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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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26th May 2021, 5:41 pm | #1 |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,875
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Simple questions on battery chargers
Hi folks
Somehow I have ended up the three enormous, variously elderly battery chargers whose control systems are either absent, or look like they spent every bit of the last 30 years they did spend, in a damp shed. None work. So now they are really big metal boxes with a heavy transformer and rectifier inside. I was looking at an easy way of making them useful, and this appeared https://www.ebay.co.uk/itm/263205621...kAAOSwmFpZuT~C But I need to ask - is it OK to use what I assume is some kind of switch-mode thing on the primary side of a big dumb transformer with a big dumb rectifier on the other side? Also, at least one of them used to control by monitoring the current it supplied (there is a large, presumably temp-stable metal strip resistance in series with the load with sensing terminals across it) whereas that Chinese device seems to work by monitoring the battery voltage. I wonder if this is important. cheers Mark
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"The best dBs, come in 3s" - Woody Brown |
26th May 2021, 10:23 pm | #2 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: Simple questions on battery chargers
I have a homebrew battery charger built around an old RS transformer with quite a few taps on the secondary, so I can set it to low, medium and high charge rates. That's all capped off with a relay and a zener that switches off the secondary circuit when V =14.8 (or pretty close) and this simple cut-off has worked very well for some years. Crucially, for me it has meters for both voltage and current, so you can see exactly what is going on. I wouldn't have the meter-less things currently on offer anywhere near the house.
The ebay module may very well do the job; for the princely sum of £3.86, it's worth a look! The rule these days with many modern batteries seems to be keep max current to no more than 4A, whereas I think higher rates were used back in the day when we all had a bottle of distilled water next to the battery charger! If it wasn't gassing nicely, it wasn't fully charged . B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. Last edited by Bazz4CQJ; 26th May 2021 at 10:30 pm. |
26th May 2021, 11:30 pm | #3 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,343
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Re: Simple questions on battery chargers
I would think, if you've got a fairly discharged battery connected, the turn on surge through the transformer would weld the relay contacts together after a while on that module.
As Bazz says, cheap enough to give it a try and see what happens but do make sure your transformers are sound before messing with them. |
26th May 2021, 11:45 pm | #4 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,349
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Re: Simple questions on battery chargers
Although I do now have modern chargers with electronic control, before I got them I used a simple car battery trickle charger in conjunction with a lamp board to limit the charging current of small lead-acid batteries by selecting a 12V bulb of the approriate wattage to determine the charging current. Bulb brightness gave a good visual indication of current and hence state of charge.
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27th May 2021, 9:12 am | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,970
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Re: Simple questions on battery chargers
I do wonder if it's sensible for the OP to spend lots of time and money trying to revive this knackered old kit, which sounds like little more than scrap metal. Power supply equipment has evolved a lot since these chargers were made, and it's difficult to imagine a practical use for them even if they were in perfect condition.
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27th May 2021, 4:21 pm | #6 |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,875
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Re: Simple questions on battery chargers
That's fair Paul. Not many people are as adverse to letting things go as I am. Well, maybe I'll have a play - I put the question up to see if (as is often the case) I am missing something straightforward and (myself excepted) widely known!
Thanks all M
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"The best dBs, come in 3s" - Woody Brown |
27th May 2021, 5:24 pm | #7 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: Simple questions on battery chargers
Quote:
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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27th May 2021, 5:31 pm | #8 |
Guest
Posts: n/a
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Re: Simple questions on battery chargers
I have a "Ring" "intelligent" charger for lead acid batteries, 6 and 12V. It does a very good job and has even recovered a couple of lost causes in it's Hospital Mode. Probably cost less than a new, branded battery.
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27th May 2021, 5:38 pm | #9 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: Simple questions on battery chargers
Quote:
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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27th May 2021, 8:21 pm | #10 | |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,875
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Re: Simple questions on battery chargers
Quote:
cheers Mark
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"The best dBs, come in 3s" - Woody Brown |
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28th May 2021, 6:20 pm | #11 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,130
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Re: Simple questions on battery chargers
Back in the days when solid state regulating circuits were just becoming available, but were hugely expensive in large sizes, a type of semi-automatic charger was popular.
This used a simple transformer and bridge rectifier and ballast resistance to give a fast but crude and not regulated charge. When a voltage sensitive relay detected that the battery was almost fully charged at say 14.5 volts, this would "trip" and substitute a much smaller fully regulated constant voltage charging circuit, this could remain connected forever without cooking the battery. I may still have one somewhere. The unregulated output was about 20 amps, varying a bit with line voltage and battery state of charge, and the regulated output was less than one amp at 13.8 volts. The relay once tripped to the "slow and regulated" charge, latched in that state and required either manual resetting or isolating and then reinstating the mains supply to fast charge the next battery. An auxiliary contact on the relay could light a lamp to advise that the connected battery was "done" The better versions had a "Kelvin connection" to the battery clamps such that the ACTUAL battery voltage was measured and not battery voltage plus losses in the cables. Standard 3 core mains flex was used, with two cores in parallel for the charging current, and the third core for the sensing connection. Black sheathed mains flex for negative and orange for positive because red not readily available. |
28th May 2021, 8:03 pm | #12 | |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: Simple questions on battery chargers
Quote:
B
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Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
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