bridge rectifier filter
bridge rectifier filter
(OP)
I am working on a boat with a 120 vdc anchor windlass. I believe the motor to be 3 HP and the 120 vdc source is from a full wave bridge (120vac input). The output of the bridge has no capacitor. Should I install a capacitor and how do I determine the proper size?





RE: bridge rectifier filter
If you add a large capacitor you will increase the output voltage of the power supply. This alone is probably enough to warn against adding the cap without other more involved mods such as changing the transformer. The rectifier will also see higher peak currents if the capacitor is installed, which may or may not be within the rating of the diodes.
Why do you want to do add a capacitor? Is the winch under-performing? Or does it just look 'wrong' without the capacitor?
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If we learn from our mistakes,
I'm getting a great education!
RE: bridge rectifier filter
thanks again.
Scrudman
RE: bridge rectifier filter
Don't forget that the relays switch a lot of current when the motor is at standstill because there is no back EMF from the armature. If the motor is separately excited or has a shunt field, there will be a powerful inductive arc at switch-off caused by the energy stored in the field circuit which will burn relay pole faces.
You say 'relays' rather than 'contactor'. For this sort of duty it would be normal to spec a contactor rather than a relay. In Europe at least, 120V DC is a fairly common control voltage and contactors are available suited to motor switching duty. If this is an industrial application look for DC3 duty contactors or maybe DC5 duty if the motor is particularly inductive.
On re-reading your post, I have assumed that the relays are failing through contact damage, not coil failure. Have I mis-assumed?
------------------------------
If we learn from our mistakes,
I'm getting a great education!
RE: bridge rectifier filter
RE: bridge rectifier filter
Would traditional diode protection across the contact(s) or motor be affected by the unfiltered-DC source?
RE: bridge rectifier filter
RE: bridge rectifier filter
If its the relay coils that are burning out Id use dc coils fed from a rectified that was connected to the supply with the output smoothed to try and reduce the ripple effect.
Rugged
RE: bridge rectifier filter