Alternator output voltage

I searched all over and couldn't find a definitive thread about the correct alternator output voltage for my 2007 DC with tow package. After towing this weekend resulting in a dead 4 your old battery, I started monitoring my alternator output voltage and was surprised to see if varying greatly outside of the 13.8V I am used to in older vehicles. On my truck, it will start at 14.2V cold and by the time I've driven 10-20 miles, it may go as low as 13.2V at idle. I took it to a dedicated shop and they load tested the alternator and it was good, so as long as yours is outputting more than 13V, it's likely fine and just thermal regulating to protect the battery from heat.

 

Wouldn't it depend on charge level of battery and/or what you have turned on? My car sits on 14.5 but will go to 13.2 with AC on and bright lights and lower if rolling pwr window down or up. Imagine if you have amp and such turning up stereo will bring it down further. Wipers, down more. Mostly, I look for 12-13 when I turn the key on before starting.(digital gauge in the 12v pwr outlet) Truck acts pretty much same way. Gauge stays in car because it sits lot more than truck. And 4 yrs is a good run for any batteries nowadays. I feel lucky to get 3 yrs out of them....and that's buying a 60 month premium one, not entry lower level cca ones....and I'm not towing and park in garage out of elements.

 

Those voltages aren't out of whack really. I'd be inclined to suggest your battery is heading south. You should have a 120 or 130 amp alternator and you'll want at least a Group 27F battery in that truck. Curious as to what you're towing.
Cheers, Jeff

 

My '14 4Runner 4.0L engine dual VVTi Grp 24F battery & '15 Tacoma 4.0L single VVTi Grp 27F battery - both read 13.4V while idling after being fully warmed up.

 

From my shop class in high school in the mid 80's, I learned alternator voltage output varies, even among same models. In general a sitting battery should read 12.4-12.6 volts. Once the car is running the alternator starts charging the battery and voltage output, ideally, should be over 13.5 but under 15. Then you do a load test at idle: you turn on several battery hungry items such is fan blower on high, hi beams, wipers, radio (but not the AC cause that puts a mechanical load on the engine). The voltage should not dip below 12.6; if it does, it indicates the battery is being discharged and the alternator needs replacing. If voltage goes above 12.6 when you increase rpm to 1500, then alternator is doing it's job but just barely because at idle it can't handle the load. A healthy alternator will lose less than a volt with this load test and still be above 12.6. This is relative - for example, if your alt currently hovers around 13.2 with this load test, then this becomes your baseline; when the voltage gets below 13, it's a sign your alt is starting to lose performance. Before doing a load test, make sure your connections are good and your cables are in good connection. Also, a bad battery can affect alt performance; so, fully charge a battery with a charger before suspecting the alt is bad. A loose or glazed belt can also affect alt performance. You should also do a voltage drop test; you can look that up on utube.

 

i got a voltage meter for my cab so i constantly know what the output is and i just got another for when i run duals. the nice thing is being able to see it at all times without having to get out, open the hood and check. great $5 mod imo

 

That is the correct voltage for your truck. There are a few mods you can do to get it up closer to 14v if you want. Also check what the new battery requires. Iirc optima and odyssey both want higher charging and float voltages.

Read through the dual battery thread. This was discussed i there as well as mike singer voltage booster thread.

 

That's with a new battery. Since I was stuck, I let the dumbass at sears sell me a 24F (I guess I'm the dumbass there). I have the 130A and tow a very small vintage trailer with a brand new 27F deep cycle. I'll probably drop the $2 on a cheap meter from Aliexpress just for some piece of mind when towing.

 

12.02 volts at
idle ,turn lights ,ditch lights ,radio and AC on it dips to 11. Rev engine to 3000rpm and no increase in voltage on my Ultra Gauge. Lplus Ultra gauge only comes back on if I unplug it and plug it back in .DonI need an alternator? My battery is only a year old . Thanks

 

Revive this thread

 

Sounds like a bad alternator, should be 13-14v depending on ambient and engine temperature.
Do you have a battery light or check engine light on?

 

No Engine lights on

 

It’s hot as hell here now also . Ultra Gauge was working fine right before I got home . So I was just checking things again . Turn all lights and radio and AC on . Volts dropped to 11 ,rev engine to 3000rpm and no change in volts . Definitely alternator.

 

More than likely it is an alternator problem.

Get it load tested free at most reputable parts houses.

 

Perfectly fine. 13.2 to 14.5v is normal.

 

This is at idle .

 

It’s under 13

 

Check the Output off the B terminal off the alternator.

Not saying the alternator is not failing but so many other factors can effect things the output getting into the system

I bought a Toyota reman from my dealer for a decent price in case yet need one.

 

Hope that denso reman lasts.