Thread: Building an electrical control box

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

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..

Yeah, thinking about it again I think I may have been making up problems.

Keep the pictures coming as it goes together.

Stuart

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.

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

Originally Posted by .RC.

In the box the components will sit on some 3 ply..

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.

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)

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

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...

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

Originally Posted by .RC.

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

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.

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.

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..

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