power supply 30VAC 300VA

[guri]

Dear Gerald,

have you tested your

300VA toroidal power supply transformer:
Primary: 230 VAC single phase
Secondary A: 28 to 30 VAC, 9 Amp max (for the Gecko's driving half-coil PK296A2A-SG7.2 motors)
Secondary B: 8.5 to 9.0 VAC, 1 Amp max (for the PMDX-122 (and rectified for the limit switches if needs be)

(http://www.mechmate.com/forums/showthread.php?t=828&highlight=secondary+output&page=2)

You can recommend for same configuration?

I can buy locally in Argentina for U$77

thanks,

[Gerald D]

Yes, have tested and can recommend that specification.

[guri]

thank Gerald... I go by another part of my cnc project

[guri]

Dear Gerald,

I have the 300VA toroidal power supply transformer
Primary: 230 VAC single phase
Secondary A: 28 to 30 VAC, 9 Amp max (for the Gecko's driving half-coil PK296A2A-SG7.2 motors)
Secondary B: 8.5 to 9.0 VAC, 1 Amp max (for the PMDX-122 (and rectified for the limit switches if needs be)

I working in the power supply
I have calculated the following capacitors and rectifiers:

for secondary A:
capacitor 22000UFX75V
rectifier bridge 25A 200V

For secondary B:
capacitor 10000UFX50V
rectifier bridge 1.5A 200V

I have the right way?

[javeria]

guri

For secondary A: 10000uF 100V
For secondary B: 2200uF 25V

would be enough

calculated per the thumb rule that 1 Amp = 1000uF of cap reqd! and voltage rating of Cap to be double of the rated DC voltage.

Larger capacitance's would not help much I think, but if you already have em - then you can use em.

RGDS
IRfan

[lumberjack_jeff]

Is a capacitor on the secondary 9VAC winding for the PMDX really necessary?

I hope not, because my pmdx is running without one.

[javeria]

Jeff - if you read guri's first post he talks about using the same power for limit switches - may be thats why he want to convert it to DC - and hence the caps

[Gerald D]

The capacitor on secondary A has two functions:
1. Smooth out the ripple of the Alternating Current
2. Keep a reserve of energy when the motors need to make a sudden move. (Also provides a place for the motors to dump energy when they have to stop suddenly)
Mariss of Geckodrive suggests this formula: C = (80,000 * I) / V which results in (a) fairly large capacitor/s. A lot of guys have gone smaller without any obvious ill effects. Guri, I think your choice is fine.

Jeff, a capacitor (and rectifier) on secondary B is only required if you want DC to power proximity switches. Guri, the proximity switches are a very nice steady load, and you don't need to use the formula for the motor capacitors. I agree with Irfan that 2200uF 25V should be enough.

Regarding the rectifiers, I always tend to use something rated much higher than needed. This is because they are inexpensive, and the higher ratings are bigger and easier to mount. Then they don't need fancy heat sinks either. The 25amp rectifier for the motor drives should be fine, but a 1.5 amp for the proximity switches sounds a little small to work with. How big is that 1.5amp, does it have a mounting screw hole, can you solder wires direct to it, etc.? (There is nothing wrong to use another 25Amp for the prox switches. . . . )

[domino11]

Guri,
I would not be worried about the 75V for the secondary A winding. The 75V cap will be fine, they always have a surge rating on top of the posted rating. Sometimes this is marked right on the can. A higher voltage cap as Irfan mentioned is fine if you have it but are harder to find. :) ( and bigger)

[lumberjack_jeff]

Thanks Guys, I misunderstood guri's post.

Whew! :D

[guri]

I can buy locally in Argentina the following items:

capacitor 22000UFX75V GIGA 65X120 21.6A .003E SIE u$35.53
capacitor 2200UFX25V RAD.105ºC 20% 13X25 RGT CH u$0,30
rectifier bridge 25A 200V VI=80V $2.43899

I can not find:

22000uf x 100V

only:

33000UFX100V GIGA 75X165 27A .016E SIE u$75

Thank very much for help me

[javeria]

Guri - chk the local scrapyard - I have so many 10000uF 100V caps from old Uninterrupted Power Supplies (UPS)

and have used tham on all my electronic projects.

[guri]

Surfing the web I have found thid pictures about toroidal trafo mounting:

http://lh4.ggpht.com/_3jgN4hqBgZg/SjvIEXWzOnI/AAAAAAAAAc4/vI7HE7VApAo/s400/toridal%20mounting.jpg

http://lh5.ggpht.com/_3jgN4hqBgZg/SjvIEkg3_gI/AAAAAAAAAc8/qVlR3ILdnoo/s640/toroi%20mount.jpg

I think the mounting epoxy may have less cooling
what do you think?

[Gerald D]

The 22000UFX75V capacitor will work perfectly.

I will never buy a capacitor secondhand - they can be old and damaged. They are actually fragile, oil-filled devices which can corrode/leak and make explosions.

Our 300VA transformers are running very cool - the mounting method will not make any difference to the cooling. The metal disk + screw method is very common and I havn't heard of any problems with it. I cannot see the benefit of epoxy for this application?