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'm going to install another 45 amp Denso alternator with overvoltage protection.
Also, I think Tracy's EM2 can be set so that a low voltage condtion will set off my
warning light.
Brian Trubee
Brian,
You realize that if you put it in the ground cable to the "frame" you will be
running starter current through the amp meter shunt. The shunt takes the heavy
current and the meter effectively measures the voltage drop across it and
reads in amps. The manufacturer calibrates for the conversion. To do this the
shunt creates a slight resistance and thus a voltage drop across it. Not a
good plan for the starter circuit.
Dale Davies
True Dale but these modern shunts have very low resistance.
Consequently the voltage drop across them is on the order of millivolts.
This voltage is then amplified by modern integrated circuit to read out
digitally (with 4 places 0.001) amps up to 500 or 1000. So they can handle a dynamic
range of several hunderad amps for starter as well as 10 amps for the running lights.
All for $75.
http://www.digikey.com/product-detail/en/DCA5-20PC-1-DC1-RL-C/811-1088-ND/1926131
Paul Lamar
--
The Rotary Engine News Letter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
You Tube key word PaulLamar2
Copyright 1998-2012 All world wide rights reserved.
