Hi Chris,
From my observations, the bigger the amp hour capacity of the lead acid cell, the better they stay in balance. I put 1200 amp hour L-16 Lifelines in Godspeed 7 years ago, and every time that I have checked, they have been within .02 of a volt or so. Thats a 2 Volt Battery. There are 12 of them in series to make 24 volts.
Dashew had it right when he designed this boat with the Batteries in the Keel. I always wonder why 99% of the boats out there don't put the weight where it should be. Such a simple thing to do. My next project will be designing and building boats, and you can bet the batteries will be in the keel.
I made this website for Godspeed, should you wish to check her out.
I worked my way up the ladder from owners representative to captain of this boat, and have now been captain for over 3 years. During that time, I have learned how to singlehandedly dock and sail the boat. Docking is interesting, Sailing is challenging, but its all possible. On an 80 footer, it is very important that everything is done at the right time.
I am now building balancing chargers. The balancer can shift a little over one amp from the top battery to the bottom battery. That doesn't sound like a lot, but over 24 hours that adds up to 24 amp hours, which is 1/8 of the capacity of a 210 amp hour battery.
I did a lot of work on Lithium Batteries and the conclusion there was they don't need much current in the balancing circuits either. The issue with batteries is any imbalance is cumulative. Even the smallest amount will be additive with each cycle. It doesn't take much to keep a healthy battery in balance.
Why do batteries need balancing? When a battery is built, it has a certain internal resistance. In a 48 volt string, with a 48 volt charger, each battery in the string receives the same current. Ohms law is v = IR or voltage = current x resistance. Since current is the same for each battery, if resistance is different, so will voltage be.
The problem with batteries when they get out of balance, they no longer have the same charge profile. If a battery is .2 volts out of balance from its neighbor the string could look like this 14.3 , 14.3, 14.3 14.5 a month later through various cycles and the string might look like this 14.25, 14.25, 14.25 , 14.65 Sooner or later the high voltage will be out of the algorithm. Each cycle then adds to the premature distraction of the battery. And it takes so little to correct it….
I think of it as an environmental issue. On average a battery lasts 3 to 5 years in a string at 48 volts. Add a balancer, have good batteries to start with, and then you get 10 to 15 years out of the battery. Plus the amp hour capacity will remain higher throughout the life of the battery.
So Logically, it makes sense to balance a battery pack. Each pack of lead batteries costs about $2,000 to $3,000 plus installation. Why not do it right and avoid replacing those batteries once or perhaps even twice?
Well thats the theory behind balancing chargers. I'm surprised that I will be the first to offer such a product. But given the potential environmental impacts, I think it is time we did something about it.
James
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Sep 13, 2018, at 9:14 AM, clh5_98@yahoo.com [electricboats] wrote:
James,thanks for your detailed reply. That's great information about waiting to get a matched set of batteries, I hadn't thought of that. As far as balancing, I've been amazed at how well my T-145s have stayed balanced over the years. Never more than 0.04 volts difference after letting them sit overnight disconnected from load/charger.Chris
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Posted by: James Lambden <james@electroprop.com>
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