Puppeteer

Author Topic: inverter based generators  (Read 20703 times)

jzeeff

  • Full Member
  • ***
  • Posts: 218
    • View Profile
inverter based generators
« on: July 13, 2009, 12:44:54 AM »
My understanding of the newer inverter based generators is that they produce a high frequency (Khz) output, rectify this to DC (around 200V) and then use an inverter to produce a very clean 60Hz 120V sine wave.    Since they are insensitive to engine RPM, they automatically reduce the rpm (and engine wear/fuel consumption/noise) when load is light.

If I could find a high frequency generator head and reasonably priced high voltage (not 12V) inverters, I would consider building something like this.  But I haven't seen either.





ronmar

  • Hero Member
  • *****
  • Posts: 1227
    • View Profile
Re: inverter based generators
« Reply #1 on: July 13, 2009, 01:13:49 AM »
I think it would be interesting to play around with the rectified output of a 3 phase induction motor feeding an inverter.  A 48V inverter would be easier to come by.  It would be a matter of exciting the induction motor with capacitance to get a DC output from the rectifier that is in the input range of the inverter...  Wether it would stay within an acceptable range to the inverter during load changes is another question.
PS 6/1 - ST-5.

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2940
    • View Profile
Re: inverter based generators
« Reply #2 on: July 13, 2009, 05:46:41 AM »
its really kind of surprising why we don't see more work in the area of "inverter/gensets" in the DIY world

it isn't rocket science and the bits and pieces are not "unobtainium"

thats where my focus is, just wish there was more interest.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

jzeeff

  • Full Member
  • ***
  • Posts: 218
    • View Profile
Re: inverter based generators
« Reply #3 on: July 13, 2009, 02:30:34 PM »
Best low cost solution I can find is car/truck alternators driving a 12v to 120V pure sine wave inverter.


roverjohn

  • Jr. Member
  • **
  • Posts: 65
    • View Profile
Re: inverter based generators
« Reply #4 on: July 13, 2009, 04:36:03 PM »
Doesn't this idea just add two more layers of conversion losses? I can see where it might be handy with a grid tie system but I'm not sure if I see the point off grid.

apogee_man

  • Sr. Member
  • ****
  • Posts: 288
    • View Profile
Re: inverter based generators
« Reply #5 on: July 13, 2009, 05:27:00 PM »
This is exactly the direction that I have been exploring.

I have been considering running a 48 volt DC forklift motor as my genset and having that feed an Outback inverter.  I called Outback and discussed this with them, and saw no reason why it wouldn't work.

I was exploring this because, with a 48 volt batt bank, I would also have a way to auto start the engine.

This can also be done using other lower voltages as well, as long as the inverter is designed for the target input voltage.

No, it wouldn't be EMP protected if we were attacked, but it would give very clean power the rest of the time.

Conversion efficiency would be in the 93% range.

Steve
« Last Edit: July 13, 2009, 05:36:24 PM by apogee_man »

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2940
    • View Profile
Re: inverter based generators
« Reply #6 on: July 13, 2009, 06:18:27 PM »
not sure you can get anywhere near 93% conversion using a forklift motor as a generator

93% is about as good as you are gonna get with the inverter, but i suspect the forklift generator
will be somewhat less efficient than the typical ST head

so overall efficiency is probably going to be quite a bit less than just using the ST head to generate AC power.


to compete favorably one will need an alternator that is more efficient than the ST head, (possible...)

then possibly with a direct drive engine, run it slower to conserve a few percentage points more in fuel

at the end of the day, if you could get within 5 points of a straight genset one would be doing very well.

bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

apogee_man

  • Sr. Member
  • ****
  • Posts: 288
    • View Profile
Re: inverter based generators
« Reply #7 on: July 13, 2009, 10:50:40 PM »
You are likely correct Bob.

I should have been more clear in my post regarding efficiency. 

Yes, that is inverter efficiency that I was referring to.

Don't know what the motor efficiency would be; I hadn't gotten that far down the path yet.

Was looking at this method because it would produce cleaner power while at the same time also giving an easy way to start the engine and would allow battery backup when the genset wasn't running.  Would also be perfect for a solar tie-in down the road as well...

Seemed like a elegant solution overall.

Still thinking on it at this end.

Thanks for the comments!

Steve

clytle374

  • Sr. Member
  • ****
  • Posts: 368
    • View Profile
Re: inverter based generators
« Reply #8 on: July 14, 2009, 12:47:05 AM »
Been thinking along this line for a while now, so if anyone does anything like this, please share with the class.  Would be a good way to tie in solar, wind and hydro with the genset. 

jzeeff

  • Full Member
  • ***
  • Posts: 218
    • View Profile
Re: inverter based generators
« Reply #9 on: July 14, 2009, 06:04:06 PM »
I agree that efficiency is a factor, although being able to run the engine slow at low electrical loads and turn it off and run on batteries at very low loads makes up for much of that.  Primary motivation is that I want perfect power - no voltage, frequency or waveform variations.  Say 70% for Bosch long haul 12V alternators and then 90% for an inverter.  Total efficiency around 60%.

There are solar inverters (from Outback, etc) that will take a range of high voltage DC inputs - like what you would get from 120V or 240VAC rectified.

I wonder how close one could get to a square wave by rapidly adjusting the field strength of a ST head.  Square waves are best for producing DC.  Or run it at a higher speed to get a higher frequency.   

Hmm, thinking about this, if one could feedback from the intermediate DC voltage produced back to the ST head regulator, then the inverter design for a modified sine wave would be very simple (IGBTs + fixed timer).    But that would loose the benefit of perfect voltage regulation.    So a transformerless PWM inverter would be best.





« Last Edit: July 14, 2009, 09:42:37 PM by jzeeff »

clytle374

  • Sr. Member
  • ****
  • Posts: 368
    • View Profile
Re: inverter based generators
« Reply #10 on: July 14, 2009, 06:40:30 PM »
I agree that efficiency is a factor, although being able to run the engine slow at low loads and turn it off and run on batteries at very low loads makes up for much of that.  Primary motivation is that I want perfect power - no voltage, frequency or waveform variations.  Say 70% for Bosch long haul 12V alternators and then 90% for an inverter.  Total around 60%.

There are solar inverters (from Outback, etc) that will take a range of high voltage DC inputs - like what you would get from 120V or 240VAC rectified.

I wonder how close one could get to a square wave by rapidly adjusting the field strength of a ST head.  Square waves are best for producing DC.  Or run it at a higher speed to get a higher frequency.   

Hmm, thinking about this, if one could feedback from the DC voltage produced back to the ST head regulator, then the inverter design for a modified sine wave would be very simple (IGBTs + timer).   




I'm thinking more along the lines of running the engine at a high load all the time and reducing the RPM to only create the power needed, should run much cleaner that way.

I don't think that you could change the field current that quickly with the amount of inductance in the field, I would think it would at least be hard on the brushes.

As far as creating good DC current, a multi phase PM alternator would be nice.  Something like the homemade windmill from a brake rotor design.  Who was the guy that builds them that joined this forum?  Is he still around?  Didn't he have one on a mini-petter and a steam engine?   Maybe build the magnet rotor into the flywheel of a Listeriod?

Cory
 




jzeeff

  • Full Member
  • ***
  • Posts: 218
    • View Profile
Re: inverter based generators
« Reply #11 on: July 14, 2009, 06:55:26 PM »
It looks like variable frequency drives (VFDs) have become inexpensive  (see ebay) - they will take in ~240VAC and output 3 phase 240VAC at any selected frequency.  Maybe set one to 60Hz output and use line-to-neutral to get a steady 120VAC waveform independent of input.  Hmm, looks like they don't supply a neutral.  So (I think) you can only get phase-to-phase 208VAC out of them..





« Last Edit: July 14, 2009, 08:01:35 PM by jzeeff »

clytle374

  • Sr. Member
  • ****
  • Posts: 368
    • View Profile
Re: inverter based generators
« Reply #12 on: July 14, 2009, 08:22:18 PM »
It looks like variable frequency drives (VFDs) have become inexpensive  (see ebay) - they will take in ~240VAC and output 3 phase 240VAC at any selected frequency.  Maybe set one to 60Hz output and use line-to-neutral to get a steady 120VAC waveform independent of input.  Hmm, looks like they don't supply a neutral.  So (I think) you can only get phase-to-phase 208VAC out of them..



All of the VFDs I have worked with must be tuned to the motor they are driving, I can't imagine them working in an environment where the load was constantly being changed.  Like if they are driving a large resistive load and then a AC motor tries to start.  I might be wrong here, anyone here know for sure?   

mike90045

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1594
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
Re: inverter based generators
« Reply #13 on: July 14, 2009, 10:52:50 PM »
Quote
As far as creating good DC current, a multi phase PM alternator would be nice.  Something like the homemade windmill from a brake rotor design.  Who was the guy that builds them that joined this forum?  Is he still around?  Didn't he have one on a mini-petter and a steam engine?   Maybe build the magnet rotor into the flywheel of a Listeriod?

Like this:  http://www.fieldlines.com/story/2007/10/26/141411/24 (scroll down a bit to the Listeroid with magnets)

or the steam engine project  http://otherpower.com/steamengine.shtml   ?

clytle374

  • Sr. Member
  • ****
  • Posts: 368
    • View Profile
Re: inverter based generators
« Reply #14 on: July 15, 2009, 03:00:33 AM »
Quote
As far as creating good DC current, a multi phase PM alternator would be nice.  Something like the homemade windmill from a brake rotor design.  Who was the guy that builds them that joined this forum?  Is he still around?  Didn't he have one on a mini-petter and a steam engine?   Maybe build the magnet rotor into the flywheel of a Listeriod?

Like this:  http://www.fieldlines.com/story/2007/10/26/141411/24 (scroll down a bit to the Listeroid with magnets)

or the steam engine project  http://otherpower.com/steamengine.shtml   ?

That's the stuff, wasn't a member here doing it?  Or am I confused?