Need to build transformer - 21vdc 900ma

[mathursharad]

Hi,

I need to build a 110VAC to 21VDC, 900ma transformer.

(This is to power an ACT Labs gaming steering wheel for which I lost the power brick)

Would someone be able to provide me a schematic of the circuit I need to build?

I am new to the transformer world, how would I control the output voltage 21VDC while also limiting the current 900ma?

Thanks!
Sharad

 

[davenn]

Hi,
I need to build a 110VAC to 21VDC, 900ma transformer.
(This is to power an ACT Labs gaming steering wheel for which I lost the power brick)
Would someone be able to provide me a schematic of the circuit I need to build?
I am new to the transformer world, how would I control the output voltage 21VDC while also limiting the current 900ma?
Thanks!
Sharad

Hi Sharad,
people dont normally wind their own transformers these days, its much easier to just go and buy one. But if you would like to see what's involved in winding a tramsformer and calculating Voltage in Vs Voltage out; turns ratios, etc
here is a good starting point tutorial......
http://sound.westhost.com/xfmr2.htm

cheers
Dave
VK2TDN

 

[mathursharad]

I guess I asked the wrong question. I want to build a power supply that will output 21vdc 900ma

I tried looking online and couldn't find a power supply that would do I what I want so I'm stuck building one.

So no I would not wind my own transformer. I would buy one off the shelf but I would have to build a circuit around it to get the 21VDC and 900ma output, and that's where I am stuck. I am just not familar with AC to DC power supplies and need help in the schematic.

So if anyone can help me with the schematic and the parts I need to get this done, I would appreciate it

Thanks!
Sharad

 

[davenn]

I guess I asked the wrong question. I want to build a power supply that will output 21vdc 900ma
I tried looking online and couldn't find a power supply that would do I what I want so I'm stuck building one.
So no I would not wind my own transformer. I would buy one off the shelf but I would have to build a circuit around it to get the 21VDC and 900ma output, and that's where I am stuck. I am just not familar with AC to DC power supplies and need help in the schematic.
So if anyone can help me with the schematic and the parts I need to get this done, I would appreciate it
Thanks!
Sharad

Actually there are masses of referrences to circuits and also to PSU's you can buy....
but here is a quick cct I put together for you
you can set the output voltage to anything between ~ 7VDC and 30VDC, if you use a metal cased LM317 (TO3 case) then 900mA to 1.5A will be no problem. make sure its bolted to a heatsink !!!

You are dealing with 110/120VAC - it can kill you, please be extremely careful.

cheers
Dave
VK2TDN

 

[Resqueline]

Just to add a note on the transformer voltage & power; to get 21V regulated @ 900mA you'll need the transformer to be at least 18V and 1300mA (23VA).

The calculation is done as follows;
Take the regulated DC voltage needed, add 3V for regulator headroom, add 2V for rectifier losses, and divide the sum by 1.414 to get transformer AC voltage.
If you want to safeguard against loss of regulation if the mains voltage should happen to be low you'll have to add 10% to the result.
Then take the needed DC current and multiply it by 1.414 to get transformer AC current. Multiply AC Volts by AC Amps to get the transformer VA rating.

 

[davenn]

Just to add a note on the transformer voltage & power; to get 21V regulated @ 900mA you'll need the transformer to be at least 18V and 1300mA (23VA).
The calculation is done as follows;
Take the regulated DC voltage needed, add 3V for regulator headroom, add 2V for rectifier losses, and divide the sum by 1.414 to get transformer AC voltage.
If you want to safeguard against loss of regulation if the mains voltage should happen to be low you'll have to add 10% to the result.
Then take the needed DC current and multiply it by 1.414 to get transformer AC current. Multiply AC Volts by AC Amps to get the transformer VA rating.

Thanks mate
I was approximating on that one was responding from work and didnt have all the data at hand hopefully between the info from the 2 of us the project will see the light on day

Dave