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Author Topic: Start O Matic Electrics  (Read 14323 times)

Holter

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Re: Start O Matic Electrics
« Reply #15 on: August 29, 2007, 11:59:16 PM »
The Plan
Step one:  Get a properly installed permitted net metering solar system.

[...]
Step one will require a grid power-down automatic site isolation switch rendering step B safe - Right?.
PV inverters usually have this protection as a built-in circuit, so you cannot use it for your Generator, if you do not connect it to the DC Side of the Inverter.

Christian

mike90045

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Re: Start O Matic Electrics
« Reply #16 on: August 30, 2007, 12:02:26 AM »
The Plan
Step one:  Get a properly installed permitted net metering solar system.

Step one will require a grid power-down automatic site isolation switch rendering step B safe - Right?.


Not Always.   I have a Xantrax GT series inverter, that electronically shuts off, if the Grid fails.  There is no transfer switch in it, it's microprocessor pings the grid a couple times each cycle, and if the grid is gone, it shuts off.  It has no provisions to switch anything.

LowGear

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Re: Start O Matic Electrics
« Reply #17 on: August 30, 2007, 06:18:47 PM »
Doug,

I guess my response about GOBing inspectors sounded a lot harsher than I realized.  I really appreciate your input on this thread.

How do I get the induction motor to be both grid compatible and stand alone capable?


Mike90045,

I got a quote on a PV system that has the collectors and inverter system some 200 feet from the meter base so it had the lockable grid switch next to the meter base rather out in the field at the water shed.  The implication that I took - right or not - about the lockable switch was that this was a requirement of the utility.

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LowGear

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Re: Start O Matic Electrics
« Reply #18 on: August 30, 2007, 06:27:16 PM »
Quinnf,

I jumped over to Harbor Freight and looked at the motors.  Thanks for the link.  How do you tell when the motor is the induction style and not what ever the other ones are?

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SCOTT

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Re: Start O Matic Electrics
« Reply #19 on: August 30, 2007, 07:00:04 PM »
Low gear

Pay attention to the service rating on those motors, if you plan on running this long hours you will want one with a continuous duty rating, which is different from a compressor motor that is not running for a majority of the time.

scott
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mike90045

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Re: Start O Matic Electrics
« Reply #20 on: August 30, 2007, 08:16:17 PM »
lockable grid switch next to the meter base rather out in the field at the water shed.  The implication that I took - right or not - about the lockable switch was that this was a requirement of the utility.

Right, but it's only to make their linemen fee safe.   It does not automatically come into play, it's a manual switch.


I suppose to make a nearly seamless switchover, you could rig up a relay, fed from the grid, and when grid fails, relay disconnects grid, and connects caps to motor.   Big surge, and chance to weld relay contacts.  I guess you need some sort of automatic transfer switch, to get nearly seamless power. (5 sec glitch)

Quinnf

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Re: Start O Matic Electrics
« Reply #21 on: August 30, 2007, 08:23:15 PM »
[Edit:  On reflection, I thought I'd better offer the opinion that if you ask that question, maybe it's better that you don't get involved in doing what you're contemplating.  Not meant to denigrate your knowledge in other areas, but electricity is a remarkably unforgiving medium to dabble in, and I don't want anyone to get hurt.]

Common garden variety AC motors like the ones in the links I posted are induction motors.  DC and "universal" (AC/DC) motors have brushes.  Universal motors are used in  portable power tools and can run off both AC and DC.

Service factor should be your guide.  Compressor duty, farm duty, etc., don't mean much other than what some marketing guy says it means.  And if you've read The Restaurant at the End of the Universe, one of the books in the Hitchhiker's Guide to the Galaxy trilogy, which consists of 5 books, then you should know where marketing people came from, and why you should take what they say with a grain of salt.  And if you don't/haven't, you should be able to google "golgafrincham ark ship" and scroll down on the Wikipedia link to Golgafrincham.

Here's a link everyone might find useful:  http://www.electricmotors.machinedesign.com/BDEList.aspx

Quinn  
« Last Edit: August 30, 2007, 09:04:36 PM by Quinnf »
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LowGear

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Re: Start O Matic Electrics
« Reply #22 on: August 31, 2007, 01:51:52 AM »
TWO IMPORTANT QUOTES

"A man's got to know his limitations."
                              Dr. Harold Callahan:

"6 times 7 or 42"
                              I'm not very good with names - please see above quote.

Plan G:

Be a little realistic about "The Plan" and realize that the power is only off for a few minutes a couple of times a year.  If it's going to be off for more than a couple of hours then I can throw the manual switch by the meter base and then go over and connect the capacitor to the inductive motor.

The next question is "what the heck is going to tune that generator to 60 hertz?"

and

Is it correct to assume that a PV inverter system would have a stand alone mode?

Last questions for this post

Does the afore mentioned 80% of rated capacity of the induction motor suggest anything about efficiency?  Is the more conventional ST head generator more efficient?

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Doug

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Re: Start O Matic Electrics
« Reply #23 on: August 31, 2007, 05:47:43 AM »
How do I get the induction motor to be both grid compatible and stand alone capable?

Low gear making an induction motor stand alone is real trick. They don't work well, better to have a syncronous ( St head ) for stand alone and swap belts for grid tye.

The next question is "what the heck is going to tune that generator to 60 hertz?"

Induction motors have no poles on the rotor, its all about the slip speed and the magentic field inside the machine dragging the rotor around ( in a motor electrical energy is converted to torque that is trying to spin at syncornous speed but since at syncronous speed there would be no dragging of flux lines across rotor bars and the associated torque and magnetic fields induce blah blah.. inductions motor slip at less the 2-5% of syncronous speed ) ) or the rotor trying to drag the magnetic field faster than the bus speed ( but this isn't possible so the power used to try and torque the field over faster is actualy converted to electriciy and power flows back onto the bus )

Does the afore mentioned 80% of rated capacity of the induction motor suggest anything about efficiency?  Is the more conventional ST head generator more efficient?

Yes, but thats just a number I pulled off the top of my head, you will kind of have to play with different speeds to find the most efficient load. You may find a higher or lower figuere is better.

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mike90045

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Re: Start O Matic Electrics
« Reply #24 on: August 31, 2007, 06:58:56 AM »
Is it correct to assume that a PV inverter system would have a stand alone mode?

Most grid tie inverters, designed to run 200-600VDC, do  NOT  have a stand-alone mode.  You need to have a battery based system, to get stand-alone (island) capability.    Even in an emgerency, with the sun shining, if the grid goes down, my 4.5KW array shuts down too. No way to bring it back up without 5 minutes of clean, 99% pure gird sine
wave + - .04HZ.

 My emergency plan is to disconnect the 300V DC lines from my PV array, and brute force a bulk charge into a dozen or so car batteries. Day 3 will see a lot of neighbors bringing batteries over, for a charge.

mobile_bob

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Re: Start O Matic Electrics
« Reply #25 on: August 31, 2007, 07:14:35 AM »

Mike:

"My emergency plan is to disconnect the 300V DC lines from my PV array, and brute force a bulk charge into a dozen or so car batteries. Day 3 will see a lot of neighbors bringing batteries over, for a charge."


i assume you are talking a series string of batteries?

if this is what you are planning you got balls the size of beach balls!

one bad battery in that string, a loose connection, short or whatever and you got a bomb to deal with.

let me know how this works for you :)

bob g
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mobile_bob

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Re: Start O Matic Electrics
« Reply #26 on: August 31, 2007, 07:22:41 AM »
low gear:

you don't have to worry about tuning to the 60hz of the grid,, you will either be producing  what the grid is in hz (right down to the decimal place)
or you will be consuming what the grid is in hz.

in comparison to the grid your genset is infintesimal and the grid can be veiwed as infinite from your gensets viewpoint.

so you won't be able to produce even 59.999 hz if the grid is 60.000, you will be motoring
and if you try to get to 60.001 you will either drop out of generation, burn up your induction motor, or load your engine beyond its capacity.

so your concerns about tuning to 60hz while grid connected are of no concern at all.

bob g
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mike90045

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Re: Start O Matic Electrics
« Reply #27 on: August 31, 2007, 02:32:39 PM »

i assume you are talking a series string of batteries?
 if this is what you are planning you got balls the size of beach balls!
one bad battery in that string, a loose connection, short or whatever and you got a bomb to deal with.
l et me know how this works for you :)


I'd planned on doing the hook-up in the AM, pre-dawn.  I have not figured how to disconnect at noontime when they are full, and boiling. I expect a glorious DC arc to remove a couple inches of wire, and hopefully not too much of the battery terminal.  I suppose a good knife switch would be in order.    The load of the bateries, will hold the PV voltage, to the battery voltage, and I only output about 10 amps max, so I am expecting to get a nice arc  @ 150V 10A DC.  Hopefully the grid stays up. and I never have to implement this idea.

Doug

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Re: Start O Matic Electrics
« Reply #28 on: August 31, 2007, 03:18:00 PM »
What you propose leaves you at risk for some unexpected safety and reliability issues.

Having taken more than one ride on the infinite bus at potentials much higher than you guys will see I can only wish you the best.

Be careful.

I have seen things that would make you crap your pants.
One bad cell in a string of 250 volts of NiCd batter bank turn into a road flare, then a the neighboring cells join in the fire works followed by all the ascociated smoke and flames and pudels of melting plastic and boiling hydroxiode electrolite in confined spaces stuff.
Net result $200,000 of scrap nickel and cadnium....

Oh the joys of working on battery banks and dropping a well taped spanner that still manage to find a return path to ground from a post. Cheer red tool and halloween orange glow from inside the steel battery compartment as you scamper out and run for a fire hose.

 
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mobile_bob

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Re: Start O Matic Electrics
« Reply #29 on: August 31, 2007, 05:49:37 PM »
yup and you haven't lived until you have had a flooded lead cell blow up in your face,
i had a good friend have one blow with his head (face) about 3 inches above the battery,, face and eyes full of acid!
not a good thing at all, and he was lucky there were two others there that could grab him and get him to water within seconds

i had one blow up on me while under a welding helmut,, ruined my clothes, ringing in my ears for days
and thank god for the helmet, i didn't get it in my eyes either.

i have a large 3 phase UPS, with a 240volt dc battery bank where one battery failed, the result was a hole blown thru three layers of 1/8" steel
that looked like a rifle shot.

DC is ok by me,, however i don't care for high voltage large strings of series connected batteries that are not contained in an enclosure.
a good enclosure,,
anything less than that is asking for trouble in my opinion
all it takes is one gassy battery to absolutely ruin your day.

bob g
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