generating 100VAC from a battery?

I have a stepper motor driver that, according to the datasheet, runs off the following:

Single phase 100V 15% 50/60Hz 1.1 A or,
Single phase 115V 15% 60Hz 1.1A

I need to use it portably though, so my only choice is batteries. I could drag around a giant car battery and a power inverter for it, but that would be unwieldy. Does anyone know of a battery-voltage-to-AC step-up chip? I guess the 100W inverters they sell for car use are fairly small; I could buy one and take it out of the plastic and it wouldn’t be too bad, but a nice IC would be better. If I could step it up somehow, do you think I could feed this thing a square wave?

I could drag around a giant car battery and a power inverter for it, but that would be unwieldy.

What other choice do you have?
Any sort of step up system that is going to provide 100W is going to require a big battery to power it.
So say you have a 12V battery, at 100W that is 8.3 Amps and assuming 80% efficiency for the converter bumps up the current draw to 10 Amps.

If I could step it up somehow, do you think I could feed this thing a square wave?

Yes defiantly, by the time it hit the coils it would be a sin wave anyway.

Whether you do it with some chip or you use an inverter the bottom line is that the same job has to be done.

Can you do a better job than the inverter makers? I only know one person who could answer that question with "yes" because that's what he did for a living, the rest of us mortals just buy an inverter :slight_smile:


I thought maybe I could just generate a 60Hz square wave with a MOSFET and then run it through a hand-wound transformer to step it up to 100 or so volts. Maybe it’s better to cough up for a commercial inverter.

Yes you can do that.

Are you up to designing a transformer to do that? It is not just turns ratio you have to watch out for magnetic saturation of the core and at 100W output that will be a problem.

I guess I'd better just buy an inverter.

How big of a SLA do I need, by the way? The local surplus store has 12v SLA batteries down to the size of a pack of cigarettes, but I'm sure these can't sustain 10A draw for the couple minutes that I need. What % of C can I draw from a SLA without sagging the voltage below 12V?

I have a 18Ah, 12V SLA which will output about 10A for around 15 - 20 mins before the inverter complains.

I've built inverters before using mains transformers in reverse. If square wave output is suitable, it's not that difficult. For example, you could take a transformer that has a 115v primary and two matched 0-12v secondary windings, and drive the 12v windings from a couple of mosfets. However, by the time you've added the other components and maybe blown a few mosfets, you might not save much compared to the cost of an inverter.

Whoa, that's a brilliant idea. Too bad my "leftover mains PSUs" box is dominated by the newer switch mode PSUs and the transformers are out of style.

There's also these:

Apart from the stepper motor driver needing the 100VAC, what are the specs on the motor ? I guess you'd be better off ditching the stepper driver is the motor isn't a 100V stepper!

It can very well be a stepper motor driver with internal switch-mode power supply, that would explain the input voltages...

// Per.

I am stuck with the driver as the stepper motor is a bizarre 5-phase configuration. I spent some time trying to build a driver from discrete components, but gave up.

A 5 phase stepper is easy to drive. You can use 5 N-channel mosfets to drive the phases.

// Per.

Actually, there is no center tap on this motor, so you would need 5 H-bridges. 5 high-power H-bridges at that. And you can't buy 5 H-bridges in a package, only 4, so you would have to buy 2 chips just to use one channel of the 2nd chip. I've been through all this already.

Ah, that's a bitch.

Last time i stumbled on a 5-phase Stepper, it was with centre tap.

// Per.