OT - how to build a forklift battery charger

If you live within driving distance of Sacramento, I know a surplus dealer who has one. He'd probably sell it for less than scrapmetal prices.

What's the voltage on the battery? If it's zero (under a volt a cell or so) it's almost certainly not going to work well, even if you charge it.

While we are working on your 24 volt charger, you can put an initial charge on your batteries with your auto charger by simply charging 6 cells at a time.

Vaughn

While we are working on your 24 volt charger, you can put an initial charge on your batteries using any auto charger by simply charging 6 cells at a time.

Vaughn

On Thu, 5 Feb 2004 17:14:18 -0800, Thomas Csibor wrote (in message ):

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 electric forklift.

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 condition.

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 reasonable.

WB ............

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.

Jim Vrzal Holiday,Fl.

Thomas Csibor wrote:

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.

RJ

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.

As a stop-gap, and to see if it works at all, you can use any 24V lead-acid battery charger.

You can even use two 12V chargers, connected across half of the battery each.

This will take days, or even weeks to charge.

And if you don't use it much a trickle charger will extend battery life greatly. The batteries do self discharge; the older the faster.

You should be able to locate some lead/acid battery chargers online or at a library. 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 vapor.

WB .............