Battery Charging and Gas Gauge

Hello all!

I am at a loss here... I ave been looking for some time and haven't had any luck finding a solution with this problem.

I have a battery/charger that I want to monitor with an Arduino. I want to know when the system is on the mains or battery, when the battery is charging, when it is fully charged, and the charge % remaining.

The battery type is debatable... Lead-acid will probably be my choice since this is sort of a UPS-type project, but if a different battery type makes more sense, I'm open to that. As long as it produces roughly 12v and has something like 10aH capacity.

I have no desire to re-invent the wheel here. I just want to know the status of the charging system without spending an arm and a leg on a beast of a charger.

I really don't want to use an off-the-shelf UPS like an APC unit... I bare board would be fine so long as it has the desired data available. I found a model by Meanwell that is close, but it only provides contact closure information - When it is on battery and when the battery is almost dead. I would prefer more information. Any thoughts?

Sparkfun sells a voltage and current monitor module for about $20 designed for the Ardupilot UAV. I actually got one for a solar charging monitor project, but the client flaked out before I built it :(, so I can only share that it looked good on paper.

I'm not converting it into mains voltage... It is just to provide backup power for a "weather station" I'm cooking up. I am going to feed it from my home power, but want it to be able to continue logging even in the event of an extended power outage.

I found the voltage and current sensor.

I think this would be great for determining the actual amount of power I'm using, but how would I translate this into battery capacity/charge monitoring?

Do you have the charger already?

Yes, sealed Lead Acid would be good for this application.

The charger type and battery type need to be matched. is a good source for batteries. I just bought a pair for my weed trimmer this summer.

Do you intend to control charging current using the Arduino?

I saw the sparkfun current/voltage board you referenced -I'm tending to think that board does not operate in the range you will want... or rather it exceeds your range by a lot and so maybe it will not be a good match for your project

I suggest you review this part (sparkfun)


for current sensing.

For voltage sensing.. I'm not sure but maybe a voltage divider will work.

For charging you only need to go up to something in the range of 14V~15V and for current draw you need to determine your load but I would guess that your charging current will be only around 3A or less.

My company uses 12V 12A-h SLA batteries so I have some experience with them although I am an ME just playing with electronics.... so ... I guess that means you should take my advice with a grain of salt as they say..

I'm actually trying to find a charger that could provide me with the data directly instead of improvising my own charge level tracker.

I'm up for good project as much as the next person... I just don't want to re-invent the wheel if I don't have to.

This is the charger/UPS I found... Obviously it is the "A" version for 12v.

I love the device's design, but it only gives me dumb signals. I would like to try to find a device like this that actually provides a data connection of some sort.

I found the MorningStar solar charge control devices and some of them do what I want, but the models that do so are upwards of $200... And waaay past overkill for my small project.

There are a lot of battery fuel gauge chips out there that will do what you want for the cell chemistry of your choosing. Dig around these sites under power management:

Put in the parameters you want, (V, Ah, chemistry, etc.) and you’ll probably find a single chip solution that has I2C or similar interface. You’ll probably want to look for an easily solderable package, but there are some out there.

And look through this forum some more. Just in the last day or two someone posted bout a shield they’d made. I’ll see if I can find it.

ETA: Here’s that link: LiPoly Fuel Gauge