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[NewAge]

My new project will be using four Optima D51 batteries (48v system). My question is should I set up my onboard charging system to utilize four 12v chargers (one for each battery) or would I achieve adequate balance with a single 48v charger. I have been reading about this and getting mixed reviews.

Wudda you guys think 

[Bogan]

Lead acid batteries should tolerate series charging well, provided you only use them all together (ie same wear).

[NewAge]

Cool Bogan, so far that answer is gonna save me about $280  Cha-Ching!

[Bogan]

and some excess weight on ur bike too id imagine

[WWC]

WWWEELLLLLL, I have to put my 2 cents in here. I'm a firm believer in the one battery - one charger theory. The batteries have a tendency to go unbalance when using a series charger. They actually make "balancers" you can place at each battery to assure a correct balance but then you are looking at like another $30 per battery (I think). While if you had individual smart chargers like a Soneil charger then they charge and maintain an even balance amongst all your batteries. And theres no feedback thru the chargers that would cause a discharge. The chargers I use are small and easy to mount (I used industrial strength velcro). Five batteries, 5 chargers. Done.

[Bogan]

my understanding was that for lithium and other types of batteries seperate chargers are a must, but the float part of charging the lead acid equalised the charge in all cells, in any case a 12v lead acid battery is made up of multiple lead acid cells and they are charged in series internally.

[WWC]

When you get your series charger hooked up and have used it for awhile. Take a reading accross each battery and let us know if they are all charging evenly. I have read many posts on other sites of guys having to charge middle batteries to bring them up to snuff. True there are 6 cells to a 12v battery and I have to charge 6 cells with one charger but now, lets say six batteries in series, thats 36 cells you are trying to balance with one charger. My 2 cents.

[Bogan]

yeh 36 cells is a lot, and you certainly couldnt series charge it for lithium batteries, but lead acid cells are self regulating, the higher amount of charge on a cell the less it charge it absorbs. Cant remember the chemical justification for this but can probly find out on google or wikipedia.

[frodus]

either way is good.... at only 48V the cells won't go out of balance that far.... you don't need balancers if you use a series charger. The problems with balancing occur with very TALL (high voltage) strings of batteries in series. Since the charger is only detecting the pack voltage and not individual cell voltage, its much harder with a tall stack.

You've got 6 cells in each battery times 4, 24 cells tall (lead batteries are really 6 smaller cells at 2 something volts each).... this is much better than a 144 pack of 12 batteries and 6 cells (72 cells)....which is why all the EV car/truck guys have balancing problems with their Manzanita and Zivan chargers.

I'd do this, get a 48V charger, and one trickle charger. Once every couple months put the trickle charger on one battery at a time over a weekend and bring them all up to the same voltage....they won't be that far off anyway.

[NewAge]

Allrighty now  Great feedback, thanks everyone and keep it coming, my existing charger is a Soneil 4808SRF and I have been very happy with it, I have taken a meter to each individual battery after a six hour charge and have very consistent readings, I have read that some builders prefer individual chargers and I wanted to hear what you guys thought.

Like the lithium batteries weren't expensive enough, it appears that individual chargers are the norm for a state of the art array  It looks like lead acid for my rat project which is still going to have me so broke that I'll be drinking powdered beer for awhile 

[dilkes]

My e-Bike uses 4 x 12V 20ah SLA batteries in series to provide 48V to a 500 watt motor. Charging is with one 48V charger. Some of us were looking at (and have done some testing) on adding an additional battery pack of 4 x 12V 9ah batteries. (We have physical room for these under the seat) connected in parallel with the larger 20ah pack. Preliminary testing indicates a more stable delivery of amps to the motor plus longer range before recharging.
 
One of our group thinks that:

• When the bike is not being used (and the batts are partly discharged), the 2 packs should not remain inter-connected as the larger one will discharge into the smaller one at an uncontrolled rate, potentially damaging the smaller pack. For this reason, he is planning to install some 25A diodes between the two packs to prevent this.
  
• The two packs need to be disconnected from each other and charged (using the 48V charger) separately and independently as charging through the main pack with both connected will cause the charger to prematurely detect full voltage and shut down early, or perhaps overcharge the smaller pack.
  
  

I personally am not convinced either of these concerns is valid, but don't want to destroy any SLA battery packs testing it. Would anyone have an opinion/experience on this?

[Bogan]

i would think its fine to use in parralel, you may run into problems using diodes as the diode voltage drop could affect the charge/discharge rates/voltages. Having a second lower ahr pack still has the same number of cells, just with less internal surface area, so it should work the same as just using on big battery, this assumes plate thickness, dishcarge rates are all very similar.

[SF EV Mechanic]

http://www.teva2.com/projects.htm
You can build this circuit yourself if you intend to use one charger.  I have used the Soneil chargers with great success.  I leave it on all the time.  It beautifully balanced the 4 50 ah batteries in my Lepton for years.  They were always in balance.  But that being said my experience with other large strings has not been so good.  I recommend voltage regulators or one charger per battery.  However you must make sure all the chargers are always working.  If one fails your battery could be ruined quickly.  It's the weak battery in the string that takes the load.