Author Topic: ST Head KVA rating and its voltage.  (Read 5061 times)

Flyingpony

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ST Head KVA rating and its voltage.
« on: October 20, 2006, 03:32:50 AM »
Been reading about ST Generator Heads and got a question regarding their rated KVA figure.

All sites quote them running at 110 volts, but when these get changed to 220 volts (as required for NZ), does this have any impact on its KVA rating?

i.e. Is a 10KVA 110volt generator still a 10KVA generator when switched to 220 volts?

Thanks.

fuddyduddy

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Re: ST Head KVA rating and its voltage.
« Reply #1 on: October 20, 2006, 04:03:20 AM »
Nope, sorry,  all sites do NOT.  utterpower (Bill Rogers) at http://utterpower.com/commercial_grid.htm   says : "Nominal voltage is defined in terms of the typical 120/240v 3-wire single-phase service, and is referenced to a 120v base."

eBay #11004424209 says about a 12 KW ST head: "It has a continuous 12 KW rating, and is 120/240v, 60hz, single phase."

ST heads are not rated in KiloVoltAmps, but in KWs.  At least, the ones I am familiar with.

Guy_Incognito

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Re: ST Head KVA rating and its voltage.
« Reply #2 on: October 20, 2006, 11:56:37 AM »
kW and KVA are interchangeable if you're driving purely resistive loads.

Reactive loads (capacitive or inductive) are a different matter - this is where kW and kVA separate and the power factor comes in. Some crappy motors have terrible power factors (0.3). Fluoro lights, computer power supplies,etc all have power factors that can make a generator (or inverter) sweat a fair bit.

For example, operating 400 Watts of CFL might require 600-800VA or more.  Large motors might have a very poor power factor when starting, needing a lot of VA per watts at that time, etc...  (Here the extreme importance of the surge capacity for an inverter when you operate large motors)

For your case, twiddling the windings around shouldn't affect the rated KVA/KW output (much....). Instead of two windings in parallel for 110V at a certain current to give you a rated power, you've two in series for twice the voltage , but only half the current.... but still the rated power.

Having said that, I've never had a look inside a ST head, so things might be different in their particular case.

« Last Edit: October 20, 2006, 01:15:23 PM by Guy_Incognito »

cujet

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Re: ST Head KVA rating and its voltage.
« Reply #3 on: October 20, 2006, 09:02:55 PM »
While the voltage rating may be posted as (110V) for instance, it is variable. You can adjust it. There is enough range of adjustment to go from 95V to 140V in some cases. That depends on many factors, including load.

In addition, the ST head has windings designed for 50HZ. Using these is simply to use the full length of the windings. The 120V winding is simply a TAP off the full winding. SO, the ST head is configurable in many ways via the posts in the "dog house" box on top. This is to make it as near universal as possible.

Take the posted rating and consider them the maximum output the generator could ever produce under ideal conditions. Don't worry about rated voltage, as you can configure and adjust to your hearts content.

Chris
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Spark_Chaser

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Re: ST Head KVA rating and its voltage.
« Reply #4 on: October 21, 2006, 04:01:58 AM »
Guy_I has it correct.

To simplify, Voltage x Amperage = Watts (power).

A 10 KW st head is 10 KW at 110 or 220 volts.

Don't get too hung up over the voltage ratings. 110, 117, 120 or 220, 230, 240. 

(These are RMS (avarage) values anyway not true peak voltages, ie 117vac reads 165vac on an oscilliscope)

Most 110 AC quipment will tolerate wide voltages ranges if given a stable frequency.

You can download a manual for the ST gen at www.listeroids.com/ST_Generators.html

It has a diagram showing the schematic and jumpering instructions for 110/120 or 220/240 50cycle or 60cycle settings.


Spark_Chaser
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Jim Mc

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Re: ST Head KVA rating and its voltage.
« Reply #5 on: October 21, 2006, 04:10:57 AM »

All sites quote them running at 110 volts, but when these get changed to 220 volts (as required for NZ), does this have any impact on its KVA rating?

i.e. Is a 10KVA 110volt generator still a 10KVA generator when switched to 220 volts?



Looks like two simple questions deserving simple answers:  no, yes.

BTW, welcome aboard.


Flyingpony

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Re: ST Head KVA rating and its voltage.
« Reply #6 on: October 25, 2006, 09:12:12 PM »
Thanks all!  Awesome replies.  Some required a bit of background reading on my part, but, they've been answered for now.

dkwflight

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Re: ST Head KVA rating and its voltage.
« Reply #7 on: October 26, 2006, 01:06:57 AM »
Hi
In New zeland. Sorry, I am not sure of the spelling.

Your power looks something like this.
     220 volt connection..........ground
On my ST it is .
110v...............ground----ground..............110volt
The center ground connections are connected by a strap/ the ground connections are connected to the earth. What we call 220volt is really two 110v circuts, each is 110volt to ground and when measuring across the two 110v taps you get 220v.

I believe that you can connect one leg of the gen to earth and have the center taps floating, not connected to ground, and the other would be 220v to ground.
I hope this helps
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

buickanddeere

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Re: ST Head KVA rating and its voltage.
« Reply #8 on: October 26, 2006, 04:51:41 AM »
  "220 volt connection..........ground
On my ST it is .
110v...............ground----ground..............110volt"

Nope

  L1  .........Neutral that's bonded to earth............L2

  Ground is the bare or green cable connected to a driven earth ground rod and to the metal chassis of electrical equipment. It only carries current when a fault occurs to "ground".
  The neutral is an insulated current carrying conductor. It happens to be held at earth potential via a bond to the ground. This prevents L1,L2 and neutral from drifting thousands of volts above true earth potential. It also reduces the chance of a tinkerer's electrical shock as 1 of 3 current carrying conductors is held at earth potential. 

Doug

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Re: ST Head KVA rating and its voltage.
« Reply #9 on: October 27, 2006, 12:25:07 AM »
One more thing about grounding and bonding....

A short circut should cause a fuse to blow or a braker to trip. Proper grounding and bonding ensures that there is a good return path for current that prevents a voltage rise between the source and the device, and that enough current flows in a fault condition to possitively trip the protection device.


The most frightening thing in industry is an old big CB that never seems to trip.
Why?
Because it might mean you may have a problem your protection system can't detect or your detection system is in bad order.

The same thing goes for your home. You should check or have checked by an electrican your connections, bonds and ground if your home is 20 years old or older. Once a year you should turn all you CBs on and off once to ensure they are functional and for the contacts to sweep and clean themselves. If you have GFI plugs or CBs you should test them once a year. And you should be prepared to spend a little money upgrading and replacing very old plugs, clearly outdated wiring and replace or repair worn out electrical devices hard wired in your home.

Loose bonds and poor grounds are a huge isue that doesn't get the attension it deserves considering the danger.

Doug

Doug