> >>>> I was planning on installing a mini alternator. But all I can
> find is
> >>>> 55
> >>>> amp in the mini's. Will 55 amp suffice with fuel injection and
> >>>> electronic
> >>>> injection. I was thinking 100 amp but that may be an over kill.
> >>>> Bob Mears
> >>>> Supermarine Spitfire
> >>>> 55 amps should do it Bob.
> >>>> --
> >>>> Paul Lamar ...No rotor no motor.
> >>> My alternator is a 60 amp Delco recommended by the local
> alternator>>> shop. 8.5 lbs, internally regulated. It actually
> puts out up to 75
> >>> amps under load.
> >>> I'd like to use an underdrive pulley for this alternator,
> since it
> >>> will
> >>> be spinning at around twice its design speed if the stock
> pulley is
> >>> used. I found the stock RX8 water pump pulley is 5-groove,
> and about
> >>> the right diameter, including the center hole. It is normally
> bolted>>> to the water pump, while the stock (Delco) alternator
> pulleys are just
> >>> held in place with friction. If I used a couple of large
> washers, is
> >>> there any reason this pulley wouldn't be OK for the alternator?
> >>> Scott Gettings
> >>> You can figure the torque on the alternator Scott.
> >>> 75 amps at 14 volts is 1050 watts. 746 watts per HP so that
> >>> is 1.4 HP. Given 80% efficient that is really 1.75 HP input.
> >>> Now you need to know what RPM the alternator puts out 75
> >>> amp and use the formula HP = T X RPM /5252 or
> >>> T = (HP / RPM) x 5252 Lets say 2 foot pounds for 6000 RPM. Bolt
> >>> the washers on and keep the alternator from turning and
> >>> apply a torque wrench.
> >>> BTW guys you can save some current drain and extend your
> alternator>>> out range by using the high pressure MSD roller vane
> fuel pump
> >>> instead of
> >>> the highly inefficient Walbro type pumps. My guess is you can
save
> >>> about
> >>> 5 amps or so. I will have more info on this shortly as I will be
> >>> testing
> >>> both.
> >>> The Walbro type pumps are ubiquities in just about
> >>> all new cars as they are very very cheap to make. Probably
> about $20
> >>> as all
> >>> they are is a small DC motor and an injected molded plastic vane.
> >>> Mazda sells them for an extraordinary $400 retail while the MSD
> >>> positive
> >>> displacement roller vane pump is $109 retail direct from MSD.
> >>> Paul Lamar ...No rotor no motor.
> >>
> >>
> >> Scott that is a nice size alternator. Where did you get it
> from? Can
> >> you
> >> tell me the depth of the unit from the rear casing to the front
> face?>>
> >> Thanks
> >>
> >>
> >> Doug
> >>
> > I spent a lot of time looking around in various places, but
> ended up
> > going to a local alternator shop and telling them what I wanted:
> > 1. 60 amps
> > 2. Internally regulated (but not computer-controlled)
> > 3. Light as possible
> > 4. Reliable
> > 5. Reasonably priced
> > 6. Standard shaft size so I could get a larger aftermarket
> underdrive> pulley if needed.
> >
> > The guy came back with a Delco early 90's GM 4 cyl engines-- the
> > numbers on it are: 1101171 D61A 7B19
> > 8.5 lbs
> > The case itself is 4" from front to back, but it is 5.75" from
> the case
> > rear to the end of the shaft (the front of the pulley).
> > The case is 4.5" in diameter.
> >
> > Scott Gettings
>
>
> Scott
>
> Thanks a lot. It looks like might just fit in the area the stock
> waterpump used to live at.
>
> Question. Wouldn't you want it externally regulated for safety
> reason?
> Cheers
>
> Doug
There has been a long and detailed thread on this topic on Bob
Nuckoll's Aeroelectric site, as well as some discussion on this
newsgroup. If an IR alternator fails so that the field remains
energized, it cannot be shut off. For this reason, many choose to use
an external regulator. In my investigation, I found that IR circuitry
is very reliable, and an external regulator can also fail in the "on"
position. My solution is to place a "battery" (continuous)contactor
inline on the alternator battery lead, to allow positive disconnection
either manually or automatically with an overvoltage crowbar. So
the "ALT" switch energizes both the field (actually the L terminal via
a light) and the B-lead contactor.
Scott Gettings
Got any schematics on this Scott?
Paul Lamar
Bob used to have schematics for overvoltage protecting relay setup on
internally related alternators, but has since removed them after much
ruckus. You see, the other problem with IR alternators is that if you
use a relay to disconnect them while they are running hard, the
alternator's output voltage may rise very quickly for a short time -
unregulated. This high voltage may damage the regulator itself. This
situation is called "load dump".
The problem with adding the relay (or other heavy duty switch/breaker)
to the system is not about the malfunctioning runaway regulator scenario
- who cares what happens to the regulator then - it's already shot.
The problem is that as soon as you give the pilot a switch to cycle, it
will be cycled.. And doing so when the alternator is working hard might
destroy the regulator - Pilots brought up in Cessna/Piper and other
externally regulated alternator systems will assume that it's okay to
cycle the alternator switch (and why not?)..
None the less, here are the designs that Nuckolls currently publishes as
a starting point for various configurations.
http://www.aeroelectric.com/articles/Rev11/AppZ_R11J.pdf
<http://www.aeroelectric.com/articles/Rev11/AppZ_R11J.pdf>
Z-24 is the one that used to have an IR alternator.
Any of the figures that have PM dynamos could use an IR alternator instead.
BTW, PM dynamos don't suffer from the same load dump severity as
regulated field current alternators - not as much energy stored, and the
regulator is already designed to control the output without control of
the field..
Matt-
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