57TOMMY
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 03-10-12 08:44 AM - Post#2200720
Hey Guys
I have added items to my car , 1000 watt amp 2 10 inch subs, colling fan to my radiator & wanted to figure out if my 100 watt alternator is big enough. Is there a simple way to calculate the best size alternator I need?
Thanks for your help
Tommy
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 acardon
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03-10-12 08:57 AM - Post#2200730
In response to 57TOMMY
A 1000 watt amplifier will draw 83 amps when it's wide open. Fans can draw 30 to 40 amps. Oops, ran out of juice already. The best thing to do is measure the current draw with everything turned on that you use constantly. In other words, don't count door locks or power windows as they are not on long enough to matter. A auto electric shop should be able to measure the current if you don't want to buy a clamp on ampmeter. Their kinda expensive.
Don
66 Corvair (driving)
57 2dr HT (restoring)
56 2dr HT (waiting to be restored)
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57TOMMY
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03-10-12 10:39 AM - Post#2200766
In response to acardon
Thank you Don
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 beejay
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03-10-12 12:58 PM - Post#2200810
In response to 57TOMMY
Tommy,
I just bought a 140A from Summit for my Elky. It has the new-fangled lights, H3 fog lights, and two electrice fans. That's plus a low-wattage radio (Sony) with two rear, 7" speakers in the rear and two small tweeters in the dash. Reason I bought it? At night, with brights on AND fans off, the lights were flickering on and off (on relays, same as fans). On dims, the lights work OK. I can just imagine what ruckus would be raised if I were on brights, and the fans kicked on, or added to that the AC was put on. Well, so much for an 80-something Amp alternator. Time to swap. Incidentally, you didn't say if you have AC, and use it. 
Bruce
'56 4-door BelAir, 350, Holley 600, Eddie intake, TKO 600, CPP P/S and A arms, Sierra Gold & Adobe Beige
2010 VW Jetta S/W, 2.5, 5-cyl,6-spd auto.
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triplefive
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03-10-12 06:46 PM - Post#2200938
In response to beejay
Audio equipment is notorious for being over-rated.
These days, most amplifiers are rated at their peak output (top of the sine waves) instead of RMS (root mean square, which is average - or true output). And then most of them just advertise a lot of downright BS on top of that. They have to do it because everyone else does it.
I have a 1000 watt Yamaha P.A. system for musical instruments and vocal. When you look at the input requirements in amperage and times it by the voltage, it actually puts out to the speakers about three times what it takes from the powerpoint. This, as we all know, is against the laws of physics, but why let the truth interfere with a good yarn. Almost all sound systems are peddled this way. There are some exceptions in the very expensive high-end studio and opera house stuff and, I think, many good quality guitar amps use RMS. That's why a good 100 watt guitar amp has no problem competing with a 1000 watt PA.
If your 1000 watt amp actually puts out 1000 watts RMS (extremely unlikely), you would need about 1500 watts from the alternator due to losses in the amplifier, but I'd be very, VERY dubious.
I'm not in any way being critical of the system you bought. It could be a great amp, but 100 TRUE watts in a car with the right speakers will almost blow you out of the seatbelt.
I've used a 300 watt sound system (150 RMS or true watts per side) for vocals and piano at a wedding in a large hall with a 25 piece bigband and it kept up no probs without being driven too hard.
If I were you, I'd allow about 10 amps for the sound system (20 max) and I think you'll have it covered. The size fuse on the + lead might be a fair guide to the real story. I bet it's not 83 amps.
Cheers.
Mike.
Mike.
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57TOMMY
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03-10-12 08:04 PM - Post#2200969
In response to triplefive
Oh. I know it's not putting out 1000 watts , thats just the amp size. I thought a 140 alternator would do the trick. But can you go overboard with an alternator. If I go to 160 or 200 will it do any harm?
Stand up for what is right ,even if you stand alone.
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triplefive
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03-10-12 08:39 PM - Post#2200990
In response to 57TOMMY
But can you go overboard with an alternator. If I go to 160 or 200 will it do any harm?
Absolutely no problem. You can go 500 amps if you want. the output will only ever be what's needed, and the load on the engine will only reflect what you are using at the time.
160 or 200 might not actually be necessary, but it can't do any harm and at least you know you won't be left short 
Mike.
Mike.
Procrastination; the one thing I never put off until tomorrow. |
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57TOMMY
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03-11-12 09:07 AM - Post#2201139
In response to triplefive
thank you all
Tommy
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 MikeB
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03-12-12 11:58 AM - Post#2201589
In response to triplefive
Audio equipment is notorious for being over-rated.
These days, most amplifiers are rated at their peak output (top of the sine waves) instead of RMS (root mean square, which is average - or true output). And then most of them just advertise a lot of downright BS on top of that. They have to do it because everyone else does it.
Well said. Custom Autosound is a big-time offender. Their overblown "specs" make them sound better than RetroSound, which uses conservative RMS specs. Kinda funny because the RetroSound probably has a much better amplifier section. One of the cleanest sounding car audio systems I ever had used a "little" 25W x 4 channel Sony amp.
Real Hot Rods have a Clutch!
1955 210 2dr: 327, Brodix IK180 heads, Jones cam, Muncie M20, Wilwood front brakes
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triplefive
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03-12-12 06:40 PM - Post#2201739
In response to MikeB
If that was RMS, I bet that 'little' 4x25 had some punch to it.
I'm not one for over-regulation, but in this case, I wish someone would legislate to make it illegal to advertise other than demonstrated proven RMS output only. I know output in watts is not the only factor to consider, but It would level up that part of the playing field at least, and you could then look at what else you want in a sound system. Much better than checking what size the input fuse is and trying to figure it out from there.
Sorry about the thread drift. I just have a thing about it that's all.
Mike.
Mike.
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jk56chevy
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03-13-12 09:13 AM - Post#2201972
In response to triplefive
Tommy:
I have 2 Arc audio amps, 600 & 400 amps, 2 10 inch subs, 2 electric fans and I went with the MSD 160 amp alternator. No problems at all for the last couple of years.
Keep in mind that MSD told me that alternator needs to excite and with everything on I need to keep the RPMS at 1000 to 14+ volts on the volt guage. I did put the smaller March Pulley on the alternator to get it to spin faster. They said it can handle 30,000 rpms.
Good Luck!
John
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 1960_Guy
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03-13-12 10:46 AM - Post#2202007
In response to jk56chevy
As stated before the current drawn from the Alternator will just be the connected load, so bigger only creates one issue, you need to size the output wire to handle the maximum alternator current or install a fuselink that will protect the output wire against handling more current than it is rated for, otherwise in the case of an overload or fault on the output wire you could do damage to it and create a fire potential.
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57TOMMY
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03-14-12 06:37 PM - Post#2202686
In response to 1960_Guy
thanks guys .looking at a 160 altenator ,see how that works
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busyguy8
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03-14-12 09:45 PM - Post#2202777
In response to 57TOMMY
Tommy, are you having problems currently? I would think the 100 amp is enough. Look up the RMS of your amp online to see if it's very high.
TOMMYYYYYYYY!!!!!!!!!!!! :-)
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2Loose
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03-15-12 09:56 AM - Post#2202957
In response to busyguy8
Interesting thread. I just got my 55 "gasser" running, and put on a fairly new single wire alternator I had laying around, not sure what it was rated at.
Lots of MSD ignition equipment, very large fuel pump, and two large fans on the radiator is about all I have, haven't run at night yet so don't know what the headlights will draw.
When driving around yesterday, fans had not come on yet, the volt meter was showing a full 13 volts. It dropped to 12 suddenly and when I stopped and checked, the fans had come on. So now I can tell when the fans are coming on and off, as the voltage shows 13 or 12 volts.
I plan on adding some sound equipment (what, isn't the blower whine and the gear whine enough???) and am thinking I don't have enough alternator output if it drops to 12 volts when the fans come on. What if I was cruising at night with the lights on and a stereo blasting away?
Is there any way to find out the output rating of an alternator when it is already installed?
Aloha,
Willy
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acardon
"9th Year" Silver Supporting Member
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03-15-12 11:40 AM - Post#2202991
In response to 2Loose
Many alternators have the output stamped on the case, but if it's been chromed or polished, it's probably been ground off. An auto electric shop can measure the alternator output and can also determine the total current required by all your devices.
What size is the alternator to battery wire? 12 volts is too low. You have to have at least 13 to begin chargeing a battery.
Don
66 Corvair (driving)
57 2dr HT (restoring)
56 2dr HT (waiting to be restored)
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2Loose
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03-15-12 12:18 PM - Post#2203000
In response to acardon
I am suspicious that my dash mounted voltmeter might not be that accurate. I connected my timing light, with has voltage indication on it, and it registered higher than the dash gage by about one volt. So 14 to 13 instead of 13 to 12. If I am really getting the higher voltage, and know what it really is, I'm ok with that and will just leave the dash gage alone. Have a very heavy cable from the alternator to the batt, and back up to the front from the batt in the trunk. Elec cut off switch on the rear cuts off everything, including the alternator.
Willy
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57TOMMY
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03-15-12 06:58 PM - Post#2203173
In response to 2Loose
it runs a little over 13 on my amp guage, is that about where it should be? 100 alternator right now. No problems right now Busy just going over the car early for hot August nights & i'll get a bigger alt if I need one. Last battery crapped out on me but it was 5 years old.
Tommy
Stand up for what is right ,even if you stand alone.
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56BUDDY
Senior Member
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03-15-12 09:17 PM - Post#2203231
In response to 57TOMMY
Tommy,
Did you get your tranny dialed in?
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57TOMMY
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03-16-12 06:34 PM - Post#2203587
In response to 56BUDDY
Hey Mel
It's better with the new govenor. Have a 4th to 2nd downshift now. wil try the 6 cyl gov when the weather gets better. Been too busy lately to work on the car
See you soon
Tommy
Stand up for what is right ,even if you stand alone.
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Bruces 57
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03-17-12 05:13 AM - Post#2203687
In response to 57TOMMY
Hello;
All this talk of alternators gets me to thinking.
My electrical system was re wired with a EZ harness. One of the features of this harness is a wire going directly to the harness from the alternator (exciter). I have a single wire on my 32 Hot Rod and it always seemed not to have much output. This car had a lot of electrical gremlins as it is a fiberglass car and the grounding was really crappy! I didn't want that on my 57. So, I read lots of articles on this subject and found that if I hooked up my alternator 3 wire, the voltage was continious at 14. Another area of thought was that (mentioned earlier) if you change the pulley on the alternator (single wire) the voltage comes up more earlier and stays higher through out the rpm range of the engine.
Single wire alternators need RPM to excite the regulator in them to put out voltage while 3 wire hook ups are at peak voltage right from start up.
I tend now to think that any internally regulated alternator works best hooked up 3 wire more than a single wire.
Bruce
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57TOMMY
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03-17-12 08:01 AM - Post#2203732
In response to Bruces 57
I am hooked up with 1 wire but might try the 3 wire to see if there is a difference. good idea
Thanks
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2Loose
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03-17-12 10:46 AM - Post#2203777
In response to 57TOMMY
A very interesting comment. I did not know that a one wire alternator could be reconnected as a three wire. How do you do that?
Willy
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57TOMMY
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03-17-12 01:02 PM - Post#2203815
In response to 2Loose
My wiring harness came with both 1 & 3 wire hookups
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beejay
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03-17-12 02:39 PM - Post#2203839
In response to 2Loose
Willy,
A "dual" alty has a rubber plug covering the two-connector where a plastic plug goes into it. One side goes to the alternator post (red wire), and the other wire goes to the an ignition switch connection to excite the process. Sooo, you have an exciter connection, a connection from the same connector to the post connection, and a connection from the post to the +. Hence a 3-wire.
Bruce
'56 4-door BelAir, 350, Holley 600, Eddie intake, TKO 600, CPP P/S and A arms, Sierra Gold & Adobe Beige
2010 VW Jetta S/W, 2.5, 5-cyl,6-spd auto.
'87 Elkie, 350 with 700r4 tranny B&M floor shift
http://www.picturetrail.com/beejay3/" |
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