I am failing the meter IQ test! Help please!I now have this meter and shunt and it has the two wiring diagrams shown. http://www.ebay.ca/itm/DC-0-300V-200A-Shunt-Voltage-Current-Panel-Meter-Digital-LED-Voltmeter-Ammeter-/271729368180?hash=item3f44551c74:g:~~0AAOSwc0FUqBWSIt was said earlier that this meter only measures "one way" unlike the Trimetric that measures both ways. I want to measure battery charging amps into the battery from converter and solar controllers. Questions:A. which of the two linked diagrams is for into the battery and which is for draws from the battery?B. in the diagram that has the controller/motor, the meter's power supply positive wire goes right to the "controller". I can't figure what that is supposed to mean. The Trimetric has four wires one of which is for its power and that goes to the battery. This meter has five wires as shown (I see it doesn't need the ground for the power supply in one diagram)Thanks

The two diagrams differ mainly in that the first one has the meter's power supply isolated from the supply for the thing being metered, while the second the meter and the thing share the power supply. Since you don't need an isolated power supply, you'd presumably use the second diagram with the controller and the motor.The + and PW+ wires go to positive from the battery (presumably via an appropriate fuse).The COM wire should go to the more negative side of the shunt, which for your use would be the chassis ground side, assuming you're putting it as usual between the chassis ground and the negative battery lead.The IN+ wire should go to the other side of the shunt, i.e. the battery side.If for some strange reason the amps reading shows the wrong direction, swap the two leads from the shunt.There's a very slight chance that using an isolated DC-DC converter for the power supply (which would be connected to the power supply + and - connection) that you might actually be able to get a current reading in both directions. You could test that by hooking it up to a 9V battery or similar, I suppose, and seeing what it does. Most likely it won't show negative current.

In diagram #2, the IN+ is on the outer end of the shunt and COM at the inner end, so it would show the amps from the battery to run the motor? If the thing is a battery charger instead, you put IN+ on the battery end of the shunt and COM on the outer end, and it will read amps into the battery from the charger?

I don't know how you can miss hooking up a meter w/ ext shunt. But I would be curious how low amps you want to read, because I have a brand new 200 amp one here that won't read anything till near 10 amps. These 200 amp meters are for reading starter current, or very big converters. They are not accurate at lower amps at all

BFL13 wrote:In diagram #2, the IN+ is on the outer end of the shunt and COM at the inner end, so it would show the amps from the battery to run the motor? If the thing is a battery charger instead, you put IN+ on the battery end of the shunt and COM on the outer end, and it will read amps into the battery from the charger?Yes and yes.It may help to understand that the ammeter part is really just measuring voltage and applying some scaling factor, and the shunt is really just a low-value resistor. The current through the resistor causes a voltage drop, and the meter part measures that voltage drop and shows it in numbers that (hopefully) correspond to the current flowing. The COM lead is the negative lead for the ammeter's voltage measurement, and the IN+ lead is the positive lead. (The PW+ lead is the positive lead for the voltmeter part of the meter, and the COM also its negative lead. Apparently COM and the power supply - are internally connected together. The + power supply lead is, of course, the positive supply for the meter circuitry.)When current is flowing from the battery to a load, the battery negative terminal is the most negative side of the resistor, so the COM lead goes there. When a charge current is flowing, the sense of the current and the voltage across the resistor is the opposite—the battery really is the load in this case, and the charger the power supply—so the end of the resistor opposite the battery is the most negative and gets connected to COM.

Thanks for the good explanation. I was able to get it to read volts but it showed "0" for amps trying it every which way. But also my test set-up may have been wrong. I don't know how many amps it should have said with the set-up I had to be able to use RJ's advice on that either. I will be using it to measure charging amps between say 156 amps down to about 20 amps. Other than that it would be for as a voltmeter. I need to set up a better test. It is getting dark, so I will get back to it tomorrow.At least now I know what to try.

Meter and Shunt Wiring Question | Good Sam Community

pianotuna
Nomad III
Nov 05, 2015
Hi BFL13,

Got a link for that poor man's device?

BFL13 wrote:
There is one that also counts AH for about $50 if you want a "poor man's Trimetric"
BFL13
Explorer II
Nov 05, 2015
You need it to show the sort of amps you charge with or draw from the battery bank (big inverter?). In my case that is more than 100 and less than 200. You need to decide which amps to measure- charging or drawing- for hooking it up.

There is one that also counts AH for about $50 if you want a "poor man's Trimetric"
myredracer
Explorer II
Nov 05, 2015
I was looking at buying the exact same thing.

Was looking at one made by Drok (ebay or Amazon) which is available up to only 100 amps. Is 200 amps needed or would 100 be okay? (Only have one battery in our case and not into solar.)
BFL13
Explorer II
Nov 05, 2015
I got the thing working! This time I connected one end of the shunt to the battery neg post and my VEC1093DBD portable charger neg clamp to the outer end of the shunt, and the positive clamp to the battery pos post.

First I tired it with the COM at the battery end like in the wiring diagrams, and got voltage and "0" amps same as before. So I swapped and put the IN+ wire at the battery end and got voltage and amps just like in RJ's photo above.

I compared the voltage with another meter's and the thing needs calibrating and compared the amps reading with the amps reading on the VEC.

VEC said 35 amps and meter said 33 amps. Next, changed the VEC to its four amp setting to see if this meter had RJ's meter problem at under 10 amps. The VEC said 4 amps and the meter said 2 amps.

So it looks like it has a 2 amp error at both 35 and at 4 amps which I will try to calibrate when I get that far in setting this all up.

LY said before that it was not the same amount of correction up the scale, so I expect to find out I need to compromise on that to the amps range I want to be most accurate.

At least the thing works now that you guys showed me what to do :)
Big_Katuna
Explorer II
Nov 05, 2015
A shunt measures current that goes thru it. If its on the wire from the alternator, it measure the alternator current.

Solar panel output wire? Solar panel current.

One lead from the battery? You are measuring current in and out of the battery.

You may want to size shunts appropriately to the current being measured. 200A on the battery, smaller on solar. For better accuracy.

Doesnt matter how you connect the voltmeter. You are reading millivolts and they will be either plus or minus depending on polarity and you are measuring charge or discharge.

Also note that if its on the "hot" wire, the entire shunt surface is "hot"and easy to short to ground with a tool, etc.
BFL13
Explorer II
Nov 05, 2015
wa8yxm wrote:
YOu want the diagram on the right. The one showing the unit hooked to the battery. If you get the wrong readings, Swap com and INPUT + wires on the shunt.

The diagram in the middle is for testing alternator output.

Isn't testing alternator output the same as what I want to measure, which is the output of a battery charger to the battery?
wa8yxm
Explorer III
Nov 05, 2015
YOu want the diagram on the right. The one showing the unit hooked to the battery. If you get the wrong readings, Swap com and INPUT + wires on the shunt.

The diagram in the middle is for testing alternator output.
BFL13
Explorer II
Nov 05, 2015
Page 8 of 8 at the bottom of this has the Trimetric 2025's diagram and a technical note about the G1 and G2 wires. I don't understand how the OP meter can work where its ground wires are common, after reading that note. Anybody? Thanks.

http://www.bogartengineering.com/sites/default/files/docs/TM-2025Install%20Instructions9-12.pdf

Apparently the OP meter's ground wire to the shunt is the same as the Trimetric's SIG and the OP's IN+ is like G2 but with G1 added --at the meter--- contrary to the Trimetirc's note to only join them at the shunt.
MrWizard
Moderator
Nov 05, 2015
use this one
RJsfishin
Explorer
Nov 05, 2015
Whats there to hate about shunts ?
I run a 50 amp meter for 15 amps on the solar, and 45 amps on the PD conv, and nothing could work any better, or be more accurate.