As a stop-gap, and to see if it works at all, you can use any 24V lead-acid
You can even use two 12V chargers, connected across half of the battery
This will take days, or even weeks to charge.
The cells are usually individually replaceable on the steel encased forklift
or walkie-stacker batteries. The sealer is knifed from between the cells,
the link is cut loose from the cell terminal with a coring tool in a drill,
then the cell is withdrawn with a hoist. The new cell is installed, and the
lead link is melt-welded to the terminals with a torch after the battery is
purged of explosive gasses. I used to do this on a former job as filler work
on nightshift. The guys on days were supposed to have the battery de-gassed
and purged properly for me when I arrived. I always made a habit of waving
the lit torch duct-taped to a broom handle, a few inches over the battery to
make damn sure they had done this properly, before starting my link
melt-weld. One night, sure enough, I got 18 mini-blasts out of the battery
filler holes. Shades of Chinese firecrackers, Batman!!. After cleaning my
pants, the next day I told the company I was through with that operation,
that I felt it was too dangerous for any employee that they cared about, so
they contracted it from outside from then on. <G>
"You're just jealous because the voices are talking to me, instead of you."
"Ian Stirling" < firstname.lastname@example.org> wrote in message
On Thu, 5 Feb 2004 17:14:18 -0800, Thomas Csibor wrote
I bought a 10 Amp, 24v charger at Wally World for under $90. Automatic charge
taper, switch for standard and deep-cycle batteries and does 12v also. I 'm
using it for an electric wheelchair whose on-board charger quit.
I went through this myself, except for a 48 volt bank on a Hyster
I wound up using a Lambda regulated power supply and ammeter, nominally
48 volts, but with adjustment, I could turn it up to about 53 volts,
where the current was what the power supply could deliver. Mind you,
this was a 600 watt power supply, and it took days to charge that much
battery. I imagine you'll need something like 27 to 30 volts. You need
a lot of current, and you won't be able to build that yourself cheaply.
Definitely you should get a specific gravity meter from the auto parts
store, and distilled water, to top up the cells and check their
Here are some more notes I made based on some research:
Lead-acid battery open-circuit voltage 2.15 V (full charge) to 1.9 V
(full discharge) (12.9 V to 11.4 V in a 12V battery). Thus a 12 V
battery has a 1.5 V open-circuit range which can be taken roughly as a
linear state of charge. Charging amperage typically 1/10 to 1/5 of
amp-hour rating. This might require 13 V at the start, 14.5 V
mid-charge, 16.2 or 16.4 V to finish, and 13.2 V to float.
Equalizing-charge voltage (controlled overcharging of 5 percent excess
voltage, applied after full charge, observe gassing, remixes electrolyte
and breaks down sulfation, read SG every hour, useful when the SG
between cells differs by 0.030 or more, finished when SG no longer is
rising) is 15.8 V. A simple "automatic" charger merely applies a
regulated voltage of about 14.4 V or 14.5 V and shuts off when the
current drops, in about 10 hours from full discharge. Charging voltage
may be lowered for higher electrolyte temps by a compensation factor of
3 mV per deg F above/below 70 deg F. Specific gravity is typically from
1.130 (full discharge) to 1.280 (full charge). Another authority gives a
lower range of 1.120 to 1.265. Cells in a fully charged, idle battery
should be within +/- 0.05 volts of each other, and specific gravity
within 0.030; if not, an equalizing-charge process may be needed.
If the cells aren't permanently bonded together, you could make a harness to
separate the cells into two 12 volt banks (6 cells x 2), and charge them in
parallel at 12 volts.
A large knife switch or a heavy duty disconnect could possibly be used to
split the 12 cells into 2 banks of 6 cells.
You'd still need a high current charger to keep the charging time
You don't need to physically separate the cells. If you can clip the
charger on to e.g. some cells in the middle of the array the cells
outside that circuit will not know the charger is there. I would not
recommend this type of "hit & miss" charging.
I would not even mess with a home built. Somebody out there is going
to have a surplus charger that will do the job. Also with lead acid
batteries you don't usually run them down to zero and recharge. This
means that at least with light use you don't need a charger than is
going to run a fistful of amps through the beast. Overnight charging
where you just replace what was used that day is more normal. For this
you need a "smart charger" i.e. one that will bring the batteries up
to full charge and then back off to a trickle current flow that keeps
the battery charged but doesn't over-charge it.
Where are you?
I have a old warehouse cart charger (24V) with built in timer sitt'in in
the garage taking up space. I'll dig it out over the weekend and take a
picture. Yours for $20 plus shipping.
Thomas Csibor wrote:
You should be able to locate some lead/acid battery chargers online or at a
Ham Radio circuit books usually have charging circuits in them.
If you don't locate a 24V charger and want to build one, some circuit
diagrams will be necessary,
A typical parts list would include a 50V center tapped high current
transformer and a temperature limit/cutout switch for it, some heavy duty
stud mount rectifiers and a heat sink, fan, a HD current shunt for
monitoring the charge rate, meters for volts and amps, fuses, solid state
switches, and a regulator circuit. A common regulator used in many power
supplies and chargers is the 723 IC.
Using semiconductors to do the full charge cutout and switching is best, so
you wouldn't have a sparking mechanical relay anywhere near the battery
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