Connect with us

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

Discussion in 'Electronic Design' started by [email protected], Jul 4, 2013.

Scroll to continue with content
  1. Guest

    The other day, I came upon this:

    It's plans for a very simple battery charger that uses a light bulb and diode in series to make a constant current battery charger. Benefits include pulse 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 different size batteries needing different size currents, I'm wondering if a dimmer 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 majorand having taken electronics courses) and want to learn all I can.
  2. mike

    mike Guest

    Incandescent light bulbs make wonderful current limiters for charging
    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.
  3. Martin Brown

    Martin Brown Guest

    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)

  4. Guest

    A dimmer alone will not work well, but a dimmer in series with a power resistor 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 least for utility grade lead acid batteries. That crummy 0.3A will take forever to charge a car or tractor or tool battery
  5. Guest

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

    A cheap 1200W dimmer:

    A cheap ammeter:

    A high power, but cheap, diode bridge rectifier:

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

    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 current, but are there any other flaws in this circuit design? Tim mentionedcharging at too high a voltage, but the article says the battery will drawjust what it needs. Is that not true? Also, I've read that charging at a slightly higher voltage and a very low current for a long time is a good wayto 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 charging lead acid batteries, the constant voltage phase with auto-shutoff when current falls to a certain level. For this, I'll use a readymade store-bought charger.)

    See, the thing is, I don't like the cheap battery chargers I can buy, and the expensive good ones are out of my price range. I have a 6v/12v Schumacher 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 some life out of old lead acid batteries, so I want to overcharge but on a lower amperage to reduce sulfation. All I need is a little electricity at night, 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 with what I have.) I just want to desulfate it to get more useful power out ofit and extend its life.

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

  7. Guest

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

    Thanks. I'm just trying to learn by doing. It's been awhile since my electronics course in college, and they didn't teach this kind of practical stuffanyway.
  8. mike

    mike Guest

    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.
  9. boB

    boB Guest

    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

  10. Guest

    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.
  11. Phil Allison

    Phil Allison Guest

    ** 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
  12. Phil Allison

    Phil Allison Guest

    "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
  13. Kanon Kubose

    Kanon Kubose Guest

    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?

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


  14. Guest

    On Friday, July 5, 2013 1:26:47 PM UTC-4, David Platt wrote:

    Go drop dead, you damned wuss! Dunno what kind of jackass thinks f'ing line voltage is lethally dangerous! Sorry-ass friggin puke pc moron! Be sure and have EMS stikcers all over the place so you know who to call when you cut your friggin finger...
  15. Kanon Kubose

    Kanon Kubose Guest

    Ok, thanks, guys. Good stuff to know. If this thread helps prevent even one accident from someone trying to implement that $3 battery charger, it'll be worth it.
  16. Martin Brown

    Martin Brown Guest

    Yes and very likely dead soon afterwards. As will be the person who
    tries to rescue him without first switching off the lethal contraption.
    The 60W light bulb limits the *current* on 120v to about 500mA. I am not
    absolutely sure what it takes to kill a human but 10mA is enough to
    prevent you ever letting go and above 25mA can kill particularly if the
    current is flowing across your chest.

    Until the light bulb heats up it will actually pass a *much* higher
    current than its nominal operating current and will not drop many volts
    doing so. More than enough to kill you. 120v US mains is slightly more
    forgiving than 240 in the UK but building this is utter madness.

    I have had to administer first aid to US installation engineers that
    checked British 240v mains wiring for being live with a wet finger.

    It would be hard to imagine a more effective death trap for the unwary!

    Definitely you are Darwin award material.
  17. rickman

    rickman Guest

    Did I miss the smilely face at the end of your post?
  18. Kanon Kubose

    Kanon Kubose Guest

    I was thinking about this more, if there was a way to make it safer. Probably the breaker, being 20 amp or so, wouldn't help, right, given that 25 mA is lethal? What about a GFI, though?
  19. Phil Allison

    Phil Allison Guest

    "Kanon Kubose"

    ** No help as the user is handling both AC supply conductors - ie active
    and neutral.

    .... Phil
  20. ehsjr

    ehsjr Guest

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day