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fstrauf avatar image
fstrauf asked

Smartshunt voltage difference

Hi,


I have a Redarc BCDC 1250D charging my batteries (sources are main vehicle battery and solar panels).


After some time of driving the incoming current to the aux battery drops down, while my 500A SmartShunt shows a SoC of not full (~80%) and ~12.69V.

The Redarc charger actually stops charging as it measures a voltage of 13.3V (measured between aux battery connection cable and ground), thinking the battery is full.


Measuring the battery directly, however, shows 12.69V.


Measuring between aux battery positive and SmartShunt-'to-system-minus', shows 13.3V.


Measuring between aux battery positive and SmartShunt-'to-battery-minus', shows 12.69V.


This state lasts only for a certain amount of time and eventually, the aux battery positive to SmartShunt-'to-system-minus' also shows 12.69V.


The issue is annoying in that my battery doesn't fully charge anymore as the Redarc battery charger thinks the battery is full, while it is not.


I feel this is some issue with the SmartShunt.


Any idea how to resolve it. It's only a couple of months old.



SmartShunt
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@fstrauf I feel this is some issue with the SmartShunt.

Probably not. The shunt is a lump of metal machined into a precision resistor.

redarc-b.png

This diagram is useful for redarc's and smartshunts.

You most likely have a bad connection somewhere. A bad cable/lug crimp, loose bolt, or grunge under a chassis earth.

The Redarc charger actually stops charging as it measures a voltage of 13.3V (measured between aux battery connection cable and ground), thinking the battery is full.

How do you know what the redarc measures? There is no display other than a few leds.

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redarc-b.png (185.0 KiB)
fstrauf avatar image fstrauf klim8skeptic ♦ commented ·

The Redarc support told me to measure between the brown and black cable (in the diagram above. That is what showed 13.3V

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4 Answers
mvas avatar image
mvas answered ·

Are you says you have a 0.6 volt drop across the Shunt terminals?
Do you have a bad connection on one, or both of the two Shunt Terminals?
Find out exactly where the Voltage Drop is occurring.

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fstrauf avatar image fstrauf commented ·
Yes, exactly that's what I'm reading.


From my measurements, it's happening between the two shunt terminals i.e. one side reads 13.3V and the other reads 12.69V.

The bolts are tightly connected.

I'm really not an expert on this, but how would you go about finding a voltage drop?

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kevgermany avatar image
kevgermany answered ·

What batteries are these? In general you should be charging at about 14.4V for AGM, slightly less for lithium. Firstly sounds as if the redarc is set too low.

I don't understand the voltage descriptions. A diagram would help. But check cabling/terminal tightness, voltage drop over fuses.

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fstrauf avatar image fstrauf commented ·

I've got two of these: https://parts.cat.com/en/catcorp/153-5720

I don't think I can set the Redarc any higher (max voltage can be set, but it doesn't impact the 13.3V for charging).

The image down below is pretty much what I have and the shunt is between system and aux battery minus.


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fstrauf avatar image
fstrauf answered ·

Just wanted to say that it's pretty awesome to receive that many comments in this short a time! Thanks a lot!

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Mike Dorsett avatar image
Mike Dorsett answered ·

Most likely to be volt drop in the cables - this is a big problem with 12v systems. make use of remote voltage sensing if available, or make sure the total volt drop in the cables at max current is <0.1V

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fstrauf avatar image fstrauf commented ·
Thanks Mike, how would I go about finding it? All I can see is a difference between the two smartshunt terminals.
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