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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Transformer in Generator Head?


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  #1  
Old 01-17-2018, 06:27:21 AM
Cavalry Cavalry is offline
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Default Transformer in Generator Head?

I have a Powr Gard 6.6kw head and was working fine until some mice made a nice conductive home across the main terminal block, now its not generating power, and it appears bad things happened. Unfortunately there is manufacturer support, no parts or prints available.

I have done some generator repairs before but have not encountered a transformer before? Its a asynchronous, with the standard capacitor and rectifier to maintain the field. The transformer clearly has damage. I have to uncouple the head off the engine and remove from the cabinet as its impossible to do any work on it in place, so I do not know what other components took a hit at this point. I will make a print when I can see everything.

-What function does the transformer perform? Does anyone have a generic print showing the purpose of the transformer?
-The transformer has no visible part numbers, so I am a bit lost on how to find a replacement other than do an autopsy and count the individual windings.
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Old 01-17-2018, 07:36:08 AM
Joe Romas Joe Romas is offline
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Default Re: Transformer in Generator Head?

This might be no hope at all but does it look anything like this?
If so it's of my Stamford Newage it's on my Boss light tower.
You might look there.
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Old 01-17-2018, 07:37:15 AM
Joe Romas Joe Romas is offline
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Default Re: Transformer in Generator Head?

It's called "Transformer Regulation" and is supposed to be robust.
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Old 01-17-2018, 07:43:01 AM
Kevin K Kevin K is offline
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Default Re: Transformer in Generator Head?

Pictures would help. I'm guessing it is a voltage regulating (sometimes called current) transformer. The transformer may have one or two primary windings, connected in series with the generator output leads. The full AC output current produced by the generator flows through these primary windings. Increasing or decreasing the current output from the transformer winding produces a corresponding increase or decrease in the current produced in the secondary winding. The secondary winding is connected in series with the circuit that supplies AC current for rectification to DC field current.
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Old 01-17-2018, 07:43:42 AM
Joe Romas Joe Romas is offline
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Default Re: Transformer in Generator Head?

Here's a 3 phase version S-N unit, sorry have no model number.
The single phase above has the diodes mounted inside the generator head.
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Old 01-17-2018, 07:44:16 AM
Thaumaturge Thaumaturge is online now
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Default Re: Transformer in Generator Head?

Likely transformer is used to scale down output voltage before comparison to an internal reference voltage, for the AVR to switch field voltage up or down. Could also supply lower voltage to AVR itself.
As to figuring out windings... that could be tough, if transformer is damaged. My suggestion would be to try subbing in another filament transformer and then measuring effect upon main output (no load). If output goes too high, increase secondary voltage of transformer. If too low then decrease secondary. (Output being a response to sample voltage.)
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Old 01-17-2018, 08:25:13 AM
armandh armandh is offline
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Default Re: Transformer in Generator Head?

simple "transformer " regulation

induction passes dc but "blocks" AC to some degree
speaker crossovers are a good example

so add series induction to a field rectifier input and
it can drop the field voltage quite a bit
but if the main output lead is wound a few turns in opposition to the loss
nothing much happens until there is some output current
then the field supply reduction is lessened
field current goes up to correct for output load
the voltage is kept constant

the transformers are wound to the specific use
the bridge rectifier usually has a resistor or a cap across the field connection to kill spikes
magniciters [the not so simple] use induction on the AC input [no cap induced lag]


older exciter generator regulation.

using a separate exciter generator, an increase in AC load causes an increase in field current
the field current passes through the exciter generator's series field coil increasing the DC output

both methods need a motive power with a constant speed across the output range.
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Last edited by armandh; 01-17-2018 at 08:48:47 AM.
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Old 01-17-2018, 09:39:48 AM
Cavalry Cavalry is offline
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Default Re: Transformer in Generator Head?

Thanks all for the information posted. Its a horrible pic but its all I have with me. I need to drag this in the shop and pull the head so I can see what is actually going on and test individual components to make sure the head is salvageable.
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Old 01-17-2018, 09:40:50 AM
Cavalry Cavalry is offline
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Default Re: Transformer in Generator Head?

Quote:
Originally Posted by Joe Romas View Post
This might be no hope at all but does it look anything like this?
If so it's of my Stamford Newage it's on my Boss light tower.
You might look there.

Thanks, This too is a light tower. I will look into it so see if its similar enough to work from.
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Old 01-17-2018, 11:03:22 AM
Cavalry Cavalry is offline
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Default Re: Transformer in Generator Head?

Any reason why I cant get a appropriately sized solid state AVR and adapt that to my generator? They are cheap enough I could put one on the shelf in case of a failure.
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