Alternator Design NERD FOOD Look At Your Own Risk

Regarding the talk about the load on the engine from a high capacity alternator.

In fact, In race cars every thing you can do to move power to the WHEELS is important.. So putting an oversize pulley on the alternator (Slowing it down and thus reducing the load on the engine) or in some cases (Quarter milers) leaving it off and running on batteries only... Gets you to the finish line faster.

MEXICOWANDERER wrote:
Umm hum but a 60 KW 12-turn generator normally weighs in at around three tons. This thing weighs less than a group 31 AGM battery.

LOL...

Yep, I agree with you, it has potential...

:)

Umm hum but a 60 KW 12-turn generator normally weighs in at around three tons. This thing weighs less than a group 31 AGM battery.

MEXICOWANDERER wrote:
The links point to SIXTY KILOWATT 300 VOLT alternators little larger than a car alternator

33.5 kg of mass is quite a bit bigger than a typical car alternator.

;)

Automotive HAIR PIN alternators are six phase. The 3, 4 and 6G ford alternators use 3 phase Y wound stators with a rectified wye connection. Eight rectifiers. I am still old-school: 3-amps and under DIODES, 3 amps and above RECTIFIERS.

The links point to SIXTY KILOWATT 300 VOLT alternators little larger than a car alternator. When someone wises up and cools an alternator with pumped transmission fluid through a cooler, uses hairpin windings and FET rectification, things are going to get wild.

Try using .01uf ceramics phase to phase, and a 10Kuf 320 volt electrolytic cap on the output to calm things down. The alternator itself uses as OEM cap anywhere from .47uf to 2.2uf.

My monster "portable" battery charger is slated to use a pair of 300 amp shottky rectifiers, a GM style avalanche rectifier bridge with six rectifiers, a 2 farad capacitor.

Mex, a little off topic but the links you provided reference 3 phase alternators. The alternators used on Ford's F53 MH chassis are 2 phase. Only 4 diodes. Can you say RIPPLE?

Richard

DryCamper11 wrote:
The problem with capacitive energy storage is that it's too easy to release the stored energy...

Yep, the instantaneous power they can release can be an issue, and a plus, but the low loss, long life, and lower environmental impact capabilities make them a possible replacement to current battery technology.

ken white wrote:
While batteries are moving forward in technology, so are capacitors, and energy stored in a dielectric field makes more sense to me than energy stored in a chemical process.

The problem with capacitive energy storage is that it's too easy to release the stored energy. I once worked with high energy capacitors - the size of a small suitcase. We had to use/store them in a steel lined room with a steel door "airlock" that wouldn't let you through the inner steel door into the room until the outer steel door was closed. There was a 1" dent in the 1/4" steel lining of the room where one of the 30+ capacitors had detonated when it failed. The bang it made during detonation was quite memorable. (The purpose of the capacitors was to turn a 4" by 1/4" aluminum rod into aluminum vapor that tagged a supersonic flow through a supersonic wind tunnel so that a laser doppler velocimeter could read the flow speeds around the test reentry vehicle model.)

MrWizard wrote:
how much HP does an automotive A/C system use ? 2 maybe 3 HP ?
your engine just idling is producing way more than that
its not about engine HP
its all about pulley ratio and 'alternator RPMs'
the 'current design' alternators in production need more RPMS to produce max output
but it doesn't have to be that way

OK, lets do some basic electrical/mechanical analysis.

Lets assume a 300 amp output to the electrical system when spinning at 1000 RPM at the rotor.

Power will be 300 amps x 13.7 volts or about 4110 watts.

If we assume a 90% efficiency at the lower RPM range then the input mechanical power to the alternator is about 4567 watts - we are neglecting other losses and loads.

The input mechanical power divided by 746W/1HP means that approximately 6.12 HP is needed.

Since HP and Torque are not mutually exclusive, the following equation can be used to figure out how much rotational force is being developed at the pulley.

HP = Torque x RPM / 5252 or rewritten, Torque = HP x 5252 / RPM -> 6.12 x 5252 / 1000 = 32.14 ft-lb of rotational force.

If we assume an alternator pulley diameter of say 6”, which is pretty big, then the radius becomes 3” or 1/4 of a foot.

This means the tangential force applied to the alternator pulley must be about 32.14 ft-lb / 1/4 ft which equals 128.6 lbs of force for a rotor rotation at 1000 RPM.

The tension and friction values required on the belt and pulley will have to be considerably higher than this value or the pulley won't turn or slipping will occur.

Since this tension force is being applied to bearings through shaft deflection, and a whole new can of worms open up.

Now couple all of the other loads being operated at the same time to the drive belt being operated at the desired RPM and tension increases even more.

So the main issue with low RPM, high current, alternators is of coarse loading of the motor, belts, pulley system, bearings, etc...

But hey, if it was easy, cheap, and small enough, then they would be standard on everything from the Prius up...

:)

ken white wrote:

MrWizard wrote:
Mexi
is entirely right
you have a 300~500 HP combustion engine sitting there
if the pulley diameter and electrical characteristics are correctly designed you can get mucho amps at idle

just remember a 6.5 HP engine can create almost 4KW of power when used in a genset

1 HP = 700+ watts
you only need to use about 7HP (or less) from that BIG engine to produce 4KW of power

Yep, 1 HP is equal to about 746 Watts...

Unfortunately the high HP numbers are developed at higher RPM's and not at idle.

AC kicking on and off at idle is in the 5-10HP and it doesn't affect modern cars one bit. back in the 60's it would drop the idle a slight amount that all.