question

charliektm400exc avatar image
charliektm400exc asked

Battery drops much faster than I think it should

I have been having problems with my battery system in my second hand caravan. I fitted a smart shunt, and watched the video on recommended settings and input them to the app.

I have 2 x 105ah AGM batteries and 2 180 w panels and a 100w blanket

Batteries are about 3 years old but probably sat for first 2 years unused but with solar input

I expect that I can bank on 100ah of usable power

settings are Battery capacity 210

Charged voltage 14.2

Discharge floor 50%

Tail current 6%

charged detection time 3 minutes

Peukert 1.25

Charge efficiency 80%

Current threshold 0.1

Batteries are charging during the day from solar, and usually get to around 95% by the time the sun starts to set (I know it sounds like I haven’t got enough solar but that’s a seperate issue I will address when I am able as I’m currently in the middle of outback Australia)

If I run things in the evening/night ( background caravan stuff, 12v TV for 3 hours and Starlink overnight) my system “Projecta” cuts out (10.5v), but the shunt shows about 80% and 64ah used, so it shouldn’t be cutting out I would think.


I would really appreciate some help with working out what the problem is.

thanks


Charlie

SmartShunt
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2 Answers
mvas avatar image
mvas answered ·

How often are your batteries back to 100% SOC, guaranteed?

14.2 Volts may be low final charge voltage?

Do you have the charging specifications from the manufacturer?

Exactly, how were these "unused" batteries on PV for 2 years?

SLA batteries "age", just like humans. Even if you keep them at float, they will not last forever.

These batteries may be getting more and more sulfated every day.

Tells us ... What is the battery voltage after you consume 64Ah?

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charliektm400exc avatar image charliektm400exc commented ·
Don’t know. Only had smart shunt for a few days as I got it to try and work out what was happening. Assuming they get to 100% while I’m driving it was a week ago it happened. Will get there tomorrow as well.


Pretty sure Johannas recommended 14.2 for solar charging in his settings video when charging off solar.

charging specs for controller unit yes, for batteries no.

The previous owner said he bought van day before 6mmonth lockdown in Victoria so no use. He said it had been out on two weekend trips since then.

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mvas avatar image mvas charliektm400exc commented ·

Who manufactured the batteries?

I still say, a terminal charging voltage of 14.2v is low.

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kevgermany avatar image kevgermany ♦♦ mvas commented ·
No, this is for the shunt, not the charger.



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kevgermany avatar image
kevgermany answered ·

Shunt tail current is too high. 4% is default, for where you are probably 3-4% better. Maybe even lower.

Detection period can be increased.

You don't mention the solar charger, guess it's not Victron. Would be good to check its settings.

With your settings, even with a good battery the shunt will synch to 100% too early. But you say this isn't the case. And this wouldn't lead to the cut out at low voltage. Simply false SOC readings.

From your power consumption figures, your battery isn't holding charge. Could be loads you're not aware of if the shunt isn't wired correctly. But probably the batteries. They may have been cooked by the solar controller. May be electrolyte stratification from being stationary too long. But you're in a hot country, so battery life is shorter. Battery centre can test them.



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charliektm400exc avatar image charliektm400exc commented ·

Thanks, I was worried about battery life when I got the van so had the batteries tested by an auto sparky. He said they were good.

will change the settings on the shunt any way

What charger settings do you want to see?


I wired shunt taking all negative leads via shunt

It’s only been the last one or two months in heat. Rest of its life it’s been in Melbourne and Tasmania.

i might see if I can get the batteries checked next time I’m in a big town.

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pwfarnell avatar image pwfarnell charliektm400exc commented ·
Most battery tests are short term tests to see if the battery can deliver a high current, which an aged battery that has lost capacity may still be able to do. Rarely do people do a slow discharge test over 10 hours to see what the actual remaining capacity is which is the important thing for caravans etc.
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charliektm400exc avatar image charliektm400exc pwfarnell commented ·
I did suspect this, but really not in a position to get this tested properly for quite some time.


Other than a slow discharge test, is there anything I can check that would give me more confidence worn out batteries are the problem?

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kevgermany avatar image kevgermany ♦♦ charliektm400exc commented ·
Absorption and float voltages from the charger. Current if there is one.
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charliektm400exc avatar image charliektm400exc kevgermany ♦♦ commented ·
Absorbing voltage 14.4

Float 13.5

Bulk current 20A

Rated output current 35A continuous


is that what your looking for.?

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kevgermany avatar image kevgermany ♦♦ charliektm400exc commented ·
Thanks. Sounds about right. You might want to increase float to 13.7 if you're going to be using it a lot. But probably better to leave it where it is for your country.
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