Geyser controller circuit


Thread Starter

M Chinamasa

I have recently been assigned to work on project which involves the control of geysers. The main objective of the project is to reduce power consumption of geyser by only switching them on when hot water is required. The geyser should be on from 0500hrs to about 0900hrs and then swicth off for the rest of the day. It should switch on again from 1700hrs to 2200hrs and then off for the night. I intend to use a programmable microcontroller but the main issue is the interfacing of the microprocessor and the geyser circuit. The geyser is fed from a 220V supply and its rating is between 4 and 6 kW. Maybe you can alo suggest the type of microcontroller to use. What type of power supply is the best for this circuit given that the whole circuit has to fit in a 20cm by 10cm box. I look forward to hear from you ladies and gentleman. Chinamasa
Hello, I think for this application (barring adding additional function to the system) you really don't need a programmable controller. I would recomend something like Allen_Bradley's electronic timer (700-HX86SA17 app. $160). As far as controlling the power end, I think I would look at using a solid-state relay(SSR), unless you don't mind a contactor (big relay) whacking off and on. Idec makes SSRs, and I know they make one for 660VAC up to 25A. You will need to allow room for heatsinking the SSR....which brings up the enclosure issue: I think you might have to use a bigger box. You won't need a seperate power supply since the SSR uses a control voltage up to 280VAC, which you can get from your power line in the box. The A-B timer is a little over 3.5 inches long and 45mm (1-49/64") square. It uses up to 240VAC for power. Anyway, hope this helps.

Curt Wuollet

HI Aren't these on-demand heaters anyay? I don't see how much savings you might realize when the units only consume power when the water is running already. Am I missing something here? Regards cww

Adolfo Jimmy Saldivias

For this application I would not use a controller but a timer for the day. Or you may want to use timer for the week. Both of them you can find in a lot of suppliers: Omron have an online store, which you can try at Also you can buy from grainger, at Most likely from any seller of electronic equipment. For the output you can use the relay that comes with these equipment. The relay will have to drive a contactor. The contactor should be sized according to your amperage needs. Regards Jimmy Saldivias TECSIM Phone: 591-4-523438 Fax: 591-4-523413