Thanks for bringing it back, mike. I've been reading all the posts very
Anyway, as an update, no delayed effects yet, thankfully. Though I'm
not willing to repeat the "experiment" anytime soon: Seems like I have
a shorted rectifier in the alternator. (Does this mean that I'm getting
voltage spikes all the time?) I'm wondering if the battery is now
"absorbing" the spikes, so it seems to boil down again to whether the
battery is acting as a large capacitor..
Thanks again to everyone.
In my experience, yes, you can expect to be getting ripple of about 1/2 volt
to 1 volt even with the battery connected. It should be measurable with a
DVM on AC voltage setting, measuring across the battery with the engine
running. If diodes in two phases (out of the three phases most alternators
use) fail the AC voltage can be over 1 1/2 volts with the battery connected.
On an oscilloscope it looks pretty radical. With one phase out the voltage
hangs around 14 volts and drops when the bad phase is called on to put out.
With two phases out the voltage hangs around 12 volts and spikes upward.
Applying AC straight from one phase of the alternator's output would harm
the battery,causing excessive heating.On one-half of a cycle,the battery
would charge just like the other phase outputs,but on the 2nd half cycle,it
would discharge(thru the ALT),maybe even provide a path for damaging
currents to be drawn from the battery.It depends on whether the diode
failed open or short/leaky.
Open failure would just remove that phase winding's output,lowering the
alternator's total output current,and giving more ripple.
Not even close. The smaller the plates of a capacitor, the less the
capacitance. The further apart they are, the less the capacitance. Lead-acid
battery plates are EXTREMELY small and EXTREMELY far apart compared to a true
If you were to drain the water from a battery and measure the capacitance, I
suspect you'd find it in the low microfarads, if not picofarads.
Sure. The capacitance I mention is more of an apparant capacitance.
It's not true capacitance per say, but the normal operating car battery
does provide a large apparant capacitance to the system. But this would
not be the case with a non functioning battery.
I use car and deep cycle marine batteries to run radios here in the
My chargers are unfiltered, but yet I have little noise to my radios.
The use of my battery as a cap is a bit different in operation vs a
capacitor, but the final apparant filtering is still there. If the
not acting as a cap of sorts, I would have hash and trash out the
I don't know if this makes any sense, as it's hard for me to describe
like this off the top of my head..
As a quite dangerous test you could try running a car radio off the
alternator with no battery connected. I bet it will be quite noisy,
unregulated as far as volume, etc vs rpm. IE: if the rpm dropped too
the radio might totally drop out due to the low voltage.
Hook the battery up, and all is smoothed out. Both as far as
and also filtering. If thats not acting like a large "apparent"
I don't know what is. The operation is different, but the end results
about the same. This is not something I've really thought about too
but I've always considered the usual operating car battery to have many
farads of capacitance, at least as far as overall function. Maybe not
in the strict sense, as far as true caps go, but as far as the end
of placing it in the system. I dunno if this makes any sense or not..
I've taken two direct strikes to my antenna mast in the last 5 years.
No damage at all. But...I ground out my feedlines when storms are
in the area. The strikes hit about 15 ft from where I'm sitting at this
puter. I was sitting here both times.
My mast is very well grounded, with low resistance. When
a strike hits that mast, it's very quiet. Sounds about like a light
bulb being thrown on the ground, and then a loud sonic boom
directly overhead. Pretty wild.. But I have no trouble at all. My
puter doesn't even flinch. You can set the station up for full time
use, even with direct strikes, "all broadcast stations are set up
this way", but it takes a detailed installation using a ground
careful single point grounding, suppressors, etc, etc.. I'm too cheap
lazy to mess with all that. :/ I just manually ground the feedlines at
As far as the car, yes, it's not good to unhook the alternator while
running. You got lucky. Many cars would have done a toasting of the
alternator in record time. You dodged the bullet this time it seems.
If it did have a problem from doing that, it will usually be blown
I would think.
Try Central Florida,the lightning capital of the US.
Also,the power density of Florida strikes are on average twice that of
northern lightning strikes.
I've had a pine tree about 300 ft from my apartment(tallest in the area)
get struck(and killed) while I was watching. The bolt travelled right down
the side,blowing a channel of bark off the tree. It took out a surge
protector on my phone line and my modem,didn't harm the phones or the
The problem is that alternators are very inductive. Without a battery,
changes in current produce wild fluctuations in voltage; suddenly reducing
the current draw by half should roughly double the voltage for a moment. At
low current I would expect the alternator and regulator to go into
oscillation without a battery to stabilize it.
The battery does as Jim said. But another condition called load dump
could have created a destructive transient. Load dump is defined by
the ISO to be as large as 270 volts on the 12 volt system. SGS
Thompson defines it as 80 to 100 volts. But then better automobiles
are designed with electronics that make load dump not destructive.
Of course when you connect a computer to the car using a discount
inverter, does it have load dump protection - or did you just save some
The damage, if it occurred, would be complete in milliseconds.
Apparently you did not suffer load dump damage. But you, like many
others who replied here, should know of load dump and what automotive
electronics (properly constructed) cost more money.
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