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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

Gas powered battery charger.



 
 
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  #1  
Old February 8th 09, 09:17 AM posted to rec.crafts.metalworking
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Posts: 1,417
Default Gas powered battery charger.


I've been thinking about mounting an automotive alternator on a small
gasoline engine to make a portable battery charger with respectable output.
The purpose would be to charge auto batteries when there are no outlets
around. Of course you could do the same thing with a generator and battery
charger but I think you can get perhaps 70 amps or more from an alternator.
It would have been nice this winter when we had the ice & snow storm and the
battery was weak on the seldom driven 4WD diesel truck. Also could be
useful for camping and boating, could recharge the trolling motor battery on
the lake, etc...

RogerN


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  #2  
Old February 8th 09, 09:24 AM posted to rec.crafts.metalworking
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Posts: 200
Default Gas powered battery charger.

On Feb 8, 8:17*pm, "RogerN" wrote:
I've been thinking about mounting an automotive alternator on a small
gasoline engine to make a portable battery charger with respectable output.

  #3  
Old February 8th 09, 10:22 AM posted to rec.crafts.metalworking
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Posts: 75
Default Gas powered battery charger.

On Sun, 8 Feb 2009 01:24:35 -0800 (PST), wrote:

A good idea, BUT....work out how much motor power you would need to
get the alternator up to 70 amps.


That's easy. 70A at 14.4V is about 1kW, or 1.4 HP. An alternator has
pretty good efficiency, so a lawnmower engine should be just fine.

..not a small motor.


My model helicopter engine weighs 406 grams, and produces 1.9 HP. I'm
not saying it would be suitable for this application, I'm just saying
the engine shouldn't need to be all that huge.

...and coupling
it to the motor is no trivial matter either - but thats OK,


In the car, the alternator is driven by a simple belt. If you can find
or make a suitable pulley for the engine, it seems quite doable.

no way
could you charge a battery at 70 amps anyway.


In the car, the battery IS charged by the alternator. You'd just have
to be careful if you use the alternator from a large car to charge a
small battery. Back off the throttle some, and you should be fine.

btw, you
would need to work out pulley ratios to get the alternator into its
power band without revving the motor to blazes -


The alternator does have a maximum limit. It also has a lower limit
where it will not produce any power at all. The lower the speed, the
less power it will deliver.

and some sort of
governor..(only if your obsessive...)


In the car, the alternator works over a wide rev range. As long as you
stay below the maximum rated speed, you should be quite safe. If you
fit an amperemeter, you will be able to see what's going on.
--
RoRo
  #4  
Old February 8th 09, 11:20 AM posted to rec.crafts.metalworking
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Posts: 1,417
Default Gas powered battery charger.


wrote in message news:d82ffccf-fad7-4a08-a367-
...

A good idea, BUT....work out how much motor power you would need to
get the alternator up to 70 amps...not a small motor....and coupling
it to the motor is no trivial matter either - but thats OK, no way
could you charge a battery at 70 amps anyway...let us know how you get
on, if you have the bits lying around then it would be fun - btw, you
would need to work out pulley ratios to get the alternator into its
power band without revving the motor to blazes - and some sort of
governor..(only if your obsessive...)

Andrew VK3BFA.


I was thinking about something like a 3hp Briggs & Stratton that already has
a governor. IIRC, those engines have a maximum RPM around 3600 so if I used
a pulley twice the diameter of the alternator pulley it would give me up to
7200 RPM on the alternator. All my autos that have tachometers show from
2000 to 2600 rpm at 60mph. The engine pulley looks (haven't measured yet)
to be 3 to 4 times the diameter of the alternator pulley. That would spin
the alternator maybe 6000 to 10,000 rpm. In my car when I have the lights
and heater on, at idle the lights dim and the fan slows, when I get over
about 1200 rpm things pick back up.

For experimenting, I could get a used lawn mower and cut the engine hole
pattern in a flat plate. Then cut holes for mounting the alternator and
install pulley and belt. It would be ideal if I could find a mower with a
deck flat enough to mount the alternator, kind of like a riding mower mount.

It would be nice to find a smaller lighter motor maybe perhaps a chainsaw
engine or good weed eater engine.

RogerN


  #5  
Old February 8th 09, 11:27 AM posted to rec.crafts.metalworking
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Posts: 75
Default Gas powered battery charger.

On Sun, 8 Feb 2009 03:17:57 -0600, "RogerN" wrote:

I've been thinking about mounting an automotive alternator on a small
gasoline engine to make a portable battery charger with respectable output.
The purpose would be to charge auto batteries when there are no outlets
around. Of course you could do the same thing with a generator and battery
charger but I think you can get perhaps 70 amps or more from an alternator.


Yes, typical alternators for passenger cars range from 50A, maybe even
less for the smallest cars, up to 70-80A, maybe as high as 100A.
Larger than that, and they'll most likely be 24V.

Note that some car manufacturers equip their cars with different
alternator sizes depending on which part of the world they will be
sold in. If you're looking for a big one, look for cars imported from
a cold part of the world.

Remember that an automotive alternator can be damaged if it is run
without a battery connected.

Also could be
useful for camping and boating, could recharge the trolling motor battery on
the lake, etc...


Check the specs for those types of batteries. They may not be able to
handle as high a charge current as a starter battery.
--
RoRo
  #6  
Old February 8th 09, 02:58 PM posted to rec.crafts.metalworking
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Posts: 4,567
Default Gas powered battery charger.

"Mach1" wrote:

Build a good cage around the alternator. At 10,000 rpm there could be
pieces going into earth orbit.


The ratio of the crank pulley to alternator pulley on cars is ~2:1. Almost all IC auto
engines can hit 5000 rpm before rev limiting takes place.

Just out of curiosity, has anyone ever had an alternator blow up from rpm?

Wes
  #7  
Old February 8th 09, 03:18 PM posted to rec.crafts.metalworking
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Posts: 506
Default Gas powered battery charger.

RogerN wrote:
I've been thinking about mounting an automotive alternator on a small
gasoline engine to make a portable battery charger with respectable output.
The purpose would be to charge auto batteries when there are no outlets
around. Of course you could do the same thing with a generator and battery
charger but I think you can get perhaps 70 amps or more from an alternator.
It would have been nice this winter when we had the ice & snow storm and the
battery was weak on the seldom driven 4WD diesel truck. Also could be
useful for camping and boating, could recharge the trolling motor battery on
the lake, etc...

RogerN


I was pretty serious about doing one of those a few years ago for
a power unit that would be used to run power tools in remote
locations. The volunteer group we work with had been building
some bridges etc. on trails in remote locations, but I never
got a roundtuit. :-) I wanted it to be realy light weight to
make it practical to carry and only needed enough power to run
a few power tools. I had a device once on a car, Subaru, that
made the alternator put out 110 V which I actually used to run
a power saw so I know it is practical.
Good luck and let us know if and when you get it going.
...lew...
  #8  
Old February 8th 09, 03:55 PM posted to rec.crafts.metalworking
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Posts: 76
Default Gas powered battery charger.


"Wes" wrote in message
...
"Mach1" wrote:

Build a good cage around the alternator. At 10,000 rpm there could be
pieces going into earth orbit.


The ratio of the crank pulley to alternator pulley on cars is ~2:1.
Almost all IC auto
engines can hit 5000 rpm before rev limiting takes place.

Just out of curiosity, has anyone ever had an alternator blow up from rpm?

Wes


Saw it happen on a 55 chevy street drag car. Missed a shift and it fragged
the alternator
pulley. Threw 4 or 5 chunks through the fiberglass hood. Alternator RPM
was probably
15,000 to 18,000 when it de-constructed.


  #9  
Old February 8th 09, 04:07 PM posted to rec.crafts.metalworking
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Posts: 762
Default Gas powered battery charger.

I'm just finishing up a class demo unit that uses a 62 amp Motorcraft
alternator. I wasn't happy with the positive ground on that unit but was
cheap and had the external voltage regulator that I needed. 62 amps at
13 to 14 volts is around 850 watts. Calcs out to 1.15 HP theoretical.
Any of the 3 to 5 hp B&S, Tecumseh, import specials, etc should work
fine at full load.

To build what you are talking about, I'd get Delco alternator with the
internal voltage regulator. If you happen to have a used one, the
rebuild kits run about $15. Amperage varies considerably from a low of
about 60 amps to around 135 on the units used on police cruisers. You
probably don't care, you don't really want to charge the battery much
faster than 30 to 50 amps.

As for how fast to spin the alternator: Here is the measured performance
curve for the Motorcraft alternator: (rebuilt unit came with a printed
inspection tag)

rpm amps
1600 11
2000 24
2500 43
3000 53
4000 61
5000 65

I'd expect the Delco units to be similar so driving it 1:1 from a
3600rpm lawnmower engine would be fine. I've tried both belt drive and
direct drive using a Lovejoy connector. Using the Lovejoy required some
special machining to get it to connect up: the armature is axilially
posititioned in the bearing by the nut on the pulley. I think I'd stay
with a belt drive for your application.

On gotcha to keep in mind: the case on the alternator is one side of the
circuit. It's tough to make a mounting where the chassis of your
charging rig is not grounded to the case of the alternator. If all the
batteries and equipment you work with are negative ground, should not be
an issue. But if you have an old positive ground vehicle or one with
multiple batteries in series, you really have to watch where you set up
the charging rig.

And a last thought: there are some aftermarket add on boxes that use a
different voltage regulation curve to get 120 volt power out. Really
trashy frequency and voltage regulation but they will run a small
universal drill. These are pretty much gone now, the decent 12 volt
inverters are much more user friendly.

Have fun!

RogerN wrote:
I've been thinking about mounting an automotive alternator on a small
gasoline engine to make a portable battery charger with respectable output.
The purpose would be to charge auto batteries when there are no outlets
around. Of course you could do the same thing with a generator and battery
charger but I think you can get perhaps 70 amps or more from an alternator.
It would have been nice this winter when we had the ice & snow storm and the
battery was weak on the seldom driven 4WD diesel truck. Also could be
useful for camping and boating, could recharge the trolling motor battery on
the lake, etc...

RogerN


  #10  
Old February 8th 09, 04:31 PM posted to rec.crafts.metalworking
external usenet poster
 
Posts: 1,417
Default Gas powered battery charger.


"RoyJ" wrote in message
m...
I'm just finishing up a class demo unit that uses a 62 amp Motorcraft
alternator. I wasn't happy with the positive ground on that unit but was
cheap and had the external voltage regulator that I needed. 62 amps at 13
to 14 volts is around 850 watts. Calcs out to 1.15 HP theoretical. Any of
the 3 to 5 hp B&S, Tecumseh, import specials, etc should work fine at full
load.

To build what you are talking about, I'd get Delco alternator with the
internal voltage regulator. If you happen to have a used one, the rebuild
kits run about $15. Amperage varies considerably from a low of about 60
amps to around 135 on the units used on police cruisers. You probably
don't care, you don't really want to charge the battery much faster than
30 to 50 amps.


I have a Ford F350 with a 7.3L Diesel and 2 batteries. On a cold icy snowy
morning I decided to try to drive it to work (4X4) and the batteries were
too low to get it started. I charged it with my plug in charger but it took
a good while to get enough charge to start. I thought if I had a gas
powered alternator charger I could use it if I had trouble starting the
truck after work. I haven't tried one but I have doubts about those jump
starters being able to get the diesel running in cold weather.

Thanks for the information on the alternator, maybe I should select a pulley
to give 5000 alternator RPM at 3600 motor RPM, giving maximum alternator
output at maximum motor RPM.

RogerN

snip


 




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