13.5 peak voltage?

[AtomikRage45]

After installing Brand new battery and rebuilt alternator (load tested good) my alternator will only produce 13.5v (car runs fine). is something wrong?

 

[spoonman]

My car while idling has a voltage of 13.9 - 14.3. Yours is not drastically low and it should be alright.

 

[DGajre777]

Alternator output is dependent on load, and believe it or not heat reduces alternator output. Start your car at night with all the interior and exterior lights off, stereo off and A/C off anc check the volts. If you see 14 volts, be happy. I see no more than 13.6 volts under normal operation (stereo, A/C, headlights, etc).

 

[Splitpi]

Where are you measuring the voltage? Across the battery terminals?

 

[KGB Pilot125]

Where are you measuring the voltage? Across the battery terminals?

That is correct isnt it?

 

[Splitpi]

That is correct isnt it?

Yes that is where it should be measured. But if I had a volt meter that was measuring at the Accessory plug in the dash or something like that, it will measure lower due the voltage loss in the line and other items tied to the accessory plug.

 

[DGajre777]

Yes that is where it should be measured. But if I had a volt meter that was measuring at the Accessory plug in the dash or something like that, it will measure lower due the voltage loss in the line and other items tied to the accessory plug.

My Stinger voltmeter connected to the 12v cig. lighter reads the same voltage as a battery terminal voltage measurement.

 

[Splitpi]

My Stinger voltmeter connected to the 12v cig. lighter reads the same voltage as a battery terminal voltage measurement.

My Apexi reads ~.4 to .6 V lower than at the terminals. But I also have a few other things running from the line (Greddy Electronic Boost Gauge, WB O2, Apexi Timer). So it can very between setups. But always, best results should be to measure at the source (across the terminals) this will tell you more accurately the voltage output of the Alternator.

 

[DGajre777]

But I also have a few other things running from the line (Greddy Electronic Boost Gauge, WB O2, Apexi Timer).

That is probably why. The only thing connected to my cig. lighter is the voltmeter.

Btw, I agree on checking voltage at the battery terminal for accurate reading. But a voltmeter in the dash is soo convenient.

 

[AtomikRage45]

i ran a 18 gauge wire from the + post into the cabin and then measure to chassis ground and its 13.5v+-
12.9 at the cigarette

 

[turboglenn]

When new the last 2 i put in both read 14.2 for the first few months, then as they get older they show less and less voltage...they usually go from 14.2 to 13.6 then down to 13.2 before finally craping out ( I'm on 13.2 now this one has lasted 2 years)

The important thing is that it keeps constant voltage with the accessories on or off. Even if you're only getting 13.6, turn on EVERYTHING , lights, hazards, heater, radio, defogger in rear, wipers and anything else you can think of. The voltage will drop when each thing is turned on but should quickly rise back up to whatever the starting voltage was with everything off. If it doesn't stay the same, replace it right away before you get stuck with a dead battery some where.

The best 2 places to measure voltage is either at the battery or watching it on the logging/sata display of your EMS (more on standalones) since part of its job is to observe direct battery output since some maps in the system are designed to change pulse width with voltage changes to keep fuel flow up to par even if the voltage is lower than normal.

I replace my alternators is when I'm at a red light at night with the heat and radio on and the tach starts to jump around at idle and gets smooth when you accelerate/rev the motor. That usually mens it's on it's last leg

 

[Splitpi]

I replace my alternators is when i'm at a red light at night with the heat and radio on and the tach starts to jump around at idle and gets smooth when you accelerate/rev the motor. That usually mens it's on it's last leg

I always thought it was just the engine dancing to the beat of the music

i ran a 18 gauge wire from the + post into the cabin and then measure to chassis ground and its 13.5v+-
12.9 at the cigarette

Why? The chassis is grounded to the negative terminal of the battery already.

 

[Defiant]

After installing Brand new battery and rebuilt alternator (load tested good) my alternator will only produce 13.5v (car runs fine). is something wrong?

Your rebuilt alternator is faulty. You should get at least 14. Try another.

 

[rodent]

Many guys have had problems with the Mitsu alt and sometimes do a Saturn alt swap-

http://www.dsmtuners.com/forums/articles-electrical-wiring/272646-saturn-alternator-swap.html

Just another option.

All mitsu alternators for dsms and gvr4s use the same POS regulator, which is normally the problem. Some owners have gone through 4 of them before they get a good alt. that produces the correct voltage.

 

[kergilman]

Your rebuilt alternator is faulty. You should get at least 14. Try another.

+1 I have just found the hard way that my 420a voltage regulator is in my ECU...after I went through a few batteries and alternators. My system would not charge over 13.4v w/ no accessory load. Waiting on new ECU...

 

[steve]

All mitsu alternators for dsms and gvr4s use the same POS regulator, which is normally the problem. Some owners have gone through 4 of them before they get a good alt. that produces the correct voltage.

There are grades of parts. The OEM regulator works great but there are cheap aftermarket parts that are as you described a POS. Guess which part most chain autoparts stores alternators use. Running without heat shields and with leaking power steering pumps don't help lifespans either.

 

[BigBob]

+1 I have just found the hard way that my 420a voltage regulator is in my ECU...after I went through a few batteries and alternators. My system would not charge over 13.4v w/ no accessory load. Waiting on new ECU...

This might Help if you havent bought the ecu yet. Check it out

420A Alternator Voltage Regulator - SymTech Laboratories