HO drops to 12 v at idle?

[Astyl 10+ year member]

ive got a 200 Amp EA Alt and it does that 12 volt thing at idle too, and it came from EA with a 10% overdrve pulley and it still does it

 

[IgnoreMe 5,000+ posts]

this is not normal. there is no time in which an alt should be at 12v at idle, unless the manufacturer designed it that way (i dont know of any that do).

this is usually based on the components used. my buddy bought a motor city reman alt with this problem. go too 1k rpm and it was 14.1v. drop to idle and it was 12.2v. they replaced it, for a brand new one, and the same thing happened. smaller pulley helped A LITTLE bit (gained .5v or so). they said his car is to blame, and thats the smallest pulley they had.

we switched it out for a mean green 200A alty, no problems ever. and on my explorer i can take my mean green down to about 200rpms before i see any drop in voltage.

i would call ohio and let them know. that is not how an alt is suppose to work.

 

[Bun-Bun 10+ year member]

Every HO alt I have ever had has had crap for charge at idle. Never had it drop quite to 12v though... usually 12.8 or 13 something.

Bigger stators need more RPM's to push a charge. Better quality alt's may be able to work around this issue... I wouldnt know as all I have ever done is had my stock alt's rebuilt with bigger stators.

 

[tommyk90 5,000+ posts]

this is not normal. there is no time in which an alt should be at 12v at idle, unless the manufacturer designed it that way (i dont know of any that do).
this is usually based on the components used. my buddy bought a motor city reman alt with this problem. go too 1k rpm and it was 14.1v. drop to idle and it was 12.2v. they replaced it, for a brand new one, and the same thing happened. smaller pulley helped A LITTLE bit (gained .5v or so). they said his car is to blame, and thats the smallest pulley they had.

we switched it out for a mean green 200A alty, no problems ever. and on my explorer i can take my mean green down to about 200rpms before i see any drop in voltage.

i would call ohio and let them know. that is not how an alt is suppose to work.

My excessive amperage is the exact same way actually, and many other people have this same issue depending on the make/model of the car and alternator. I guess it depends on who makes the alt as well.

 

[mikey7182 10+ year member]

Could be belt slippage... check and see if there is any belt residue on or around the alt pulley...

 

[shpatb 10+ year member]

yeah it confuses me because once im going at 1k rpm to 1.5 k rpm, i can have both heated seats on heat, rear defrost, and my system cranked and nothing dims. but as soon as the rpm drops it goes down hardcore.

 

[scottiej 10+ year member]

I dont think you guys are hearing what I am saying about "actual" output at idle... if the alt does low amperage at idle then the vehicles stock electrical needs may exhaust what the alt can supply at idle... this would cause the voltage to drop to 12 or below depending on the state of the battery. I agree, an alt should not do this unless specifically designed that way (like our SPL alt) Hence the reason I suggests our 200A units that do 125-140A at idle //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[SPL140.2 5,000+ posts]

I dont think you guys are hearing what I am saying about "actual" output at idle... if the alt does low amperage at idle then the vehicles stock electrical needs may exhaust what the alt can supply at idle... this would cause the voltage to drop to 12 or below depending on the state of the battery. I agree, an alt should not do this unless specifically designed that way (like our SPL alt) Hence the reason I suggests our 200A units that do 125-140A at idle //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

I agree Iraggi makes a few of those as well, no charge at idle. I know a smaller pulley helps at idle though with most of his alternators.

egg

 

[audioarsonal 10+ year member]

There are many factors I have found when upgradeing to a "HO" alt.

1.alts are tested at 2400rpm alt speed so to make up for the differance they will include a smaller pulley which usually puts you at 3 to 1 ratio alt rpm to engine rpm.But if your car only idle's at 700 rpm that would only get you 2100 alt rpm.So you would a smaller pulley that puts you at 4 to 1.

2.What size is your crank pulley ?This will tell you the ratio on the above statement.Measure the size of your crank pulley then your alt pulley and then divide.This will give you the ratio the alt pulley is spinning in relation to the engine.Maybe you idel at 800 rpm but you only have a 2 to 1 ratio.This would only put you at 1600 alt rpm.

3.These factors also come into play when you have it "bench" tested as the motor and pulley they use will change everything once again.I would advise haveing the alt tested while on the vehicle under a true load if your are concerned about the output of your alt.

I hope these things are helpful in solving your problems.

 

[shpatb 10+ year member]

sorry but i dont know what a crank pully is :x and i idle at 600-800, its never at one place.

 

[terra 5,000+ posts]

i idle around 600 and if my stereo is off my loadboss 250amp alt never drops voltage below 14.9

 

[shpatb 10+ year member]

yeah, if my stereo is off everything is fine... but thats not the reason i got a HO alt in the 1st place...

 

[audioarsonal 10+ year member]

sorry but i dont know what a crank pully is :x and i idle at 600-800, its never at one place.

If you don't know what a crank pulley is???????//content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

 

[terra 5,000+ posts]

yeah, if my stereo is off everything is fine... but thats not the reason i got a HO alt in the 1st place...

well idling with everything playing hard i drop to around 13.9/.8

 

[skydeaner 10+ year member]

I idle at 1800 or so engine rpms. Sooo i should be fine lol???