Transformer Question

[Bimmerkc1]

I picked up a transformer from Grainger today. I'm building the hobbycncpro kit and was trying to get a transformer that was rated at 24vac 10a.
The transformer they had is rated at 24vac 40a. Will the 40 amps be too much or will the extra amps just be unused overhead? i'll be running 3 200oz steppers and driving the hobbycnc board.


Thanks,

Scott

[Lionclaw]

The extra amps are not a problem. The board will only draw what it needs.

[scratch_6057]

Just for reference, what was the part number for
the transformer from Grainger? 120 Volt I assume?

I ended up using one from MPJA.COM ‘7846 TR’
( http://www.mpja.com/productview.asp?product=7846+TR )
on a HobbyCNC (pre Pro) board. After rectifier & caps
I’m getting 31.5 VDC, not quite the 33 calculated but useable.

[lerman]

Are you sure that you didn't get a 40VA transformer? That would be rated at 40/24 = 1-2/3 amps.

[erase42]

what is the purpose of listing a transformer that way? I use them sometimes doing hvac work, they are 75va or whatever. what is the advantage of this description instead of simply 24v 2a?

[Al_The_Man]

This question came up before http://cnczone.com/forums/showthread...ight=va+factor
The reason is a transformer is an AC device and depending on the load, the peak current and peak voltage may not coincide, therefore if the current and voltage are not in phase because of this, you would need a larger transformer.
For the average person building a DC power supply, it is usuall to use A x V for power rating of a transformer, and not be concerned with power factor etc.
Al.

[Bimmerkc1]

Thanks for the quick replys.
The part number from Granger is 6WU91.
It's price was $10.45
Here are a few pics.

Thanks,

Scott

[vulcom1]

Scott,
Wrong one. I would see if you could return it. Divide your va by the voltage and it gives you about 1.6A I think you need for 40amp at 24 volt about 960va
John

[scratch_6057]

Sorry but that transformer is rated 40 VA Not 40 Amps
that does come out to 24 Volts at 1.6 (1 & 2/3) Amps
the one I posted in the MPJA.com Link IS 24 Vac @ 10 Amps
$17.99 + shipping

You Could remove and replace the secondary from a
surplus Microwave Transformer, but that is hardly
worth the trouble for this (24V 10A) kind of output.

[Bimmerkc1]

Bummer, I guess that's the last time i listen to the counter guy.

[scratch_6057]

OK, Bimmerkc1 (Scott) had PM'ed me about the MPJA.COM
Transformer I had posted about. He had some wiring questions
and I did not see a way to attach a picture to A PM reply, so
I'm posting this diagram here for Scott and others.

You Guys who know more than me are welcome to reply,
just don't SMACK me too hard with that chair.

[Bimmerkc1]

Thanks for the great drawing.
We are having a killer ice storm in the mid west this weekend so i'm thinking it will be a great time to built my power supply.
Thanks again Mike and Al.


Scott