Need Help Before I Kill Myself!! (Aka: How do I connect Transformer)

[diarmaid]

Hi all, sorry about the dramatic title, Im nearly ready to connect my HobbyCNC kit upto some electrical power. But I have a few questions otherwise I might end up a sticky mess! The connected transformer in the 2nd pic below is NOT MINE. Its from the sellers site.

Ok, I will ask the questions one at a time and move on after I have an answer so no-one gets fed up reading!

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[diarmaid]

I have a transformer as shown in the pic's below. I also have regular 13Amp Mains cable to run TO the transformer. I have 10Square cable to run FROM the transformer to my rectifier, smoothing cap and on to my driver board. I need 24V coming out of the transformer, and it will be at 500VA (Approx 24Amps). My mains voltage is 220v.

Shown below is the terminals on the transformer, and I re-wrote the text on the sticker so that it could be read. I also re-wrote into the pic the numbers on each terminal.

SO:

Into which terminals do I connect my Live and Neutral Wires from my Mains and Into which do I connect my Live and Neutral wires of my 10^2 grey cable ?

Thanks a lot folks. Please don't give me any guesses as Im trusting my life to some strangers on the internet here. Im not an electrician!

Edit: I have typed up the instruction sheet shown below and posted it in the next post. Thanks again in advance.

[diarmaid]

Here are the instructions in the photo in the previous post.
I inserted the red line myself to show where the screencaps changes because I couldn't fit it all into one pic.

Im thinking that my Inputs are terminals 2 & 4, and my Outputs are terminals 5 & 8 with a connecting wire from 6 to 7. Maybe someone can confirm this. Also If this is correct Im not sure whether the live should go into 2 or 4 and the neutral 4 or 2 respectively. Likewise for live and neutral with 5 & 8. Thanks.

[pastera]

For a 240 volt input your input terminals are 1 and 4 with terminals 2 and 3 linked. This puts the two primary coils in series.

Output is between terminals 5 and 8 with terminals 6 and 7 linked. This puts the two 12 volt coils in series for 24volts out.

You can hook this up through a 75 watt light bulb (incandescent) to limit current in the event of a miswired connection.

Aaron

[diarmaid]

Great, thanks pastera.

Now for my second question.

As you can see in the above photos my 13Amp mains cable is 3 core, and in the photo below I have wired my plug to include the earth connection.

A) Is the external place indicated on the photo below anything to do with my earth connection?
I think not, because of the Note in the instructions as shown in my previous post that says "The center tapping of this winding has not been taken to earth but this can be done by linking between terminal 6 and earth"

However if I connect my mains earth wire to terminal 6 how does this affect your previous instructions and do I connect the earth from the other side (ie: My driver board side) of the transformer anywhere??

B.1) Essentially, do I connect the earth, and if so, how?

B.2) If not, should I disconnect the earth on the plug and cut it back to the white shell?

Thanks again for any help.

[diarmaid]

Argh! I forgot to ask Pastera or anyone else. referance Pastera's post number 4, do I put the brown (live) wire into terminal number 1 or number 4?

And on the output side, do I put the brown (live) wire into terminal 5 or 8?

Does it matter which way around the live and neutral are?

Thanks.

[diarmaid]

Ok, since Im impatient and I've had no reply about the earth wire yet, Im going to try without connecting the earth and see how it goes. Fingers crossed!

[diarmaid]

Oh no...

I connected up terminals 1 (Positive) and 4 (Negative) and linked between 2 and 3. Then I decided to check my voltages at the input and output terminals before going any further.
I used my voltmeter on the output terminals and wasn't getting ANY reading between 5 and 8.

So then I decided to check my 220V between 1 and 4. I touched my negative off terminal 1 and my positive off terminal 4. When the positive touched 4 there were sparks and I tripped a fuse switch in the house. Terminal four is covered in black oily burned looking stuff and the tip of my voltmeter negative lead melted onto terminal 1.

What went wrong?

Im going to try again but need advice first. Will my transformer even work now or did I just destroy it?

Im very upset. Wanted to get my driver board tested tonight.

[bigz1]

I am going to put the earth to my metal driver case. I am using 6 pin connectors to hook up my steppers, and 3 pin(1 pin not used) connectors for the homing/limit switches. All wire is shielded and will be earthed one end to the case. This way I can discount the driver case and plug it in on another machine.

[djake89701]

Just a guess here. but it sounds as tho you connected your meter set to read amps across the 220v main. it would be normal for the circuit breaker to pop under this condition and your transformer should still be fine.

As for your ground wire, this is connected to the chassis of the housing,the transformer is also bolted to this housing so i usually use one of the mounting bolts and a ring terminal to make this connection.

As for earthing term 6, this center tap and output is not described as being used for your desired purpose but the reason grounding it would be desirable(for one who would want it) is that this would allow full wave rectification using 2 diodes.creating a dc supply of aprox 170 vdc. or using a full wave rectifier a split supply .. +170vdc and -170 vdc with common at earth ground.

hope that helps.. id try you test again with your meter set to measure volts. if your meter is like mine pay attention where those probes are plugged in. this is a common "got ya"

[diarmaid]

Thanks for the advice folks.

djake: I apologise for my lack of experience, but I have three plug slots on my meter:
'10 ADC - Max 10A UNFUSED'

'V[ohm symbol]mA' and below this in red it says 'CAT II MAX 600V 200mA Fused'

'COM 600V MAX'

which should I plug the red and black leads into?
Thanks.

[jderou]

Black in the 600v com (common), red in the 'CAT II MAX 600V 200mA Fused'

[diarmaid]

Thanks jderou. that worked fine. I also tested it on a 1.5V battery first this time!
New problem! Im getting 225V across my input but nothing across my outputs. Im thinking maybe its because the connections need to be made between them so Im going to connect the relevant wire and I'll get back to you all. Transformer is at least still working!

Thanks for the help. I was quite nervous (In a mature respect for electricity kind of way) every time I had to touch my leads off those terminals!

Brb.

[diarmaid]

Thanks folks. I now have 225V Input, and 23.7V output!

Now for question 3! ........and a sub kinda minor-question!

Below is shown my 50v 25Amp rectifier and my 25V 27,000uF Capacitor.
I assume that I simply connect these in series, rectifier first followed by the capacitor. If wrong please correct me.

So:

These each have 4 unmarked terminals.
Which terminals do I connect the live and neutral wires to?

I will go and add some heatshrink tubing onto my transformer wires while waiting for a reply. Thanks.

Minor question: I want to check my output amps from my transformer. Which slots on my ammeter do I plug my red and black ammeter leads into to do this? (I've forgotten what I had them in during the earlier unpleasantness!)

[diarmaid]

Here's is two pics of my connected transformer to keep everyone interested!

Can anyone answer the question in the previous post please?

[Al_The_Man]

Make sure your ground conductor connection is not connected to any primary wires, use the ground stud provided, leave all secondaries unconnected you should read 12vac between each secondary 0-12 outputs.
If you make a mistake series-ing up the secondaries you will not do any thing drastic like connecting in parallel the wrong way, as all that will happen is that the output will be zero across the outer ends.
The bridge rectifier has a flattened corner, this is the DC +ve, the opposite diagonal corner will be the DC-ve.
The other two with the ~ sign is the ac input, again, diagonal corners.
Do not ground either ac secondary, I personally prefer to ground the DC-ve and set up a ground bus where this would be taken to, some systems frown on this, but I always do it as a matter course if it is possible.
The ac secondaries connect directly to the ~ signs and the capacitor + & - connect to the bridge + & -, directly,
When feeding amplifiers/drives, take a pair of +- to each amplifier from the bridge/capacitor, do NOT daisy chain from one amp to the next.
Hook the rectifier up first if not sure and check for DC output.
Al.

[diarmaid]

Thanks Al. I think I got most of that. Still not sure what you meant about the ground. Where exactly is the ground stud provided?
going to try and connect the rectifier now and the capacitor and see what happens.
Brb.

[Al_The_Man]

Thanks Al. I think I got most of that. Still not sure what you meant about the ground. Where exactly is the ground stud provided?
.

It is the copper lug you showed in one of the photo's bolted to the txfmr frame.
Al.

[djake89701]

on that bridge rectifier.which is square except for that one corner that looks flattened. that corner is + -(neg) is in the corner oposite an the two remaining are ac in

[diarmaid]

Thanks for all the advice folks. It all seemed to work out ok.

I have 24.6V Going INTO my rectifier.

58.9V Coming OUT of my rectifier INTO my capacitor (Its only a 35V capacitor.....hope thats output voltage!)

29.8V Coming OUT of my capacitor. Woohoo.

Al, thanks for that, so would I be correct in saying that I just connect my mains earth wire to that copper lug?

Thanks again.
Im going to try to test my driver board now and I'll post up pics. My setup is far from permanent. I have to build a wooden box for all of this to sit into, its just kinda hanging there at the moment!

THREE LAST QUESTIONS (I think! )

1) Connecting the positive and negative 10Square wires to the poles on my rectifier and capacitor is a pain in the b*#t. The wire is SO thick and the connections so small. Do I really need such a thick wire coming out of my transformer? Its only going about 12inches to the rectifier and another 4 inches to the capacitor and another 12 inches to the driver board.

2) There is white powdery stuff coming out of the 10square wire when I cut the outer shell. It seems to be around the inner unshielded core. What is this?

3) What slots do I plug my two ammeter cables into on my ammeter to check the amps coming from my transformer?

Thanks again for all the advice folks. Im not electrocuted!! (Touch wood)