Battery Capacity Testing in the Real World

[conachair]

Originally Posted by hellosailor

I would have thought that the percent or original cranking amperage (CCA) could translate fairly well into percent of AH remaining, for deep cycle batteries.

But if not...surely there's something in the "under a grand" price range? Or the $40 carbon pile testers have some use? Given all the variables with "capacity" they wouldn't have to be anywhere near dead accurate to still be useful.

A quick Google says no...
http://batteryuniversity.com/learn/a...d_cranking_amp

" The DC load method has the advantage of detecting batteries with a partially shorted cell (low specific gravity) but the device cannot estimate battery capacity."

The thread was started asking about making an inexpensive data logging microcontroller based tester. Shouldn't be that difficult, I'm itching to have a play but several thousand miles from the boat

Sim card adaptors can be had cheaply for an arduino board ad well, so shouldn't be too hard to text your boat and get it to text you back with battery voltage and temp or something useful

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[Lake-Effect]

Originally Posted by conachair

Sim card adaptors can be had cheaply for an arduino board ad well, so shouldn't be too hard to text your boat and get it to text you back with battery voltage and temp or something useful

Or if you use a Raspberry Pi and your marina has wifi, the Pi could wake up and email you periodically.

[conachair]

Originally Posted by Lake-Effect

Or if you use a Raspberry Pi and your marina has wifi, the Pi could wake up and email you periodically.

I suspect the majority of people who can afford to keep their boats in marinas might not be quite so obsessed with self reliance

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[conachair]

Update, finally got to play, early days but didn't take long at all to get an arduino logging voltage data, image is of 75 seconds as solar panels and other bits get turned on and off, logging once per second.
Now just waiting for several temperature sensors and a couple of current sensors to turn up from eBay. Plus a smaller arduino copy board, which was £10.00.

[Oceanride007]

Interested to know how you can get voltage/time or current charts, I understand some fancy battery monitors may have an output to your computer with special software. Is there any other way?.
Years ago, on the ships we used charge discharge curves, which in theory were pretty good, I know manufacturers like secrets and I understand the limitation but still useful I feel, any thoughts?.
In regard to Discharge test, I think 12 monthly, but Mainsails comment about PITA adjusting to 20Amp rate, either couldn’t a current generator be made up or even better use a inverter with resistive ac load, as a bonus you get a low volt S/D, consistent anyway.

[conachair]

Originally Posted by Oceanride007

Interested to know how you can get voltage/time or current charts, I understand some fancy battery monitors may have an output to your computer with special software. Is there any other way?.
.

Another way there is......
One of these;
http://www.amazon.co.uk/Arduino-Mega...duino+mega2560

With one of these and a micro sd card;

http://www.amazon.co.uk/Ethernet-W51...et+card+shield

Then a few lines of programming writes the data to the card as often as you want, wake up in the morning and it's waiting for you as a csv text file

The microprocessor only measures up to 5v so a little voltage divider is needed, then I worked out the calibration with a Fluke meter and altered the numbers in a spreadsheet which went into a little graph program, voltages seem to be accurate down to tens of millivolts against the Fluke. I programmed it to take the average of 20 readings once per minute.

I've 8 temperature sensors (cos they're so cheap) and a couple of current sensors on the way from eBay so with a power transistor or 2 and some 12v lights as a current drain I should be able to rustle up a constant current battery discharge tester at whatever current draw and down to whatever cut off voltage you want, while measuring the voltage and temperature of each cell along the way. All for the price of an average meal for 2 which should be interesting, after a solar panel took instead of giving I have 4 apparently trashed batteries onboard so it will be interesting to find out how much, if any, they come back to life with a load of equalising.


It's all very good fun and very cheap.



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