I've been experimenting with a BMS from www.guantao.com on a 300v 40Ah LiFePO string. The BMS has a CANbus output, both to control the charger(s) and to communicate with the VCU in the event of an over-current, over-temperature, under-voltage, or over-voltage condition. The CANbus also allows the user to monitor all the functions accessed in the BMS touch screen. The system is a little pricey for the average boat, however, and not nearly robust enough to even withstand cabin duty. My partner in China has been working at the factory for the past week to develop a fully potted version with sealed interfaces. She says they'll be testing it in a few months according to IP64.
For our test boat at Advanced Marine, we'll be adding individual 12v meters for each battery in the string. The PakTrakr we tested did not like the marine environment, and lost its display after taking a wave across the bow. It gets a little splashy in SF Bay occasionally...
Be Well,
Arby
Advanced Marine Electric Propulsion
From: Angela <mstafford@natca.net>
To: electricboats@yahoogroups.com
Sent: Mon, October 18, 2010 7:24:55 PM
Subject: [Electric Boats] Re: Battery chargers: Bulk or Individual
Thanks Arby for hard learned lessons shared. The key in either string or individual charging is how each sub-cell is doing. We can't know without an individual cell monitoring scheme, which is only possible on LiFePO4 or those odd 2V single cell lead acid batteries. With flooded lead acid batteries (FLA), overcharging a cell is no problem (just add water later). Overcharging a SLA battery in a high voltage string is problematic... usually kills the battery. A per-battery overvoltage cutoff circuit would eliminate this weakness with SLA, since the cells internal to an SLA are very closely balanced in their charge and discharge characteristics, and the conservative cutoff voltage would render inconsequential any minor discrepancies.
Appreciatively,
Mark Stafford
PS I was sailing opposite direction to the incoming armada of boats leaving Fleet Week on Saturday for the Alameda Estuary.
--- In electricboats@yahoogroups.com, "RagnvaldB" <arbybernt@...> wrote:
>
> Two Advanced Marine conversions experienced problems with battery chargers last week after particularly deep discharges. I've been a strong advocate of the DualPro PS-4 chargers, and have installed many, including in our own Ericson 27. Last week, San Francisco Bay hosted the Blue Angles and many others to perform for several hours to the delight of many. The Tradewinds Sailing School had their Catalina 30 out, and it spent many hours running under power, far more than usual. It came back with fully depleted batteries, and was plugged in dockside upon its return. The next day, the chargers were showing odd levels of charge, having been plugged in all night. Normally, the boat charges fully overnight. We felt the charger, and it was piping hot, a condition which caused one or more of the chargers to drop out. This probably had happened the day before as well, and as a result, the boat had gone out without a full charge in each battery. After 24 hours on the now fan cooled charger, we had all green LED's, thank goodness. The second boat, a Columbia 27, had a similar situation when the charger timed out.
> Brian, the Mainfuse at Trunderstruck-EV, advocates bulk charging for just this reason. He's had several instances where a fresh string has been ruined by an individual charger dropping out and one or more batteries being reverse polarized. Consider that the string current flows through each battery equally, and when a cell is only partially charged, that same current will gradually cause the voltage on the weak cell to reverse as a result.
> In conclusion, I'll still use a multiple output charger for equalization every so many cycles, but from now on, all new conversions will get chargers for the entire string. Leaving the dockside with one flat battery is far worst than leaving with a partially charged string. Thanks for the advice, Brian. I wish I had listened the first time...
>
> Arby Bernt
> Advanced Marine Electric Propulsion
>
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