# Convert a dual signal circuit to control 1 coil

#### curacor87

Joined Oct 16, 2023
3
Hello everyone,
I have several industrial board powered by 24v dc that control valves using double magnets with 24V to turn the valve in ON and OFF state with impulses as the valve retain the position.
During the decades a new model have been created that control similar valve using coils (24VDC) that are energized for the whole time the ON state is needed.
There is a way i can create an adapter circuit to control the newer valves?
As of my experiments the old boards have 24V+ always on the magnets side and the control is using the negative.
New valves have typical current of 125mA per coil at 24V.

Sorry for my bad english e hope to get an answer from you!

#### Alec_t

Joined Sep 17, 2013
14,214
Welcome to AAC!
What you need is a latch circuit which is set by an 'on' command pulse and reset by an 'off' command pulse.
Are your present control pulses positive-going or negative-going, and what is their duration and repetition frequency?

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#### crutschow

Joined Mar 14, 2008
34,044
the control is using the negative
Does that mean the control signal is a negative going voltage or that it's switching the negative side of the 24V supply?

#### curacor87

Joined Oct 16, 2023
3
The positive is always connected to the magnets, while the "signal" is the negative of the double magnet coil which will be on or off.
The frequency is variable from 50 Hz to 300 Hz with 50% to 70% duty cycle for some valves, but can also be a repeated signal to maintain the position of the magnet every 2-3 seconds then switch to the other position with a command and again with mantaining position for the other valves.

Joined Jul 18, 2013
28,513
How many valves will be on at any one time?
The new valves will require constant current so the PS will have to handle this new load.

#### MisterBill2

Joined Jan 23, 2018
17,790
Without any more information about the rest of the control scheme the very best the TS can hope for is random guesses. Consider that at some time some portion of the control system decides that the valve needed to be switched on, and so a "open valve" pulse was sent. So the valve opened and something flows, but the condition requiring the valve to be open does not change instantly. So there already exists a signal, some place, that still wants that valve open. THAT could be used to switch on 24 volts to hold the valve open until such time as the condition changes and the valve needs to be closed. So the condition changes, which would then remove the 24 volts from the hold open coil and possibly apply it to the close valve coil, if there is a second coil. Many valves that require constant power to stay open, close when that power is removed. SO it seems that the control scheme is rather different.
In addition, maintained position valves are still available from a number of suppliers, although probably not local stock.

So really we need a bit of description because it seems like a great deal of simplifying could be done. the alternative is to create an add-on that patches the new valves into an old system, which will then be much less reliable, and MUCH more complex.

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#### curacor87

Joined Oct 16, 2023
3
How many valves will be on at any one time?
The new valves will require constant current so the PS will have to handle this new load.
Amps aren't a problem as there is a 24V 10A psu for 8 boards. Anyways no more than 4 valves will be on at the same time per board so 500mA.

#### MisterBill2

Joined Jan 23, 2018
17,790
I repeat the request for more details about the control scheme. Without additional information it is not likely that any useful suggestions will arrive, but rather just random guesses based on very little information. Certainly not needing to switch the valves allows a quite different and better, control scheme. Not just a bandage.

#### Alec_t

Joined Sep 17, 2013
14,214
The frequency is variable from 50 Hz to 300 Hz with 50% to 70% duty cycle for some valves, but can also be a repeated signal to maintain the position of the magnet every 2-3 seconds then switch to the other position with a command and again with mantaining position for the other valves.
I'm not sure if I understand that. Are some of the valves proportional (hence the variable duty cycle) and the other valves simply fully open or closed? Can you provide links to the old and new valve specifications?

#### MisterBill2

Joined Jan 23, 2018
17,790
The comment about duty cycle in post #4 totally alters the control issue. Post#1 told us that the valves were two position maintained, while post #4 implies quite a different situation.
To operate valves that need a continuous voltage to operate it will simply be required to adjust the duty cycle for the valve open coil to 100%. And if there is no second coil to close the valve, the adjust that duty cycle to zero, and do not connect the wire to the coil not present.

OR, provide the more detailed description that I have requested twice.