Circuit question

Yes. Basic operations.

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1. Set your multimeter to read > 6.2VDC, hook up your equipment like this, and make a note of the voltmeter reading:

. +-----+ .MAINS>---|~ +|----------------+ . | | | . | | [VOLTMETER] . | | | .MAINS>---|~ -|----------------+ . +-----+ CHARGER

1. Disconnect the charger from the mains, connect an 8.2 ohm resistor in parallel with the multimeter leads, plug the charger back into the mains and make a note of the multimeter reading.

. +-----+ .MAINS>---|~ +|-----+----------+ . | | | | . | | [8R2] [VOLTMETER] . | | | | .MAINS>---|~ -|-----+----------+ . +-----+

1. Compare the multimeter readings.

If they're both close to 6.2V, then the charger is regulating its output at no load and at full load into a resistive load.

Keep in mind that this is a battery charger designed to feed a battery load, and not a general purpose power supply, so you may be in for a nasty surprise unless you can fully characterize its outputs into whatever load you have planned for it.

Just as an aside, be aware that 6.2 volts into 8.2 ohms will cause the resistor to dissipate about 5 watts, so make sure you use a resistor adequately rated; 5 watts or greater if you plan to leave it connected for a long time.

-- JF

8.2 ohm will draw 0.75 A at 6.2 V. The adapter is rated for 0.72 A You are overloading the adapter.

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pim.

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Right you are!

I misread the 720mA as 750, so what value of resistor (resistance and
wattage) should he use?

The 30 mA additional current is negligible unless it will be applied for =

long-term continuous use, and at the extreme ambient temperature and = heat=20 dissipation conditions. Also the 8.2 ohm (standard value) resistor you=20 suggest is probably 5%, so it may actually draw 720 mA.

As I'm sure you are aware, overloads on transformers and simple power=20 supplies are well-tolerated, and it is generally a matter of holding a = duty=20 cycle in order to keep the temperature from exceeding a safe level. An=20 overload current of 41% will usually be allowed with a 50% duty cycle, = and a=20

2x overload current for 25%. Depending on thermal mass, the actual ON = time=20 may vary from several seconds to several minutes.

This entire discussion seems to be futile in terms of helping the OP. = You=20 can get a 5V 4A regulated wall-wart for about $6:

And a 4 port USB hub for about $6:

o=3D7248125&CatId=3D392 Or even $4: o=3D7248141&CatId=3D4753 And a powered hub for $15: o=3D1187799&CatId=3D4753 or $10: o=3D7248128&CatId=3D4753

I know some people who will spend hours trying to make some sort of=20 ill-fitted surplus or freebie device work, often without success, than = just=20 buying what is needed and have done with it. As a learning experience, = maybe=20 it's valid, but otherwise, not so much.

Paul=20

It doesn't have to be that precise just to determine whether the supply is regulated or not. I was going to recommend 10 ohms at 5 watts.

Good Luck! Rich

OK, to look for significant voltage change after giving the AC adaptor a small load.

V=IR P=VI=V*V/R

I don't have any 5W resistor. Could I use 2 1/4W 100ohm instead?

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12 would be better.

Anything that will draw more than voltmeter draws will give you some idea of whether or not the thing is regulated. But I'd put maybe 5 or

10 of those things in parallel - you could also use a 6V lantern bulb.

Good Luck! Rich