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Still need help with current backfeed problem

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gerryr1gerry

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I need something which will stop backfeed on the attached (Rough) circuit.This is one of 15 circuits exactly the same.

My problem is that no matter which power source I use , both LED warning lights come on.

The circuit uses 24VAC.

If it were 24VDC I would imagine I would put a diode in each circuit to stop the backfed but that dont help with the 24VAC.

Can anyone suggest a device which will stop the current from backfeeding to the unpowered side of the circuit.

Thanks
 

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That is a problem. As you note, there is no "diode" that can block the direction of AC current.

Can you change the on/off switch to a double-pole? That way you could use the other contact to control one of the LEDs and inhibit the operation of the other.

Alternately is there a definite load current when the circuit is energized? If so you could perhaps detect the current in each branch and use that to light the LEDs.
 
You can activate a DPST or DPDT relay from the output of the timer and the switch and use the relay contacts to switch the power to the load and to the led.

Alternately, if the timer has multiple output contacts & you can replace the the switch with a multiple contact switch (as suggested above), you won't need the relays.
 
Thanks guys. As there are 15 circuits it would be quite costly to put a relay into each circuit I think.The on/off switches have an inbuilt LED to indicate On/Off.The Timer circuit has a seperate LED in the line to indicate if that is on or off.Wasnt quite sure what you meant by "definite load current when the circuit is energized? If so you could perhaps detect the current in each branch and use that to light the LEDs."
The On/off switches have a five pin configuration at the back

1 2


3 4 5



Currently I am using 4.......power In
5.......power out
5 and 1 bridged to provide LED power
2 led neutral

I'm not sure if this is any use. The switches came without diagrams and I found by trial and error that this sequence worked.
 
Actually even a SPST relay would be fine; the indicator connects across the relay coil & the relay contacts switch the power to the load. I'm not sure what your target price is, but as an example, this 24VAC relay is AUD2.79 (ea), so <$90 for 15 units. https://au.element14.com/te-connectivity-schrack/rt314524/relay-pcb-spco-24vac/dp/1629047

Or you can use a AUD0.87 24VDC relay with a bridge rectifier & 10uF filter cap for around $2 per assembly; so ~$30 for all 15 units. https://au.element14.com/te-connectivity-schrack/pb114024/relay-pcb-spco-24vdc/dp/1175078
 
Thanks heaps Dougy83 this seems to be the perfect answer. I had'nt realised the relays were that cheap.Really appreciate your input and thank you to the other respondants.
Problem Solved (I think):eek:
 
Glad to hear it. If you do go with a DC relay, this is the setup I'd use (for the relay given in the above post). The specified parts can be substituted for cheaper or more available parts.
 

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Thanks Dougy but I am not familiar with electronics so will have to get a friend to translate the schematic for me.

By the by what do you think of leaving everything the way it is, including the diodes still in place and placing a bridge rectifier in each of the output circuitsfrom the programable timer to convert the AC to DC. Then would'nt the diodes work with the DC output.

The solenoids dont care if its AC or DC and I could use another rectifier to convert the input power to manual on/off switches to DC.

I had a bridge rectifier and tried it out on just one circuit and it seemed to work fine.

As I said I know nothing abour electronics so can you point out any problems that you think might arrise.

Appreciate your input

thanks

Gerry
 
what do you think of leaving everything the way it is, including the diodes still in place and placing a bridge rectifier in each of the output circuitsfrom the programable timer to convert the AC to DC. Then would'nt the diodes work with the DC output.

The solenoids dont care if its AC or DC and I could use another rectifier to convert the input power to manual on/off switches to DC.
Well if it works acceptably, then great. I take it you have access to both leads of the solenoid to connect the bridge rectifier to? (i.e. no common return connected to the AC neutral/return). If you do, then 2 bridge rectifiers would do the trick. LEDs go on the AC side, of course (you should also connect a diode in series with the LED to stop it conducting backwards - I'm not actually sure if this would otherwise damage the LED...).

The only problem I can think of is the possibility of magnetising the solenoid - but I don't know if this is a real possibility; maybe someone else knows better.
 
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