Seemingly elementary question I can't find a useful answer to...

[Don Bruder]

A situation I've never encountered, so I've never thought about...

If I've got a 12 volt lead-acid battery, and, for whatever reason, the
charging source decides to start feeding between 6 and 15 volts of AC to
it, what's the most likely result? I'm hoping for something a bit more
useful and specific than "you'll end up with a dead battery" - That's
only too obvious. Should I expect the battery to heat up? Explode? Just
not take a decent charge? Not be affected in any noticeable way? Grow
legs and start dancing the cha-cha? Start reciting Shakespeare?
Something else?

I ask because an ATV we've got here on the ranch appears to be doing
exactly what I described - Depending on engine RPM, the battery
terminals are seeing between 6 and 15 volts of AC. It seems pretty
obvious that the alternator/magneto/whatever-it-is output is going
straight to the battery without regulation or rectification. Trouble is,
doing something about it means putting the machine out of service for at
least a couple of days while we tear the engine down so we can get
access to the regulator/rectifier. (both are INSIDE the engine for some
reason known only to the brain-surgeons at Yamaha) Taking the rig out of
service for more than an hour or two is something that HAS to be avoided
if there's ANY way of doing so.

HELP!!!!

 

[Gerard Bok]

A situation I've never encountered, so I've never thought about...

If I've got a 12 volt lead-acid battery, and, for whatever reason, the
charging source decides to start feeding between 6 and 15 volts of AC to
it, what's the most likely result? I'm hoping for something a bit more
useful and specific than "you'll end up with a dead battery" - That's
only too obvious.

But oh so true
You are 'charging' it with it's average DC component.
And the average DC component of an AC signal is ?

Should I expect the battery to heat up?

That's the next thing. You are not charging the battery but yet
feeding it energy. A battery doesn't move, doesn't shine, so that
energy is likely to end up as heat.

Explode?

If you feed enought energy, almost anything will.

 

[Don Bruder]

But oh so true

And you figured I didn't "get" that because... ?

You are 'charging' it with it's average DC component.
And the average DC component of an AC signal is ?

So it's not *QUITE* safe to think of it as "half the cycle it's
charging, the other half, it's discharging"? That's the mind-picture I
was coming up with.

That's the next thing. You are not charging the battery but yet
feeding it energy. A battery doesn't move, doesn't shine, so that
energy is likely to end up as heat.

That's what I figured, but wasn't sure, so I asked in hopes of getting
confirmation.

If you feed enought energy, almost anything will.

Is that any relation to the observation that "Even a brick flies quite
nicely when you strap a big enough jet engine to it"?

 

[Don Bruder]

Why not let's just call it a wild-ass-guess, shall we?

Sheesh... Gimme a break, John - It's AC. It may have been 30 years ago
that I learned to operate a VOM well enough to distinguish AC from DC,
but underneath the extra functions and LCD displays that show you
numbers an inch high, instead of needing to squint at a needle and
remember which scale you're supposed to be reading from, the basic
functionality and methods are still pretty much the same, y'know?

 

[Bob Eld]

Why not let's just call it a wild-ass-guess, shall we?

Sheesh... Gimme a break, John - It's AC. It may have been 30 years ago
that I learned to operate a VOM well enough to distinguish AC from DC,
but underneath the extra functions and LCD displays that show you
numbers an inch high, instead of needing to squint at a needle and
remember which scale you're supposed to be reading from, the basic
functionality and methods are still pretty much the same, y'know?

Well, it could be and most likely is DC superimposed with AC as one of the
rectifier diodes fails in the reverse direction. In this case it will
probably still charge the battery if only poorly.

If it is truly AC with a low impedance bi-directional drive on both the
positive and negative swing (like a wall plug) then the battery will become
discharged to zero. Something will get warm (hot) depending on the actual
impedances of the source and battery.

The fact (impression) that the ATV apparently still starts indicates that
the battery is not being discharged completely.

You do need to fix it. Sooner or later it will fail completely probably by
becoming open circuit and unable to charge anything.

It is unlikely that the battery would do the Cha Cha Cha. The battery and
alternator might do the Tango though!

 

[Don Bruder]

Well, it could be and most likely is DC superimposed with AC as one of the
rectifier diodes fails in the reverse direction. In this case it will
probably still charge the battery if only poorly.

Fine, let's go with "it's exactly what you're saying", just for gits and
shiggles. Whether it's AC biased into wiggling above or below the zero
line is a detail that just plain doesn't matter - the result is the
same: The battery isn't charging, and it's getting hotter than hell.

If it is truly AC with a low impedance bi-directional drive on both the
positive and negative swing (like a wall plug) then the battery will become
discharged to zero. Something will get warm (hot) depending on the actual
impedances of the source and battery.

I checked the empirical data - I put blisters on my fingertips by
touching the battery case after having the rig running for a while. Yep,
sure enough - It gets hot...

As of this morning, the battery reads somewhere in the 11-14 volt range,
no-load, but immediately drops to about 4-5 volts when I hit the starter
button.

Which pretty much confirms the "not charging" theory, regardless of
whether the juice is a flat line or a wiggly one. (and without any
interest whatsoever in whether the wiggle is above or below the zero
line.)

The fact (impression) that the ATV apparently still starts indicates that
the battery is not being discharged completely.

It starts - By me pulling on the rope. For the time being, I've
disconnected the battery for fear of completely cooking (assuming that
hasn't already happened...) or exploding it.

Pull-starting this thing is a stone BITCH, though... If I'm reading
right, it's a 400CC engine, and as a rough guesstimate (comparing the
effort required to pull the thing to life to the effort involved in,
ferinstance, handling hundred pound hay bales or 50 pound feed bags) I'd
say it takes close to 250 pounds of pull to fire it up. Not fun...

You do need to fix it. Sooner or later it will fail completely probably by
becoming open circuit and unable to charge anything.

It's already at the "unable to charge anything" point. Exact failure
mode seems pretty much irrelevant at this stage. Doing some online
research to find out what fixing it will take is making the idea of
"scrap it and find a different one" look like a viable option.

Apparently this failure is common on this model, and according to
several boards that cater to the ATV community, trying to find the parts
to do the fix is like trying to find hen teeth. And on the off chance
that you DO manage to find a source, the prices are through the roof.
Never mind the "to do this repair, you must remove the engine from the
ATV, then strip the engine down to the point where you might as well go
ahead and take it apart the rest of the way and do a full rebuild"
factor. Which puts the machine out of commission for what I suspect will
be AT LEAST 2-3 days, which in turn puts *ME* out of commission for the
duration of the project, which means that the livestock goes hungry,
which just plain ain't acceptable, PERIOD! Hiring the job out is likely
to cost as much, or more, than just finding a different machine just in
the labor charges, never mind whatever the parts end up costing. (again,
assuming they can be found)

<sigh> If only it were as simple as the tractor, or my car: Loosen the
belt, unscrew two bolts, unplug one connector, remove one nut holding
down another wire, slap new $50-ish unit in place, replace connector,
wire, hold-down nut, and two bolts, re-tension belt, 15 minutes plus
sending somebody to the parts store have elapsed, time to get back to
work!

It is unlikely that the battery would do the Cha Cha Cha. The battery and
alternator might do the Tango though!

The Tango, or the Tango Uniform?

Unfortunately, either way, I'm afraid that tune is already on the
turntable.

 

[Don Bruder]

What about it?

So that we have something to argue about, let's forget about the fact
that to a battery, they're the same animal unless the zero line is being
crossed. You are aware, that a battery will charge just fine (although
it will obviously take longer) off the raw output from a half-wave
rectifier, right? Hard to get much less "filtered" than that, no? If we
were talking about a 'scope trace, it'd be a different story, sure - and
it wouldn't be possible to mistake one for the other unless you were a
blind man. But since we're talking about a battery, it's a distinction
which makes no operational difference.
Great, you got the cover-all. Here's yer fruit basket.

Look, John, I'm not interested in playing games of theoretical pedantry.
In the realm of the lab, or in the math, sure - It's likely to be
important. Perhaps even critically important, depending on exactly
what's being done/attempted.

Here in the real world, where I'm playing, the distinction is utterly
meaningless. I've got a battery seeing what appears to be AC rather than
the expected DC. Whether the appearance comes from piss-poor filtering,
a total lack of rectification, or AC modulation riding on top of a
too-low DC "carrier" voltage means nothing - The battery is effectively
seeing AC instead of the DC it wants.

You guys want to play the pedant game, you go right ahead and enjoy
yourselves. Meanwhile, I've got more important things to worry about -
like how to transport the several hundred pounds daily of feed to (and
resulting "output" from) 20-odd head of horses who don't give a tinker's
dam about electrical theory except in regard to how it bites them on the
ass when they back into the fence.

 

[Bob Eld]

Fine, let's go with "it's exactly what you're saying", just for gits and
shiggles. Whether it's AC biased into wiggling above or below the zero
line is a detail that just plain doesn't matter - the result is the
same: The battery isn't charging, and it's getting hotter than hell.


I checked the empirical data - I put blisters on my fingertips by
touching the battery case after having the rig running for a while. Yep,
sure enough - It gets hot...

As of this morning, the battery reads somewhere in the 11-14 volt range,
no-load, but immediately drops to about 4-5 volts when I hit the starter
button.

Which pretty much confirms the "not charging" theory, regardless of
whether the juice is a flat line or a wiggly one. (and without any
interest whatsoever in whether the wiggle is above or below the zero
line.)


It starts - By me pulling on the rope. For the time being, I've
disconnected the battery for fear of completely cooking (assuming that
hasn't already happened...) or exploding it.

Pull-starting this thing is a stone BITCH, though... If I'm reading
right, it's a 400CC engine, and as a rough guesstimate (comparing the
effort required to pull the thing to life to the effort involved in,
ferinstance, handling hundred pound hay bales or 50 pound feed bags) I'd
say it takes close to 250 pounds of pull to fire it up. Not fun...


It's already at the "unable to charge anything" point. Exact failure
mode seems pretty much irrelevant at this stage. Doing some online
research to find out what fixing it will take is making the idea of
"scrap it and find a different one" look like a viable option.

Apparently this failure is common on this model, and according to
several boards that cater to the ATV community, trying to find the parts
to do the fix is like trying to find hen teeth. And on the off chance
that you DO manage to find a source, the prices are through the roof.
Never mind the "to do this repair, you must remove the engine from the
ATV, then strip the engine down to the point where you might as well go
ahead and take it apart the rest of the way and do a full rebuild"
factor. Which puts the machine out of commission for what I suspect will
be AT LEAST 2-3 days, which in turn puts *ME* out of commission for the
duration of the project, which means that the livestock goes hungry,
which just plain ain't acceptable, PERIOD! Hiring the job out is likely
to cost as much, or more, than just finding a different machine just in
the labor charges, never mind whatever the parts end up costing. (again,
assuming they can be found)

<sigh> If only it were as simple as the tractor, or my car: Loosen the
belt, unscrew two bolts, unplug one connector, remove one nut holding
down another wire, slap new $50-ish unit in place, replace connector,
wire, hold-down nut, and two bolts, re-tension belt, 15 minutes plus
sending somebody to the parts store have elapsed, time to get back to
work!


The Tango, or the Tango Uniform?

Unfortunately, either way, I'm afraid that tune is already on the
turntable.

Well, I guess you'll just have to replace the whole unit. How about getting
one of those diesel "mules" Kawasaki?

Somewhere above I saw that you have 20 horses? Perfect short term solution:
Hitch up a horse to a cart or even to the ATV and you can deliver hay all
day long, just like the old school. What the hell did your grandpa do?

 

[Gerard Bok]

If you just need a band-aid until you can get a proper repair done,
couldn't you just connect a big-ass diode in series with the output lead
from the regulator?

My first guess also. But I didn't mail it, as I realized that a
rectifier in series with the load also forces the source to carry
DC too.
As OP mentioned an altenator, forcing that to carry DC may have
very serious consequences,
And the alternative (one diode in series and one diode over the
source to carry the other halve of the wave) may have rather
serious consequences also (over current situation by almost
shorting half the wave)

 

[Don Bruder]

---
Geez, sorry to get you so upset...

If you just need a band-aid until you can get a proper repair done,
couldn't you just connect a big-ass diode in series with the output lead
from the regulator?

I thought about that, but doesn't that have the potential for some
pretty severe consequences to the magneto, and/or the wiring from it?
Seems that it would be effectively shorting it out each half-cycle,
which I can't imagine being anything like good for it. Assuming, of
course, it isn't fried already... that oddball 6-ish volt reading I'm
seeing at low RPMs has me wondering if it isn't a three-phase setup,
with one or more of the phases fried. On second thought, if that's the
case, where's the 15 volts coming from when I wind up the engine?
(pardon my stream-of-conciousness...)

Of course, if I try the diode trick, there's the "fun" of trying to find
one that can handle the 410 watts the magneto is supposedly rated for.
Let's see... 410/14 is a little under 30 amps, if I haven't misplaced a
decimal point. Biggest diode I can put my hands on right now (Without
going downstairs into the parts box to look for sure, I think the
biggest diode I have on hand is either a 1N1005 or 1N1006) is rated for
an amp or less. Somehow, I suspect all the "magic smoke" would leak out
of one of those in a matter of milliseconds if I dropped it into the
mix. I imagine I could find/order something designed to go in a welder,
but that's likely to be fairly pricey, and take at least a few days to
arrive. Damned if I do, damned if I don't... <sigh>

 

[Don Bruder]

My first guess also. But I didn't mail it, as I realized that a
rectifier in series with the load also forces the source to carry
DC too.
As OP mentioned an altenator, forcing that to carry DC may have
very serious consequences,
And the alternative (one diode in series and one diode over the
source to carry the other halve of the wave) may have rather
serious consequences also (over current situation by almost
shorting half the wave)

OK, that's what I suspected, as posted in my other message - I thought
about doing just that, but then had the suspicion that it might cause
other/more troubles.

I'm not CERTAIN if this thing has an alternator or a magneto - Both
terms get used on the spec-sheet I found, but I don't know if either can
be trusted, since it APPEARS to have been put together by a third party,
rather than being an actual "Yamaha approved" document. If there's an
official Yamaha document available online, I haven't managed to find it
yet, but I'm still looking.

 

[Don Bruder]

Well, I guess you'll just have to replace the whole unit. How about getting
one of those diesel "mules" Kawasaki?

We're looking into that general idea. Meanwhile, it's "pull-start or
nothing" for the forseeable future.

Somewhere above I saw that you have 20 horses? Perfect short term solution:
Hitch up a horse to a cart or even to the ATV and you can deliver hay all
day long, just like the old school. What the hell did your grandpa do?

Heh... While I'm qualified to drive singles, doubles, 4, 6, and 8 horse
teams (Including having driven one of the Budwieser Clydesdale hitches,
and the Coor's Belgian hitch, both in full regalia), the horses here are
all the "prissy" types - they jump and do dressage, they (turn on the
most scandalized "Bonnie Blueblood" inflection you can) DON'T pull
wagons, perish the thought! That's just plain beneath their dignity! Or
so they'd tell you, anyway. None of them are harness-broke, so it would
be a pretty good rodeo for the first few weeks, I'd imagine. Never mind
getting the harness and rolling stock to hook 'em to.

You'd be AMAZED at the price of horse-related leather work... Hell, I'm
in the biz, and *I'M* frequently left speechless when I see the prices
horse-folk pay for horse-related leather goods! As an example, one of
the boarders here just recently bought a headstall - Not a full bridle,
with bit and reins, JUST the part of the bridle that the bit and reins
attach to. If you were *EXTREMELY* generous (and rather creative,
besides) with the measurements, you *MIGHT* be able to figure out a way
to call it 50 square inches of leather. Throw in half a dozen "Chicago
screws" (Basically tiny nuts and bolts, but chrome-plated, and made with
no sharp edges, so that no matter what happens, they can't damage the
horse), four buckles, a few inches of stainless steel wire, and a few
dozen yards of thread, and you've got the whole thing. The price she
paid for it could have easily kept me AND my two horses fed - and fed
WELL - for a month, with money left over for a couple trips to the
movies. A decent harness can run into the price of a car. And that's
just the harness - never mind the bits, bridles, lines, and hookup
hardware that doesn't come as part of the basic "harness" package. You
don't even want to know about how much the price jumps when you move
from the plain-jane "working grade" gear into the "show grade" stuff
with all the silver and spots and crystals and crap... Just thinking
about those prices is enough to give a guy nosebleeds and altitude
sickness!

On the other hand, there IS the entertainment value to be considered - I
can imagine the scene... Jane Boarder drives up to see her precious
high-points jumper hitched to a cart full of shit. She immediately goes
into full freak-out mode, causing her blood pressure to jump so high
that her head explodes like a cantaloupe in a microwave oven...

Of course, the downside of that is me being the one who would have to
sweep/scrape/shovel up and dispose of the mess... <bleah>