[dmgdesigns]

I have 3 Relience E712 Servos. Will this transformer provide enough current? Should I just get a 12Kva? One of the many things that confuse me is the 60v ~22amp output, then it goes on to say 11.5 amp output. I noticed several people on the forum have these motors. What transformers do you use?

BTW is this a good price?


http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

My machine has 53"X34"X6" travel made of alu. plate thomson bearings 1" on X 3/4 on Y I added the material, motors, router, etc and the gantry weighs about 130 lbs. I plan on cutting 3/4 Oak, Mdf, Pine.

Thanks

[marvinstov]

I think there is a thread here somewhere discussing this particular transformer, can't remember if it's here or the Yahoo CCED forum. Sorry but that's all I can help you with since I'm not one of the all knowing and seers of electrons. (But I'm still trying to learn)

Marv

[arvidb]

*snip* One of the many things that confuse me is the 60v ~22amp output, then it goes on to say 11.5 amp output.*snip*

It says 22 amps at 44.5 VAC output. After rectification this becomes at best about 15.5 A at 60 VDC. (44.5 VAC * sqrt(2) and 22 A / sqrt(2) to make output power = input power.)

Also the text says "11.50 DC amps while running cool in the chassis". So I guess it either not runs cool at 15.5 A, or that the voltage have dropped a few volts at that current, or both .

Arvid

[jfirey]

I am the Ebay seller on these. Arvidb explains the conversion (and conservation) or energy quite well. The "11.50 DC amps while running cool in the chassis", helps to define the capacity. Many commercial transformers will run quite hot at full load. I have issues with the industry standard definitionof ful load. Many xformer suppliers rate FLA based on max core and insulation temperature, resulting in a HOT xformer. These are wound of much smaller wire gauges, resulting in high copper (I2R) losses dissipated as heat.
If your application can allow for some heat, though nowhere near as bad as commercial xformers, then you could run this for a 22~25 Amp DC load. Beyond this, you push the core design. The limits are the wire size (which is well oversized) and the core, which is good to just over 1900VA.

[jfirey]

BTW, The 11.5 Amp is the DC load, after a bridge rec and a cap, given a form factor of 1.8 due to the pulse current output using this style of rectification.

[CRFultz]

jfirey,
will you be selling more of these?
I won't be after this one ..Mark has it...but i will be needing one soon..
Chuck

[Bloy2004]

I have those motors too and will be using this power supply:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5712776324

It actually reads 52VDC (unless my meter is off). It is a switching supply but well made. Marisse said that switchers are just fine....just add the filter cap 20000uf or maybe two in parallel. This supply came already and performs great with these motors...used my existing g320 geckos.
one nice thing, it has an amp readout on the front that tells you what you are drawing under different loads.

[jfirey]

CRFultz/all,

No problem, I have several on-hand. Send me a PM, and let me know what current/voltage you need. These are handwound, so I wind them as needed, for whatever voltage/current needed.

Fair warning: I tend to wind them generously on the wire gauge. I have been beat up on this in the past. I won't sell little things that run so hot you can cook with them.

They don't run hot, they don't drop voltage much, and they'll handle a lot more load than I'll admit to.


My Rant
They are wound by hand, with multifilar winding techniques passed down for several generations. Every winding and each wire laid in as tight as possible. I do believe that any machines built can wind xformers like these. The advantages of multifilar winding techniques are not 'mainstream' because they cannot be automated. Combined with flat wire and new age strip laminated toroidal cores, these are the best xformers I can produce, and they are not available elsewhere.

I built them for my CNC/servo stuff and though some others out there might appreciate them as well.

The inductance is strong and each one is tested and trimmed for voltage before shipped.

Be aware, when we get above the ~48VDC range, you can get much more seriously zapped. Please be sure you are being safe.

Switchers:
Switchers will work fine, and it looks like the one above is a good deal. It is not always easy to find a high current switcher that will provide 100% duty cycle. It also involves waiting for one to show up on Ebay, or in your local surplus shop and then taking your chances on whether it works or not.

So if you can't find a switcher, battery bank, forklift charger, or the one you got doesn't work, these are available. And you don't have to bathe in high frequency EMF.

[Bloy2004]

yah! those toroids are nice!
I got one of these:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3823295926

on chance I could use it, but after applying 120VAC to the primary and rectifying it I ended up with 90+ VDC. Way too much, but have it until I learn how to bring the voltage down, or if I ever need the 90 VDC.
It is HUGE!

[jfirey]

Bloy,
I saw those also. I thought about getting some, but I prefer to run with my own. It wouldn't be right to build them and not use them, eh?

Bloy: Put a variac in front of this you'll have whatever voltage you need. Just turn it up and down! When they are gone, I'll still be here.

DO NOT USE A VARIAC WITHOUT AN ISOLATION TRANSFORMER. You risk become the conductor is certain circumstances.

[Bloy2004]

hah! Yah!...that's what I meant about "learning to lower the voltage" ! DANGER DANGER! I've been looking for a good buy on a variac....and the isolation trnsformer, But I really like that MPR25 supply.
By the way, at this time there aren't any of those big, huge, heavy toroids offered on ebay....they may be out.

[dmgdesigns]

Thanks for the help.

BTW, The 11.5 Amp is the DC load, after a bridge rec and a cap, given a form factor of 1.8 due to the pulse current output using this style of rectification.

What? :drowning: Right over my head.

This brings up another question, rec. and cap. V & A rating. Should the ratings be just enough to cover the max load that will ever be used and avaiable or it does not matter as long as it will cover the load?

[CRFultz]

Mark, I could be wrong, but I think the drives will pull what they need.
Someone correct me if this isn't right. VA is volts times amps...in my case I was thinkin that 10 amps would be more then enough to drive my steppers, and I wanted 48+vdc available so 480va rating on the transformer would be about right....I guess a switcher thats puttin out 48 at 25amps is overkill.
Other then the ac amp draw being higher, I don't think it's a problem. I hope not...done bought it.
Chuck

[jfirey]

The rec ratings should be more than enough to cover the amps. The amps result in heat across the rec, so it will 'burn up' if it isn't large enough. Try a 35 amp bridge, about $5.
The cap should be rated for voltage well above the run voltage. At least 85V, more like 100V if you can get it.
The drives will draw what they need in the sense of watts. The voltage (and the current) are pulse width modulated, or tuned on and off to achieve your desired current setpoint. This setting is a feature of your drive.
Think of the motors as 'watt consumers'. I am not familiar with your motors, but lets say they are rated for 100 watts at 60VDC max. You'll need 300 watts available for three motors to run at continuous rated torque. Peak ratings on the motors may allow a short duration at some higher wattage, say 500 watts. Allowing for a motor to pull peak watts, while the others maintain torque ratings might require 800 watts. Any capacity above this will not be used. A little oversizing of the power supply allows the transformer to supply more constant voltage wth less drop at FLA, and will run cooler.

[dmgdesigns]

Thanks jfirey
I did purchase the transformer and 35A 1000V rec. I will be using Gecko 320 drives.

These are the spec on the motors.

Nominal Voltage Rating 60V
Maximum Continuous Current 8.9A
Maximum Peak Current 44.5A
Motor Terminal Resistance .75-1.02 Ohms @ 4A

[Bloy2004]

Remember, you will have three motors that at some time under load may be drawing quite a bit of amperage. The 25AMP supply I feel is more than enough, but why not have that reserve?

I may be out on a limb here, but I think too that the quickness that a supply can put out the amps is a factor?

Any comments?

[jfirey]

Bloy2004,
I agree that reserve is good. You should have heard the criticism when I offered 1800 watt transformers. It doesn't really hurt to have it and not use it, as long as the inrush doesn't trip breakers. With your switcher, the inrush isn't an issue.

[Bloy2004]

If you are referring to the back amps/volts from an energized motor, then yes. I had switched off the DC output while the motor was spinning and it tripped the supply. i.e. the green led turned red, and I had to power down the supply to reset it. BUT...
I then used the 20,000uf cap and now it handles the situations.

[jfirey]

dmgdesigns,
If you intend to run these motors at 8.9 A /60VDC each to achieve max continuous torque, you'll need ~534 watts per motor. That is a pretty healthy load, near 3/4 hp each.

Assuming three motors, you'll need ~1600 watts to achieve max torque. This transformer will run at 1Kva and run fairly cool. It will run very warm at 1.5Kva . If you like, I can wind build you a 1.9Kva unit.

It really depends on the actual load you'll be placing on the servos. If you won't need all that torque all the time, than the 1Kva unit will be fine.

If you want the extra watts available, especially if you intend to run four motors, like on a gantry machine under high constant loads, you may need a larger one. If you want higher watts, just say so. It will take a few days to wind up the larger one. Either way, the labor of handwinding is about the same, and the additional copper costs are minimal, so same price.

J

[Bloy2004]

Jfirey,
would you have a web site or photos of your winding shop/area? I've always considered winding transformers as an art form rather than exact science. I'd like to see your equipment.

John