I've got a power supply for a cordless drill that's supposed to output
22V 450mA but only gves 2V. I've checked the (4) diodes and they're
OK. There's a capacitor in there that I haven't checked.

What might be the most likely cause?

Art Deco ) writes:
I've got a power supply for a cordless drill that's supposed to output
22V 450mA but only gves 2V. I've checked the (4) diodes and they're
OK. There's a capacitor in there that I haven't checked.

What might be the most likely cause?


If the capacitor is bad, there'd be some drop in output voltage, but
not that much.

What you may be seeing is simply whatever voltage remains on
the capacitor, and there is no voltage going into it.

Check the AC connector for continuity. If it's not
a relatively low resistance, there's either a bad connection or a blown
fuse, or a switch if there's a switch (assuming there's no other
circuitry on the primary). And in
some low end equipment, the fuse is inside the transformer, making it
problematic to fix.

If the primary seems okay, then check continuity on the secondary.
If it too is a relatively low resistance, then fire it up and measure
the voltage going into the bridge rectifier. There should be somewhere
close to 22volts AC there. If it's not, but the primary is okay,
then there would seem to be an open secondary on the transformer.

Unless there's actually more circuitry than you say, this can't
be much simpler a circuit.

Michael

On 22 Sep 2006 07:33:46 GMT, (Michael Black)
wrote:

Art Deco ) writes:
I've got a power supply for a cordless drill that's supposed to output
22V 450mA but only gves 2V. I've checked the (4) diodes and they're
OK. There's a capacitor in there that I haven't checked.

What might be the most likely cause?


If the capacitor is bad, there'd be some drop in output voltage, but
not that much.

What you may be seeing is simply whatever voltage remains on
the capacitor, and there is no voltage going into it.

Check the AC connector for continuity. If it's not
a relatively low resistance, there's either a bad connection or a blown
fuse, or a switch if there's a switch (assuming there's no other
circuitry on the primary). And in
some low end equipment, the fuse is inside the transformer, making it
problematic to fix.

OK, thanks.

There is no other circuitry on the primary side and the primary side
is open circuit.

If the primary seems okay, then check continuity on the secondary.
If it too is a relatively low resistance, then fire it up and measure
the voltage going into the bridge rectifier. There should be somewhere
close to 22volts AC there. If it's not, but the primary is okay,
then there would seem to be an open secondary on the transformer.

Unless there's actually more circuitry than you say, this can't
be much simpler a circuit.

No, that's all there is on the secondary side: four diodes and a
capacitor.

Art Deco wrote:
On 22 Sep 2006 07:33:46 GMT, (Michael Black)
wrote:
Art Deco ) writes:

I've got a power supply for a cordless drill that's supposed to output
22V 450mA but only gves 2V. I've checked the (4) diodes and they're
OK. There's a capacitor in there that I haven't checked.

What might be the most likely cause?

There is no other circuitry on the primary side and the primary side
is open circuit.

thats the prob then. Basic chargers like that are simple to replace,
just enure the replacement is not rated at higher current, since its
primarily the transformer R that controls the current in this case.


NT

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.


--
_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day
I measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)


--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.

- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)

David Nebenzahl wrote:
Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day
I measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)


It's real easy to measure an erroneous voltage with a DVM...phantom voltage.

jak

"David Nebenzahl" wrote in message
s.com...

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If open,
zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day I
measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)

A DMM is crap for checking a lot of things - high impedance. A good old 5K
per volt unit is often better.


--
_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/

jakdedert spake thus:

David Nebenzahl wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other
day I measured something with a very low voltage; turned out I was
trying to measure an AC source with my (analog) multimeter set on DC.)

It's real easy to measure an erroneous voltage with a DVM...phantom
voltage.

Explain "phantom voltage", please. Never heard of it.

Sounds scary.

D "woooo ooooo oooooo" N


--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.

- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)

David Nebenzahl wrote:
jakdedert spake thus:

David Nebenzahl wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.


The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.


But the OP reported low voltage. A transformer is like being
pregnant: either you is or you ain't. As you point out, either open
or not. If open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other
day I measured something with a very low voltage; turned out I was
trying to measure an AC source with my (analog) multimeter set on DC.)

It's real easy to measure an erroneous voltage with a DVM...phantom
voltage.


Explain "phantom voltage", please. Never heard of it.

Sounds scary.

D "woooo ooooo oooooo" N




A high impedance meter will often pick up a few volts out of the air.
Place one probe in a live wall outlet without making a complete circuit
and you'll likely see a volt or two on the meter.

James Sweet spake thus:

David Nebenzahl wrote:

jakdedert spake thus:

David Nebenzahl wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being
pregnant: either you is or you ain't. As you point out, either open
or not. If open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other
day I measured something with a very low voltage; turned out I was
trying to measure an AC source with my (analog) multimeter set on DC.)

It's real easy to measure an erroneous voltage with a DVM...phantom
voltage.

Explain "phantom voltage", please. Never heard of it.

Sounds scary.

D "woooo ooooo oooooo" N

A high impedance meter will often pick up a few volts out of the air.
Place one probe in a live wall outlet without making a complete circuit
and you'll likely see a volt or two on the meter.

Aha, so it's a matter of high sensitivity to ambient EMF. Gotcha.

I'm glad I still have my trusty old analog VOM.


--
Napoleon won the battle of Waterloo. The German Wehrmacht won World War
II. The United States won in Vietnam, and the Soviets in Afghanistan.
The Zealots won against the Romans, and Ehud Olmert won the Second
Lebanon War.

- Uri Avnery, Israeli peace activist
(http://counterpunch.org/avnery09022006.html)

"David Nebenzahl" wrote in message
s.com...

Explain "phantom voltage", please. Never heard of it.

Put any DMM on the lowest AC voltage range, hold the leads in your hands and
look at the reading. Move the probes around. It won't read zero.



--
_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/


--

....

....

In article m,
David Nebenzahl wrote:
The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

DVMs have a very high input impedance and will give strange readings due
to capacitive etc coupling. An old fashioned moving coil meter with an
impedance of 1000 ohms per volt AC is often more useful for this sort of
testing.

--
*Gun Control: Use both hands.

Dave Plowman London SW
To e-mail, change noise into sound.

In article m,
David Nebenzahl wrote:
A high impedance meter will often pick up a few volts out of the air.
Place one probe in a live wall outlet without making a complete circuit
and you'll likely see a volt or two on the meter.

Aha, so it's a matter of high sensitivity to ambient EMF. Gotcha.

I'm glad I still have my trusty old analog VOM.

As an addition to a DVM, though, I hope? ;-)

--
*Save the whale - I'll have it for my supper*

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 22 Sep 2006 14:08:53 -0700, David Nebenzahl
wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.

The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.

But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day
I measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)

Possibly the voltage I was reading was the residual voltage on the
capacitor, as someone suggested. In the event, it turned out to be
open circuit on the primary side.

Art Deco wrote:
On Fri, 22 Sep 2006 14:08:53 -0700, David Nebenzahl
wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.
The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.
But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day
I measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)

Possibly the voltage I was reading was the residual voltage on the
capacitor, as someone suggested. In the event, it turned out to be
open circuit on the primary side.


If you had the meter on the ac range (as you should have to read the
voltage on the transformer), you picked up a stray voltage...or not. If
not, then more investigation is necessary. I believe somewhere in the
thread, you stated the transformer was open on one side or the other.
If that's the case, you picked up a stray reading...phantom reading
which is indeed real, but not useful with respect to a determination of
your problem.

jak

On Sun, 24 Sep 2006 00:40:25 -0500, jakdedert
wrote:

Art Deco wrote:
On Fri, 22 Sep 2006 14:08:53 -0700, David Nebenzahl
wrote:

Homer J Simpson spake thus:

"Art Deco" wrote in message
...

No, that's all there is on the secondary side: four diodes and a
capacitor.
The primary side should be around 2,000 ohms (wide variation)

The secondary side should be around 10 ohms (wide variation)

If no continuity on either it's toast.
But the OP reported low voltage. A transformer is like being pregnant:
either you is or you ain't. As you point out, either open or not. If
open, zero volts. How do you get 2 volts?

I wonder if the OP was measuring correctly. (Don't laugh: the other day
I measured something with a very low voltage; turned out I was trying to
measure an AC source with my (analog) multimeter set on DC.)

Possibly the voltage I was reading was the residual voltage on the
capacitor, as someone suggested. In the event, it turned out to be
open circuit on the primary side.


If you had the meter on the ac range (as you should have to read the
voltage on the transformer), you picked up a stray voltage...or not. If
not, then more investigation is necessary. I believe somewhere in the
thread, you stated the transformer was open on one side or the other.
If that's the case, you picked up a stray reading...phantom reading
which is indeed real, but not useful with respect to a determination of
your problem.

OK, but why would I put the meter on the AC range when the transformer
is supposed to be outputting rectified voltage?

Art Deco ha escrito:

On Sun, 24 Sep 2006 00:40:25 -0500, jakdedert
wrote:

If you had the meter on the ac range (as you should have to read the
voltage on the transformer), you picked up a stray voltage...or not. If
not, then more investigation is necessary. I believe somewhere in the
thread, you stated the transformer was open on one side or the other.
If that's the case, you picked up a stray reading...phantom reading
which is indeed real, but not useful with respect to a determination of
your problem.

OK, but why would I put the meter on the AC range when the transformer
is supposed to be outputting rectified voltage?

A transformer doesn´t output rectified voltage. It outputs AC voltage,
which is rectified and filtered by the diodes and capacitors following
the transformer. That´s why there are diodes, capacitors and voltage
regulators after the transformer: to convert the AC unregulated voltage
of the transformer into regulated DC.

On 24 Sep 2006 06:46:15 -0700, "lsmartino"
wrote:


Art Deco ha escrito:

On Sun, 24 Sep 2006 00:40:25 -0500, jakdedert
wrote:

If you had the meter on the ac range (as you should have to read the
voltage on the transformer), you picked up a stray voltage...or not. If
not, then more investigation is necessary. I believe somewhere in the
thread, you stated the transformer was open on one side or the other.
If that's the case, you picked up a stray reading...phantom reading
which is indeed real, but not useful with respect to a determination of
your problem.

OK, but why would I put the meter on the AC range when the transformer
is supposed to be outputting rectified voltage?

A transformer doesn´t output rectified voltage. It outputs AC voltage,
which is rectified and filtered by the diodes and capacitors following
the transformer. That´s why there are diodes, capacitors and voltage
regulators after the transformer: to convert the AC unregulated voltage
of the transformer into regulated DC.

OK, so why would I put the meter on the AC range to check the
regulated DC voltage coming out?

"Art Deco" wrote in message
...

OK, so why would I put the meter on the AC range to check the
regulated DC voltage coming out?

For well regulated DC you wouldn't.


--
_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/











....

....

Art Deco spake thus:

On 24 Sep 2006 06:46:15 -0700, "lsmartino"
wrote:

Art Deco ha escrito:

A transformer doesn´t output rectified voltage. It outputs AC voltage,
which is rectified and filtered by the diodes and capacitors following
the transformer. That´s why there are diodes, capacitors and voltage
regulators after the transformer: to convert the AC unregulated voltage
of the transformer into regulated DC.

OK, so why would I put the meter on the AC range to check the
regulated DC voltage coming out?

It sounds like your mixing up a *transformer* with a *power supply*. A
transformer *always* outputs AC. A power supply (which may include a
transformer) rectifies, filters, and sometimes regulates this into DC.
So you'd always use an AC range to measure a transformer's voltage, but
you'd use a DC range to measure a DC power supply's voltage. (There are
AC power supplies too.)


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

On Sun, 24 Sep 2006 22:46:58 -0700, David Nebenzahl
wrote:

Art Deco spake thus:

On 24 Sep 2006 06:46:15 -0700, "lsmartino"
wrote:

Art Deco ha escrito:

A transformer doesn´t output rectified voltage. It outputs AC voltage,
which is rectified and filtered by the diodes and capacitors following
the transformer. That´s why there are diodes, capacitors and voltage
regulators after the transformer: to convert the AC unregulated voltage
of the transformer into regulated DC.

OK, so why would I put the meter on the AC range to check the
regulated DC voltage coming out?

It sounds like your mixing up a *transformer* with a *power supply*. A
transformer *always* outputs AC. A power supply (which may include a
transformer) rectifies, filters, and sometimes regulates this into DC.
So you'd always use an AC range to measure a transformer's voltage, but
you'd use a DC range to measure a DC power supply's voltage. (There are
AC power supplies too.)

OK, I meant the output from the power supply. Apologies for any
confusion.

BTW as I understand it, some power supply output is only
half-rectified. Is this correct?

Art Deco spake thus:

On Sun, 24 Sep 2006 22:46:58 -0700, David Nebenzahl
wrote:

Art Deco spake thus:

On 24 Sep 2006 06:46:15 -0700, "lsmartino"
wrote:

Art Deco ha escrito:

A transformer doesn´t output rectified voltage. It outputs AC voltage,
which is rectified and filtered by the diodes and capacitors following
the transformer. That´s why there are diodes, capacitors and voltage
regulators after the transformer: to convert the AC unregulated voltage
of the transformer into regulated DC.

OK, so why would I put the meter on the AC range to check the
regulated DC voltage coming out?

It sounds like your mixing up a *transformer* with a *power supply*. A
transformer *always* outputs AC. A power supply (which may include a
transformer) rectifies, filters, and sometimes regulates this into DC.
So you'd always use an AC range to measure a transformer's voltage, but
you'd use a DC range to measure a DC power supply's voltage. (There are
AC power supplies too.)

OK, I meant the output from the power supply. Apologies for any
confusion.

BTW as I understand it, some power supply output is only
half-rectified. Is this correct?

Yes, but I think all wall warts use bridge rectifiers (meaning full-wave
output), since the parts are, like, about a dime each.


--
Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

On Fri, 22 Sep 2006 08:15:57 +0100, Art Deco
wrote:

I've got a power supply for a cordless drill that's supposed to output
22V 450mA but only gves 2V. I've checked the (4) diodes and they're
OK. There's a capacitor in there that I haven't checked.

What might be the most likely cause



I had a Shure wireless mike receiver power supply last week that was
supposed to output 18V that was outputting 2 V dc. It turned out the
secondary windings of the transformer shorted out. Chuck