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Old 18th Nov 2022, 6:40 pm   #21
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Default Re: Battery Charger Puzzle

Quote:
Originally Posted by MotorBikeLes View Post
A caution for anybody repairing a very old charger.They were originally equipped with metal rectifiers which have a fairly high voltage drop.
That would be correct for the typical ones built into a tin plate box or similar, probably the same type as the one mentioned by Rog in a previous post. I suspect that it was the old metal rectifier developing a very high resistance that caused his charger not to be able to overcome the battery terminal voltage that he related about in his post.

This Lucas 'wall-wart' type charger is completely different in that there would never have been room for a metal rectifier. The small solid state bridge rectifier block with its flat protruding terminal connections looks to be an original fit with the way they're formed into the confined space within the charger.

I'm now charging the forth battery with this charger and it's another car battery of unknown age that I was given a few years ago. It's quite old and has the six removable plugs for topping up the cells. Bulb light up was normal when first plugged in and charging current was a good 1.25 amps. I've just left this one charging and when last checked, the terminal voltage of the battery was 14.9 volts and the current was 0.8 amps. It's not been an age since it was last charged, but was obviously due for one, so we'll see how it goes - no Variac in line with this one this time.

As regards the bright flash of the lamp when first plugging in that the OP related, I think that this may be down to the charger seeing a high impedance from the combined series resistor and the possibly slightly sulphated cell he's charging - perhaps something to do with the transformer inductance and seeing little load on first plug in, a bit like those gel batteries that sometimes need to wake up a bit before they'll pass full current, but just guessing really.
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Old 19th Nov 2022, 7:48 pm   #22
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Default Re: Battery Charger Puzzle

That last battery was left on charge all day and wasn't taken off charge until late in the evening. It settled down to a terminal voltage of 15.0 volts and a charging current of 0.8 amps, the mains voltage was at 241 volts when I finally disconnected the charger and the final terminal voltage at that mains voltage was actually 15.05 volts, so it's pretty much running at a steady 15 volts at 240 volts mains. The current measurement was monitored on the 10 amp range of an AVO 8, so a bit cramped down the bottom end of the scale for reading 800ma. You can't use a lower range such as the 1 amp range, due to the internal resistance of the meter skewing the readings, also it's safer (for the meter) using the 10 amp range in the event of the current suddenly going up for any reason.

It was an old battery, so I wasn't too bothered about a possible slight overcharge voltage and I wanted to get the charger warmed up to prove that nothing untoward was going to happen and the charger just ran slightly warm. The lamp having started off at a reasonable brightness, dimmed down to probably half of its full brightness level.

Was it worth bothering with this old charger? Probably not, but it's a family heirloom that's been brought back to life and an interesting old relic from the mid 60s. I would probably have never bothered to do anything more with it if I hadn't recognised it as being the same type of charger that the OP had started the thread about - it's a pity the thread title couldn't be changed to assist with future 'searches'. I struggled to find my old thread on this charger from back in 2015, as I'd forgotten that I'd titled it 'oldest wall-wart' and not the actual make and model of the charger. I'd even wondered where I got those adverts from in that other thread and it wasn't until I worded the search term in a particular way that I found them - it has to be Lucas MajorCharger, with major and charger being all one word...it doesn't work if you separate them as you might think.

I spent some time today going through some of my late parents old paperwork and believe it or not I actually found the original instructions for this charger. Not only that, but I also found the mid 60s instructions and guarantee card for the 12 volt car battery that the charger would have been bought at the time to charge. The battery was of the new design type (at the time) which had glass marbles in the top of each cell for venting and I actually remember this battery and being fascinated by the marbles in it as a child. What was interesting about all these instructions was that nowhere was there any mention of the terminal voltage of the battery being kept at no more than 14.4 volts. It did say regarding the charger that shorting the connections of the charger output would burn out the bulb and connecting the connections the wrong way round to the battery would blow the internal fuse, so it must have been that my father connected it reverse polarity that caused the failure. I think he did this more than once, which is probably the reason for an excess of added red tape on the positive wire and blue tape on the negative to help remind him of which way round it was suppose to go in a dark 60s garage.

There's absolutely no mention or pictures of these chargers, other than period magazine adverts, anywhere on the 'net, so they must be quite rare...it's a shame that mine isn't in better condition. I wonder if the OP knows any history regarding his particular charger?
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