Mark Stafford here agreeing with OakBox about the "very, very slow pulses" to finish charge lead-acid batteries. Define very very slow: 1.5 seconds between voltage spikes. This lets the nascent hydrogen or oxygen bubble dissipate instead of grow.
I can't document this 1.5 second number; I only recall it being between one and two seconds from previous info hunting. You could experiment with a fully charged FLA, then vary the pulse frequency to avoid bubbles over time. Or observe the behavior of smart chargers prior to float charging: they pulse about every 1.5 seconds.
Or just buy super cheap 10A LA or Li chargers from batteryspace.com. If they are not conformal coated already, you could disassemble and spray/paint/dip the boards for better moisture resistance.
Mark Stafford
--- In electricboats@yahoogroups.com, oak <oak_box@...> wrote:
>
> How are you stepping UP your voltage?
>
> Also - be careful about the PWM. Â If it were very, very slow pulses, then that might be ok. Â But if you're using fast pulses (in the sense of pwm), you could have problems. Â The following couple of paragraphs were in the BatteryUniversity.com web site under Lead Acid Charging:
>
> Ripple voltage imposed on the voltage of large stationary batteries also causes a problem. The voltage peak constitutes an overcharge, causing hydrogen evolution, while the valleys induce a brief discharge that creates a starved state that results in electrolyte depletion. Manufacturers typically limit the ripple to five percent, or 5A for a 100Ah battery.
> Much has been said about pulse charging of lead acid batteries. There are apparent advantages in reducing sulfation; however, manufacturers and service technicians are divided on the benefits, and the results are inconclusive. If sulfation could be measured with accuracy and the pulses applied as a corrective service, then the remedy could be beneficial. Assumptions without knowing the underlying results can be harmful.
>
>
> ________________________________
> From: "dominic.amann@..." <dominic.amann@...>
> To: electricboats@yahoogroups.com
> Sent: Tuesday, October 29, 2013 2:26 PM
> Subject: [Electric Boats] RE: Battery Charging Basics - homebrew chargers
>
>
>
> Â
> 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. Â 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. Â 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. Â (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?Â
>
> 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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