Will a dimmer switch work instead of an incandescent light bulb in a simple battery charger?

The other day, I came upon this:

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It's plans for a very simple battery charger that uses a light bulb and dio de in series to make a constant current battery charger. Benefits include p ulse charging for desulfation and the fact that it can charge batteries of any voltage.

Well, with incandescent light bulbs getting scarce and me having many diffe rent size batteries needing different size currents, I'm wondering if a dim mer switch would work instead? If so, what kind? If not, can you tell me wh y? I'm just getting into this stuff (despite being a computer science major and having taken electronics courses) and want to learn all I can.

Reply to
kanon11
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Good gawd. It may not raise the average intelligence of the human race by killing the one who builds it, but it may well take out his kids.

Drawbacks include -- oh, where to start?

How about a wall-wart and a resistor? Or maybe even just the right wall- wart. Go shopping at rummage sales and garage sales -- if you hit one that's selling wall warts they'll be cheap. Or go check your local Goodwill store.

The incandescent light bulb acts as a resistor -- a 100W bulb is going to limit the current to somewhere between 1/2 and 1A (I'm not sure how much, because the average voltage on the bulb will be less than 60V, and the bulb resistance will drop with temperature). A dimmer won't do that; you'd always have either way too much current or none.

Note that lead-acid batteries don't put up well with being charged to a too-high voltage. Read this:

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There's not much "simple" that you can do to prevent it -- you pretty much need a specialized charging circuit.

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Tim Wescott 
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Reply to
Tim Wescott

Incandescent light bulbs make wonderful current limiters for charging batteries as long as you watch the voltage and don't overcharge. But you'll forget and you WILL overcharge. But use a transformer to keep from electrocuting yourself.

I won't argue the merits of pulse charging, but most any battery charger will do the same thing that this one does.

And that same goodwill store will sell you an actual battery charger for about the same price.

Or you can go to harbor freight when they have the light duty one on sale for $5 less the 20% off coupon.

Reply to
mike

Anyone daft enough to build it is surely heading for a Darwin award. I this doesn't kill them then something else will.

Death of the user or his kids seems to be the most likely side effect. (either way it qualifies for a Darwin Award)

eg

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Reply to
Martin Brown

rbattggn.htm

iode in series to make a constant current battery charger. Benefits include pulse charging for desulfation and the fact that it can charge batteries o f any voltage.

ferent size batteries needing different size currents, I'm wondering if a d immer switch would work instead? If so, what kind? If not, can you tell me why? I'm just getting into this stuff (despite being a computer science maj or and having taken electronics courses) and want to learn all I can.

A dimmer alone will not work well, but a dimmer in series with a power resi stor will work well. The circuit in the link should be plugged into a GFCI for safety. It's main weakness is the charging current is too small, at lea st for utility grade lead acid batteries. That crummy 0.3A will take foreve r to charge a car or tractor or tool battery

Reply to
bloggs.fredbloggs.fred

rbattggn.htm

ferent size batteries needing different size currents, I'm wondering if a d immer switch would work instead? If so, what kind? If not, can you tell me why? I'm just getting into this stuff (despite being a computer science maj or and having taken electronics courses) and want to learn all I can.

A cheap 1200W electric heater with overheat protection and thermostat wired short:

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2327efdf83

A cheap 1200W dimmer:

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A cheap ammeter:

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A high power, but cheap, diode bridge rectifier:

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A little know-how, and you'll have yourself a REAL battery charger.

Reply to
bloggs.fredbloggs.fred

Well, true, 110 volt ac current is more dangerous than a wall wart's output , but a circuit like this can't be THAT dangerous, can it? More so than an old incandescent lamp? I know people who lost their houses in fires caused by old wiring, but a little circuit like this properly insulated, monitored , and kept away from flammable objects and enclosed spaces... is it really that much of a problem? Of course, one should always be careful around ac c urrent, but are there any other flaws in this circuit design? Tim mentioned charging at too high a voltage, but the article says the battery will draw just what it needs. Is that not true? Also, I've read that charging at a s lightly higher voltage and a very low current for a long time is a good way to desulfate a battery. As for leaving it on too long like Mike mentioned, I could just attach a timer. (I do know that there's a second phase to cha rging lead acid batteries, the constant voltage phase with auto-shutoff whe n current falls to a certain level. For this, I'll use a readymade store-bo ught charger.)

See, the thing is, I don't like the cheap battery chargers I can buy, and t he expensive good ones are out of my price range. I have a 6v/12v Schumache r right now, and it will only do 2, 4, or 6 amps. This whole thing started because I wanted something that would charge at whatever amps I want. If I could vary the voltage too, that'd be ideal. I like the pulse idea, though some say that's not what actually desulfates batteries. My Schumacher goes into 2 amp trickle charge mode after shutting off. I'm trying to squeeze so me life out of old lead acid batteries, so I want to overcharge but on a lo wer amperage to reduce sulfation. All I need is a little electricity at nig ht, and an old car battery that came with my trailer was working fine. (Yes , the previous owner replaced the deep cycle with a car battery. I deal wit h what I have.) I just want to desulfate it to get more useful power out of it and extend its life.

Finally, Fred says a dimmer switch will work, but Tim says it will always g ive too much current or none. Is it that the heater combined with the dimme r will make it work?

Thanks.

Reply to
kanon11

The cheap electronic chargers (switching regulators) usually won't charge a totally dead battery. You need an old-fashioned transformer-rectifier charger, or a bench supply, or some kluge, to get them going.

Reply to
John Larkin

One more question, since people like the wall wart idea better: I've charge d with them before too, but my question is, what does the current do? Say I have a 14 volt wall wart with a current rating of 500 mA. If I try to char ge a car battery with this, will it pull too many amps and overheat? Is a w all wart a way to do constant voltage charging? Is there a way to limit the current?

Thanks. I'm just trying to learn by doing. It's been awhile since my electr onics course in college, and they didn't teach this kind of practical stuff anyway.

Reply to
kanon11

There are as many different types of wall warts as there are wall warts. Just use a 19ish volt laptop power supply and a 12V car tail/stop light. That will give you four possible currents. And the series mode will let you start with a dead/dead/dead battery and not blow up the light.

Reply to
mike

Hmm, the name of the guy posting the $3 battery charger is gogetumnow. I suppose that's what the mortuary manager will say to the hearse driver. Tom

Reply to
Tom Hoehler

The problem with this is that it is uncontrolled and will end up prematurely hurting the battery rather than charging it properly by regulating the voltage during its finishing charge. Look up 3 stage charging profiles for an introduction to this. Any good charger will work that way and will also take into consideration battery temperature to vary the constant voltage portion.

Light dimmers (triacs) has been used a lot in the past because it can control the voltage as well as control over-current conditions. Microprocessor or logic controlled of course. One problem with this, commercially is that it has poor power factor which is another problem altogether.

boB K7IQ

Reply to
boB

Yes, if you use the dimmer then you need a significant resistance in the circuit to limit the current. You can't rely on the battery resistance because it is too small. If all you want is less than an amp, then use a 120W bulb in series with the dimmer.

Reply to
bloggs.fredbloggs.fred

** You reckon AC current will charge a battery ?

The original idea was to use a lamp and diode in series.

Include the diode and most dimmers will stop working.

.... Phil

Reply to
Phil Allison

You could go dimmer, lamp (or high wattage resistor), bridge rectifier in series and feed the battery from the bridge DC side.

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Reply to
Paul Hovnanian P.E.

** OK , I missed the post where that was mentioned by fred.

However, the whole idea is completely nuts and super dangerous.

.... Phil

Reply to
Phil Allison

I'd say "Hell, yes".

Standard incandescent lamps and fixtures are designed to keep the voltage away from the fingers. When wired and used as designed, the outer shell of the socket is connected to neutral (which is close to ground voltage) and the "hot" voltage is exposed only on the contact inside the socket. As soon as you start screwing the bulb into the socket, "hot" is physically inaccessible. Hence, as long as you don't stick your finger down into the socket itself you're reasonably safe.

This "charger" circuit is intended to be connected to lead/acid batteries, which often have completely exposed connections. Someone who doesn't know what he's doing, might wire up this circuit with the "battery" leads ending in alligator clips, for connection to a battery's terminals.

It would be dangerously easy for somebody to have this thing plugged in ("hey, it's low voltage, right?"), reach down towards the battery with one alligator clip in each hand, and have their fingers touch the metal on the clips (or the battery terminal itself) when the battery is not yet fully in circuit. At this point, the circuit will be delivering half-wave-rectified line voltage, with the "current limit" being that of a dark light bulb.

Likely result of this: many times the potentially-lethal "shocks your heart into fibrillation" current, going right across the chest from one arm to the next. Darned near a worst-case physical scenario for effective electrocution.

Reply to
David Platt

Did you re-hearse that line? :)

Reply to
Michael A. Terrell

Thanks for the explanation, David. This is the kind of thing I need to know. I do have a few questions, though:

  1. With the device plugged in, with alligator clips in each hand, assuming they're unshielded clips like many are, wouldn't the person already be exposed to the half-wave-rectified line voltage?

  1. Why won't the light bulb limit the voltage to non-lethal levels? What does it being dark have to do with it?

Thanks,

Kan> >Well, true, 110 volt ac current is more dangerous than a wall wart's output, but a

Reply to
Kanon Kubose

Isn't it obvious?

The resistance is at its lowest when the bulb isn't lit. It doesn't limit voltage, it limits current. These questions belong on news:sci.electronics.basics

Reply to
Michael A. Terrell

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