Simple is good. I like simple.
Someone mentioned that a small charger could take a VERY LONG time to charge a battery bank.
True. But my battery bank is fairly modest (~100AH per charger / bank), and it's looking like Lead batteries don't do well if you discharge them all that deeply, which at least diminishes the amount of charging required. :)
The other thing in my favor is that my boat sits at a dock at least overnight (on the charger), and often for a week between uses. So lots, and lots of time to charge.
The real QUESTION I have is whether I need to charge by current (create a current source), or if I need to charge by setting a variable power supply to be (battery voltage + 2volts), run through a current limit resistor, and increase the power supply voltage as the battery is charged, until the stage2 voltage is reached. (though isn't this basically the same as using a current supply)?
From: Kirk McLoren <kirkmcloren@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Tuesday, October 29, 2013 2:32 PM
Subject: Re: [Electric Boats] Battery Charging Basics - homebrew chargers
hard to get into trouble with a trickle charger.
On Tuesday, October 29, 2013 11:41 AM, oak <oak_box@yahoo.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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