Power adapter question

Higher current rating is fine.

The only potential problem is if the product needs a closely regulated

12V DC. The voltage of "unregulated" plugpacks can vary a lot depending upon the load. At no load it could be as high as 16V for instance. However, most commercial products are designed for use with unregulated plugpacks, so you should be fine.

If you really want to be sure, get a 12V DC 1A+ regulated plugpack, such as the Jaycar MP-3486

Dave.

That's how I understand it. If you use a power-pack which is below, it may exceed its max-current. Higher power-paks are OK. In fact I use a 1.5A power supply with switched output voltages which cover the couple of rechargeable torches with no problems. I wouldnt use a different voltage however.

Most old mini B&W TVs, came with 12v 1A power-paks. Just make sure the polarity is correct. These days I notice the majority is +ve inner, -ve outer.

Jason

"David L. Jerkoff"

** Doesn't exist in stores yet.

DSE have this one:

...... Phil

Thank you guys for the replies, very helpful.

Cheers

Be carefull that the polarity is correct BEFORE you connect it.

John G.

"John G"

** Hey - don't spoil his fun ...

.... Phil

Ok so stupid question, how can I check that? All I can see is the plug and the label telling me the required power.

I appreciate the help.

Cheers

I have a safety switch and fire extinguisher, will that cover me? ;)

These days all plug-paks have a small diagram on the front showing the plug as a symble: a circle (outer) with a dot in the middle,..meaning inner conductor. The polarity is then shown. If the PP you have is of the older type without the diagram, use a voltmeter, $15 from most Supercheap.Clints etc, worthy investment.

Jason

Thanks Jason. I'm sure the PP from DSE or wherever will have that, but how do I then translate that in to the device I'm plugging it into? It doesn't say, and I don't have the original PP to compare.

Cheers

"Han"

** Have you ever seen the film of " Catch 22 " ??

It's a bit like that.

....... Phil

Do you have a digital multimeter?

Does the gadget have any other connectors with a common ground? If it does then you could measure continuity between each pin of the DC connector and the ground of the other connector to find which pin is ground.

2nd option with a digital multimeter would be to simply measure the resistance on the DC connector.If you get a reading in one direction and no reading in the other, then the one with the reading shows the correct polarity. This only works if the unit has a series protection diode. Some products may show a value both ways.

Another option is to open up the unit and inspect the circuit board and connector. If the connector is wired to the circuit board and it uses red and black leads, then red is likely the positive one. For a circuit board mounted connector, the ground pin is most likely the one connected to a big copper ground plane (if there is one).

Other options involve inspecting the circuitry, but that's a bit harder to explain.

Otherwise your odds are better than 50/50 that the center pin is the positive one. Murphy's Law will however ensure that you get it wrong, and that the unit won't have reverse polarity protection :->

Dave.

Pretty much sums up the chances of most things I do being successful, so worth a shot ;)

Thanks a lot for the very detailed reply, I'll buy a PP and just give it a shot.

Cheers

:)

Note that some equipment is not very well protected against reverse polarity. So guessing is not a good idea the cheaper you go.

If you're confident with taking things apart, have a purve inside the gear, it sometimes gives you glaringly obvious clues as to which way around it goes.

Things to look out for:

Larger areas of copper tracks usually point to negative.

Fuses, though technically could be placed anywhere, are generally placed on the positive line.

Polarised capacitors for filtering at the input are dead giveaways.

Sometimes (but only where it's fused), you can find diodes placed 'wrong way around' across the input to forcibly blow the fuse in that event. That is also a dead giveaway.

Short of other obvious clues, you need to trace the lines to see what circuitry it goes to and make a determination from there. But you're likely to see the more obvious clues before then anyway.

--
Linux Registered User # 302622

"Han"

** OK - so must be familiar with Eastwood's philosophy on this point.

That is, his famous " punk probability " quotient.

" Was it 5 or was it 6 ?? How lucky do you feel ...... "

Completes Einstein's " e=mc*2 " & Heisenberg's uncertainty triad.

Mind bending stuff........

...... Phil

In that situation, I would remove the covers of the device you intend to power,..look for any large electrolytic capacitors on its circuit board. Now these are polarity sensitive, and if there is a largeone near the plug-socket or elsewhere on the board, it's a fair bet they will indicate what polarity the device is. eg electros often have an exposed case,..this will be negative, and if it is very low resistance (equal to, or less than a fraction of an ohm) to the outer plug-socket, you solved your problem. It could be the device is positive earth, which in that case, the resistance will be quiet high from the electro-cap case to the socket outer, but it's positive lead will be a very low resistance to the outer plug-socket connection. It's common practice for circuit designers to employ some capacitive filtering at the DC input socket, or close to it.

PS. if you are using a cheaper multi-meter as a resistance or ohm-meter,..touch the 2 probes together on the range you intend to use (20 ohms fullscale, for example) and note the "probe short-circuit or zero ohms residual reading. The cheaper digital m-meters usually have a short circuit or zero resistance reading of less than ohm. You then subtract this reading from any measurement you make.

Hope this helps,..Jason

Thanks again to everyone for the help. I'll take it apart tonight and see if I can check the polarity from the obvious and what people have advised.

Cheers