plwsm2000 Posted August 22, 2020 Share Posted August 22, 2020 mikefitz - 2020-08-22 2:09 PM The timed period for the charging cycle only starts when the bulk stage is completed. The charging process starts in the morning, when the solar input voltage exceeds the battery volts by a few volts. The first phase of charging is the bulk stage that operates with maximum current from the MPPT process, raising the voltage until the target volts, 14.4, is reached. The timed duration of the absorption stage at constant voltage follows. The time allocated by the controller depends on initial battery voltage and bulk time. Following the computed time at absorption volts the controller goes to float mode. In real life the solar energy input will not be constant and various loads may be applied to the battery. This may cause the controller to return to or stay in bulk mode for some time, perhaps all day if the the solar input cannot keep up with power demand of loads and battery charge requirements. Mike I find that the bulk stage is normally very short unless your batteries have been heavily discharged. My batteries rarely get below 12.7V when left over night (obviously no solar and no EHU) and go into the main charge almost immediately at sunrise. The Votronic manual shows a graph of the charging process with a deeply discharged battery (starting at about 8V) and is only applicable "in Case of Sufficient Solar Power" (first graph attached). In normal usage, you don't have sufficient power in the early morning. The second graph shows a 24 hour period (3am to 3am) that was logged on my system while we were away a couple of weeks ago.You can see that the habitation battery never gets to the 14.3V expected main charge voltage (for the Gel setting) and drops back a trickle voltage of about 13.7V just after mid day. This is typical day. You can also see some strange behaviour at first light (starting about 5:30am) where the Votronic draws pulses of current from the battery. There is not sufficient solar energy even to keep the solar controller powered up this early. (This is also why I am a bit sceptical about panels in series rather than parallel). Sometimes what you get in datasheets does not always represent real life usage. Link to comment Share on other sites More sharing options...
spirou Posted August 23, 2020 Share Posted August 23, 2020 Coincidentally found this video from Victron this morning regarding Vp vs Vbat startup voltage. Interesting bit starts at 4:16 Link to comment Share on other sites More sharing options...
davida Posted August 23, 2020 Author Share Posted August 23, 2020 So it’s possible it won’t reach 14.4v at any point in the day, despite the input voltage not being less than around 22v typically? And so the batteries won’t charge? Should it not reach the 14.4v at some point if the batteries need charging, provided the input voltage is higher than that? The fridge require 30amps per 24 hours and I have 2x100ah batteries. With little other use, no TV. If I begin the night fully charged, the fridge will draw around 15ah before sunrise, so the batteries have plenty left when charging begins. Link to comment Share on other sites More sharing options...
Charles Posted August 23, 2020 Share Posted August 23, 2020 We've got a similar set up to you Davida. 150w panel and Votronic Duo 250 regulator. It's 1pm and a bit cloudy today so we're only charging at 3 amps and 13.5v but usually at this time if sunny, we're well into the fourteenth volt (actually 15th technically but you know what I mean) , it will stay at 14.4v with less current for a while (gel battery) and then drop to float charge while we're out. So your's maybe faulty or your not getting enough sun. We are in Spain though :-S Link to comment Share on other sites More sharing options...
plwsm2000 Posted August 23, 2020 Share Posted August 23, 2020 davida, It is not just the voltage you need to consider - it is the power available that matters. An MPPT controller tries to maximize its output by adjusting the output current to the point where the panel generates its maximum power. Too much current will cause the input voltage to drop if there is insufficient solar energy, and too little current means that you will be wasting power. The MPPT controller will always try to optimize both the panel voltage and current for the amount of available sunlight. You may find that although it produces 22V, the output current could be quite low and not sufficient to supply your fridge and to top up the batteries at 14.4V. it just depends on the available sunlight available. Link to comment Share on other sites More sharing options...
colin Posted August 23, 2020 Share Posted August 23, 2020 davida - 2020-08-23 11:31 AM So it’s possible it won’t reach 14.4v at any point in the day, despite the input voltage not being less than around 22v typically? And so the batteries won’t charge? Should it not reach the 14.4v at some point if the batteries need charging, provided the input voltage is higher than that? The fridge require 30amps per 24 hours and I have 2x100ah batteries. With little other use, no TV. If I begin the night fully charged, the fridge will draw around 15ah before sunrise, so the batteries have plenty left when charging begins. My experience of using 12v for fridge, is that (in general) overnight the fridge uses much less power, and during the day it uses a lot. This suited our 'dumb' solar power set up very well. Link to comment Share on other sites More sharing options...
spirou Posted August 23, 2020 Share Posted August 23, 2020 A compressor fridge is quite a handful for a mere 150W panel in hot weather. I find my 320Wp is just right to cope even in less than ideal conditions (not parking in full sun all day). So, considering all symptoms, is it possible your battery is starting to fail from being worked hard? Link to comment Share on other sites More sharing options...
davida Posted August 24, 2020 Author Share Posted August 24, 2020 Thanks all. Turns out it does eventually get up to the 14.4v, once the sun comes out. So I’ve learnt a bit and appreciate that. Maybe there is no problem. Fingers crossed. Link to comment Share on other sites More sharing options...
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