Weird PV1 reading once battery is below 70%

[Marco P]

Hi,

I'm currently on a boat with a solar setup that I don't know much about.

Everything seems to be running fine, but once the battery is below 70%

I get this weird reading of 240 Amps on PV1.

The debugging screen shows a 1.8V measurement on the PV1+ shunt.

What could be the cause of this?

Cheers,

   Marco

[Dacian Todea (electrodacus)]

Marco,

You have a bad contact to one of the two sense wires coming from the PV shunt. Likely is the connections on the SBMS0 but could also be at the shunt.

So because one wire gets disconnected you see the max current that is 240A for a 200A 75mV shunt.

To be more exact is the PVn connection that is open circuit so check that wire.

[Marco P]

Hi Dacian,

> So because one wire gets disconnected you see the max current that is 240A for a 200A 75mV shunt.

yes, that would make sense, but it doesn't explain why it works most of the time.
I disconnected that wire yesterday for a quick test to see if it's broken and it went from like 4A to 240A.
So I don't think it's a lose wire, but maybe reconnecting it helped, but I haven't been below 70% charge when this usually happens.
Any other ideas?

Thank you!

[Dacian Todea (electrodacus)]

It is an intermittent contact so most of the time it makes contact. There can not be any relation between SOC and this symptom.

The wire was inside the connector but maybe not under the spring contact just sitting on it so maybe when ambient was slightly colder the wire contracted just slightly enough not to be in contact with the spring contact.

[Marco P]

I've finally found the time to open this thing up and check both ends of the wires.

The contacts seem fine and also the wire itself looks fine to me.

It behaves very strangely. You are right that it's not related to the SOC, that was more of a coincidence.

But I've witnessed it fixing itself this morning. PV was showing 240A all night, and as soon as the sun came up it gradually went down

starting to show a reasonable value of 1.8A.

This doesn't feel like a bad connection to me.

Thanks for your help!

  Marco

[Dacian Todea (electrodacus)]

Marco,

In diagnostic screen in the photo you shared PV1 showed as 32694 calibration value (that means zero current) and 65535 current read value meaning max ADC voltage reading.

Maybe the coincidence of showing a more normal value in the morning has to do with temperature change. At night when is colder all wires will be shorter and as temperature increases in the morning the wires will become slightly longer possibly making contact.  It can be that the wire itself (I assume is a solid wire CAT5) can be broken and as it gets colder the two pieces of wires geeing shorter will fail to make contact.

If both PVn and PVp are removed the current will show as 0A but if PVn is removed and only PVp makes connection then you will see the 240A

So the PVn wire is broken somewhere if you checked the connections and those are OK.

You can remove both PVn and PVp wires from the SBMS for a few days and you will always see 0A PV reading demonstrating that the issue is the wires and not something else.