transformer sources

[thielert]

I took a bit of a sabbatical from power supplies while building up my mill. Now it’s time to finish the control box. I am using 32v 10Amp servos with geckos.

The geckos say not to exceed 5 volts over the servos rating. The evil power monger in me interprets this to mean that you can exceed the voltage by up to 5 volts. I am open to arguments against this.

I will need around 35Amps between 32v and 37v DC.

I recall seeing that the voltage is increased when the AC from the transformer is converted to DC. What factor is this increase? I.e.: What voltage transformer do I need?

I hate to ask others to do my work for me, but I sure could use a hand in figuring out what toroidal transformer to use, what rectifier to use, and what cap to use. And then on top of that could someone point me to a reference on how to hook all of this up safely?

Thanks,
Tim

[Al_The_Man]

Tim, The voltage on a full wave rectified DC supply will be 1.414*AC, If you are using a bridge rectifier there is approx 1.5v drop across each conducting rectifier (1.5*2). For the Capacitance some use 7000mfd per amp.
It depends on how much ripple you want to tolerate, if you want to calculate using a calculated ripple voltage the formulae I use is (1,000,000*I/120)/Vr. = the total in MicroFarads.
Where I=Max amps Vr=maximum ripple.
In other words if you can tolerate a maximum of 2v ripple at maximum current of 35amps.
Then this would be 145,833 mfd round off to at least 150,000. So you would go up from this minimum.
Al

[radio-op]

This is a dumb question, but I'll throw it out there anyways: can you combine the output of two same sized, seprate cores, transformers? If I remember correctly they would need to be magnetically linked, yes?
Bill

[rdudley]

Unless your going to run all the servos at the same time at full speed you don't need all that current. I have eleven routers running and only use a 12 amp power supply on them. I don't see ever using the servos at full amperage on a cnc router. To test this just hook up one on the bench and see what current it pulls. Oh-oh, what a surprise!!! Now hooked up thru a ball screw you can even multiply the torque. Remember the turns your ball screw makes per inch, multiply this by the inches you want per minute for the router to move and you have your max rpm. Cutting through 1" wood pine I can cut at 40" per min which means my servos are running at 200 rpm! That is a long way from the max amperage of the servo rating. Mine run at less than an amp for the most part and that is under quite a load!!! For rapid moves without a load it is probally at its highest pull. I would be interested in hearing from anyone on this subject since I'm electronic as well as tool and die and have built several routers and tested them under varing loads and speeds of cutting different materials.

Originally posted by thielert I took a bit of a sabbatical from power supplies while building up my mill. Now it’s time to finish the control box. I am using 32v 10Amp servos with geckos. The geckos say not to exceed 5 volts over the servos rating. The evil power monger in me interprets this to mean that you can exceed the voltage by up to 5 volts. I am open to arguments against this. I will need around 35Amps between 32v and 37v DC. I recall seeing that the voltage is increased when the AC from the transformer is converted to DC. What factor is this increase? I.e.: What voltage transformer do I need? I hate to ask others to do my work for me, but I sure could use a hand in figuring out what toroidal transformer to use, what rectifier to use, and what cap to use. And then on top of that could someone point me to a reference on how to hook all of this up safely? Thanks, Tim

[doug6949]

35 amps? I'm guessing that you have multiplied the max motor current by the number of motors to get this figure. If so then your supply is going to be overkill. For cnc servo applications you will only need half that capacity as the motors only hit this current during acceleration. And it is rare for more than two motors to be pulling against a cut at any given time.

Doug

[Al_The_Man]

Originally posted by radio-op This is a dumb question, but I'll throw it out there anyways: can you combine the output of two same sized, seprate cores, transformers? If I remember correctly they would need to be magnetically linked, yes? Bill

If you mean in series, no problem, but transformers intended to be paralled are would bifilar i.e. wound together for accurate balancing. So you may have a problem in parallel if they are not completely the same, also you would need to phase them correctly.
Al

[Phooey]

you wouldn't have to worry about anything if you used two rectifiers and combined the DC though, is this right?

[Phooey]

Sorry i forgot to ask this in my previous post- its been mentioned that you can overvolt the stock steppers (i have a bridgeport series 2, BOSS6, 50V originally i think) as long as the amps are controlled (people were saying < 8A, yes?). 74V seems scarry- is this safe, or should i use 65V @ 15.4 amps max (the supply, not motor current). Just trying to chose between two different torroids (46V 1KA, 52V 1.5KA). How much is "beefy" and how much is TOO much? Thanks!