Solar pump relay switch.  Need help - Page 1
Forum section: electronics / beginners

author: .RC.
author_rank: Frequent Contributor
timestamp: March 17, 2023, 10:45:27 am
content: I have a surface mount solar pump I bought from China. It is one of the brushless type motors. This one came with it's own inbuilt controller. No instructions or anything. Just two wires coming out of the pump.The pump itself works fine however I need to add a tank high and tank low setup.I found if I briefly short the two pin header (black one in photo) the pump stops slowly, then it will restart within ten seconds after the pin is no longer shorted.I have a double magnetic float switch. Essentially two floats on a rod. Either switch can be configured NO or NC.https://www.ebay.com.au/itm/125654993571I made up this wiring diagram. It should work like this.Tank full as per picture. Tank level dropping the high level switch will go closed, relay stays off.Tank drops blow bottom switch, it goes closed, relay goes on, opening the header pins. Pump starts.Tank fills, bottom switch goes open, but the relay remains on.My question is. What reliable relay do I get? I might be able to get 5V off the control board, or is there something the solar panels could power?For those interested the other (orange) two pin header if shorted puts the pump in a low well condition (I guess this as other pump controllers have this feature) as it will keep the pump shut off for half an hour or so before restarting. The idea being when the water level rises to above the sensor, it gives the well another half an hour to make water up.No idea what the five pin header is for, but I suspect it is for programming the STC controller chip.

author: m k
author_rank: Super Contributor
timestamp: March 19, 2023, 01:11:39 pm
content: Check how commercial stuff treat hostile environment, septic tank is one place.Reed relays are usually pretty hermetic, though not completely if it is not mentioned.If environment is too hostile the control must be taken out.

author: SmallCog
author_rank: Frequent Contributor
timestamp: March 20, 2023, 04:27:19 am
content: Your plan with a latching relay should work fineYou might find that there's a suitable voltage rail on the control board you can borrow, be surprised if there's not.Use a decent quality relay, I mostly use Omrons and Finder but there's plenty of decent stuff around provided you shop with reputable sources - there are counterfeit relays on ebay (but they probably work OK for this anyway...)If you use a short bit of Din rail and a screw terminal relay base it will look like a proper professional bit of kit if someone else ever opens whatever box you mounted it in.Some of these styles of relays will feature a little indicator LED on them, might be handy for fault finding as light on should mean pump on

author: themadhippy
author_rank: Super Contributor
timestamp: March 20, 2023, 04:51:30 am
content: QuoteWho mentioned a latching relay? the circuit is a common ole garden self hold/zero volt drop out set up that uses a bog standard relay,the only special consideration is the relay needs 1 more switching contact in addition to whats required to switch the load

author: .RC.
author_rank: Frequent Contributor
timestamp: March 20, 2023, 10:37:44 am
content: Thanks. I have had a slight change of plans. Rather then find 5V off the board as I am not sure where to look. I found there are LM2596HVS powered buck converters that can handle up to 50V input, the solar panel no load voltage can get up to 48V or so. So I ordered 4 for under $7 delivered. With one of these hooked in I can then use a 12V relay, automotive or whatever.

author: SmallCog
author_rank: Frequent Contributor
timestamp: March 20, 2023, 09:43:44 pm
content: Quote from: themadhippy on March 20, 2023, 04:51:30 amThe DPDT relay from my understanding of his description is wired in a 2 button latching configurationThe "start" position of the float switch sets the latch state, whilst the "stop" position of the float switch breaks the latch state.

author: themadhippy
author_rank: Super Contributor
timestamp: March 21, 2023, 12:12:28 pm
content: The circuit may act as a latch,but a latching relay is a different beasty and using the term may confuse people.