higher-amperage alternator question

[rrubel]

I'm looking to replace (again) the alternator in my '86. Since I've got higher-wattage headlights, plus an auxiliary fan that I control manually, plus a number of other electrical devices, plus I sometimes use an inverter for my laptop computer, I was considering an aftermarket higher-amp alternator. Stock for the 86 is 105 amps, which seems low anyway. A company that sells on eBay (among other places) has a claimed new AC Delco CS130 that they've reworked to produce 180 amps, for $130. They say it's a direct bolt-on for 86-91 Vettes, although a thicker output wire might be necessary.

My question is this: what problems might I be causing by installing a 180-amp alternator vice the stock 105 one? It's been a LONG time since high school electricity class...

Thanks.
[RICHR]

 

[vader86]

You could install a CS144 alternator as well, you just file down the AIR bolt on top 5/16" and I think we have to throw away the rear bracket because the 144 is longer. Its whats used on LT1s. It puts out 140 A.

I dont think youll run into any problems with higher ampage so long as you have good grounds and no bad wires.

 

[Magmotor]

The higher wattage lights will pull more current (amps) through the associated circuit their on. That means the wires and devices that are on that same circuit has to be rated at a higher amperage than what the lights will pull. Or pop goes the fuse or light switch or wires slowly melting. When you say higher wattage, how much higher?? flood lights or?? You have to calculate out what amps these lights will pull, especially high beam and find out what the devices are rated at that are on the same circuit. You can put a 400amp alternator on, doesn't matter, just what's on the circuit is what counts and what everything is rated for. Hope this helps...

 

[LuckyVette]

here's a tip for choosing the amp rating you need:

this my or may not make sense, but you can actually calculate the power increase you are taking with all the extra items you were talking about

Equation:
power(watts) = current (amps) * voltage (volts)

1)take each of your upgraded items and look at the manuals and see how many watts it takes to power them.

2)add this wattage together

3)use the equation above: divide the wattage by the voltage your alternator puts out (my '86 puts out about 14 volts) - this gives you the amps your extra items need

4) assume that the reason the stock alternator is 105 amps is because that is close to what a stock '86 needs.

5) add 105 + the amps you calculated for the extra items and make this number, say, 80% of what you really need so that you are not overloading your next alternator

6) buy an alternator with at least the rating of what you calculated in #5 above

7) you've also got to make sure the wiring is rating for the current you are sending through it as the previous posts mentioned

hope this helps

 

[rrubel]

So if I'm reading this right, I can put on whatever amperage I want, as long as I don't draw more than the wiring can handle. The headlights aren't WAY higher; I think stock is 45 and these are 55. Fog lights are mildly higher as well (not like my Outback, which had 100w lows and 130w highs until things started melting ). The DC inverter uses about 8 amps, less than I thought.

Voltage regulator is internal to the alternator, right?
[RICHR]

 

[geekinavette]

So if I'm reading this right, I can put on whatever amperage I want, as long as I don't draw more than the wiring can handle.

Yes.

Voltage regulator is internal to the alternator, right?
[RICHR]

Right again!

 

[oldace84]

Tuff Stuff has an alternator rated at 140 amps....and chrome plated also...
I use one on my '84....works great...
Just a thought....
tony

 

[Eagle85C4]

My 85 Z-51 came with a 120 amp stock...the current Delco replacement for it is 124 amp. I have upgraded the fog lights to 55 as well as upgrading the headlights to 80/130 watt bulbs with no problem at all.
You can put in any size alternator you want. The current rating is what the alternator is capable of...not what it is putting out at any given time.

The formula above is correct but needs to be changed to provide for the current rating. Power (watts) is equal to the voltage multiplied by the current, to transpose...current is equal to the power divided by the voltage...stock bulbs are 35 watt....so 35 divided by 12 equals 2.91 amps or rounded off at 3 amps. 55 watts divided by 12 volts equals 4.5 amps. So by upgrading the bulbs only adds another amp and a half to the circuit. Not a whole lot to worry about. Also that is per bulb so the total is 6 amps for the 35 watt bulbs and 9 for the 55's...

 

[Magmotor]

Eagle,
That is not correct. Your bulbs and lights are all on a parellel circuit. The formual is different. Current is the resiprical in a parrellel and added in a series. Your adding as if they were on a series circuit. If that was the case. If one bulb went, they would all go.

 

[geekinavette]

Mag, maybe I misunderstood your post, but....

You're talking about resistance...not current. If you have a number of resistors (or light bulbs) in a series circuit then the resistance of each resistive element is added to get the total resistance. Divide the voltage applied by the total resistance to get the series current...which MUST be equal through each element in the series (regardless of the individual values), not added to obtain the total series current.

In a parallel network (ie two bulbs in parallel), then the total resistance would be the reciprocal of the sum of the inverse of each resistance. Rt = 1/(1/R1 +1/R2 +1/Rn) where n is the total number of resistive elements in the parallel network. In this case then the current in each element (V applied / R) would add up to the total circuit current.



Bill

 

[Magmotor]

Bill,
You didn't misunderstood, I jumped in a little quick on this but I find it hard to beleive that the source wire for the headlights is carrying 9 amps. Not too mention it's on the same circuit as the tail lights.

You are correct in the total resistance formula. I got my resistance and current formula mixed up.. In a parallel circuit the source current divides among the available paths. The total current of each leg has to add up to the source current. Maybe I'll go stick an ammeter on the source wire and see what's it pulling. I was just thinking that there would be a lot of dead mechanics if that were the case.
Hope I didn't misslead or get anyone upset...like I said, i jumped a little quick...

 

[SPANISHVETTS]

I’ve been running one of these alternators for almost 10Kmiles now in 90º+ weather. It is working great.

I’m not going to get involved in Ohms Law with you guys. IF anybody wants to throw an unlimited number of stones into an infinite pond and discuss Laplace Transforms I am all ears.