Homemade DC to AC Inverters

[Matt]

I have stumbled across a method of making a very high wattage inverter out of a old UPS or battery backup.

Most all use only one set of power transistors and therefor generate on average 1100-1500w of power.

By adding in more power transistors and larger transformers you can take these little guys up to about 8-10kw.

I am using the IRFP260N which I got from here : http://cgi.ebay.com/IRFP260N_W0QQitemZ220208760190QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item334577057e&_trksid=p3286.m20.l1116

I can push out 500w per pair and have 20 pairs that I will be running for a total of 10kw. I will be using microwave transformers that I re-wrap to have a 48v center tap primary and a 220v secondary. I plan to use 4 transformers with 5 pairs of transistors per transformer.

Anyone else have a need for such a monster?

Matt

[Graybeard]

I'm still ask skeptical as I was when we talked about it here. 

[billy_56081]

Matt 8 to 10 KW I'd a lot of power therefore a lot of heat. What is the percentage of loss in the conversion from DC to AC? I would use as much DC as possible to power things in my house.

[Matt]

Well from what I am seeing on the net the best way to reduce the loss through heat is to step up the DC side which is the reason I am going 48v. The heat sinks I have to use each weigh about 10lbs and are solid aluminum. I will also have fans to help cool the system.

I also think that using DC for lighting and such is the smartest way to go so you have less AC requirements.

Matt

[billy_56081]

One thing about heat loss is that in a cold climate that energy is not wasted if it is used as heat in the house. I would imagine it would take a lot of battery storage to run 8 to 10 Kw.

[billy_56081]

A 12 volt putting out 100 amps at 12 volts for one hour would be 1.2 kwhrs.

Oops had to modifie that with an extra zero.

[myronman3]

i can hardly wait until my kids start having brain-childs and all my tools and materials start disappearing.      
   you go, matt. 

[mechanic]

Matt,
Some of the lift trucks I am working on now use a 48 volt battery inverted to 3 ph. AC.  I can't get in my head how it works but a 200 amp draw on the battery corresponds to almost 250 amps to the load at 34 volts AC.  These units use high frequency switching transistors, with a frequency above what I can read with my hand held.  My lab scope was stolen a few years back.  I'm trying to compute how you get more than you give with this set up.  Perhaps your UPS will do the same as you  plan to configure it.

[dpe.ahoy]

Wouldn't that take a battery bank half the size of my cabin to operate?  I only understand about 1/4th of what you guys talk about, but am looking at getting power to a cabin with out spending ten-eleven grand to run power lines.  DP

[Graybeard]

Not unless you have a real small cabin. Matt says he's gonna use my barn as a test bed for this idea of his. So far we've got it wired but haven't had the power company hook to it yet. We just use a drop cord from the house up to it to power it when we need power but really need a better solution than that or the generator we some times use there as well.

I have the pole and box just haven't made a hole for the pole yet so Alabama Power can hook to it from the pole they have already set for it.

[dpe.ahoy]

I'll follow this, just like I have the thread on using treadmill moters for a wind generator.  Thanks for all your knowledge and being willing to share it Matt.  DP

[Glanceblamm]

i can hardly wait until my kids start having brain-childs and all my tools and materials start disappearing.      
   you go, matt. 

That is not funny myronman3 as it actually does happen...It includes son-in-law's also. grumble, grumble, grumble. I do get quite a bit of work out of em but they also eat a lot, hard to get ahead.

[myronman3]

oh, believe me, i know.   

[efremtags]

Sounds like a recipe for burning the house down.

A well designed 3kW inverter sells for about a $1/watt. You simply can not take a 1kW inverter and add transistors to generate 10kW continuous power.

Transistors conduct power, but the control circuits in the unit are typically matched to drive the power they are designed for. I believe with better component selection and some additional forced air cooling, doubling the power is very feasible.

You are neglecting little things like circuit trace weight, transformer sizing, capacitor sizing. When driven 10x the power (IE 10X the current if voltage is constant), the power on these devices goes up by current sq so a factor of 100x. There is no way a cheap product is made to handle 100x power loss increase otherwise they would not be marketable and profitable. They tend to design o nthe hairy edge.

Sounds like a fun experiment to learn a little, but I would not fool around with running a real system at that rating.

[Matt]

Sounds like a recipe for burning the house down.

Maybe not...

A well designed 3kW inverter sells for about a $1/watt. You simply can not take a 1kW inverter and add transistors to generate 10kW continuous power.

Well yes you can, the control circuit is the same on a 750w as it on a 12.5kw. The driver circuit changes as you go up in output as does the number of and rating of the output transistor's / FET's and of course the heat sinks and fans change with output. As to the transformer I do have that covered as I have one from a 15.2kw backup power system I got in a gov surplus auction which weighs about 125 lbs and looks to have 4ga primary and 6ga secondary windings.

Although I will admit after much more playing around I have decided that 10kw is just not feasible as the power requirements are ridiculous. several 3.5kw - 5kw inverters could be used in a daisy chain configuration or similar and get the job done with a lot less power consumption. 

Matt

[efremtags]

you need to be able to sink the ac waveform when used in tandem with other inverters. A phase sync relay can be used.

regarding the controls, you are partialy correct. The control chip may be the same,but the compensation loop providing the PWM likely needs serious adjustment. You are changing the xfmr and should have a proportionate change in your in and output filtering to compensate for the greater power. These all effect thefeedback compensation. It can potentially oscillate or provide poor load performance with motor or pump loads. .

[Glanceblamm]

I would also add that you need to polish the transponders or you could end up with a discombobulated frantastat but I really don't want to be banned from this place at this time 

This is a good read on the whole and I really do enjoy these ideas.
Thanks!

[tomtomz]

Are we talking about powering servers for this site?

Plenty of Telco rated servers can be powered by 48VDC. Why not use one of those and forget the AC requirement?

Google "Sun Netra" to see a list of older, but still good used servers that run on -48 VDC.