Akternator output voltage

[xvprado Senior Member Find all posts View Profile Close xvprado]

Having razzed a good battery on my camper trailer, I went looking for the problem
Think I have found it. My alternator is putting 13.4 volts out to the main battery on charging, this voltage is consistent to the second battery and also the anderson plug at rear

Clearly insufficient to supply more thna a float charge

Sooooo...does anyone know what their alternator is charging at, or if not, anyone keen enough to go out to the garage, start her up and stick a multimeter on their main battery and give us a report on the voltage being supplied at charge...Thanks

Particularly interested ina D4D

Regards
Glen

[Big Fella Senior Member Find all posts View Profile Close Big Fella]

Hey XV,

this is being done from my driveway on the car right now, gee I love technology

Main battery at rest 12.71v
Dual battery at rest 12.79v

Main battery on charge 13.74v
Dual battery on charge 13.74v

Readings taken off a 2007 D-4D Auto Diesel.

Hope it helps

[xvprado Senior Member Find all posts View Profile Close xvprado]

Thanks Andrew
That indicates to me that I have a problem, I would expect maybe close to 14 volts under load with lights on

Cheers
Glen

[Damien Parker Advanced Member Find all posts View Profile Close Damien Parker]

Yeah, i would have expected around 14.4 V under charge, which is the norm for Auto stuff i would have thought.

[samo Addicted PP Member Find all posts View Profile Close samo]

at rest i have 12.5 and 12.7 volts in both batteries, engine idle have 14v charging on both batteries. hope this helps

[Justo Advanced Member Find all posts View Profile Close Justo]

Just ran the multimeter over mine.
At rest........................12.12v
On charge at start up...14.25v
then settled at idle.......14.12v

Have you tried testing the voltage while the engine is under load or increased revs. If you are charging 3 batteries and running other accessories at idle may be an indication of why your voltage is down a bit. I would have thought 13.4v would be a minimum charge rate and is probably ok at idle.

[Chippy Addicted PP Member Find all posts View Profile Close Chippy]

Main battery ................. 14.33 V
Aux battery .................. 14.33 V
Anderson plug (to CT) ... 14.31 V

Cheers
Chippy

[Big Fella Senior Member Find all posts View Profile Close Big Fella]

Chippy,

You've got some good power readings there, what sort of RPM are you doing to get that?

[mav Addicted PP Member Find all posts View Profile Close mav]

Whilst driving at around 2200 RPM with aircon and radio etc on my scan guage is showing a voltage of 13.7 VDC.

[Chippy Addicted PP Member Find all posts View Profile Close Chippy]

Chippy,

You've got some good power readings there, what sort of RPM are you doing to get that?

That's 30 seconds after starup ... still at that cold start fast idle.

Cheers
Chippy

[MTpockets Advanced Member Find all posts View Profile Close MTpockets]

Good thread this. I will test mine tonight.

[plucker Advanced Member Find all posts View Profile Close plucker]

Dont know what the specs say is ideal but I would suggest at idle and the battery fully charged 13.4 should be good.
If your battery is flat it will take ages even with high revs to bring it to a good level.

[steve120 Lurker Find all posts View Profile Close steve120]

XV...the specs from the Toyota Service Manual CD are as follows:

13.9-15.1 volts with the engine running at 2000 rpm and 25 deg C (77 F)
13.5-14.3 volts with the engine running at 5000 rpm and 115 deg C (239 F)

Same for all engine types (but I don't have the latest CD with the D4D numbers - someone else may have these ?)

Either way, 13.4 volts looks to be just out of spec (more so if measured when cold).

Perhaps try to isolate as much load as possible and aux batteries and see if anything changes. Then re-load things one by one. (A bit like Apollo 13 )

Otherwise suspect alternator/regulator?

[Guest Close Guest]

umm

Found some of the points about the DB systems interesting. Firstly without sounding like a smart ass, there is more than volts at play in these situations. You may have for example 13 volts @ 20 amps or 13volts @40 amps and unless you use a good shunt, meter etc you may not get a true indication of what is exactly going on. If the system were “was floating” it would not charge if I understand what is being said correctly. If this were the case, the car would prop not start after a while because it could not recover the energy to start the vehicle etc.

Hope this helps or throws a bit of light on the subject

Cheers
:wink:

[MattWhite Advanced Member Find all posts View Profile Close MattWhite]

I do get what you're saying Donk. Sometimes a 'perfect' voltage of 14.4 actually indicates a faulty battery due to it not accepting charge and also voltage while cranking is more important than static. I also agree with Steve. Three average batteries and an alternator only at idle really is a mis-match. Isolate your starting battery and see what that has at idle. High thirteens would be acceptable. I know after a camping trip it takes the whole trip home for our camper battery to really charge up.
Thanks
Matt