Alternator for racing?

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bsnova
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Alternator for racing?

Post by bsnova » Sun Apr 30, 2006 12:38 pm

I need to buy a racing alternator and would like input on how many amps I need. Do alternators that output more amps take more HP to drive? My car is a typical drag only car with elect. fan, water pump, fuel pump, msd, etc. It is a class car so I am concerned with not loosing HP from installing it. Any input would be appreciated. THX--BS

BCjohnny
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Sorry no free lunch....but gains are also there......

Post by BCjohnny » Mon May 01, 2006 11:48 am

All alternators take power fron the engine to create electrical energy....basic physics.

It depends on alternator efficiency as to exactly how much, but 100amps takes approx 3bhp. Scale it down by working out your current draw, so if you're drawing 30amps it's about 1 horse. You still have to factor in inertiaral losses caused by having to accelerate the alternator rotor, but this would be quite small. And theres some belt friction too, so if you can run a "poly V" (serp.) type, but again it's a small loss relative to the whole.

I have however read reports of people picking up good power gains by running an alternator, due to ignition gains, 10bhp or more is not uncommon.

You stand to gain more than you will lose, on average.

As regards type, you can buy a high-dollar upgraded piece most places......but my advice is to scour the local breakers and find the smallest "Nippon Denso" (later ones just marked "Denso"), "inner ventilated" alternator you can find (some Hondas, most Toyotas). They are the base units for a lot of upgraded types sold, and the small frame ones weigh less than 10 pounds.

John.
"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

T RICK
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Post by T RICK » Mon May 01, 2006 10:32 pm

A trick we did years ago was to install a wide open throttle swich that opens the feild and does not let the alternator charge. Then you don't have an inconsistant load on the charging system. no toggle switch to forget either.

Rick

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Post by BCjohnny » Tue May 02, 2006 4:21 am

Yes disabling the field takes the need to drive the magnetised rotor freeing up, as said above, around 1bhp. You also lose all the gains that can be found running the ignition at its intended voltage (unless you run an extra cell type battery).

One point I failed to make, as I thought it was a bit obvious, is to make sure the battery is as fully charged as possible before racing. That way you're not "charging up" the battery at the track but merely "topping off" the charge. If you can find a charger with adjustable/high charging settings so that you overcharge the battery (that is above normal system voltage of 14.5-15v) at about 16v. Do this the night before and let it settle overnight. Connect when you get to the track. Yes it will shorten the life of the battery but not as to break the bank, but it also fools the alternator into "thinking" the battery's fully charged (the surface voltage is higher), allowing the alternator to supply mainly system loads. Be careful when charging this way as more "gassing" occurs so do in a well ventilated area(observing all charger manufs. recommendations) and if possible choose a battery with removable filler caps, and re-fill with de-min water regularly.

John.
"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

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Post by #84Dave » Tue May 09, 2006 12:53 am

Nova........ I'm an oval track racer but we've used the Jacobs DC-DC converters for years. And no alternator on the car. I've looked at the voltage output, with an o'scope, of a battery and battery/alternator combination on an engine under power. The voltage is so 'ratty' it makes one wonder how things could function electronically. Look at the output of the Jacobs converter and there's only 3 milli-volts of bi-phase noise riding atop the 16 volt output. The bi-phase noise a function of the internal 64KHz 'chop'. The Jacobs takes 12V in from the battery and turns it into 16VDC. The beauty of the unit? The battery voltage can decrease to 9.5VDC and the Jacobs still outputs 16V. We use the 16V to power our MSD crank-trigger ignition, the tach, run the fan on the radiator, and the fan on the quick-change oil cooler. I've looked at the converter output while turning the 10-amp radiator fan on/off and the output 16V doesn't budge! The only Accuvolt unit Jacobs manufactures now is a 100-amp output converter. The voltage output is adjustable from about 13.5 - 16.2 VDC. Jacobs is now part of the Mr Gasket Performance Group and the Part number for the Accuvolt is #510064. A great device and we've never experienced a failure all the years we've used them.

Dave

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