70 Volt, 1.5 Amp power supply Help!

Thread Starter

nenadilic84

Joined Aug 7, 2009
62
Hi, I'm working on some motor speed control project and I need a 100w power supply that has 70 volts output. Any suggestions on how to build the power supply. I need it to be compact and at the same time cheap :)
Maybe the best way is to build a transformer.
Power source is 220V 50Hz

Thanks,
Nenad
 

steinar96

Joined Apr 18, 2009
239
If it's a AC motor you might get away with a step down transformer. Otherwise you are looking at a big linear supply or a design heavy switch mode power supply. At least if you insist on building it yourself.
 

Tahmid

Joined Jul 2, 2008
343
Hi,
If your output is DC (assuming it is, as you mentioned power supply), a switch mode power supply won't be all that hard provided you have the experience and knowledge. If not then the linear transformer + diode + filter + regulation(if needed) method would be easier, although much more bulky.
If it is AC you require, only linear transformer will do. If you plan the SMPS route, then your power supply must have a full-bridge section to convert the dc to the required frequency.
 

Thread Starter

nenadilic84

Joined Aug 7, 2009
62
I have a signal generator, and I'm tyring to build an amplifier, but the amplifier requires a mentioned power supply, so I need 70 Volts DC and about 1.5 Amp from the AC grid (220V 50Hz).
Please direct me to some circuit or tell me where to start... I'm stuck :)

Thanks,
Nenad
 

jj_alukkas

Joined Jan 8, 2009
753
Its easy to build a PS from a transformer + rectifier + filter and mostly you wont need regulation as is for Amplifier.Its the cheapest soln. Do you need Dual supply??
 

Thread Starter

nenadilic84

Joined Aug 7, 2009
62
Its easy to build a PS from a transformer + rectifier + filter and mostly you wont need regulation as is for Amplifier.Its the cheapest soln. Do you need Dual supply??
I agree, but in my area I can't find a transformer suitable for my setup. I think I have to build a transformer. Dose anybody have an experience on that?? Help :)

Thanks,
Nenad
 

jj_alukkas

Joined Jan 8, 2009
753
Building one requires a lot of working knowledge and experience if its a big one like yours. If it was for just coil gauge calculation and length, it would be easy, but you also need to calculate the core and flux. There are people in this forum who can guide you. Wait for them. You could also order them online or from a dealer to make one for your specifications. I get them made for any non-standard voltage.Also a 220 to 35-0-35 transformer will work if you omit the centre tap and use only the ends. But then you will need one with over 2 amps or maybe 3. But it is an option.
 

t06afre

Joined May 11, 2009
5,934
Remember that the max DC value you will get from the transformer mentioned by Joseph Alukka will give you up to 70*1.41 volt and that may fry your motor, unless you regulate the voltage.
 

jj_alukkas

Joined Jan 8, 2009
753
Remember that the max DC value you will get from the transformer mentioned by Joseph Alukka will give you up to 70*1.41 volt and that may fry your motor, unless you regulate the voltage.
True, but when we get a transformer here, we ask for one which GIVES 70 after rectification. Sorry if it mislead you guys. Hope 25-0-25 would be fine for the case.
 

jj_alukkas

Joined Jan 8, 2009
753
Thats a big job. When you use a 25-0-25 itself, you need 1.5x2 = 3A transformer and voltage = 70.5
When you use 12-0-12, you get 35v DC and if you intend to use a voltage doubler, your current will half, i.e, you need to use a transformer with atleast 7A to get what you need considering the efficiency of such a circuit which is very complex. You could build an SMPS compared to building a voltage doubler.
 

Thread Starter

nenadilic84

Joined Aug 7, 2009
62
Thats a big job. When you use a 25-0-25 itself, you need 1.5x2 = 3A transformer and voltage = 70.5
When you use 12-0-12, you get 35v DC and if you intend to use a voltage doubler, your current will half, i.e, you need to use a transformer with atleast 7A to get what you need considering the efficiency of such a circuit which is very complex. You could build an SMPS compared to building a voltage doubler.
Any suggestions on building a SMPS??? Can you give me some directions on any book or html source or some basic circuit, I would be very grateful. I have an experience with 555 timers and software for circuit simulations.

Thx,
Nenad
 

jj_alukkas

Joined Jan 8, 2009
753
I am no expert on SMPS and its topologies. If you are determined to go for SMPS rather than simple transformer, I suggest contacting Tahmid, the guy on the third post of your thread. He knows a great deal on SMPS.
 

nicsky

Joined Aug 1, 2009
11
a quick solution might be to connect a low voltage high current amplifer say 12V to a transformer of apropriate current rating
you could use one that is normaly made for 120Vac
This would save you having to get a 70v DC supply
 

Thread Starter

nenadilic84

Joined Aug 7, 2009
62
Is there some one who can help me with building a switch mode power supply. I have experience with 555 integrated circuit and with software for simulation of circuit operation. Can you point me to some website or ebook on SMPS. I will appreciate your help...

Thx,
Nenad
 

jj_alukkas

Joined Jan 8, 2009
753
You can't use a PC SMPS for a dynamic amplifer. However there are certain classes which are linear. You can only use it on them. Best of all is to avoid using it.
 
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