shunts

hi all

i am new here, so please go easy.

basicly, the story goes, i have a camper trailer, and i am re-wiring it and adding meters so that i can moniter the state of my battery. i have purchased

2 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5580&keywords=5580&form=KEYWORD"[/URL]

1 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5575&keywords=5575&form=KEYWORD"[/URL]

and 1 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5412&keywords=shunt&form=KEYWORD"[/URL]

now, i have managed to get the voltage add on board going, but i for the life of me can not work out how to get the shunt to display on the meter.

i quite enjoy electronics, and i have been doing it for years, but for the life of me, can not work this one out.

cheers

jbates58

Try your post again with real links.

jbates58 said:

hi all

i am new here, so please go easy.

basicly, the story goes, i have a camper trailer, and i am re-wiring it and adding meters so that i can moniter the state of my battery. i have purchased

2 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5580&keywords=5580&form=KEYWORD"[/URL]

1 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5575&keywords=5575&form=KEYWORD"[/URL]

and 1 of thease: [URL="https://www.jaycar.com.au/productView.asp?ID=QP5412&keywords=shunt&form=KEYWORD"[/URL]

now, i have managed to get the voltage add on board going, but i for the life of me can not work out how to get the shunt to display on the meter.

i quite enjoy electronics, and i have been doing it for years, but for the life of me, can not work this one out.

cheers

jbates58

Click to expand...

Ok,,..... Now you want to install this digital ammeter to measure your battery drain.... Fine... Connect the shunt which you got it from jaycar...in series to the load. Then take out two wires from both sides of the shut and give this line to the ammeter...

Make sure you have got he correct spec shunt for this... WHat is your maximum battery drain ? What kind of load are you driving? What kind of battery are you using ... Dry battery, lead acid, SLA...?

Do not try to put the ammeter shunt in the positive battery lead, or you will exceed the common-mode input spec on your DPM used for the ammeter. It only allows a common-mode voltage range of +-1V.

You can put the shunt in the battery negative lead if you can disconnect all of the loads in the trailer from frame ground (unlikely). See the attached diagram. It shows the voltage divider for the voltmeter, and the method of connecting the shunt. This will not work if you cannot isolate all the loads.

You will need an LM7805 to make the 5V to power the DPMs.

btw- I did this in my trailer, but I used LCD DPMs. They draw so little power that I leave them on without a power switch. Your LED DPM will have to be switched off so that you dont kill the battery....

A much better way of doing this is to use a high-side-current-monitor (Like the ZXCT1009). This lets you put the shunt in the battery positive lead, and tailor the gain so that you could get 20A full-scale instead of the 200A you will naturally get with the +-200mV DPM. A better choice for the shunt would be 10mΩ (10mV/1A).

MikeMl said:

Do not try to put the ammeter shunt in the positive battery lead, or you will exceed the common-mode input spec on your DPM used for the ammeter. It only allows a common-mode voltage range of +-1V.

You can put the shunt in the battery negative lead if you can disconnect all of the loads in the trailer from frame ground (unlikely). See the attached diagram. It shows the voltage divider for the voltmeter, and the method of connecting the shunt. This will not work if you cannot isolate all the loads.

You will need an LM7805 to make the 5V to power the DPMs.

btw- I did this in my trailer, but I used LCD DPMs. They draw so little power that I leave them on without a power switch. Your LED DPM will have to be switched off so that you dont kill the battery....

A much better way of doing this is to use a high-side-current-monitor (Like the ZXCT1009). This lets you put the shunt in the battery positive lead, and tailor the gain so that you could get 20A full-scale instead of the 200A you will naturally get with the +-200mV DPM. A better choice for the shunt would be 10mΩ (10mV/1A).

Click to expand...

Could you please tell me....how the common mode voltage exceed if you connect the shunt in positive line of the battery?

Unless there is a current imbalance in the line...how the CMV will change?

Rajaneesh said:

Could you please tell me....how the common mode voltage exceed if you connect the shunt in positive line of the battery?

Unless there is a current imbalance in the line...how the CMV will change?

Click to expand...

The common-mode range for the DPM is measured with respect to the DPM's own - power supply pin, which is connected to the battery negative pole (0V). If you put the shunt in the high-side, the differential drop across the shunt will sit on top of the battery voltage (~13V), i.e. the common-mode voltage applied to the DPM +-inputs will have 13V on them with respect to the DPM's - power pin.

MikeMl said:

The common-mode range for the DPM is measured with respect to the DPM's own - power supply pin, which is connected to the battery negative pole (0V). If you put the shunt in the high-side, the differential drop across the shunt will sit on top of the battery voltage (~13V), i.e. the common-mode voltage applied to the DPM +-inputs will have 13V on them with respect to the DPM's - power pin.

Click to expand...

But i have tried this way....and it was working fine in my lab for the last 7 years......... Wondering..!!!

Some DPMs have a transformer-isolated switching power supply, so the common-mode range of their differential inputs might be higher than the DPMs the OP posted. The ones he posted specifically said the CMR is +-1V.

MikeMl said:

Some DPMs have a transformer-isolated switching power supply, so the common-mode range of their differential inputs might be higher than the DPMs the OP posted. The ones he posted specifically said the CMR is +-1V.

Click to expand...

Appreciated.....

Thanks...

Hey, it occurred to me that you could put the shunt in the battery negative lead and leave the loads grounded as shown here.

wow, i am so lost. lol. this is so confusing. i have ysed a 5V+ Regulator, (lm7805 for memory) to provide me with the 5V for the DPM's, but i spoke to a fella at jaycar today, and he was going on about needing ohms law to calculate the type of shunt i need, and resisters etc... but when i brought all this with the idea of doing it, the fella said that thease shunts are designed to work with their DPM's, the most i'll ever pull would be 20A, but i think my shunt is a 50A shunt, becaust it was only $1-$2 more than the 20A one. and i also allows me to have a spike if needed. so, my understanding from what he told me, was that i just needed to place the shunt inline from +on the batt, then to supply, and that the probes on the shunt will just go to the DPM. and i think it works, because when i get my DMM, and set it to millivolts, i get a reading, for example, i gave it a known load of 6A, which the meter displayed, and then i ran the same load through the shunt, and put my meter on the probes on the shunt, and i got the same reading. so i now just need to know how to get it to work with the DPM, and like i said, i doubt i'll ever pull anymore than 20A, but if i do, i'll connect that straight to the battery. i think the most i'll ever need is 10A. so can we work it on those figures, or do i need to know the most ill need to draw?
also, if possible, please keep it simple, i can read a circuit diagram, but am a little fuzzy on the symbols etc...

cheers

jbates58

I already told you that the 1mΩ shunt you bought will read 200mV (full-scale on the DPM when it is set up that way) when 200A flows through the shunt, so 1mV per 1A.

The problem with it is that you will only have a resolution of 1A, i.e. the DPM will read ...,-1A,0A,1A,2A,3A,...

If you used a 10mΩ shunt, you could resolve 0.1A, i.e. ...-1.0A,-0,9A,-0.8A,... 0.0A,0.1A,0.2A,...

MikeMl said:

I already told you that the 1mΩ shunt you bought will read 200mV (full-scale on the DPM when it is set up that way) when 200A flows through the shunt, so 1mV per 1A.

The problem with it is that you will only have a resolution of 1A, i.e. the DPM will read ...,-1A,0A,1A,2A,3A,...

If you used a 10mΩ shunt, you could resolve 0.1A, i.e. ...-1.0A,-0,9A,-0.8A,... 0.0A,0.1A,0.2A,...

Click to expand...

ok then, so if thats the case, am i able to use a resister from the leads on the shunt to the DPM to give me a more accurate reading? and also, i am unsure of how to wire it to the DPM, i have tried to probe it to the signal in lines, but they are both + power, so it wont create a circut.

cheers

jbates58