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tinnemaha(at)hotmail.com
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 Posted: Sat May 12, 2007 5:13 pm Post subject: Battery Capacity Check/CHT |
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How about the CHT going in the red? Would the alternator in its "max
effort recharge event" make the engine work that much harder, or was
there some sort of momentary sensor problem? Grant, did
power/mixture settings, environmental conditions, flight attitude
change during the recharging cycle?
David
Hi David,
Good question. I've wondered too if the readings were an anomoly or if the
alternator made the engine work that much harder. Although I was in a slow
descent (~100-200 fpm), the conditions of the flight remained the same. I
only had two CHT probes on (Cyls #2 & #4) & only #4 read abnormally high.
On the other hand, however, on an earlier flight I accidently knocked the
master to 'Batt Only' for a while & got also got very high CHT readings on
Cyl #4. So, although I cannot imagine or think of a reason why, I've
noticed the same condition twice now.
I've moved my other CHT probe to Cyl #3 & plan to test the waters again
after I upgrade my b-lead fuse.
The older get, the less I know.
Grant
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dave(at)abrahamson.net
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| Posted: Sun May 13, 2007 3:40 am Post subject: Battery Capacity Check/CHT |
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Well, I hope others and Bob chime in on this issue. In the car world
it is said you'll get better gas mileage if you have less electrical
doodads on, and I accept that the alternator puts some drag on the
engine. However, that it puts so much strain on the engine as to
redline the CHT is bizarre. Yours being a pump-pad alternator (I
have one too, in addition to a belt-driven B&C 60A) begs the question
about how much "drag" it -- and a constantly working vacuum pump --
puts on the engine. Perhaps there is data on this issue in the
engineering world?
David
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cjensen(at)dts9000.com
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| Posted: Sun May 13, 2007 3:58 am Post subject: Battery Capacity Check/CHT |
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A 60amp alternator, operating full out, will draw the equivalent of
something like 1-2 hp, so the redline CHT is unrelated to the engine
load. It's probably unrelated to CH temps also. Given your cited
experience, there seems to be a connection between your electrical
system and the #4 CHT. If you hadn't guessed---not normal.
Chuck Jensen
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klehman(at)albedo.net
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| Posted: Sun May 13, 2007 4:07 am Post subject: Battery Capacity Check/CHT |
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Even allowing for conversion losses it only takes about 1 hp to generate
about 35 amps at 14 volts. That can make a difference on a race with
millisecond timing but you aren't going to notice it on CHT.
Something else is going on. Is your instrument powered by the battery
and sensitive to voltage? Do you have a bad ground in the alternator
circuit such that one of the CHT wires is carrying a smidgeon of
alternator current? Magnetic coupling between the B+ line and the CHT wires?
Ken
David Abrahamson wrote:
| Quote: |
<dave(at)abrahamson.net>
Well, I hope others and Bob chime in on this issue. In the car world
it is said you'll get better gas mileage if you have less electrical
doodads on, and I accept that the alternator puts some drag on the
engine. However, that it puts so much strain on the engine as to
redline the CHT is bizarre. Yours being a pump-pad alternator (I have
one too, in addition to a belt-driven B&C 60A) begs the question about
how much "drag" it -- and a constantly working vacuum pump -- puts on
the engine. Perhaps there is data on this issue in the engineering
world?
David
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matronics(at)rtist.nl
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| Posted: Sun May 13, 2007 4:10 am Post subject: Battery Capacity Check/CHT |
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Your B&C alternator delivers 12V x 60A = 720W of electricity at maximum
rating. Assuming (big assumption) that the alternator is about 75%
efficient, that would be about 1KW or 1.3 HP of energy taken from the
engines output. You can apply the same formula to the pump-pad driven
version.
Rob
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