500VA Toroid - Relay or Contactor?

[Neale]

Those look like useful little devices, Lee, and a good price. One thing that they never seem to tell you, though, is the coil operating current which would be useful for the OP trying to decide if his 24V PSU has the spare capacity to operate it. Personally, assuming that transformer switch-on doesn't trip the supply breakers, I wouldn't bother with a soft-start at these relatively low power levels and just switch directly. Mine seems fine without (650VA toroidal).

Here's a question for the gang, though. Like a lot of small contactors, this is designed to handle 3-phase and therefore has 3 main N/O contacts. If you are using it on single phase, would you just use one contact, wire all three in parallel, or all three in series?

[Lee Roberts]

Those look like useful little devices, Lee, and a good price. One thing that they never seem to tell you, though, is the coil operating current which would be useful for the OP trying to decide if his 24V PSU has the spare capacity to operate it.

Well I do know the models of a DC flavour have low consumption coils, the idea is you can use them with a PLC directly, no interface relay required.

I probably don't know enough to comment but I would think the coil uses such a small amount it would be negligible?

Catalog: Miniature Contactors CWC
http://www.weg.net/files/products/WE...re-english.pdf

[Neale]

You have to dig deep in the catalogue to find the numbers, but it looks as if the 24V DC version takes around 150mA. The low-power version is about half that.

[Lee Roberts]

You have to dig deep in the catalogue to find the numbers, but it looks as if the 24V DC version takes around 150mA. The low-power version is about half that.

So the question now is...can m_c spare the 150

[m_c]

So the question now is...can m_c spare the 150

Should be fine. I've got 2.1A of 24VDC, which sole purpose in life now the old controller is gone, is to power a few relays and sensors. If need be, I can upgrade it or fit a second supply.
.
I've ordered a suitable ABB contactor that only takes 3.5W coil power from RS, as I get free next day delivery. I even ordered one with a NC Aux contact, which I can use to switch in a drain resistor for the capacitor, rather than have the resistor continually warming things up.

[Lee Roberts]

Should be fine. I've got 2.1A of 24VDC, which sole purpose in life now the old controller is gone, is to power a few relays and sensors. If need be, I can upgrade it or fit a second supply.
.
I've ordered a suitable ABB contactor that only takes 3.5W coil power from RS, as I get free next day delivery. I even ordered one with a NC Aux contact, which I can use to switch in a drain resistor for the capacitor, rather than have the resistor continually warming things up.

Good stuff, I like the drain resistor idea its also something I thought about doing for the caps on my driver PSU, dont forget the pics once installed ;-).

[Tom J]

I use the softstart, via 240v switch, than contactor via fail safe latching, but after reading few post will try MCB type D without softstart - will upload results.

Meantime here is my softstart



It switch primary coil via 4x10W resistors just to kill in rush current and after second small relay bypassing resistors before they became too hot. This delay is enough for peak to go down.
This is only inconvenience for toroid trafo I know.

[cropwell]

Hi

I have had a dig around the WEG site and I saw consumption figures for the CWC16 coil. The C03 coil takes 2.6 to 3.7 Watts and the L03 coil takes 1.7 to 2.7W. 2.7W at 24v is 113 mA, so it shouldnt tax the power supply a great deal.

I have just measured an ABB contactor with a 24v AC coil which gives 5.5ohm - that would be taking about 100w on 24vdc, I don't know what the impedance to 50Hz AC is, but it still seems a hefty whack.

The WEG wee beastie is pricey though in the WEG catalogue - so £12 from Chalon seems a damn good price, especially if you get the L03 coil.

Cheers,

Rob

[routercnc]

Here's a question for the gang, though. Like a lot of small contactors, this is designed to handle 3-phase and therefore has 3 main N/O contacts. If you are using it on single phase, would you just use one contact, wire all three in parallel, or all three in series?

If I understand the question I connected live and neutral (brown and blue) to the contactor so they were both switched. See second photo in post #102. Earth was permanently connected elsewhere. I controlled the switching using 24V DC logic (white wires) from the estop circuit
http://www.mycncuk.com/threads/6988-...cnc_MK3/page11

[Neale]

That's a good answer to a slightly different question! No problem at all with that, if you want to switch neutral as well as live. Perfectly reasonable thing to do. What I was thinking about more, though, was the case where you are just switching live (which is what I do, and leave neutral connected). In this case, you might think of putting the contacts in parallel, to reduce the current through each contact by sharing it across all of them. However, when you switch off (probably worst case for arcing at contacts), inevitably the contacts will open at slightly different times so you will end up with one contact set, the last to open, switching the full current. I have seen suggestions that it is better to wire the contacts in series, which can reduce arcing. Some heavy-duty switchgear works like this, especially if switching DC. Anyway, it's all a bit academic if you are working within the spec of the contactor (or relay), I would hope.