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## Rickles

1410 posts

Uber Geek

Topic # 216670 7-Jul-2017 09:40

I've seen a few USB style voltage testers about the place, but is there a simple, plug-in style tester that can be used for wall chargers that have no specs printed on them?

Is there some way to ascertain the voltage and amperage of a wall charger ( one with plug connector, not USB).

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## solutionz

358 posts

Ultimate Geek

Subscriber

You just need any basic multimeter to measure the voltage however "amerage" is based on how much the device is drawing and how much the charger can provide before overheating or self-destructing.

If you simply want to know how much current the device is drawing you can also use a multimeter (set to Amps).

If you want to know how much current a charger is capable of supplying (without opening it up) you will need to add DE-creasing levels of known resistance (i.e. "resistors") for a period of time (10-60min) until the charger starts to overheat, smell etc.

Then calculate the current supplied as: Current = Voltage / Resistance

Then take 50-80% of that value as a safety factor.

If you provide more details on the charger, voltage, what you're trying to charge I can provide more specific instructions.

EDIT: decreasing NOT increasing... thanks @cadman

## Rickles

1410 posts

Uber Geek

>If you provide more details on the charger, voltage, what you're trying to charge I can provide more specific instructions.<

Thanks for that.  The unit is an Alcatel wall charger that was originally for their model/s 735 and 332 phones.  I cannot find any specs online for those phones, or separate charger (too old).

It seems to work fine for recharging my GPS, but wanted to ascertain its Amp and Volt specs (I assume it's 5 volt standard at least).

476 posts

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One person supports this post

solutionz:

You just need any basic multimeter to measure the voltage...

But you'll need to have a load on it before a switch mode power supply will turn on and a high impedance multimeter won't supply such a load. But you can use a resistor like a this. If it blows you have more than 5W output at the PS's rated voltage.

solutionz:

If you want to know how much current a charger is capable of supplying (without opening it up) you will need to add increasing levels of known resistance

Not add resistance - reduce resistance. Start high and lower the resistance until it gets warm.

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling which thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
- John Stuart Mill

476 posts

Ultimate Geek

One person supports this post

Rickles:

It seems to work fine for recharging my GPS, but wanted to ascertain its Amp and Volt specs (I assume it's 5 volt standard at least).

Yikes. I'd never plug a PS of unknown output voltage into sensitive electronics.

But since you already have... you can just probe into the both sides of the PS lead at the same time with the multimeter leads to check the output voltage of the unit while it's plugged into your GPS. The meter becomes a high impedance load in parallel with the GPS.

But determining it's amperage capability is still the same procedure as your GPS will only draw what it needs up to a maximum.

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling which thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
- John Stuart Mill

## Rickles

1410 posts

Uber Geek

>Yikes. I'd never plug a PS of unknown output voltage into sensitive electronics.<

Ha ha ha ... fools rush in

## Rickles

1410 posts

Uber Geek

>But since you already have... you can just probe into the both sides of the PS lead at the same time with the multimeter leads to check the output voltage of the unit while it's plugged into your GPS. The meter becomes a high impedance load in parallel with the GPS.<

Sorry, don't understand.  If the supply is plugged into the mains, and other end connected to GPS, where does one use the multimeter probes?  Presumably this is with mains turned off?

## solutionz

358 posts

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One person supports this post

Rickles:

>But since you already have... you can just probe into the both sides of the PS lead at the same time with the multimeter leads to check the output voltage of the unit while it's plugged into your GPS. The meter becomes a high impedance load in parallel with the GPS.<

Sorry, don't understand.  If the supply is plugged into the mains, and other end connected to GPS, where does one use the multimeter probes?  Presumably this is with mains turned off?

i.e. You carefully stick some pins / probes through the insulation of the cable (not near each other) on the output side - NOT on the MAINS VOLTAGE SIDE

476 posts

Ultimate Geek

solutionz:

Rickles:

>But since you already have... you can just probe into the both sides of the PS lead at the same time with the multimeter leads to check the output voltage of the unit while it's plugged into your GPS. The meter becomes a high impedance load in parallel with the GPS.<

Sorry, don't understand.  If the supply is plugged into the mains, and other end connected to GPS, where does one use the multimeter probes?  Presumably this is with mains turned off?

i.e. You carefully stick some pins / probes through the insulation of the cable (not near each other) on the output side

I should have mentioned that haha

solutionz:

- NOT on the MAINS VOLTAGE SIDE

And certainly not on the 20VDC range setting!

"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling which thinks that nothing is worth war is much worse. The person who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
- John Stuart Mill

## 1101

1085 posts

Uber Geek

Rickles:

Is there some way to ascertain the voltage and amperage of a wall charger ( one with plug connector, not USB).

If its an unmarked power pack, throw it away. It might even be AC coming out , that would be a disaster for some devices.
If its an unmarked/unlabled power pack, its probably of dubious quality

The ONLY way to check the max Amp output of an unmarked wall charger is to pull it apart & check the specs of components & design of
circuit.
There is no other way, you CANNOT tell max safe/rated output by checking with a multimeter etc
Sure, just because it will deliver say 2A in testing,for a short amount of time, doesnt mean its designed to do so .

I could drain my car of oil & still drive it for 15 minutes. It doesnt mean thats the amount of oil I need.

Also, unloaded voltage can be very different from voltage under load. To much load/current draw & the output may start to get ~noisey~

## Rickles

1410 posts

Uber Geek

Thank you all for your input.

## Rickles

1410 posts

Uber Geek

>If its an unmarked power pack, throw it away. It might even be AC coming out , that would be a disaster for some devices.
If its an unmarked/unlabled power pack, its probably of dubious quality
<

I agree, but this unit did come out of a fully sealed pack that is marked for the Alcatel One-Touch mobile 'phone, so I have a "fair idea" of its specs, viz. unlikely to be AC, unlikely to be more than 7V, and unlikely to be more than 2A.

## richms

19919 posts

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One person supports this post

All power supplies should be labeled. Its part of the standards requirements for most countries. Believe me if apple could get away without putting words on things they would do, and even apple put all that labeling on their power supplies.

A proper safe power supply should be safe in all situations, overload it and they should limit the current to their max, and shut down if they overheat. The problem is there are plenty of crap ones around that do not. 4 port USB ones are one of the worst offenders. Just all the ports in parallel off a single 5v supply, able to pull 4+ A off one port with no problem if the others are unused, and put 4 power hungry devices on them and watch them cook up and let out bad smells.

Richard rich.ms

## MikeAqua

2721 posts

Uber Geek

As others have said I would bin it and buy a suitable power supply for your application.  They aren't expensive.

The GPS should have the volts and amps it requires written on it.

Mike

## 1101

1085 posts

Uber Geek

richms:

All power supplies should be labeled. Its part of the standards requirements for most countries.

I guess that would have made it illegal to originally have been supplied in that state . No label=no NZ compliance sticker .

## Rickles

1410 posts

Uber Geek

>I guess that would have made it illegal to originally have been supplied in that state . No label=no NZ compliance sticker<

Interesting point ... as best I can tell the phone, and consequently the charger, dates from 2003.  I wonder what the compliance requirements were then?

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