# Re: [EVDL] Zener regs: Can I get use 'em & still get a full charge?

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Re: [EVDL] Zener regs: Can I get use 'em & still get a full charge?

Steve Kobb wrote:
> US Battery says that I should charge up to a maximum of 7.75v x 26 =
> 201.5v... the higher-voltage zener is 6.8v. If I were to put these
> regs on my pack, how would I ever get a full charge?

The zener-lamp regs balance by bypassing *some* of the charging current.
The higher the voltage, the more current they bypass. They don't stop a
battery from charging, but they "lean on" the most-charged battery so it
gets less charging current once the voltage has gone above 13.5v.

My 12v regs draw under 0.001a at 13.5v, but 0.5a at 15v. Let's say
you're charging at 1 amp at the end of your charge cycle. Then the "not
full" batteries at 13.5v are getting 1 - 0.001 = 0.999 amps, while the
"full" batteries are getting 1 - 0.5 = 0.5a charging current. If this
goes on for the last couple hours of each charge cycle, then the regs
result in a 0.5 amps x 2hours = 1 amphour correction. Say, 49ah went
into the most-charged battery, and 50ah in the least-charged one. A 1ah
correction per charge cycle on a 50ah battery can deal with a 5%
imbalance. This is generally enough for reasonably good batteries.

At the end of your charge cycle, all batteries will still be at 15v (and
all regulator lamps will be lit); but some will have lit early, and some
later as the balancing takes place.

> If I were to select 7.5v zeners, would that affect the other part
> specifications? Would I need differently-sized resistors, or
> different bulbs, for example?

For 6v batteries, I use one 6.8v zener and one #43 lamp in series. I
then have a pair of these in parallel. This halves the voltage, but
doubles the current (to 7.5v at 1 amp).

Note that for flooded batteries, you usually don't need regulators.
Since you can add water, the usual method is to balance (equalize) by
overcharging, and then replace the lost water periodically.

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