There are obviously a few factors I have overlooked and a few more I could understand better. Thank you for your time Mario. I will give an update at some stage.

 

 

 

Cheers

 

C Martini