Battery Charging Adapters....

[John Rumm]

You could stick a switch on the side for NiMH/NiCd ;-)

(not looked at charging ICs lately, but I wonder if there is a way of actually detecting the cell type electrically from the outset)

[usenet]

Like my 'higher end' Ferm combi for example! :-)

[The Natural Philosopher]

Correct.

Most delta peak chargers use switched mode regulators that automatically adjust the voltage to whaveter is necessary to get te charge curent.

[The Natural Philosopher]

The delta peak on NiMh is less than 2mV, but its about 3-5mV on NiCd.

IIRC.

The NiCd setting is eneeded to fully charge the NiCd which oterwise would terminate a bit early.

Easy once you have a feedback and computer system to drive it...

[The Natural Philosopher]

Such cahrgers are avaialable at any model shop where e.g. electic racing cars or aircraft are sold.

Price typically 30-50 quid for and up to 14 cell, fully regulated NiMh/Nicd etc etc design. Chrage currents up to 6-8A usually.

Mostly they are designed to run off 12v sources though.

>

[Andy Burns]

At least that way when it burns up your batteries you can blame the user, not the design of the charger!

I remember seeing a photo somewhere of a rapid charger that was melted and not far short of catching fire, it had the remnants of NiMH batteries in it, but the switch was set to NiCd (or vice-versa) can't find it again to post a link :-(

[Lobster]

You're not alone; although I'm very careful about physically labelling every new wallwart as it comes through the door, to avoid muddling them later, I do have a boxful of the damned things in the garage, belonging to sundry expired electrical devices - mostly mains adapters but some chargers.

Unfortunately, I haven't a clue which I could safely use on other equipment, so I don't. I (and certainly my kids) have multiple battery-operated devices around the home, fitted with sockets for a mains-adapter which I don't have. I look wistfully at my box of old wallwarts before deciding I can't risk it, and so go out and buy another pallet-load of Duracells or... yet another wallwart.

Is there anyway of working out where it would be safe to use old wall warts? Reading the other posts in this thread hasn't helped my confusion on the issue.

For example, my 'intelligent' battery charger (which takes 4x1.2V NiMH cells) has a wallwart rated 3V @ 2.5A. The charger for my son's RC car (6x1.2V NiCd cells) is rated 9V @ 200mA. The mains adapter for my cordless doorbell (which is otherwise powered by 4x1.2V cells) is 9V @

300mA.

Don't get it!

David

[John Rumm]

The appliance will often be labeled with at least the voltage and the polarity required by its power connector. Hence matching on that basis is a good start. There are two other issues, can the wall wart meet the power requirements, and does the appliance require a regulated supply (most don't)

The power usage is easy enough to test, guestimate the power requirements and select a wall wart from your box with the right voltage and "enough" power. Hook it up but via a DMM set to read mA (a butchered lead from another wall wart will help here, because the DMM will need to be in series with the supply). Switch on, and monitor the current draw for a bit. If the current draw is way over the rating of the wall wart you can disconnect sharpish (assuming it doesn't do it for you ;-), if it is way under the wall warts capability, select a similar but lower power one from the box, and keep the bigger one for something that needs it.

Don't forget some devices will have built in voltage regulators, and hence may have supplies with a voltage somewhat higher than the battery voltage. Some devices will work over a big range of supply voltages, and hence can use a lower voltage supply than the sum of the batteries in the same way they will work from partially exhausted cells.

Your battery charger in the above example may be a slightly different type of beastie... it is possible that it charges cells individually rather than all in series (does it charge one or two at a time, rather than needing 4 cells?). If this is the case then 3V is plenty to charge a single 1.2V cell.

[manatbandq]

butchered

CHECK THE POLARITY FIRST!!!

The commonly used DC connectors can have the positive either in the centre or on the outer conductor. Also, is the wall wart AC or DC? What does the equipment expect?

MBQ

[John Rumm]

I thought I said that... no need to shout.

Errrm, yup you could be right.... or are some the other way round?

With one or two rare exceptions (modems, low voltage lights etc), DC.

[manatbandq]

Sorry, you did.

At the risk of sounding like IMM, I am right:-). I have one of each on my desk at the moment.

Every PC in our office has speakers that have an AC wall wart. I don't think they're all that rare.

MBQ

[John Rumm]

Perhaps you missed the irony of what I was saying... ;-)

You said "The commonly used DC connectors can have the positive either in the centre or on the outer conductor", which does kind of wrap up all of the available posibilities don't you think? Hence why I said you could be (i.e. must be!) right given that it will be one way or the other.

To be fair, that is still a sample of one (i.e. one type of speaker presumably)... I would maintaing that ones with AC outputs are outnumbered at least 10:1 by DC ones in general use.

[Stefek Zaba]

Certainly consistent with my collection of wallwarts: the great bulk of 'em are DC, just about the only AC ones were for modems which for some reason (an addiction to 50Hz as a source of timing? but then it's 60 in some benighted parts of the world) seemed to be about 50:50 in preferring AC:DC.

Of course, some - as the Scarecrow said - go both ways...

[Huge]

Good news; I have a boxfull of wall-warts which I could look through and gather some data.

Bad news; ICBA.

:o)

[Dave Plowman (News)]

Technically, it's a better solution to have the wall wart as AC only and the rest of the PS in the appliance - you get a lower impedance supply that way, with less chance of RFI in either direction. Also allows a bigger transformer - ie more current - in the limited space.

I wonder in the case of modems whether it's also to do with minimising the risk of putting anything nasty down the telephone line - but that's only surmising.

[Stefek Zaba]

Good news: Humph's put his tongue across the one marked '9V DC'.

Bad news: it was adequately isolated from line.

Good news: it *was* adequately isolated from line, but then...

And now, late arrivals at the Part P ball.

Here's Mr & Mrs Icy, and their pleasant son, Nice.

Here's the Iranian couple, Mr & Mrs Al Oda Coblaz, and their peasant revolutionary son, Wat.

Here are Mr & Mrs Works - and their younger son, Minor.

And is that - yes it is, Mr & Mrs Pection, and their son Richard dressed as, well, some sort of a mixture of clown and Victorian novelist - yes, it's Pierot Dickens!

[John Rumm]

That reminds me... phone call a good few years ago from girl who would later become my SiL.

SiL: "My Saga GameGear is not working" Me: "Perhaps the batteries are flat" SiL: "I have not got any spare batteries, so I am using the mains adapter" Me: "Is that working?" SiL: "I don't know... how can I tell?"

Me: ponders, how to remotely diagnose function of a wall wart with no test gear, and a non techie proxy...

Me: "Just touch the jack plug on your tongue, if it is working you should get a little tingle..." SiL: "Is it safe?" Me: "Yup, you will be fine, it is only 9V"

Pause...

SiL: "Yooowwwwwwwwww! that hurt" Me, and future SWMBO in unison (4 feet away from phone): "OK that's working then!"

Ponders... Hmm it was an unregulated supply, so with no load it probably had 16V on it.... ;-))

Argggg... now that was bad, now please go test one of your spare wall warts using the above test procedure....

Oh a late arrival: Mr & Mrs Bel-plyance, and their lovely, but alas excluded daughter, Porta.

[Stefek Zaba]

I felt the passing of the illusion of teenage invulnerability keenly some years ago, when wondering whether to put my tongue across the PP3 powering the RS232 tester I wasn't sure was working; I'd often tested PP3s this way in my youth and fancy I can still tell the difference between fresh and aged. The realisation that this was a NiCd, with a somewhat lower internal resistance than the zinc-chloride batteries of my youth (hear that Hovis advert ;-) came while the terminals were still a couple of feet away ;-)

[Dave Plowman (News)]

Thought the resistance of a half inch or so of tongue would have made the internal resistance of the source irrelevant? Unless of course you'd been eating something strange?

Many of my colleagues test radio mic PP3s like this. I just replace them. ;-)

[Stefek Zaba]

I 'spect you're right about that - but the evolving caution made me reluctant to try it.

Besides, what resistance? They don't call me 'silvertongue' for nothing ;-)