OT: Voltage / ampage question

[guddler]

[ukvac] OT: Voltage / ampage question
Hi Guys,

Just been to a car boot sale, and one of the things I picked up was a ghetto
blaster. Now it was pretty obvious that it was going to be shot as the guy
was flogging it with a UK plug and a quick inspection revealed it was US
120v input, but for £2 the missus wanted to take a chance (altogether now,
Bless!!!).

Anyway, hopes were raised when I opened it up to find a blown fuse, then
dashed again when I tested the transformer, and with 120v going in, nowt
comes out.

So, I guess then that I can just run it on a normal DC adapter wired to the
battery input point. It takes 10 bateries at 1.5v = 15v.

All good so far, BUT, what about juice?

On the back it reckons 40W @ 120v, which I reckon is 333mA. Is that correct?

I've rigged up an AC/DC converter to battery terminals before when I was a
kid, but being slightly more knowledgable now, I'd like to solder in a
proper connection and ensure I don't meltdown the adapter.

Am I right to assume I can probably drive this thing from a 12-15v 300mA
adapter? Or thereabouts?

Cheers for any info,

Guddler.

------------------------
Guddler's Arcade
http://www.guddler.co.uk

 

[P-Man]

Re: [ukvac] OT: Voltage / ampage question
yeh you can, however, i'd go for a 500ma or 750ma or even 1A if you can get
it.. the higher rated the better i say.

Andy Welburn
www.andys-arcade.com

 

[guddler]

RE: [ukvac] OT: Voltage / ampage question
Oh well, looks like something more than just the transformer and a fuse blew
when some monkey connected it to 240v mains as supplying 15v DC to the
battery connectors (just to see if it works before getting a proper adapter)
doesn't do anything either.

That was from my Taito rig with 12v adjusted up to 14.9v, so plenty of juice
:O(

Unless of course I've overlooked something?

Don't think so though...

 

[d-type]

RE: [ukvac] OT: Voltage / ampage question
Transformers are typically rated at their output, although inputs are sometimes specified as well.

40W @ 120V = 1/3 Amp input. However, 40W at 15V = 2 2/3 Amp output.

Use something too small and you'll blow it's fuse or melt it.

You're looking at a linear xformer something the size of a large brick, which you'll probably find
hard to find.

Alternatively, you could try an arcade or PC AT switcher. Should do the job at 12V but you'll
probably need to load the 5V with a big (and I mean BIG) resistor as the 12V is often generated from
the 5V.

Ni-Cad rechargeable batteries are 1.2V each, thus 10 x 1.2 = 12V, and they will typically run a
ghetto blaster OK.

You could make your own switcher, I've seen quite a few projects for this around the net. You can
buy a switched mode power supply IC and then get the datasheet from RS, and build your own.

You can then tune it to what ever voltage and current you like from the instructions.

I found out a bit about them when I was repairing the switcher on my Sharp MZ80K, they're dead
simple really - don't let a PC one put you off!

D-Type

>

 

[guddler]

RE: [ukvac] OT: Voltage / ampage question
I guess this is getting even more OT, but hell it's all to do with theory,
so it's more on T than some posts :O)

Anyway, I have a few things to check out before chucking the unit, and then
once i know for sure whether it works or not the problem is indeed where to
source a reasonable supply. If I knew the specs of the secondary winding on
the transformer then I would buy a 240v replacement transformer block, but
alas there's barely any markings on it at all!

For a moment last night it looked like Maplin did the perfect adapter for it
- 3A @ 15v. Alas just like most stuff that we find useful in Maplin -
DISCONTINUED with no recommended replacement - doh!

Oh well, maybe ni-cad batteries aren't such a bad idea. I need some new AA
ni-cad's too, so perhaps a new charger as well.

Anyway, thanks for all the suggestions on and off-list. Who'd have thought a
2 quid item from a boot sale could supply so much bank holiday
entertainment!!

Gudd.

 

[d-type]

RE: [ukvac] OT: Voltage / ampage question
However... I don't know what kind of ghetto it is, but 40W is an awful lot of watts. At the right
frequency, 2 or 3 watts can be v. loud.

On normal volume, that's probably all it's taking.

I'd be tempted to by a UNIROSS 1200R mains adapter, like the one I have. It's adjustable between 1.5
and 12V, gives out 1.2A, but most importantly it's a big heavy chunky barstard and about the size of
a _small_ brick.

When you're talking transformers, size matters! It runs just about anything I've tried, including
stuff rated at 2A, and it was about 15 quid. I think I got that at Maplin. They might even sell them
at Argos.

It has a bunch of adapters so it's fits allsorts and it's regulated. I don't know about this model,
but voltage regulators ICs usually have over supply protection - if you short out the output, it
lowers the output voltage to protect itself.

This will be heard at the ghetto as an unplesant distortion, just like your battery-powered radio
does when the batteries are on their way out.

I'd give that a try. If it starts getting hot, turn down the ghetto volume, but I thinks your ears
would tell you before it got hot. Even if it's no use at all, at least you've got yourself a handy
power supply.

<POSSIBLY DODGY WARNING, BUT FUN ANYWAY> You could try running it off a car battery charger. I've
done this lots of times with car stereos in the garage. If you're lucky, you won't get any added
noise on the output.</DODGY>

D-Type

>

 

[guddler]

RE: [ukvac] OT: Voltage / ampage question
Ahhh, we live by "dodgy" :O)

I like the sound of that!!

 

[zepromz]

RE: [ukvac] OT: Voltage / ampage question
At 13:19 25/08/2003 +0100, you wrote:
>However... I don't know what kind of ghetto it is, but 40W is an awful lot
>of watts. At the right
>frequency, 2 or 3 watts can be v. loud.

The 40w figure quoted on the back of the unit is going to
represent the power consumption, not the output wattage.
Your average cheap amplifier circuit is going to swallow as
much as 3/4 the input wattage, then you have the power
required to run the motors etc, an RMS output of about 8-10
watts is more likely what this box is putting out. Any claims to
more than that on the box/casing are almost guaranteed to
be measured in "PMPO" (peak music power output) and will
be blatant overstatements of the potential output of the device,
usually measured with a square wave running at 1v peak to
peak, driving the amp as far as it can go into distortion, then
measuring the highest transient peak in a 5 minute run.
Divide by at least 4 to get a realistic figure.
This goes doubly so for in-car hifi, as Kev will testify

 

[Outrun]

Re: [ukvac] OT: Voltage / ampage question
yup.... those "Boss Sound" and "Pro Sound" 1000w car amps for 50 quid which
only have a 25 amp fuse in them...

Hmmmm i think not

Kev