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Old 11-14-2010, 12:18 PM   #1
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How can I visually monitor electrical current flow?


Hi! First of all, I'm new to this forum, and I would consider myself a novice in regards to understanding some aspects of electrical. More specifically, I'm not too savvy when it comes to Volts vs. Amps vs. Watts, and how they all correlate one with another, so please, bare with me.

What I'm trying to accomplish is to be able to visually monitor current flow to an electric water pump on my truck. Idealistically I would like to have an LED inside the cab of my truck that will stay lit while the pump is running, but shut off the moment the pump stops.

I have been having intermittent problems with the water pump shutting off, causing my truck to get nice and toasty, and I hate seeing the truck hit 260* before I ever get any notification from the truck that something is awry. If I had an LED that would shut off when the pump quits working, I can catch it before it overheats.

I've gone over the obvious. Ensured it has a good ground and power supply, checked for loose connections, and corrosion. I've not found anything obvious, yet. It seems that every time it happens, I either don't have a light tester with me to track down the break in power, or by the time I get under the hood to check it, it starts working again. I really need to track this little gremlin down.

So how would I go about setting up an LED as a current flow monitor? In my mind, it seems I should be able to just wire an LED inline with the pump power supply, but I don't know how the amperage draw of the pump would affect the LED's longevity. I don't know for sure what the pump draws, but I would guess anywhere between 5 - 10 amps.

I can't imagine I would be able to get away with wiring a 1/2 watt 12 vdc LED inline on the pump's power lead without burning the LED in short order. It seems that most LED's are only rated to around 20 or 30 mA, much less than what the pump will be drawing.

Could anyone shed some light on this for me? Thanks in advance!

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Old 11-14-2010, 01:07 PM   #2
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How can I visually monitor electrical current flow?


if you have voltage to the pump and it stops working, it is the pump. If you lose voltage to the pump, it is in the power supply or controls for the pump. You wouldn't have to have proof of current, just voltage at the pump from how I see it.


so, you wire an LED and appropriate resistance (led's don't run in 12 volts) parallel to the power circuit for the pump. Basically, that means you tap the wires at the pump for both your + and - source and simply run the wires into the cab and connect your LED unit. There are a lot of LED's already assembled for various uses in vehicles. It would be simplest to purchase any of those and use them as your tell tale light.

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Old 11-14-2010, 01:41 PM   #3
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How can I visually monitor electrical current flow?


Connecting a LED across the power leads at the pump is one step as NAP pointed out but using a small 12 V light like an amber clearance light would be pretty easy to do too. I don't know how permanent you plan to make this. The lamp would be on when there is voltage to the pump and off if the voltage dropped. The one problem with this setup is the lamp could be on but the pump not running, so if you see the temperature start to climb and the lamp is on, then you know the pump quit working.
If you want to actually monitor the current flow to the motor, go to an auto supply store and see what they have from amp meters. Do you have any idea how much current the motor draws when it is running? You don't want an amp meter with a full scale reading of 60 amp when the motor only draws 3 amps. You won't see much of a reading.
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Old 11-14-2010, 07:39 PM   #4
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How can I visually monitor electrical current flow?


Wind wires around the power wire,
Like a current transformer.
Use small wire, wind say 100 turns and measure the output with
an voltmeter.
Keep winding until you get enough to light a small led.

Quote:
Originally Posted by Boostjunky View Post
Hi! First of all, I'm new to this forum, and I would consider myself a novice in regards to understanding some aspects of electrical. More specifically, I'm not too savvy when it comes to Volts vs. Amps vs. Watts, and how they all correlate one with another, so please, bare with me.

What I'm trying to accomplish is to be able to visually monitor current flow to an electric water pump on my truck. Idealistically I would like to have an LED inside the cab of my truck that will stay lit while the pump is running, but shut off the moment the pump stops.

I have been having intermittent problems with the water pump shutting off, causing my truck to get nice and toasty, and I hate seeing the truck hit 260* before I ever get any notification from the truck that something is awry. If I had an LED that would shut off when the pump quits working, I can catch it before it overheats.

I've gone over the obvious. Ensured it has a good ground and power supply, checked for loose connections, and corrosion. I've not found anything obvious, yet. It seems that every time it happens, I either don't have a light tester with me to track down the break in power, or by the time I get under the hood to check it, it starts working again. I really need to track this little gremlin down.

So how would I go about setting up an LED as a current flow monitor? In my mind, it seems I should be able to just wire an LED inline with the pump power supply, but I don't know how the amperage draw of the pump would affect the LED's longevity. I don't know for sure what the pump draws, but I would guess anywhere between 5 - 10 amps.

I can't imagine I would be able to get away with wiring a 1/2 watt 12 vdc LED inline on the pump's power lead without burning the LED in short order. It seems that most LED's are only rated to around 20 or 30 mA, much less than what the pump will be drawing.

Could anyone shed some light on this for me? Thanks in advance!
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Old 11-14-2010, 08:04 PM   #5
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How can I visually monitor electrical current flow?


Would that work with DC? I could see it working with AC, though I've never thought of trying it. Gives me an idea for another project though.
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Old 11-14-2010, 11:06 PM   #6
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How can I visually monitor electrical current flow?


How about a shunt? Anybody familiar with them? I've just learned about their existence today, and what they do. It seems like that would do the trick of dropping the current down low enough to run an LED in series along with a couple of 330 ohm resistors.

The only question I have in regards to a shunt is understanding the specifications.

Take, for example, the following shunt: Shunt; 15 A; 50 mV; 1%; 0.065 Ohms; Screw; 10-32; 5 ft. Leads

So, to my limited understanding, this shunt is capable of passing 15 Amps of current through it, and that's about as far as I think I fully understand. Past that, it gets a little hazy.

1) Does 50 mV indicate a drop of 50 mV from the original "Voltage In" to the low current lead out, or is that implying that the shunt emits a 50 mV signal?
2) 1%. What does this mean? Is this saying that the current flow through the low current leads of the shunt is 1% of the actual flow, or is it saying that the ratings are accurate + or - 1%?

Any insight would be greatly appreciated!
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Old 11-15-2010, 11:36 AM   #7
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How can I visually monitor electrical current flow?


A shunt is a low resistance, high wattage, precision resistor. It creates a way to measure current flow by measuring the voltage drop across the precision resistor. By knowing the voltage drop and resistance you can calculate the current using OHMs law I=E/R.
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Old 11-15-2010, 11:37 PM   #8
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How can I visually monitor electrical current flow?


Quote:
Originally Posted by a7ecorsair View Post
A shunt is a low resistance, high wattage, precision resistor. It creates a way to measure current flow by measuring the voltage drop across the precision resistor. By knowing the voltage drop and resistance you can calculate the current using OHMs law I=E/R.
Thanks, that helped me not at all!

I already know the definition of a shunt. I was asking more specifically about voltage output of the shunt, and a few other things related to the specifications of a given shunt.

I already found the information I was looking for, and it turns out that the shunt, while passing the full current flow of the original circuit, only emits around 50 - 100 mV (depending on what it's rated for), and as such, will not work for the intended purpose I had in mind.
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Old 11-16-2010, 01:19 AM   #9
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How can I visually monitor electrical current flow?


so what are you actually trying to do? If you want to know the current flow, get an ammeter that registers low enough to show the current of the fan. Be aware though; just because current is flowing, it doesn't mean the fan is running nor does it mean it is running a proper speed

If you want to know if there is voltage at the fan, I gave you the simplest method.

Hook up both and you can watch both.

but then again, just because you have voltage and current flow; doesn't mean the fan is running properly.
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Old 11-16-2010, 08:45 AM   #10
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How can I visually monitor electrical current flow?


Quote:
Originally Posted by Boostjunky View Post
How about a shunt? Anybody familiar with them? I've just learned about their existence today, and what they do.
Quote:
Thanks, that helped me not at all!

I already know the definition of a shunt. I was asking more specifically about voltage output of the shunt, and a few other things related to the specifications of a given shunt.
Why did you ask? BTW, the only thing a shunt emits is heat
Good luck with your project..
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Old 11-16-2010, 05:10 PM   #11
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How can I visually monitor electrical current flow?


Yes 50mv is the voltage drop across the shunt,
But for your pump it wont matter.
1% is the accuracy of the resistance value.

The simplest method to monitor current flow is to
use an automotive amp meter.
Look around at the automotive dissmantlers,
you will find one easily enough.
Or you can use any type of dc meter with
the right shunt.

Quote:
Originally Posted by Boostjunky View Post
How about a shunt? Anybody familiar with them? I've just learned about their existence today, and what they do. It seems like that would do the trick of dropping the current down low enough to run an LED in series along with a couple of 330 ohm resistors.

The only question I have in regards to a shunt is understanding the specifications.

Take, for example, the following shunt: Shunt; 15 A; 50 mV; 1%; 0.065 Ohms; Screw; 10-32; 5 ft. Leads

So, to my limited understanding, this shunt is capable of passing 15 Amps of current through it, and that's about as far as I think I fully understand. Past that, it gets a little hazy.

1) Does 50 mV indicate a drop of 50 mV from the original "Voltage In" to the low current lead out, or is that implying that the shunt emits a 50 mV signal?
2) 1%. What does this mean? Is this saying that the current flow through the low current leads of the shunt is 1% of the actual flow, or is it saying that the ratings are accurate + or - 1%?

Any insight would be greatly appreciated!

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