[SOLVED] control 220V AC pump with SSR

Hi,

I am try to turn ON and OFF a 220V gardening pump (220V, 800W -> 3.6A) with a Raspberry Pi.
The GPIO pins on the Raspberry can easily be controlled. They produce 3.3V (and max 16 or 20mA).

I understand that i will need some sort of relay to do this. I was about to buy a simple SSR relay (Fotek SSR-25 DA), but a friend pointed it out that it's for controlling resistive loads, whereas a motor is an inductive load.

I am not an engineer by training, so I spend the last 6 hours reading about Triac relays, zero-crossing, random, SPDT, etc...but still pretty confused. I also read a LOT of contradicting information.

So I am looking for AS SIMPLE AS POSSIBLE a solution (and cheap) to turn ON/OFF my pump (through a Raspberry Pi).

Some people suggested buying a power switch with a remote, and then hacking the remote control. But I don't find this a very elegant and neat solution.

Can someone help?

Thanks a lot in advance.

I'm regularly turning AC water pumps on and off with an SSR, the pumps range from about 0.5HP to 4HP (about 400W to 3000W) and have never had any trouble, I use SSRs to replace mechanical switches because they are so much more reliable. Just make sure the SSR is conservatively rated, bearing in mind that water pumps may have a substantial mass of water to get moving so for a few seconds they may draw more power than their normal rating.

Brian.

drakongetes said:

Hi,

I am try to turn ON and OFF a 220V gardening pump (220V, 800W -> 3.6A) with a Raspberry Pi.
The GPIO pins on the Raspberry can easily be controlled. They produce 3.3V (and max 16 or 20mA).

Click to expand...

If you want to end up with an “elegant” solution, add an R-C snubber to an SSR (see Brian’s post), as shown in this AppNote:
**broken link removed**

:wink:
IanP

betwixt and IanP, thanks to both of your for your reply.

Betwixt, just to make clear, the SSR you are using are using, are they specifically designed for inductive loads (but cost about £30-40), or are you using the cheaper ones (about £5), normally designed for resistive loads?

The SSR I mentioned (Fotek SSR-25 DA - specs below) - do you think it would be adequate? As a reminder, the pump is 800W (3.6A) and the SSR is rated for 25A.
http://www.fotek.com.hk/solid/SSR-1.htm

thanks a lot in advance

The one you listed should be fine.

If I'm in a hurry, I use these: https://uk.farnell.com/omron-industrial-automation/g3na-210b-5-24dc/ssr-10a/dp/1181259 or it's higher curent rated versions.

If I'm doing a complete bottom up design I usually build the SSR out of a triac or a pair of SCRs in conjunction with a MOC3041. Be aware that unlike a mechanical switch or conventional relay, a SSR will have some leakage current. Normally it isn't a problem but keep the wiring well insulated just in case. For heavy duty and critical safety applications I use two high current mechanical relays AND a triac/MOC3041. One relay is to completely disconnect the supply, the other and the triac are in parallel. An MCU sequences their operation so turning on first enables the isolator, then turns the triac on to handle the current surge then finally shorts the triac out with the second relay. The sequence is reversed to turn it off. That gives me absolute isolation for safety, zero crossing to prevent EMI and motor load problems and then minimum voltage drop. As a bonus, none of the relay contacts open or close with any substantial current through them or voltage across them.

Brian.

Hi brian,

thanks a lot for your reply and the info.

Would you happen to have a schema of the Triac and MOC3041 (sorry might sound dumb, but I am still a beginner!) went your built the SSR yourself?

Also, I bought the Fotek SSR-25 DA SSR I mentioned before.

But do you think I need some sort of protection (assuming I am only using it with my 800W pump) either on the AC side (maybe a MOV?), or on the DC side (maybe some sort of fuse?)?

Michael.

The schematic is much as in the data sheet for the MOC304x series.

Bigger commercial SSRs use two SCRs back to back rather than a triac but their operation is very similar.

I would certainly place a fuse in the live (line) side of the AC - before the SSR. You can add other components to clamp spikes and interference but you probably don't need them. One word of caution though, depending on the purpose of the pump (is it portable or a permanent installation?) and local regulations in your country, it may be necessary to feed it from an RCD circuit breaker to guard against leakage to ground.

Be EXTREMELY careful to insulate the circuit, you don't get a second chance if you touch live parts!

Brian.

great, thank a lot Brian. The info will be useful for the next SSR I build!

I received the Fotek SSR-25 DA SSR (mentioned above), connected it to the pump (with a 6A temporised fused 220V live) and all is working fine so far

Michael.