Hot Rods generator question for the Jr. stock guys

I am going to put a little higher rpm cam in my 57 and wonder how much rpm the generator will take before I start spinning the windings loose. I was told that is what will happen. Thanks

 

No idea when, or even if that would happen but I guess you could substitute a larger diameter pulley to slow it down. Keep in mind that if that is done you lose some generator output at idle and low RPM.
Moroso has cast aluminum large diameter generator pulleys that were a must have on Jr. Stockers BITD.

 

I used to explode generators pretty regularly at 6-7K rpm on a Ford I had... and it's usually the commutator that comes apart. In those days it wasn't a big deal, good used ones were $10-15 at the wrecking yards. They're not so easy to find these days. As noted, a larger pulley on the generator will cure that but if you do much in-town driving, you'll have issues keeping the battery charged.

Alternators are immune to this, you might consider switching.

 

I'm at this point now on my 64 Fairlane, I gave up and lost all the weight of the generator and cast iron bracket.

 

I Shift the 283 in the old Jr. Stocker I have at 6000 and never had a problem. That said I did lose some of the cooling fins on the generator on my 34 but I shift it at about 7500.

 

Way back in the early 60's when alternators were the new
thing, a friend bought a new 64 Comet 289-4 speed and after adding
a cam and other goodies began grenading generators on a regular
basis. End story was that Mopar, then GM [in '63 IIRC] went to alternators and Ford put a smaller pulley on their generators to
compete, because they were last to the alternator party by a year.

Solution was to put a pulley off an earlier Ford generator.

 

I was around a lot of dirt track racers in Central Texas in the early 70's who didn't run any charging system, just a belt that turned the water pump. The guy who owned the shop I worked in carried a couple of extra batteries for their modified but seldom changed one between heats.
I'm not sure if Jr Stock classes required the generator to actually turn while making a pass though.

 

Yes they did.

 

Yes but if you wanted to push the rules a bit you just added a switch to open the fields for less drag then closed it for checking.

 

A smaller pulley will turn the generator FASTER.

 

Well, 6000 will be tops for mine anyway so I'll just give it a try. Thanks fellas.

 

When you disable the generator you are shooting your self in the foot. Coil out put is dependent on coil in put. 12 v verses 14 v. THe higher the voltage the wider the plug gap. With a fully charged battery the drag is what ever the ignition draws.

 

Joe drive it off the drive shaft. Cleans up the engine compartment and cures the problem of engine RPM.

Ok I am going off memory here and have not played with an generator race car since the early '70s but it seems to me like the magic number was 6500 before we started slowing the genny down. Take it with a grain of salt but that is what I remember.

 

Zip offers a 3 5/8" standard corvette pulley and a 4" FI hipo Pulley.

 

Agree with Beaner--shifted at 63-6500 never lost a generator but it would chuck fan belts quite often. Doubled the arm and put a small rod off of it about 1/4" above the belt running.

 

Let me see if I can extract the bullet in my foot. And advice our less learned friends. In a normally charging system, functioning correctly, charging with an alternator/generator utilizing a lead acid 12 volt battery a fully charged battery normally has MORE than 12 volts stored when fully charged.

When functioning properly a generator/alternator MUST apply AT LEAST 13.2 volts to the lead acid battery before it will take a charge. The 13.2 volts is what is termed "Overcome voltage" and is a constant, it ALWAYS must be applied to charge a lead acid battery period. BUT at only 13.2 volt input it would take a LONNNNGGG time to charge the battery so the system produces more. (see below)

So all 12 volt fully charged batterys are charged to AT LEAST 13.2 volts NOT just 12 volts. You can check it yourself make a run down the expressway so the battery is fully charged and look at your voltage gauge with the engine off and you will see there is 13+ volts in your 12 volt battery.

And yes indeed a proper system will produce 14-16 volts SOMETIMES. If the battery is fully charged to 13.2 volts the generator/alternator STOPS PRODUCING more than 13.2 volts always that is the function of the regulator.

So with a fully charged battery the generator/ alternator are NOT outputting 14-16 volts they are just cruising along doing nothing (unless you start a high draw application).

So the bottom line is with a fully charged 12 volt battery, with a functioning normally, charging system utilizing either a generator or alternator there is negligible difference between system output and battery voltage. It is NOT 12 volt vs 14 volt constantly that situation only occurs with a discharged battery that needs charging.

So if your system is working correctly and you pull to the line and open the fields with a switch you are getting at least 13.2 volts to the coil not 14-16.

Does it work? Is it worth the effort?

If you open the fields you will see an immediate increase in idle speed normally from 800 rpm idle speed to at least 1000 rpm due to the less parasitic drag of the charging system. Someone with better math skills should be able to calculate exactly how much horsepower is recovered in as an example 200 HP engine at idle with the fields open and or closed and it has to be substantial. Personally I picked up 0.20 ET opening the fields.

And the NHRA knows this otherwise they would not have promulgated this rule: From the NHRA rule book;

Alternator or generator must be engine-driven and functioning. Belt must be tight ...

Now you know as they say the rest of the story.

 

A fully charged battery is 12.6 volts. 2.1 volts per cell, normal charging system voltage is roughly 13.6 volts, they should not see 15 or 16 volts.


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Use the Smokey Yunick approach and see what the rule book DOES NOT say. Does the generator have to work? If not press the shaft out of the armature, use bearings, not bushings, in both the front and back plate and you will have an generator shaped idler pulley you can spin 20k rpm with no harm.

 

Without regard to Generators and disassembly at high RPM, to completely recharge any battery a voltage needs to be applied that is approximately 2 volts above and beyond the open circuit voltage of the battery. This is somewhere around 14.6 volts for a lead-acid automotive battery. That's at 77° F, the "standard" temperature for the charging tables. As the temperature goes down a correction factor is applied to the correct charging voltage, as the battery internal resistance increases. At 20° it's a full volt. So over 15 volts is not out of line to fully charge a battery when it's below freezing. Generator charge tables are even about 1/2 volt higher than alternators at any given temperature. I think this is because they are mechanically regulated versus diodes.

 

Joe, you're too damned old to be turning anything at 6500 rpms.

 

From the NHRA rule book:
Alternator or generator must be engine-driven and functioning. Belt must be tight ...

BUT it doesn't say functioning CONSTANTLY so a little creative interpretation of the rules it is functioning until you open the fields when making your runs then at the end of the run you close them again and it returns to functioning.

 

Trying to make this thing about 1966-or so . I did not have an alternator till I bought my first Mopar.

 

Sorry, fat fingers, should be about 14.6 volts max, above about 14.8 volts the battery can start overcharging and gassing off so I stand behind my should not see 15 or 16 volts.


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That would be true if the temperature never strayed from 80 deg F., a battery won't boil off at the higher voltages when it gets cold, the correct charging voltage is always based on temperature, there is a correction factor applied on the table to compensate for the increased internal battery resistance as the temperature decreases.

At 20° F it is an additional full volt higher than at 80° F. At temperatures higher than 80° the charging voltage needs to be decreased than what the table allows at 80°. In extreme cold, 14.8 volts is basically just a float charge.

 

^^^^^

When I first started tuning for Donnie he was running a D Stock '57 Chevy. He had a 12.300 dial and one day when we were running heads up at a track I removed the belt and rolled a smaller belt over the water pump and lower pulley. A trick I learned when I was in high school. On just battery it moved his ET to very high 11s or very low 12s depending on how well he rowed the gears that pass. Well someone noticed us charging the battery between rounds (jumper cables may have been a give away). They didn't black flag us but they did make me reinstall the belt and re-tech.

Part of the reason that I got my 4,000 LB brick of a C-10 into the 12s (on street tires) after driving 150 miles to the track was that I was not running a fan and could disable the alternator and cooling fans in the staging lanes with the flip of a switch.

Very very old racing trick in a non street class was to run sans a charging system and it is common to this day to see men charging their batteries in the pits between rounds.

@loudbang is a smart man. Don't tell anyone I said that.

 

Truck 64 is right on about battery charging voltage. I will be back tomorrow to explain my lack of knowledge on race car tuning.

 

Ok, well I guess somehow my stuff charges at -40.


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So my other question becomes how do our old cars charge in all weather conditions? The voltage regulator has no way to know temperature. What am I missing here?


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For the record I had a blown 283, 55 pickup, Several 7300 rpm moments, an will be using the same stock gen. On my coupe... Stock pulley also

 

You made a nice truck out of the ol girl, Benno.