Simple AC to DC Circuit - Capacitor?

I have recently put together a makeshift pool filter for my wife's wading pool. I used a 5 gal bucket with upholstery fill fabric for the filter, PVC piping to transfer the water out of the pool, through the filter and back into the pool and my pump is a 1100 GPH 12V bilge pump. When it came to the power for the pump, I used an old Intermatic 12VAC landscape lighting power supply fitted with a bridge rectifier to convert the 12VAC to 12VDC. For Just running the motor on the pump, do I need a capacitor also...?


by bobphoenix
July 18, 2021

When you say "bilge pump" I assume you are referring to one made for a boat...If this is the case it will very likely have a brushed dc motor (not "brushless dc") and you have a lot of leeway in voltage and ripple. So to answer your question, no you should not need a filter capacitor. Just be aware that the 12VAC will be rms volts and what the motor sees is average dc volts from the rectifier which will be considerably less than 12vdc. This won't hurt a dc motor but it will simply run somewhat slower than you expected.

by Foxx
July 19, 2021

Just checked one of my reference books from many years ago and found the dc output voltage will be 0.9 times the ac voltage so the motor will only run at about 90% speed. Probably still no problem.

by Foxx
July 20, 2021

Thank you for these responses. I was expecting a drop in efficiency because of the AC/DC conversion and decided to run a 1100 GPH pump (where 750- 900 GPH was needed).

Cheers, Bob

by bobphoenix
July 22, 2021

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