PicAxe Mains (DeepWell Pump) Control

[w7ky]

I'm ready to take my PicAxe deepwell pump control circuit from breadboard to PCB. The recent PicAxe/Mains thread unsettled me a bit. I plan to switch my 240vac 1/2hp pump with a 240vac/75A SSR controlled directly by a 14M. The pump is already in the well, so I don't know the exact amp draw. I think it's around 7A. I thought the 75A SSR mounted to a commercial heatsink would handle the inductive load. Now, I'm not so sure how great the inductive load might be. The pump has capacitive start circuit and the start surge may last several seconds. Maybe I should use a small 10A SSR @ 110vac to control a mechanical 240vac relay.

The SSR, a Magnecraft W6275DSX-1, has the following specs:
Motor Load Rating [rms] 25 A

Non-Repetitive Surge Current (1 cycle) 1150 A

Max. RMS Overload Current (1 second) 150 A

I've been focused on my circuit and code and just assumed I was within tolerance on the 240vac pump/75aSSR/heatsink. I chose the 75A relay because it's the largest SSR in my parts box. The PicAxe and 240 switching are 2m apart. Might the start/stop surge might damage the SSR? I would appreciate your thoughts.

 

[Michael 2727]

SSRs have standard Triacs inside them for the switching.
It would take onehelluva load to fry your 75A Triac.
I would be quite happy to use the 75A unit for a motor
10A to 20A. A zero switching device may be the better
but I wouldn't worry too much, being underground noise wise.

 

[leftyretro]

Well 1/2 HP is only 375 watts and that would be around 1.5 amps running at 240vac. Allowing a 8 to 1 startup surge would be around 12.5 amps so I think your SSR would work fine and worth a try.

Lefty

 

[w7ky]

Thanks for the feedback. I probably shouldn't react to threads I read after midnight (-:

 

[moxhamj]

Just an educated guess but if you already have installed a pump then you probably can do mains wiring as well. Just build the mains side of things to a high standard. Maybe look at DIN rails in a cabinet in a shed.

I've switched 1Hp pumps using SSRs with no problems.

The only thing would be to watch for the picaxe resetting when switching mains. You might need to keep the two apart from one another and/or shielding the picaxe. Also write the code to handle a reset - eg if the first thing on startup is to check a switch and if the switch is on then turn on the pump and the system is resetting then it will keep cycling the pump on and off. Put in some delays. I've resorted to using a picaxe to trip a 555 in the past as 555s are more immune to noise.

 

[w7ky]

DrAcula

I did install and wire the pump myself last year. I'm still managing the water system manually, but the controller is nearly finished. I'll install the 240v SSR in it's own cabinet next to the existing manual switch and comply with local electrical codes. The controller will be indoors, 2m or more from the mains and the 5vdc supplied from the house 120vac service.

My code is pretty simple and it handles reset OK on the breadboard. I plan to post my schematic and code to the forum before building the PCB. I'm still a beginner with PicAxe micros and some of my projects didn't perform as expected in the field.

I appreciate your help. This is a good opportunity to thank you and your forum-colleagues for sharing your knowledge and experience with such patience and diligence. Although I don't post often, I read the forum every day and have learned much from just following the threads or searching the archive. Much of my experimenting is pieces of code or circuitry from someone else's project. I've never had so much fun with electronics.

 

[moxhamj]

Sounds like you almost have it all working. http://drvernacula.topcities.com/RFDataLink.htm and scroll down half way down the page for some photos of my pump controller. As you can see - neat and tidy mains but outside the box is the messy low standard picaxe wiring.

Another thought - every controller I built had a switch with 3 positions - off, manual and automatic. So the mains controller box has the three position switch and it worked on manual for a while when I was building the next controller which was a manual switch that switched 12V. Once this was working the mains controller went over to automatic and the box outside the mains controller box took over. This also had three position switches = off, manual and auto. Then a picaxe took over the automatic and the manual box went over to auto. Finally the last layer of control was a computer.

But if the computer fails one can go back to the previous layer which is a picaxe and if that fails one can go back to manual. A fiinal layer of control can be via the internet.