# analog three phase circuit

#### blainezxap

Joined Aug 9, 2008
2
Would anybody know where to get a simple circiut for an analog three phase generator. All of this is at 24 volt level no particular application yet depending on the final outcome. Just sticking my hand back into the designing of small systems again.

Thanks for any help.

#### Ron H

Joined Apr 14, 2005
7,014
If you mean a signal generator, I saw this recently.
This circuit may not be simple, but it's pretty cheap, and very flexible. There are a couple of errors in Figure 1. Outputs A and B are grounded, which is, of course, wrong.

#### stephenzxap

Joined Aug 9, 2008
3
By the way if your seeing a different name on the response is because I had trouble getting back in with the password.

Not quite what I was looking for. The circuit would actually output the 3 phases like the electrical lines at most power stations but only at 24vac. I work with equipment that does this already, but your thaking alot of $$to do a simple project. Theirs' run on industrial size batteries 24vdc and 36vdc conververtered to 3phase ac. I'm just looking for the not so$$$way of doing my own. And thanks for the reference. #### SgtWookie Joined Jul 17, 2007 22,210 What frequency output are you looking for? What kind of power output? #### stephenzxap Joined Aug 9, 2008 3 400 to 1500hz variable frequency. small output of about 15 to 25 amps like I said it is a small project to try to get into things. #### SgtWookie Joined Jul 17, 2007 22,210 Ahhh, 24V three phase @ 15 to 25 amps isn't exactly small. If you said 1.5 to 2.5 amps - sure, that would be small. But if you're wanting to run 15 to 25A per phase, that's a pretty good bit of power. 24VAC = 33.94V P-P, if you're talking true sinewave. Let's go with 20A for the moment. 24 x 3 phases x 20 Amps = 1440VA If you had a switching/buck converter that was 90% efficient, you'd need 1600VA. Running from a 120v outlet would require 13.333...Amps. Now if you want to get some reasonably efficient supplies and wire them in parallel, MPJA.com has various supplies in various voltages: http://www.mpja.com/products.asp?dept=465&main=1 But, at the kind of power you're talking about, you'd need multiple numbers of their 150W supplies - and those run about$41/each.

But then there's the 2KVA Variac they have:
http://www.mpja.com/prodinfo.asp?number=15163+TR
\$105. You'd have just one unit; you'd need a rectifier and filter though - and the output wouldn't be isolated from the mains - safety issue. You can pick up heavy duty rectifiers just about anywhere; caps too. You'll need some big caps. No regulation, of course.

The easiest way to get your three phases would be to use a microcontroller to drive three H-bridges. That way you would have complete control over the frequency and the "dead time" for the H-bridges.

#### stephenzxap

Joined Aug 9, 2008
3
Thanks for the refrerence to the other sites.
Okay next question, what if I'm not trying to run from any house voltage but stand alone on battery power. I don't think I gave enough details before. I'm trying to run from batteries soley recharging is not a problem.

I came across an old circuit from a book and I'm looking to compare them.

#### SgtWookie

Joined Jul 17, 2007
22,210
I don't have a schematic for you.

However, were I to do something like that from scratch, I would use two VNH2SP30-E - Automotive Fully Integrated H-Bridge Motor Drivers, which can handle up to 30A at 41V, and control them using a PIC microcontroller, something from the 8-bit PIC16 series. One-half of a VNH2SP30-E would not be needed.

Basically, that's three IC's - plus the programming. You'll also need a 5v regulator for the PIC, and some sort of method for either changing the PICs clock input (to change the output frequency) or simply do all that via software. The outputs will be square waves, not sine waves. If you want sine waves, that will take more work and a different approach.