Read Battery Charger status from a device.

So I’m building a portable battery charging station for my team. A really cool idea I have, is mounting a old surface pro on the side, with the screen showing out that some how shows what percentage each battery on the charger is. Is there any device or system that I can use which reads the current battery status (while the battery is still plugged into the charger), and relays that information to a app on a external device. Such as a surface pro or tablet. etc.
Thanks in advace

You can make a voltage reader for each battery port by splicing a voltmeter into the output wire of the charger. If you wanted to interface with a tablet, you would probably need some kind of microprocessor to compile the voltmeters’ readings and send them over serial to the tablet. Or you could just use voltmeters with built-in LED displays.

If I do that, won’t i just get the voltage that the charger is outputting not the current voltage of the battery?

It will probably be something you have to make yourself.

I would check out the documentation on the Battery Beak

If I spliced in a voltmeter between the charger and the battery, would I get the reading of the output of the charger, or the Voltage on the battery?

If the charger is on, and charging the battery, you will get the voltage of the charger.

If it’s an intelligent charger, then it will depend on the ‘state’ of the charger.

If I’m using the frc charger (which is “smart” i believe : Battery Charger 3 Bank 6 Amp Dual Pro RS3 with SB50 Connectors - AndyMark, Inc)

would I just be reading the volts of the battery after the charger stops charging it?

Oh, I forgot about that. Maybe you could send an output from the tablet through the microprocessor to a switch to turn off the power to the charger for a second every minute or so and take readings then?

Obviously full disclaimer: I have never done this before.

Ya, maybe I can use a arduino and a relay, to turn it on and off. But I guess I also don’t want to do that, because it would be interrupting the charge of all the other batteries on that charger. So that might get annoying. Don’t know. Too bad the frc chargers don’t have a serial output on them, lolz.

Or is there maybe a way that you could measure if its full or not based on and amperage reading? Or would a amp reader also just show the amp output from the charger. It probably would. (in case you guys haven’t realized yet, electricity isn’t really my thing :slight_smile: )

I could just use a volt reader like this : https://www.adafruit.com/products/460 but so no need for a tablet interface, but it wont be effective, since it would just show the volt output of the charger right?

Reading the amperage between the charger and the battery will only give you the charging current, which is usually limited (purposely) by the charger (to either 2 or 6 amps).

To measure the battery appropriately you’d want to measure the internal resistance of the battery. This can only be done when not charging the battery (you actually need to draw current from the battery)

I can’t say about the amps, but you could do some testing with a clip-on ammeter to see if there’s a correlation.

I was thinking of using something like what you linked. Make sure whatever you use is rated high enough for the current these batteries can produce. Maybe mount a button next to the output displays that says “PUSH TO TAKE READING”. The button would be wired to a relay to control the charger. Then the charging is only interrupted when you want a reading. The button would also need to switch on some kind of load. It wouldn’t allow for continuous reading, but if that wasn’t a feature you needed, it should be a fine way to go.

Probably the easiest thing to do would be cracking open the case of the chargers, and soldering wires to both sides of the LED’s, soldering the common ground and using digital inputs on an arduino to sense the LED state.

That would be ok if you only want a boolean, charged or not charged. I assumed the OP wanted a numeric value of how charged the batteries are. Maybe I could be wrong.

In order to know the “battery voltage” while actively charging, you will need to measure the charging current I[SUB]c[/SUB] as well as the terminal voltage V[SUB]t[/SUB], and have a good idea of the “internal resistance” of the battery, R[SUB]i[/SUB]. Then, V[SUB]batt[/SUB] ≈ V[SUB]t[/SUB] - I[SUB]c[/SUB]R[SUB]i[/SUB]. Ideally, you’d measure R[SUB]i[/SUB]
yourself, but if you just want a nominal value, a study by team 1640 a few years ago indicated that a good FRC battery has an internal resistance of about 0.02Ω. Alternately, if you use a 2A trickle charger, the difference would only be about 0.04V, even when still charging at full current.

Ideally yes I would like a measurement of how charged they are, but if that’s super impossible and hard, then maybe ill just settle with off or on. IDK

You could get a charger that does give you the percentage and read the LEDs from the display.

http://www.amazon.com/Schumacher-SC-1200A-CA-SpeedCharge-Maintainer/dp/B000BQSIWK/ref=sr_1_1?ie=UTF8&qid=1450240546&sr=8-1&keywords=Schumacher+charger