nuckolls.bob(at)aeroelect
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 Posted: Fri Apr 29, 2016 3:23 pm Post subject: 24V B&C starter current? |
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At 12:35 PM 4/29/2016, you wrote:
| Quote: | --> AeroElectric-List message posted by: "digidocs" <junk(at)dcarr.org>
Hello AeroElectric,
Does anyone have data on the approximate starting current for the 24V B&C starter?
I spoke with B&C briefly and the best data they have easily available is 250-300A. This was higher than I was expecting. For example, Skytec claims 85-125A on their 24V NL/ec starter. |
Depending on the size of the engine, temperatures
and engine condition, both figures may be correct . . .
but different for another engine/wiring combination.
As a general rule, we don't concern ourselves with
the actual numbers for cranking current . . . because
it varies so much on an airplane by airplane basis.
What we DO concentrate on is battery condition. A
fresh, off-the-shelf 18 a.h. SLVA battery shouldn't
even breath hard to dump 600-700 amps at 9v.
Keeping voltage drops in the cranking current
circuits low is the secret to getting the most
from what ever battery you choose . . .
If I were asked to put a figure of merit on
starter A vs. starter B vs. starter C. I'd
have to load them with a constant torque
representative of a worst case engine (6 cycl
lyc cold soaked) then measure rpm at load
and watt-seconds consumed for some benchmark
cranking interval . . . say 10 seconds.
But after posting figures for the three devices,
I'm betting the percentage of market share for
the different offerings would not change materially.
Compared to boat-anchor Prestolites, the cranking
performance for all modern starters is so much
better for less weight that energy consumed
is irrelevant.
No starter will require more than 5% of total
energy contained in an 18 a.h. battery to
get a well tuned engine running. So if the
three samples took 1.8, 2.3 and 2.9 percent
of total energy, it's more likely that
the builder would choose the least expensive
with an acceptable field performance as opposed
to any choices about conserving watt-seconds.
What is the basis for your concerns?
Bob . . .
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