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kwame

Member
HI FOLKS
I HAVE JUST ORDERED 12VDC LINEAR ACTUATOR WHICH I WANT TO USE FOR SOME HOBBYIST PROJECTS.I HAVE A 220VAC -12V TRANSFORMER AND BRIDGE RECTIFIER TO SUPPLY ELECTRICITY TO LINEAR.DUE TO BRIDGE RECTIFIER,THE OUTPUT VOLTAGE IS 15VDC INSTEAD OF 12VDC.THE CAPACITOR IS 3300uF ,35v.CAN A CAPACITOR WHICH RATED AT 30V OR 25V BE USED FOR THE BRIDGE RECTIFIER TO GIVE ME 12VDC OUTPUT?
WILL 15VDC CAUSE ANY DAMAGE TO THE LINEAR ACTUATOR ?
 

carbonzit

Active Member
CAN YOU NOT POST IN ALL CAPS? IT HURTS OUR EARS.

There, that's better.

Don't know why you'd think a higher-voltage rated capacitor ill reduce the output voltage; it won't. The output from a bridge rectifier is actually 1.414 (2√2) times higher than the AC input (minus two diode drops).

So far as whether 3 V overvoltage will damage your actuator, well, I'm not going to advise you that it won't. I wouldn't do it.

If you're concerned about the motor, get a 12 V voltage regulator that can handle the load current.
 

crutschow

Well-Known Member
Most Helpful Member
Certainly you can buy one.

You can also use a regulator to drop the 15V to 12V such as the LT1083. You will need to attach the device to a heatsink sufficient to keep the regulator case temperature below 70 degrees C while dissipating 20W .
 

RCinFLA

Well-Known Member
If this is a motor driven linear actuator, most DC motors are perfectly happy with rectified DC without any filtering cap.
 

crutschow

Well-Known Member
Most Helpful Member
But that won't solve his overvoltage problem.
It will because the unfiltered rectified average voltage is equal to the RMS value not the peak value.
 
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kwame

Member
Hi folks
i have also thought of an alternative solution.Most local electric technician are good transformer rewinders.
Im thinking of getting a good rewinded 9VDC transformer from them and them when attach the full wave rectifier;i should get extra 3VDC from the latter.This would bring the total voltage to 12VDC (9VDC +3VDC ) or not?
By the way, what is the lifespan of rewinded transformers.This is the best tech forum on the planet.

KWAME
 

carbonzit

Active Member
In English the word is "rewound". There's no such word as rewinded.

The bridge rectifier doesn't add 3 volts. That's not how it works.

Sounds like an awful lot of trouble when there are other, easier alternatives.

I have no idea what the lifespan of rewound transformers are compared to un-rewound ones. If you have to ask this, then how can you say that "most local electric technician(s) are good transformer rewinders"? If done correctly, should be no different from the original life.
 

ronv

Well-Known Member
Most Helpful Member
12 Volt Transformer

I wouldn't change a thing. The capacitor when you have no load will charge up to the peak voltage. Once you apply the load the voltage will fall depending on the load.
 

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kwame

Member
Hi folks
i want to use the PC power pack and simply tap the 12VDC output.Put the PC power pack has so many cables and next to impossible to differentiate one cable from the other.How do i identify the 12VDC cables?How do i determine which cable is 12V,120V, etc
 
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