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Discussion Starter · #1 ·
I decided for lead acid 144V 100A deep cycle batteries in my first conversion, simply because the car can carry them easily and because they were cheap.

But now, how do I charge them? The instructions only explain charging a single battery. Can I keep them in Series and multiply their Volts by twelve, keeping the Amps the same?
 

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The best method for FLA is a 3 stage charging algorithm:

First Stage is called Bulk Charge where a safe constant current is supplied up to a set voltage per cell. Typical charge current is C/10 up to a set voltage point. The voltage point depends if the batteries are pure lead, calcium, or lead antimony but somewhere around 2.25 to 2.45 volts.

Second stage is the Absorption Charge which is a constant voltage, current limited taper charge. Initially the current is limited to C/10 or same as the Bulk Charge. As the battery resistance rises the current will taper of and the cycle is ended when the current tapers to about .03C. The voltage is again dependent on the lead chemistry but between 2.35 to 2.6 vpc.

The third and final stage is the float charge. It is a constant voltage charge and left on the batteries indefinitely until unplugged and used. The voltage level is less than the Bulk and Absorption charge. The actual voltage again depends on the battery chemistry. but typically around 2.2 volts per cell.

There is a much easier but much slower method, and that is just a Float Charger, same as the Float Charge in a 3 stage system. Constant voltage is applied and current limited to C/10. It can take up to 24 hours as compared to 10 hours of 3 stage. Float chargers are more geared to utilities where the batteries are not cycled, but rather used as emergency standby power. Used in that way fast recharge times are not necessary. Float mode keeps the batteries at 100% SOC 100% of the time to overcome self discharge.

Almost forgot there is also a 4-stage algorithm. It is the same 3 stages as above except a Equalization Mode is added. EQ mode is same as Float except at a higher voltage per cell. of about .1 vpc higher than Float.
 

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Discussion Starter · #3 ·
So I charge the whole series of batteries at once with 72 * 2.6V = 187.2V? Or each battery individually (which would be a lot more expensive in chargers)?
 

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My Elcon PFC 1500 for my nominally 72V pack charges to 86.4V @ 14 amps then does an absorption phase at this voltage with diminishing ampage. It then does a balance at a low ampage (which is adjustable) but I turn it off when it reaches this point.
I think, if you havenot bought one already, you need to invest in an intelligent charger. It will treat your batteries kindly and extend their life. Mine cost around $500 so if you ruin a set of batteries with a seemingly simpler and cheaper system it is likely to cost you more money in the long run. I also have a Ctek 12V charger which is useful to charge batteries individually. It charges to 14.4V and was good for initially charging the batteries when I got them to try to make them as equal as possible. It cost <£50.

As a further caution from someone who didn't listen to advice, because I trusted to luck and my own instincts, I have managed to cut the achievable range of my vehicle by being far too hard on the batteries.

I now beleive that if you intend your FLA pack to last any time you should not let your voltmeter drop below 12V per battery ie. 144V in a 144V pack. This figure is not the resting voltage, but the voltage under load. Any lower than that may be OK in the short term, or very occasionally, but it will shorten the life of your pack. I could go over 25 miles when I got the pack but only half this distance before I saw <72V uphill or during accelleration. If I had used this figure as my range and not done 25 miles on about 20 trips, where the voltmeter dropped to as low as 60V, I would expect that my pack would still seem to perform much as it did in those early days.

Andrew
 

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and if you are using floodies, it is well worth time and battery life to buy a central watering system. that chore drops from an hour of peering into cell hole, to about one minute w/ hand pump.

...I am selling my flow-rite watering system by the way (48 cell caps and connectors), as I am upgrading to lithium. see the Classifieds in the forum for more info.
 
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