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PF Hz and Volts

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Posted by Rob.....in Courtice on October 8, 2008, 11:08 pm
 
    I have a 900W 2-stroke "King Canada" generator.  (Inherited it).  On my
day off decided to see what it would run.  I have a six circuit manual
transfer panel hooked up to the house service. And a Kill a watt meter.

Running a trouble light, 60 watts @ 61- 62 Hz and a Pf of 1 @ 120 - 121 v.

Running the fridge drawing about 350 watts @ 61-62 Hz and a Pf of .9 @
120 -123 v,  it sounded  about right, about 1 of what the gen had to
offer.

Running the furnace (20 yr old, 1 hp blower I think)  drawing about 300
watts @ 69 - 73 Hz and a Pf of .6 @ 130 - 135 v  (it sounded as if the
generator was putting out about all it had).

Because the Pf is so low, would that cause the voltage\Hz to go so high?
Also, is running the furnace at this voltage/Hz gonna wazzoo the motor?

 I also have a 1k Yamaha inverter-generator  which can run the fridge, but
will not start the furnace, again about what I expect between reading this
NG and playing with it.

    TIA
              Rob....................




Posted by Vaughn Simon on October 9, 2008, 12:54 am
 


   If you get creative, you should be able to figure out how to make that Yamaha
start that furnace.  I would start by adding some starting capacitance to see if
that reduces the starting surge.
  You may also try plugging in a moderate load to get the generator to rev up
before you try to start the blower.

Vaughn



Posted by Rob.....in Courtice on October 9, 2008, 2:52 am
 Hi Vaughn,

 > I would start by adding some starting capacitance to see if

  Probably a good idea, but over my head.



I will try this. Never thought to try without the eco throttle.  My next
experiment (?) is to try running half the generator panel off one generator,
and the other half off the other.

 My next question for the group.  I have NO 220V loads, and both gens have
floating neutrals.  I have the 'twist lock' plug split into 2 extention
cords.  3 on one side, 3 on the other.  I'm concerened about all the
neutrals being bonded.  The two hots are, and will remain seperate.  My
thoughts are that since  I run some circuts off the generator, and some off
the grid at the same time, running 2 generators on the trans panel should be
a similar situation.  But I though I'd ask first.

 Using the eco mode on the yamaha for light variable loads, and the
screaming 2-stroke (not really that loud) for the loads that require full
(?) power, and run often.

 Before my dime runs out.... will the fulcuating Hz hurt the furnace motor?

thanks for reading :)

.........Rob





Posted by Martin Riddle on October 9, 2008, 2:30 am
 

Sounds like the real power required by the furnace is around 450w and
its inductive.
The generator may have a problem with inductive loads. I would try the
fridge and another load to see
what the max is. According to the King web site its a kcg-950 with 800w
rating.
 A good old transformer/rectifier battery charger may add enough
capacitance to find out if that is the case.


Cheers




Posted by Neon John on October 9, 2008, 3:58 am
 

The problem here, I suspect, is that the crappy waveform from the cheap
generator and moderately low PF are fooling the KAW.  It is almost impossible
for that little generator to run that fast.  That would be 3600 * (69/60) =
4140 RPM.  It would have been obvious to you if the generator had been
screaming like that.  If this is the kind of generator that I think it is, the
field would probably have lost excitation, cutting off the output.

On the other end, the fan motor would have been over-speeding, at minimum,
making a racket and at worst, the blower wheel would have come apart.

A couple of things you can try.  One is to connect a resistive load of a
couple hundred watts to the generator.  This may clean up the waveform enough
that the KAW is no longer being fooled.

Another thing you can do is to run the furnace blower for awhile (hour or two)
while monitoring its temperature.  If it were really operating on power that
far out of spec, it would likely overheat rapidly.  If you can lay your hand
on the motor casing without getting burned, then the motor is OK.  Be sure to
leave the cover on the air handling unit except for when you're checking.
Letting the blower pull ambient air instead of from the return duct will
overload it.

The generator has to supply the "wattless current" that the motor draws
because of the low PF even though it's not "real" power.  The term is "lagging
VARs" (Volt-Amp Reactive).  Leading VARs can also be supplied by a capacitor,
the process being known as "power factor correction."  A capacitor of suitable
size is simply connected in parallel with the motor.

One can calculate the size cap to supply the appropriate amount of leading
VARs but it's easier to simply substitute a variety of caps while watching the
line current upstream of the cap.  Select caps until the line current drops to
the minimum value.

A motor run capacitor just like the one already on the fan works fine.  I'd
start out with about a 25 microfarad unit.  Using utility power, watch the KAW
and see what the PF and amps do.  Add another unit of capacitance, say, 5 or
10 uF.  If the PF improves and the amps drop, you're on the right track.  If
they don't then you already have too much capacitance.

Shop around for the caps.  Many HVAC shops will give them to you from removed
old units.  So will electric motor shops.  New, the cap shouldn't cost over
$0.  I've been working with almost the same problem with someone else via
email and I've been amazed at the rip-off prices some outfits quoted him.  One
was >$00.

The reason that you want to do this is that it will unload the generator so
that you can run other loads simultaneously.  300 watts is about right for a
1/3 hp blower motor.  With the PF adjusted to 1, that leaves you 600 watts for
other loads.  As it is, even though the real power is only 300 watts,
supplying the necessary VARS is heavily loading the generator, leaving little
room for other loads.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
Some people are like a Slinky .. not really good for anything
 but you still smile
when you shove them down the stairs.


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