12v siren on M38A1 24v

[LeonidasGR]

Hi.
I have a M38A1 (24V system) and i want to connect a 12v siren. Can i use the same ground for negative and connect the siren to the + pole of the first battery with fuse box and switch? The siren will work as you can imagine very little, only for parades and shows. Thanks

The siren is Elektror FS1A


and my jeep

 

[someoldmoose]

I'm gonna say that with the infrequent amount that it will be used, Yes, BUT not as you describe. Wire it direct to a battery with BOTH connections on the same battery. Your plan will still be 24v. The BEST option is to "hide" ( I know, difficult in an M38 ) a dedicated 12v battery for the siren. Even with infrequent use you will still be creating an unbalanced draw on the 24v system. That siren probably draws at LEAST 60 amps while spooling up ( basically it's a starter motor with a fan / air chopper attached ). Just my $ .02. Really cool siren though.

 

[LeonidasGR]

Thanks for the reply. The siren draws 23amps. You are right about the unbalanced power draw, i thought that for that little use it wont be a problem for the battery.
This is what i was thinking to do

 

[jasonjc]

You better use a relay. Thats a lot of amps for a switch.

 

[someoldmoose]

As I said, if you connect the ground ( - ) to the chassis you will be attached to the 24 v system. You will have to connect the positive ( + ) and negative ( - ) directly to the terminals of the same battery in order to only get 12 v. Also from your drawing, a 25 amp fuse won't cut it. You said it draws 23 ( possible when running at full speed, not while getting "up to speed" ) so even if that were true your fuse needs to be twice the circuit load or your siren will only groan instead of scream. If I were installing this I would use a starter solenoid ( old school Ford type ) between the battery positive and the siren with a MAX50 fuse in a covered holder between the battery and the solenoid. Then wire the momentary switch (es) to the "S" terminal of the solenoid. You do want want the full draw going through the switch. Your diagram would have you replacing fuses probably every time you hit the switch, and replacing switches often. Good luck and PLEASE, post a video of it screaming when done.

 

[LeonidasGR]

First, is the wiring correct or i will have a problem? Second i dont know how to wire the relay or what type should i use. I am thinking to use a heavy duty push button (similar to start button). It says 12v 30A or 24v 15A

 

[tennmogger]

First, is the wiring correct or i will have a problem? Second i dont know how to wire the relay or what type should i use. I am thinking to use a heavy duty push button (similar to start button). It says 12v 30A or 24v 15A
View attachment 733478

Nothing wrong with keeping it simple like you wired it. That switch will handle the load fine. If the siren has 23 amps on data plate then that already includes the start-up spike and the motor probably draws much less while running.

The siren can use the chassis ground where it is mounted without becoming part of the 24v system. Just tap the positive "bottom" (12v) battery to get 12v, just as you drew it. You do not have to run the siren ground to the 'bottom' battery to avoid the 24 volt system.

Of course this load on one battery will unbalance the batteries but for occasional use simply recharge both batteries separately when the parade is over, Then you are back to 'balanced' for the remainder of the year. Just use a simple 12v charger, and no, you do not have to disconnect the batteries at the vehicle. Simple.

 

[LeonidasGR]

Thanks. I think i will keep the simple wiring. Anyway its only for shows.

 

[LeonidasGR]

OR this?