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Current Meter for 12V Solar System

Hello,

I'd like to create a current meter for a small solar system that I've
built. The system has a couple large deep cycle 6V batteries hooked up
in series. It's mostly used in the evenings and the load is one or two
amps. However, sometimes I like to use some short duration, high
current loads on this system (hand power tools). These loads are on
the order of 30-40A. I've looked into setting up a shunt resistor in
series with load, but I don't like the idea that I could (a) cook that
resistor, or (b) that it's wasting my precious solar electrons with
resistive heating. So, knowing just enough to be dangerous, I've
looked into using some flavor of Hall Effect sensor to measure current
without introducing a resistive load. The H-E sensors that I've looked
at have different sensitivities at different currents. For example, a
0-20A H-E sensor gives better resolution at, say, 3A than a 0-100A H-E
sensor. Given that, I was wondering whether it would be okay to hook
both 0-20A and 0-100A H-E sensors in series with my load. When the
draw is below 20A, read the 0-20A sensor, when it's above, read the
0-100A. If I'm going about this all wrong, then I'd love to hear your
solution.

Thanks in advance,

-mt
 
T

Tom Woodrow

Jan 1, 1970
0
www.allelectronics.com search for "shunt" about 1/2 way down the page
there is a 600, 50 and 100A current shunts that might meed your needs.

Tom Woodrow
 
A

amdx

Jan 1, 1970
0
I don't think you need to worry about your losses in the
shunt IF you start with a 50ua meter movement. Off the top of my head you
might dissipate 1 watt in the shunt with a 40 amp (480watt) load.
You just need to know or measure the internal resistance of the meter and
calculate the shunt resistance.
Or, you could buy two .01 ohm resistors put them in parallel and use a
cheap digital meter on the 200mv range to measure the voltage across the
resistor. This would be 40 amps full scale.
 
R

Robert Monsen

Jan 1, 1970
0
Hello,

I'd like to create a current meter for a small solar system that I've
built. The system has a couple large deep cycle 6V batteries hooked up
in series. It's mostly used in the evenings and the load is one or two
amps. However, sometimes I like to use some short duration, high
current loads on this system (hand power tools). These loads are on
the order of 30-40A. I've looked into setting up a shunt resistor in
series with load, but I don't like the idea that I could (a) cook that
resistor, or (b) that it's wasting my precious solar electrons with
resistive heating. So, knowing just enough to be dangerous, I've
looked into using some flavor of Hall Effect sensor to measure current
without introducing a resistive load. The H-E sensors that I've looked
at have different sensitivities at different currents. For example, a
0-20A H-E sensor gives better resolution at, say, 3A than a 0-100A H-E
sensor. Given that, I was wondering whether it would be okay to hook
both 0-20A and 0-100A H-E sensors in series with my load. When the
draw is below 20A, read the 0-20A sensor, when it's above, read the
0-100A. If I'm going about this all wrong, then I'd love to hear your
solution.

Thanks in advance,

-mt

You can also use a current sense transformer for things like this.
http://tinyurl.com/4tl8v

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
R

Robert Monsen

Jan 1, 1970
0
Robert said:
You can also use a current sense transformer for things like this.
http://tinyurl.com/4tl8v

Oops, you want DC. These won't work for that, they are only for AC.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
J

Jack Hayes

Jan 1, 1970
0
Hello,

I'd like to create a current meter for a small solar system that I've
built. The system has a couple large deep cycle 6V batteries hooked up
in series. It's mostly used in the evenings and the load is one or two
amps. However, sometimes I like to use some short duration, high
current loads on this system (hand power tools). These loads are on
the order of 30-40A. I've looked into setting up a shunt resistor in
series with load, but I don't like the idea that I could (a) cook that
resistor, or (b) that it's wasting my precious solar electrons with
resistive heating. So, knowing just enough to be dangerous, I've
looked into using some flavor of Hall Effect sensor to measure current
without introducing a resistive load. The H-E sensors that I've looked
at have different sensitivities at different currents. For example, a
0-20A H-E sensor gives better resolution at, say, 3A than a 0-100A H-E
sensor. Given that, I was wondering whether it would be okay to hook
both 0-20A and 0-100A H-E sensors in series with my load. When the
draw is below 20A, read the 0-20A sensor, when it's above, read the
0-100A. If I'm going about this all wrong, then I'd love to hear your
solution.

Thanks in advance,

-mt

One other method if you can tolorate just fair accuracy is to measure the
drop across a battery cable, this can be measured with a very low cost 0 to
200 mv digital meter powered by a 9 volt battery. Just put a NO PB switch in
the 9 volt battery lead, then you have push to read.

Jack
 
Thanks very much for all the great responses!

Another twist in my scheme that I should have included in my original
post is that I'd like to read the voltage on the [shunt, hall-effect
sensor, garden gnome...] with a 10 bit resolution ADC. If the ADC
measures from 0-5V and the shunts range is 0-50 mV, then I'm thinking
that my 10 bit ADC is not going to cut it. Back to the drawing board.

Either way, ya'll have given me a lot of great ideas to work with.

-mt
 
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