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From: John De Armond
Subject: Re: Auto Alternator Driven by Honda Engine
Date: Tue, 30 Nov 1999 16:45:04 EST
Newsgroups: rec.outdoors.rv-travel

> While I have never built one <disclaimer> it seems logical that mounting
> an alternator on an old lawn mower or similar inexpensive power source
> would be a very cheap way to generate 12VDC to recharge batteries.  If I
> was dry camping in the boonies for an extended period of time, I'd build
> one.  Many alternators come with an internal regulator thus eliminating
> the need for one more item.

Back in 92 I designed a device we marketed as a cordless battery
charger to the auto racing community.  It consisted of a 20 cc
weed-whacker type motor and a motorcycle-style permanent magnet
alternator along with a microprocessor-based control system, all in
a 12 lb package.  It would charge at a maximum rate of 60 amps. 
Since the alternator had a permanent magnet field, speed control was
the only practical method of charge rate control. The microprocessor
varied the engine speed to create the desired charging profile.  It
would charge a battery, equalize it if desired and then turn itself

We sold a few of them before I ran out of money.  I talked to
Coleman about manufacturing it but nothing came of the talks.  A
couple of years later, they came out with essentially the same unit
but without the electronic controls and with a 120vdc output for
lighting.  Home Depot sold them for awhile.  They were IMHO fairly
poorly made and very noisy.  I suppose Coleman liquidated the
inventory because I now hear them being hawked by Art Bell on his
all night conspiracy nutcase show as the ultimate solution for Y2K.

I was marketing the generator to the drag and other racing community
where total-loss ignition systems are common and batteries must be
rapidly charged in a short period of time between rounds.  Hmm, with
RVing taking off like it is, perhaps I need to resurrect my design. 

I had bopped along all these years thinking I had invented the
concept of a handheld gas powered battery charger  until the Daytona
Turkey rod run last weekend. There in the antique engine section was
a guy displaying a japanese made 10 amp charger that was not much
larger than an old-style quart oil can!  It used an engine that
looked a lot like one of the larger model air plane engines and a
tiny permanent magnet generator.  It might have weighed 5 lbs
soaking wet.  What a cute little gadget!

I've played around with this concept for years.  Hooking a car
alternator up to a gas engine works but a few parameters have to be
met.  First, a conventional alternator needs to turn at least 5000
rpm to generate at its capacity.  A Briggs type engine can do that
if the unit is geared up.  At that speed the cooling fan will absorb
nearly as much power as the alternator!  A better technique is to
get one of the aftermarket high output single wire alternators aimed
at the high power stereo crowd.  These things will typically put out
85% of their rated amperage at idle (about 2500 rpm on the
alternator)  These can be direct coupled to a small engine and run
at 3600 RPM or above, or can be belt-driven so the engine can turn
slower and quieter.

A weed whacker type motor is perfect to direct-couple to an
alternator.  They typically run about 5000 RPM which is perfect for
the alternator.  I still have my prototype cordless battery
charger.  It uses a 40cc leaf blower motor and an alternator from a
Toyota Camry.  The engine loafs with 60-80 amp output and the
alternator is self-excited (one wire).  It cost about $150 in parts
to build, including buying the engine with a keyed shaft from
Techumse (sp).

Lastly, Honda used to make a similar unit using a 4-stroke engine. 
Northern Hydraulics used to sell them.  Significantly larger than
the weed whacker engined ones but much quieter.  don't know if they
still make that or not.

> While it is true that a 3 or 4 stage battery charger will do a better
> job of completely refilling your deep cycle batteries, this, for a
> hundred bucks or so facinates me.
> Romeo Raabe

From: John De Armond
X-Source: The Hotrod Mailing list
Date: Apr 1992
Subject: Re: Auto Trans.

>>I have a prototype of a nifty little 11 lb cordless
>>battery charger here that will become a product someday.  This thing
>>consists of a 2 hp weed whacker engine, an alternator and some
>>custom controls.  I designed this thing for drag racers and others
>>who need to rapidly charge a battery away from electrical outlets.
>>This thing generates 60 amps (alternator's limit, not engine's).
>>The alternator is directly driven at the two stroke's 5800 rpm peak
>>power point.
>That's a pretty Wattey Weed Wacker John ;^)  What size cables did
>you put on this thing??

Went down to the locak K-mart and bought an el-cheapo set of jumpers.
A quick snip of the dykes in the middle and viola!  Two cables.
These are the el-cheapo ones with the 6 gauge wire and half an inch
of rubber so they look REALLY big and REALLY good.  I selected that
size on purpose.  On a flat dead battery, the alternator turns into
a horsepower sink that can stall the engine.  Instead of addressing
this in my controls with extra complexity, I simply include enough
resistance in the hookup leads to prevent the stall most of the time.

------- quick context switch ------------

New addition to my test equipment stable.  My new  Fluke 80i-410
AC/DC Hall Effect clamp-on ammeter probe just arrived. Costs
about $130 and works with any meter that can display AC/DC
millivolts.  This thing is very accurate as compared to my
laboratory shunt and has none of the static offset problems of
the asian clone I'm about to toss in the trash that I paid about
the same for. The display changes less than 0.1 amp while moving
the wire anywhere inside the opening, again in stark contrast to
the clone. Can't beat American engineering and now apparently,
american pricing.

My Fluke 88 automotive DMM has a peak/hold feature and so with this
thing I can grab peaks such as starter motor peak draw and the like.
I has a high enough bandwidth that I can measure the current draw of
a fuel injector with a scope attached.  I compared it against
a shunt hooked inline with my test bench and saw no difference in

Best of all, the manual has a schematic with part numbers.  This
looks trivial to build into an existing AC clamp.

Highly recommended.


From: John De Armond
X-Source: The Hotrod Mailing list
Date: Apr 1992
Subject: Re: charging system.

>In regards to that "11 pound battery charger", have you tried to charge
>a low or nearly dead battery with it. I'm not sure I'd believe it could
>do that with an alternator, as alts tend to need 12V +/- a volt or so
>just in order to activate the field.  I've never seen an alt charge a
>dead battery.

No problem.  Actually the field needs only a volt or two to
generate  full output at high RPM.  Given an ample supply of
power (NOT the case in my generator), the output voltage and
current will reach an  equilibrium with the state of the
battery.  I think - but have not  proven - that the magnetic
path saturates in the process. Where power is limited, the
alternator CAN pull the engine all the way down.  That's why in
the unit with the Rev 1 controller, I included leads with a bit
of resistance to inhibit the problem.    Nifty thing about these
leads.  They heat up a bit almost immediately and the positive
tempco of copper increases the resistance when it's needed and
then cool down as the severe load decreases.  sorta self-regulating.

In Rev 2, the controller excites the field only based on RPM
feedback until the full charge voltage  threshold is reached.
The alternator is excited to keep the engine fully loaded at all
times.  This has been demonstrated to be almost the  fastest way
to charge a battery.  Rev 3 will likely trend the charge
voltage and predict the charge endpoint.

It's interesting dealing with the torque curve of the two stroke
engine.  It does not have enough torque when starting to generate
the amp or so needed to excite the field.  What I had to do
is resistively bleed some current into the field to get the first
voltage and then after the engine is up to speed, apply whatever
field is needed.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Cordless Battery Charger progress report
Date: Tue, 23 Jan 2001 02:55:35 -0500

I've posted some pictures of my cordless battery charger development
prototype.  Look here:

The design goal for this project is a portable charger that will
charge my house batteries (2 Group 27 deep discharge) from a full
discharge in about an hour.  For our normal pattern of use, it will
require no more than 1/2 hours' running per day. Even our Crazy
Canucks should be able to tolerate this. Weight as photographed is
55 lbs.  An aluminum frame is  in the works.  That should cut 10 lbs
off the weight. I'm posting these pictures in case someone else
might be interested in this project.

We gave it its first field test this weekend.  Headed off to the
mountains near Tellico Plains, TN and dry camped high enough to get
ourselves snowed in.  At the end of the first day, I cranked this
little puppy up in 15 degree weather (on the second pull) and
charged away.  Charge was finished in a little over 30 minutes.
Second day, I crank the thing, the engine hits two or three strokes
and *PING* - cratered.  More specifically, the cam timing belt
broke, bending the valves, etc.  I found metal in the oil at the 5
hour oil change so I wasn't really terribly surprised.  We'll see
how well Northern Tools/Honda honors their warranty tomorrow.

As the picture shows, I'm using the Cruising Equipment/Heart
Interface InCharge smart alternator controller along with the 185
amp Cadillac alternator converted to external regulation.  This
regulator works with significant manual intervention.  There is no
temperature compensation so the absorption voltage must be manually
set to the battery ambient.  And it does not measure the charge
current so the absorption cycle is terminated strictly by elapsed
time.  The better method is to terminate the absorption at something
like 10% of the initial absorption charge rate.  I'll continue to
use the InCharge so I can dry camp in luxury while I design a
controller from scratch to do it my way :-)

As configured, this unit is quieter than my Onan AJ generator in my
MH.  (not ready to post sound numbers yet)  The engine itself is
almost silent with no valve train noise at all.  It had a bit of rod
knock but I suspect that to be part of the mfring defect that caused
it to crater.  I have left room in the frame for an additional
external muffler which will quell the only major source of noise,
the exhaust.  Honda was so nice as to leave a couple of mounting
holes on the muffler for a spark arrestor that I can use.  What's
really nice is that once the regulator transitions from bulk to
absorption charging, the engine can be throttled down from its
normal 3600 RPM speed to as little as 2200 and still maintain full
output.  This is MUCH less annoying than the 3600 RPM sound.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Cordless Battery Charger progress report
Date: Tue, 23 Jan 2001 16:21:29 -0500

Will R wrote:

> John, Here is another Idea for you.  Talk a standard cheep walk behind
> mower, remove the blade and install a pulley, cut a hole in the deck
> to mount your alternator through, making brackets so you can adjust
> the alternator.  Find the correct belt size and your set!  Seen them
> at the races many times.
> You can probably find a "used" mower cheeper then that honda engine
> you are using on your rig.  I checked out your "invention" and you go
> good work!


First off, thanks!  I appreciate that.

About using a lawn mower, I gave that brief consideration but there
are many factors militating against it.  First is the noise.  This
little Honda engine is amazingly quiet, much quieter than the
typically VERY cheezy engines used on lawn mowers.  The belt-driven
overhead cam is one factor but there are other subtle features that
might escape most folks.  The block is molded from a very "dead"
aluminum.  Whereas with most engines, when one strikes a cooling fin
and gets a loud ring, with this engine, one gets only a dull thunk.
Same with the fan blades on the flywheel.  Quiet operation is very
important to me so that was an over-riding consideration.  I'm not
ready to toss out numbers yet because I have not yet made scientific
measurements but offhand measurements with a db meter indicate this
unit to be at least 10 db quieter than my Onan AJ.

Another consideration is weight.  This engine weighs 29 lbs wet.
It's one of the lightest engines of that horsepower out there.  The
frame adds another 5 lbs or so.  It is very important that I be able
to pick the generator up and carry it with one hand because the
place I store it at home is at the bottom of some stairs. Plus I
carry it on a frame/bumper mount during fair weather.  Another
consideration for weight is that I will use it for the same purpose
I used "Cordless Battery Charger I" with the 2 stroke engine - as
"cordless jumper cables".  Fairly frequently I have to boost off a
customer's car at the restaurant and it's much handier to grab this
thing than try to squeeze another car close enough to run jumper
cables.  This thing has enough grunt to start small engines and will
charge the battery of larger vehicles enough to crank in 5 or 10
minutes. CBC-1 is only capable of 60 amps (but only 13 lbs) so using
this new one for boosting is worth the additional weight as long as
I can lift it.  Wheels don't help - remember the stairs.

Which leads to the next consideration, size.  I have a frame/bumper
mounted bracket I built that normally carries my lounge chairs, a
tent or a load of fire wood, depending on what I need.  The genny is
designed to fit on this bracket in fair weather.  In foul weather, I
simply set it inside the door.  The frame size allows enough room to
get around it when it's sitting in the door.

Lastly is the matter of esthetics.  I didn't want this thing to look
like a refugee from Sanford & Sons :-)  Because I want the footprint
to be as small as possible, I looked at using a vertical shaft
engine with a fabricated frame.  Problem is, no one makes a small
vertical shaft engine that is also quiet and of high quality.

On the cost side, this engine is amazingly cheap, only $189 from
Northern's web page or $192 from their store.  That was another
major consideration, as one of the project goals is a design that
can be built for under $500.  Easily achieved, even if one had to
pay for the machining I do at my friend's machine shop.  The
alternator cost about $100 from the alternator shop equipped with
heavy duty diodes and a 1 wire regulator (which I removed).  I'd
expect it to cost no more than $60 without the 1 wire regulator.
The InCharge regulator cost $189 from West Marine but I'd not use it
again, based on what I know now.  I figure the $200 was worth it as
a learning experience so I could see how they actually implement 3
step charging as opposed to how they describe it.  A simple $14
external regulator, a pot and a spring wound timer will achieve the
same functionality for this application.  Probably $30 worth of cog
belt pulleys, steel tubing, etc.  About $30 for the welding cable
and high quality clamps.

"Cordless Battery Charger II Rev 2.0" will have a direct connected,
shaft mounted alternator.  I'm currently scouting around for an
alternator that has torque/speed curves that match the engine
curves. This will lop a good 20 lbs off the thing.

I have a feeling this is going to end up as a product one of these
days :-)  Oh my!  I wonder if the Bozo Brigade will insist I stop
posting about it ;-)


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Cordless Battery Charger progress report
Date: Wed, 24 Jan 2001 01:14:22 -0500

Tarmagost wrote:

> >I've posted some pictures of my cordless battery charger development
> >prototype.
> Nice work, John!  I particularly like the vibration isolation...the
> whole thing reminds me of the work my dad used to do (he makes harps
> now).  Did you do the welding also?  Nice to have friends with machine
> shops...!  (also nice to have friends with restaurants)
> Tim, Denver
Thanks much, Tim.  I've been fighting the issue of vibration dampers
for gas-powered gadgets I build for years.  It's very difficult to
buy isolators in small quantities from OEMs and buying them as spare
parts is very expensive.  This idea hit me in the shower (one of the
places I do my serious thinking :-)  It works absolutely superbly.
This genny can sit on my bench shaking like Janet Reno and
absolutely nothing on the bench moves!  Since I took the photos,
I've fitted stiffer hydraulic hose that doesn't sag like that air
line does.  I may end up welding cups around the lower posts to
constrain the movement of the hose.

Welding's all mine.  Many years ago I got TVA to send me to welding
school (stick and TIG) so I'm a pretty decent welder.  This was done
with my brand new Millermatic 1200 MIG welder.  This is one SWEET
welder!  I have effectively never used a MIG welder before buying
this unit and I've put perhaps a couple of hours on it, using maybe
a pound of wire.  This is my first significant project.  This thing
makes welding almost like squirting filler out of a caulking gun.
Compared to what I've seen other people fight with using cheap
welders, this is a dream.  Even wifey's been using it.  She wants to
be able to make her own lamp bases and frames for her stained glass
work.  She's never touched a welder in her life.

Friends with machine shops are nice.  I grew up with this fellow and
he likes my BBQ about as much as I like his tools so there are
trading possibilities :-)  Besides I do his CNC work for him.  His
dad buys old surplus machine tools and I put CNC controllers on
'em.  We're currently working on a HUGE turret lathe that came out
of the aerospace industry.  SWEET unit!  Anyone need any trailer
axles machined from billet? :-)


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Alternative to Generator/Solar
Date: Mon, 26 Feb 2001 19:32:44 -0500

Bob Giddings wrote:

> . On Mon, 26 Feb 2001 15:26:44 -0500, Neon John
> <> wrote:
> >
> >
> >snip
> >
> >If you don't want to build a CBC or install a second alternator (the
> >other option), you can for much more money get a small generator
> >like the Honda EU-1000 and a smart multi-stage charger/converter and
> >achieve the same thing.  My CBC cost about $450 to build.  The honda
> >is near $700 discounted on the net and a high current multi-stage
> >charger/converter can run from $250 to $400.
> >snip>
> >John
> True, but a little misleading.  The converter (Intellipower 9130) came
> with the trailer.  The "charge wizard", which makes it 3 stage,
> supposedly, was $27.  The EU1000, delivered to my house, with DC
> charging cord, was $665, for a total cost of $692 beyond the price of
> the trailer.  Since it was a Mallard, I assume every manufacturer has
> by now gone to intelligent chargers on new trailers. so for those of
> us who bought new that expense is already met.

Not misleading.  I assume this guy wants to charge his batteries
rapidly regardless of the controller.  Your converter is a 30 amp
unit, right?  Not exactly a quick charge for 200+ amp-hours of
batteries.  My comments are in regard to higher current chargers
such as the large Magnetek ($329 from on up to the Heart
or Trace units.  The 1000 watt generator would be capable (ignoring
losses) 67 amps @ 15 volts.

> Of course since you built it for fun, your time and labor do not enter
> into your calculations.

Of course.

>And why do I think your homemade charger is a
> little on the loud side?

As it exists now, it's about the same loudness as my AJ mounted in
my MH.  Which is to say not quiet, though not contractor-grade
noisy.  Very careful sound surveys show that almost all noise from
this engine comes from the exhaust, thanks to the timing belt cam
drive.  When I fit the aux muffler, the sound level will be down
with the modern Onans.  There is a little noise from the cog belt
drive of the alternator but that's easily shielded with a guard.
There's also a little cooling fin ringing but that's easily damped.
Finally, the engine runs at high speed only during bulk charging.
The rest of the time it is idled down to 1800 RPM or below.  Amazing
the difference in the annoyance factor between 3600 and 1500-1800

Another saving grace is that it only has to run for an hour a day.
If that bothers someone, they can move or pound sand!


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Alternative to Generator/Solar
Date: Wed, 28 Feb 2001 15:44:50 -0500

Mike Nash wrote:

> Neon John wrote:
> >
> snip
> >
> > IN contract, my Cordless Battery Charger (engine driven alternator
> > with multi-stage controller) will put 100 amp-hours in the batteries
> > in a little over an hour.   The difference is the multi-stage
> > controller's voltage setpoint is from 14.8 to 15.2, depending on
> > temperature.
> >
> I'm interested in your design. Not to mention how you are using the
> alternator to start the engine. Care to share any details?
> Mike

Go to my personal web page below, click "files", then "RV" then
"Cordless battery charger"  Several pictures there.

The pictures show me using the Cruising equipment multi-stage charge
controller.  It's OK but not optimum for this application.  I'm
currently employing a Parallax Basic Stamp-based controller that
does the multi-stage charging plus some other goodies that I can't
yet talk about as I am filing a patent application on certain
aspects.  The unit in the pictures is my mule for control system
development.  I eventually will go with a direct driven alternator
with a permanent magnet field to reduce the weight and complexity.
My goal is 30-35 lbs.

Driving the alternator as a motor:  The alternator looks remarkably
like a 3 phase synchronous motor with a wound field.  Therefore one
can motor it by simply driving it with 12 volt, 3 phase AC.  The AC
is generated by a simple trio of transistor switches driven with the
proper 120 deg phase relationship.  For proof of concept, I used a
Basic stamp to generate the drive but this pretty much maxes out the
Stamp plus it can't generate a high enough frequency to turn the
alternator as fast as it needs to go.  I'll probably re-implement
this the old fashioned way with shift registers, probably using a
PAL.  The trick to making this work is to ramp up the "step
frequency" just like one must do with a more conventional stepping
motor. This allows the rotor to stay locked as it accelerates,
thereby achieving the maximum possible torque at the drive level.

The Honda engine I'm using has a compression reducer to make
cranking easier, therefore not much torque is needed.  If more
torque is needed, one can drive the stator with "H" type push-pull
output stages.  This complicates things both in the driving
circuitry and in the alternator, as the wye-connected stator must be
reconnected to bring both ends of all three phases out.  This
involves digging out the common point and breaking the connection,
then attaching wires and bringing them out.

I'll make schematics and maybe even code available after I get my
patent pending grant.  I'll probably provide no cost licensing to
individuals who want to build their own.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel,alt.rv
Subject: Re: Home made 12V charging unit???
Date: Wed, 11 Apr 2001 17:37:55 -0400

Lou Schneider wrote:

> As far as noise, you'd better be a long way from your neighbors!  Go out back
> and fire up your gas powered lawnmower.  Run it through some weeds at full
> throttle.  Now imagine transplanting that noise to a quiet boondocking
> campground for a couple of hours while you recharge your batteries.

If the genset is designed correctly, the engine never runs full
throttle.  It runs at its optimum BSFC RPM which is usually pretty
near the torque peak.  Once the bulk charge period is done, the
engine then slows (or is slowed by the operator) as the current
demand decreases.

> Seriously, noise is one of the biggest problems.  Most of the noise generated
> by small, air-cooled engines is mechanical - bolting a bigger muffler onto the
> engine won't do any good - you have to build a sound proof enclosure that
> doesn't interfere with the flow of cooling air.  Not an easy task for the
> do-it-yourselfer.

Actually with the new generation of OHV and belt drive OHC engines
made from "dead" alloys, exhaust and intake noise ARE the bulk of
the noise.  The little belt drive OHC engine I used on my cordless
battery charger (CBC) is mechanically almost silent without the
intake and exhaust noise and that is easily damped.  I was able to
get rid of most of the tiny bit of residual mechanical noise by
applying some high hysteresis rubber to the cooling fin edges.

At this point in the development, the predominant noise maker on my
CBC is the whine of the cog belt.  That is easily tamed by drilling
a vent hole in each tooth.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: home made 12 volt generator help (long)
Date: Wed, 16 Oct 2002 12:16:11 -0400
Message-ID: <>

On Tue, 15 Oct 2002 23:13:33 +0000 (UTC), "Gazz"

Sorry to delay on this thread but the blue smoke leaked out of my PC's power
supply last week.

>i'm saying i'd use a 5 hp engine, but i realise that may not give enough
>torque to turn a fuly loaded 60 amp alt, i'd like to use enough alternator
>power to keep up with a 600 watt inverter runing at full power.. so 60 amps
>is even pushing it, a 90 amp unit may be best, but that size engine over
>here is hard to come by, into the ride on mower leage here i think, and big
>fuel consumption.. i want to use as little fuel as possible.. the van is
>diesel, so i'd have to carry petrol about as well (could go for LPG, as i
>have the tank. but it's only a small tank because of the little lpg i use),
>and petrol is very expensive in england,

First thing to do is to look here.

This is my last machine, a 150 amp smart charger driven by a 4 hp engine.  It
has evolved quite a bit since this series of photos was taken but this set
shows a very functional unit.  It uses the commercially available Heart
Interface InCharge smart alternator regulator.  This regulator implements a
fairly decent 3 stage charge routine.

There are some problems with this implementation:

1) The regulator will attempt to maintain the set voltage regardless of engine
speed.  This means that if the engine speed drops under a certain RPM, the
torque requirement of a fully excited field will stall the engine. This makes
regulating the engine speed problematic.  The large dropping resistor seen in
the photo is a field current limiting resistor.  This is somewhat of a jerry
rig but it worked well enough for the purpose.

2) The speed is still manually regulated.  It must be run wide open for
probably the first 10 mins and then it can be ramped down.  After about 30
mins, the engine speed is at its minimum and can be left there.

3) The absorption phase is simply a timed phase instead of one that monitors
the charge current.  This can lead to overcharging on small batteries.  Not a
problem on my rig, as I have 320 AH of batteries and I carefully calibrated
the timer to my situation plus I am disciplined as to when I run the
generator.  I watch my E-meter and run the generator when a certain discharge
level is reached.

The Cruising Equipment smart regulator addresses most of these problems but is
more expensive.

I later designed a BASIC Stamp based controller that does the smart charge
properly and controls the throttle as you desire.  The circuit is pretty
simple - PWM control of a solenoid tugging on the governor just like the
manual throttle does.  subsequent to that I built a 68HC08-based unit.  It
does PWM for both the throttle and the field control.  If you look here:

You can read about this EFI controller that I've been involved with.  This
board can be used as the generator controller basically with no circuit
change.  Only some software change.  The injector controllers (2) are PWM
controlled in hardware inside the chip.  These can control the field and
throttle.  The board already samples the 12 volt supply so that can be your

These guys also periodically organize a group buy of just the processor and
programmer board kit so if you wanted to save some bux you could go that
route.  The chip's about $8 ea and the programmer board kit about $20. I
recommend you download the schematic at least.  The chip is a self-contained
computer and needs little more than power and a crystal oscillator to run.
The FET drivers let the processor drive the FETS very fast, fast enough not to
need heat sinks.  If you got ambitious, you could use the EFI part to fuel
inject the engine at the same time :-)

>i don't want much do i, high power, low fuel consumption, low revs, low
>noise, quick charge times (actually i only want fast charge times for when
>the inverter is running at max power), rest of the time 10 to 20 amp charge
>would be fine, only got 2 x 110 Ah batteries, so 22 amp charge is recomended
>(C10 charge) i think, and with the inverter off, its only flourecent lights,
>TV and video (dvd player later.. but they pull around the 1 amp range.. so
>genny wont be used then),
>i guess i should really concentrate on putting the charge back in the
>batteries as fast as possible, and running the engine as little as possible,
>so maybe a motorcycle fixed field alternator may work, if it can vary the
>revs to a 3 stage charge load.

I use my CBC two different ways.  When I'm dry camping I charge the batteries
as fast as I can to minimize the noise, normally with an hour or less run time
a day.  When I need to run the AC I run it on an inverter with the CBC
supplying the power.  The CBC is quieter and more fuel efficient than my
ancient Onan.  This is a temporary remedy until I replace the Onan.

I'm working on a new project to be used with both my RV and my personal
electric vehicles.  This involves a Honda Mini-4 stroke engine and a pair of
surplus permanent magnet motors driven as generators.  This is followed by a
switch mode regulator that also controls the engine throttle.  This little
package will weigh barely 10 lbs and will charge 12 or 24 volt batteries with
the flip of a switch.  Preliminary tests indicate 55 amps at 14 volts and half
that at 28 volts.  This one won't charge as fast as the big CBC but it will
fit under my sink in the MH and I can wear it as a backpack when I'm tooling
around town on my electric scooter.  Several months away from having anything
to show publicly.

Yeah, Chris, ya could buy a Honda EU and a Trace smart charger/inverter but
that wouldn't be nearly as elegant nor fun :-)


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Question-fast battery charger?
Date: Tue, 10 Feb 2004 12:37:45 -0500
Message-ID: <>

"Apparently?"  Well harumph.... :-)

Anyway, just a note about the Cordless Battery Charger.  It has gotten a
hammering over the last month or so that no charger would see in normal RV
use.  I have my RV parked out at the new drive-thru restaurant site so that my
employees can have a restroom while that construction is underway.  Between
the outside lighting and the electric 'fridge, about 60 ah a day is consumed.
The CBC is operated every day or so to replenish this energy.  It has worked
perfectly and has given my employees absolutely no problems.  This is more
usage than one would see in a year doing normal RV'ing.


On Tue, 10 Feb 2004 13:11:12 GMT, Chris Bryant <> wrote:

>On Mon, 09 Feb 2004 20:09:58 +0000, Rider1958 wrote:
>> Hi,
>>  Would anyone be able to answer this:
>> Instead of using solar cells (long charging time period and subject to
>> sunny days only) or coach generator (uses quite a bit of fuel to slowly
>> charge), why not use a small (2 to 5hp) Briggs&Stratton to run a 100-amp
>> automotive alternator to quickly recharge the coach batteries? Whouldn't
>> that be more efficient? What would the drawbacks be? Thanks,
>> Ron
>As Vince said- the voltages on a standard alternator are not enough to
>quickly recharge a deep cycle battery. Neon John built one using an add on
>Heart 3 stage regulator which apparently worked well. You can see his
>pictures here-

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: FAO neon john : 12 volt genny
Date: Sat, 19 Mar 2005 06:17:52 -0500
Message-ID: <>

On Fri, 18 Mar 2005 20:45:13 -0800, "Ulysses"
<> wrote:

>Well, I sure missed the thread a few weeks ago and I guess I'm just not very
>good at googleing.  Do you remember what the thread was called?

It's actually the beginning of this thread.  Hairy Arse and I have
been discussing engine driven chargers for at least a week.  There was
another thread a couple of weeks ago but I don't recall the title.
Googling for my name should be easy enough.  I've written about my CBC
several times.  I've always been Neon John but I recently registered a
domain and changed my email from
(Leave in the anti-spam when searching.)

>> Have you not seen the thread on this very subject that several of us
>> have written about in the last week?  You can look on my web site for
>> my version that I call the Cordless Battery Charger.
>> BTW, the stuff on that website is crap.
>Of course, but it has sources for alternators and couplers.  I spent quite a
>bit of time looking for couplers and never found any.  Looks to me like they
>didn't even consider that the oil might need to be changed someday.

Yeah, that too.  With my first prototype I tried the direct coupling
method.  Lovejoy couplers lasted a few hours before the neoprene
insert literally smoked. The semi-rigid high temperature one lasted
only a little while longer.  A roller chain coupler, the only other
type available to me at a reasonable cost, only lasted a little
longer.  The problem is that you have a lightweight engine crankshaft
accelerating and decelerating rather rapidly every other revolution
driving a relatively high inertial load.  It hammers the couplings

If you can guarantee perfect alignment then a rigid or semi-rigid
coupling would probably work.  That involves more precision machining
that I want to spend money on.

It dawned on me that I could achieve the least volume (approaching a
cube) by stacking the engine and generator and coupling them with a
highly efficient timing belt.  Again, I used what was available on the
shelf at the local machine shop supply house.  There are better and
quieter timing belts available but what I used is doing the job.

BTW, you're going to be very hard-pressed to beat that Honda GC series
engine like I used.  It's Honda's low end throw-away engine that
competes with the Briggs stuff.  But it's also the quietest utility
engine Honda makes, the quietest one I've found.  The simplicity of
design, the use of sound damping aluminum alloy and the timing belt
cam drive make it very quiet.  Northern sells that engine for under
$200.  At least they did when I bought mine.


From: John De Armond
Subject: Re: car engine battery charger
Date: Mon, 30 Jul 2007 01:46:45 -0400
Message-ID: <>

On Mon, 30 Jul 2007 02:52:33 GMT, Q <> wrote:

>For years I've been using an engine/alternator to top up my battery bank
>during those no sun/low sun days during the winter. I have a 16 hp OHV
>Briggs engine off a lawn tractor coupled to a 100 amp truck alternator,
>and a 5 hp Honda engine coupled to a 65 amp alternator. Both have worked
>well and are pretty quiet with extra large mufflers. This winter I'm
>considering trying something different, a truck alternator attached to a
>Geo Metro. Someone gave me a free one that runs well. I've heard the 1L,
>3 cyl, TBI engines are very efficient and am wondering if the idling Geo
>engine would be more efficient than the small engines. Anyone have any
>thoughts on the subject?

You're experiencing engine overkill!  100 amps at 14 volts is 1400 watts, a little
less than 2 hp.  Even with the lousy efficiency of an automotive alternator factored
in, call it 3 hp.  That 5 hp engine is more than enough.

A few years ago I built a 10KW generator around a Metro engine.  It worked quite well
and was very quiet.  It was economical to run but since economy wasn't my primary
concerns (clean power and quiet operation for that application), I don't have any
concrete numbers.  I'd save that engine for a larger generator and go back to the
utility engine for your application.

I suggest using the 5 hp engine, gearing it to run at a low speed.  That's the
approach I take with my Cordless Battery Charger.  You'll want to experiment with the
combination of field excitation and engine speed that gives the best economy.

The built-in voltage regulator by itself is not a good solution for this application,
as it slams full field current to the alternator whenever the voltage is lower than
setpoint.  This results in the alternator attempting to operate at low speed and high
torque which isn't a good match to the engine's power curve.

Controlling/limiting the field current externally lets you position the alternator's
speed and torque requirements to match the engine.  A simple power rheostat in the
field lead will do the trick.

In general, it is better to operate the alternator at higher speed (weak field)
because that enables the fan to provide adequate cooling. Copper's resistance goes up
with temperature and that increases the losses in the stator which causes more
heating, etc.  Both the stator and diodes are happier and healthier with the rotor
spinning fast enough for good cooling.

Here are some very old photos of the prototype of my Cordless Battery Charger.  This
one used an off-the-shelf analog smart charge controller and a fixed resistor in the
field circuit to limit the alternator's torque demand.  Now I do it digitally but
this analog system worked almost as well for basic battery charging.

The alternator is a 150 amp model from a late 90s Cadillac.  I chose that alternator
because this particular caddy used a conductive thin film on the windshield for
defrost which resulted in a high and continuous current draw.  This is one of the few
automotive alternators that can sustain its rated output in continuous duty.  I have
a local alternator shop build these for me sans regulators as I need them.

If you want to go for the ultimate in economy and noise reduction then you might
consider duplicating my CBC (or maybe talking me into building some more :-)  It
operates similarly to the Honda EU series, with a servo-controlled throttle that
chooses the optimum engine speed for each point in the charge regime.  I use an RC
model servo which is trivially easy to control from a BASIC Stamp or something

RE: drive.  I highly recommend the cog belt drive pictured in my photos.  The drive
is quite efficient, very quiet and very durable.  Other than breaking a belt early on
from debris getting between the belt and pulley, I've never had a belt failure.  My
personal CBC that I use when RVing has close to 1000 hours on it.

One last comment.  Were I designing a CBC from scratch today I'd go with a permanent
magnet alternator, perhaps followed by a PWM controller.  This would be a much more
efficient arrangement for two reasons.  One, car alternators are designed to saturate
early and limit the current output over a wide range of voltage and speeds.  Not
terribly efficient.  Two, the field consumes considerable power and contributes to
the heat load on the alternator cooling system.

I'd take a good hard look at the larger motorcycle and 4-wheeler alternators.  These
use the cup shaped flywheel/permanent magnet field and an inside stator.  The larger
ones are capable of a KW and that can probably be increased with careful rewinding
and cooling.


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