Hi volks, Bit of background.. my alternator is giving 14.2 volts at the battery with no electrical load at idle, great! But, as I start to load it up with the heavy electric consumers that voltage drops to 12.6 volts at the battery. Ordered a new voltage regulator (cheap and easy fix) but the new one has a resistor installed. Fitted it anyway but the alternator output is worse at 11.6v at the battery, no load. Anyone got any idea why this resistor is fitted? Looks like I could just cut the resistor out and it will then be same as my old one but not too sure about this approach? Any ideas happily received. Thanks guys.
What's the output like at 2000rpm. Depending on what rating your alternator is / state of the windings it may not be capable of 14v at idle with all loads on.
Yeah, output doesn’t increase as revs raised to 2000+rpm. I’ve looked on the alternator to see if there’s an amp rating on it and there ain’t unfortunately. But thanks for checking.
Might be best off buying a decent uprated alternator maybe?. My Golf has a later Polo one iirc (6 PK belt) and sits happily at 13.5 to 14v at idle under load. Is that resistor in case the bulb fails in the dash?. Could be wrong but I believe of your alternator / battery light fails the car won't charge. Most of my knowledge is on bikes really (3 phase stators and magnetic flywheel / rotor).
Yeah, think I’ll look into that upgrade. And it’s entirely possible if the lamp fails the car won’t charge, I’ll have to have a deeper delve into the wiring diagrams. Thanks.
We have had some cutting out issues on the Golf (albeit a TT 3.2 VR6) and so we did some testing. The Alt supplied 14.6 at idle with no loads. With blower on full, heated seat on, all lights on and heated rear screen on the reading was about 14.15 at idle. There is deffo something not right with your new regulator. I would suggest, for what they cost, a new higher output Alt is a good way to go. In the end our issue was the resettable fuse supplying everything but the starter/alt. It was momentarily tripping at high loads. Replaced with a permanent fuse, problem sorted.
I think the main problem here could be a bad connection between alternator and battery. Could be the positive lead or the earth, or both. Some easy measurement can tell you which connection is worst. Refit the original regulator and load it up to get back to your situation where the 14.2V has dropped to 12.6V at the battery. Measure from alternator output stud to battery positive to see how many volts are being dropped on that connection. To check losses in the earth path, measure from a scratched-clean bit of the alternator casing to battery negative. Whichever of these is the highest number is the one that will improve matters most when you improve it by cleaning ends or replacing cables.
Thanks for all the input guys. EZPete, I have throughly cleaned all the main load leads from alternator to starter motor and then onto the battery but I’ll definitely do those drop tests and see where that leaves me. If no joy I’ll update the alternator as Phil suggests. Thanks again
