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Offline Hood

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Re: Power Supply Unit
« Reply #90 on: January 16, 2011, 05:08:04 PM »
I thought that aluminum is not a good conductor and I was planning to use a steel flat bar 1/8” thick to mount all the grounding wires.



Alu is quite a good conductor, lots of high voltage power cables are Alu, its not as good as copper but a heck of a lot cheaper. Another place its often used is transformers in big welders.
Hood
Re: Power Supply Unit
« Reply #91 on: January 16, 2011, 05:08:18 PM »

When there is that much metal involved, the difference in conductivity between steel and aluminum is negligible.  You have to get into pretty small wires, or pretty high currents for that to be of any concern.

Regards,
Ray L.
Regards,
Ray L.

Offline kolias

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Re: Power Supply Unit
« Reply #92 on: January 16, 2011, 06:53:15 PM »
That is a pretty impresive cabinet Ray and very well organized, thanks for sharing

I will assume the big round piece at the bottom of your cabinet is a toroidal transformer; the 2 big cables going to a terminal strip to the left and the 2 going to a board above it are they covered with some kind of a jacket? what kind it is?

Also when you say “The AC ground connection is tied, through a heavy conductor, to the 1/4" plate” how big of a conductor we are talking here? like 12 or 10 gauge?
Nicolas
Re: Power Supply Unit
« Reply #93 on: January 16, 2011, 10:14:30 PM »
Yes, some of the wiring is covered with split plastic tubing, available from most electronics stores, and some hardware stores.  Like this:

http://www.allelectronics.com/make-a-store/item/SLT-14/1/4-SPLIT-LOOM-TUBING//1.html

The ground wires should be at least as big as the biggest wires on that supply.

Regards,
Ray L.
Regards,
Ray L.

Offline kolias

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Re: Power Supply Unit
« Reply #94 on: January 17, 2011, 08:16:19 AM »
I was reading through a document from the web and noticed two paragraphs saying:

“There is a special consideration if the power supply voltage will be at or near the maximum
voltage rating of the drive. If the motor will be rapidly decelerating a large inertial load from a high
speed, care has to be taken to absorb the returned energy. The energy stored in the momentum
of the load must be removed during deceleration and be safely dissipated. Because of its
efficiency, the drive has no means of dissipating this energy so it returns it to the power supply. In
effect, instead of drawing current from the power supply, the drive becomes a source of current
itself. This current then may charge the power supply capacitor to destructive voltage levels.

If more than one drive is operating from the power supply this is not a problem since the other
drive will absorb this current for its needs, unless of course it is decelerating as well. For this case
or for a single drive it may be necessary to place a voltage clamp across the power supply in the
form of a zener diode. The voltage of this diode must be greater than the maximum expected
power supply voltage, yet low enough to protect the drive. A good choice would be either 82 volts
or 91 volts as standard values.”

Based on the above two paragraphs, I don’t want to sound like an expert or go against this forum’s knowledgeable people but I would like to know if we have sized the capacitors big enough to accept the motors deceleration energy or if I should install a voltage clamp across the power supply.

Nicolas

Offline stirling

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Re: Power Supply Unit
« Reply #95 on: January 17, 2011, 08:48:09 AM »
Hi Kolias - yes this is from the document I linked above - the geckodrive "stepper motor basics guide".

Personally I wouldn't worry too much about this. Note the opening sentence that you've quoted - "There is a special consideration if the power supply voltage will be at or near the maximum voltage rating of the drive."

Your PS voltage is going to be 34Vdc and your drive's limit is (if I remember correctly) 42Vdc. Not what I'd call "at or near" - others may disagree.

Even if you DID decide to be concerned - the solution would be the voltage clamp - not to increase the capacitor's rated voltage - others may disagree.

Ian

Offline kolias

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Re: Power Supply Unit
« Reply #96 on: January 17, 2011, 03:22:18 PM »
Ok Ian sounds good

I was disappointed today because yesterday I email my order to mpja.com (Canadians can’t order online) and today they phoned and said that they can only ship to Canada by UPS. Items imported to Canada with any carrier company go thru custom brokers and you pay their service fee, a minimum of $45.00 plus they add all taxes and duties and it becomes a very expensive item whatever you ordered.

With USPS you don’t have the above because items are processed in Canada by the Canadian Post Office who they only check the parcels at random. If you are the unlucky one then you pay all the taxes and duties but there is no brokers fee. On my present CNC I got all my items for free but on my 1st CNC I was caught once and had to pay $35.00.

So now I have no transformer and no bridge rectifier and the online stores I know they don’t have these items with my specs. I will try again to see if I can find another place to order these parts
Nicolas

Offline kolias

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Re: Power Supply Unit
« Reply #97 on: January 18, 2011, 09:42:51 AM »
I have located some transformers and bridge rectifiers and have list them in the attached one page Word document.

Can someone pls suggest which one meets my specs?

Thanks
Nicolas

Offline Hood

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Re: Power Supply Unit
« Reply #98 on: January 18, 2011, 11:04:20 AM »
For the transformer I would say probably this as the best

Avel Y236652 250VA 25V+25V Toroidal Transformer
Your Price:  $53.48 EA   
Sku 122-625: In Stock

Few others you could use but are overkill or getting right on the max voltage your drives can accept so probably not worth taking the chance.


Link to the rectifier is not working for me.

Got your caps sent off today, took them yesterday but they wouldnt accept as the plastic lathe tool box, I had them in, wasnt big enough for the customs label ::) Put them in a jiffy bag and posted today, they say 4 to 5 day delivery.

Hood



Offline kolias

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Re: Power Supply Unit
« Reply #99 on: January 18, 2011, 01:32:28 PM »
ok I will order the transformer you suggested Hood (unless there is another snag and fail again – seems I dont have a good luck sourcing my parts LOL

Digi-key have a weird site so I will copy the specs, like the transformers and post it back for suggestions

Much obliged for the caps and your help
Nicolas