Brad.Kahler@141.com wrote:
> > >Engineering books state a belt driven fan takes away 6-9% enginepower.
>
> What does the engineering book say about the extra horsepower needed
> to keep the battery fully charged ?!!?
The fan uses 6 to 9% @7.5% of the total HHP, assuming a 100 BHP car,
that's 7.5BHP. If you workthat out in kW as a rough gide I'll use a
conversion of 2.2 kW per BHP. Thats 16.5kW at peak revs.
The electric fan for Michael's GT6 drew a current of 10 Amps. 10A * 14V
= 140W. Assuming an altinator efficiancy of 50% the extra load on the
engin if the fan is on all the time is 280W. This is reasonable because
this is probebly what the mechanical fan draws a idle. Even if I got
the conversion wrong and its 2.2BHP per kW, it is still 280W when
compared to 3400W.
You also have to take into account that the figure is for max RPM's
the higher your engin revs (or the grater the difference between idle
and max RPM's) the higher the %. The other thig is the drain at lower
revs is probebly more than at maximum. You don't get that much air
through the radiator so the air the fan is sucking will be a lower
pressure. Hence like a blocked vacume cleaner the motor spins faster,
using less power. This is probebly why when my frend did a test he came
up with 15 to 20%. At lower RPM's the fan will have to move higher
pressure air, so the load/rpm's will be higher.
The next thing to remember is when the car is traveling at speed it
dosent need the fan, and so you will more than likly find that it is
only used 5% of the time. On a hot day in a trafic jam my car with a
BMC 'A' serise engin came on 25% of the time. You will also find that
the cooling fan is only used when you don't have lights, heated rear
windscreen etc. on, because your not ushaly get stuck in traffic with
the engin overheating in that situation.
So you made it to the end.
James
--
James Carpenter
Yellow '79 spit wired by a trained marmot
|