Hi John,
I am embarking on a similar project. I expect to use a PWM source signal to charge the batteries. Ultimately, my goal is to have a super-charger, capable of having several inputs connected simultaneously (solar, alternator/generator, wind, "pushed" electric motor), charging multiple banks of batteries using per-bank profiles, and covering all popular types - FLA, AGM, Lithium. A smart controller such as the Arduino would be at the heart of the system - and it could produce a NMEA message string output for standardized monitoring.
At the moment, I have a basic one-profile (FLA) charger configured that can control a single input between 8 and 18 v (yes, it will "step up") and charge the battery smoothly in the "best" time.
I will open source the arduino code (written in "wiring") once I have properly tested it.
In the end, the connectors will cost more than the MCU.
---In electricboats@yahoogroups.com, <electricboats@yahoogroups.com> wrote:
I hope this will be both fun and educational....
I'm trying to build a small, home brew battery charger. From what I see, it sounds like the primary difference between FLA, AGM, and Li batteries (from a CHARGING) perspective is the charging profile - notably, the voltage level of the charge.
Granted, if you're trying to do a FAST charge with lots of amps, there are a lot more details to worry about. But given the limits of readily available parts, I'm looking at 1-2 amps charging current - so I think I can simplify things a LOT.
It sounds like building a "constant current supply", attaching it to the battery (at 1-2 amps), and monitor the battery till the battery voltage comes up to the prescribed level, then disconnecting the current source.
According to the Battery University (http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery), it looks like I can use a constant current source for the primary charging (stage 1), then maybe connect to a regulated power supply for the topping charge (stage 2), and then use a small microcontroller (Arduino) to monitor the voltage over the next few days / months, and occasionally turn on the "float charge" voltage for a couple of hours. (stage 3)
Does this sound reasonable?
For charging Lithium batteries, is there any difference, other than paying a LOT of attention to the voltage levels for the peak charge level?
From the BatteryUniversity.com site, it sounds like charging Li batteries to 4.1V per cell, and stopping there will extend the life of the battery bank, and provide a bit more guardband to avoid problems.
Thoughts?
Thanks!
John
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