Interpreting the Victron Solar Controller App after Dry Camping

Fiddlinmike

Hello everyone. We have a 2019 Tab 320 with a factory installed solar panel. The Tab came with an Ultrapower R24 marine battery that has a sticker on it saying its reserve capacity is 125 minutes at 25 amps.

We are the people for whom these stock batteries are intended.  We typically camp with electric hook-ups, and our dry camping rarely extends past a day.  We also have the luxury of storing the 320 in our garage. So it’s nearly always connected to power.  Batteries and solar power don’t often figure into our camping experience.  

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 Alde, 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…

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)?

Thanks for your thoughts on this!

Sharon_is_SAM

@Fiddlinmike - first, did you program the controller?  Not sure if it asks any battery info or not.  If I calculated correctly, your battery only has about 50 Ahr, so only 25 Ahr before you are discharged 50%.  Also, voltage readings during charge and under load are not the same as resting voltage.  Lastly, if you discharge at a faster rate (fan turned to 40%, lights, etc) your actual capacity is lowered.  You are correct in your assumption that the battery is designed for those who use electric hook ups - not for dry camping.  Not surprised that you had low voltage readings.  

Fiddlinmike

Thanks for the response Sharon_is_SAM (and all your responses!).

I saw where one can apply user settings for charging through the Victron Connect App, but I can’t find any recommended settings for my Ultrapower R24 battery.  After extensive searching, I emailed a dealer, but no response.  So, I’ve never changed the settings from the factory default (Gel Victron deep discharge(2)).  Maybe there are better generic lead-acid settings I should use.

I understand voltage readings during discharge and use are not the same as resting - I’m hoping that means that the actual resting voltage across the battery terminals never actually dropped to 10 volts, but I wonder what the point of the high and low readings are in that case. I’m happy to disregard them as a casual user, unless I need them for something.

Thanks for the tip on rapid discharge.  After thinking about it the overnight drop seems about right for my battery, but still the 10V thing bothered me, and I don’t understand the “consumption” line, and the way I look at the bulk charging numbers is telling me I had solar capacity to spare in the early days of my trip.

Sharon_is_SAM

@Fiddlinmike - I did a search and can’t locate that battery.  Assume maybe regular deep cycle.  Find a controller setting for that? Someone else that is familiar with the SmartSolar will hopefully chime in.  My best advice is get a bigger battery with at least 100 Ahr.  Even if you only dry camp overnight, more capacity is better.

BrianZ

@Fiddlinmike, I found this in the Victron controller manual:
"Consumption (only on 100/20 models and smaller)
Shows the energy consumed by loads connected to the load output terminal."
So, I'm curious what loads you(or NüCamp) have connected to the load terminals on your controller.  I'm not familiar with how NüCamp wires them, but we don't have anything connected there, since all our loads go through our Victron battery monitor shunt.

Regarding the History page in the app showing the total Wh of solar power each day, I've been interpreting that as the total power generated & used to recharge/maintain the battery each day.  Also, if you divide that number by 12 (volts), you'll have the number of Amp-Hours (AH) you've needed each day, which you could use to estimate your average daily power needs.  On our first trip using solar, we averaged around 18AH per day, using propane for both fridge & Alde, with other typical usage for lights, water pump, charging cell phones, and occasional use of a cell phone signal booster.

In your case, your fan might have been the biggest draw.  For example, if it was a 60 watt model, divide by 12 and that's a 5 amp draw; but if you used only 40%, that's still 2 amps.  Ten hours of usage per day would then consume 20 AH, or 80% of your available 25 AH of battery power before you fall below 12V/50%.  The 5 AH remaining won't go very far. 

This may be getting off the topic a bit, but some of us have modified our stock ceiling fans to reduce both power consumption & noise while saving power by running it at a very low speed using a PWM controller device.  I agree with @Sharon_is_SAM, that you could benefit from a larger battery, if you want to avoid running your battery down.  I doubt you did any major damage, by the way, but might have shortened battery life a little bit.  We replaced our stock battery with a 150AH golf cart battery & can get by with a single 100W panel.  These mods are  documented here, if you search for them.

Fiddlinmike

Thanks a bunch, @BrianZ .

A responder on the Victron forum told me that the measurements in the “consumption” line are phantom readings from the load output and they can be ignored.  That makes sense to me because we have nothing wired to the load terminals on our controller. 

The other information you provided makes me feel much better about my understanding of what’s going on with our consumption and production - it’s all starting to make sense and appears in line with your experience. You’re dead on with the fan observation.  Our battery just doesn’t have much capacity and otherwise my calculations line up exactly with yours.

I’ve convinced myself that the 10V minimum reading in the Battery max and min area must be some kind of instantaneous measurement affected by load or generation, and not at all a representation of the actual resting state of the battery.  It makes no sense to me that we could have either drawn our battery that low, or recovered from it if we had.  As I said, until that one evening we barely used the battery, and it looks to me like our bulk and absorption charging regularly replenished the battery long before we lost sun power.  Do you have an opinion on that? 

I really appreciate everyone responding to these questions.  I’m going to try to do the same if I can catch someone else’s question before the experts chime in!

PS… we’re from Abingdon, Virginia - I’ll put that in my sig.

pthomas745

It makes no sense to you because...you probably didn't use 40 amp hours of your 80 amp hour battery.

12 hours of the Maxx Fan might use 12 amp hours.

The LED lights in the trailer hardly use a third of an amp per hour.  2 reading lights for 4 hours might use 2 amp hours.

The pump...will only draw power when actually pumping water.  Not really a factor.

The phone and Ipad charging will draw power, but those are small factors, also.....

If you ran those items at the same time.....and looked at your battery reading when you first turned on your fan...you would probably also got the same "low" battery reading, even though your battery was "over 13" just a few moments ago.

The only way to get an accurate measurement of a battery is:  with no charging coming in, and no draws going out.  If you are running anything in the trailer and look at your Victron, it will always read low. 

The only good way:  "resting the battery." Turn the battery switch off.  Not much to do with the installed solar input, so maybe you can turn the charging off in the app, or just wait until there is no solar input after sunset. Wait a few minutes.  Then look at the battery status.  The photo below shows the idea: on the left, I'm running a fan in my trailer.  12.09!  On the right, the fan is off, the battery switch is off...and the state of charge has settled "up" to 12.46.....

Fiddlinmike

Thanks a lot, @pthomas745 !   I think that clears up what’s left of my confusion.  I appreciate everyone’s time on this.

pthomas745

You can do the same type of comparison yourself. It is a little harder with the installed solar providing charging with the sun up. In the settings section for the battery there is a "Charging off" toggle switch.  So, with the charging off and the trailer battery off, you should be able to get a "rested" battery reading in a reasonable 10 minutes or so.  There are also many different descriptions in the Forums of measurements of the amp hour usage of the items in the trailer.

PS:  There is the possibility that you might not have been charged as well as you thought when you started your "test".  The 13 or so you were reading could also have been a false capacity reading.  (But, it certainly looks like your solar was cranking away very well.)

Jkjenn has been one of the guru's on battery management, and of measuring the items in the trailer for their power use.  This file has a spreadsheet that has the numbers. 

https://jenngrover.com/power-consumption/

ColoradoJon

As others have mentioned, it is very difficult to interpret the power consumption based on the charging graphs from the charge controller.  Without a shunt and meter like @pthomas745 BMV-712, measuring your usage will be a guessing game.  Your voltage readings will include loads and charge so they will read low and high respectively.

You should see the charge logs from my 1920 watt off-grid solar cabin.  They are only useful for gauging the health of the system, not the power consumption.  I have a BMV-712 for that.