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I am new here and do not have a lot of electronics experience, so please be nice haha.

Anyways, I bought a 100W CO2 laser on eBay at a good price but the reason was that it is actually was sent to USA by mistake and it is 220VAC all the way... including a pump that I am trying to hook up to an SSR now, because for some cheap reason they decided to not hook it up to Ruida controller but make a physical button.

Long story short, I am hooking this up as normal to 15A small ACDC SSR, but because the pump is only 40W on 220V it draws very little current. So it doesn't trigger the pump sadly. I did check it with larger load and the SSR works fine, just not the pump. Due to my lack of electronics experience I came here after unsuccessful 30 minutes on the web I came here to ask for help and advice. I was thinking of simplest ideas, like adding a resistive load or a capacitor, but with 220V being in play I do not know how to calculate that and maybe its just easier to get another SSR from Amazon, in which case I also do not know which model will actually trigger at such low current.

TIA!

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    \$\begingroup\$ Welcome to the site. Would you mind giving us the datasheet of your SSR, as well as a schematic showing how you're hooking everything up? \$\endgroup\$
    – Jonathan S.
    Commented Dec 26, 2022 at 22:47
  • \$\begingroup\$ Hi Johnathan, there are not many ways to hook up an SSR, and I don't really want to draw that. Its a basic connection, I hooked these up many times, but never to a 0.18A pump. I hoped experienced folks over there would just guide me in a direction to a correct part or keyword, no way that such low current SSR doesn't exist, it's just hard to find on google based on just description of what I need and I dont see minimum current mentioned anywhere on those relays online. And AFAIK all SSR are based on MOSFET, hence the name - solid state. Mosfet, optocoupler, etc. Basic architecture for that. \$\endgroup\$
    – Vlad
    Commented Dec 26, 2022 at 23:30
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    \$\begingroup\$ We really can't find out what exactly the problem is if you don't tell us which SSR you're using. Most SSRs are also not based on MOSFETs, but on thyristors / TRIACs, which have a minimum holding current. MOSFET-based SSRs can operate down to 0A. \$\endgroup\$
    – Jonathan S.
    Commented Dec 26, 2022 at 23:32
  • \$\begingroup\$ This is a LLIRD relay directly from Chinese big manufacturer, not from public market in USA. Its a very good quality relay and I have already spoken to manufacturer directly, and they confirmed that current is too low. So I never asked to diagnose my existing relay here, but just suggest a solution around it, either a load or another SSR. I also have around 100 of those relays and I tested 5, so I know SSR isn't defective, they just perform as designed, current is just too low. Also good to know about TRIACS etc, I guess TRIAC is my case then, thanks for the explanation! \$\endgroup\$
    – Vlad
    Commented Dec 26, 2022 at 23:36
  • \$\begingroup\$ I wish I could just open one for the heck of it and see what's inside, but they are extremely well glued, and I honestly just want a working solution and as little tinkering as possible. In recent years I dont find myself enjoying fixing such things, I prefer to buy a proper part that will just work. And I understand that this isnt the correct part now, for my applicatio. However, when I google MOSFET based SSR, it doesn't give any reasonable results to me. Seems like manufacturers dont even mention this spec at all, at least on amazon etc. \$\endgroup\$
    – Vlad
    Commented Dec 26, 2022 at 23:39

1 Answer 1

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If you can find one, a correct SSR is probably best.

In a perfect world, the way to find the current draw of the pump is to look at the nameplate -- with luck it'll tell you not only the running current, but the starting current.

If that doesn't work, then remember that power = current times voltage. So go with \$(40 \mathrm W) / (220 \mathrm V) \simeq 0.18 \mathrm A\$.

I'd look for a relay that's guaranteed to stay on down to 100mA (0.1A) or less, and guaranteed to handle up to at least 2A, although I'd spend a bit more for 5A (because I'm already not trusting your setup!)

I strongly recommend that you go with a really-o truly-o electronics distributor. Places that don't specialize in electronic components don't always do well at supplying them.

In the US, in 2022, the go-to distributors for general electronics are Digi-Key, Mouser and Newark -- any one of these should have what you want. For stuff that connects to the mains, I think I'd add GreyBar to the list, and I'd check GreyBar and Newark first.

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    \$\begingroup\$ There are also MOSFET-based SSRs that don't have a minimum hold current. One of those is likely ideal. \$\endgroup\$
    – Jonathan S.
    Commented Dec 26, 2022 at 22:54
  • \$\begingroup\$ Thanks for your reply Tim. I am new to electronics, not to physics :) lol. I figured anyone here will come to 0.18A themselves, but I appreciate that patience :) I also know all the suppliers and amazon, the problem is again: I cant find the correct part not the correct supplier. MOSFETs - I have a lot of them, as I used to sell them in my store even, they are not rated for 220V, and I have never seen one that is, that and AC. If anyone has any parts in mind or even keywords, I would appreciate. I just need a way to find them. Not familiar with glossary, plus second language too. \$\endgroup\$
    – Vlad
    Commented Dec 26, 2022 at 23:08
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    \$\begingroup\$ @JonathanS. was suggesting a SSR that has a MOSFET inside -- not that you roll your own. Looking at what's out there -- hmm, the supply does seem to be thin right now. There's no reason you can't go with a plain old mechanical relay, assuming you can find one designed for a similar-sized motor. \$\endgroup\$
    – TimWescott
    Commented Dec 26, 2022 at 23:14
  • \$\begingroup\$ Also, to address the "MOSFETs are not rated to 220V" remark - that's not true. In fact, Infineon has MOSFETs rated to 1700V. You could use a photovoltaic optocoupler and a pair of anti-serial MOSFETs to construct your own SSR if you can't find one that suits your needs. However, just buying a MOSFET-based SSR is much simpler. \$\endgroup\$
    – Jonathan S.
    Commented Dec 26, 2022 at 23:37
  • \$\begingroup\$ I get it, but nevertheless I was not able to find any part on a market that matches your description. While responding I was actually searching all your advices online. I searched this on amazon, ebay and google. I do not go to specialty places as they are way too complicated there, and I dont have part numbers, accounts and time to wait 10+ days to get the part. \$\endgroup\$
    – Vlad
    Commented Dec 26, 2022 at 23:43

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