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@substack

Light rain and darkness today. We didn't get much of a charge, but the batteries are at 12.1v at 18:30 with both laptops running. Our truck's right front tire blew out while leaving the driveway, so we'll need to get a tow into Pahoa to get a replacement before everything closes for xmas.

@substack

The voltage has been pretty good tonight! We kept running both laptops until 21:50 and it never got below 12.0. It's back at 12.1 with one laptop running now. I put some washers on the battery terminals on Sunday and I think that helped a lot. Today while the batteries were charging the highest voltage I saw was perhaps only 12.8 or 13.0 and a lot of ~12.5 even in the middle of the day. Tomorrow I might double up some of the wires to reduce the resistance further. #solar #offgrid

@substack

Much lower voltage and darker today with light to medium rain all day. We're already down to 11.9/12.0 at 18:00.

@c3

i don't know your setup, but don't you have to get deep cycles up to 14.2--14.4v to consider it 'full'? i.e. it seems you're damaging your batteries by consistently running them below 12v - I consider 12.4 to be 'empty/do not use unless emergency' on mine. at 12.0 i'd be running a generator/alternator, and freaking out at the damage.

@substack

Here's a chart I found:

voltage.png

from https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html#Battery%20Voltages:

Batteries that are being charged will be higher - the voltages while under charge will not tell you anything, you have to let the battery sit for a while. For longest life, batteries should stay in the green zone. Occasional dips into the yellow are not harmful, but continual discharges to those levels will shorten battery life considerably.

This page gives a scenario for depth of discharge effect on a gel battery: https://www.energymatters.com.au/components/battery-voltage-discharge/

A Sonnenschein Solar Bloc 100 AH Gel Battery discharged to a depth of 70%, i.e. with only 30% or 30 AH (amp hours) remaining, will have a lifespan of around 1200 cycles, which is quite impressive. However, if it’s only discharged to 50%, the expected number of cycles skyrockets to around 1700! If a cycle is a day, that adds over 1.25 years to the life of the battery.

#solar #offgrid

@c3

I guess I am a bit more conservative in this regard, I hope to get a decade from my batteries. however I think you're not charging them enough? because even though rest voltage is going to 12.7 for you, the charge voltage needs to reach 14v

http://www.qsl.net/wb3gck/gel-cell.htm

In this mode, the battery is charged with a fixed charging voltage until the terminal voltage reaches 2.40 to 2.45 volts per cell (14.4 to 14.7 volts for a 12-volt battery) at 20° C. The battery is then held at this voltage until the charging current drops to a value of 0.01 x C amps (where C is the battery's amp-hour rating). At this point, the battery is fully charged and you must either stop the charging or switch to the float-charging mode. Continual charging in the fast charge mode will overheat the battery and damage it. Do not let the battery voltage exceed 2.45 volts per cell or allow the charge current to exceed 0.20 x C amps.

In this mode, the battery is connected to a constant voltage source of 2.25 to 2.30 volts per cell (13.5 to 13.8 volts for a 12-volt battery) at 20° C. Provided that the charging source is regulated at the proper float voltage, the battery will establish its own current level and will be maintained in a fully charged condition. Gel cell batteries can be left in the float charge mode for extended periods of time without damage. This mode is often used to maintain gel cell batteries used in backup power applications.

so if you don't charge it enough to get to full and back to float, you're destroying the battery! if you physically can't get to this amount during a day, you need more panels!

@c3

notice the table linked on the energymatters site, they are saying 25% is 12.0v and 50% is 12.30v which is vastly different to the solar-electric table! ouch!

@Ben

Yeah, I reckon you might need more solar panels @substack. Our 100W solar panel at kiwiburn (regional burn) gets the portaparty battery (40ah) up to ~14 volts in a few hours of the morning (the portaparty is a boombox with an amplifier + LED disco light rig that consumes about 2-3 amps while running).

If you felt like building something with arduinos, you could put hall sensors on the feeds going to and from the battery bank to get an idea of how much you're consuming (in watt hours) versus generating (in watt hours).

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