Ac/DC

[carlb23]

Hi all,

I am running a 6/1 with a 4kva head that i would like to extract DC current from ( At night) to hook to one of my grid tied inverters.  Can i use a standard bridge rectifier say 35 or 50 amp @ 500volt and hook it up to the 2 120 volt leads comming from my generator and get 240 Volts DC.  My inverter will operate in a wide input range 150 to 5oo VDC so it would be in the voltage range. 

Do you think any kind of filtering to smooth out the waveform would be necessary and if so how would i do that?


Thanks

Carl

[SCOTT]

Carlb23

You will see ripple out of the single phase rectifier in the neighborhood of 30%+.   Solar inverters are set up for “real” DC, where there is no ripple.  Rectified DC (wind, micro hydro or Lister) is a different animal.  From my research there are some inverters that can be fed rectified DC with ripple not more than 5%.  I suggest you call the manufacturer and verify the allowable ripple (if any).  You don’t want to fry an expensive inverter and void your warrantee.

Scott

[carlb23]

Scott,

Thanks for the info.  I certainly don't want to fry my inverter

Carl

[jzeeff]

Some amount of capacitors will smooth it out.   

 I agree that 240V AC generator rectified to 240V DC + a solar grid-tie inverter is a logical way to spin your utility meter backwards.

A 3 phase generator would be even better (less ripple).

[Doug]

Doesn't exactly work out that way.

What we refer too as 240 AC is actualy the RMS value of the AC wave or the DC equivelent for doing current and load calculations.

http://en.wikipedia.org/wiki/Root_mean_square

So lets say you full wave rectify the the RMS voltage 240 vac what you actuly get ont he other side is the rectified Peak value and thats closer to 340 VDC if my memory serves....

Things can get realy wierd now if you take a multy meter and read that pulsing 340 vdc because the average meter will read the average voltage and depending on the riple that can be much lower ( if you want to take a guess at how low it can be multiply that 340 by .9 to get the average I think ). Now if its a three phase source and or a capacitor to filter you will have less riple and the average voltage will be higher.

Speaking of higher, I'm having flash backs to 1 year electrical at NOITT learning and puzling over all this shite. Oh college daze

Also good reading and much better math and explainations than me...
http://en.wikipedia.org/wiki/Voltage

If you own a volt meter like this
http://en.wikipedia.org/wiki/Image:Digital_Multimeter_Aka.jpg
Flll those two sockets with silicon to the left of the leads....
Someday if you get into the habbit of using them you will forget and change the range on your meter to do a voltage check and poof! You may also get burned or shocked, much better to buy a proper clip on amp meter....

Doug

[ronmar]

Hi all,

My inverter will operate in a wide input range 150 to 5oo VDC so it would be in the voltage range. 

Do you think any kind of filtering to smooth out the waveform would be necessary and if so how would i do that?


Thanks

Carl

Sounds like an unusual inverter with that input range...  What do you normally feed it with that outputs that much DC?

Ron

[carlb23]

Ronmar,


I am using a Fronius IG3000 inverter and I feed it with two strings of 8 panels @187 Watts each.  Each panel is rated @ 32.7 volts 7.25 amps. Each string is  has a max output of 1496 watts.  The spec sheet shows the input voltage from 150 to 500 DC and an operating range for 10 amps to 18 amps input.

carl

[carlb23]

Doesn't exactly work out that way.

What we refer too as 240 AC is actually the RMS value of the AC wave or the DC equivalent for doing current and load calculations.

http://en.wikipedia.org/wiki/Root_mean_square

So lets say you full wave rectify the the RMS voltage 240 vac what you actually get Ont he other side is the rectified Peak value and that's closer to 340 VDC if my memory serves....

Things can get really weird now if you take a multi meter and read that pulsing 340 vdc because the average meter will read the average voltage and depending on the riple that can be much lower ( if you want to take a guess at how low it can be multiply that 340 by .9 to get the average I think ). Now if its a three phase source and or a capacitor to filter you will have less ripple and the average voltage will be higher.

Speaking of higher, I'm having flash backs to 1 year electrical at NOITT learning and puzzling over all this shite. Oh college daze

Also good reading and much better math and explanations than me...
http://en.wikipedia.org/wiki/Voltage

If you own a volt meter like this
http://en.wikipedia.org/wiki/Image:Digital_Multimeter_Aka.jpg
All those two sockets with silicon to the left of the leads....
Someday if you get into the habit of using them you will forget and change the range on your meter to do a voltage check and poof! You may also get burned or shocked, much better to buy a proper clip on amp meter....

Doug

Doug,

Doug thanks for all the helpful info but, since I am not that good with electronics I think I will not worry about trying to hook up my AC gen to my inverters at this time and risk damaging an expensive inverter.

Thanks

Carl

[carlb23]

I have several Shunt wound DC motors available to me in HP ratings > 3hp i think they are 190VDC.  Can these be used as a DC generator with good clean output?


Thanks

Carl.

[jzeeff]

Solar grid-tie inverters are quite flexible and take in voltages in the 240 to 600 VDC range.  I don't know how steady it has to be but I don't think your inverter dies when a plane flies over your solar panel (casting a shadow and putting a blip in the output).

I guess these inverters are for buildings with a roof full of solar panels.

[Doug]

Yes Carl any dc motor will make good DC. I would probably add a filter capacitor just to clean up any noise.

You do have to watch them though they require a little more attension because of the brushes.

[carlb23]

Yes Carl any dc motor will make good DC. I would probably add a filter capacitor just to clean up any noise.

You do have to watch them though they require a little more attension because of the brushes.

Doug,

I found a Baldor cd7503 3hp Shunt wound motor that might want to try.    I didn't get to take a look at the wires yet. Do you know if this motor self excite?

[Doug]

Yes it will but if you like you can motorize it first or when ever it fails to self start.

You can also use it as a starter motor that charges once up to speed.

Wires will be F1 and F2 field..... A1 and A2 armature......

Baldors are one of the better DC motors out there.

[carlb23]

Doug,

I assume i connect F1+A1 and F2+A2 together.  I can't use it as a starter since I dont have 180VDC to  to start the motor

Carl

[jzeeff]

I did the calculation and to smooth out 50 amps of 240V AC rectified to DC, you need 8 of these.

http://theelectrostore.com/shopsite_sc/store/html/high-voltage-electrolytic-capacitors-400v-3900uf.html

Probably far less if the inverter has a wide input range.  Also much less if you have a 3 phase generator.