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trickle charger

Discussion in 'Electronic Design' started by Damien, Nov 8, 2003.

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  1. Damien

    Damien Guest

    I'm trying to find a circuit diagram for a trickle charger capable of
    charging a 12V motorcycle battery. I've got a 4A charger which works well
    enough, but a trickle charger would be preferable for helping ensure the
    battery has a long life. I've looked everywhere I can think of online except
    for here, and was hoping someone might be able to help!

  2. mike

    mike Guest

    Assuming you have an automatic 4A charger that shuts off when the
    battery is charged, you can put a tail light bulb in series to limit
    peak current.

    The typical 4A charger will typically taper quickly to a much lower
    current. You have the option not to worry about it.

    If you want to leave the charger on all the time, you want a float
    charger. It's about the same thing except that it shuts off at a lower
    voltage. You can approximate that by putting a diode in series with your
    automatic 4A charger.
    But I'd be inclined to use a faster charger to the higher voltage and just
    charge it every month or so instead of leaving it on charge 24/7.

    What you do not want is a current source. You want a current limited
    voltage source. Might even want to consider temperature compensation if
    you experience wide temperature swings.

    That's the best I can offer not knowing anything about your application.

    Bunch of stuff For Sale and Wanted at the link below.
    laptops and parts Test Equipment
    Honda CB-125S
    Color LCD overhead projector
    Tek 2465 $800, ham radio, 30pS pulser
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  3. default

    default Guest

    I built a small trickle charger for my MC using a TO92 size LM317
    regulator. The voltage is set for 14 volts and the regulator limits
    current to ~100 ma.

    If you leave the bike for months without riding it you may want to
    consider a "Desulfator" as well. Zaps the battery with a reverse
    voltage to knock sulphur off the plates (or so the theory goes). I'm
    finding that despite my trickle charger, the battery impedance keeps
    rising - that doesn't happen when I ride often.
  4. default

    default Guest

    You got me thinking about prolonging the life of batteries and one
    thing leads to another . . . This might be of interest to a MC rider:
    Prolonging the Useful Life of a Lead Acid Battery
    by K.L. Martin, B.Sc.(Hon)(London)

    Very few lead acid batteries are replaced because they stop
    working. In almost every case the battery is replaced because it
    doesn't work _well enough_ anymore. What is not generally realized is
    that something can be done at this stage which may prolong the useful
    life of the battery - quite often by many years, and that the same
    treatment carried out earlier in the battery's life may well have
    stopped the symptoms from occurring in the first place.

    The reason for a battery failing is due to the chemical processes
    which take place in each cell when the battery is not fully charged.
    Even the slightest discharge condition allows both plates to react
    slowly with the sulfuric acid electrolyte to form lead ions. It is
    these lead ions which cause problems; they combine with sulfate ions
    in sulfuric acid to form highly insoluble lead sulfate. When this
    coats the plates of the battery, it fails to deliver enough power to
    be of use.
    The battery may well be serviceable every other way - only the
    "sulfating" stops the battery from delivering enough power to be of

    The sulfating can effectively be removed, or prevented, by adding
    to each cell a chemical called tetrasodium ethylenediaminetetraacetate
    (often abbreviated to tetrasodium EDTA). This chemical forms
    co-ordination compounds with many metal ions, including lead ions
    formed in the discharge cycle of a battery. The compound formed by
    lead ions and the EDTA ion is not particularly stable in the acid
    medium of a battery, but when it breaks down again any lead
    sulfate regenerated tends to drop to the bottom of the cell where
    it lays harmlessly since it doesn't conduct electricity. Any
    regenerated EDTA ions are free to continue their work.

    This is likely to occur if the motorcycle is used just for short
    trips, is infrequently used, or has at any time suffered from an
    inefficient charging system. Treating with the chemical can also help
    keep an original battery in use, and can help in bringing back into
    use a stored battery. It is also a once-only treatment, lasting the
    life of the renovated battery.

    EDTA is relatively non-toxic, inexpensive, and readily available one mail order source $12 a
    pound (lifetime supply?) schematics links for simple
    pulse desufators (go for one of the nchannel versions finding P
    channel mosfets is costly) The one I plan to
    build . . .
  5. Heh. I hit those sites, along with several others in the past couple of
    days. I hit google for "lead-acid battery charger circuits" and "sulfaction"
    and got *lots* of hits, and snagged a lot of files. Now to find the time to
    digest all that stuff...
  6. You probably want a device that not only charges, but keeps the
    battery in a good shape. Here are a couple of rules:
    Never let the baterry go empty, not even half-way. Never store the
    battery in cold places, especially when they are not completely full
    (when it freezes, an empty battery could get useless in only one
    night). Use the battery's often: this means you should keep them as
    full as possible, but draw current from them, charge them, again etc.
    Charge them up to for example 13.8 Volts (= 90% full). Or 14 V.

    A couple of years ago Elektor (Elektuur here in the Netherlands)
    published some electronics that charged and also did the trickle


    Pieter Hoeben
  7. default

    default Guest

    On Sat, 08 Nov 2003 22:41:01 -0500, "Roy J. Tellason"
    Amazing amount of stuff. Who knew?

    It looks to me like some of the desulfator schematics have a common
    error, including the one I was planning on building. I notice two
    schematics where the timing cap of the 555 is returned to supply not
    ground as is normal . . .

    Thinking about it some more, the object is to zap the battery with a
    high current pulse at a 1000 HZ rate. I'm leaning towards rolling my
    own using a DC/DC step up 300 volt source and just sending a pulse
    from a charged 1 micro farad capacitor through the battery via an SCR
    in the ground leg. Similar to a CD ignition circuit.

    Reading some of the forums it looks like 555 and mosfet failures are
    too common in the inductive circuits. I get the impression from the
    forums that most of the folks building the things have limited
    electronics experience and are more interested in the homesteading
    aspect of doing without electrical service.

    Using an external source and incorporating a trickle charger into the
    device I could keep the sulfate out while keeping the battery charged.
  8. A fully charged battery normally will not freeze, and the cooler a battery
    is, the less it's going to self-discharge.
    Nope. Lead-acid batteries won't last as long being continuously cycled as they
    will being kept fully charged.
    Got any URLs? I'm collecting battery charger info, along with desulfator
    info, before I go ahead and build something to take care of my own needs

    Anybody else?
  9. I haven't hit those files yet, been working on the chargers. But I also
    won't say that a 555 can't work in that configuration, at least not until I
    give it a look. You can do some truly amazing things with that chip.

    For example, one solar panel setup that I saw had the two inputs normally
    used to control a 555 as two trip points, each having a 1uF cap to ground
    and a resistor to the positive rail, maybe a trimpot in there too, I can't
    recall at the moment. For some reason not apparent to me they also had pin 5
    (!) clamped with a 6.8V zener diode and a resistor, and were using this
    whole setup with a bipolar transistor and a FET in the _negative_ rail, the
    reason for that not being apparent to me either. Still, it's a pretty nifty
    I'm not up on those.
    That may be a part of the problem they're having, then. :)
    I have a number of gels on hand here, and a couple of rather large (group 27)
    deep cycle batteries, most of which I've had for a while and not done much
    with. My main interest at this point is to de-sulfate them (yes, I've been
    neglecting them lately -- the 6v unit I'm pushing 16v into right now still
    drops below 3v when I turn the power off) first, and then get them fully
    charged, and keep them that way. Being able to hook various loads up to
    them would be nice, too, when I get to that point.

    I remembered seeing an SCR circuit (used two of them) WAY back when, I think
    it might've been in the GE transistor manual or similar. I did find that
    sort of a circuit in the pile, but there are things about it I don't like
    too much.

    The chargers I have on hand fall into two categories. The simpler one is just
    transformer, rectifiers, and that's it, and they limit the current based on
    the transformer design, I guess. The "automatic" ones seem to include an
    SCR with a couple of resistors, one small cap, and a zener diode, but I
    can't find the bit of paper where I'd sketched out that one, and don't know
    how I'd set up different current limits for such a circuit (assuming I had
    enough transformer capacity to push it hard enough). Settind different
    current levels is going to be important -- the smallest of those gels I have
    here is only 2.3AH! (Camcorder-style battery, used on my old cell phone

    I like the idea of using SCRs, since we're switching pulsating DC here
    anyway, and also like the idea of using such generic parts as the 555,
    rather than any more specialized single-source chips. It also helps that I
    have bunches of them (and 556s, etc.) in my junkbox, along with piles of
    discrete components.

    Now I just need to come up with a good design for this...
  10. default

    default Guest

    I gave it a quick look and (without dragging out the 555 schematic) it
    looks kinky to me. That doesn't mean it won't oscillate but it does
    look like there is no charge-discharge path for the timing cap.

    The 555 is notorious for false triggers with some line noise that may
    be what keeps the circuit oscillating - I noticed on the forum that
    some folks complained about their circuits not oscillating, but didn't
    want to follow the whole thread.
    I'm familiar with it. Uses the two internal comparators as a sort of
    window comparator. Used in battery chargers to provide one setting
    for "charge" and another for "stop." Didn't see the circuit with pin
    five clamped but did see it with an offset voltage to pin 5.
    Capacitive discharge ignition systems use the standard automotive
    coils in a non-standard way. Instead of relying on the kick from the
    inductive collapse they use it as a pulse transformer and goose the
    primary with a 300-500 volt pulse by discharging a small (1 µf cap)
    through it with a triggered SCR (when the points open). The coils are
    good for it because they are designed to run at 1.3KHZ (eight cylinder
    running 10 KRPM).

    I think this is the method some experimenters use for generating HV
    using lamp dimmers and auto ignition coils. Fire the Triac at peak
    line (50% dimming) and you hit the primary of the coil with 120 volts.
    Foolhardy if you ask me - most coils are sealed in an oil bath; if
    that were to vent there'd be a fire.

    I would only use the 300 volt cap and discharge that through the
    battery instead of a coil at 1KHZ or less. Vary the capacitance and
    it would vary the amount of energy dumped at each shot. 300 volts
    into a battery in the milliohm range should get the 600 amp pulses
    they measure.

    The thing I still have to do is read the patent on one to see what
    really counts here - total energy, rep rate or pulse current.

    I notice the "armageddon now" crowd is concerned with size and they
    are going over the edge trying to increase the size of the inductors
    in their large battery bank desulfators. My SCR idea seems a lot
    easier in that respect. Mosfets don't handle some of the peak
    voltages the inductors can generate and SCR's don't need the
    inductance with a capacitive circuit. SCR's are damn reliable.
    The further afield one gets . . . some folks that believe the earth's
    magnetic field is about to switch polarities, causing cataclysmic
    events had info on storage batteries and desulfators.
    I've got some gells that I use for hurricanes and can't seem to get
    around to charging on a regular basis and a MC battery that sees
    sporadic use.
    I may have seen what you are talking about in your automatic charger -
    I repaired a Sears brand charger for a friend at work and it sounds
    like you describe.

    You could probably just switch in a resistor to limit current. I have
    done that using the big (10 amp) charger on the MC and gells. There
    was an old Malory vitreous enamel 150 watt ten ohm rheostat that I
    found in a surplus catalog for a few bucks. I use it to adjust the
    charge current and then forget about it - the Heathkit works with it
    and the battery reaches full charge.

    The Heathkit uses an SCR and all discrete components. The circuit was
    published in one of the encyclopedia of electronic circuits series. I
    had some problems with lightning wiping out the diodes (leaving it
    outdoors during storms, with a long extension cord) I put in an MOV
    and grounded the negative lead and haven't blown a diode since. The
    internal circuit breaker died and it now has a magnetic one on the AC
    line. The meter was never accurate and that got replaced with a 8 amp
    one. It has been working for >20 years. My OM has one that has 30
    years and no failures (different part of the country and in a garage).
    Post your design on the binary 'lectronics group.
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