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24v dc relays not de-energising

7552joel

New Member
Hi there. I have two panel mount 24v relays which are driven by 24v switch panel. Both relays when energised turn on a dc-dc converter 24 down to 12v then the loads connected to each relay are 12v loads. Problem I have is when both switches are turned on then one back off the relay stays energised which makes me think the 24v on the common is travelling back through the coil keeping the “off” relay energised. Any ideas would be great sorry for the bad drawing.
BA3C52FB-3BBB-4812-8932-1CD49B4EE127.jpeg
6F014D72-30BC-4CA8-B55B-0680E587AF99.jpeg
 

sagor1

Active Member
Drop out voltage for a 24VDC relay is only 2.4V, any ground loop may hold it in still.
Are all the grounds tied together? Is the 24/12 converter also using the same ground?
Re-check your wiring....
 

Les Jones

Well-Known Member
Most Helpful Member
When both relays are energised the two 24 volt sources are connected in parallel via the sets of contacts that switch the 24 volts being in series between the two 24 volt sources. So when the second 24 volt source is removed there is still 24 volts available to energise the relay that was initially powered from the second power supply. Your diagram is not very clear as it does not show if the switching is done on the output of the 24 volt power supplies or the power input (240 V AC ?) to them. It is possible that the power supplies could be damaged if they are back fed with24 volts when the input power source is removed. If you tell us EXACTLY what you are trying to achieve it will help us with providing you with a solution. (This may just require adding a few diodes to to the circuit.)

Les.
 
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7552joel

New Member
Thanks for the response that’s exactly what I think is happening with 24v being present on the coil from the second circuit . I know the drawing is bad sorry for that. The source is a single 24v battery and the input to the individual relays is from a switch board. It’s in a boat. Both relays share a common ground. The 12v loads share a common ground from the output from the dc to dc converter. Again drew it poorly. Any suggestions on what size diodes I would need to put in? Keeping in mind the maximum power with both loads on is 2a at 24v into the dc to dc converter
 
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sagor1

Active Member
Is there a reason why you can't use a DPDT switch on the 24V source AND the 24-12V converter? If you had a DPDT ON-OFF-ON switch, center positiion would be OFF. Turn on at the 24-12 converter and 24V relay (which turns on +12V to device) at the same time via the switch.
In fact, they make 4PDT switches, that can switch everything without relays, just feed the +12V from converter to one of the 4PDT poles and feed to device. 3PDT may even work, but 4PDT may be easier to find. Most switches like that will handle 2A easily.
 

Les Jones

Well-Known Member
Most Helpful Member
I am assuming that each of the two switches is to control the two 12 volt loads and that you have the following four conditions.
1, both loads off.
2. Load 1 on and load 2 off.
3. Load 2 on and load 1 off.
4. Load 1 and load 2 on.
Following sagor1's suggestions this could be done using two DPST switches. (But DPDT switches may be easier to obtain.) This would not require any relays. This may require more wires between the switch locations and the other parts.
Diagram 1 shows the way I would do it. (Depending on the physical location of all of the parts.)
Image1170522.jpg


If you have already wired it up as in your diagram then adding a diode between each 24 volt relay contact output and the input of the converter would probably be the simplest way. (The diode cathodes to the converter input.)
The diode current rating would need to handle the maximum input current to the 24 to 12 volt converter.
Probably the simplest way to mount the diodes would be to use a bridge rectifier as shown in diagram 2. The negative output of the bridge would not be connected to anything. Using the diodes would drop the input voltage to the converter by about 0.6 volts but I don't think this would matter.

Les.
 

7552joel

New Member
I am assuming that each of the two switches is to control the two 12 volt loads and that you have the following four conditions.
1, both loads off.
2. Load 1 on and load 2 off.
3. Load 2 on and load 1 off.
4. Load 1 and load 2 on.
Following sagor1's suggestions this could be done using two DPST switches. (But DPDT switches may be easier to obtain.) This would not require any relays. This may require more wires between the switch locations and the other parts.
Diagram 1 shows the way I would do it. (Depending on the physical location of all of the parts.)
View attachment 137147

If you have already wired it up as in your diagram then adding a diode between each 24 volt relay contact output and the input of the converter would probably be the simplest way. (The diode cathodes to the converter input.)
The diode current rating would need to handle the maximum input current to the 24 to 12 volt converter.
Probably the simplest way to mount the diodes would be to use a bridge rectifier as shown in diagram 2. The negative output of the bridge would not be connected to anything. Using the diodes would drop the input voltage to the converter by about 0.6 volts but I don't think this would matter.

Les.
Thanks Les that’s incredibly helpful. I will be using a bridge rectifier like your second suggestion. Reason being is the 24v switch panel has about 50 switches on it and is not easy to modify and I’ve already got the 24v relays wired up :).
 

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