[ceencee]

Okay, I have picked my drivers out...I want to supply 25 amps to each driver at 170 volts. I have 3 drivers so do i need to bridge rectifier that puts out 3 times those amounts in volts and amps or is it just the volts. Since most bridge rectifiers are standard amounts ..do you just round up the number required?
If i have 120v ac going into the transformer,how many amps does it need to be also,my common knowledge says 3 times the motor amount,but thats a large load. I have the DC volts= AC Voltage x 1.414...but is the total combined voltage or just 1 motor. Any insight would be welcome, and i must say this cnc build has become such a learning experience, i think i might have to YOU TUBE the build just for memory sake lol.

Thanks
Wade

[Al_The_Man]

Is this the motors on your other post?
They show constant torque at 6.5A?
If you used the numbers you have, you would need a 9KVa transformer!
AC secondary is .707xDC, so you could get away with a common 120V secondary transformer if you wish.
The bridge rectifier needs to be sized for current and something called PIV (peak inverse voltage), or what the bridge voltage is subjected to when the rectifiers are reverse biased.
Bridge rectifiers are cheap so you can oversize without the need to size tightly because of cost.
So you need the I, current value, lets say 50amps and a PIV of, in the case of a bridge, 200~250PIV.
I don't see you requiring anything larger than 1.5Kva for a supply.
You also need 250vdc rated electrolytic capacitor(s).
By my reckoning you would need ~8000µf-12,000µf, for a DC p/p ripple of =or<10vdc.
My suggestion anyway.
Al.

[ceencee]

Thank-you Al....you are the man. I understand about 25% of what you said ,so after i do some research on what you stated so that i can understand the reason why you gave these numbers, i might ask a few more questions to get it down...i dont like just doing things, i like to know why they need to be done also. I will do some homework and get this figured.

Thanks
Wade

[ceencee]

okay..you are saying the voltage of the secondary winding of the transformer is equal to .707 x the DC voltage required for 1 motor. So 1 motor requires 176 volts DC max. 176 x .707 =124 which makes a 120 volt secondary winding acceptable. Ok....there are 3 motors...does this matter or having the three motors share the load is ok?
Hope im not way off base.

Thanks
Wade

[Al_The_Man]

If using one P.S. for all drives, then the voltage is the same whether 1 or 3.
The current will be a product of the combined current for the total number of drives, it is going to be seldom, if at all, where all three motors require maximum current at one time.
This is generally taken into account when sizing the KVA rating of the supply.
(.707 is the reciprocal of 1.414 you mentioned earlier).
Al.

[mike_Kilroy]

u r correct, u want 120vac secondary for about 160vdc bus. yes, all 3 motors work off this same dc bus. if 6.5a each rated continuous, AL was trying to tell u the xfmr would be around 6.5*3 motors*160vdc=3.1kva but not all 3 will work 100% at the same time so half that size shud be fine; thus his 1.5kva xfmr size. bridge rectifier rating shud be then 1500va/160v= 10 amp so buy the cheap $ 3.oo 25amp one. u r going right direction, keep going.

hee hee - looks like i wrote this at same time AL gave his similar reply

[ceencee]

Thanks guys...slowly beginning to make sense...if i have any more questions or aha moments i will let you know.

Thanks
Wade

[ceencee]

i see where i went wrong now...i was using the 35 max amp as my amp used per each motor and i was thinking that all the motors where being driven hard non-stop lol. Well i learned alot today...but the day is young!!

Thanks
Wade

[mike_Kilroy]

feel free to click on Al and/or my 'buy me a beer tab when you get-r-running!

[born2bewilder]

I've been working on a similar power supply for an as-yet unbuilt system. So, one caveat: my knowledge is all theoretical, at this point.

From searching ebay and surplus shops, I've not encountered much in the way so-called 'isolation transformers.' That seems to refer to transformers that don't change voltage from primary to secondary, e.g. 120VAC primary, 120VAC secondary. I have seen a number of 'control transformers' and 'general purpose' transformers. Typically (in the US at least) these seem to be 480VAC or 240VAC primary (or both) and 120VAC or 240VAC secondary (or both). If you have a 240 volt circuit available, this would probably work best.

I like to use the web form calculator at Online Calculator .:. Linear Power Supply Designer

A few notes on usage:
1.) This calculation seems to be extremely conservative regarding the smoothing capacitor volt rating requirements (165vdc output suggests 300vdc rated caps. Elsewhere I've seen it suggested that a 20% margin is fairly safe to assume).
2.) A high voltage supply probably would not need regulation, so ignore that parameter. Rather, if you insert the max desired voltage ripple, it will give you a reasonable capacitor size value (i.e. 165vdc output x 10% ripple = 16.5vdc voltage in the 'regulator' voltage drop field).
3.) I've heard it suggested that rectifier ampacity ratings should be at least twice what you expect to use. I've bought 50 amp bridge rectifiers off ebay for a couple dollars a piece (albeit from china). There are some 150amp modules I've seen for less than $20. If your volt ratings are enough (600v and 1000v units seem common) and you amp ratings are sufficient, it apparently comes down to having a big enough heat sink to keep it cool during operation.

I plugged in 37 Amps and it suggests an 8kva transformer is necessary. I've seen them on ebay at 7.5kva, 10kva sizes, mostly 480x240 primary, 240x120 secondary; I think these would work well. Since units this size weigh about 150 lbs, what kind of a deal you get might depend on whether you can find one locally.

Just curious, what drive are you planning to use? 25 amps per axis is some pretty serious power for any project. Is this for servo motors?

Let us know how it turns out when you get it figured.

-b2b

[Al_The_Man]

Just curious, what drive are you planning to use? 25 amps per axis is some pretty serious power for any project. Is this for servo motors?

Let us know how it turns out when you get it figured.

-b2b

Previous post suggest these are 6.5a @ continuous torque servo's, the 25a quoted was peak torque, usually max before demagnetization takes place, which should never be reached.
BTW, if the drive has isolated input control, and many do, it is possible and feasible to use 120ac direct supply without transformer.
This is done all the time with A-M-C drives and others that have built in P.S.
Obviously with this method you cannot connect P.S. DC common to earth ground, as you could with a isolation transformer.
But many do not anyway.
Also the link to the linear supply is a regulated linear, which is not necessary for stepper/servo supplies.
Al.

[ceencee]

b2b that 25 amps was almost full load for those servos. Al the Man steered me straight and told me I only need to use the continuous rating for the servos which is 6.5 amps. They are large servos.I got an industrial morbidelli u46 router less most of the control for nothing so im turning it into a 4x8 flat vacuum table unit. I still want to retain all the spindles and drill blocks but it is becoming very fun to figure it all out. Its a heavy machine, the base was weighed when i took it out of the scrap yard and it came in at 4200 lbs. The bottom screw on the x axis is 2" around i believe. I could never do a build of this caliber if it was not for the free router in the first place.

thanks
wade

[born2bewilder]

Ok. That clears things up. I bought a couple surplus servos myself, and it's troubling to try to find components that match up with it. One was rated 24 Amps continuous(75 Amps peak!), the other was about 30 Amps continuous. Drives that can power those are out of my price range...

Yeah, peak power would probably be considered a 1% duty cycle type of usage. I've read that general purpose transformers can often handle peak loads of 4x rated current for short periods (< 1min?). I would expect peak power could not be applied much more than that without overheating the motor also.

So, 60% of 6.5 Amps x 3 is about 12 amps. I read in another thread that you may have 3 phase power available. I think I've seen some 3kva 3 phase transformers on ebay before... cheaper than 1 phase ones. Good for rectification as well. Less smoothing needed.

[Al_The_Man]

Ok. That clears things up. I bought a couple surplus servos myself, and it's troubling to try to find components that match up with it. One was rated 24 Amps continuous(75 Amps peak!), the other was about 30 Amps continuous. Drives that can power those are out of my price range...
.

I have scooped a few bargains on ebay for the AMC 100a peak models similar to this ebay 160472811315, this is a sinusoidal version, if you have brushed motors you need either the plain 100A40AC or B100A40AC.
Al.

[LUCKY13]

I have trouble understanding all this electrical and I was wandering about the same thing for my setup.


My servos are 8.5 continues, peak at 38amps. They said they are 70v servo's but they match up in specs to some 90v servos of the smae size.


Voltage wiss if I understand right all I will loose is some RPM if they are 90v and I run 70v?


I have a 72v 6.5amps X 2 1000watt supply. This supply claims it will double up under load for a few minutes so I guess it can push 13amps per line at peak. It has two lines out.


Will this supply carrry these three servo's. It seems a bit on the low side to me but i am not sure if I am figuring right. I could parrallel both sides ( The supply company says it will do this) and get 13 amps that would peak at load at about 26amps, but it would have to feed all three motors.

Now my drives will limit to 20amps per servo, but there so on the edge for these servo's I am thinking about getting more drivers to run with them.

Al, will this setup play together?

What if I did get 40 amp drives? ( I believe they are 20amps with 40 peak).

What does it really take to feed these servo's like they should be? They are the common 850 servo's that most places sale around here. Its my thoughts that the better I get this all matched up the better it will work, and last. I do have a smaller machine I could take the drives and power supply and use with smaller servos if I have to. I have noticed others running the same setup as I listed having problems with tuning and faulting when they get a load on there machine. Ofcourse there can be other factors involved there, but this same setup with smaller servo's tends to run better than the bigger ones. I have only bench tested so far so its hard to tell much like that, but I am thinking its all on the edge of being enough power.

Thanks Jess

[Al_The_Man]

What kind of supply is this? does it have two separate DC supplies from two separate secondaries?
1Kva supply is about minimum for the motors you have.
Al.

[Jackal66]

Jess,

I have 90vdc Electrocraft servos on mine. They are 20 amp peak, 12 continuous.

Thanks to Al's help, I took windings off of the transformer, and got the voltage down to 77 VDC through the capacitor & rectifier.

Everyone said I wouldn't notice the difference in speed.

My transformer is 1.6kva, factory Hurco.

The new drives are Gecko 320x's.

Hope this helps a little.

JAckal :cheers:

[LUCKY13]

The manufacture I believe is Antek ( although this one came supplied through a different company under there name).


Yes it does have two DC outputs, each 6.5 amps continues. Antek claims there transformers will output double of rating for a few moments so each side should supply 6.5 amps, then peak to 13 amps under load, X 2 .


These servos are rated at 8.5 amps continues, with a 40amp peak. There will be four axis.


I have X & Y running on one side ( getting 6.5amps witih 13 peak), and the Z on the other right now.


It sounds like I am on the edge of bear minimum then with this PS. I had researched Anteks products and intended on running there 1500watt setup which has two sides, at 10 amps continues with a 20amp peak.

This is what I thought I was getting but after looking into it I can see this PS is not the 1500watt transformer, all though they claim it is 1440. It might be able to do something like that at peak, but if so the true 1500watt transformers would do even more.


I think this is going to put me at a comprimize with my setup and only very conservative tunning will allow it to work. Being dissabled this makes it kinda hard because I cant afford to make changes to it. If I can geather funds maybe by getting rid of something else I was thinking of buying a second PS from Antek. If I get a second one at 1500watts with 10amps per side I could take the first one and run it parralle and use it on the Z axis by itself. In parralle this would give it 13 amps continues with a 26amp peak. The driver will hold it back to 20 though.

Then I could use the second PS split with one side feeding the X and the other feeding the Y. This would give them 10amps continues each, with peak of 20 each ( matches the drivers perfect that way).


Might be a bit overkill but its the cheapest option I see right now. I would then have to add a power board with a regenerative breaking to keep everything under control from back EMF so it doesnt over power the drivers.




I understand that all axis will not be drawing at once, but these mills have a heavy head and that along, plus a few 100lbs on the table could get me where two axis was drawing hard at the same time.



One way to help this I believe wouldl be to run 4 or 5 to1 belt/gearing. This would help take a load off but I am having a hard time finding such gears that will fit my shaftes and servo's. If I stick around 3 to1 I can find gears but this is going to give higher loads and slower accell. But I will figure, or find something on this in time so its not big problem, just take some time or work.


Thanks Jess

[LUCKY13]

Thanks Jackal66


yea I believe Al know what he is doing for sure. In your case I wouldnt think the lower volt would be to bad. You have enough amps to carry your system and to me the amps is the real need, the volts will effect RPM which can be worked around. Those servos of yours are great quality also. Mine may be pretty good but I really dont think there anywhere near whats put into the ElectroCraft motors. Mine need alot of amps to really make there specs. Yea you can run them at lower power but on a heavy mill its going to cause some problems in certian condisions.


What hurts in my case is if I had gotten a little bigger PS it would be ok. I dont think you can do any tricks to make the transformer put out more amps, unless you start adding copper.

The difference in just weight between the 1000watt PS and the 1500PS is double. The 1000 wieghts 16lbs and the 15000 weights 30lb.

Jess

[Jackal66]

Jess,

It sounds like you have a good plan.

Antek was the brand I was looking at in case a transformer had to be bought.

Good luck, and keep us posted.

JAckal