Selsyn Motor Theory

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IG88

Member
Hey, Iam wondering if anyone would know what the effects would be if you ran a Selsyn motor with DC on the rotor instead of AC? Would this not become a generator and still turn the secondary rotor?

Thanks guys
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Welcome to the forum! :)


I think that the DC on the rotor would mean it cannot generate stator current unless it's rotating.

Doesn't the AC applied to the rotor permit stator output even when the rotor is slow or stationary?

Or am I confusing Selsyn motors with servos?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So, it does behave like a servo, and I believe I'm correct that AC must be applied to the rotors (or at least the transmitter.)
 

Besoeker

Senior Member
Location
UK
Only twenty years? About 45 years ago, one of the tasks at my first industrial job was testing selsyns, don't think that I have seen one since.
You must be nearly as old as I. ;)
I did learn about them but I can't honestly say I have ever come across any.
Yes, mercury archaic rectifiers, Ward-Leonard sets, power Mag Amps, Thyratrons, Carbon Pile regulators, and all manner of weird on wonderful things that were around before the Dead Sea reported sick.
But, sadly, no Selsyns.
You've made me feel like a child with a deprived upbringing, that I have missed out on an essential slice of experience, and realise just how empty and meaningless my life has been.....
:grin:
 

Ken9876

Senior Member
Location
Jersey Shore
This is funny, we still use Selsyns on draw bridges, if fact they are still buying and installing these things when they rehab a bridge. I heard they have about a 16,000 price tag for the pair.
 

dbuckley

Senior Member
Common uses for selsyns from the past - Radar systems, old school with the rotating line on the radar screen - the line deflection is kept in sync with the radar antenna by selsyns. Another use is Cinerama - three projectors were used for cinerama, and they were kept in frame accurate sync with selsyns.

Ham radio operators used surplus selsyns so they could display which way their beam antennas were pointing, though that was before I got licenced, so it must be prior to the 80s as they had all but gone by then...

Perhaps my yearage was a bit out... But I'm even more stunned that they are even still manufactured!

But I can confirm they're not as much fun as mercury arc rectifiers :) And the last time I saw the term "Ward-Leonard" was on a lift (elevator) control panel as a kid :)
 

Speedskater

Senior Member
Location
Cleveland, Ohio
You must be nearly as old as I. ;)
I did learn about them but I can't honestly say I have ever come across any.
Yes, mercury archaic rectifiers, Ward-Leonard sets, power Mag Amps, Thyratrons, Carbon Pile regulators, and all manner of weird on wonderful things that were around before the Dead Sea reported sick.
But, sadly, no Selsyns.
You've made me feel like a child with a deprived upbringing, that I have missed out on an essential slice of experience, and realise just how empty and meaningless my life has been.....
:grin:

You can read about my 68th birthday in your local newspaper next month.
It was at Lear Seigler testing military areo/space equipment. Don't remember much but I think that they were for guidance control of small armed rockets.
 

Besoeker

Senior Member
Location
UK
You can read about my 68th birthday in your local newspaper next month.
Congratulations, old fellow!
But somehow, I don't think even such a momentous event will get coverage in the Dunstable Herald & Times. ;)
It was at Lear Seigler testing military areo/space equipment. Don't remember much but I think that they were for guidance control of small armed rockets.
My recollection is that the theory, in my case, was also related to weapons guidance. Static installations of gun turrets I think.

Life moves on. We still use position control in our drive systems. We do some high performance drive systems mainly for the machine tools market. Typically the dynamic response requires the motor to stop from 10,000 rpm within half a second and to within half a degree position accuracy. We use shaft mounted resolvers.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Hey, Iam wondering if anyone would know what the effects would be if you ran a Selsyn motor with DC on the rotor instead of AC? Would this not become a generator and still turn the secondary rotor?

Thanks guys

Well Larryfine is correct the rotor needs ac to excite the stator windings just say it did work dc the dc would need to be less meaning voltage wise you just might burn out that 2 wire rotor . But dont do it why waste a good motor.

Heres a tought why not make a pulse modulation dc power source your own freq drive dc and drive it that will work .

From what ive read they are servos and they are still in use today on ships and panel meters can i ask what you are building these for or are you just asking the question ?
 
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