Which size DC connector do I need?

[Joe Shmoe]

Hi folks, I've been posting quite a few electrical questions of late, and you've been so knowledgable, I wonder if you can advise me on this?

I need to buy a new battery charger, but I can't work out what size DC connector I need. From reading up, the most common sizes tend to be 5.5mm outside diameter, and either 2.1mm or 2.5mm interior diameter.

Too hard to measure with a ruler, so I used drillbits instead, thinking it would be obvious.......

I don't have a 2.1mm bit, so used a 2mm. While loose in the hole, I still feel tension in the little springy connectors either side, so a 2.1mm will be even better.

The 2.5mm drillbit doesn't need to be forced into the connector, but it's a nice snug fit, I'm not sure if it's too snug?

Any ideas?

 

[Eric The Viking]

What is it for?

Step one: look at the data plate on the old PSU/charger - make a note of these things:

AC out, or Unsmoothed DC (dashed and straight lines one over t'other), or smoothed DC (used for audio and most computer applications)?

Voltage out?

Current capability (in mA usually).

The official reason there are several pin sizes is because of the need for a bigger pin for higher current uses. Actually I think they only do it to annoy. But look at the actual pin on the whatever-it-is. You can usually get a set of digital calipers to pinch the end of it enough to measure it (be VERY careful not to short the second, spring contact with the vernier jaws while doing this!). If it helps, 2.1mm cable connectors won't fit into 2.5mm sockets on kit, because the pin won't go into the cable connector, and 2.5mm cable connectors usually won't fit 2.1mm sockets because they won't go past the outer plastics.

It looks to me that you have a 2.5mm connector there, and that is more likely for any sort of tool charger. There is a Wikipedia page here: https://en.wikipedia.org/wiki/Coaxial_power_connector , but to be honest it's no help really, as the 'system' is completely messed up with no consistency.

Final important thought: there is NO STANDARD for polarity either - the pin can be EITHER the positive or the negative terminal. This should also be on the PSU's data plate, with a little icon/diagram indicating which polarity, but historically some manufacturers, notably Sony, bucked the trend, and made their centre pins opposite from everyone else! So check that too, and if the PSU is dead, try a meter very carefully on the socket on the equipment (again be careful not to short it.

Sorry - always been a horrid problem, no simple solution.

E.

PS A magnifying glass and a strong light usually helps when reading the wretched things!

 

[Joe Shmoe]

Cheers very much, that's great infomation.

In desperation after reading that, I've just bought a 2.1 and 2.5mm DC connector from local electronics place, so I can plug it into the battery and see which it is.

So for the grand total of less than a quid, I now know it's. 2.5mm like you reckoned.

What a nightmare.

On to finding a charger and checking the polarity.... Oh joy.