Thread: Building an electrical control box

the fuses you have do both the motor and primary side of tranny...mmm may I suggest that you protect the primary side of the tranny with fuses that are more closely rated to the capacity of the tranny

The 24V DC is because that is what was available on ebay at the time... $20 for 2..

Motor size is 2.2kW

I probably will fuse the transformer, but finding an appropriate 415V fuseholder and a fuse in 500mA is difficult.

what size is your motor?
i'll have a looksee for a suitable 24vac contactor you can have for zilch

that way you wont need to fit a rectifier

Originally Posted by .RC.

The 24V DC is because that is what was available on ebay at the time... $20 for 2..

Motor size is 2.2kW

I probably will fuse the transformer, but finding an appropriate 415V fuseholder and a fuse in 500mA is difficult.

just use these .... scroll down to page 127 code 37181 auto type fuse holders

http://www.legrand.com.au/en/en/libl...10_122-136.pdf

these din rail mount and are rated to 240v and is all you need on each leg of the tranny
each phase is only 240v to earth/neutral

there are also the glass auto type fuse holders available also suitable for din rail mount, but you will need to source them

Originally Posted by eskimo

what size is your motor?
i'll have a looksee for a suitable 24vac contactor you can have for zilch

that way you wont need to fit a rectifier

shhhsh!!!!
i'll read next time...2.2 kw eh?

I have a 2.2kw and a 4kw? contactor or is it a 7.5...hard to read ... its physically bigger than the smaller one so has to have higher capacity...the bigger one would have heaps of contact life under load for a 2.2kw motor

which do you want

both are new but shop soiled

one other thing...a standard HRC fuse holder and 2 amp fuse should be suitable if space is available

got lots of 2nd hand fuse holders 2...probably some 2amp hrc fuses to boot

Originally Posted by eskimo

just use these .... scroll down to page 127 code 37181 auto type fuse holders

http://www.legrand.com.au/en/en/libl...10_122-136.pdf

these din rail mount and are rated to 240v and is all you need on each leg of the tranny
each phase is only 240v to earth/neutral

there are also the glass auto type fuse holders available also suitable for din rail mount, but you will need to source them

So you think 240V rated fuse holders would do on each leg of the transformer?

The 2.2kW contactor would do for this job... The slotter won't be getting a lot of use.. Damn handy when it does though... I will PM you my address..

Hi .RC, Eskimo,

Nice one eskimo, I did say $20 was hard to beat, but looks like you've done it.

Regarding protection, have you considered using a MCCB circuit breaker rather than fuses?

Fuses to protect the transformer, would seem appropriate. And as eskimo says they should be sized to suit the transformer.

One other point, it is usual practice to kill all power when you hit the e-stop, that requires a separate latching contactor to kill all the power from the entry point down. I assume you only have one motor? If there was more than one motor you would definately want a separate isolation contactor.

Regards
Ray

Originally Posted by rrobor

If you are determined to build this thing, get yourself some 1000pf capacitors. fit one across each leg of the bridge. The 75ohm 5W is fine but not the 4700uF, that is overkill and a half. Maximum needed would be about 100uF. It it was me I would feed that to a 3 pin regulator. (input 36V, centre to neutral of system and output 24V) that needs a 0.001uF on input and output legs as near to it as possible, Also fit that on a plate of metal to loose heat.
So head to Jaykar or similar get a piece of fibreglass strip board with holes drilled. ($4.00)
Get 6 X 0.001uf (66c) about 250VDC capacitors a 7824T ($6.50) regulator A silicon washer ($1.50) for it or heat paste. some solder and advise some solder wick when you stuff up, and a 100uF63V low ESR105deg electrolytic (0.52c) and use a 10ohm 5W resistor (47c)
The stripboard has lines of copper so you have to cut and remove bits if you dont want the line to continue. Personally I would fit a 2.2 M ohm half watt resistor across the 100uF as a bleader when the power is off but thats not so important You will also need some insulated jumper wire to jump from track to track. If you have never soldered the only trick is keep the iron clean and heat the joint and with the joint getting heated add solder. If the board is dull polish it with oo steel wool.
Please note Prices are from another catalogue and were trade +GST
Other thing is I suspect you have some huge bridge block, If you have, get a 1.5A bridge (55c)
Put that together and you have a safe smooth supply and no issues.
Thinking on it I would add a small chofe (coil) on the output with another 0.001uF to neutral to reduce splash on switch off hitting the regulator.

If this how you would wire this regulator?

I drew this one in TinyCAD, a great little program for schematics like this.. it is free and I recommend it for quick and dirty work SourceForge.net: TinyCAD - tinycad

Originally Posted by RayG

Hi .RC, Eskimo,

Regarding protection, have you considered using a MCCB circuit breaker rather than fuses?

Fuses to protect the transformer, would seem appropriate. And as eskimo says they should be sized to suit the transformer.

One other point, it is usual practice to kill all power when you hit the e-stop, that requires a separate latching contactor to kill all the power from the entry point down. I assume you only have one motor? If there was more than one motor you would definately want a separate isolation contactor.

Regards
Ray

I thought circuit breakers a bit overkill for this application, and expensive..

It only has one motor and on both my mill and lathe the E-stop only kills the main motor... Lights and coolant pump still work..

Originally Posted by .RC.

If this how you would wire this regulator?

I drew this one in TinyCAD, a great little program for schematics like this.. it is free and I recommend it for quick and dirty work SourceForge.net: TinyCAD - tinycad

where ya gunna fit the contactor thats in the post..i note that its not included in your wiring diag


and I agree...Tiny Cad is good ......but I do prefer Visio

Originally Posted by .RC.

I thought circuit breakers a bit overkill for this application, and expensive..

It only has one motor and on both my mill and lathe the E-stop only kills the main motor... Lights and coolant pump still work..

Hi .RC,
Fair enough, that makes sense in this context.

Hi rrobor,

Regarding your earlier post on using a three terminal regulator for the (now not needed) 24v dc supply. I wouldn't recommend this approach for switching contactors, the problem is that the in-rush current often trips the overcurrent protection in the regulator and it goes into shut down, same thing often happens when driving large capacitative loads.
Second point is that the normal maximim Vin for 3 terminal regs is 35volts, this system is dangerously close to that limit, which would destroy the regulator anyway. You can get versions that have maximum Vin of 40 volts, so you would have to be carefull to get the right version.
Thirdly, you keep referring in you post to "neutral" i assume you meant to say isolated 24v ground. When you have an isolated supply, like this is, you don't want connections to neutral.

Hope you don't think that's being too critical, I just want to make sure someone coming along in 5 years time doesn't get the wrong idea.

Your comments earlier about EMI, are good warnings to keep in mind, but in reality, the amount of energy radiated is very small, and probably wouldn't even register outside the metal enclosure. Randomly resonant circuits of metal and stray capacitances not withstanding. I have, in years past done c-tick certification, I've got the odd few spectrum analysers kicking about, my favourite for this type of work is the Anritsu MS2651B, but admittedly I don't have calibrated antennas. I can borrow a Rhode&Schwarz with calibrated antennas if I ever need it.

Otherwise all good information, and well worth keeping in mind.

Regards
Ray

Originally Posted by .RC.

If this how you would wire this regulator?

Hi .RC,

I think we cross-posted, check my comments in the previous post, especially with regard to the Maximum Vin.

Edit: I think you have drawn a LM317 adjustable regulator in your diagram?

Edit2: With the 10 ohm resistor, that should stop the in-rush current tripping the regulator overcurrent protection.
Also you need to have a capacitor on the input side of the regulator 1000uF 63v should be ok. ( rule of thumb is 1000uf per amp)
It's usual practice to put a 0.1uf ceramic across the regulator output for high frequency stability as well.
The rest of your circuit looks fine, with those above changes, just check the Maximum Vin rating and you should be ok.

Edit3: I think you should be ok, for maximum Vin, I just checked a few manufacturers and most rate the 7824xx regulators for 40v Vin.
All the other output voltages are 35V max.


Regards
Ray

Here is the revised version.