Author Topic: st 10 kw gen head  (Read 5952 times)

toydiesel01

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st 10 kw gen head
« on: July 22, 2011, 03:40:09 AM »
I have a st 10 kw gen head running at 1800 rpm 4 pole 120/240.  I have it jumped in the dog house for 240 per the instructions.
so I have 120 x2 with a newtrel .
problem - when putting a load on more than 10 amps the voltage drops down 120 down to 109 the frequency stays at 61Hz thou .
 I have checked all connections and checked the contact of the brushes with the slip rings - with a meter less than 1 ohm no open windings either and the windings read the same on the meter
rectifier tests OK

Any ideas i can try  to find out whats up?

Tom

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Re: st 10 kw gen head
« Reply #1 on: July 22, 2011, 05:13:50 PM »
Is that 10 draw at 120 or 240 volts?
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

ronmar

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Re: st 10 kw gen head
« Reply #2 on: July 22, 2011, 10:41:55 PM »
Good question Tom, is the load spread evenly across the two 120V legs?  Even if the losd is only on one leg, that is still a pretty good drop.  How exactly did you test the bridge rectifyer?  It might check OK with a VOM, but one of the diodes may be breaking down as the field current thru it increases with load/Z winding output.  I would swap it with another and see how that works...  I think surplus center has them pretty reasonable.
PS 6/1 - ST-5.

Tom

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Re: st 10 kw gen head
« Reply #3 on: July 22, 2011, 11:04:20 PM »
Also is the load inductive or resistive.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

toydiesel01

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Re: st 10 kw gen head
« Reply #4 on: July 24, 2011, 06:09:56 PM »
well I have 240 going to the panel box in the house with a newtral, from the panel box it come out as 2 120v.  each side of panel is 120 .  I have only tryed 1 side of the panel box at 1 time  but both sides the drop is the same.  I tryed an electric water heater element and also a electric 5 hp motor.  heater element stayed at 109 volts and the electric motor went to 105 on start and then stayed at the 109v.  I tested diodes with a digital volt ohm meter with the generator off -- curent flows in 1 direction only.

do I want to change the diodes or the total bridge rect ?
A few months ago I had a crazy thing happen - was powering the total house no problem and then had  nothing, thinking i blew some fuses in the line, shut off the generator and tested the fuses but found none blown. Re-started the generator and this is how it works now--- if this helps thats why I got into testing the brushes and windings and diodes, but i can't seem to locate the problem

ronmar

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Re: st 10 kw gen head
« Reply #5 on: July 24, 2011, 07:16:33 PM »
Replace the chinese cobbled together bridge with a good quality solid state unit.

IE: Buy 2 of these(one for a spare) from surplus center and don't look back:)  These have a conveniently mounted center hole and you can just bolt them to the wall of your doghouse/junction box for a heat sync.  You hook the AC symbols to the Z winding wires, and the DC output to the brushes/field.  It would help to measure which lead going to the brushes/field is positive with a meter on the existing bridge while running, to make sure you hook the new one up the same way.

https://www.surpluscenter.com/item.asp?item=22-1206&catname=electric

If that dosn't solve it, you have something else breaking down when current flows thru it, either a bad piece of wire, or more likely a bad connection.  I went thru my ST and soldered all the crimped terminal lugs/wire unions before I ever put it into service...  But since all the input or output from the diode bridge is combined, your symptom of always falling to 109V leads me to believe it is a diode, as you are loosing the same relative precentage of field drive, such as the loss of 1/4 that a single bad diode would cause.
PS 6/1 - ST-5.

toydiesel01

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Re: st 10 kw gen head
« Reply #6 on: July 24, 2011, 07:21:02 PM »
thank you very much ronmar
will try it

toydiesel01

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Re: st 10 kw gen head
« Reply #7 on: July 24, 2011, 07:40:59 PM »
also before i set up the machine - i did go through it and checked all connections, soldered and installed hose on wires where they went through  the jaggered metal housing and cable tied everything tight - found 1 broken wire on a new gen head--- cheap Chinese wires
bob f

Tom

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Re: st 10 kw gen head
« Reply #8 on: July 25, 2011, 03:46:59 AM »
The rectifier on my st5 lasted until the first heavy load was plugged in. Replaced it with one like recommended by Ronmar and have been good for the last 5 years.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

toydiesel01

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Re: st 10 kw gen head
« Reply #9 on: July 25, 2011, 05:59:39 PM »
thanks tom, i did have a heavy load when things went crazy
placed the order for 4 of them today
bob f