Topic: Will I make it home (battery)

[bggann]

I find the discussion my little battery question started quite intersting - particularly to somebody with a EE degree(s).  This discussion has had a lot more basis in fact and reality that many of the electrical discussions I see.  I also run the audio/visual systems at churches and the discussion groups about audio/video are full of more myth about electricity than fact. 

This discussion has been just stock full of really good information - the rundown on power consumption was incredibly useful for my 'power plans' - and yes - I know that the Dyna 5ohms will not use less power than Honda 5ohms - now that I know the Honda's are 5 ohms (thought they were 3) - although there is the whole 'on/off' time part..  But if I'm gunna spend that power - a hotter spark seems is worth it.

Twotired - too bad so much today is "IC's" and unrepairable - this has, IMHO, stolen much of the practical learning from our younger generations.  I learned most of this stuff while building shortwave radios - from (what was the name of that company - started with an "H" I think.). My Bogan stereo had tubes - and that was great!  One of the real joys of my 400f is I can work on her - which I can't do with my car really  (Drive a chevy HHR).

There are really only a few key laws you need to know for electrics at the level of a cb400f.  One is Ohm's law - which I've seen stated here a number of times.  Ohm's law relates:

Power, voltage, current and resistance.  That covers everything on the bike but the alternator, and for that you need Maxwell's laws.

The "water" standard is think of Voltage as "pressure" as in water pressure.  Think of current (I) as flow - as in gallons per minute.
R - resistance is the resistance of water in the pipe.

Intersting history - Westinghouse (I think) and Tesla (sure) - fought AC/DC battles.  Tesla was an advocate of AC (and he was right).  Westinghouse (I think) was an advocate of DC.  One of the things Westinghouse did was point out that the Electric Chair used AC - so AC must be dangerous.

Actually, current is what is dangerous - AC/DC doesn't matter - within limits.  (At very high frequency, AC does not penetrate, but stays on the 'surface' of the conductor.  What this means is that when I was younger, me and my compatriots built a Tesla Coil - which is basically a high frequency step up transformer.  250,000 volts at some thousands of cycles per second (can't remember what the frequency was).  We coud pull 1-2 foot arcs (sparks) from the tesla coil to a wrench in your hand- and the current would flow down "your skin" to the ground.  Tended to leave burn marks in your soles - but didn't kill you).

It also destroyed all TV reception in the neighborhood.....

High Voltage was fun if you survived.

Back to Ohms law...

So - lots of pressure = Lots of voltage
Lots of flow (big pipe) = lots of current.
Little pipe = large resistance

The equations are:
V=I*R or
Or - I=V/R

The power (DC) is 
P=V*I (voltage times current). 1 amp at 12 volts = 12 watts.  At 60 Hz (household) - this works for AC too.  For AC, you use Z = Impedance, instead of R= Resistance, so for higher frequencies, Z changes.  But I digress.

You can substitute these things around
P=V*I and I=V/R - then P = V*(V/R)= V²/R. 

When you get into alternators - rotating machinery - it is MUCH more difficult.  Heck - I was having trouble following the magnetic flux discussions - and I used to teach EM theory at the college level (been a while).

Rectifiers =  bunch of 1 way valves in the pipe.  Think of the water flowing in and out of a pipe going into the bottom of a bucket.  With no 1-way valve, it does not fill the bucket.  With a one way valve - the water flows "into" the bucket, but when it flows out - the valve closes and stops it.  Sooner or later, the bucket (battery) fills.  The only limit is the pressure in the bucket (the voltage of the battery and the charging system.) If the pressure in the bucket is to higher than the pressure in the pipe - the valve does not open and the bucket (battery) does not fill (charge).

Diodes = they are the 1 way valves.   A rectifier is a bunchodiods in a certain configuration.

Direct Current (DC) = flows one way like water in the pipe.

Alternating Current (AC) = flows back and forth - would have a hard time filling the bucket with this w/o the 1-way valves.

Advantages of AC over DC = transmission loss.  We could not have the power grid today using DC because most of our power would be lost in the resistance of the wires.  With AC, you can step the voltage up and cut the current down and still deliver power

(remember P=V*I.  So 10 watts can be 1 volt at 10 amps, or 100 volts at .1 amps or 1000 volts at .01 amps.)

But - why do we have an "alternator" in the bike?  Don't need long transmission lines there and the lights and stuff are all "DC"  (remember, can't store AC in a battery).  Weight.  Alternators are lighter.  So it is lighter to put an alternator and rectifier (to convert the AC to DC) than a generator (Generators generate DC Current).

Well - I'm rambling - but I'm jazzed by all the neat learning that is going on here. 

BGann again.

[TwoTired]

Twotired - too bad so much today is "IC's" and unrepairable - this has, IMHO, stolen much of the practical learning from our younger generations.  I learned most of this stuff while building shortwave radios - from (what was the name of that company - started with an "H" I think.).

You thinking about Heathkit?

[alltherightpills]

Thanks a lot for the links TT.  I am going to print some of that stuff out so I can actually read it.

Thanks Bggann for taking the time to type that out.  I copied and pasted it into a document so that I can print it out.  It's starting to make more sense now.

Part of the reason why I wanted an old bike was so that I could learn how to do stuff and I wanted to learn how things work.  I appreciate the mechanics of a carb more than I do the computer programming of a fuel injection system.  If it's mechanical and it breaks you can probably fix it yourself.  If it is a computer and it breaks, well you are probably up a creek.  I think this has not only created a generation who doesn't know how to fix stuff, it has also created a generation of stuff that can't be fixed and is therefore thrown away only to be replaced by more things that will break and not be fixed.  Sorry for the slight hijack.  Please continue on with your electrifying discussion.  (Sorry, I couldn't resist)

[bggann]

You thinking about Heathkit?

Yeah- of course - how could I forget.  Built a number of Heathkit projects.  Then I got a car and graduated to beefing up the stereo in it.

Learned about fuses the time I shorted the 10ft line running from my battery (under the back seat) to the fancy radio.  Filled the car with really nasty smoke..

[TomC]

Hi Bggann
     "But - why do we have an "alternator" in the bike?  Don't need long transmission lines there and the lights and stuff are all "DC"  (remember, can't store AC in a battery).  Weight.  Alternators are lighter.  So it is lighter to put an alternator and rectifier (to convert the AC to DC) than a generator (Generators generate DC Current)."
     Generators do not generate DC current. They generate AC current and use a mechanical rectifier. The commutator in a DC generator converts AC to DC by connecting coils as the current is flowing in the same direction. Commutators leave some thing to be desired. At high speed they fly apart. At any speed they seen to be what limits the amount of current that a generator can output. This is one of those design problems. Put more copper in the segments of the commutator to conduct more current. More copper means more weight so more likely to fly apart as it gets spun faster. Look at the commutator of a generator then look at a slip ring on an alternator. Which is easer and cheaper to make? My guess is cost of manufacture is the real reason for the switch from generators to alternators.
          TomC in Ohio

[TwoTired]

DC generators have a commutator and brushes.  These wear and produce dust as the commutator sections saw into the brushes. A closed system means that dust is retained to interfere with operation.   Also, pulling 10-20 amps out of a commutator requires substantial surface area, meaning a large commutator, brush, brush holder, etc.  Further, DC Generators have the large currents developed in the armature, these bulky windings are subjected to ever greater inertial forces as the RPMs increase. The winding insulation is highly stressed under these conditions.  Finally, there is the inertial mass's resistance to speed change that slowe engine rev up response in small displacement engines.
At high RPM, drawing current through the fast moving commutator/brush interface becomes more difficult.  Usually requiring multiple brushes and a bigger commutator segment section on a larger diameter commutator.  But, this is a trade off, as larger commutator diameters are subject to higher centrifugal forces.  Commutator segments are bound together with an insulative resin, whose adhesive qualities are taxed under the effects of brush contact heating and centrifugal forces trying to remove the commutator segments from the armature.  You could design a speed reduction device so the armature spins slower than the crankshaft.  But, that adds complexity, bulk, and weight, too.
A 10,000 RPM,  150 Watt DC generator, I would expect to weigh twice what the alternator in the SOHC4 does, and have a far shorter maintenance free life.

Even slip rings in Alternators incur brush repair intervals.  But, only the small weight/wire size field coil is powered with relatively low currents (~2 amps) and has a fairly small rotating mass.  Even so, these rotors imply centrifugal stress on the windings, the winding wire insulation breaks down, causing field coil shorts and operational failure.

The early SOHC4 alternator, has all the major output current flowing through a fixed position Stator.  The field coil is also stationary.  Only the rotor pole pieces rotate which are simply, formed lumps of metal.  It is essentially maintenance free.
Which, many might determine is a fair trade off for a non-linear output characteristic.

That's just my unsolicited thumbnail analysis...

Cheers,

[bggann]

    Generators do not generate DC current. They generate AC current and use a mechanical rectifier. The commutator in a DC generator converts AC to DC by connecting coils as the current is flowing in the same direction. Commutators leave some thing to be desired. At high speed they fly apart. At any speed they seen to be what limits the amount of current that a generator can output. This is one of those design problems. Put more copper in the segments of the commutator to conduct more current. More copper means more weight so more likely to fly apart as it gets spun faster. Look at the commutator of a generator then look at a slip ring on an alternator. Which is easier and cheaper to make? My guess is cost of manufacture is the real reason for the switch from generators to alternators.
          TomC in Ohio

TomC is of course correct, a "DC Generator" is really an AC generator with a mechanical rectifier.  I was taking a more macro view as I didn't want to dive into the details of what is inside.  In other words, a "DC Generator" must have the commutator inside it - it is part of the function.  So what you get on the output terminals is rectified (albeit, not all that cleanly) DC current.  In an alternator, the rectifier is a separate part - sometimes mounted on/in the alternator (most automobile alternators these days have the rectifier built in, or at least "mounted" in it - as is the VR).  In many older applications, the rectifier is bolted on somewhere external.

The other distinction is that an alternator can work just fine without a rectifier -but it creates alternating current.  The DC generator, because the 'rectifier' is part of it, will not.

As for speed - at the higher reaches of 10K and so, brushes and such are a problem and they do require maintenance.  All part of the reason that alternators (and AC induction motors) became popular.

Today - virtually all power (except solar cells and some wind turbines) is generated by alternators.  They typically rotate at 1800 or 3600 RPM (unless you are in a part of the world that runs at 50Hz, then the rotational speed will be different). 

BTW - I was wrong about the Tesla/Westinghouse battle.  Westinghouse was on Tesla's side in the AC/DC battle, it was Thomas Edison who promoted DC.

There are some real advantages to DC.  You can store it in batteries.  You can parallel DC generators easily (you must precisely match the frequency and phase of AC generators, or they will smoke each other - and I mean _precisely_.  It is really pretty amazing that the AC power grid works at all given how carefully the frequency and phases need to be matched.)

Anyway - yes - a DC generator is an AC generator with a 'mechanical' rectifier.

As for why Alternators in cars now (the transition happened in the 60/70's).  Cost, size - they are really different expressions of the same thing. 

Of course, all of this is realtively mute as the bikes all have alternators....

[Spikeybike]

I wonder how many readers out there have glazed eyes?

this thread reminds me how much i really don't know

[TomC]

Hi Baggann
     "The other distinction is that an alternator can work just fine without a rectifier -but it creates alternating current."
     I have a Bultaco that runs the lights and horn on AC. No battery of course.
          TomC in Ohio
PS Baggann looks like you were about 1 1/2 years old when Chrysler Corp. introduced alternators across the board.

[bggann]

Hi Baggann
     "The other distinction is that an alternator can work just fine without a rectifier -but it creates alternating current."
     I have a Bultaco that runs the lights and horn on AC. No battery of course.
          TomC in Ohio
PS Baggann looks like you were about 1 1/2 years old when Chrysler Corp. introduced alternators across the board.

Cool - what runs the ignition?  Is there a rectifier - or does it use a magneto (or is it diesel )
I wasn't working as a mechanic yet at 1 1/2... - never really did much work on Chryslers anyway.  Were they as peicemeal then as they were later (meaning - they changed the parts on a whim..)

(Never been called bag-gann before.... new nickname! )

[TwoTired]

I wonder how many readers out there have glazed eyes?

this thread reminds me how much i really don't know

If you're smart, that's something you'll realize throughout your life.
IMHO

[Spikeybike]

If you're smart, that's something you'll realize throughout your life.
IMHO

well put , my friend