How to make a latching timer for the hot water?

[cjard]

ive a timer and a thermostat in the cylinder; presuming that the thermostat is normally closed until temp reached, then switches open, and also presuming that the timer is normally open, and closed for the programmed period.. What other component would I need and how to wire it so that:

If the thermostat is closed(cold) and the timer closes, the heating begins, until the thermostat opens (temp reached) deactivating both the hot water and the timer's ability to activate the hot water again until the next programmed period (ie until the timer has cycled to open and closed again?

I'm trying to avoid the water cycling on and off if the timer is closed for a long time, temp is reached soon, the thermostat opens, the cylinder cools, thermostat opens again, hot water activated again....

Is it possible with simple components, or does it need some intelligence in the timer? I did wonder if it could be done with a relay where the relay output is also connected to its energising coil, so once the relay is activated eg by a brief pulse from the timer, it would stay closed (because it's own output keeps it closed) until the thermostat in series opens and kills power to the relay?

 

[deadshort]

If the timer is closed i would assume your are looking for hot water during the timer 'on' periods ? Why would you also want to inhibit the thermostat operation during the timer 'on' period ? I'm lost !!!!!! and in cold water !

DS

 

[endecotp]

I'm trying to avoid the water cycling on and off

Mechanical thermostats tend to have a fair amount of hysteresis, so any cycling will happen over a longish period.
Is this a real problem, or are you perhaps overthinking?

 

[cjard]

Yes, I want to call on the boiler for DHW when the timer is closed and when the hermostaticbath is closed, I.e. When the tank is cold and once a day at 1pm til 2pm, call for DHW. The boiler (a heat pump) seldom takes more than an hour to produce a tank of hot water, but I don't want a nearly hot tank at 1pm to cause the heat pump to cycle on and off if the timer closes and then the thermostat cycles because he tank temp is hovering around 50 degrees..

Hence I was looking for a circuit design where the timer could maybe kick things off at 1pm and then heating the water just goes until the thermostat is happy.. Either that or some way of the thermostat cancelling the timer's closed status?

 

[endecotp]

Anyway, if you like 19th century electromechanical steampunk it can be done with a latching relay or two.

Personally I prefer transistors but that seems like "new fangled witchcraft" around here....

 

[EFLImpudence]

If the thermostat is closed(cold) and the timer closes, the heating begins, until the thermostat opens (temp reached) deactivating both the hot water and the timer's ability to activate the hot water again until the next programmed period (ie until the timer has cycled to open and closed again?

Yes, as it should be. If water still hot, no need for power.

I'm trying to avoid the water cycling on and off if the timer is closed for a long time,

Why? That's how it maintains the temperature - if you have used some hot water.

temp is reached soon, the thermostat opens, the cylinder cools, thermostat opens again, hot water activated again....

Yes. Heating activated again IF needed.

Is it possible with simple components, or does it need some intelligence in the timer? I did wonder if it could be done with a relay where the relay output is also connected to its energising coil, so once the relay is activated eg by a brief pulse from the timer, it would stay closed (because it's own output keeps it closed) until the thermostat in series opens and kills power to the relay?

That's what it does.

When the thermostat opens it doesn't matter if the timer is closed.

The purpose is to heat the water to the required temperature; not limit the timer operation.

 

[cjard]

Perhaps it is overthinking; no idea what the hysteresis on my current setup is.. I suppose I could give it a go. I've also ordered some thermostats from fleabay that are digital and have a programmable hysteresis so that could be another option..

 

[deadshort]

Anyway, if you like 19th century electromechanical steampunk it can be done with a latching relay or two.

Personally I prefer transistors but that seems like "new fangled witchcraft" around here....

Please practice your witchcraft ! Share ! or we will never learn the ways of the semiconductor world ……….. o great one

DS

 

[EFLImpudence]

What are you trying to achieve?

You could do the same with the central heating - but you may not be warm enough.

Reduce the length of time the timer is closed.

 

[cjard]

.

The purpose is to heat the water to the required temperature; not limit the timer operation.

Yes, but this isn't an immersion heater with limited consequences of toggling it on and off frequently; it's an air source heat pump and they apparently don't take kindly to being cycled to keep a vat of hot water topped up (though it's less of an issue for central heating mode because the compressor doesn't activate as aggressively for CH as it does for DHW. By the way,heat pumps generally do DHW or CH, not both simultaneously and in CH mode they will cycle though the control software in mine limits the number of cycles per hour for CH)

Currently I control it manually, flicking a light switch that calls for DHW, monitor the return temp of the heat pump water circuit and knock it off at 52 degrees.. Tank of hot water then lasts a couple of days before I do it again. It works well, and my electricity Bill is 2/3rds of my father in laws; his system spends all day and night cycling on and off keeping the tank hot

Was hence after an automated replication of my manual control, and have it be something that would only fire up once a day max

 

[John D v2.0]

Interesting problem. I think for simplicity I'd just go for a relay.
Timer on for 5 minutes, connects relay. Relay also latches via itself and the thermostat in series, so after 5 mins it's holding itself on. Heater is connected to the timer output.
Only risk is you get 5 minutes of heating even if it's already up to temperature. If that's a problem add another thermostat in series with it, or use a dp relay.

 

[endecotp]

Do what John D says. I was going to suggest using a "two coil latching relay". Difficulty is it needs a thermostat that turns ON when hot enough, and I don't think cylinder stats typically have that connection, do they?

Or:

 

[EFLImpudence]

Yes, but this isn't an immersion heater with limited consequences of toggling it on and off frequently; it's an air source heat pump

Should I have known that?

ive a timer and a thermostat in the cylinder;

 

[ericmark]

The STC-1000, MH1210A and the InkBird and many other units are designed to work with refrigeration units. In the settings there is a delay feature, some only work with cooling, I have both the STC-1000, and MH1210A but not in this house. The STC-1000 has two relays so can run heating and cooling, the MH1210A has a single relay and can be set to heating or cooling, both same size and both need an enclosure. The InkBird ITC-308 is ready built, they are used in the main by home brewers and keepers of reptiles.

As well as the delay time you can also set slewing range of temperature 1~30ºC. This is the difference between switch on and switch off, depends which model your using.

Is this what your after?

 

[endecotp]

Should I have known that?

He mentioned it first in post 4.