[sixpence]

The hobby cnc board is assembled. I had to purchase a 20V AC 10Amp transformer . I am not sure as to where the capacitor fits into the circuit pls help.

[mvaughn]

I can't offer any help, but I do have a question.

I've been researching and looking at all the CNC information I can get my hands on. But it seems that the most elusive part of the equation is the electronics. I see pics of extremlely complex electonics setups involving transformers, huge capacitors, and toroids. I haven't been able to find out what this is for. Are they just home-brew power supply setups?

[Ferenczyg]

the Cap (-) to the (-) of the bridge diode and acting as the (-) of the supply , the Cap (+) to the (+) of the bridge diode and acting of the (+) of the supply.

I think the image will be useful for both of you. Just ignore the values of the example, or use the equations to prove if your values are OK

[Zagroseckt]

Well on most circuits the cap would be conected to the your hot lead (probly the red wire) That is an AC downstep right?

The cap should be there to help handle any spikes and to clean up the power.

I cant quite see the whole asimbly there but it definitly looks as if it's designed to be in series with hot.
Screw taped to boot if this stuff came ot you pre asimbled id say that dangling red line with the should screw quite nicly into it and the return on the other side (or the other end of the hot leading into the circuit.)

I'm saying this becos i dont thank a steper would use such a big cap on it's own....
Arouter moter would... but it would just be wierd in series with hot

Do you think you could give me a better picture of the asibly showing where all the wires are heading And any open ended red lines.
Thers enough info in that pic for me to guess but not be sure.
If you got a scan of the wiering diagram then i could definitly tell ya for sure.

[Zagroseckt]

hmm DC converter with a bridge rectafire. havent seen one of those diagrams since i was in school...

If that is the case that cap could simply be a filter running between poles yes ...
But isnt this missing somthing...
HAA im to sleepy to think...

Yes if the cap is merly acting as a line filter then conecting between (+) and (-) would be the way to do it. umm i'd maby stick a small resister in there someplace tho... ive seen that kind of filter pop the cap with a spike.
But it may have a built in stopgap.
Man it's ben so long since i've dumied up a circuit so much im so fregen used to switchmode....

[ynneb]

Have a look at this technical artical that is in the forum here http://www.cnczone.com/modules.php?s...ticle&artid=10

[DR-Motion]

"The hobby cnc board is assembled. I had to purchase a 20V AC 10Amp transformer . I am not sure as to where the capacitor fits into the circuit pls help."


Frankly, it scares me when I hear a question like that... from your picture I see a 75WVDC 18000 microfarad capacitor sitting next to a 24V 250 VA transformer... and a "where the capacitor fits into the circuit pls help"

Please take the time to learn a bit about power supplies before you start to play with this "toy" because if you blindly follow directions and hook this to here and this to there as suggested by well meaning helpers... you could be left in a potentially dangerous situation.

For example, suppose you hook up everything correctly... which means the wire from the labelled "+" terminal of your bridge rectifier ( looks like it is hanging off the edge of the table) and the wire from the labelled "-" terminal of the same rectifier are connected to the similarly labelled "=" and "-" terminals on the capacitor. Now you power up the supply ... well if you ( and please DO NOT DO THIS ) were to place a screwdriver across the terminals of the capacitor... it would probably melt in a far too exciting pyrotechnic dislay!

However if you were to unplug your supply and wait ten minutes and then try the screwdriver trick... IT WOULD STILL HAPPEN!

Large capacitors hold a LARGE charge.

To prevent this dangerous situation connect a 1K 2 watt resistor across the terminals (which means connect the plus to the minus with the resistor) of the capacitor. A 1K resistor will consume a mere 24mA and will ensure that the capacitor will discharge safely after the supply is turned off.

Excuse me for being such a worry wart but I'd like to read about your next success will your machine, hopefully typed with both hands intact.

Best regards Gary

[JFettig]

Make sure your capacitor is rated about 2x what your transformers 'rated' output is, Instead of 24v, youll end up with about 30v maximum, that is unless you suck everything it can put out hook up a voltage regulator.

A bridge rectifier(ac to dc converter) is needed to convert the ac current into ripply dc current, then the capaictor is used to 'un-ripple' the curent. Just a simple capacitor as specced in the gecko drive manual probably wont get all the ripples out, but its ok for the application.

Jon

[Clyde]

The instructions tell you to hook the CAP to TB10 +/-, it's there in the instructions.
Be sure to read the instructions (I'm not taking responsibility for it).
I have this kit also, and TB10 label gets obscured by the terminal block soldered into TB10.

[MisterB]

When I was a kid I found an old police car strobe assembly at the local landfill, with dual capacitors about that size. I hooked it up to a car battery and one thing lead to another and next thing I know I hear this loud bang like a .22 caliber pistol, and I ended up on my back in the dirt with a 3/8" crater in my finger from the arc. I learned my lesson about capacitors that day.

[DR-Motion]

Glad to here you're OK MisterB ( hope they didn't call you Master as a youngster ).

Capacitors can be dangerous but as long as you are aware of this fact they are exremely useful.

Remember Capacitors Don't Kill People... Wives who discover how much there husbands spent on that Damm Hobby Kill People.

Be safe everybody.

[m1911bldr]

I have the "factory kit" Hobby CNC board built. The capacitor goes to the "+" and "-" terminals on the power input terminal board, right next to where the AC inputs from the transformer go. From your attachment, it looks like you have Hobby CNC's silkscreened board and are adding your own components. If you do have the silkscreened board, you'll see a "+" and "-" pair of terminals as part of the terminal board for the transmormer inputs. This is where the capacitor connects ("+" to "+" and "-" to "-"). Like everyone is saying, be VERY CAREFUL once you have powered up the board. The capacitor will power the fan for about 15 seconds after you turn the power off and there is still a KILLER charge left in the capacitor even after the fan stops running. Put the board in a good case and INSULATE the capacitor terminals to save yourself some serious grief.

[sixpence]

I may have put my question badly but the info has been invaluable since my electronics knowledge is not as healthy as my as my respect for capacitors. That is why I am asking the questions to make absolutely certain that I don't make a mistake.(Well, trying not to make a mistake). Do I wire the power supply to the circuit board here?

[sixpence]

I am sure my dunce status in the electronics dept. is abundantly obvious since the word power on the board should make it clear.
I just don't want to mess it up and I am rather fond of my fingers.
Here are the wiring diags I have.

[sixpence]

here it is hopefully. Having trouble ataching it

[sixpence]

here it is hopefully. Having trouble ataching it

[sixpence]

"Remember Capacitors Don't Kill People... Wives who discover how much there husbands spent on that Damm Hobby Kill People"

I am the wife.

There are distinct advantages to this.
I have free reign to all household appliances. i.e. 1.the iron for etching the circuit board form Geoff Williams, Hobby cnc book
2. All glass bowls are freely available to use as acid baths.
3. No heavy lifting.I add those to the honey do list
4. I receive an abundant supply of help from hardware stores without damage to the ego because I am not genetically supposed to know what I am talking about.
5. I can get away with using terms such as doodad and thingymajig without anyone batting an eyelid.
6.Discounts seem to be in direct proportion to the length of my skirt in some sectors.
7. Best of all the grocery budget can get cut at will!!

[m1911bldr]

Yes! That's where the cap goes. Just be sure to connect the cap to the terminals "+ to + and - to -." My board is up and running and I'm very hwppy with the initial results. Now I'm messing with the pulse width and frequency trying to get the best top speed and the smoothest step-to-step operation of the motors. It's looking good so far.

[m1911bldr]

OOPS, forgot to mention that your transformer goes in the "AC" terminals and the cap in the "+ and -" terminals . The transformer doesn't have any polarity , since it's AC - just use the two secondary leads that give you the 30 VAC output on your voltmeter. If the transformer has three secondary (output) leads, one of them will be a "common" and it will read approximately half the total output voltage when read to the other two leads. In other words, if you have three output leads, say named A, B and C, you will see half the AC output voltage between A and B and half the output between B and C. You want to use A and C leads - they will read the "full" output voltage on your meter. Just cap and stow the third, or common, lead.

[DR-Motion]

"Remember Capacitors Don't Kill People... Wives who discover how much their husbands spent on that Damm Hobby Kill People"

Whoops, did I say that out loud?

No offence meant Sixpence... some of my best friends are female. My poor, male-centric thinking was influenced by the still relative scarcity of female techies ;-)

One thing I've learned is to test everything twice before committing to anything... at least I make less mistakes these days.

Bring up your power supply gracefully. Measure that all your voltages at the transformer primaries, secondaries, at the bridge, at the capacitor ... are all what you expect them to be... before connecting to your board.

This ritual helps keep the smoke in your electronics. This ritual works for building anything... test each subassembly before combining it to another ( already tested ) subassembly. It is the basis behind "Object Oriented Programming" and "Lego"

Peace, Gary