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120VDC supply 20A output

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tday99

New Member
I am looking for some ideas on how to build a 120VDC power supply that will be regulated some how so the output voltage won't drop under load. I am currently using a full wave bridge rectifier utilizing line voltage of 120VAC with no filtering. I am not too concerned about ripple or noise as I am using it to test 120VDC solenoids. I do vary the input voltage as low as 70VAC to check minimum pickup of the solenoids. The power supply I am currently using creates a problem because of the unstable voltage under load. I have searched the site but could not find any answers. Any suggestions would be appreciated.
 

Hero999

Banned
If you have a filter capacitor on the output, the RMS output voltage will be 170V which might cause the solenoids to overheat.

I think the only viable option is to buy a 120VDC switched mode power supply. You could use a linear regulator but it's too inefficient.
 

JimB

Super Moderator
Most Helpful Member
What is the current rating of the solenoids?
How many will be connected to the PSU at the same time?

At a quick guess I cant see the solenoid taking more than 100mA, unless it is one BIG solenoid!

I dont think you really need a PSU rated at 20 amps.

JimB
 

Hero999

Banned
Yes, [email protected] is 2.4kW, I assumed that there are other loads connected apart from the solenoids.

I agree with Jim, I don't believe that the solenoids take more than a 100mA
 

tday99

New Member
Some of the solenoids draw over 12 amps so I just wanted to make sure the supply was a rated a little higher than that. They are not holding solenoids and only operated for a second or less.
 

RODALCO

Well-Known Member
He may be testing heavy solenoids for circuit brakers.

We use 6 and 8 kW rated solenoids on 33 kV OCB's

they draw 60 to 85 Ampères at 110 Volts dc.
 

bountyhunter

Well-Known Member
I am looking for some ideas on how to build a 120VDC power supply that will be regulated some how so the output voltage won't drop under load. I am currently using a full wave bridge rectifier utilizing line voltage of 120VAC with no filtering. I am not too concerned about ripple or noise as I am using it to test 120VDC solenoids. I do vary the input voltage as low as 70VAC to check minimum pickup of the solenoids. The power supply I am currently using creates a problem because of the unstable voltage under load. I have searched the site but could not find any answers. Any suggestions would be appreciated.
You want to build your own off-line 2.4kW power supply? That's not really a home project. We built 1kW to 10kW lab supplies where I worked and they are not trivial. You can buy them cheaper than you can build them. I recall the best source used to be EMI (electronic measurements incorp).
 
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tcmtech

Banned
Most Helpful Member
A big variac and your rectifiers and a good sized capacitor bank would give you full adjustable voltage from 0 to near your RMS peak of the variacs output. Depending upon the application and working conditions an isolation transformer may be needed though.
Its not ideally regulated or isolated from the mains power but simple easy and reliable. Once set properly the loaded voltage will stay stable within reason.

Just a thought.
 

Hero999

Banned
He may be testing heavy solenoids for circuit brakers.

We use 6 and 8 kW rated solenoids on 33 kV OCB's

they draw 60 to 85 Ampères at 110 Volts dc.
At what duty cycle?

I doubt they're rated to 9.35KW continuously.

Surly charging a large capacitor would do the job?
 

crutschow

Well-Known Member
Most Helpful Member
If you have 3-phase power available you can built a 3-phase bridge rectifier (6 diodes) which will have much less ripple and better regulation than a single-phase source. Of course, you will also need a 3-phase Variac.
 
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