Hi,
I'm a total newbie in the field of electronics, so I've decided to ask for your opinion.
There's a small experimental project based on raspberry pi. The micro computer, and some other devices are powered by a car battery with attached solar panel.
It's easy to imagine that the efficiency of this charging means is not always reliable. Therefore, it would be nice to monitor the level of remaining power in the car battery.
My idea was to connect arduino to raspberry pi and some kind of sensor to arduino - voltage sensor? So the first question - are there good and safe to use electronic devices for this purpose?
What kind of parameters are important? I guess that 12-25V range is correct, but what about the max current? I know that car batteries can deliver hundreds of ampers for short periods of time. So is it possible to safely measure its capacity? And the most important question - can I charge and measure voltage at the same time?
Any kind of other solution that allows measurment and connecting to computer would be good - any ideas? Thanks!
I'm not a battery expert and I don't know exactly how battery voltage relates to the state-of-charge. It's not linear... But, voltage is the only practical thing to measure.
Load testing (high current) can tell you about the charge condition (or the battery's condition after full-charge), but it requires a big high-power resistor and of course, load testing drains the battery... You wouldn't want to load-test your car battery in the morning because there might be just-enough energy remaining to start the car and the car might not start after testing... You should only load-test the battery if you are prepared to re-charge it.
The Arduino runs at 5V and if your Raspberry Pi and all of the other electronics are running at 5V, the battery can discharge down to around 6V (leaving enough voltage to run the voltage regulators) and although the battery would be considered "dead" at 6V and wouldn't start your car, the electronics will run fine. (So, you can actually get more Amp-Hours/Watt-Hours than the battery is rated for.)
can I charge and measure voltage at the same time?
You can but the reading will be meaningless, it will just measure the charging voltage. Unless the charger is limiting the charging current the voltage will not tell you anything about the state of the battery.
but what about the max current?
The current being drawn from the battery has no effect on your voltage measurement, unless the current is so high that the voltage from the battery drops, due to the internal impedance of the battery.
why not get a car battery charge indicator? they are specifically built to do the job that you wanted. Costs about 10 to 20$ and some of them even come with an inbuilt voltmeter.
Noobian:
why not get a car battery charge indicator? they are specifically built to do the job that you wanted. Costs about 10 to 20$ and some of them even come with an inbuilt voltmeter.
The thing is - I want to read the measurments from the computer, so just a simple indicator won't do. Unless it has an interface I could connect to my raspberry pi or arduino?
The only way to accurately measure the state of charge of a lead acid battery is to measure the specific gravity of the battery acid with a hydrometer.
You can get electronic hydrometers but they arnt cheap.
The usefulness of the battery can only be tested electrically, under load, however. If the plates are
sulfated the state of the acid isn't a great help!
A good charging system has the ability to monitor the voltage unloaded, under discharge to a dummy load,
and under charge, the combination of all the readings says more than any one parameter. You can test
under high current for only a few microseconds if you don't want to drain the battery much.
