Gee- I had overlooked the current draw for the injectors! It would
seem that a 40 amp alternator is not sufficient for my application,
and I have pretty minimal draw after accounting for fuel pump,
injectors, and minimal avionics. This would explain why I'm getting
good voltage on the ground at 1800 rpm, but not in the air at 6400rpm.
Anyone know what the injectors draw?
There is a 45 amp alternator that fits my mounting application, but
only bumping it up 5 amps is not enough. I might have to see about
mounting a second alternator. Sort of a PITA. That Ammeter from
Digikey looks good though.
Brian Trubee
Unplug one and use an ohmmeter to measure the coil resistance.
The max current can be found by dividing the number of ohms found
into the max voltage or 15V.
Which injector are you using. Some of the older ones used peak and
hold and the above scheme won't work. If it is around 10 or 12 ohms
it is not peak and hold.
If it is 12 ohms it is drawing 1.25 amps wide open max. However they
never run wide open all the time so 80% of that is about right. Say
1 amp. A larger alternator won't hurt.
Paul Lamar
Just ordered the ammeter and shunt. The bigger issue will be where
to install the second alternator. Not an insurmountable problem.
Brian Trubee
Brian,
Not a suggestion, but information.
The standard alternator for the Renesis engine is 100A .
The secondary alternator, gives you more backup, however.
Rich
I have the standard Mazda alternator on the standard location on the
2nd gen. My other alternator, a Kubuta, is mounted where the vacuum
pump was originally mounted. The Kubuta is quite a bit smaller and I
was able to use the vacuum mount as well with just a bit of
modification to the alternator. I have considered replacing the
Mazda Alt due to weight, but it fits so nicely for now.
Chris
Houston
As Brian is finding, light weight is not the only criteria to consider. You
have to have the balls to get the job done. A small second backup alternator
is a good idea.
Dale Davies
A couple of questions here, 1/ If the alternator wont operate without
the battery as previously mentioned
what happens if the battery fails in flight and has to be isolated. Do
you still have reliable alternator power?
2/ If electrical power fails altogether for what ever reason, The EFI
fuel pump stops along with the engine, the Wright bros fuel metering
system might be a necessity ?
Comments please!!!
The outboard alternator and a normal alt seems a good Idea as belt
failure is covered for redundancy. The PSRU alternator as designed
seems a very good idea.
Graeme Riley
There is such a thing as a permanent magnet alternator that works without a battery.
Most are rather small with modest output.
Paul Lamar
Many alternators are self-exciting if they don't get stalled..
There's enough residual magnetism to generate field current. ie, if
you take the battery out, the alternator will continue (and even start
on its own) to produce regulated voltage, though ripple and noise
performance may suffer.
If you stall the alternator by shorting its output (with a heavy
load), its ability to turn back on and start making power can be
compromised.
And, even a battery with a shorted cell - bringing the stack voltage
down to 11v or so is enough voltage to get a conventional alternator
going - even if the alternator isn't the self-exciting style. Just
have to put enough current in the field to get things going.
Discussed way long ago: mount a PM alternator rotor on the back side
of the flex plate - stator in the end housing. Harley (or outboard)
parts. Eshaft speed ensures good output. Parts aren't expensive.
Regards,
Matt-
Here are some good ones, lots to choose from
http://www.qualitypowerauto.com/catalog.php?item=165
Graeme Riley
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