high power supply

Thread Starter

spankey666

Joined Nov 30, 2011
91
I would like to make a high current power supply, i have 2 x 3.3kw transformers rated at 110v, i would like to take the voltage down to 10-25v. is it possible to put a triac based dimmer type circuit on the primary ?
ultimately i would like to make it variable cv and cc, but there is nothing i can find on google that will allow me to construct something to utilize the full current capabilities which wont generate loads of heat. so at the moment just a variable rectified dc output will suffice. should i try to reduce the voltage just using one transformer ? or would it be alright to run one off the output of the other bringing the voltage down to an estimated 60v and go from there ?
any pointers and links most welcome,
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
after more googling, it would seem that triacs on primaries dont work is it is an inductive load :( but what about on the secondary before the bridge rectifier ?
 

R!f@@

Joined Apr 2, 2009
9,682
Are u crazy....that things is 220VAC to 110VAC step down transformer...

U cannot use it to regulate anything concerning ur requirements....the voltage is simply too high for n00bs and it isn't easy to design high voltage supplies.
 

K7GUH

Joined Jan 28, 2011
190
Do NOT try to build a high current supply with that particular transformer. You might squeak through with a variac controlling the primary voltage, but that's something you would have to determine by trial and error. Better you should try to find a transformer which provides 60 volts at the current you wish to have. If this supply is intended to run anything important, do not try to cut corners with components that don't even come close to the desired voltage and current output.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
Are u crazy....that things is 220VAC to 110VAC step down transformer...

.
LOL .......More eccentric than mad :)
this is why i asked before going steaming in.
The reasons being I have several of these transformers kicking around.and as my ps has just died, I thought it would be a good opportunity to do some research first. (why spend money if you can make something you've already got work ? )
I've looked into controlling the o/p with large mosfets controlled by pwm, which looks do-able, but seeing as i dont require a nice smooth filterd output, i was looking to see if there was any other options. like a variac type of design. My ideal ps would cover 0-100v at as many amps is i can get at the 10-25v range, at higher voltages the current is less important for my application.
There is even less information on google regarding piggybacking 2 transformers.
so please humour me on this one,
If anyone can point me towards any links or any practical advice it would be very much appreciated.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
for starters, if i connect the second transformer (also 240v : 110) to step down again, what sort of current draw could i pull if its giving out 60v ? i'm not sure on the maths when a 240v transformer is only supplied 110v as i this scenario. both are 3.3kva,
thanks
 

R!f@@

Joined Apr 2, 2009
9,682
let's see...

220VAC ≈ 110VAC ( /2 ) = 110VAC >>> to 220VAC ≈ 110VAC ( /4 ) ≈ 55VAC

with two TX connected secondary to primary will give u an out put of 55VAC.
At 3.3KW, assuming 100 % efficiency u will get a secondary current of 3.3K/55 ≈ 60Amps /2 = 30Amps

Nothing is 100% effective so. U will need to load the Tx and find ur continues current rating. To do this U will need a resistive load like a umm...3KW Rheostat.

Find one and I will build ur PSU any day. :D

How's that for a start.
 
Last edited:

pilko

Joined Dec 8, 2008
213
The transformers are 220V/110V rated at 3.3 KW therefore the max secondary current rating is 3300/110 = 30 AMPS.
The OP also stated:-
" i would like to take the voltage down to 10-25v."

pilko
 

t06afre

Joined May 11, 2009
5,934
It is very hard to make a 0-100 volt high amp power supply. That at the same time do not need much cooling. So why do you need 0-100 volt and at the same time high amp. Can you tell us more about your application. That would help.
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
let's see...

220VAC ≈ 110VAC ( /2 ) = 110VAC >>> to 220VAC ≈ 110VAC ( /4 ) ≈ 55VAC

with two TX connected secondary to primary will give u an out put of 55VAC.
At 3.3KW, assuming 100 % efficiency u will get a secondary current of 3.3K/55 ≈ 60Amps /2 = 30Amps
excellant :) this is the bit i was confused with, with these transformers are designed so that effectively halving the input voltage, you can double the current available on the output, so why on the second transformer do i not get 55v at 60 amps (loaded )? where does the /2 part come from ?
 

R!f@@

Joined Apr 2, 2009
9,682
It's tht the secondary is always capable of 30 Amps....P = VI

Where 3.3KW = 110VAC X 30 Amps

The secondary coil cannot withstand more than 30 amps ( the wire gauge )

So now u can make a PSU of Variable voltage with a Max current capability of around 30 amps.
Voltage can be 0 - 70V DC.
 

pilko

Joined Dec 8, 2008
213
As I mentioned in post 13, the max rated secondary current is 30 Amps.
If you apply 240V to the first primary you will get 60V at the second secondary.
If you apply 120V to the first primary you will get 30V at the second secondary.
If you apply 110V to the first primary you will get 27.5V at the second secondary.
(I said 22.5V, that was a mistake.)

pilko
 

Thread Starter

spankey666

Joined Nov 30, 2011
91
I did make any thing more than 40V. I do have a schema of 0 - 35 V ..at 10 Amps
is it linear or sm ? ive found a couple of linear circuits on the web, but absolutely nothing on cc + cv pwm. except for driving LEDS. there also seems to be confusion with regards to CC and current limit on any psu designs ive found, calling CL cc etc. :(

i have now rewound the seconday to 24v 3kva.
so now i have 24vac and looking at the possibility of scr switching as ive done a bit of design on this before.
thanks for the help so far
 
Top