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5th March 2011, 07:34 PM #1Pink 10EE owner
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Building an electrical control box
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When I got my slotter earlier in the year it came with a broken and dangerous start stop switch that looked like this
I decided to make a much safer start stop system so as to not electrocute myself..
I bought a contactor off ebay with a 24V DC coil in it and also a green push start switch and an emergency stop switch. I then purchased a 40Va 415-24V transformer as the slotter has a 415V motor and I do not have 5 pin sockets in my shed (which would give me 240V at the machine) I also bought a bridge rectifier to convert the 24V AC from the transformer to DC to power the contactor.
I have made up a box to house the components out of 1.6mm steel.... It is not the best as I have no proper sheet metal working equipment but adapted a press brake to my press which allowed me to bend up paret of the box.... Parts of the box still had to be bent by hand and 1.6mm sheet is quite hard to bend with a hammer... It is drip proof and lockable though... And could probably withstand being run over without deformation.
In the box the components will sit on some 3 ply..
I have also made a panel fuse holder to house fuses for the transformer.... I would like to fuse the 415V before it goes into the transformer but I am yet to find 3AG panel fuse holders rated to 415V, 240V is easily available but 415V seem as scarce as hen's teeth..
I still have to do some more shopping for some glands for the input and output cables, the aforementioned fuse holders and 415V fuses, plus odds and ends... It does seem to be coming together OK for the time being..
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5th March 2011, 09:30 PM #2GOLD MEMBER
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16 gauge with a hammer(and I assume a vice?). "respect" lol
Shame you live so far north, there is an electrical control box on the bay sitting at $49
You think the 3 ply will live with that transformer hanging off it?
You may have a voltage problem but for the minute I'll leave that to others that know more, hopefully they will help or say that a 24VDC coil should be ok on 24VAC fullwave rectified.
Stuart
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5th March 2011, 09:55 PM #3Pink 10EE owner
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I have tested the contactor.... It works with 24V AC through the bridge rectifier... The transformer is only a kilo or a bit heavier... It is pretty small..
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5th March 2011, 10:09 PM #4GOLD MEMBER
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Yeah, thinking about it again I think I may have been making up problems.
Keep the pictures coming as it goes together.
Stuart
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5th March 2011, 10:25 PM #5
24V through a bridge will rise so your 24V will likely be in the mid 30sDC, it will be rough as guts and the chances of a long life for your coil aint great. There is a good chance though that radios ets for miles around will howl when this is on.
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5th March 2011, 10:51 PM #6GOLD MEMBER
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rrobor
I think I am right in saying
The V RMS after the bridge would be 22.6V.
The V RMS wont increase to 32ishV unless .RC. adds a cap.
Still 32ishV peak might still be a little high.
No idea about the radio interference, AM? FM? both?
Just as long as he doesn't mess with my Wi-Fi
Stuart
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5th March 2011, 10:52 PM #7
The usual convention is to build up the 'internals' on an aluminium panel instead of the ply you have used.
It is also usual to have a 'earth point' in the form of a stud (screw inserted from behind) on the panel and 'star' washer to bite in (hence to use of a conductive metal rather than timber).
I like the case.
It is best that DIYers use metal enclosures and ensure that each panel is earthed using a separate wire back to the 'earth point'. The alternative is 'double insulating' but it is definitely not for the uninitiated.
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5th March 2011, 11:00 PM #8Pink 10EE owner
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I was looking at the control boxes in my factory built machines and they use some plastic (bakelite?) material for the backing... I have drilled a hold in the box for an earth, as well the transformer frame will get an earth, as will the motor and the box with the start/stop switch..
The factory items is what I have been basing my build on... They are modern (newer then 2000)
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6th March 2011, 12:06 AM #9
Hi .RC,
You need to have a capacitor across the bridge output. Without the capacitor, the coil will probably buzz as the volts goes through zero, if the buzzing is bad enough to cause the contacts to break then you
could cause the RFI that roborr mentioned.
24V AC will give you around 34V DC when rectified and filtered, probably will drop to 30V or so under load depending on the size of the capacitor and the current drawn by the coil, (after the initial turn on surge).
So, check the ratings on the contactor coil, and see if it can handle the higher voltage.
Regards
Ray
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6th March 2011, 07:13 AM #10Pink 10EE owner
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Hi Ray, I have already tested it by connecting it to the 24V output in my milling machine... It did not chatter with the bridge rectifier in place...
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6th March 2011, 08:30 AM #11Pink 10EE owner
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I am wondering how many fuses I will need....
I would like to fuse protect the transformer... Should I just put one single fuse on one of the legs or fuse protect both input wires (since they are both active wires being 415V)
Since I cannot find any 415V rated 3AG fuse holders I was looking at using these
FUSE HOLDER DIN MOUNT - SOCOMEC 32A - gl Max (eBay item 180629355606 end time 23-Mar-11 12:03:00 AEDST) : Industrial
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6th March 2011, 10:17 AM #12
Use two fuses - one in each active.
The holder is a good type of fuse holder, but check that you can get a suitably rated fuse to suit your set up.
If you have trouble finding fuses (or fuse holders), try Swe-Check - The Fuse Warehouse . It might be worthwhile checking with them anyway as they have one of the most comprehensive ranges of fuses and associated circuit protection gear in the country.
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6th March 2011, 10:20 AM #13
I honestly dont know why you are spending so much effort when there are far simpler and safer methods. Use 240V and you can buy an off the shelf supply for 10 bucks regulated filtered and safe. What you have is a massive transformer when you only need half an amp or so. If you look at the powerfeed thread, that will show you the sort of circuit you need but you are making difficulties that you dont need. RMS is 1.414 but you have full wave and if filtered as it must be will be higher
a 240V input in a TV filtered gives somewhere about 360 or 370V so if you drop a zero there is where you are.
V=IR I=V/R R= V/I given that, you can find out by calculations the different points a 240V fuse will blow if you increase the voltage, At a guess say instead of say a 2A fuse you would use a 1A fuse. But again You are making it tough for yourself.
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6th March 2011, 11:02 AM #14Pink 10EE owner
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I don't have 240V... All the 3 phase sockets in the shed when installed by the electrician a few years ago were 4 pin sockets.. So I don't have a neutral to the machine or indeed any of my machines..
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6th March 2011, 11:12 AM #15GOLD MEMBER
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rrobor
If he uses a 240V supply the machine will have two plugs. One 415V 3phase and one 240V single phase. I wouldn't call that the best solutions either(although that is exactly what some of my machines have.)
Sure the transformer is over kill, I doubt he will need anything like 500mA but being to big isn't going to hurt anything.
Stuart
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