Dual Alternators on a Race Lola

Ron Earp · Jul 23, 2009

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ersonal; mso-style-noshow:yes; mso-style-unhide:no; mso-ansi-font-size:10.0pt; mso-bidi-font-size:11.0pt; font-family:"Verdana","sans-serif"; mso-ascii-font-family:Verdana; mso-hansi-font-family:Verdana; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; color:windowtext;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Calibri; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.0in 1.0in 1.0in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style> Has anyone ever run a dual alternator configuration before? We are dead serious about the 13 hour attempt in the Lola this year since RCR is now building the car and can get the job done. I’m putting together a team of drivers and starting to consider various failure modes of a race car. I’ve only been racing about four years but in that time I’ve seen four or five alternator failures on cars I’ve either owned or been crewing for. It seems like one of the more common failure modes and when they fail it has, at least in the ones I’ve witnessed, been the voltage regulator or a coil issue. The alternator still turns fine so not a seizure or anything mechanical.<o

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On the Lola I put a single wire alternator like this:<o

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Powermaster 8-57100 - Powermaster Race Alternators – SummitRacing.com<o

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But I could envision a dual alternator setup with maybe the second unit being an alternator that requires field coil activation that is controlled by a switch. That switch would disconnect the single wire alternator when it failed and turn on the second alternator. <o

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Anyone out there have any experience with dual alternator setups, beyond the configuration commonly seen on diesel trucks?<o

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576103 · Jul 23, 2009

Ron,

I don't know nuthin' 'bout 'lectricity so I can't tell you if a dual setup would work or not.

But I can tell you that I've seen lots of race cars that power their alternators not from the engine, but rather by a pulley inserted between one of the gearbox output flanges and the driveshaft. It frees up horsepower and gets the alternator into a slightly cooler environment.

The disadvantage is that it only charges when the car is actually moving, making it impractical for a street car. But if your race cars is running, but not moving, you've got bigger problems to worry about. :cheesy:

Ron Earp · Jul 23, 2009

Mike Drew said:
But I can tell you that I've seen lots of race cars that power their alternators not from the engine, but rather by a pulley inserted between one of the gearbox output flanges and the driveshaft. It frees up horsepower and gets the alternator into a slightly cooler environment.

I've seen those too but I'm not a big fan of them since the engine mounted unit in my case is accessible and easy to tend to. I think they were used in cars where the front dress was particularly tight and they wanted to have access to the unit easily. They look cool though.

As far as freeing up hp, that won't work. Nothing is for free. For example if you need 500W out of the alternator to run the race car the alternator going to draw 500W (0.66 hp) no matter where it is connected, to the engine, half shaft, or running off of a fifth wheel lowered under the car.

Dave Deerson · Jul 23, 2009

Some of the "race" alternators I have seen are very small and seem to be built for sprint racing and lack in the cooling/longevity dept. Look at some of the race alts. output,they have one amperage rating to start and another much lower rating when hot. I ended up going with a slightly larger unit from a Honda Civic,which is the next larger Nipondenso case than most populal "race" units.It is already designed for installation on an engine that can spin up to 8k rpm and when freshened up will last for many seasons if cooled properly. I just converted it to single wire and have my "race"alternator for a fraction of what HRP get for the Canton units . I have used this type of alt. in the last 3 race cars I have built.

RamboLambo · Jul 23, 2009

If I was doing twin alternators I would probably connect them via steering diodes so you dont have to switch them over if one fails. Also with the steering diodes, you would have both alternators operting in parallel so in effect halving the load on each alternator. I would also under drive them so they are not spinning their wee hearts out for the duration of the race! Keep them cool as well. I saw under the bonnet of a Beemer the other day, a factory built cover over the rear of the alternator that extended via piping, out into the front of the car for cold air.

Keith1 · Jul 24, 2009

What would be the maximum current draw from the battery at full racing speed (with all toys engaged using zero diversity) and are you expecting to have to use headlights?

IanAnderson · Jul 24, 2009

Hi Ron

I have looked into the alternator drive from driveshaft before and one of the reasonings is that you do not have to spool up the extra alternator mass at each gear change.

People go to great lengths reducing mass - skim flywheel etc but still spool up all the anciliaries ALL the time

I have also heard that a common reason for failure on the alternators is spinning them too fast (more heat generated) and then they fail

So logic would say mount it on the driveshaft - at race it would be reasonably constant RPM and should never over rev. You could still mount 2 - one on each drive shaft if you want backup

Back in Formula V days we had to run a standard fan and housing but we found that if we ran the belt so loose that you could touch it together between pulleys that the engine would spin up considerably faster thatn having to haul the fan, generator etc up each time you accelerate throught e gears. (The ones on the know reconed this was worth about 10hp during the "slip" time)

Ian

Veek · Jul 24, 2009

Ron,
If you hook up a single wire (internally regulated) set up, you can change an alternator in under 10 minutes so I'm not sure it's worth the weight penality and the complexity of the belts etc. I would run dual coils with a switch though. As mentioned earlier, you'd also want the low drag pulley so you don't over-rev it.

Johann · Jul 24, 2009

Ron,
In my rally car in South Africa we used 2 alternators and two batteries because of the nature of the off road stages and also using up to 6 headlights for night rallies.
We found that battery failures are much more common than alternator failures.
One alt. was on the motor and the 2nd alt. on the drive shaft. We had a battery on each side of the car to balance the weight. I also noticed that in NASCAR battery failure are more common than alt. failures.

Ron Earp · Jul 29, 2009

Keith1 said:
What would be the maximum current draw from the battery at full racing speed (with all toys engaged using zero diversity) and are you expecting to have to use headlights?

Worst case:

6 amps for the MSD, 1 amp per 1000 RPM quoted from them.
4 100 W lights, P = I * E, E = 12V, 400/12 = 33 amps
Radio, video, and illuminated number panels, 5 amps tops.

Everything else on the car is old fashion analog stuff.

So, maybe 50 amps worst case.

Johann, that isn't a bad idea with two batteries. I have seen a battery failure too at the 13 hour.

We'll only spin the alternator as fast as needed to get the proper output. But there is no free lunch - if the alternator needs to produce 50 amps then it'll draw P = I * E, P= 50A * 12V, 600 W and that is in a perfect world. It probably is only 90% efficient, maybe worse. So figure 660W, or 0.86 hp.

Ron

Mark IV · Jul 29, 2009

Ron,

Start with a good alternator, not a rebuilt discount store unit. Either confirm best quality bearings or replace them yourself. Many units have very cheap Aisian bearings, I used to buy alternator bearings for the pulley end for around $4.00 for a sleeve of 10.....how good do you think those are? Having the rotor balanced is a good investment also to keep strain on the bearings/case/mountings down.

The right pulley to keep speeds down and proper cooling (a duct if needed is a good investment) and a good, large capacity battery to handle any draw spikes and you should be good to go. I really don't see the need for dual alternators, that is a "band-aid" on the real problem, crap alternators!

2124 · Jul 29, 2009

Ron,

Run a good unit and "gear it down" so that it doesn't spin so fast.

Cliffbeer2 · Jul 29, 2009

Ron, since you say it's typically the voltage regulator/coil that fail, why not run duel regulators/coils (one in the alternator, and one wired remotely) in order to avoid the weight and drag of running two separate alternators? Some kind of selector switch between the two perhaps in order to change it up when one fails.

Dual Alternators on a Race Lola

Ron Earp

Mike Drew

Ron Earp

Dave Deerson

BruceA

Keith

Ian Anderson

Pat

Johann

Ron Earp

Rick Muck- Mark IV

Pat Buckley

Cliff Beer

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