Running an alternator

[Mike Jones]

Originally Posted by Mark Yacavone

Yes, it has to be in place, and turning with the engine ;-)

I have one of those.
Mike A114
P/SA

[Coleydog]

Back in the day we ran a alternator, under driven, charged up for Friday nite then ran Sat and Sunday, had no battery charger at track, 12 volt system. Never a problem starting or running. Let the fan motor run awhile, spray it down, set around waiting with no hassles for the next round, everyone else like ants on candy. Same procedure I'll use on the new car.
Might add, main purpose was to keep 13 volts to run the components not to keep battery charged, alt ran everything, not the bat. Bat just for starting.

[MR DERBY CITY]

Originally Posted by Mark Yacavone

Yes, it has to be in place, and turning with the engine ;-)

Oh the good ole days....remember it well the springnats in Columbus ,Ohio...after rd 2 the techman checked all the winners for a functional working alternator....guess that was before the hollowed , stripped out alternators stated showing up....LOL.......

[Robbie Welch]

Thanks again for the response's. My concern is load on the alternator possibly changing during a run and the affect it would have (if any) on the run.

[House of Darts]

Isn't there a way to have an alternator configured for full charging at low rpms? According to a municipal mechanic, police and EMT vehicles charge 100% between idle and 2500 rpms. At those levels, much move effective charging in the staging and return lanes. Cut off switch for racing.Best of both worlds.

[Hacksaw]

Originally Posted by Robbie Welch

Thanks again for the response's. My concern is load on the alternator possibly changing during a run and the affect it would have (if any) on the run.

Years ago we calculated that an alternator consumed approx. 3 to 5 hp. I would kill the field wire with a switch before the run. The battery supplies power to all the electrical devices and the alt. replenishes voltage back to the battery. So, IMO, if you maintain your batt. voltage to the same level before each run and let the alt. do it's job, then basically your run charge cycle will always be the same and the variables don't change. So it should not make any difference on the et.

[Nmbr1GMfan]

Originally Posted by House of Darts

Isn't there a way to have an alternator configured for full charging at low rpms? According to a municipal mechanic, police and EMT vehicles charge 100% between idle and 2500 rpms. At those levels, much move effective charging in the staging and return lanes. Cut off switch for racing.Best of both worlds.

Yes that will work great.
An rpm window switch and a relay will turn the field off consistently every time too.

[Coleydog]

Originally Posted by Robbie Welch

Thanks again for the response's. My concern is load on the alternator possibly changing during a run and the affect it would have (if any) on the run.

Imo if using 12 volt battery the loss of volts, during the run, will lose as much as an alternator using hp. 16 volt bat is another thing. With all the different electrical components on the cars today that bat will go down quick. An example, run a fuel pump at 12 volt than at 11 then 10, see how much it drops off. Now add the fans-computers-data loggers-ignition and other things, keeping 13-14 volts supplied the whole run is better and far out weighs the 2-5 hp loss (depending on how fast the alt turns at speed). Furthermore setting in the staging lane for hours makes it hard to recharge your battery. I for one will never run a car without an alt.

[buzzinhalfdozen]

Originally Posted by Robbie Welch

Thanks again for the response's. My concern is load on the alternator possibly changing during a run and the affect it would have (if any) on the run.

Robbie, not sure what type of alternator you're running but most of the one wire units are set up for a specific voltage and amperage target. With that one would assume the load being exerted by the alternator on the engine would remain fairly constant. As I stated about my sons bracket car (has a one wire alt.) there is no effect on E.T. with his set up Alt. is active at all times (not being shut off during the run) many runs per race. This is a big block combo so maybe that makes a difference of that I'm unsure.

[Lew Silverman]

All else being equal, an alternator is going to output somewhere between 13.7 and 14.2 volts on a 12 volt system, normally with a load and at idle. A well charged (100%) battery is right around 12.7 volts, so you get at least a 1 volt "boost" with the alternator running properly. It would be interesting to see what the effect of the load of a alternator would have on a vehicle with a fully-charged vs. under-charged battery. Could it be done on a dyno? From personal experience I've discovered that a one-wire unit needs to "spool-up" before it begins to charge, so it's either a small crank pulley or large one on the alternator, not BOTH!!