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Backup Battery Charging - pros and cons - Page 3

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Posted by Curbie on July 9, 2009, 4:45 pm

As I understand your post, both your primary AND backup sources of
power is the I.C.E. with an automotive DC alternator which produces a
far greater battery charge per gallon of fuel that did an AC household
voltage generator through your inverter. Since you have two inverters
you feel comfortable that as long as you can keep your battery bank
charged you should be fine with this setup, which made your greatest
priority in your decision "battery charge per gallon of fuel".

If I got that right it makes sense to me.

When you talk about setting engine speed for the ultimate desired
voltage, is this because you've disabled the alternator's voltage
regulator, so the engine's RPM will dictate output voltage?

Have you read BobG's post on OtherPower:

I thought it is a pretty nice place to start on this kind of setup, do
see something I'm missing?

Thanks for the light.


Posted by Ulysses on July 10, 2009, 3:13 pm

The output voltage is controlled by a combination of the field current on
the alternator and/or the engine speed.  I manually adjust (usually only
needs to be done once) the field current for the best results (maximum
output without overloading the engine) and then adjust the engine speed as
needed.  The pulley ratio is selectable too but I've found somewhere around
2:1 is about right for my setup.  It is possible to simply adjust the engine
speed so that the ultimate voltage will equal your desired Absorb rate (59.5
volts in my case) or Float or Equalize.  However, it will take longer to
reach that voltage if charging at a lower rate and I have a pretty good idea
how long it will take based upon experience so I run it faster until it gets
to Absorb, then adjust it so it stays there.  If you are using something
like an OutBack inverter/charger you would still need to determine the
duration for your Absorb charging so there's not that much difference
between the two, except the OB is more automatic.  If you want to equalize
with the OB system you still have to do it manually.

Other advantages to this type of charger are durability and economical
repairs, as others have pointed out.  The engine I'm using only cost $00
(current price is $10) and you can get an alternator for about $5 that has
new brushes and bearings and comes with a warranty.  Many alternators and/or
engines may be substituted.  Repairs are much simple since there is no
generator head that might need to be removed from an engine, however I would
trade that convenience for a direct-drive setup.

I don't know if I've read it but I will.

Posted by Ulysses on July 10, 2009, 4:02 pm

What I read was that there are other alternators that can be used that may
be better than a Delco 10SI.  This is something that I have in the back of
my mind for future reference.  For the moment I'm content with the Delco
because it will deliver my C10 charge rate and I can have another one in my
hands in less than 35 minutes (assuming the stores are open).  Plus I
understand how they work.  I have a lot of information on the Delco and it
took some time to accumulate so I would need to do the same with another
alternator.  To me the main point that BobG made was the use of double
belts.  I have found that a single belt may work OK for up to about 4 HP but
my 6.5 HP engine destroys a single belt very quickly if ran over about 30
amps (at 51+ volts).  Right now I'm searching for double pulleys and trying
to learn about the different types of belts.  What I end up with will
probably depend upon what is readily available.  I don't want to use
something that is difficult to find or obtain if something more easily
obtained will do the job just as well.

Another factor that should be a concern is the power curve of small gasoline
engines.  They tend to develop their maximum horsepower very near their
rated operating speed (usually 3600 rpm).  Running them at a slower speed to
drive an automotive alternator does not seem to be an issue, at least not
for me.  The current output from the alternator is lower (at a lower speed)
so the engine does not have to work as hard and it doesn't seem to be any
less efficient.  The whole thing ends up being quieter and the engine is
likely to last longer and need fewer oil changes.

Posted by Curbie on July 10, 2009, 5:31 pm

Do I understand this to mean:
1)    The voltage regulator is disabled?
2)    How is the field current manually adjusted?

Between the gear ratio you're using and engine I can certainly see why
you twisting V-belts, BobG's double V belt & pulley or cogged belt &
pulley is a more expensive route, but should replace you desire for a
direct-drive setup and seems like a must, just too much tension for a
single V-belt.

I get your decision on going with parts you have, but do you think
I'll gain anything going with BobG's setup to start with and learn on,
I'm a little more interested in reliability and long-term cost than
initial cost.

Thanks for sharing your experience!


Posted by Curbie on July 11, 2009, 7:09 pm

If I remember correctly, rheostats where used as light dimmer knobs on
old cars, maybe you'll run into one sometime?

Thanks for all your time and help!

OtherPower's PMA battery charger

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