Every morning after greeting the dogs I pull down a journal and record the starting temperatures and the battery voltage. Not sure why, it’s of little use, but sometimes I do refer to records if only for comparison.
Above the voltage readout there’s a little chart that supposedly tells me the battery state of charge from the reading…
Most of the readings are supposed to be made ‘under load.’ But the source I cribbed the chart from didn’t say what the load was supposed to be. Will a single 12v LED do, or should I plug in a power saw? Because I happen to know it makes a difference. 🙂
On a similar theme, if you’ll allow me to stretch the point, yesterday on the road I read a Tolkien short story you might like. Not being religious at all myself I find most religious allegory obvious or boring or both, but this one snuck up on me. I’m certain I read it before but I don’t remember where or when, and I must not have finished it because it didn’t affect me then but this time I got more of it.
It’s called Leaf by Niggle and it’s available free at the link and probably elsewhere. It put me in mind of that William Blake quote,
To see a world in a grain of sand and heaven in a wild flower.
Hold infinity in the palms of your hand and eternity in an hour.
Give it a try if you’re into that sort of thing.
One of my favorites. Try also “Smith of Wooton Major”, and in longer form, “Farmer Giles of Ham”.
All new to me, thanks for mentioning them.
Me too. Something new to read.
All three are classics, & rightfully acknowledged as such.
As an old EE who remembers vacuum tubes – the “under load” test is usually considered 50% of whatever the power source is capable of producing, so a 100 A/h battery with a draw of 50 Amps would be considered under load if I were testing the battery or whatever the battery is feeding. So yes, the LED is a load, maybe drawing between 10 and 150 mA, that power saw probably needs a 10 amp spike to get it turning and draws 5 amps running, of course if it needs 120 VAC and you are running off an inverter to a 12 V battery, hmm, let’s say the inverter 100% efficient for simplicity (it is probably between 85% and 95%) that saw is drawing about 50 A at 12 volts, so that would be a good test load, for about 1 hour before the battery dropped below safe levels YRMV. And I read every darned one of the EE Doc Smith series as a kid – great space opera and of course all spaceships landed on their tails, how else would the launch up again! Even Tin Tin knew that!
http://scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf
That is very useful Malatrope. Just keep in mind that the curves presented are only good for one temperature. In winter add a bit, and in summer subtract a bit. (One reference I have here says .03 volts/degree C.)
Also, here is a rather good 83-page tome on the subject, courtesy of your favorite gubmint.
http://www.usbr.gov/power/data/fist/fist3_6/3-6.PDF