Amp Meter Issue

[fastcompacts]

Hi all. I am having a problem try to measure the amps to my cell. I have to different amp meters. One is wired into teh car which i wanted to use on a permant basis. It is 100Amp DC meter. when i hook it up to the cell (using the shunt) it will max out the meter almost instantly. And yes i do have a PWM and no matter what setting i have it on i run into this issue with the amp meter.( and yes the PWM is functioning properly). The other Amp meter i have is a craftsman mutli meter with the capabilities of reading up to 20 amp both AC and DC, but again when i hook it up to the cell i can hear the PWM straining and the meter almost instantly maxes out. Any info to help me out would be greatly appriciated. If you need any more info to help diagnose my problem please ask. And THANKS in advance.

[fastcompacts]

Shane, thanks for the speedy reply. I have attached a document that shows how my shunt is wired up. sorry for the art document but the digital camera is acting up currently, but i think it still illustrates the point. But i think this is how it is suppose to be hooked up, but i could br wrong as this is my first ampmeter that i am wiring up. any more help would be great. again thanks in advance

[lhazleton]

I'm not a wiz kid on electrical stuff, but I think the shunt is supposed to be hooked up inline on the negative side only. The picture you posted shows the pos. & neg. going to the shunt. I may be mistaken, but it sure looks like a dead short to me.

[fastcompacts]

I'm not a wiz kid on electrical stuff, but I think the shunt is supposed to be hooked up inline on the negative side only. The picture you posted shows the pos. & neg. going to the shunt. I may be mistaken, but it sure looks like a dead short to me.

this makes sense but what should I do with the positive side of the shunt?

[Philldpapill]

Ouch! The way it's hooked up right now, you have a direct short across your PWM or battery! I hope you haven't let it sit there for long, or you might A) burn the shunt/wiring up or B) damage the PWM.

[fastcompacts]

The attached document show how i have my ampmeter currently hooked up but it has some weird readings. With the car off but the cell is on the meter will first read low somewhere around 3-4 amps but then it will go way up into the 80 amp range. when i try to adjust the PWM the meter will go up to 99 and then it will not show any values. If i turn my car on and have the cell on the amp meter will not show any values. There doesnt appear to be any shorts or anything. You guys have been great so far. thanks for all the help, but im still lost in the woods on what to do. as always thanks in advance.

[fastcompacts]

Shane is that how it is suppose to be wired? If so ill try it out.

[Philldpapill]

fastcompacts, a little background about how shunt meters work might help you get a better understanding of how it should be wired.

To start, you would need to understand a very fundemental law called "Ohm's Law". It is expressed as a simple equation that relates voltage, resistance, and current. If you have a resistance(such as the very small resistance of a the shunt), you can calculate the current through the resistance if you know the resistance, and the voltage dropped across it. Likewise, you can calculate the resistance of the shunt if you know the current and voltage, OR you can calculate the voltage that should appear across the shunt if you know the resistance of it, and the current.

In other words, the following equation sums it up:

V = I x R

Where V = Voltage across the resistance, I = current through the resistance, and R = the resistance of your resistor/shunt. A shunt meter works by measuring the very small voltage across the shunt. The meter is already caliberated to know the precise resistance of the shunt. From the voltage measured, and the known resistance, you can get an accurate measurement of the current through the shunt.

From that, it should be a little more clear as to why your first arrangement didn't work. You were providing a very direct path for the current to flow through the shunt, directly back to the battery. A very bad scenario.

[fastcompacts]

Here this might help:



I am guessing your meter has 4 wires?? If so you have a pos, gnd, input +, input -.

I tried hooking it up the way you have shown. With just the amp meter on and no power to the cell i am getting a reading of 4 amp... as soon as i turn the cell on via my PWM(30 amp PWM) the amp meter readings will go up until it maxes out. I can adjust my PWM either to very little or full blast and the amp meter will not give a reading once it maxes itself out. I am totally lost and aggrivated as to what to try. I also have a digital craftsman multimeter that is able to read up to 20 amps. Is there a way for either device so that i can get a reading as to how many amps i am pushing to my cell. I really want to run my set up but without knowing how many amps i am pushing to my cell i am worried that i will over work the alternator.

[lhazleton]

Why not just connect the ammeter directly in-line with the negative line?
(batt. neg.) - wire-(ammeter in)-(ammeter out)-wire-(reactor neg.)

I you keep maxing out the amps, you may have a short in your reactor.
Wouldn't be the first time it's happened.