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How does an AC latching solenoid work?

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eddyj443

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I have a part from a dual zone fridge which I have been trying to figure out how it works. I have read lots on solenoids but it still confuses me.

I believe it is a 3/2 latching solenoid for controlling the flow of refrigerant to the two compartments in the fridge with two input terminals that accepts AC. I don't understand how the position is changed from one outlet to the other using AC input?

I have managed to slide off the coil to expose the core. It contains a permanent magnet in the middle (can be seen as the white corrosion ring in the photo). Manually moving a magnet over the core produces an audible "click" and the outlet is changed (the cooling changes between the compartments). When moving the magnet away the valve stays in the same position, even when the fridge is turned off.

The controller board for the fridge is broken, I am not concerned with fixing it, I am just wanting to understand how it can change the outlet position using AC (as shown on the label). If it was DC I would expect it to reverse the polarity.

I believe I have found the item for sale but it doesn't not have a data sheet - http://shanghaitoulon.sell.everychina.com/p-91857699-pulse-solenoid-valves-sdf-0-8-3-2.html

Hopefully someone can explain how this works as it is driving me crazy :)

Thanks
 

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alec_t

Well-Known Member
Most Helpful Member
Perhaps the device has two coils: one for 'set' and one for 'reset', much the same as DC dual-coil latching relays. The magnet provides the latching function.
 

schmitt trigger

Well-Known Member
There are two ways to perform the latching function;
in the old times it was a mechanical function, much like the escape gears on a mechanical watch.
But nowadays, I believe what Alec has mentioned is the norm.
 

ronsimpson

Well-Known Member
Most Helpful Member
upload_2018-3-9_7-23-6.jpeg
I found a picture of how this one works. I think it is a DC relay. One coil pulls the magnet over center one way and the other coil culls it back.

I have some AC relays. Two separate coils. The arm is spring loaded "over the top" latch.
Sorry for the bad drawing. The arm hold to the left or right but does not stay in the middle.
I drew two coils (left and right) they are elector-magnets. That pull the arm over, past center.
upload_2018-3-9_8-33-29.png
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
This could actually be a DC relay, except that when used in the fridge a diode is used in the AC to change the polarity. Pulsating DC would still be DC.

The DC latching relay usually comes in two varieties: Single coil where polarity is used and Dual coil (set/reset)
 

ronsimpson

Well-Known Member
Most Helpful Member
There are many different kinds of latching relays.
Some have one coil and (+) or (-) to set/reset the relay.
Some have two different coils.

This kind comes in AC or DC. It is two relays pushed together. In the middle there is a spring latching white piece of plastic.
No power, it will remember.
With one coil powered it pulls all contacts one direction.
With both coils powered; the left coil is pulled to the left and the right coil is pulled to the right. Which ever coil is released first will move to match the coil still powered. (I have used these to choose which button was pushed first/last in a game show.)
upload_2018-3-9_10-27-51.jpeg
 

eddyj443

New Member
View attachment 111458
I found a picture of how this one works. I think it is a DC relay. One coil pulls the magnet over center one way and the other coil culls it back.

I have some AC relays. Two separate coils. The arm is spring loaded "over the top" latch.
Sorry for the bad drawing. The arm hold to the left or right but does not stay in the middle.
I drew two coils (left and right) they are elector-magnets. That pull the arm over, past center.
View attachment 111459
Perhaps the device has two coils: one for 'set' and one for 'reset', much the same as DC dual-coil latching relays. The magnet provides the latching function.
Thanks for the info, I am pretty sure this only has one coil which is the reason why I don't understand how it works

This could actually be a DC relay, except that when used in the fridge a diode is used in the AC to change the polarity. Pulsating DC would still be DC.

The DC latching relay usually comes in two varieties: Single coil where polarity is used and Dual coil (set/reset)
Thanks for your help, this makes sense and I am tempted to cut the coil open to take a look inside however if internally it was rectifying the AC into DC, how would it change the position of the valve? i.e move from one output to the other
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
From your datasheet.

Solenoid valve to control the power: Solenoid valve driver
need not less than four half-wave sine 50/60Hz positive or
negative pulse(See drive pulse waveform)
, It is not less
than 30s of the interval when a state transition to another
state of the switch

Typical Chinglish.

The diode would be external if it had a single coil.
 

eddyj443

New Member
From your datasheet.

Solenoid valve to control the power: Solenoid valve driver
need not less than four half-wave sine 50/60Hz positive or
negative pulse(See drive pulse waveform)
, It is not less
than 30s of the interval when a state transition to another
state of the switch

Typical Chinglish.

The diode would be external if it had a single coil.
Thanks, so maybe the 240vac label on the solenoid is misleading me. Perhaps is uses diodes to rectify the AC in positive/negative DC pulses. I will take another look at the controller board to see if it backs this up (when I am home).
 
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