does an increased load on the alternator result in a greater parasitic horsepower drag on the engine? for example, to free up horse power you remove the mechanical water pump, fan, fuel pump and generator. then install a new high output alternator to power a remote waterpump, electric fans and fuel pump. would you gain any horse power out of that? or would the encreased electrical demand cancel out the gains?
Mechanical fans draw alot of power. I dont think an alt. would **** that much power, at least not if the bearings are good.
Uh....yes, more current generated more horsepower required to turn it. (remember there is no free lunch). I remember asking why the stock cl*** racer twisted his drive belt with 2 cresent wrenches before he made a run.....I was about 12 years old and got ushered out of his pits. It seems the belt would fly off after leaving the line freeing up some power and still legal by the rules!
Depends on the load amount required to run all the accessories at that time of use, the necessary speed of the alternator to supply that demand if possible, pulley diameter ratio, SOC of the battery(s), cable gauge and length, and the rpm range of the engine intended.
An alternator with increased output will require more horsepower, thus negating a lot or all of the gains from electrical fan or water pump when used on the street. The electric fan can be a gain in some cases when a car is traveling at highway speeds and there's enough air flow to cool the engine without the fan, thus reducing electrical demand. In drag racing, where the engine has an electric water and fuel pump, and electric fan, the alternator can temporarily be switched out of the circuit and the electrical components run on "total loss" battery power, thus eliminating the power demand. Bob
I don't know......take a 100 amp alternator running at full load at 14.5 volts. That's 1450 watts.A 3 hp engine can deal with 1450 watts.100 amps can run a **** load of cooling fans and electric water pumps.Reality says there's some loses here so let's say it takes 5 hp to run the alternator. So how much power does a mechanical water pump and fan take? Probably more than 5 hp? maybe 10? Is there any actual facts from a real life example? Too much complication maybe,pilots used to say two engines doubles the chance of an in flight engine fire
Perhaps another way to look at it is when the power goes out in your home you may use a portable generator to power the vitals, fridge/sump etc. When plugging into the generator it bogs quite a bit.....I'm sure you can realte to an automoble's charging system.
Anyway,I don't care for the hum when electric cooling fans come on at idle. Big mechanical clutch fans are not that noisy at idle,roar a bit when the engine is first started but generally quiet at road speeds unless the fan is locked up for cooling.
I am also interested in this. I am building a 327 for my truck and have a complete march pulley set-up I got from a friend. Debating on running mech fan instead. I like the simplicity and originality concept. What are the HP downsides of mech fan vs elec fan?
You won't notice the difference power wise, also a electric fan may not be able to cool your ride on the street. For a drag car however I like to put a microswitch on the carb so that when your at full throttle is cuts the alternator off while making a p***, but lets the alt come back on and charge the battery when you let off, and idle around the pits (you of course could not do this with a single wire alt).
Yes, there is no free lunch. But consider what is actually happening. An alternator only makes power when it is being used. Bigger alternators are not harder to turn at the same draw. If your electric fan only comes on at idle, an goes off at cruise, the few hp the mechanical fan absorbs is gained in practice. But don't expect to measure much difference in performance. Paul
This will absolutely will not work at all. You would be lucky to get even 30% of your power back. It will likely be more on the order of maybe ALMOST 10% of your wasted power returned if you are very good at design. That would be like the kid on a bicycle who uses a wheel driven generator to power a motor that drives the wheel, which pushes the generator, etc and then wonders why the bike doesn't just take off and run. There is no such thing as a perpetual motion machine. Electric fans are beneficial for a different reason. The reason a mechanical fan almost always eats more power than an electric is that the mechanical fan has to deliver very good air-moving performance (cooling) at low speeds. When you rev it up much higher, it has a great power-robbing OVER-CAPACITY that serves no purpose other than to eat up cheap horsepower. An electric fan does not do that. It does NOT **** extra power at higher engine speeds. Electric fans (and electric water pumps) use no more power at high engine speeds than they do at low engine speeds. The mechanical fan "over-capacity" when revved up uses up much much more power than it really needs to, but an electric one will stay the same. Go ahead, put a generator on your bicycle back wheel, and an electric motor on your front wheel. Notice how much harder it is to pedal to get your "magic power machine" to move down the street. Also note that is does NOT power itself on down the road. It eats up your pedaling energy and comes to a halt even faster than before. I am sure you will remove the power-robbing parasitic drag of the "magic free energy machine" very quickly in favor of the old pedals. Part Two- OF COURSE an alternator has very low drag at low outputs and a much heavier drag when putting out higher outputs. I thought everyone, or at least every CAR GUY, has heard a running engine slow down or labor a bit when you jumper a car with a dead battery. Just listen to the idling engine when you hook to a dead battery. Almost always you can even hear the "alternator-whine" sound get louder as it works harder. Hook up that last cable to a dead battery, and you will hear the "donor" car's engine slow down and labor a bit as the alternator starts working harder to supply power to the dead system. I though everyone knew that, and has heard that happen many times. I thought this was a CAR GUY place. I can't believe CAR-GUYS didn't know that. (uh oh, how many enemies did I just make? sorry) A previous post was CORRECT in saying that a larger capacity alternator does not add extra drag at low power outputs. It only adds extra drag when it has to labor hard to put out MORE power to meet bigger demands. At very low power demands it is freewheeling or very close to freewheeling. That is correct. It does no harm at all to engine power output unless you ask it to work hard at the wrong moment. Yes, turning off the alt for a few moments will free up a few HP (if your battery is so charged up that it doesn't need alternator help for a while, the alt has already "turned itself off" for a while anyway), but a bigger capacity alt will NOT add drag unless you also add more loads such as lots of lights, radios, etc to also make it work harder.
It is fairly easy to get an approximation of the gain/loss of an electro/mechanical system. Figure that most rotary electrical devices are 50% efficient 1 hp = 746 watts. Knowing the watt load (from mfg. specs) of the fan, water pump, fuel pump and ignition you can figure the total load and the resultant power drawn from the alternator. Convert watts to hp, double it and you have the hp required to drive the alternator. Figuring the hp required to drive a mechanical fan or water pump is a bit more complicated but can be done in the home shop.
Keep in mind that an electric water pump puts essentially the same load on the system at all engine speeds, unlike a mechanical pump that is basically a little dyno putting and increasing load on the engine as rpm increases. Same for an electric fan vs. mechanical. There are a few additional variables in both equations (thermostatic switches, fan clutches, and variable hydrodynamic resistance from the thermostat jump immediately to mind; there are certainly others). In any case, the differences are likely to be small enough that you would have to work really hard to measure them.
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