Winston wrote:

Michael A. Terrell wrote:
"DoN. Nichols" wrote:
On 2009-05-08, Michael A. Terrell wrote:
wrote:
On Thu, 07 May 2009 18:21:54 -0800, "Paul Hovnanian P.E."
wrote:
[ ... ]

And there are two diodes in series.
And you sure as heck won't be pumping 115 volts into the battery!!!!!!

Here is the newer rectifiers for alternators.

http://www.ixyspower.com/images/technical_support/Application%20Notes%20By%20Topic/Automotive%20Applications/IXAN0018.pdf
Actually -- that is not a bridge rectifier to convert three
phase AC to DC, but rather a bridge of mosfets to convert DC to three
phase AC -- as in a VFD. (It will need more logic to drive the gates to
do it right, but that is at least a start.)

Not at all sure that the voltage ratings there have any bearing
on what would be found in an alternator. Instead, it is described as
being to drive things in the automobile which *need* three phase



The same circuit can be used as an active rectifier. It has the
advanage of a lower Vf, which reduces the heat generated in the
alternator housing. It also means that trying to use it as a straight
single phase rectifier won't work.

Three phase synchronous rectifier?
Very kewl idea!

But,

1) They appear to be using the MOSFET body diodes to do
~ 10% of the rectification rather than using them as
voltage clamps (protection devices). This appears odd.

2) Though the MOSFETs *are* bidirectional, they are shown
installed 'backwards' from conventional usage.
During power production, the drains are negative in relation
to the sources. Strange.

3) I didn't see the gate drive circuit for the MOSFETs.
I assume it includes a charge pump to keep the high side
MOSFETs saturated during peaks.

4) This is a bridge all right but it's really to be used as
a source of 3 phase power, not a rectifier. Look at it
that way and items 1 and 2 are non - issues because
the current would flow in the opposite direction.


What is shown in a data sheet is never the full schematic. they
always have errors, on purpose, to prevent a direct copy.

Synchronous rectifiers have been around since at least the '40s, in the
form of synchronous vibrators. More that one OEM mentions FET power
rectification in their automotive sections.

--

Don't *faff*, dear.


--
You can't have a sense of humor, if you have no sense!

Winston writes:

?Short? I do agree that current limiting will be a major issue.

228 A through a 50 A alternator. Until a real short shows up,
this will do nicely.

So your portable one-lung generator will source 228 amps? At 120V that
means 27 KW. The small portable gas generator in my garage is a lowly
0.75 KW; I'm jealous..

A friend has a 7.6KW model for his house; when his 5KW well pump starts,
it audibly stumbles for a few seconds and recovers; even when it is the
sole load. If he has other loads on it, it sometimes just stops.

In short, the model involves some non-linear components; pretending
they are linear won't do justice. (No rotating generator can be modeled
as a pure voltage source.) For example, if the battery is quite dead,
its resistance will be quite high & it will not take a charge at
first. Patience shall be required.

If he can get the generator to idle; that will be a big help.

The only weakness in Pete and Paul's otherwise brilliant solution is
that Clack implied that we cannot change the voltage coming from the
generator:

"(...)power from the generator which is making 110 volts
AC(...)"

Based on 20 years of listening to Click & Clack; I'd say their Puzzler
limits are not THAT cast in stone. (But then, I just watched Kirk beat
the Kobayashi Maru exercise.) After all, it is described as an "electric
drill" he has, not an "electric motor with chuck that can drill holes OR
spin the alternator.."

You can try using the drill, but the trigger speed control may object.

I suspect that the drill will run happily (at significantly reduced RPM).
It has a source of DC that pulses from 0 to ~150 V to 0 every 16.66 mS.
We only need it to run for a few minutes so cooling shouldn't be an issue.
Lock the trigger down full and try the headlights in a few minutes.

One issue on the drill is while its nominal reactance is well suited for
our needs; it will draw a lot more in locked rotor mode. If it does not
quickly get out of that mode and to a reasonable RPM, will it still
be a suitable current limit....?

If he has a plastic bucket, water, and some salt [including that
morning's used beer]; he can use a salt water bath resistor scheme. I
know of a supersonic 10'x10' wind tunnel that uses that approach.

Drill is *much* safer and much faster to implement. And *way* more
pleasant to be around.

Salt water resistors are used in some interesting places. For example,
for the 87,000 HP drive motor system on a NASA wind tunnel.

I suspect the salt in new beer is sufficient...but agree it would be
a sin to waste beer..


With no DVM, you could use a headlamp as a current indicator; dim
will be several amps; full brightness is ~10A.

Or one could look at the drill motor nameplate and subtract ~60%.

Lamp is at least resistive, and linear over the DCish waveform.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

David Lesher wrote:
Winston writes:

?Short? I do agree that current limiting will be a major issue.

228 A through a 50 A alternator. Until a real short shows up,
this will do nicely.

So your portable one-lung generator will source 228 amps? At 120V that
means 27 KW. The small portable gas generator in my garage is a lowly
0.75 KW; I'm jealous..

The generator is an unknown. Is it a 6 cyl. diesel behind the cabin
or a nice little Honda inverter?

All we know is that our intrepid cabin builder will get nowhere fast
by connecting it to the truck without any current limiting.
The generator is not going to 'grunt and supply'. It will
fail safe or short out or it will take out the alternator and attached
wiring. None of these options will get our guy back on the road and
to dinner.

One issue on the drill is while its nominal reactance is well suited for
our needs; it will draw a lot more in locked rotor mode. If it does not
quickly get out of that mode and to a reasonable RPM, will it still
be a suitable current limit....?

It will be out of 'locked rotor' mode very quickly.
As you point out, these drills use phase modulation to control speed.
I figure that 90% of half wave should spin the drill at about 40%
of maximum RPM with no mechanical load. That'll do and it'll charge
our guy's truck battery at a fast, yet safe rate.

(...)

Or one could look at the drill motor nameplate and subtract ~60%.

Lamp is at least resistive, and linear over the DCish waveform.

I didn't see a lamp in the inventory. A headlamp will have
only 10% of the resistance we need anyway.

I am embarrassed for not suggesting that our intrepid cabin builder
just swap out his battery for the charged one in the back of
his truck. If you can materialize objects into the scenario, I can
too, right?

MR. SPOCK: Say again, captain? You want me to beam down
a *truck battery*?

CAPT. KIRK: Yes and don't suggest that I should mine some
lead and begin looking for some lemons.



--Winston



--

Don't *faff*, dear.

On Sat, 9 May 2009 14:12:04 +0000 (UTC), David Lesher
wrote:

writes:

The generator, the alternator, and the battery are connected to each
other; and NOT to anything else in the car. {Well; hot side; they share
ground.}

Actually you are not correct in your assumption. The radio on almost
all cars in the last 20 years is permanently connected to the battery.
Clock too. EFI computer and trans computer as well. Not to mention the
power lock control if so equipped.

Please explain how the above are "permanently" connected to the
battery. Every car I have ever seen [even British ones!] has a
removeable, replaceable, battery. You unbolt either the old top post
clamp; or the new banjo side terminal bolt. When you do, everything is
disconnected. Pull both cables and the mounting bolt; you can take the
battery out of the car!

[Of course, GM could have now come up with a car with a non-replaceable
battery. They ARE the people who welded the doors in place on the
Vega. And Apple sells iPods, iPhones and laptops where you have to junk
the gadget when the battery dies; so are cars far behind?]


The last descriprion, where the output from the alternator of the
vehicle AND the pos of the battery are disconnected, and the output of
thew (115vAC) generator is connected to the battery POST and the
alternator output TERMINAL addresses all the issues.

By "permanent" connection I meant unswitched and simply removeing
either the alternator output OR the battery positive and connecting
the genset would have subjected those devices to possibly harmfull
voltage conditions.

jeff_wisnia wrote:

Joe Pfeiffer wrote:

jeff_wisnia writes:


I'm thinking that all else left alone, it probably doesn't matter
which way the shaft of an automobile alternator is rotated since the
machine produces ac which is then rectified to create a polarized dc
output.

Am I right about that?

The question came up just now when eldest son and I were kibitzing
about this week's "Car Talk" puzzler:

http://www.cartalk.com/content/puzzl...918/index.html



My drill is reversible, so it doesn't really matter anyway...



And all my 120 volt drills turn only CW. (That tells ya
how olde they (and I) am. G

Son just pinged me to say that if you ran the alternator belt over the
alternator pulley and then over the drill chuck you could point the
drill in the appropriate direction. That may be the answer the Car Talk
guys are looking for, as it's not likely there'd be enough room under
the hood to connect the drill through a socket directly to the
alternator shaft nut.

But, you could always unmount the alternator and.......

Jeff



The "official answer" from the Car Talk boys is:

http://www.cartalk.com/content/puzzl...18/answer.html

But I do have trouble buying it, there just can't be very many vehicles
around with enough physical space in front of the alternator pulley to
cram a typical 120 volt electric drill into.

But maybe I don't know where the "chock" is on a drill. G

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

On May 4, 3:09 pm, Cydrome Leader wrote:
jeff_wisnia wrote:

I'm thinking that all else left alone, it probably doesn't matter which
way the shaft of an automobile alternator is rotated since the machine
produces ac which is then rectified to create a polarized dc output.

Am I right about that?

The only issue should be the cooling fan. If it spins the wrong way, it
won't cool anything.

I built an inboard boat. Chev 283. The alternator hung off one
side too far, interfering with the sidewalls of the compartment, so I
made a new bracket and turned the alternator around, facing the engine
and closer to centerline. The angled-blade fan I replaced with a
straight-blade fan (blades directly radiating from shaft) from the
junkyard, some cars had them and it doesn't matter which way they
turn. That alternator ran for hundreds of hours before I sold the
boat. The brushes in all the alternators I've had apart point straight
at the shaft and they don't care about rotation unless they're badly
worn and the holder has let them cock and wear at an angle. The output
will be the same in either direction.

If the battery is totally dead the alternator won't pick it up.
Its rotor won't hold enough magnetism to generate enough voltage to
overcome the diode drops, especially if there's any load present, as
there always is. Leaned this the hard way, towing a dead truck to try
to start it. Engine turned merrily but would not fire. Had to jump it.
Generators, on the other hand, have field pole shoes that will carry
enough flux to bootstrap the system. No diodes there.

In about 1977 I bought, for $27.95, a black box that, once wired
into my pickup, would generate 110VDC for series-wound power tools and
the like. Before I put it in I took it apart to see what I had paid
$28 for. It was: One plastic box; one 110VAC household duplex outlet;
one DPDT toggle switch, one neon lamp assembly (NE-2H, IIRC), and one
resistor of something like 33K. Total cost in those days of about $4.
The outlet was wired through one pole of the DPDT switch to the
alternator output. The other throw of the same pole went to the
battery +. The other pole of that switch simply switched the
alternator's field between the regulator and the battery +. The neon
assembly, with its suitable resistor to make it fire at 110V, was
across the duplex outlet's terminals. So with the switch "off,
everything worked normally. With it "on," the field got full battery
voltage and the alternator's output, freed of the battery via the
switch, generated increasing voltage as the throttle was opened until
the light lit up and you wnt to work for ten of 15 minutes, then
switched back to normal for a minute or so to recharge the battery.
The diodes in the alternator took this for as long as I had the truck.
My only peeve with it was being hosed so badly for a handful of
cheap parts. No magic in that box at all. Disappointing. $28 in 1978
was worth something. I could rent an airplane for an hour for not much
more than that.

Dan

On Mon, 11 May 2009 18:05:09 -0400, jeff_wisnia
wrote:

jeff_wisnia wrote:

Joe Pfeiffer wrote:

jeff_wisnia writes:


I'm thinking that all else left alone, it probably doesn't matter
which way the shaft of an automobile alternator is rotated since the
machine produces ac which is then rectified to create a polarized dc
output.

Am I right about that?

The question came up just now when eldest son and I were kibitzing
about this week's "Car Talk" puzzler:

http://www.cartalk.com/content/puzzl...918/index.html



My drill is reversible, so it doesn't really matter anyway...



And all my 120 volt drills turn only CW. (That tells ya
how olde they (and I) am. G

Son just pinged me to say that if you ran the alternator belt over the
alternator pulley and then over the drill chuck you could point the
drill in the appropriate direction. That may be the answer the Car Talk
guys are looking for, as it's not likely there'd be enough room under
the hood to connect the drill through a socket directly to the
alternator shaft nut.

But, you could always unmount the alternator and.......

Jeff



The "official answer" from the Car Talk boys is:

http://www.cartalk.com/content/puzzl...18/answer.html

But I do have trouble buying it, there just can't be very many vehicles
around with enough physical space in front of the alternator pulley to
cram a typical 120 volt electric drill into.

But maybe I don't know where the "chock" is on a drill. G

Jeff
Click and Clack are idiots anyway.

wrote:
On Mon, 11 May 2009 18:05:09 -0400, jeff_wisnia
wrote:


jeff_wisnia wrote:


Joe Pfeiffer wrote:


jeff_wisnia writes:



I'm thinking that all else left alone, it probably doesn't matter
which way the shaft of an automobile alternator is rotated since the
machine produces ac which is then rectified to create a polarized dc
output.

Am I right about that?

The question came up just now when eldest son and I were kibitzing
about this week's "Car Talk" puzzler:

http://www.cartalk.com/content/puzzl...918/index.html



My drill is reversible, so it doesn't really matter anyway...



And all my 120 volt drills turn only CW. (That tells ya
how olde they (and I) am. G

Son just pinged me to say that if you ran the alternator belt over the
alternator pulley and then over the drill chuck you could point the
drill in the appropriate direction. That may be the answer the Car Talk
guys are looking for, as it's not likely there'd be enough room under
the hood to connect the drill through a socket directly to the
alternator shaft nut.

But, you could always unmount the alternator and.......

Jeff



The "official answer" from the Car Talk boys is:

http://www.cartalk.com/content/puzzl...18/answer.html

But I do have trouble buying it, there just can't be very many vehicles
around with enough physical space in front of the alternator pulley to
cram a typical 120 volt electric drill into.

But maybe I don't know where the "chock" is on a drill. G

Jeff

Click and Clack are idiots anyway.


I can't agree with that statement, Claire.

They are merely playing to the level of their current radio audience,
and their show has remained on the air for over 30 years now.

Both of them graduated of my alma mater a few years after I did and in
1999 that school (MIT) honored them by having them as that years's
commencement speakers.

I've met them both a few times in a non-radio show setting and they sure
didn't sound like idiots to me.

And I still get a chuckle if I'm in Harvard Square, Cambridge and see
"Dewey Cheetham and Howe" on that office window

http://image07.webshots.com/7/0/25/8...3kDHlbw_fs.jpg
Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

On Sun, 17 May 2009 17:23:43 -0400, jeff_wisnia
wrote:

wrote:
On Mon, 11 May 2009 18:05:09 -0400, jeff_wisnia
wrote:


jeff_wisnia wrote:


Joe Pfeiffer wrote:


jeff_wisnia writes:



I'm thinking that all else left alone, it probably doesn't matter
which way the shaft of an automobile alternator is rotated since the
machine produces ac which is then rectified to create a polarized dc
output.

Am I right about that?

The question came up just now when eldest son and I were kibitzing
about this week's "Car Talk" puzzler:

http://www.cartalk.com/content/puzzl...918/index.html



My drill is reversible, so it doesn't really matter anyway...



And all my 120 volt drills turn only CW. (That tells ya
how olde they (and I) am. G

Son just pinged me to say that if you ran the alternator belt over the
alternator pulley and then over the drill chuck you could point the
drill in the appropriate direction. That may be the answer the Car Talk
guys are looking for, as it's not likely there'd be enough room under
the hood to connect the drill through a socket directly to the
alternator shaft nut.

But, you could always unmount the alternator and.......

Jeff



The "official answer" from the Car Talk boys is:

http://www.cartalk.com/content/puzzl...18/answer.html

But I do have trouble buying it, there just can't be very many vehicles
around with enough physical space in front of the alternator pulley to
cram a typical 120 volt electric drill into.

But maybe I don't know where the "chock" is on a drill. G

Jeff

Click and Clack are idiots anyway.


I can't agree with that statement, Claire.

Clare, not Claire - and if they are not idiots they are playng to the
lowest common denominator.
Their show is more humour than mechanics the few times I've had the
opportunity/inclination to tune in. Mebee I just hit them on their off
days.

They are merely playing to the level of their current radio audience,
and their show has remained on the air for over 30 years now.

Both of them graduated of my alma mater a few years after I did and in
1999 that school (MIT) honored them by having them as that years's
commencement speakers.

I've met them both a few times in a non-radio show setting and they sure
didn't sound like idiots to me.

And I still get a chuckle if I'm in Harvard Square, Cambridge and see
"Dewey Cheetham and Howe" on that office window

http://image07.webshots.com/7/0/25/8...3kDHlbw_fs.jpg
Jeff

jeff_wisnia wrote:

And I still get a chuckle if I'm in Harvard Square, Cambridge and see
"Dewey Cheetham and Howe" on that office window

http://image07.webshots.com/7/0/25/8...3kDHlbw_fs.jpg


You can't cheat a honest ham.


--
You can't have a sense of humor, if you have no sense!