Alternator capacity test?

[BananaDan]

Is there a procedure that will allow me to determine how many amps of capacity my alternator has left in it?  It is a 65A modern (ACDelco) alt.  I am considering adding an amp and sub for my stereo system this winter and want to figure out if my alternator can cover the extra gadgets or not.

Dan

[b5blue]

  Dan, with it idling let it sit in gear if an automatic, with the wipers on one by one turn on EVERYTHING else while looking for any drop in the speed of the wiper arms. If they stay steady start turning things on higher settings like high blower and high beams. Watch the gauge while doing this, you should only see a reaction bip on the needle as alt. output adjusts then stabilizes. If the wipers slow down it's a good sign you have run out of idle amps. (The weakest alt. output available.)
  The Denso 120amp alt. I converted to (from MRE) was the only alt. I found that passed this test with flying colors and room to spare that sill uses factory type wiring routing. (Idle amp capacity of 65-80 amps.)  It's not going to tell you WHAT is left but at least tell you if anything is left. (At idle.)   

[BananaDan]

Thanks Neal, I'll give that a try.  With a 100+ Amp Alternator, didn't you have to run a thicker wire from the alt through the firewall?  I have heard if you upgrade you should do that because the harness wire isn't thick enough to carry that load of amps.

[b5blue]

  No but what you don't want to let happen is have a battery that is discharged heavily as this would heat strain the harness. (Or worse.) I've done testing for over a year now. I have no radio plate in my dash and have been reaching inside the dash and touching the main feed wire and back of the gauge's connector studs to monitor heat buildup. The only time it heated up was after a bunch of cranking when I had a ignition problem that had discharged the battery over 20% and then I just ran it 4-5 minutes shut it down for 10-15 (I was checking other things while off.) then repeated that cycle again and drove home.
  Nacho's recommended control relay and wiring modification suggestions are a well thought of help but as the battery is recharged through the AMP gauge even then no one should ever be charging a "dead or near dead" battery with the car.
  My "plan" for my harness will involve adding an "alt. output stud" to the area next to the alt. with a large capacity short feed wire feeding it. From this "Terminal" I can feed any heavy loads like a big draw amplifier, powerful fog lights or as in my plans a 110V A/C convertor. These feeds and (Much as Nacho's outline.) other high draw components will be controlled with 40 amp relays that are controlled with the dash switches or switches added.
  I posted a topic with details and photos on "Denso 120 amp alt." it should come up on a search. It shows everything done. (If you can't find it let me know I'll dig it up.)
     

[BananaDan]

Thanks dude.

[b5blue]

I rebooted the topic for you...

[John_Kunkel]

To alleviate the draw through the ammeter just run a 6 wire directly from the BAT terminal on the alternator to the battery along the core support. The ammeter won't be accurate but it should show some charge/discharge.

[Charger RT]

+1^ what he said plus run a fused power lead into to car to power the new load.
Tim

[BananaDan]

To alleviate the draw through the ammeter just run a 6 wire directly from the BAT terminal on the alternator to the battery along the core support. The ammeter won't be accurate but it should show some charge/discharge.

Is there any difference between this and Nacho's parallel alt <-> amm gauge <-> battery mod he wrote up?  I guess the ammeter accuracy is one difference, but anything else?  If I don't want to lose the ammeter accuracy, wouldn't Nacho's mod provide the same results as what you proposed John?

[Nacho-RT74]

John, actually ammeter won't show anything, and if some, won't never be a real one.

what John proposes is what everybody who doesn't care about the ammeter function and to save the ammeter "trouble maker" deal, what won't be a troublemaker if everything gets propperly mantenience and fit.

[Charger RT]

the parallel circuit sure does help with the old problems of wire issues at the firewall both in and out but it falls short on the fact the amp meter was sized for a 30-40 amp alternator. It is not the correct amp meter for a 120 amp alternator and there is not a drop in unit available. People will say that you should not do this or that and keep the amps within range of the meter and do this or that to keep it low. If I'm going to not use my 120 I'll put a 30-40 back in. Plus I'm not the only driver of my charger. Why should I make it a car a mechanic can only drive.

My view is the amp meter was a bad design that every OEM stopped using 35 or more years ago because there were better ways to do things. A volt meter is one. I would love it if the aftermarket made a volt meter that would replace my amp meter and look like mopar put it there. New cars run the alternator cable right back to the battery. In as short a run as possible. This keeps cable size smaller. The longer the run the bigger the gauge it needs to be for the same current load. So if I am going to update my alternator to give me more amps and to fix the low charge at idle issue. If I'm going to add electrical devices that were not on the car new and some not invented. Add this or add that why not bring the wiring up to todays standards. Patching it is not bringing it up to standards.
Tim

[Nacho-RT74]

well I understand what you say Tim, ( is an old discussion and opinions are respectable ) but if we start from  good alt charging at iddle, the ammeter won't need ever to sense any power going to batt since consumption is just right before the amm ( if everything is rightly sourced )and batt won't loose charge ever, so never will get that ammount of juice to get charged back...

JUST if batt dies, the ammeter will get thar amount of full juice from alt if you make the mistake of charge back the batt on car... or JUST if alt dies, and you have LOT of accesories on your car, what on that case, you must run your car without accesories untill get the alt fixed, but thats the rule also on stock systems like on last statement

rest of regular situations, ammeter won't never get the load coming from alt and will get a death centered needle...

but at the end its at each own and its about tastes and how you want your car working

myself, and knowing what I know, I fully trust on what I made and how its working all the stock system and gauges, since is an small upgrade on the stock system keeping the car working like factory did, what is at the end what a restoration means

( beside even with the cons about the lenght and thick of the wire involved, I trust more on an ammeter reading showing the power source status )

[2Gunz]

I think that if your car is bone stock doing the parallel wiring thing is a good way improve the electrical system.

But once you start adding stuff I think bypassing it is the only way to go.

My biggest problem with the parallel wiring and amp gauge is that I have yet to see any real world data on what it is capable of.
Whats the gauge rated to handle? I dont know, my guess is somewhere around 60 amps.
But guessing and guessing wrong are the things that leave you walking home and leaving your car in the bad part of town.


Anywho.....

I have 2 Amps in my car.  a 4 channel  for the front and rears and a 2 channel run in bridged mono for the subs.
Ive upgraded the alt and bypassed the gauge. Works and sounds great with no trouble.

If you Get a decent sub amp I doubt that the stock alt will last very long.

Do some research and check into Class D amps. They tend to not sound as good as Class A or A/B Amps..... but they draw
a lot less power.  Still need to upgrade the alt... but you will have a shot of being able to charge at idle with the radio jammin.