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Bernie, et. al.
Battery amp-hour ratings are usually at the 20 hour discharge rate, i.e. a 20 amp-hour battery *may* deliver 1 amp for 20 hours. As the current goes up, the delivered capacity drops. At 20 amps, a 20 amp-hour battery will deliver considerably less than 1 hour of current.
Tracy once said that allup load to run the EC-2, pump, and ignition/injectors was almost 13 amps, if Bernie is getting only 7.8 amps that is an interesting data point. At what rpm was that Bernie? Rusty just quoted 12.1 amps at 1500 rpm, with 4.4 going to the Davies Craig water pump. That would be consistent with Bernie's if his measurements were at similar rpm.
The higher rpm sucks more power because of the coils and injectors. I doubt if the fuel pump changes much, since we bypass fuel at low rpm anyway.
Drawing ~8 amps on a 17amp-hour battery would be consistent in it coming down in about an hour.
Bill Schertz
KIS Cruiser # 4045
----- Original Message ----- From: "WALTER B KERR" <jbker@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, May 14, 2005 11:58 AM
Subject: [FlyRotary] Re: How long can you fly on your battery??
Ian wrote:
Asuming a 15Ah battery, you are using 15 amps to power your systems. That
is
an awful lot. Did you shut off the alternater field?
The usual FI 13B in a plane will go for about 3 to 4 hours.
______________________________________
I measured the amps to run the engine as 7.8 amps. Hard to believe a FI
13B can run 4 hours. Tracy seemed surprised that it only need 7.8 amps. A
15 amp-hour battery will not deliver 15 at that load. If you read the
fine print, the rating is at a couple of amps load. Do not know when this
battery would drop off like a rock at some voltage. When I ran it with a
ground test at 12 amps, it bombed at 11 volts and 12 amp hours.
Bernie, a neophyte on electrical stuff, but this is what I have observed
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