alternator power loss question
#2687934
08/15/19 08:55 AM
08/15/19 08:55 AM
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Joined: Oct 2003
Posts: 4,013 South Park, Pa.
68LAR
OP
master
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OP
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Joined: Oct 2003
Posts: 4,013
South Park, Pa.
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How much power does an alternator pull from an engine ?
4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
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Re: alternator power loss question
[Re: 68LAR]
#2687940
08/15/19 09:16 AM
08/15/19 09:16 AM
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Joined: Feb 2005
Posts: 20,174 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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How much power does an alternator pull from an engine ? Probably less than running with a over worked battery. Been there done that and I Will never race without one again
Last edited by pittsburghracer; 08/15/19 09:17 AM.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: alternator power loss question
[Re: 68LAR]
#2687959
08/15/19 10:10 AM
08/15/19 10:10 AM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
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Milwaukee WI
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Calculate with an ohms law chart. P=watts 1 hp = 745 watts
Last edited by TRENDZ; 08/15/19 12:44 PM. Reason: Mo info
"use it 'till it breaks, replace as needed"
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Re: alternator power loss question
[Re: 68LAR]
#2688050
08/15/19 02:09 PM
08/15/19 02:09 PM
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Joined: Aug 2003
Posts: 43,185 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,185
Bend,OR USA
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Dyno testing years ago on a motor with battery only(two fully charged dyno batteries) feeding the MSD 7Al2 ignition made less power than with a alternator mounted and working on the same motor twenty minutes later (2 or3 HP,CRS) I saw the same thing at the track with my alternator gutted by bypassing the blue Holley fuel pump using the Carter NASCAR Hemi mechanical fuel pump only, MSD race ignitions need and like good voltage and current As already pointed out the cars current requirements will have a large effect on any testing, especially with large draw electric water pumps and fans
Last edited by Cab_Burge; 08/15/19 02:10 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: alternator power loss question
[Re: 68LAR]
#2688051
08/15/19 02:15 PM
08/15/19 02:15 PM
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Joined: Jan 2003
Posts: 31,036 Oregon
AndyF
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I Win
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Oregon
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How much power does an alternator pull from an engine ? Describe your setup and we can tell you. Electric fuel pump? Big MSD ignition system? Electric water pump? Electric fans? Anything else?
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Re: alternator power loss question
[Re: AndyF]
#2688082
08/15/19 03:43 PM
08/15/19 03:43 PM
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Joined: Oct 2003
Posts: 4,013 South Park, Pa.
68LAR
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OP
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Posts: 4,013
South Park, Pa.
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How much power does an alternator pull from an engine ? Describe your setup and we can tell you. Electric fuel pump? Big MSD ignition system? Electric water pump? Electric fans? Anything else? Nothing to extravagant, MSD 6AL, and electric fuel pump. That"s it unless I run at night, then we got to consider head lights. Thanks for all the replies, by the way. I appreciate it.
4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
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Re: alternator power loss question
[Re: 68LAR]
#2688209
08/15/19 08:30 PM
08/15/19 08:30 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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New York
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Math is fictional. What matters is how you feel about things.
Boffin Emeritus
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Re: alternator power loss question
[Re: AndyF]
#2688248
08/15/19 10:17 PM
08/15/19 10:17 PM
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Joined: Feb 2005
Posts: 20,174 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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I bought my stock Chevy one wire off a table at Norwalk over five years ago for 25.00. It puts out 50-60 amps. It runs my taillights, BG400 fuel pump, miesere water pump, two fans, racepak, MSD7al, electric shifter, and probably a couple of other things. I race sometimes several times a week and charge my battery once a month to top it off.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: alternator power loss question
[Re: 68LAR]
#2688391
08/16/19 12:27 PM
08/16/19 12:27 PM
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Joined: Mar 2007
Posts: 3,277 West Coast, USA
jbc426
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On a side note, a single V-belt's ability to transfer power is about 5hp max. I found that out when I was upgrading my alternator to increase the amp output at idle. Had to go with a GM CS-144 for that duty, as it puts out over 115 amps at a low idle. Bolted right in too.
Last edited by jbc426; 08/16/19 06:17 PM.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: alternator power loss question
[Re: AndyF]
#2688392
08/16/19 12:27 PM
08/16/19 12:27 PM
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Joined: Jan 2003
Posts: 7,490 Minnesota
Hemi_Joel
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The formula assumes zero friction. I don't know how much power the v belt saps but I'm sure there is some. Same with the bearings inside the alternator and the little cooling fan and all that jazz. I don't have any numbers for all the little friction loads but I'm sure it adds up. My guess is the alternator costs about 1 hp even if it is only charging 20 or 30 amps. Bottom line I don't think it matters much. If I was building a bracket car to go rounds I'd put an alternator on it. It is only a few pounds of weight and a very small power drain but it cuts down on the monkey motion in the pits. I'd rather not have to hook up the generator every time I pull back into the pits. It is just one more thing to remember to do. Plus the power required to overcome the inertia of the armature as the engine rpm climbs in each gear. I suspect that in the lower gears, this could be more than the power required for producing electricity.
Last edited by Hemi_Joel; 08/16/19 12:29 PM.
[img]http://i.imgur.com/boeexFms.jpg[/img]31 Plymouth Coupe, 392 Hemi, T56 magnum RS23J71 RS27J77 RP23J71 RO23J71 WM21J8A I don't regret the things I've done. I only regret the things I didn't do. "Wise men talk because they have something to say; fools because they have to say something. ~ Plato"
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Re: alternator power loss question
[Re: AndyF]
#2688488
08/16/19 05:19 PM
08/16/19 05:19 PM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
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Aurora, Colorado
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The formula assumes zero friction. I don't know how much power the v belt saps but I'm sure there is some. Same with the bearings inside the alternator and the little cooling fan and all that jazz. I don't have any numbers for all the little friction loads but I'm sure it adds up. My guess is the alternator costs about 1 hp even if it is only charging 20 or 30 amps. Bottom line I don't think it matters much. If I was building a bracket car to go rounds I'd put an alternator on it. It is only a few pounds of weight and a very small power drain but it cuts down on the monkey motion in the pits. I'd rather not have to hook up the generator every time I pull back into the pits. It is just one more thing to remember to do. Like Andy mentioned, the loss to electrical load alone is pretty small. Once the battery is fully charged the alternator need to supply the amperage to run whatever electric items the car is using, maybe 20-30 Amps unless you have a killer fuel pump or cooling fan. Note that the electrical load loss in not related to RPM. The other alternator losses like the cooling fan, (drag force) increase with RPM. The mass of rotating parts and friction will create a load when changing speed (acceleration) or F=Ma As I understand it, In theory friction force does not increase with velocity, but I think real friction forces (viscous and unbalance of rotating parts) increases with both Velocity and Acceleration.
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Re: alternator power loss question
[Re: Chip]
#2688987
08/18/19 08:58 AM
08/18/19 08:58 AM
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Joined: Feb 2005
Posts: 20,174 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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Double check those fans as that seems awful high.
Last edited by pittsburghracer; 08/18/19 08:59 AM.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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