Motorised Valve motor - switch circuit.

[samjmann]

I'm in the process of making a modification to our Y plan central heating system. All that's involved is the addition of SPST mains relay switching the inductive load of a 6Watt synchronus motor.

The relay needs to be able to switch 3A amp easily. What do I need in the way of suppression across the mains relay coil, and the contacts themselves. There are devices with 100R resistors built into caps, as well as MOV devices, of which I know nothing about!

Any thoughts?

Regards, SJM

[samjmann]

Here's a diagram of the internal wiring of the valve. The white is the Heating on, and Grey live when hot water off. Orange is on for the boiler and pump. The valve is left with the motor stalled, this buzzes at night hence the modification.

SJM.

[Station X]

A full explanation of how the valve works can be found here:-

http://wiki.diyfaq.org.uk/index.php/...position_valve

[samjmann]

Thanks Graham, that's exactly where I got the modification from!

It's the suppression that I'm wondering about. I've heard about MOV's but had no experience with them.

[Station X]

I have one of these valves in my heating system and it isn't very reliable. In ten years I've had to replace the actuator twice as the motor had burnt out. The actual valve leaked water too, but I fixed that with a new 'O' ring.

[samjmann]

Mine's 15 years old, so it's not done bad. The whole system was badly sludged, and even the pumps impellor blades were full of rust. The sludge had got into the valve as well. There was hot water going into the rads when the CH was off! The water side is now fine, this is a bit of refinement.

[Hartley118]

Originally Posted by Station X

I have one of these valves in my heating system and it isn't very reliable. In ten years I've had to replace the actuator twice as the motor had burnt out. The actual valve leaked water too, but I fixed that with a new 'O' ring.

The motorised valve is a reliability disaster. I’ve given up replacing ours. The result is that both the hot water and radiators have run at boiler temperature for a few years now. It’s not what was intended, but is acceptable.

Martin

[Trevor]

I changed my system from why plan to S plan in my opinion much better
Trev

[Ed_Dinning]

Hi I have had a similar system with 4 zone valves and pumped primary (hot water). It has been in use for 45 years and has had 5 valve motors and one valve body in that time, so full marks for reliability. System has also had 1 pump and several thermocouples.

A normal mains relay with DP contacts, often about 5 to 10A rating (plug in octal type) is actually overkill for this job, but they are cheap and plentiful.

You probably need to flush the system and remove rads to hose out. Then refill with inhibitor solution, this has helped with the longevity of my system
I believe the control system has saved me a lot of money over the years and keeps the house and water at comfortable temps.

If you want further details please mail/ PM me as it is getting away from a main forum topic

Cheers, Ed

[samjmann]

Thanks Ed, it's just the electrical side I need a bit of advice on. I'm thinking of fitting a MoV across the relay coil. But the value such I can only guess at. I don't want ' thread drift' too much!!

[Ed_Dinning]

Hi Sam, mine don't have any filters fitted and do not give any problems. An MOV at the powers involved would be a bit of an overkill.
The CR networks were often a Rifa type, that died quite often.

If you can 'scope it safely you may find there is no problem, or see the effects of a small (10nF?) X cap and possibly 100R

Ed

[Lucien Nunes]

The DC resistance of these small motors and coils is high enough to prevent much RF emission on switching, as the transient is soon damped. Normal central heating controls don't have RC suppression across their contacts as even small capacitors can pass enough current with the contacts open to cause a miniature relay to pull in or a valve motor to develop measurable torque.

If you want to put an MOV across an inductive device, don't forget that when the device is energised it will be trying to suppress your entire house mains, not just the target device. A heavy transient that exceeds its energy rating can cause it to self-destruct, so it needs to be appropriately fused as per surge suppressors in mains power strips etc. MOVs normally show in their key data table a maximum continuous applied voltage and this would typically be 275V AC for a device on UK mains.

I just did a test with a DAC90 sat next to my heating programmer and wiring centre, none of which has suppression. When detuned in the middle of the MW band, I can hear a faint pop when switching the pump but not when switching only a valve motor. With a reasonably strong station tuned in, I can't hear anything when switching the pump, valve or boiler gas valve. So I wouldn't bother adding suppression unless I discovered a specific problem with interference.

[samjmann]

Thanks Lucien for such a detailed reply. I'll simply construct this without suppression, it's clearly not needed.

The test for contact noise on your system with the AM radio, reminded me of a problem with DTV in the early days before the analogue turn-off. To precis a long story, the aerial lead was routed in an airing cupboard past a motorised valve. This valve had half seized and was continually cycling. The pulses from the internal switches upset DTV but not analogue! This was the first digital TV the lady had owned, she insisted it was faulty of course! I said you need a plumber, not a TV engineer.... We found the cause with a little portable AM radio.

Thank you everyone for the help with this, very much appreciated. Possibly close this now, we don't want to drift towards plumbing too much!!

SJM.