Pipestat query

[cygnusv]

I want to use the pipestat to turn a 12 volt circulating pump on at 30C and keep the pump running until water temp drops below 30C again.
Whichever way I connect the stat it isn't doing what I want it to. There are 3 electrical connectors in the stat.
As you may have guessed, I'm not a pro, just a willing amateur looking for advice.
Am I using the right type of kit?

 

[Harald Kapp]

We will need more info on the pipestat. Make, model, any schematics available (at least for the terminals)?
Which pump, which connections did you try?

 

[cygnusv]

We will need more info on the pipestat. Make, model, any schematics available (at least for the terminals)?
Which pump, which connections did you try?

Hi Harald, many thanks for the reply.
Details
Greenbrook thermostat
TH90CS-C
15 amp resistive load
2 way switching
UK eBay 1118 0846 3501

Hope this helps, Stu

 

[Harald Kapp]

The datasheet for the thermostat says on page 2:

The thermostats are equipped with an accelerating resistance which must be connected to the mains in order to ensure the indicated control performances.

(emphasis by me) which means you may not be able tp use them with a 12 V pump.

 

[Alec_t]

I want to use the pipestat to turn a 12 volt circulating pump on at 30C and keep the pump running until water temp drops below 30C again.

That may not be possible with a simple mechanical thermostat, which will have ~ a degree or two of hysteresis between the turn on and turn off temperatures. The purpose of the accelerating resistor is to help minimise the hysteresis. Hysteresis is generally desirable, to avoid the pump cycling on and off frequently.

 

[cygnusv]

That may not be possible with a simple mechanical thermostat, which will have ~ a degree or two of hysteresis between the turn on and turn off temperatures. The purpose of the accelerating resistor is to help minimise the hysteresis. Hysteresis is generally desirable, to avoid the pump cycling on and off frequently.

A degree (or 10) differential wouldn't be a problem. The only reason for fitting this is so that the pump will start and stop itself without boiling or running all the time when the water is cold. We don't want to hear the pump any more than necessary.

 

[cygnusv]

The datasheet for the thermostat says on page 2:
(emphasis by me) which means you may not be able tp use them with a 12 V pump.

Ouch! I hope that's not the case. Can you get a 12 (or 24) volt pipe stat?

 

[Alec_t]

I don't see any DC current rating in the datasheet for your stat? Methinks you could get contact arcing/welding .

 

[Harald Kapp]

Can you get a 12 (or 24) volt pipe stat?

I don't know. Please have a look yourself - I'd have to run a search, too.

 

[Alec_t]

One option would be to use the existing stat to switch the coil of a standard automotive relay or similar. Such a relay has a relatively low coil current well within the stat's rating and its contacts are designed for relatively high DC currents (check the datasheet). Or for a solid-state option the stat could switch a power MOSFET to drive the pump.

 

[Harald Kapp]

One option would be to use the existing stat to switch the coil of a standard automotive relay or similar.

The automotive relay will not tolerate the mains voltage required by the thermostat.

You could, however, use the thermostat to control mains power to the 12 V DC power supply - provided this is a mains powered power supply. So instead of switching the 12 V output from the power supply you turn on/off the power supply by switching mains.

 

[Alec_t]

The automotive relay will not tolerate the mains voltage required by the thermostat.

True, but as I understand it (if this thread relates to a previous one of his), the TS is not using mains voltage; just a 12V supply on a boat. Perhaps he can enlighten us?

 

[cygnusv]

True, but as I understand it (if this thread relates to a previous one of his), the TS is not using mains voltage; just a 12V supply on a boat. Perhaps he can enlighten us?

Yes it is 12 volt, but not actually my boat this time. We're actually 24 volts.
I've wired the stat thru the common, marked number one, to terminal three ( make on rising temperature). The original problem I had was due to my own fault, a badly made connection. The stat is now working correctly.
As usual, many thanks for your always welcome help and comments. Stu

 

[Alec_t]

Glad you've got it sorted.