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Old 11-17-2011, 09:20 PM
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Amperage draw estimates

Hey!....Can anybody steer me to a list that shows (estimated) amp draws for the components and accessories on our cars? I'm gonna add an electric fuel pump, later on an electric cooling fan....who knows what else. I'm trying to decide which alternator would be best for my Buick GS. I suppose I could just use the 94 amp 12si model but is that considered "overkill"? Reading Mark Hamiltons tech pages at MAD Electrical gave me some great info, but I'd like to know what y'all think....Thanks......

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Old 11-17-2011, 10:12 PM
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Most electrical devices have a rating of amps drawn, like a fuel pump, (Use a four amp fuse) or have a rating in Watts. A 55 wall halogen Headlight will draw about 4.6 amps.
(55/12)
Start adding.
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Old 11-18-2011, 05:38 AM
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94a would be a good choice..... cost between the smaller 53 amp and 120 amps isn't much, so IMO going with the larger one from the get-go is the right choice.
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Old 11-18-2011, 07:26 AM
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Quote:
Originally Posted by bobsessed
Hey!....Can anybody steer me to a list that shows (estimated) amp draws for the components and accessories on our cars? I'm gonna add an electric fuel pump, later on an electric cooling fan....who knows what else. I'm trying to decide which alternator would be best for my Buick GS. I suppose I could just use the 94 amp 12si model but is that considered "overkill"? Reading Mark Hamiltons tech pages at MAD Electrical gave me some great info, but I'd like to know what y'all think....Thanks......
It is just as important to make sure you have the right size battery.

Personally I would not use anything smaller that a 100amp alternator and put in the biggest battery that will fit. Stay away from the Optima and other specialty batteries. My experience is they are not as good as a quality regular battery.
Exide in my opinion makes the best car batteries.
Napa batteries are re-branded Exide's.
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Old 11-18-2011, 09:26 AM
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I guess there's no good reason not to go with the hi-output unit. I found a good deal on a 78amp that I thought I might jump on to save some cash, but it's probably better not to. Thanks guys....anything else you might wanna add to this discussion will be of great help to me.
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Old 11-18-2011, 09:44 AM
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So T Bucket.... My battery is less than a year old and is the one that "the book" calls for (650/525cca). Will I need bigger than that?
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Old 11-18-2011, 09:51 AM
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I would start by having the battery load tested. If it tests good, have the alternator tested on the car if possible.
Just because the battery is new doesnt mean it is good.
Also does it only die after sitting for several hours, you may have something drawing it down.
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Old 11-18-2011, 01:43 PM
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As long as your alternator is sized to handle all loads, the battery only needs the required cranking amps and not a huge reserve capacity rated in A/hr. A typical group 27 flooded battery is around 65 a/hr, thus could run (2) 55 watt headlights a bit better than 10 hours. As soon as the engine starts, the alternator takes over the loads and charges the battery for what was taken out of it for the start. If you never want to deal with corrosion and want to save about 45 lbs of battery weight, go with the Odssesy PC 680. It is a dry, absorbed glass mat battery that has the dual personality of both a cranking battery and deep cycle battery, and weighs 15 lbs. I've run this battery for 17 years in the Track-T, pulled it out and it now starts my garden tractor. Have also run (4) in series for a hot rod scooter that can out accelerate my Corvette to 40 mph.

Just remember that tasty PIE, P (power in watts) = I (current in amps) X E (electromotive force, volts). So, if something like a starter draws 300 amps at 12 volts = 3600 watts / 746 (watts for 1 hp) = 4.8 hp.








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Old 11-18-2011, 02:00 PM
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A larger battery will keep the load down on the alternator and avoid some of the surge loads. In a car with a lot of accessories the battery needs to be larger. If you look at all the heavily loaded luxury cars they have huge batteries as well as huge alternators. You know if it was not needed the automobile manufacturers would not have put them in as it cost money.
In a T-bucket or similar there are very few electrical accessories so a small battery is fine, I have a small one in mine. In a normal vehicle with heat, ac, electric windows etc a larger battery is a must.
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Old 11-18-2011, 06:29 PM
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Yeah....It's not that I'm having a problem....except for dim lights. My car still has the 61a , externally regulated alternator, and it works....
okay. The only thing I've done so far is to add the Mallory Uni-Lite distributor. I'm finding out that I'm gonna need a beefier system soon, and I was just curious as to what some of you were doing for power. I'll be adding some "extra power demands" soon, so now I have a better idea of how to proceed. In the guitar and music related forums that I visit, I don't always get help with my questions. It looks like hot-rodders are a way friendlier bunch.......Thanks again for all your help.
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Old 11-19-2011, 04:16 AM
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Best thing I have done for my old girl was to switch over to a internal regulated 110 amp alt. I was haveing the flickering light when the heater was on, dim lights etc.... Zero problems after I switched, I used the original sized battery and have had zero issues with that also.

Attached is DOC's dia...... that's how I wired mine before I did a complete re-wire.
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Old 11-20-2011, 11:16 AM
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Go Big

Bobsessed, if you plan on going with electric fans in the future I would go with the biggest alternator (within reason) that you can fit in there.

Some of the larger electric fans draw major current, for example the original V6 fan in my car uses about 13 A, and it is not a large one. A pair of larger fans like the 3.8 L Taurus uses are up around 20 A each. The surge current when the fans are first turned on can be up around 40 A.

Additionally, the alternators are not rated at engine idle speed, so your 63 A alternator is not producing that much current at idle.

Under periods of extended idling and in high temperatures where the fans would be called on a lot you want heaps of current available. Go big!
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Old 11-20-2011, 11:34 AM
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More than you probably want to know on the subject....

http://tbuckets.lefora.com/2011/02/0...ctrical-loads/

And a little something on AGM batteries......

http://tbuckets.lefora.com/2011/01/2...he-ugly/#post3

Enjoy,

Bob
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