Solar charge profile

mjh73mjh73 Registered Users Posts: 4

Hi everyone,

I'm a complete and utter newbie to the forum and to the world of PV, I was hoping to ask for some help/advice......

I live in the UK and have just recently had a 100W solar panel fitted to my caravan to keep the leisure battery (sealed Lead-acid, Yuasa - L36-100 ) topped up, to provide power when we are not connected to an electrical hook up and to power the caravan motor mover. It is controlled by an Epever MPPT Solar Charge Controller - although not sure of the exact model (I do know that it is an XTRA*****N-XDS2 model with the advanced display, sorry not sure of current rating).

We bought the caravan with battery fitted last year, the battery had been fitted from new in 2017, the bloke we bought it off ALWAYS had his caravan plugged into the mains to keep the battery topped up with the in built multi-stage charger.
Now we have it it is stored 30miles away from our home but has a tracker on it that tells me the position and battery voltage at roughly 6 hour intervals, over the winter I noticed voltages of 14v, 14.4v, 14.9v and yesterday 15v.....As expected ? (see below link)

I managed to visit the van yesterday and saw the battery voltage (measured on internal systems) drop from 13.4v to 12.6v with a small load of LED lights on for 30mins or so. Checked the battery it was cold to the touch, not hot at all.
See the charging profile of the solar charger Page 23

Basically what I'd like to know is if everything looks alright or is the battery on its way out as the charge voltage is constantly high.
Should I replace the Lead Profile with a User Profile with lower voltages?
Is this normal to see in winter?

I hope I've included enough detail for you experts to garner a picture of my set-up, is there any additional info you guys need?

Any help/advice would be greatly appreciated!

Many thanks in advance,



  • BB.BB. Super Moderators, Administrators Posts: 33,140 admin
    Welcome to the forum Mark,

    Most people "murder" their battery bank from under charging/over discharging. Taking Lead Acid batteries to less than 20% SoC and charging the next day, or even to 0% or "worse" (taking battery below "dead" some cells can reverse charge) and it ruins the battery.

    So--At least you are not doing that.

    However, the next issue is over charging... You need to check your battery manual, but I would guess that charging voltage is around 14.2 to 14.4 volts for your sealed battery. Over charging a sealed battery generates hydrogen and oxygen gasses internally--Which can overheat the battery and cause it to vent gasses (and electrolyte mist). Since most sealed batteries cannot be refilled, this shortens their life.

    Your controller should have a remote battery temperature sensor--That is a good option (lead acid batteries need higher charging voltage when cold, and lower charging voltage when hot).

    The next question--Do you know that the battery voltage readings are accurate? Sometimes the remote meters can report "bad" readings.

    Assuming the readings are accurate... Then look at the charge controller. It has SEL (sealed/default should use ~14.4 volts), GEL (uses lower charging voltage of ~14.2 volts or so), and FLD (Flooded--uses ~14.8 volts or so)...

    Section 4.1.2 of your manual has the SEL/GEL/FLD voltage defaults... And Sealed looks OK for a sealed battery.

    Another question... Guessing you are around Newcastle upon Tyne and it is near 0C at night... The battery is pretty cold. For Lead Acid batteries, they typically offset the charging voltage by -5mVolts per degree C per cell (25C is standard temperature):
    • -0.005 volts/C/c * (0C ambient -25C std temp) * 6 cells (12 volt battery bank) = +0.75 Volt offset for 0C
    • 14.4 volts + 0.75 offset = 15.15 volts charging (appears to be 15.0 charging voltage "hard limit" in controller--4.1.2)
    If the trailer is outside, and near freezing or below battery--Then 15 volts would be normal charging voltage.

    When the battery is "warm" (20-25C), you should see closer to 14.4 volts charging.

    Clear as mud?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mjh73mjh73 Registered Users Posts: 4
    WOW..........Thanks for your reply Bill, I think I've paid hard earned cash for less comprehensive reports than that!

    Glad to hear that there may be nothing wrong with the system, based on your assumptions - all of which were correct!

    I'm picking up the caravan this weekend so will get a voltmeter on it to check the reported votage.

    Could you plese tell me what the remote battery temperature sensor might look like; ie. colour of wire, thickness, any other kind of indication, so that I can see if one is fitted.

    Since the charging voltage is temperature dependent, I should be seeing that drop as we move into warmer weather?

    Many thanks for your support/advice.

  • BB.BB. Super Moderators, Administrators Posts: 33,140 admin
    edited February 2022 #4
    You are very welcome Mark.

    Note that was the Charging Voltage (battery actively being charged after loads--Such as overnight with cell phone/data connection). The same calculation should give you a lower voltage with Float Mode (float being just high enough voltage to keep the battery from self discharging and support day time loads--Not actively charging). Float mode is round 13.8 Volts @ 25C.

    You don't want a fully charged battery at 14.4 volts @ 25C all day long either (especially when the system is not being used). Holding charging voltage all day long is not great for battery life either. 

    If actively using the battery camping--Yes, you want the battery to be at 14.4 volts for something like 2-6 hours per day to be fully recharged after a night (or cloudy day) of use (Absorb state of charging).

    Doing a quick search, the remote battery temperature sensor for an EPEVER solar charge controller may look like this:

    The metal tube is usually a temperature sensitive resistor... I.e. the resistance goes down as the resistor gets hot (NTC--Negative Temperature Coefficient or PTC--Positive Temperature Coefficient--I don't know which exactly here).

    The tube should be attached to the side of the battery-u-And some folks put a piece of Styrofoam over the sensor to ensure it is measuring the temperature of the battery and not just air temperature (some have a holder that bolts to the negative battery terminal).

    In your manual link, there is more information on Page 2 and Page 11 (apparently, there is an air temperature sensor option too--The green plug with a small resistor connected), You can search for "sensor" for a few other mentions in the manual.

    Yes, you should see the charging & float voltages fall as the battery warms up. And it will fall below 14.4 volts as the battery gets to 35C+.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mjh73mjh73 Registered Users Posts: 4
    Cheers for your comments Bill, I will have a look at the battery and see what is attached to it.

    Many thanks, 

  • mjh73mjh73 Registered Users Posts: 4
    All seems good, I appear to have a battery and air temperature sensor.
    Thanks for your help!

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