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Old 30-01-2016, 08:54   #1
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Wema Am mater installation problem

Hello,

Today I installed a shunt and meter to the boat. The idea was to have simple Am reading of the load / charging. I don't need / trust more complicated amp hour meters.

Anyway the installation of the shunt went smoothly and I was able to tidy up some earlier connections in the process. Changing, main switch etc. are all working. I also installed the meter itself and run the cables to the shunt.

But all I am getting on the meter is "-155". This reading comes up whatever I do. I check the wiring at least dozen times and it should be correct. I also tried reversing the wiring to the shunt, tried with and without shore power changing etc etc. But I cannot get anything other the "-155" in the meter.

Any ideas? Does anyone else have this meter installed?

Here is the installation instructions for the device:

http://www.wema.com/publish_files/J-...perpometer.pdf
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Old 30-01-2016, 15:12   #2
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Re: Wema Am mater installation problem

Did some research of Ammeter and shunts in general. Most of the time the shunt has only two wire terminals towards the ends of the shunt. And this is logical since the meters are actually measuring voltage drop over the resistor.

So I begun to wonder we my Wema has three wire terminals on the shunt and one of them is to be connected to ground. Also as far as I understand on of the terminals is connected to positive pole of the battery via the ignition / separator switch. This seems odd to me. Anyone with understanding to electronics care to comment?
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Old 30-01-2016, 16:04   #3
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Re: Wema Am mater installation problem

Shunts usually have 2 heavy and 2 light terminals. The heavies go in the cable and the lights to the gauge. Then on the gauge there is a terminal to ground. The gauge runs on the power you're monitoring + the ground makes a circuit.
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Old 30-01-2016, 16:27   #4
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Re: Wema Am mater installation problem

Electronic meters sometimes I believe need power to operate, and sometimes a wire for illumination.
Seems odd to me as of course both wires going to the meter are powered.

But we guessers could have you burn the thing up by hooking it up wrong, have you looked for a manual on line?


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Old 30-01-2016, 16:27   #5
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Re: Wema Am mater installation problem

Quote:
Originally Posted by Kaptah View Post
Did some research of Ammeter and shunts in general. Most of the time the shunt has only two wire terminals towards the ends of the shunt. And this is logical since the meters are actually measuring voltage drop over the resistor.

So I begun to wonder we my Wema has three wire terminals on the shunt and one of them is to be connected to ground. Also as far as I understand on of the terminals is connected to positive pole of the battery via the ignition / separator switch. This seems odd to me. Anyone with understanding to electronics care to comment?
Well, this is the new way of electronics and what you have is best described as an "electronic shunt"; I wouldn't be surprised if the sensor wire from the shunt to the meter has a digital signal .

Forget whatever you knew about "old shunts".

This shunt needs a pos and neg supply to the shunt as well as the signal (sensor) wire to the meter. Of course it also needs the big supply and load wires

The meter also needs a pos and neg supply along with the sensor wire from the shunt.

As to why it isn't working, I can't really help except to say it must be wired as per the instructions and it is possible that you have cooked either the meter or the shunt by reversing stuff.

You may find the -155 is a fault code but I have no idea if this is true. Maybe google fault code for this meter.

Good luck!
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Old 30-01-2016, 16:31   #6
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Re: Wema Am mater installation problem

Looking at your attachment, I'd ignore the back light for now, that only leaves three wires to hook up.
You have an option of either red or yellow back light, and that is what is connected switched power.


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Old 31-01-2016, 01:08   #7
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Re: Wema Am mater installation problem

Thanks guys for your input. I didn't find anything usefull about the "-155" on google. I guess this meter is not very commonly used because of the pricing. I only bought this because I got gift card to my local chandlery for a friend...

I already tried removing the back light wiring and that didn't help. Meter worked some way except no back light :-)

I go back today and double check everything again...
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Old 31-01-2016, 07:33   #8
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Re: Wema Am mater installation problem

Short update. I went through all the wiring and couldn't find anything wrong.

I measured the current using a clamp meter and it was about 4A with lights on and heater running. And there was 12,5 volts over the positive (the leftmost pin on the picture) and ground. But there was only 7,3mV over the signal pin (in the middle) and ground. The sticker on the shunt indicates that there should be 0,5 - 4,5 volts. To me that suggests there is something wrong on the shunt. Maybe it is downright broken / malfunctioning. I need to contact Wema for more information, the two page manual is useless on the error detection.

I also started wondering why most of the shunts are usually on the negative poles, but the installation instructions clearly suggests that this should be connected the positive pole on the battery and loads(s).
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Old 31-01-2016, 07:49   #9
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Re: Wema Am mater installation problem

Most shunts are on the negative pole because it is more costly to measure a voltage that is exactly at the max positive voltage.

Measuring at the negative side is cheaper. But that requires isolating the battery minus from boat ground which is hard to do sometimes.

This shunt is more than a shunt. It has some electronics inside. If you flipped the polarity of the two power wires to the sensor then possibly the electronics inside the shunt are fried.
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Old 31-01-2016, 09:16   #10
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Wema Am mater installation problem

It may also be a little safer to measure the negative side as the signal wires do not carry power.
-155 sure sounds like a fault code?

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Old 31-01-2016, 12:26   #11
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Re: Wema Am mater installation problem

Quote:
Originally Posted by Kaptah View Post
Short update. I went through all the wiring and couldn't find anything wrong.

7,3mV over the signal pin (in the middle) and ground. The sticker on the shunt indicates that there should be 0,5 - 4,5 volts.
What if you take same reading with wires going to the meter disconnected? And what readings you get between big terminals on the shunt?
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Old 31-01-2016, 14:07   #12
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Re: Wema Am mater installation problem

Quote:
Originally Posted by Kaptah View Post
Short update. I went through all the wiring and couldn't find anything wrong.

I measured the current using a clamp meter and it was about 4A with lights on and heater running. And there was 12,5 volts over the positive (the leftmost pin on the picture) and ground. But there was only 7,3mV over the signal pin (in the middle) and ground. The sticker on the shunt indicates that there should be 0,5 - 4,5 volts. To me that suggests there is something wrong on the shunt. Maybe it is downright broken / malfunctioning. I need to contact Wema for more information, the two page manual is useless on the error detection.

I also started wondering why most of the shunts are usually on the negative poles, but the installation instructions clearly suggests that this should be connected the positive pole on the battery and loads(s).
OK, from you have already posted and the installation link, the shunt and the meter are both electronic devices. The 0.5V to 4.5V is becoming a common transducer / meter range for many applications especially in the automotive market.

You can easily check either the meter or the shunt by doing the following.

Meter:
1. Connect the meter to a 12 V power supply (either a bench supply or just any 12V battery). Observe correct polarity which in this case is pin 1 (blue) -ve and pin 2 (red) +ve.
2. Connect a voltage somewhere between 0.5 to 4.5 V to pin 3 (black). This must be +ve. The meter should now provide a reading whose value will be dependent on the actual voltage you applied. You can use a resistor network or a pot or similar to create this test voltage but a simple way is just to use a 1.5 volt dry cell with the -ve side connected to the -ve of the meter supply and the +ve going to pin 3 (sensor).

This will prove if the meter is serviceable or not.


Shunt:

1. Apply a known current flow though the shunt say by using a 60W lamp and 12V battery which will give 5 amps.

2. Connect a 12V supply to the small shunt terminals again observing the correct polarity.

3. Measure the output voltage on the sensor terminal of the shunt. It should be between 0.5 to 4.5V positive with respect to the -ve terminal and the actual value is proportional to the current flowing through the shunt.

This will tell you if the shunt is serviceable or not.

Good luck!
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Old 31-01-2016, 14:36   #13
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Re: Wema Am mater installation problem

Slight thread drift alert
Quote:
Originally Posted by transmitterdan View Post
Most shunts are on the negative pole because it is more costly to measure a voltage that is exactly at the max positive voltage.

Measuring at the negative side is cheaper. But that requires isolating the battery minus from boat ground which is hard to do sometimes.
...........
How is it more cheaper to use the negative pole?
Genuine question BTW

Quote:
Originally Posted by a64pilot View Post
It may also be a little safer to measure the negative side as the signal wires do not carry power.
-155 sure sounds like a fault code?

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I never understood this "safer" idea when applied to recreational boats. Almost all boats do not have a chassis ground (-ve) except for the engine which in effect means all wiring (pos & neg) carry "power". I accept some steel /aluminum hulls are connected the -ve pole and in those limited cases, yes, the positive wiring is live with respect to the chassis but otherwise it isn't as there is no conductive chassis
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Old 31-01-2016, 15:19   #14
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Wema Am mater installation problem

The safer is because with a negative wire, it has to short to a pos to cause a fire. Positives are rarer than negatives, most all my electronic chassis are grounded as an example as is most of the metal in my boat, although I see your point as I have a plastic boat.
I installed a shunt recently on the pos side of my alternator to read its output, because it was on the positive side, I needed to fuse both wires right at the shunt.
If I had a neg isolated alternator I could have installed it in the neg side without fuses but I didn't think about an ammeter when I ordered the alt.
I used an analog ammeter, but originally started looking for electronic ones, electronic ones that can be used on the positive side are more expensive, I don't know why.

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Old 31-01-2016, 15:29   #15
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Re: Wema Am mater installation problem

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Originally Posted by Wotname View Post
Slight thread drift alert

How is it more cheaper to use the negative pole?
Genuine question BTW


I never understood this "safer" idea when applied to recreational boats. Almost all boats do not have a chassis ground (-ve) except for the engine which in effect means all wiring (pos & neg) carry "power". I accept some steel /aluminum hulls are connected the -ve pole and in those limited cases, yes, the positive wiring is live with respect to the chassis but otherwise it isn't as there is no conductive chassis

The meter will be powered by the battery. So if the shunt is plus side connected then the electronics have to subtract two millivolt level voltages. One of these voltages is exactly the battery voltage. Depending on voltage drop one or both voltages may even be higher than the meter + power. Op amps are usually used to do the analog math. Finding op amps that can handle inputs that are at the + rail used to be rare and expensive. Even then it requires resistors with high relative precision and low temperature drift.

Measuring in the low side is easier and most op amps can easily do it. The more to chose from the cheaper they can be purchased.

I'm not sure about safety. Maybe that is true. In the old days the mechanical meter could be either in the + or - side so using - side meant the voltages on the meter were near zero. In this case it appears the OP has damaged the shunt electronics from reversing battery plus power. I guess if that turns out to be the case then there is some additional risk of damage due to high side sensing.
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