Getting 14.4V From A 7.2V - 14.4V Charger

[Wire]

Hello, I need a 14.4v voltage source and had a drill battery charger lying around that apparently charges at this voltage. Here is a photo of the unit:

When plugged into a wall socket I used a multimeter to test the voltage output, when connected to the positive and negative ports (labelled left and right of the hole in the photo) I get 38v.

Inside the hole there are two more ports at the top and the bottom labelled 'T' and 'S', when i connect the positive pin of the multimeter to the 'T' output of the charger, and the negative pin to the 'S' output of the charger I get 2v.

When I connect the positive multimeter pin to the + output of the charger and the negative to the 'T' output of the charger I get 33v.

When I connect the positive multimeter pin to the + output of the charger and the negative to the 'S' output of the charger I get 35v.

When I connect the positive multimeter pin to the 'T' output of the charger and the negative to the '-' output of the charger I get 5v.

When I connect the positive multimeter pin to the 'S' output of the charger and the negative to the '-' output of the charger I get 3v.

What I would like to know is how do I get 14.4v out of this supposedly 14.4v charger! :S

Any help at all would be greatly appreciated!

Many thanks

 

[SPECIAL LOCATION]

Posted Today, 01:21 AM

Hello, I need a 14.4v voltage source and had a drill battery charger lying around that apparently charges at this voltage. Here is a photo of the unit:

When plugged into a wall socket I used a multimeter to test the voltage output, when connected to the positive and negative ports (labelled left and right of the hole in the photo) I get 38v.

<.......................CUT...............................>

What I would like to know is how do I get 14.4v out of this supposedly 14.4v charger! :S

Any help at all would be greatly appreciated!

Many thanks

Hello....

first:   Don't think you can add a photo/link until you have 10 posts..     [to stop some spam apparently?]

(I THINK ADMIN CAN DO A TWEAK TO YOUR PROFILE TO LET YOU POST A LINK, TO SAVE ADDING LOADS OF SHORT POSTS}

Second.....

the voltage output:-

I think unless you have a proper load connected to the charger/transformer then you will see apparently excessively high voltages with a typical DIY/Hobby/Electronics multimeter....

Can you get your meter probes in when a typical load is connected to the charger?????

Welcome to the madhouse!!

Guinness

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Guinness

 

[SLIPSHOD & SLAPDASH]

Yep , as above, you cant accurately measure the load on modern power supplies  without special equipment.

 

[ProDave]

If this is a charger for a NiCad battery, then it's probably a typical cheap and nasty one.

NiCad's should be charged with a constant current source. That requires some electronic components.  To save a few pence, often they just use a slightly higher voltage unstabilised dc power supply, with a resistor connected in series.  This gives a not very good approximation to a constant current source.

If that's the sort it is, then the open circuit voltage will be much higher than it's spec, but will drop rapidly as you start drawing load from it.

You need to tell us more about what this 14.4V is required for. That's a fairly precise figure. If it really needs to be that accurate, then get a proper regulated dc power supply and forget this old drill charger.

The pins you measured low voltages from are sensing pins. There's often a sensor in the battery pack that senses (rather crudely) when the batteries reach full charge. They are of no relevance to your application. 

 

[Apache]

You can do links now.

 

[Bruspark]

Agree with prodave, There's no way you will get a 14.4V stable output from that charger, the 14.4 is the nominal discharge voltage of a battery that will need up to c22v to fast charge it.

14.4 is a slightly unusual power supply voltage but there are plenty of cheap CB / ham radio /hobby power supplies that will deliver a regulated 13.2 13.8 or variable 0-16v any of which would be able to do the job safely given sufficient current capability. If your device is rated for 12-14.4 V there is a much bigger range of sealed unit /wall-wart adapters available. Check maplin or Cpc Farnell

HTH