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Topic: Fire siren project, relay help needed. (Read 8459 times) previous topic - next topic

Fire siren project, relay help needed.

I'm a vol. emt and fire fighter, I have two identical sirens that I've been running paralell to each other with a dual throw toggle switch, I need to redo these.  I dont have room for the dual throw switches, theyre too bulky.  so I thought I'd try relays.  what I had in mind was, in the first pic. if they make such a thing, using a dual throw relay.  i'm not sure if this will work.
relay design.jpg (56.4 KB)
In the second set up, running two relays, one after the other, using the coil side of the relays in a bridged set up. power wire into relay 1 pos, thenfrom relay 1 neg. to relay 2 pos. then from relay 2 neg. back to the battery.

relay design 2.jpg (45.7 KB)     

in the third,  I'm illistrating the idea of using one sirent to trigger the relay to start the other siren. 

relay design4.jpg (31.6 KB)



what do you guys think would be the easiest, what relays would you reccomend?
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Fire siren project, relay help needed.

Reply #1
I would go with the two single pole relays in your second example.
The relays should be in parallel instead of in series as in your example.
With the relay coils in series, you would need 6 volt relays as the 12 volts would be divided between the two relays.
Wire the +12 volts from the switch to the + side of both relay coils and the negative side of both relay coils to ground.

Fire siren project, relay help needed.

Reply #2
Are these electronic sirens or the old motor driven ones?
I think the old style motors used a lot of power, so you will need to size the relays to handle the current load.

Fire siren project, relay help needed.

Reply #3
yeah theyre electrical sirens  are you sure I only need 6 volts if I spit the power wires and run them seperately from one switch?
86 Thunderbird TurboCoupe, 66 289 HI-PO, auto.
--------------------------------------------------------------
Hoof beats may be faster than heartbeats, but birds are faster than ponies!

Fire siren project, relay help needed.

Reply #4
so it would be more like this, are you sure it would split into 6 volts per relay, or would it stay 12 volts per relay?


86 Thunderbird TurboCoupe, 66 289 HI-PO, auto.
--------------------------------------------------------------
Hoof beats may be faster than heartbeats, but birds are faster than ponies!

Fire siren project, relay help needed.

Reply #5
i'm pretty sure the voltage will stay 12v, but the amperage will drop
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Fire siren project, relay help needed.

Reply #6
Quote from: shameless;368325
so it would be more like this, are you sure it would split into 6 volts per relay, or would it stay 12 volts per relay?



Use 12 volt relays in this example. You have the relays wired in parallel.

Your previous example had them in series.

Fire siren project, relay help needed.

Reply #7
Relays in series use 6 volt relays.

Fire siren project, relay help needed.

Reply #8
Relays in parallel use 12 volt relays. This is the way to go.
You will have 12 volts applied to both relays. Not 6 volts as shown.

Fire siren project, relay help needed.

Reply #9
Quote from: softtouch;368335
Relays in parallel use 12 volt relays. This is the way to go.
You will have 12 volts applied to both relays. Not 6 volts as shown.

12v at both relays with a drop in amperage, compared to running a single relay, correct?
ShadowMSC.com < < Still Under Construction

R.I.P. 'Zump' 8/29/86 - 11/11/11
3- 87 TC's / 1 really mean 83 Capri RS / 94 Sonoma SAS Project on 37x12.50 TSL Radials / 88 S10 that's LITERALLY cut to pieces / 84 F150 SAS, 351M, 39.5 TSL's / 85 Toyota regular cab, 22R 5spd, 3/4" drop, my little junkyard save/daily driver

Fire siren project, relay help needed.

Reply #10
Quote from: Shadow;368336
12v at both relays with a drop in amperage, compared to running a single relay, correct?

Nope. Two relays in parallel will draw twice the amperage of one relay.

Fire siren project, relay help needed.

Reply #11
really? interesting.. always thought it was an amperage drop because the single +12v supply can only feed so much
ShadowMSC.com < < Still Under Construction

R.I.P. 'Zump' 8/29/86 - 11/11/11
3- 87 TC's / 1 really mean 83 Capri RS / 94 Sonoma SAS Project on 37x12.50 TSL Radials / 88 S10 that's LITERALLY cut to pieces / 84 F150 SAS, 351M, 39.5 TSL's / 85 Toyota regular cab, 22R 5spd, 3/4" drop, my little junkyard save/daily driver

Fire siren project, relay help needed.

Reply #12
There would be 2 12v sources. The first is a low amp switching signal from a toggle. The second would be a fused direct source from the battery using like 10ga wire. The Toggle source only activates the relay, it doesn't power whatever accessory. Then the 12v output (12v from bat) goes to said accessory. And of course there is the ground for the relay. If you picked up a 30amp 5 blade relay, then you would only need 1 as there are 2 12v output blades. Mount the relays some what close to where you have the sirens mounted. You won't but a little amperage drop/loss that way and almost a full 12 volts to the sirens.
Wire size and length plays a big role in amperage loss


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Fire siren project, relay help needed.

Reply #13
If they are electronic sirens how much current do they DRAW. I service ambulances and with the units we service the sirens only draw 4 AMPS. So two would draw 8. Not a great amount of current. The ambulances we service dont use relays. But if you want relays use 2 separate ones with 2 separate feeds. Just in case one circuit fails. Normally relays are not used unless the current is HIGH. Not knowing the current draw of your units i cant say whether they would need slave relays. But for safety reasons use identical circuits completely independent of each other. Don't over design circuits. I see people over design circuits all the time and in some cases it is USELESS. Example on a 550 ford ambulance the DOME light is controlled by a switch and relay. Kind of over kill i would say. Thanks

Why would you hook the relays energizing coils in SERIES ???? With the coils in series they would have 6 volts across them. Note by the way they will work that way . But it is not correct by any means.

If you want separate relays design them independently for fail safe situations. This way you can loose one circuit and still have a siren operational
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Fire siren project, relay help needed.

Reply #14
Quote from: 1BadBird;368352
There would be 2 12v sources. The first is a low amp switching signal from a toggle. The second would be a fused direct source from the battery using like 10ga wire. The Toggle source only activates the relay, it doesn't power whatever accessory. Then the 12v output (12v from bat) goes to said accessory. And of course there is the ground for the relay. If you picked up a 30amp 5 blade relay, then you would only need 1 as there are 2 12v output blades. Mount the relays some what close to where you have the sirens mounted. You won't but a little amperage drop/loss that way and almost a full 12 volts to the sirens.
Wire size and length plays a big role in amperage loss

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