Re: My Yamaha Generator Arrived Yesterday

On Thu, 15 Dec 2005 11:29:46 -0800, altar@xxxxxxxxxx wrote:


>>Not really. My Cordless Battery Charger produces 150 amps max, weighs
>>around 40 lbs and isn't much larger than a 5 gallon gas can. 150 amps
>>at 15 volts is still just 2250 watts, not a large unit at all. About
>>the size of an EU2000. In fact, the first time I find an EU2000 with
>>a burned out inverter, I'm going to grab it, rewind it for 12 volts
>>and make yet another CBC.
>
><sigh> I should only have that much talent.
>
>Tom

(Thanks, BTW). You probably do, you're just not using it. It takes
two basic things to do stuff like this. First, the willingness to
step way outside the box and color outside the lines. Second, a good
working knowledge of the First Principles that govern whatever field
you're poking around in. First Principles are the basic physical and
chemical laws that govern things. Ohm's Law, Maxwell's law and stuff
like that. This is hands-on, working knowledge and not book learning.
I started learning First Principles about electricity and motors in
the early grade school era when my dad (who was a CPA and not a nerd)
would sit down with me and we'd make elemental motors, generators and
such out of nails, bell wire and wood.

Anyway, some First Principles for converting an EU to a CBC. I know
that for a given magnet strength, the voltage generated is
proportional to both the number of turns of wire in the coil and the
speed of the magnet. That's really the most important one.

When I get the EU, I'll take it apart, then lop off and discard the
inverter. Next I'll crank the engine and run it at some known RPM,
say, 1000, and measure the phase to phase voltage. I'll write that
down.

Next, I'll remove the stator and study it carefully. I'll identify
each of the three phase windings and count the turns. I'll also
figure out if it is wired delta or wye, almost surely wye.

Since I know the turns and the voltage at a given RPM, I can compute
the volts per turn at that speed. Since both the volts vs speed and
volts vs turns are linearly proportional, I can compute the values at
any other speed.

Let's say that the phase voltage is 150 volts at 1000 RPM and there
are 75 turns. 1000/150 = 6.667 revs per volt. 150/75 = 2 volts per
turn.

I want to use the maximum HP the engine can make so I want the voltage
at the highest power demand to be made at the peak HP. The highest
power demand will be at the end of the bulk stage when the current is
still constant but the voltage has risen to the transition point. 14.8
or thereabouts. Let's call it 15 to account for losses.

I'm guessing that the engine makes its peak power at 4000 RPM (I'd
measure it in real life). By simple ratios:

The voltage at 4k = 150 * (4000/1000) = 600 volts.

I want 15 volts at 4000 RPM so I change the number of turns, again a
simple ratio.

75 turns * (150/600) = 18.75, call it 19 turns.

(I'm drawing out the math to make things clear. I could do the whole
calc with one equation.)

Now I know that I need 19 turns of wire on each phase. The wire will
need to be much larger to handle the high current. Fortunately this
has been figured out long ago by motor rewinders. Charts are
available, in my books and probably on the net, called "slot filling
charts". For a given stator slot size, the chart shows how many turns
of each size wire the slot will hold. Because large wire wastes a lot
of space as it stacks up in the slot, I'd use 2-4 lengths of smaller
wire in parallel. (I know this stuff from moonlighting at my friend's
electric motor shop.)

I'd wind the stator, then take it to the electric motor shop for a
varnish dipping and baking. I'd connect the windings in the wye
configuration - one end of each winding connected together and the
other end of each of the three brought out as the three phase output.

I'd connect up a simple 6 diode three phase rectifier and bring the DC
out to a set of cables and battery clips. A simple manual throttle
completes the setup. Optionally a volt and amp meter.

With this scheme, the output voltage and thus the charge rate is
controlled by the engine speed.

Up to this point, all the work can be done in any home workshop with
hand tools.

To make the unit fully automatic, I'd gin up one of my microprocessor
control boards based on a BASIC Stamp. The Honda already has a servo
on the throttle so that aspect is simplified. My board measures the
output voltage and controls the throttle servo to implement the smart
multi-stage charge algorithm. In this way, the engine speed varies
according to the load.

An additional enhancement is to split each phase winding into two
parts and add the relays to either series or parallel them. In
series, the engine only has to run at half speed for the same voltage.
Thus at low charging currents, such as during the float or the tail
end of absorption stage, the engine speed can be reduced in half.

See how easy that is? :-)

John
---
John De Armond
See my website for my current email address
http://www.johngsbbq.com
Cleveland, Occupied TN
A foolish consistency is the hobgoblin of little minds.-Ralph Waldo Emerson
.

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