I have bought a solenoid magnetic mechanical switch, it requires 12V, 18Amp to work. The thing is that i couldn't find a power supply to afford these values in local market, I would like to build one that can supply these values. What are the requirements and parts that i need, what could be the simplest diagram for the circuit ( i haven't built one before ) ?

 

Assuming the power source is the AC mains, then you could use a (rather large and expensive) transformer. If the solenoid needs DC then you would also need a rectifier and you may, or may not, need a smoothing capacitor.

If the solenoid is to be operated briefly and occasionally then you could use a rechargeable battery to supply the 18A that the solenoid needs and a much lower current charger to maintain the charge in the battery.

 

Welcome to AAC!
Do you mean the coil current needed is 18A, or is 18A the rating of the contacts?

 

Another idea - some PC power supplies can supply 20A from the +12V rail.

Do you mean the coil current needed is 18A, or is 18A the rating of the contacts?

Good question.

 

Assuming the power source is the AC mains, then you could use a (rather large and expensive) transformer. If the solenoid needs DC then you would also need a rectifier and you may, or may not, need a smoothing capacitor.

If the solenoid is to be operated briefly and occasionally then you could use a rechargeable battery to supply the 18A that the solenoid needs and a much lower current charger to maintain the charge in the battery.

So i understand the idea of building a AC -> DC power supply is kind of hard and expensive for such current?

 

Welcome to AAC!
Do you mean the coil current needed is 18A, or is 18A the rating of the contacts?

To operate the device 18A is required from the supply

 

So i understand the idea of building a AC -> DC power supply is kind of hard and expensive for such current?

It's easy enough, but the transformer won't be cheap.
One off the wall suggestion would be to rewind the secondary on an old salvaged microwave oven transformer. There are plenty of sites and videos describing how to do this. This would be cheap, if a little time consuming.

 

I have bunch of transformers however, i don't know which one is good for this purpose some of them are large.. is there any information i shall look for to know how much suitable would be the transformer?

 

Can you establish whether the solenoid needs smooth DC or if it would work with the unsmoothed, full-wave rectified output from a transformer?
You would need a 12V output from the transformer if the solenoid will work with the unsmoothed output and 8-9V if smoothing is required (smoothing increases the effective output voltage).

Do consider the PC supply option. They can be obtained remarkably cheaply and provide a ready made smooth 12V DC.

 

Do you have the info about your solenoid magnetic mechanical switch, any pdf file or links?

 

To operate the device 18A is required from the supply

12V @18A = 216W.... that's a fairly big solenoid.

While it may require 18A to initially operate the solenoid it definitely will hold on a much lower current so you don't need a supply capable of 18A continuous. The supply only has to be capable of providing 18A for a few seconds and then you can arrange a circuit to reduce the holding current to probably 6A or less but we need more information on the solenoid.

Can you provide the DC resistance of the solenoid coil?
What are you intending to use the solenoid for?

 

Easy mate, get yourself an Atx psu...

 

Hi,

The requirements of the power supply are not that clear.
What is this giong to be used for? That's an important question.

If you are maknig a DC power supply then the simplest is a 12v transformer with rectifiers, and a filter cap.

There are ways to cheat if your device to be powered is not too fussy about the smoothness of the DC it needs. Some 12vdc devices can be run off of 120vac with a bridge rectifier and series resistance. The series resistance limits the voltage and current getting to the device. For example years ago i ran a 12vdc air conditioner compressor clutch from 120vac with a bridge rectifier and series 120vac light bulb. The wattage of the light bulb was chosen to limit the voltage to 12v at the clutch terminals. The bulb wattage has to be chosen carefully and you have to be careful because this kind of circuit is not isolated from the dangerous line voltage.
This doesnt work for everything either.

 

There are ways to cheat if your device to be powered is not too fussy about the smoothness of the DC it needs. Some 12vdc devices can be run off of 120vac with a bridge rectifier and series resistance. The series resistance limits the voltage and current getting to the device. For example years ago i ran a 12vdc air conditioner compressor clutch from 120vac with a bridge rectifier and series 120vac light bulb. The wattage of the light bulb was chosen to limit the voltage to 12v at the clutch terminals. The bulb wattage has to be chosen carefully and you have to be careful because this kind of circuit is not isolated from the dangerous line voltage.
This doesnt work for everything either.

Any such resistor would have to dissipate 108V * 18A = 1944W. That's one heck of a light bulb.

 

Well, thanks for all of your responses. As rheber1 said I am gonna switch it on for few seconds. the device description is http://www.murphybyenovationcontrols.com/uploaded/documents/pdfs/00092.pdf

I am going to use it in controlling a small gate ( Open/Close) for few seconds of operating time in my project.
If i have understood the specs wrong please guide me through.

 

As the model RP2307B.
Energize Coil:
I = W/E =624W/12V = 52A
I = W/E =624W/24V = 26A
I = W/E =624W/30V = 20.8A

Hold Coil:
I = W/E =18W/12V = 1.5A
I = W/E =18W/24V = 0.75A
I = W/E =18W/30V = 0.6A

 

As the model RP2307B.
Energize Coil:
I = W/E =624W/12V = 52A
I = W/E =624W/24V = 26A
I = W/E =624W/30V = 20.8A

Hold Coil:
I = W/E =18W/12V = 1.5A
I = W/E =18W/24V = 0.75A
I = W/E =18W/30V = 0.6A

I think to turn it ON, coil is mean to be ENERGIZED
Oh so its not 12V 18A, according to the tables ( & calculations).. Computer powersupply wont do the job for me.
What shall i do?

 

I am going to use it in controlling a small gate

The stroke is only 1" or 1.5" (depending on model). Doesn't seem suitable for gate opening/closing. IMO you need a geared motor, not a solenoid. Slamming the gate open/closed with a solenoid could be dangerous.

 

The stroke is only 1" or 1.5" (depending on model). Doesn't seem suitable for gate opening/closing. IMO you need a geared motor, not a solenoid. Slamming the gate open/closed with a solenoid could be dangerous.

1 or 1.5 not the Energize options ? If you check the datasheet there is HOLD,GND, ENERGIZE. What is the hold pin ?
And for safety it is just a model for gate not a real one to satisfy the project.

 

I think to turn it ON, coil is mean to be ENERGIZED
Oh so its not 12V 18A, according to the tables ( & calculations).. Computer powersupply wont do the job for me.
What shall i do?

You can buy two 12V/30A industrial power supplies to in series then you can get 24V/30A.