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Post Info TOPIC: Amp meter and shunt problem.
iana


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Amp meter and shunt problem.
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I have installed a shunt in the charging circuit of the MPPT regulator, its a 50 amp Jaycar one c/w meter. I am on the second unit, the first just registered in the negative, no matter which way the signal wires were attached to the shunt. I took pictures of the wiring to Jaycar and they couldn't fault it, and so gave me a replacement. This unit is reading a little better, still in the negative, but does move into the positive on a good (winters) day. Still not accurate as I know the fridge draws 7.5 amps so the charge coming in must be above that. 

I also have an amp meter as supplied by Jayco, but that reads the resulting power of battery use, not power coming into the battery from the regultor. Is it that the meter just won't read such low readings, is it that the suppliers have mixed up meters and supplied a 100 amp meter for a 50 amp shunt?

But before I can begin to tackle the problem again, we have to move out of this caravan park and hope where we go will have sunshine.

Has me bushed Ian.



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T1 Terry


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Hi Ian, can you post the two Jaycar part numbers so we can look up what the specs for each product is and if the shunt voltage (mV) matches the meters required input.
It would be helpful if you can find someone with a DC clamp meter so they can measure the actual current so a comparison can be made to determine the degree of error. I gave up on those EvilBay digital meters that showed voltage and current because no two read the same and none of them were anything like accurate through the range. I could calibrate them at zero, but they would have up to a 10% error at 20 amps, if I calibrated them at 20 amps they were incorrect below and above that current. Some of those read negative when zero current was flowing.

T1 Terry

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markf


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T1 Terry wrote:

<deletia> I gave up on those EvilBay digital meters that showed voltage and current because no two read the same and none of them were anything like accurate through the range. I could calibrate them at zero, but they would have up to a 10% error at 20 amps, if I calibrated them at 20 amps they were incorrect below and above that current. Some of those read negative when zero current was flowing.

T1 Terry

 

Having said that Terry, they are a useful thing to throw in your kit while travelling as long as you understand that the best they can do is provide a ball park indication of what's happening. I don't leave home without one and if I need to take accurate measurements it can wait until I get back home where I have a properly calibrated (read expensive) instrument.



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T1 Terry


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Fair enough Mark, I carry one of these for that purpose www.ebay.com.au/itm/UNI-T-UT203-Digital-Handheld-Clamp-Multimeter-Tester-Meter-DMM-CE-AC-DC-Volt/264259901733%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20140106155344%26meid%3Df716289c678447099a1abbe8b4edb4a4%26pid%3D100005%26rk%3D1%26rkt%3D12%26sd%3D112524733527%26itm%3D264259901733&_trksid=p2047675.c100005.m1851 maybe not the most accurate meter around, but it certainly gives a quick reading indicate just what is going on.

T1 Terry

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iana


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I think I have found the answer, just looked at the specs again, and the 50A shunt and meter doesn't read accurately under 6A. so what to do have two shunts 0-6 and 6-50 switchable.

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Whenarewethere


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Have you tried RS online:

Analogue 50, 80 & 100 amps DC, there is technical data as well.

https://au.rs-online.com/web/c/automation-control-gear/panel-meters-components/analogue-panel-ammeters/?applied-dimensions=4294645230,4294644061,4294644515,4294644060

 

I have a Kyoritsu 2046R clamp meter, couldn't live without it.



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T1 Terry


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The great thing with a clamp meter is you can loop the cable around the tongs and divide the reading by the number of loops. Great for tracing very small current flows down to the milli amp level while still maintaining a level of accuracy.

T1 Terry

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iana


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Yes Whenarewethere, I did check, was a bit taken back by the price. Anyway we are not going to get any solar for a while yet, have a look at Perths weather.

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Whenarewethere


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T1 Terry wrote:

The great thing with a clamp meter is you can loop the cable around the tongs and divide the reading by the number of loops. Great for tracing very small current flows down to the milli amp level while still maintaining a level of accuracy.

T1 Terry

 I never thought of that, gave it a go. Good to half rounding errors. Thanks!



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Jaahn


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iana wrote:

I think I have found the answer, just looked at the specs again, and the 50A shunt and meter doesn't read accurately under 6A. so what to do have two shunts 0-6 and 6-50 switchable.

 Hi smile

The inaccuracy at low current is in the meter. The shunt is perfectly linear by definition. But the crappy meters are just that, crappy. So you need a 50mV meter that is accurate down to 0 and reads correctly to a modest accuracy. So when a few amps flows the shunt gives a few mV 's and the meter should read the few mv's with reasonable accuracy, just the same as it does at higher amps. Digital meters have various ways to be inaccurate including the supressed zero and the +_  digital error. They only look more accurate and steady by tricks.  

Your multimeter may read the low readings with more accuracy. Possibly ?? depending on what quality it is too !

Jaahn

PS I could not actually understand that gibberish on Jaycars website about the shunt and the meter setup ?? I have made up my own shunts and calibrated them to meters for larger genny outputs up to 250A DC.  

 



-- Edited by Jaahn on Thursday 4th of July 2019 08:46:38 PM

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iana


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Thanks for that Jaahn. If you go to the Altronics sight, you will see the same shunt and meter, but at 100 amps. So the answer is to get a better digital meter.

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Jaahn


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iana wrote:

Thanks for that Jaahn. If you go to the Altronics sight, you will see the same shunt and meter, but at 100 amps. So the answer is to get a better digital meter.

 Hi iana smile

Yes get a better meter. The trouble is the cheap ones are all sus and also digital meters require power too. This is what I would use probably, as I am old fashioned, an analogue meter. This one is a higher accuracy than the others on ebay class 1.5(not 2.5). No power required either aww Might not be super accurate but you can set the zero to ..... zero !!! so it is accurate down there and full scale should be reasonable.

  https://www.ebay.com.au/itm/44C2-Class-1-5-Analog-Panel-Current-Meter-Ammeter-Gauge-DC-0-50mA/331641405242?epid=1738435229&hash=item4d375e3f3a:g:r5IAAOSwtplZ0DP- 

Jaahn

One is amused by this sort of accuracy statement on the ebay class 2.5, $5 meters; "The measurement allowed error is +/- 1-3cm."    WTF.

 



-- Edited by Jaahn on Friday 5th of July 2019 09:12:40 AM

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Whenarewethere


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I put in analogue meters for voltage & amps to keep vampire draw to a minimum. 

Personally they actually look a lot nicer than digital. They are not difficult to read. It's a bit like the car speedo, I never really look at the digital output, pretty much always the analogue dial & knowning where the needle should sit is enough to know whether you are a bit under or over, same with my solar setup.

I have found my analogue meters to be very accurate against my clamp meter & certainly more than accurate enough for the intended purpose.

5 analogue meters in this photo:

normal__MG_2513.jpg



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