I want to be able to tell when my potable water pump is operating. With my
old pump, I simply put a remote light in series with the B+ supply to the
pump. The new variable speed pump does not lend itself to this...I need to
sense current, not voltage. I have researched magnetic reed switches but
even a relatively large reed switch requires 70 to 80 ampere-turns to cycle.
The new pump draws about 3 to 4 amps so there would be lots of turns around
the reed switch.
Any ideas?
Thanks-
Charlie

On Tue, 30 Sep 2003 14:00:28 GMT, "Charlie J"
wrote:

I want to be able to tell when my potable water pump is operating. With my
old pump, I simply put a remote light in series with the B+ supply to the
pump. The new variable speed pump does not lend itself to this...I need to
sense current, not voltage. I have researched magnetic reed switches but
even a relatively large reed switch requires 70 to 80 ampere-turns to cycle.
The new pump draws about 3 to 4 amps so there would be lots of turns around
the reed switch.
Any ideas?
Thanks-
Charlie



(-) on pump---|---.33 ohm 10 watt fuse resistor----ground
|
100 ohm 1/4w resistor
|
|
2N2222 base


+12V-------470 ohms 1/2w------anode LED cathode----2N2222 collector

Ground the 2N2222 emitter (-12V)

At a little more than 2A, the voltage drop on the left side of the .33
ohm "shunt" resistor the pump's current is going through exceeds the
6V required to turn on the base of the 2N2222 (or any common NPN
transistor, about 10 cents). This turns on the 2N2222 from Emitter
(ground) to collector and lights up the LED. When the transistor is
saturated, like it would be at 3A, easily, the 470 ohm resistor limits
the current through the LED (light emitting diode) to around 20
milliamps which is quite bright. If it's too bright, make the
resistor bigger (more ohms). Any pump current over 2A will make the
LED light up.....at almost no current drain at all.

If you put the parts on a small piece of perfboard (or even a little
piece of plastic with holes drilled so the wires go through to hold
the parts in place), you can mount it right on the back of the led
holder. The LED will be running after everyone on the newsgroup has
died of old age..... Should cost under $5 at Radio Shaq. If you want
it to come on at a lower current, raise the .33 ohm to .47.

If you use a .33 ohm fusistor (boxy ceramic resistor, usually buff
colored) you can eliminate the motor fuse. 10W at .33 ohms is 5.5A
which lowers the motor voltage by 1.8V at 5.5A....way more than it
should draw, which is acceptable. It'll blow about 7-8A more quickly.

Make sure the wires to the big fuse resistor can handle 10A to be
safe....same size as the motor wires are now.....

Lemme know here how it works for ya....



Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?

"Larry W4CSC" wrote in message
...

(-) on pump---|---.33 ohm 10 watt fuse resistor----ground
|
100 ohm 1/4w resistor
|
|
2N2222 base


+12V-------470 ohms 1/2w------anode LED cathode----2N2222 collector

Ground the 2N2222 emitter (-12V)

At a little more than 2A, the voltage drop on the left side of the .33
ohm "shunt" resistor the pump's current is going through exceeds the
6V required to turn on the base of the 2N2222 (or any common NPN
transistor, about 10 cents). This turns on the 2N2222 from Emitter
(ground) to collector and lights up the LED. When the transistor is
saturated, like it would be at 3A, easily, the 470 ohm resistor limits
the current through the LED (light emitting diode) to around 20
milliamps which is quite bright. If it's too bright, make the
resistor bigger (more ohms). Any pump current over 2A will make the
LED light up.....at almost no current drain at all.

If you put the parts on a small piece of perfboard (or even a little
piece of plastic with holes drilled so the wires go through to hold
the parts in place), you can mount it right on the back of the led
holder. The LED will be running after everyone on the newsgroup has
died of old age..... Should cost under $5 at Radio Shaq. If you want
it to come on at a lower current, raise the .33 ohm to .47.

If you use a .33 ohm fusistor (boxy ceramic resistor, usually buff
colored) you can eliminate the motor fuse. 10W at .33 ohms is 5.5A
which lowers the motor voltage by 1.8V at 5.5A....way more than it
should draw, which is acceptable. It'll blow about 7-8A more quickly.

Make sure the wires to the big fuse resistor can handle 10A to be
safe....same size as the motor wires are now.....

One caveat: if the .33 resistor or fusistor blows, you get 12V through 100
Ohm at the base of the transistor. This will produce a current of 120mA at
the base, which will kill the transistor. A base resistor of 2k2 to 4k7 will
do the trick.

Meindert

Thanks to both of you...Meindert-I don't understand the notation "2k2" or
"4k7" in your post. Would you please explain?

73-
Charlie

One caveat: if the .33 resistor or fusistor blows, you get 12V through 100
Ohm at the base of the transistor. This will produce a current of 120mA at
the base, which will kill the transistor. A base resistor of 2k2 to 4k7
will
do the trick.

"k" stands for thousand


"Charlie J" wrote in message
...
Thanks to both of you...Meindert-I don't understand the notation "2k2" or
"4k7" in your post. Would you please explain?

73-
Charlie

One caveat: if the .33 resistor or fusistor blows, you get 12V through
100
Ohm at the base of the transistor. This will produce a current of 120mA
at
the base, which will kill the transistor. A base resistor of 2k2 to 4k7
will
do the trick.

"Erik the Bold" wrote in message
...
"k" stands for thousand



Erik...it wasn't the "k" I was referring to, it was the numbers after the
k's.

73-
Charlie

"Charlie J" wrote in message
...
Thanks to both of you...Meindert-I don't understand the notation "2k2" or
"4k7" in your post. Would you please explain?

The k means thousand and is used as decimal point. So 2k2 means 2.2 kOhm.
And the reason I'm using the 'odd' numbers like 2k2 instead of 2k is that
they are standard values in the 5 to 10% precision range and thus easily
obtainable.

Meindert

2.2 K ohms.....2200 ohms.



On Wed, 01 Oct 2003 12:43:02 GMT, "Charlie J"
wrote:

Thanks to both of you...Meindert-I don't understand the notation "2k2" or
"4k7" in your post. Would you please explain?

73-
Charlie

One caveat: if the .33 resistor or fusistor blows, you get 12V through 100
Ohm at the base of the transistor. This will produce a current of 120mA at
the base, which will kill the transistor. A base resistor of 2k2 to 4k7
will
do the trick.






Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?

Meindert,

That is a new notation for me. Is it a European thing? I like it.
Compact!

Doug

"Meindert Sprang" wrote in message
...
"Charlie J" wrote in message
...
Thanks to both of you...Meindert-I don't understand the notation "2k2"
or
"4k7" in your post. Would you please explain?

The k means thousand and is used as decimal point. So 2k2 means 2.2 kOhm.
And the reason I'm using the 'odd' numbers like 2k2 instead of 2k is
that
they are standard values in the 5 to 10% precision range and thus easily
obtainable.

Meindert

"Doug Dotson" wrote in message
...
Meindert,

That is a new notation for me. Is it a European thing? I like it.
Compact!

Hi Doug,

Might indeed be a European thing. I checked some 'US based' schematics and
indeed, it is never used there. Funny how such common things are 'unusual'
to others :-)

Meindert