Power supply help

[osdhillon]

Hi,
I need help in determing the power supply for the following DC servo motor.

nominal terminal volt = 120

Max continous current = 4 amps
Max Peak current = 20 amps

I looked at various threads and am able to inderstand some of the terms, but I am not a electrical guy. If I am provided with the diagram then I can solder and assemble it together.

everybody suggests torodial transformer (What specs? I am using 4 motors so 120X4 = 860 VA. On Plitron website I can see one at 1500 VA with 117 volts output, does that means 1150/117 = 12.82 amps. Is this amps enough?)

Also what else do I need to construct the power supply. What kind of bridge rectifier, capacitor etc, wire gauge etc. Your input is appreciated

thanks
Onkar

[Al_The_Man]

Are these 120v DC motors? you could probabally get away with that VA as allowing for average duty cycle, you will probabally never pull 4 amps on each motor at once, the 20 amps is the peak rating of the motor which you should never see if the amplifiers are capable of current limiting to 4 amps. You will need around a 85vac secondary to give you the 120vdc. The Capacitor size will depend on what your required DC voltage will be.
You can use a 12,000µfd capacitor to give you 2.5% ripple at 12a 120vdc.
Al.

[osdhillon]

Al
Yeah These are 120v DC motor. The transformer I specified, Is it the right one? What kind of brige rectifier and capacitor I need. What else do I need. I already built one using the kit fron Dan. That one is running is fine (36 vDC 25 A). Does somebody have schematic for torodial one. Thanks
Onkar

[Cyclone]

you might want to pick one up like this...toroidal ...Can't beat the $15.00 price considering that they sell between $100 - $200..unwrap the outer primaries (easy job) and rewind with 12 or 14gauge wire to up the amps(16gauge now) I also used the help from this forum and the great guys here. I posted this schematic a few days ago on another thread but here it is anyhow, hope it helps.

[Al_The_Man]

Originally Posted by osdhillon Al Yeah These are 120v DC motor. The transformer I specified, Is it the right one? What kind of brige rectifier and capacitor I need. What else do I need. I already built one using the kit fron Dan. That one is running is fine (36 vDC 25 A). Does somebody have schematic for torodial one. Thanks Onkar

The one you indicated in your first post was 117vac, this would give you around 165 VDC when rectified and smoothed, Take the desired DC voltage that you want to end up with and multiply by .707 +2 equals the secondary AC voltage of the transfomer you need.
These motors ideally should be run at 100 to 120vdc, otherwise you will not get the maximum power out.
A torioid is wired exactly the same as a common square type as far as primary and secondary connections are concerned.
Al.

[osdhillon]

Al
thanks for clearing things up. I was under impression that the volts specifed are DC (I wasn't aware of the rectifier converting AC to DC) Does the DC amps remain the same as AC amps. To run motors fully at 120 vDC I figured 120*.707+2 = 86.9 vAC
I am getting one from "avellindberg", the specs are 1000VA (secondary volt = 45+45)
ie 90 volts (which gives 125v DC output, 11.11 amps) the other one is (Secondary volt =40 +40) which gives 110 vDC,12 apms. Which one do you recomend? how about the amps. This is part I am having hard time to understand. Do I need total of 16 apms (4 motors at 4 amps each) or less?

cyclone , your schematic is great, thanks, I have to modify it to my specs. Any suggestions?

Thanks
Onkar

[ViperTX]

You should be fine with either toroidal transformer...but before you proceed....which driver are you using to drive the servos?

[osdhillon]

I am using MACH3 controller and probably Rutex drives. I am very comfortable with Gecko, due to voltage limitation I have to go to other source.

How can I convert 12 amp into 20 or 30 amp. What is the real purpose of the capaitor? Does it do more that just storing the power? Does it increases the amps too ?

If I cannot increase the amps, then should I connect two transformer in parallel to get the desired amps. What safe amps should I looking at (4 motor 4 amps each at full load)

thanks
Onkar

[DieGuy]

The general rule of thumb for transformer sizing is about 2/3 total load. It is unlikely that you will be drawing full load on all 4 motors at the same time.

[osdhillon]

Originally Posted by Cyclone you might want to pick one up like this...toroidal ...Can't beat the $15.00 price considering that they sell between $100 - $200..unwrap the outer primaries (easy job) and rewind with 12 or 14gauge wire to up the amps(16gauge now) I also used the help from this forum and the great guys here. I posted this schematic a few days ago on another thread but here it is anyhow, hope it helps.

What is the max amps I can get out of it ans using what gauge of which wire. Sorry to ask so many questions at once but I am trying to learn
Thanks
Onkar

[Al_The_Man]

Originally Posted by osdhillon I am getting one from "avellindberg", the specs are 1000VA (secondary volt = 45+45) ie 90 volts (which gives 125v DC output, 11.11 amps) the other one is (Secondary volt =40 +40) which gives 110 vDC,12 apms. Which one do you recomend? how about the amps. This is part I am having hard time to understand. Do I need total of 16 apms (4 motors at 4 amps each) or less?

I would go with the 40+40.
As two of us have pointed out you probabally will not be drawing full load at any given time, theoretically the full load would be 4x4=16amps only if the motors were all in a full load state, in normal use any motor can be anywhere from 0 to 4 amps at any given time so a duty cycle factor is used to give you an average.
The output of the rectifier is a 120 cycle ripple so the capacitor is used in order to provide steady state DC as near as possible under all loads.
There is plenty of information in previous posts as this subject has been covered many times.
Al

[osdhillon]

AL

Thanks
Looks like I am on the track. Once I get my parts in, Probably I will help again (Wnat to do it right the first time). I was recommend from the guy selling me motor to use 750 VA each axis along with recifier and capacitor for each axis and the price near to $ 200 each axis.
Thanks
Onkar