24volt stereo

np · Post by np » 04 Dec 2004, 01:34

My dumper truck at work runs a 24volt system.The stereo in it is a 24v Clarion unit,which is no good.I have a new 1 but it is a normal 12volt unit.I`m going to check tomorrow with my multimeter,but i dont think there is anything 12v in it.How can i reduce the voltage to get 12v?Our new dumpers have a reducer in them for the 12v stereo & powerpoint,but i cant get one of them & its a fairly big unit.Is there a small inline reducer or something i can get?Any help would be great as i`m feed up with no sounds for 9 hrs a day.[:(]
Failing everything,i `spose i could get a small car battery & run it off of that.Thanks[:)]

Post by **martyhopkirk** » 04 Dec 2004, 01:49

Dropper resistors i suppose - Thats how the majority of 24v - 12v adaptors work.
Funnily enough im just scratcing my head trying to work out the correct resistor to use to drop 12v to 3v to drive a blue LED - Used to do these sorts of calculations a lot.
Use 1W resistors if going this route ( I would anyway). Someone else may be able to suggest another method. Most truck stops and CB radio shacks (B&D @ Forton services for instance) will have 24v to 12v droppers.

dnsey · Post by **dnsey** » 04 Dec 2004, 01:50

Two approaches occur to me.
If you know an elecronics enthusiast (or your local TV shop is friendly), it would be an easy job to build a regulator to do the job.
The other way, depending on the construction of your battery, would be to tap off 12V above earth (six cells)for the radio supply.

dnsey · Post by **dnsey** » 04 Dec 2004, 01:54

Sorry, Marty, dropper resistors on their own won't work, as the current draw varies considerably, so a resistor which gives 12V under heavy load would allow too high a voltage when, for example, the output is low during a quiet passage. It needs a proper regulator circuit.
For your LED dropper, use the LED specs to calculate the required volt drop and current (don't go too high on this), and use Ohm's law: R=V/I

bikeboyz · Post by **bikeboyz** » 04 Dec 2004, 02:07

You will need a Voltage Dropper designed for use in a commercial vehicle, available from any good truckers shop or CB radio outlet. Try http://www.kcb.co.uk they have them starting at £15, or maybe high street store like Maplins.

np · Post by np » 04 Dec 2004, 02:25

Maplins,£50,KCB,£15.Thanks to all,i`ll have a good look at KCB bikeboyz,£15 is alright.That would do it nicely.I only want to run the stereo,so that 1 should do.Looks small aswell.Bit pushed for space in me dumper.Cheers.

tomsheppard · Post by **tomsheppard** » 04 Dec 2004, 13:44

blue Led Vf= 3V. Vreg =14.4V. Drop across resistor= (Vreg-Vf)= 11.4V Iled
=10mA. V/I=R
11.4/.01=1140 Ohms.
Nearest preferred value is 1.2K
If that's too dim,and the led will do 20mA then 600 Ohms,
or if too bright, 2.4K.Maplins now only sell resistors in tens so buy ten 2k4 resistors and wire two in parallel for 1200 and four in parallel for 600.

Post by **martyhopkirk** » 04 Dec 2004, 14:09

Thanks Tom - been a LOOOOONG while since i did calculations like that. It comes as no surprise to hear my B-Tec PSU project went BANG in a big way when i first powered it on in 1988 as I wired a huge .5 farrad elecrolytic in the wrong way round.
Domestic wiring - much simpler affair, - tellys, videos and radios on the other hand - buggered if i know what goes on inside its all witchcraft to me!
Now bodies, THAT is simple.......

np · Post by np » 04 Dec 2004, 18:41

Well,i checked everything inside today with my multimeter,its all 24v.But checking the batterys i get 14.1v from one,11.7v from the other.I think i will run a wire from the battery with a inline fuse to the stereo,its only 3ft away.I have a earth point next to stereo,& theres only 2 speakers,so 6 connections in all.If not,KCB do a reducer fo £13 that plugs into a 24v cig lighter,with a 12v cig lighter outlet.£18 all in for next day delivery.

tomsheppard · Post by **tomsheppard** » 04 Dec 2004, 19:57

'Ang on! You have two batteries in series? Easy. Find the one that goes to earth and stereo earth goes to that, Run a FUSED wire from the positive terminal of this battery to the stereo positive terminal. Done.

Post by **martyhopkirk** » 04 Dec 2004, 21:58

Not a 24V battery? 2 12V batteries!?!
DOH! (should have asked really!)[:)]

dnsey · Post by **dnsey** » 04 Dec 2004, 23:41

I shan't say 'I told you so!'[}:)]

vanny · Post by **vanny** » 05 Dec 2004, 00:30

Is there such a thing as a 24v battery?
EVERY truck or comerial i've worked on that is 24v is just two 12v's in series, great when your working as a sparky and people are too soft to realise they actually DO have 12v and 24v in the same truck , but have wondered if 24v bateries exist?

Post by **martyhopkirk** » 05 Dec 2004, 14:06

Unsure of that - apart from odd voltage sealed LA bateries used in some alarm installs only other ones i have come accross are 6v DC - old Spugs and submarines (friend of mine - BOB has his workshop and cottage wired up (wia an expensive invertor) to an arsenal of HUGE (and i do mean HUGE) old 6V sub batteries which are charged from a couple of large solar panels and a small wind generator. Cut his elcetrickery bill to less than half what he was using before.
Mind you this is the bloke who used some old drain pipes and polyethene sheets to make his own solar powered water heater... Looks bloody ugly, but works. Never even occoured to me that it would be 2 12volters. (permission to kick me up backside)

np · Post by np » 05 Dec 2004, 19:51

Got all me bits to fit it.There looks to be a small wire coming off the terminal on one of the batterys,so will take the feed from that.Will let you all know the out come tomorrow.