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  1. #1
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,121. Received thanks 233 times, giving thanks to others 5 times.
    This is more out of curiosity, but what would you pick to switch a 500VA toroid?
    .
    I was going to use a contactor, but I think the coil requirements might just push the available power supply over the edge, so I'm now swaying towards a big relay, but the ones I've looked at so far are all out of stock at suppliers.
    And it's got me thinking what other people would use.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  2. #2
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 19 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,156. Received thanks 209 times, giving thanks to others 5 times.
    Not a recommendation (haven't used it in earnest yet, just initial testing) but I'm using a relay from Electric Center (how it pains me to use that spelling...). For less than a fiver or so, seems to do the job. Contacts look reasonable. My control box has a 650VA toroid. Switching on, there's just the load of charging the capacitors. Switching off is when there might be a bigger load, but only on hitting the e-stop which should be a rare event. I hope. Normal switch-off is lightly loaded as no motors turning, so only breaking relatively low currents. That's my thinking, anyway. If it does fail one day, then it's a fiver and an unplug/plug job to swap it.

    OTOH, my lathe uses a chunky multi-pole contactor that sounds like the crack of doom when it operates, but then it's switching a 3HP motor on load. 3-4 times the price, typically multi-pole so bigger physically. But probably last for ever in this application.

  3. #3
    Personally, one of these:
    Click image for larger version. 

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    Or, if you can spare £1 on eBay, a 25A SSR:

    Click image for larger version. 

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    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #4
    Quote Originally Posted by Jonathan View Post
    Personally, one of these:
    Click image for larger version. 

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ID:	19581

    Or, if you can spare £1 on eBay, a 25A SSR:

    Click image for larger version. 

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ID:	19580
    I didn't have much joy using an SSR to switch my toroid supply on. Can't quite remember what it did now but something didn't work. I then read they aren't good with these types of loads. They also fail ON. Swapped it out for branded contactor (controlled by 24V logic on an estop circuit) and it works fine. Thanks to a kind forum member for sending me that part FOC !
    Would go the contactor route if I ever built another. The inrush current bothered me but then it not really my area to comment in detail.

    The mains switch made me chuckle. Should also be fine but then it's not part of a safety circuit if you want to have that feature in your system
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #5
    Quote Originally Posted by routercnc View Post
    I didn't have much joy using an SSR to switch my toroid supply on. Can't quite remember what it did now but something didn't work. I then read they aren't good with these types of loads.
    This could be because some SSRs switch only at the nearest zero crossing point, which is the point that gives the highest inrush current for a transformer, so not such a great idea. Other than that I can't think why they wouldn't work well.

    Quote Originally Posted by routercnc View Post
    They also fail ON. [...]The mains switch made me chuckle. Should also be fine but then it's not part of a safety circuit if you want to have that feature in your system
    I agree neither is going to fair well with any modern safety inspection.
    Old router build log here. New router build log here. Lathe build log here.
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  6. #6
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,121. Received thanks 233 times, giving thanks to others 5 times.
    I did look at a peak switching SSR, but after seeing the price, quickly abandoned that idea.
    .
    I'll probably just go for a contactor. The E-stop relay in this machine did power the original drive power transformer, but it was a 300VA aprox. <mind has gone blank, but square iron/steel type> transformer. So not only was it smaller, it wouldn't have the same power on surge as a toroid.
    .
    The toroid will be controlled via the E-stop circuit, which runs on 24VDC, but I think it's not that large a supply. I meant to check it's output today, along with the E-stop relay rating but forgot. Last thing I want is it to cause a brownout when the contactor gets powered up, as the 24V also powers various sensors.
    However, having just checked the wiring diagram, I could always just use a 230VAC contactor...
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  7. #7
    Quote Originally Posted by m_c View Post
    And it's got me thinking what other people would use.
    I have a switch with fuse and filter like this one...

    Click image for larger version. 

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    ...and after that a slow starter like this:

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    Switching on slowly means no "bang" and current rush. Switching off is no issue at all. The currents are MUCH less than a vacuum cleaner.
    Last edited by A_Camera; 09-11-2016 at 12:26 PM.

  8. #8
    Quote Originally Posted by m_c View Post
    I'll probably just go for a contactor. The E-stop relay in this machine did power the original drive power transformer, but it was a 300VA aprox.
    I'm going to be using a WEG Mini Contactor, CWC16.

    16a for £12, my TR is also a 500va

    http://chaloncomponents.co.uk/index....actors-7a-16a/

    Rectified I'm getting 42v, the drivers are MSD542 x3.
    Last edited by Lee Roberts; 09-11-2016 at 01:15 PM.
    .Me

  9. #9
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 19 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,156. Received thanks 209 times, giving thanks to others 5 times.
    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?

  10. #10
    Quote Originally Posted by Neale View Post
    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
    Last edited by Lee Roberts; 09-11-2016 at 08:06 PM.
    .Me

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