Stuttering Relay

Please excuse me, I am an electronics beginner.

I built a kit circuit "kemo b048" which is a temperature activated relay.

I bridged the + to one of the relay contact points and ground to the other, so that when the relay activates it also closes the switch between +12v which puts current across the relay switch and then back to the ground in the circuit to power a fan.

When the relay activates, it stutters for a moment. A strong temperature change has a min stutter, but a minor temperature change has a long stutter.

I am guessing that when the fan activates it causes a minor voltage drop in the circuit which interferes with the circuit.

I am also guessing that a well placed capacitor might relsolve this issue. I know that often a capacity is placed parallel to the motor to reduce interference however I am unsure if it will assist in this situation. I understand that the capacitor in parallel reduces noise caused by the contact of the brushes but will it also assist with the initial load of powering the fan also?

hi,
It could be due to lack of hysteresis in the circuit, do you have a link to the circuit diagram of the Kemo.?

https://www.kemo-electronic.de/datasheets/b048.pdf

Many thanks for your assistance.

Please scroll to the bottom of the linked pdf for the circuit diagram.

note : it doesn't include the modification I made as described above, using the circuit supply to power the fan.

I'm just waiting for moderator approval to my link. I don't know if that will happen shortly so perhaps I can say h++p : / / www . kemo-electronic . de/datasheets/b048.pdf

scroll to the the bottom of the pdf.

Try it without the fan connected and see if it still stutters.

I tested it without the fan, and also removed my modification for powering the fan so the circuit should be exactly as designed, but it still stutters. ?

Then it is most likely a lack of hysteresis. Not a voltage drop associated with the fan.

Thanks for you help, so either I have stuffed the build or its a bad design.

I have doublechecked all my soldering, and cleaned up anything potentially sus so I guess I should consider another product?

Look at R1 in the circuit. What value is it? I believe R1 is the feebback resistor for your hysteresis. You can try increasing the value of R1 which should increase the hysteresis zone. With a quick look, the circuit looks prettyy standard and should work assuming everything is wired correctly. Wired correctly being obviously very important.

Ron

Your DC Power Supply may not be well regulated or filtered. Try another known good power supply or +12V battery to isolate problem.