Outer Limits 4x4 Board

Doing some wiring upgrades due to fitting a new stereo, and my bling new positive terminal clamp has a volt meter on it. Wired it up ... 13V across battery with engine off (about right - battery has been used in a boat for the last week), 14.1V charge initially when started but then climbing to 15.4V steady over time!

Thought it'd be a dodgy volt meter so cracked out the multimeter and found the same - running at 15.4V charge.

Have had it in for about 5000 clicks and not had any problems, but when first installed I measured it at 14.4V charge.

Any idea what might be causing the higher charge voltage, and is it likely to cause issues? Am a bit reluctant to drive it until I'm sure it's okay...

Sounds like the internal regulator may be stuffed. It should max out at around 14.2v when your reving at about 2000rpm. It shouldnt get above 14.2v.

Layto....

Thanks Layto, but I don't actually reckon the regulator's stuffed. Stuffed regulator tends to mean voltage increases with revs - the voltage here stays stable.

Interesting quirk I've just noticed in fiddling with it is that with the internal ventilation fan off, voltage is 14.4V on the dot. Turn the vent fan on (with or without AC running) and voltage immediately jumps by 1V. Voltage is stable no matter what revs.

Any ideas?!?

Still sounds like a regulator problem to me. After all this is what governs the output voltage of the alternator.

JrZook wrote:Still sounds like a regulator problem to me. After all this is what governs the output voltage of the alternator.

x2.

altenator has a set of rotating diodes in it,which generates an AC input from the stator through a set of slip rings ,into a voltage regulator ,and turns it into a DC output to charge your battery,if the voltage in the battery is low,it will pump out more charge amps to get the battery up to req voltage,as the charge voltage of the battery increases,the charge amps decrease,but it should be around 13.8/14.1 ..you may have a dodgy diode in the volt reg.if you leave it ,it will just kill your battery as it will be charging too high!!

Think I've found the answer

The regulator has a "sense" lead input. The regulator attempts to maintain the voltage detected via the sense lead to 14.4-14.5V thereabouts (set by the alternator manufacturer).

In my case (and likely many other Sierras) this sense lead comes off the wiring loom under the dash somewhere, NOT directly off the battery. So if there is voltage drop between the battery and the sense line due to accssory draw (say 1V drop to 13.4V) then the alternator senses that voltage is low and increases it back up to 14.4V at the sense location.

On my car with the vent fan running, I have 15.4V across the battery. But measuring inside the car at the interior light I have 14.6V and the cigarette lighter has 14.5V. Voltage between alternator case (ground) and alternator positive was 14.4V on the dot.

So the answer in my case will be simply to bridge the alternator output to the sense terminal (ie fix it to 14.4V constant and ignore any voltage drop in the loom) and then upgrade the feed to the main fuse box to 8G cable to minimise voltage drop.

By the way - modern calcium batteries (as fitted to mine) apparently have a recommended charging voltage of 13.8-15V, but up to 15.6V is allowable if rapid charging is desired but with a slight reduction in battery life.

Apparently CAT batteries come with a 6 month warranty and a 650cca only costs $150. I'd suggest these batteries to anyone with extra load on a battery, it just might pay for itself.

Hmmm. Well. Regulators don't like pushing 15.4V for any length of time. Did the alternator in last week.

Have just fitted another 100A alt in there and want to know if anyone absolutely definitively knows which lead goes to where on the alternator? Cos even with both leads disconnected I don't get an alternator warning light in the cab I'm not real keen on cooking the new one...

i have a vitara, when the alternator gets caked with mud it burns out, no alternator light on dash at all, and when the alternator is not plugged in there is no alternator light either when reds r on..
funny that...
not detecting that their is none plugged in or not working.

u will only know if its the right plug by pluging one in and turning your reds on to see if the light turns on..