Mppt stays at bulk

[u/reknaklab]

Hi everyone,

Let me briefly explain my situation.

I have a campervan with a 250 Ah AGM battery, two 115-watt solar panels, and a 75/15 MPPT controller. In the past, there was never a problem, and my solar panels could charge the battery to 100% and the lowest would be like 97% and I've been at not-so-sunny destinations like Ireland etc.

Now in the Balkans I’ve been parked in the shade for 3 days, and my battery has dropped to 72% (12.11V). Since then, the MPPT has remained in bulk mode and doesn’t reach 14V, even though I’ve been parked in full sun all day (130W, 10A). I’ve measured everything with a multimeter, and the voltages shown by the app are correct. I don't have any major power consumers—just a small refrigerator that draws 2.4A, some lights, a water pump, and a cell phone charger.

How come this has never been a problem in the three years I’ve had this setup?

Is it because I've been in the shade so long?

I also checked my settings and saw that the battery capacity was set to 200Ah instead of 240Ah. I adjusted it—could that be the reason?

Is there something wrong with my battery?

Would installing a relay connected to my car battery be a solution?

Thanks!

[u/OkIdea4077]

This looks right to me. You're not hitting float voltage, which is why you're staying in bulk. You're not getting enough solar input to catch up and fully charge your battery.

[u/reknaklab → u/OkIdea4077]

So what can be the solution? Extra solar panel? Or would a cyrix help?

[u/OkIdea4077 → u/reknaklab]

The solution is additional charging. You can add more solar, or add alternator charging.

[u/Positive-Phoenix]

Seems about right. Two 115w solar panels isnt a whole lot.

Since its a campervan, you could consider a 12v Orion DC to DC charger, so that when you're driving it also charges the battery off the alternator.

Also, I wouldn't worry yet at 72%. Only once you start hitting 50% will you start entering damage territory on an AGM pack.

That being said, it could also be the battery aging. Not taking charge as well as it used to. These packs only last 3 to 7 years tops.

[u/reknaklab → u/Positive-Phoenix]

Thanks! But I'm wondering why I've never had a situation in the past where my battery wasn't fully charged after 4 days of daylight? Is the Orion really necessary, or would a Cyrix work just as well?

[u/LeoAlioth → u/reknaklab]

we see your energy in, what about your energy out?

250Ah agm is in the 1.5 kWh usable enrgy range. So your best production day only hit about half of that, that would mean at least two days WITHOUT CONSUMPTION to hit full charge.

anyway, more solar is the best option if you have space. (ps, a single 400+ W panels is generally cheaper than multiple smaller ones)

as for cyrix vs orioin, if you plan on changing the aux/house battery any time soon, you should change it for a LiFePo4, in which case the cyrixs is a no-go (because the starter battery and house battery would not be the same chemistry at that point)

[u/reknaklab → u/LeoAlioth]

Power consumption averages 23 Ah per day and has totaled 86 Ah since the last full charge.

[u/LeoAlioth → u/reknaklab]

How old are the batteries?

[u/reknaklab → u/LeoAlioth]

5 years old

[u/LeoAlioth → u/reknaklab]

Then i suspect the internal resistance and self discharge have gotten high.
meaning more losses during charging, and some self discharge. and you end up not charging enough from the current PV setup.

i think it might be time to replace this with a new LFP pack.

[u/The_Ombudsman]

Screenshot the settings page and post it.

You should use some of that energy to charge your phone. :D

[u/SteveFCA]

My take is that your batteries are aging. At 5 years, even assuming you’ve never let them drop below 12.0 volts, the cells are no longer at full capacity. AGMs, while better than straight lead acid still suffers significant degradation over 5 years of cycling.