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fiddlinmike avatar image
fiddlinmike asked

Help interpreting theSolar Connect app

I have a 2019 NuCamp Tab 320 camper with a factory installed solar panel and an Ultrapower R24 marine battery that has a sticker on it saying its reserve capacity is 125 minutes at 25 amps.

For 3 days this week we went dry camping, with good sun exposure. We have no battery monitor, so we started cautiously using the battery - no hot water, fridge on gas, limited use of lights and fan. The solar panel seemed to have no trouble keeping the battery fully charged with our conscious attention to consumption. On the 3rd night, I decided to push it a little. We ended the sun-day with a battery over 13 volts. That night we ran the MaxxFan all night at maybe 40%, used cabin reading lights maybe 3 hours, used the water pump for flushing and brushing teeth but little else. We also charged an iPad and an iPhone. In the morning I read the battery charge using the Victron Connect app on our solar controller - it was 11.97. I was surprised it was that low - we hit the 50% capacity limit from what I understand. On reflection maybe that’s what I should have expected. I know you don’t want to regularly run the battery this low if you don’t have to.

The purpose of my post is to get an interpretation of the history report I’m seeing on my Victron app…

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What scares me is the “low” battery voltage readings near 10 volts on two of the days. If that’s right, wouldn’t I have ruined my battery? The column labeled “3 days ago” was the day that ended with a full battery and started my aggressive experiment with our overnight power use. The column labeled “2 days ago” was the morning I awoke having drawn our battery from +13 volts to 11.97 volts and towed the camper home. Back at home I had a full +13 volt charge, and all is apparently well. Every time I’ve checked the battery with a voltmeter at the battery terminals it has registered the same as the voltage indicated on the Victron app.

So, what accounts for the low voltage readings? Also,what accounts for the “consumption readings” of 10Wh in 3 of the columns? If our bulk and absorption periods totaled about 170Wh in “3 days ago” does that give me a rough indication of how much energy I drew from the battery during the prior day (assuming no other charging from A/C or the tow vehicle and low power use while charging with the solar panel)? Does the low bulk and adsorption total on the “2 days ago” indicate I was getting a significant charge from the tow vehicle (the sun was bright driving south that day)?

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spirou avatar image spirou commented ·
First the consumption row: it's a ghost reading from the load output. Ignore


Looking at all the data together I have a feeling the battery is quite small. Can't find anything with that name on google but I guess it's not even the "standard" 90Ah used in most MH. So the min.voltage is no surprise really and you might want to look into upgrading if you want any proper autonomy. Because your "heavy" use wasn't that unusual at all.


The yield data does give you a rough estimate of use. But it will always be greater than consumption to account for charging efficiency/losses and any extra loads during the day that are powered (almost) directly from the panel.

Low yield on 2 days ago is indeed most likely due to power coming from the alternator.


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fiddlinmike avatar image fiddlinmike spirou commented ·
Thanks for responding. It is a small battery - 125 minutes at 25 amps. Installed for people who are use to plugging in, I’m sure.


I’m happy to ignore the ghost consumption numbers! And thanks for confirming my reading of the solar charging.

Still, I have this weird 10V minimum reading from VictronConnect. I know battery voltage readings can be off (of a true resting voltage) if they are taken under load or while charging. Is that a possible reason I would get a 10 volt minimum battery reading at some point during a day? It makes no sense that the battery would have actually dropped to 10 volts when it almost certainly was full each evening when the sun went down and barely used overnight. And, as I said, my “heavy” use started at +13v in the evening and dropped to about 12v the next morning. It feels like the 10v showing for that day and the prior one is some measurement quirk - I can’t see how the battery could have regained a full charge if it really dropped that low.

Clearly, I’m either misunderstanding what “min” means on the battery report or it’s another thing to just ignore.

Again, thanks for the response.




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spirou avatar image spirou fiddlinmike commented ·

Converting the reserve capacity numbers (usually used for starter batteries) to the regular Ah capacity metric used for house/aux/deep cycling batteries gives the likely result of 55 Ah. Which is tiny to be honest. And fits perfectly with the results you are seeing.


A fridge running all night will use about 15 Ah. Some lights, TV, water pump etc. And you're looking at 20-30 Ah. Converting your yield numbers into Ah confirms that estimate of 15-25 Ah.

An abused small starter battery being drawn down to 50% SOC (when new) will soon develop exactly the symptoms you are seeing. It simply won't hold the voltage as high as you expect and will soon be toast. Just not designed for such use. Of the 55Ah when new you're possibly down 1/3 already, round it up to 40Ah remaining. So the 15-25Ah used per day is well into or below 50% advised range.

Bare in mind also that a battery down to 80% original capacity is considered past its life span.

As a comparison... I have 180 Ah (2x90) dual purpose Varta and after a normal night (~20 Ah down) the min voltage will register around 12.3 V. The min number is obviously under load but still.



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fiddlinmike avatar image fiddlinmike spirou commented ·
Very helpful! Thanks so much for your time on this.
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Scott Gardner avatar image
Scott Gardner answered ·

Mike, I agree with the answers above. Does the solar app have a line chart that shows voltage etc over time? My suspicion is the 10+V reading you are seeing is a momentary voltage from when the battery was already low and a water pump or something started. it would be easier to tell with a chart over time. I use VRM for the most part. If you want to routinely use the camper in this way (which is great!) then upgrade your battery bank and also have something like a honda suitcase generator for cloudy days. Also is this battery also for your engine or is this a trailer? If so then certainly want to isolate house loads from engine batteries to make sure you don't get stranded.

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