Is this power supply logic workable?

[carlyai]

I have a small dual output water timer switch (similar to the model 1180e). It runs off 2 X 1.5V batteries. 

 

I don't think the batteries will last long, so I'm thinking of buying a SM-PLG06A-03,  220V to 3V power supply to power the water timer. I'll install rechargable batteries and connect the DC supply output across the battery terminals. 

 

Does this sound OK?

[OneMoreFarang]

I have no idea about your device.

But there is a BIG difference between batteries and a mains to 3V power supply.

Water and mains don't mix very well.

So whatever you do make sure there is absolutely no possibility that the water will come in contact with the mains power supply!

Maybe just use rechargeable batteries and charge them every couple of days or weeks.

[Crossy]

Possibly. Or it may smoke the timer, batteries and power supply.

 

Have you checked the current drawn by the timer? It may be a lot less than you think.

 

If you really want to go mains powered you'll need a power supply around 5V (a USB charger would do the trick) and a current limiting resistor of about 100 ohms, I'd stick a low current diode (1N4148) in series too so when the power is off your batteries aren't feeding back into the power supply.

 

The resistor will limit the charge current to the batteries to around 20mA which should keep them topped off without over-charging.

[carlyai]

3 hours ago, Crossy said:

Possibly. Or it may smoke the timer, batteries and power supply.

 

Have you checked the current drawn by the timer? It may be a lot less than you think.

 

If you really want to go mains powered you'll need a power supply around 5V (a USB charger would do the trick) and a current limiting resistor of about 100 ohms, I'd stick a low current diode (1N4148) in series too so when the power is off your batteries aren't feeding back into the power supply.

 

The resistor will limit the charge current to the batteries to around 20mA which should keep them topped off without over-charging.

 

[alacrity]

Why not buy a timer which incorporates rechargeable batteries?

 

They generally only use battery power to maintain the timer settings when the mains drops out and already have the circuitry for safe charging of the cells.

[carlyai]

On 2/22/2020 at 8:07 PM, alacrity said:

Why not buy a timer which incorporates rechargeable batteries?

 

They generally only use battery power to maintain the timer settings when the mains drops out and already have the circuitry for safe charging of the cells.

Yes, a new approach is needed. When I built the house I put down 2" pipes in areas that were to be built over, with the plan of having a microprosessor control watering zones. 

Still the plan, but lovely wify thought a 7 year wait for automation was a bit long hence the store bought timer etc.

I think Crossy was right in that my timer probably wouldn't use that much juice, so will I'll wait and see how long the batteries last before re-thinking. 

The timer switches on the water to two different zones for 20 mims. every 24 hr, so 40 mins. per day.

Thanks.

 

[carlyai]

Previously I thought that power would be consumed when the switch was thrown from closed to open, for 20 min, but now I'm thinking power will be consumed for a short period as the switch changes states. Will see.

[Metropolitian]

5 hours ago, carlyai said:

Previously I thought that power would be consumed when the switch was thrown from closed to open, for 20 min, but now I'm thinking power will be consumed for a short period as the switch changes states. Will see.

If you hear/feel a tick when it change state from either off to on or on to off, it then use a bit more power when output is powered from the input.

Thats an relay in action which needs energy to keep the state. Once it loose the energy it changes it state.

Most timers are NO (Normaly Open) if the relay is not energized.

[Metropolitian]

Closed and open with electronic/mechanical relays is reversed as with valves/watertaps.

Open it means no electical current flow trough, water is.

Closed it means electrica current can flow trough as the ring is connected, water instead comes to an halt.

[carlyai]

20 minutes ago, Metropolitian said:

Closed and open with electronic/mechanical relays is reversed as with valves/watertaps.

Open it means no electical current flow trough, water is.

Closed it means electrica current can flow trough as the ring is connected, water instead comes to an halt.

This seems strange to me, as I would expect that the device would use current when the valve was open and water flowing, as it's going to be off more than on. In my case only on for 20min but using battery supply for the other 23 odd hours. 

Can't you have a valve that is only in the operation state as it switches between open and close and closed and open?

[Crossy]

45 minutes ago, carlyai said:

Can't you have a valve that is only in the operation state as it switches between open and close and closed and open?

 

Indeed you can, motor-operated valves only consume power when they are moving.

 

I suspect the timer actually has a latching solenoid valve, again this only consumes power for a short time. Connect the juice to the coil one way round and it opens and stays open when power is removed. Reverse the polarity to close the valve (and it stays closed).

 

Have a look at this teardown 

https://www.digikey.com/en/maker/projects/teardown-automatic-garden-timer/12d2b38e2a1348ecbfa0e976d5a4915b

 

Quote

The valve of this timer is comprised of a solenoid, an ABS tube, a male GHT fitting, and a female GHT fitting. This valve latches open and latches closed by alternating the polarity. The solenoid is switched by an H-Bridge comprised of Q8, Q9, Q10, and Q11.

 

EDIT  https://www.solenoidsolutionsinc.com/specialty-valves/latching-solenoid-valves-low-energy/

 

[OneMoreFarang]

1 hour ago, Metropolitian said:

If you hear/feel a tick when it change state from either off to on or on to off, it then use a bit more power when output is powered from the input.

Thats an relay in action which needs energy to keep the state. Once it loose the energy it changes it state.

Most timers are NO (Normaly Open) if the relay is not energized.

That is not entirely correct. Have a look at "Latching relay":

https://en.wikipedia.org/wiki/Relay#Latching_relay

 

Just for keeping the time a coin cell is good enough for years!

See: DS3231

[carlyai]

Here is a pic of the water timer, just incase someone needs one. I had it all in a power plastic box and a blue pvc pipe male thread through the top into the female tap thread, but the thing leaked as the TPI of the blue plastic aren't the same as the TPI of the tap. 

The installation doesn't look very elegant, but that's it until it melts in the Isaan sun.

[Metropolitian]

6 hours ago, carlyai said:

This seems strange to me, as I would expect that the device would use current when the valve was open and water flowing, as it's going to be off more than on. In my case only on for 20min but using battery supply for the other 23 odd hours. 

Can't you have a valve that is only in the operation state as it switches between open and close and closed and open?

 

6 hours ago, OneMoreFarang said:

That is not entirely correct. Have a look at "Latching relay":

https://en.wikipedia.org/wiki/Relay#Latching_relay

 

Just for keeping the time a coin cell is good enough for years!

See: DS3231

I am correct. For an forced connected relay.

Indeed you are right if about the latching relay, which only use energy when activated either way open or closed.

 

I didn't know what type of timer the OP has, as I was using TV on my phone didn't catch all information.

The bug currently with TV and my browser (fox) withheld me for using the computer.

 

I was thinking about an regular timer, same as for switching the light or the pool pump, connected to an electronic valve. Not just an all-in-one device.

I just saw the picture the OP posted.

This time, my post wasn't really accurate to this thread.

 

The one the OP has could have an solenoid valve without the spring (thus an latching mechanism) (like in this youtube video) OR an ordinary motor with gearbox (like this one in the teardown youtube video from Julian.)

 

Either way, with the latching relay system, the device in rest with only the timer won't use more then 0.03mAh.

As the OP already posted I read, just wait out how long the current batteries will do before deciding to mod the device.

With Alkalines you will get a long long time before it will run out of energy.

 

Rechargeable batteries are better then making an auxiliary input from the AC, dangers of electrocution and a poor waste of energy.

If the OP like to mod, consider a small solar panel same as in those garden lights to keep the batteries charged.

 

 

 

 

[carlyai]

Metropolitian said: 'If the OP like to mod, consider a small solar panel same as in those garden lights to keep the batteries charged.'

 

Yes I thought about that yesterday. Would probably be a nice solution if need be.

Thanks for the reply.