# car stereo mains

Discussion in 'Electronic Basics' started by [email protected], Feb 19, 2006.

1. ### Guest

How would I go about powering a car stereo from the mains? I'm guessing
the most logical way is to get some sort of transformer to step down
the voltage to that of a car battery. Is there an off the shelf
device/transfomer that I can just plug into the mains and step down
from 240V to 12V? (particularly with no additional soldering/wiring
required).

If anyone has any links/diagrams to anything like this please let me
know.

Thanks.

2. ### ChrisGuest

Hi, Will. A transformer won't cut it -- transformers put out AC
(alternating current) voltage, which will ruin your car stereo
instantly. It wants direct current.

You're looking for a 13.8VDC bench power supply. Since you didn't
mention the power requirements of your car stereo, and you're on the
other side of the pond, I'd suggest you look at the bench supplies from
Maplin, and pick one:

http://tinyurl.com/7koln

If you know the wattage of your car stereo, just divide by 13.8 to find
the current requirement. (e.g. 60 watt stereo means 60 / 13.8 = 4.35
amps. And, for car stereo use, be sure to size the power supply for
continuous duty (it will be on and at volume for more than a minute).
The biggest of these is only rated for 7 amps or 96.6 watts (13.8V * 7
amps).

The ones with current foldback protection are helpful if you're
repairing car stereos, or there's a chance of an accidental short
circuit.

If your stereo is more than 100 watts, you can look around and google
something under "13.8V bench power supply". Try to get a "linear" or
transformer-based supply. Units over 100 watts pretty much have to
have a fan, which might be annoying.

I had a great car stereo on my workbench with a 13.8VDC bench supply
for many years.

Good luck
Chris

3. ### Guest

Excellent. Thanks very much.

4. ### Peter BennettGuest

The device you want is called a DC power supply. You will need to
determine the current your car stereo requires, and get a power supply
that can deliver at least that much.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

5. ### Phil AllisonGuest

** First off - use "googlegroups" correctly.

Do NOT simply hit reply !!!!!!!!!!!!

That way we can see who you are replying to and about what.

* Verrrrrry simple.

Use a good car battery and a charger to keep it topped up.

The cheapest & best way.

A DC supply that can do as well costs MORE than your POS stereo.

....... Phil

7. ### ChrisGuest

I suppose the "elite" here have some unofficial rules, which us
groundlings from Google Groups must follow. Most of it has to do with
conforming to standards which will simplify things for newsgroup

1) Always apologize for being a groundling. We are indeed children of
a lesser god, and not worthy of taking up space on their store-bought

2) In Google, you click on the "show options" link at the title bar of
the post, then click on "reply". That will give you a formatted post
with the entire previous post already shown (with the > character
preceding each line, allowing the newsreaders of the gods to optionally
obscure it). In days of yore, when 1200 baud modems ruled the earth
and bandwidth was an important consideration, it was considered bad
form to include all the stuff which had preceded. You just included
enough to keep the conversation going. However, it's still considered
good form to do some editing if it's getting long.

3) It's considered good form to bottom post. This allows the person
who's seeing the post appearing out of nowhere to follow the thread.
That merans putting your response after the prior post, even if you
have to summarize.

4) Execeptions to 2) are typically made in cases of general short
responses like OK, thanks, "plonk", &c. Yours was one of these, so I'm
not sure where the other post is coming from.

There are also unofficial rules relating to common courtesy. Groups
which cater to newbies are assumed not to have people waiting to ream
them for their ignorance. If they wanted that, they didn't have to
post on a newsgroup -- they just could have gone to their mother-in-law

My bench stereo was an OEM from "the best car I ever had" -- a
comfortable, loyal little Toyota Corolla that lasted forever. The 20
watt OEM stereo lasted for more than a decade after the car wore out at
almost 200,000 miles. It cheered me up quite a bit, not least because
it had wonderful signal sensitivity, and good fidelity. The original
owner paid a good price for the stereo upgrade. It was even easy to
repair. A remarkable example of good engineering. Or, as the other
post would say, a POS stereo. Whatever.

Cheapie Automotive battery: 22 pounds
Cheapie charger: 11 pounds
Total cost 33 pounds

Maplin XM20W 2 Amp Continuous 13.8VDC Bench Power Supply: 15 pounds
Total Cost: 15 pounds

Not only that, but you don't have to worry about disconnecting the
charger during use, and reconnecting and recharging after use. The
battery charger typically puts out around 15 to 16VDC, which stresses
out the stereo if it's running hot.

The economics change somewhat for higher wattage stereos, but there are
other considerations. Running a stereo at 100 watts is a lot like
quickly, which really isn't good for automotive batteries. You might
improve on this by placing batteries in parallel, but that doubles or
triples the cost, and has it's own set of problems. If the batteries
are not perfectly matched, the one with slightly higher voltage will be
doing most of the work, and will want to charge up the lower voltage
battery. Not an optimal solution.

Of course, if you're just repairing stereos, it _is_ more economical to
pop a battery, put in a series fuse, and have at it. No cost at all,
and after your stereo is repaired, just put the battery back
(recharging if necessary). No cost at all. But I didn't get the
impression you were repairing.

Again, sorry. S.e.b. is supposed to be newbie-friendly.

Good luck
Chris

8. ### John FieldsGuest

---
No, they're just guidelines which we should all follow in order to
make life a little easier for all of us. The recent problem has
number of the truly clueless has invaded Usenet, to the detriment of
all.

Phil Allison is _definitely_ not one of the "elite" here, no one
really is, and his behavior is far from what you might expect from
the rest of us.
---
---
Not really "standards", per se, just netiquette.
---
---
Plus, you're not allowed to use sarcasm!
---
---
It came from a misanthrope.
---
---
This is such a group, and newbies don't usually get reamed for their
technical ignorance, the "motto" of the group seeming to be "There
is no such thing as a stupid question here."

What they might (and often do) get reamed for is attitude and
thoughtlessness.

9. ### Guest

you can't blame Phil. He is annoyed at me for being a Pomme. His
grandfather was a rapist.