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Old 07-15-2017, 10:59 AM   #1
Corvette_Ed
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Default In need of some alternator advice

I was driving around last weekend in my 08 vert when I noticed that the voltage was showing to be running much lower than it should have, at 13.4V. Granted, it was about 107 degrees with the Texas heat index, and I know this played a part, but I do run a 900/5 amp on my aftermarket sound system. I checked the voltage again yesterday morning before the sun was up, and the DIC showed me running at 14.0-14.2V, and this was with the stereo cranked, A/C on, and headlights on. My concern is that the combination of heat and power draw will result in poor charging of my relatively new Optima Red Top, killing the battery.

I'm pretty sure I need to get a high output alternator, and BlownblueZ06 with RKT Performance has a polished billet alternator in stock that I can go and pick up directly from his shop as we are in the same general area, but wanted to get some additional opinions before I drop $500+ to replace a perfectly good alternator that works just fine at any other time of the year.

To clarify a little more, when the DIC was showing the 13.4V, my car was running just fine, the A/C was pumping very cold air, and the radio was pumping out the music just as it always does.

So what do you think? Do these symptoms warrant purchasing the high output alternator, or am I just being overly cautious and concerned? TIA
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Old 07-15-2017, 11:22 AM   #2
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Maybe have it load tested? Load testing on the car can also help locate other issues. Take it to the place with the billet unit and if it fails you can make the swap right there. Alternators can lose up to 10% of their efficiency just getting to operating temp. Also, if you were reading that voltage at idle you would have lost a bit too. Add in 100+ temps and I can see where it would drop that much. Personally, given the conditions I think it was working at its peak at the time but still within parameters. Heat is a killer in electrical systems though. I am planning a move to AZ in a few years and will be upgrading the electrical system to handle it.
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Old 07-15-2017, 11:25 AM   #3
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My 07 was doing the same thing. One time low voltage, next time normal. Then it went bad. I now have the machined 170A alt you talk about. 14.6 V all the time now. Also replaced the wire going to the starter from the Alt as he suggested.

Worth the money IMHO. Not much more than an OEM replacement but much better.

New 0/0 wire compared to stock small one.
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Old 07-15-2017, 11:39 AM   #4
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battery?
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Old 07-15-2017, 11:57 AM   #5
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Originally Posted by LowRyter View Post
battery?
Battery tested just fine, and as I mentioned, the system appears to work normally when temps are in the 80-90 range. It's the triple digit temps that seem to be the primary cause. I do plan on load testing the system before I make a final decision, though.
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Old 07-15-2017, 11:59 AM   #6
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Originally Posted by jmeirhofer View Post
Maybe have it load tested? Load testing on the car can also help locate other issues. Take it to the place with the billet unit and if it fails you can make the swap right there. Alternators can lose up to 10% of their efficiency just getting to operating temp. Also, if you were reading that voltage at idle you would have lost a bit too. Add in 100+ temps and I can see where it would drop that much. Personally, given the conditions I think it was working at its peak at the time but still within parameters. Heat is a killer in electrical systems though. I am planning a move to AZ in a few years and will be upgrading the electrical system to handle it.
Planned on doing the load testing this weekend. The voltage reading was checked while I was driving at highway speeds.
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Old 07-15-2017, 12:45 PM   #7
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Do you have a capacitor in-line for your amp??? This will make a BIG difference here and the amp will draw power from the capacitor vs the battery
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Old 07-15-2017, 12:48 PM   #8
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Go and buy the Mechman 170 amp unit. You can't go wrong, and worth every penny. I have one and it stays at 14.7 V all day long with everything running wide open. It takes 10 mins to install, very easy.

-Michael-
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Old 07-15-2017, 12:51 PM   #9
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Originally Posted by 2L8LUZ View Post
Do you have a capacitor in-line for your amp??? This will make a BIG difference here and the amp will draw power from the capacitor vs the battery
No capacitor. Only thing in-line is the fuse.
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Old 07-15-2017, 12:53 PM   #10
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Originally Posted by ValegoC6 View Post
Go and buy the Mechman 170 amp unit. You can't go wrong, and worth every penny. I have one and it stays at 14.7 V all day long with everything running wide open. It takes 10 mins to install, very easy.

-Michael-
I'm not asking which alternator to buy as I've already decided on the one I will get. The question is whether or not I need to buy one.
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Old 07-15-2017, 01:05 PM   #11
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Post # 3 was having the same issue, replaced it and all is well. Sounds like yours is on the way out also.
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Old 07-15-2017, 01:12 PM   #12
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Quote:
Originally Posted by Corvette_Ed View Post
No capacitor. Only thing in-line is the fuse.
Bingo!! Your going to want one new battery or not...the bass will hot harder because the amp has constant 14.0 juice to draw from...

There only $50 for a 2 Fray... takes 10 mins to install inline
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Old 07-15-2017, 01:25 PM   #13
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Quote:
Originally Posted by ValegoC6 View Post
Post # 3 was having the same issue, replaced it and all is well. Sounds like yours is on the way out also.
That doesn't necessarily mean my alternator is bad, it could be nothing more than extreme heat causing the problem. My car only has 40k miles on it and never had a problem until I was running the new sound system in triple digit temps. The problem doesn't duplicate when temps are in the 80-90's.
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Old 07-15-2017, 01:27 PM   #14
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Originally Posted by 2L8LUZ View Post
Bingo!! Your going to want one new battery or not...the bass will hot harder because the amp has constant 14.0 juice to draw from...

There only $50 for a 2 Fray... takes 10 mins to install inline
What does this have to do with the alternator? I'm not understanding what a capacitor between the battery and the amp has to do with the charging voltage.
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Old 07-15-2017, 01:48 PM   #15
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I would not necessarily be too concerned just as long as your battery charge is being maintained. My Silverado has been doing a similiar thing for years now with my high end sound system in it. At one point though I did put a larger CCA battery on it. Do you have or considered larger cables between the battery and the alternator?
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Old 07-15-2017, 01:56 PM   #16
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Quote:
Originally Posted by Corvette_Ed View Post
I checked the voltage again yesterday morning before the sun was up, and the DIC showed me running at 14.0-14.2V, and this was with the stereo cranked, A/C on, and headlights on.

This is good, since the alternator puts out 14.7, will see about 14.5 on the battery, and the DIC should be reading 14.3 with the car idling and the A/C and radio turned off in your case.
Note, DIC and even the dial voltage gauge on the dash is telling you the voltage at the ECM, not the voltage on the dash. The entire dash is digital, and sent this information to read out via the GM land bus by the ECM (yes, even the dial type dials)


As for the lower reading on the DIC of 13.4V, lets get a few things straight.

When you are sitting at a light and the car idling, the OEM valeo alternator is only putting out about 14amp. The car itself pulls down about 10 amps, but when you start adding in the AC running that will have the radiator fan running close to full blast to pull air through the heat exchanger (over just the engine being hot to turn the fan on starting at 15% spin when the engine gets up to 199*,not ramping up the radiator fan to 100% until the engine gets to 225*), then it can pull down about 15 amps, then you have the radio amp that is pulling down amperage as well.

So sitting at a stop light with all that running, the OEM alternator has no chance in hell keeping up with the needs, and it not until you start to drive the car and get the RPM up so the OEM alternator is putting out close to it normal full tilt amperage of 140 isntead. Hence if you are driving with the car around 2K, then lets just say that it will take about 15 mins before the OEM alternator may have the battery full charged instead.

Where the OEM and billet alternator differ, is not so much on there max output at full rpm spin (145 verse 170), but the design of the alternators instead. The OEM has three poles, while the billet is a 6 pole design instead. This means at idle, where the 3 pole oem is only putting out about 14 amps, the 6 pole billet at idle speeds is putting out close to 65 amps and keeping up with the all the cars demands, even in hot weather with the radio and A/C running with the radiator fan dam near full blast..


So really, with the the DCI at 14.3, and the 13.4v being a fluke once in a while, may not need to change the Oem alternator out to start with. I would just pull the OEM alternator to give it a good cleaning/clean its inner contact points, and them go through the electrical charging system wires to give them a good cleaning and make sure that all the connectors are clean and tight as well.

Here is a write up I did on the OEM to go through and clean it up,
Note, need to re-link the photos since photobucket changed it policy and they are not showing up any more.
https://www.corvetteforum.com/forums...placement.html

Now starting with the alternator output lug, clean up that back connector on it and the positive wire connector, the other side wire connector to the starter and the battery wire off the starter terminal (bottom terminal on the starter in the below photo with the two wires), the battery terminal wire connection from the starter to the battery, the engine fuse box terminal connector wire off the battery, then the battery to ground wire on the engine block (top wire in the below photo to the engine block), as well as the small ground wire off the battery terminal to the chassis ground.
Note, have seen problems with the electrical system resolve by just cleaning up and reconnecting the alternator back lug and the connector to it alone.




Also, reach behind the passenger engine side between the back of the head and the firewall, and trace the wire/ wire loom down from the positive battery terminal to the starter. The positive wire is in a wire loom, and the loom is supposed to have a retainer that keeps the loom from rubbing on the back of the head, but some vets did not get this keeper (or it busted) and the loom and positive wire can rub through at the back of the head to cause a short in the wiring.

Last edited by Dano523; 07-15-2017 at 02:11 PM.
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Old 07-15-2017, 02:13 PM   #17
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Originally Posted by Corvette_Ed View Post
but I do run a 900/5 amp on my aftermarket sound system.
900/5 amp ...im assuming that means 900 watt 5 amplifier system?

If that is what you have.... I would recommend that you run a high output alternator.

I installed a high output alternator (240 amp) in my convertible for the same reason (I have an aftermarket 2,000 watt sound system).
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Old 07-15-2017, 02:26 PM   #18
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900/5 amp ...im assuming that means 900 watt 5 amplifier system?
900W 5-channel amp. 300W going to front/rear speakers, and 600W to my two subs.
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Old 07-15-2017, 02:36 PM   #19
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Originally Posted by Dano523 View Post
This is good, since the alternator puts out 14.7, will see about 14.5 on the battery, and the DIC should be reading 14.3 with the car idling and the A/C and radio turned off in your case.
Note, DIC and even the dial voltage gauge on the dash is telling you the voltage at the ECM, not the voltage on the dash. The entire dash is digital, and sent this information to read out via the GM land bus by the ECM (yes, even the dial type dials)


As for the lower reading on the DIC of 13.4V, lets get a few things straight.

When you are sitting at a light and the car idling, the OEM valeo alternator is only putting out about 14amp. The car itself pulls down about 10 amps, but when you start adding in the AC running that will have the radiator fan running close to full blast to pull air through the heat exchanger (over just the engine being hot to turn the fan on starting at 15% spin when the engine gets up to 199*,not ramping up the radiator fan to 100% until the engine gets to 225*), then it can pull down about 15 amps, then you have the radio amp that is pulling down amperage as well.

So sitting at a stop light with all that running, the OEM alternator has no chance in hell keeping up with the needs, and it not until you start to drive the car and get the RPM up so the OEM alternator is putting out close to it normal full tilt amperage of 140 isntead. Hence if you are driving with the car around 2K, then lets just say that it will take about 15 mins before the OEM alternator may have the battery full charged instead.

Where the OEM and billet alternator differ, is not so much on there max output at full rpm spin (145 verse 170), but the design of the alternators instead. The OEM has three poles, while the billet is a 6 pole design instead. This means at idle, where the 3 pole oem is only putting out about 14 amps, the 6 pole billet at idle speeds is putting out close to 65 amps and keeping up with the all the cars demands, even in hot weather with the radio and A/C running with the radiator fan dam near full blast..


So really, with the the DCI at 14.3, and the 13.4v being a fluke once in a while, may not need to change the Oem alternator out to start with. I would just pull the OEM alternator to give it a good cleaning/clean its inner contact points, and them go through the electrical charging system wires to give them a good cleaning and make sure that all the connectors are clean and tight as well.
The thing that had me concerned is the 13.4 wasn't a fluke. I was running at 13.4-13.8 consistently while cruising at highway speeds (70-80 mph) during the day in triple digit temps. I was just out for a drive trying to find a shop to do a load test, and I was seeing it drop down to as low as 12.6 at a steady 45 mph @ close to 2k rpm. Unfortunately, it looks like I'm going to have to wait until next week when I can get by my buddy's shop after work to have it load tested.
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Old 07-15-2017, 02:58 PM   #20
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Originally Posted by Corvette_Ed View Post
900W 5-channel amp. 300W going to front/rear speakers, and 600W to my two subs.
Since you only have one 5 channel amp, the cost of a high output alternator is a little harder to justify.

I have 3 amplifiers that are capable of drawing over a 100 amps (combined). So in my case, it was a lot easier to justify the cost.

Last edited by v8rx7com; 07-17-2017 at 06:52 PM.
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