Q about Battery Charging

Yes! Yes! Yes!

john

It's an ordinary wall wart.

1. yes, it probably can, "for capacities up to 18Ah".

1. Did you read any of the words there?

"Note: Charger should not be left on battery indefinitely. Optimum charging time can be calculated by figuring the following:

Capacity / 0.6= maximum charge time (assuming completely drained battery)

So for a 4.5Ah battery use the following equation - 4.5 / 0.6 = 7.5 hours maximum charge

Please note that overcharging a sealed lead acid battery can permanently damage the battery, or reduce the capacity of the battery."

So, yes, it's likely to damage the battery if you neglect to follow the instructions.

Good Luck! Rich

Interesting that the picture actually shows an AC adaptor with the diagram on the front for a standard DC appliance plug on the output. This, plus the fact that the unit is only rated for 6V 600mA (you are not going to be able to charge an 18AH battery properly with this) leads me to believe either the picture is wrong or that the Marketing department were a little hung over when they wrote it (or more likely both).

Misleading data supplied next to picture seems to indicate a 600mA constant current source

maximum charge. Something is definitely not right.

Avoid this product as if it were a pile of dead chipmunks!

And no, you cannot use a standard wall wart to charge a sealed lead acid battery, without additional circuitry to correctly charge and protect the battery. At least they got the fact that the battery should not be left on this "charger" indefinitely.

If you want to charge a lead-acid battery without damaging it, then I suggest one method is to build yourself a regulated power supply with a LM317 or similar, which could then be powered by some kind of wall-wart. You can adjust this to the voltage which the battery manufacturer recommends, e.g. look on the Yuasa web page, they have quite a bit of info. If the power source which is driving your LM317 would be damaged by a high current flowing then my approach has been to put some form of current limiting between the power source and the LM317, at its simplest this could just be a resistor in series with the input terminal of the LM317, which causes the LM317 to drop-out when the battery draws more current than the power source could safely supply. I also was worried that the battery might be discharged if the mains power failed during the charging process so I put a diode between the LM317 and the battery, but note that if you do this then the voltage from the LM317 definitely needs to be increased so that you get the right voltage after the diode. It is very important to measure the voltage at the battery terminals and check that this is correct according to the battery maker's instructions. The LM317 will probably need a heatsink. I suggest you put a fuse in series with the battery terminal to reduce the risk of fire if something in your circuit gets shorted.

Chris

Norm Dresner wrote:

The wall wart puts out a nominal 600 mA at 6 volts. That's approximate; those ratings they print on wall wart labels are not real exact.

6 volts is pretty flat for a "6 volt" lead acid battery, but if a battery really is that low and you put it on the wall wart, it would deliver ballpark 600 mA into the battery. As the battery takes on charge and its voltage rises, the current coming from the wall wart decreases. If the wall wart is pretty well matched for charging "6 volt" sealed lead acid batteries, then as the voltage gets around 7.2 to 7.5 volts, there will still be some current, but nowhere near the original 600 mA. This is called "taper charging," which is a fancy word for CHEAP UNREGULATED CHARGER. The problem lies in the fact that open circuit voltage on the wall wart is likely to be significantly higher than is healthy to expose the battery to, which is why you can't leave a battery on a "taper" charger indefinitely. It might go up to 10 volts eventually and damage your battery. And in the worst case, maybe this could happen even without the battery getting a full charge in the process! Proper charging for lead acid batteries calls for putting enough charge into them at a limited current until the voltage gets up to 2.4 volts per cell (flooded type) or as much as 2.5 for AGM batteries (sometimes called sealed or valve regulated). Then the charging protocol calls for holding a constant voltage on the battery for some time; the current flowing into the battery will decline eventually, and when it gets to about 3% of the amp hour rating of the battery, the battery is considered charged and should be taken off the charger or maintained at a float voltage of about 2.2 or 2.3 volts per cell. I charge batteries all the time with just a transformer and rectifier, but I know what I'm doing. Timing the charge isn't really the best approach.

I've found the following site useful...

They have "Powersonic" lead-acid chargers in a variety of capacities. They also sell a 6 volt lead acid in a "lantern" form factor. I've used these for several years and the PSC-61000A charger.

Jim Veale

"Norm Dresner" writes:

Sealed lead-acid batteries should be charged at constant voltage and a 6V SLA requires a fixed voltage of nominally 6.8V. (If you really want to do it properly, the voltage should be temperature compensated - can't remember the mV/C adjustment required OTTOMH, but a quick Google should throw up all the info you need. This would provide optimum protection for the battery for long-term use, but charging at 6.8V at normal room temperatures is good enough for most applications).

Any half decent charger will usually include some form of current limit, but this is usually for the protection of the charger itself, as opposed to the battery, which can handle quite large currents.

One of the appeals of sealed lead-acid batteries is that they can be left on 'float charge' on a suitable charger pretty much indefinitely, with the charger and battery taking care of themselves without the need for intervention or monitoring.

However, the charger shown in the link doesn't come close to being a 'good' charger and should only be used with care - the SLA would almost certainly be damaged if left connected to such a supply for any length of time.

Ted

6.8 volts is good for float, but if you want to charge a battery in any reasonable time you need a higher voltage than that..