Using 12V car battery

[willemvdm]

I know this is slightly off topic, but I recall threads here about DVD players, so I'm hoping you can help me.

I've got a portable radio that can play with 8 x 1.5V batteries. My question, if I connect a 12V car battery to the terminals, will it damage the radio?

Any other sugestion on how I can implement a sound system without AC power and without spending to much cash. Would like it to run off car battery, as replacing ordanary batteries will be too expensive. Ni-MH batteries also expensive, besides 3V or 6V devices won't be loud enough. Need it for outside at my stables.

Thanks for any advice.

 

[daysleeper]

Rather don't!

You must remember that even though its the radio is 12V, batteries only deliver a small amount of amp.

car batteries deliver enough to swing the starter motor and solenoid, so there are far more amps on the battery.

also keep in mind, that the alternator has a built in regulator, to when you are driving happily and you put on you head lights, the rail will drop, then seconds later it'll "spike" to 14,8 volts odd, when the car tries to charge the batteries.

the same thing happens when you buy those cigarette lighter charges, the cheep no name ones can actually damage the ics and tracks in the phone because of this fluctaution.

remember that the lighter plugs through a fuse probably like 5A or so, but other than that, its raw rail that your poor little battery powered radio is tasting.

other devices like car radios usually have some type of in-line fuse on the red wire that shorts out if it gets to hot. and the radios themselves and dvd players have these sort of things build in.

also remember that when you used these sort of DC devices at home, the adapter that does the ac - dc thing uses a diode to convert the current, and then also uses a transformer to drop it down for 240 to 12 or like 14.8 on your router ect. so this also protects these devices and gives them more or less steady direct current, because if you want to get really technical, the transformer creates an semi independant circuit by using electromagnetic means (remember the right hand rule) so the DC circuit is not acctually physically connected to the AC circuit in theory.

what you are trying to do is rather dangerous, and i wouldn't leave it unattended because you could start a fine in the car, and fire and petrol= booom!

rather just get stuff ment to work in cars.

get rechargable batteries they save you money.

 

[Gaz{M}]

I say go for it. Connect a fuse inline like this:

(BATTERY +) ---------> (FUSE) --------> (Radio +)

then

(Radio -) --------> (BATTERY -)

A 3A - 5A fuse should be plenty.

You are going to have to poke around inside the radio's battery compartment to find the contacts that are + and -. How are the batteries arranged inside the radio? 2 rows of 4 facing opposite directions? This is important, since if it is 2 rows or 4, then somehow the rows are connected in series, maybe like this:

+[]- +[]- +[]- +[]- B

-[]+ -[]+ -[]+ -[]+ A

with point A connected to point B if you see what i mean, creating 8 batteries in series all facing - to +. Can you give more details on the battery arrangement?

 

[werner]

it will work just fine (mostly)

the amps is not a problem, as the battery is only capable of delivering the amps that the radio requests. it doesnt "pump" the amps out like the potential difference (voltage)

a car battery is just a series/parallel configuration of cells, normalls hooked up to give 12.4v if i remember correctly. it doesnt go to 14 or whatever volts unless the alternator in a car is charging it...so a battery sitting on it's own, fully charged, will pump out 12.v volts at the required amps the device needs. luckily, a car battery can deliver loads of amps, which is why it is handy for starter motors etc.

the amps usage of the device will determine the runtime of your radio..and i guess a normal 12v radio will run into days if not weeks on a car battery...easy peasy. a pretty normal 60ah car battery will give 60 amps for one hour before being too flat to be useful. or one amp for 60 hours...you get the idea.

the only problem i can see is the fact that normal alkaline cells dont really pump out 1.5v when under load. so if the radio specs enough batteries to give 12v, when they are under load it will sag to probably 11v or so, whereas the car battery will happily carry on at 12.4 volts. luckily, most electronic circuitry has enough of a buffer that they tend to run on voltages which are "close enough" on the higher side, and on the lower side. so it *should* be perfectly fine.

put a fuse on the + side of the battery between the radio, as it is true that a car battery has enough amps to solder spanners together, so frying a radio is a piece of p1ss a 3amp fuse will be plenty as (volts x amps= watts) so 3amps x 12v =36 watts. if the radio is not capable of drawing more than 36watts (which, for a portable radio running off c cells or d cells is a heck of a lot...more than likely going to be around 10 watts) at full power then no need for a bigger fuse.

assuming the radio does 12 watts (this makes my calculation easy)...12 watts at 12 volts=1amp...and will run for 60 hours on a 60ah battery 5 hours or so a day will mean 12 days runtime.

hope the horses enjoy the music some mozart should get them in a happy mood.

 

[Hein_JHB]

I will use a 12v rechargable alarm backup battery those that they use for electric gates and house alarms. I got about 3 of them and i used 1 before to power my portable cd player with a converter and it worked very good

 

[Nod]

You can use a voltage regulator (LM7812) to put a ceiling on the amount of volts. See this URL for details. Very simple to do, and very effective.

 

[Gaz{M}]

You can't use a 7812 voltage regulator on a 12V battery. The voltage regulator only works properly when connected to a 14V or higher source, as it has what is called a 'drop-out' voltage due to its internal circuits.

 

[willemvdm]

At daysleeper: Not going to use radio in car, so spikes, petrol and booom not applicable.

At Gaz: Yes, you got battery config right there. Two rows of 4 each in different directions. I have located the two points to attatch battery to.

it will work just fine (mostly)

the amps is not a problem, as the battery is only capable of delivering the amps that the radio requests. it doesnt "pump" the amps out like the potential difference (voltage)

Thanks werner. That is the part I was worried about. The radio I got don't get used at all, so if it do go POOF it won't be that serious, but still wanted to make sure before I try it.

I got wires with clamps to put on the battery, must still build a shelve or something high enough so horses and people don't mess with the radio and then I must get the battery itself. Then I'll give it a try.

The fuse is a good idea. Where would I get something like that. Will I be able to get a fuse that I can put on the wire at a car electrical place? I suppose the normal fuses you get in the fuse boxes won't work for that or will it.

Thanks for the help.

PS. Country music is more my stile.

 

[bullfrog]

Like said before, voltage is the amount of electrons a battery can push through a certain thickness pipe. Doesn't matter what amp's the battery can provide, it can still only pump so much electrons through the same pipe. Like water pressure if you will. That is why the voltage thing is in existance, to tell you the potential difference between the two points on the battery connector plates. So i see no reason why it shouldn't work.