Friday, July 8, 2011

RE: [Electric Boats] Re: Thoughts on regen and batteries

 

I've got both a Zivan Ng-1 48 volt charger and a Dual Pro Quad also. I use the Zivan for bulk charging at anchor then either switch to the Dual Pro or let solar and the wind generator top things up. If I happen to be at a dock I'll just use the Dual Pro. I bought the Dual Pro because I wanted to keep my 8A4D 48 volt AGM  bank in balance and to have another battery charger as backup to the Zivan. One thing I have noticed when using the Dual Pro is that you never can tell which battery will finish charging first. Sometimes it's the lowest battery (negative) in the bank sometimes the highest (most positive). Nice thing about the Dual Pro is I can see instantly via the multi display LED's which battery is lagging behind the others. Happily, so far after four years there is no one battery that consistantly shows it being weaker than any of the others when it comes to charging.  Even though the most negative battery (which supplies voltage for the Paktrakr) shows consistantly lower voltage in normal operation than the other three batteries will sometimes charge up first before the other batteries. I'm not sure I would benefit by installing a BMS system on my boat but, I'm curious to hear of the experience of others.
 
Capt. Mike


--- On Thu, 7/7/11, Steve Dolan <sdolan@scannersllc.com> wrote:

From: Steve Dolan <sdolan@scannersllc.com>
Subject: RE: [Electric Boats] Re: Thoughts on regen and batteries
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Date: Thursday, July 7, 2011, 5:01 PM

 

Keith and Mark,
I've installed (part at least) the HDM balancing system
http://www.hdm-sys.com/
and will soon report on the results. I had an issue with one of the 4 units and HDM figured it out to be a hardware/software issue for my system so are beefing up the board. I've been running the other units with no issues so once I get #4 back I'll do some testing and get back to the group with the results. I'm not sure if the BMS can look at the lowest battery and "stuff" it first but if the batteries are all closely balanced to start with then the Regen power can be spread over all with no low battery. Just with the partial system up and running I have seen longer run times and smoother balancing but again it's not completely setup so I'll hold judgment until it's up and running and happy with the PakTrakr.

Steve in Solomons MD
Lagoon 410 SE

Keith,

Unfortunately, charging a 48v series string of batteries undercharges the weakest one and overcharges the fullest one. Something about internal resistance being proportional to voltage, but in the wrong direction for naturally balancing batteries.

This is true for lead-acid chemistry, but reportedly not true for some lithium chemistries. Lead acid cells naturally and slowly diverge over charge-discharge cycles. That is why flooded lead acid batteries are "equalized", or more accurately, severely overcharged, so that each internal cell of the battery is absolutely full, or equal in voltage to it's neighbor.

AGM lead batteries should not be severely overcharged... it drives off the irreplaceable moisture. That is why AGM smart chargers are required for long-term AGM battery health.

It would be marvelous to have a BatteryManagementSystem that took what little regen was available, and stuffed it into the weakest battery.

Gonna sail Constance (e-H55) monday.
Mark Stafford

--- In electricboats@yahoogroups.com, "aweekdaysailor" <aweekdaysailor@...> wrote:
>
> Thinking about the case of a weak battery in a string (say 4x12)...
>
> In the above scenario (and there is _always_ 1 weak battery in a string...) - isn't any 48+V charging source selectively charging the weak battery (more charge acceptance)?
>
> Sailing around in good wind this weekend and getting 1-2amps regen pretty consistently according to my CycleAnalyst...it ain't much, but when I did have to motor up, it seemed that my voltage stayed higher, for longer, than this small about of charge would account for...which got me thinking....
>
> Since the weak battery ultimately determines the effective voltage of the string (and hence your range) - is it possible that just looking at overall watts in isn't telling the whole story? Can we capitalize on that (BMS system, etc)?
>
>
> -Keith
>

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