Intermittent power cut-outs and battery dying

[michaelbrown1995]

Hi there everyone.

For the last few weeks I’ve been having electrical issues with my car. At first I thought it was a faulty Halfords battery not charging properly, going completely off of negative feedback from friends who swore it would definitely be that because apparently Halfords sell naff batteries. I have no evidence to back that up and needless to say, the poor reputation they apparently have is not grounds to jump to a conclusion, and after replacing it and finding it to not be the battery I simply assumed it was the alternator… well, I say assumed – I listened to about 5 different people who all said the same thing. “If it ain’t the battery, it’s the alternator” 2 of these were professional and experienced mechanics, and the others were people who presumably once watched an AA guy change a wheel on their lowered 2016 Corsa and so now think they know all there is to know about motors. So I ordered a new alternator, expecting that to be the fix.

Anyway, as you can guess, the battery continued to die so as a temporary measure I purchased a cheap battery charger from screwfix, which has been a lifesaver and has enabled me to get to and from work, but not much else. I work mostly nights, so the lights put more of a strain on the battery, and I found the speedometer to get very dim, but then occasionally it would go back to full brightness, for instance if I went over a slight bump in the road. My immediate thought was that this was then an earthing problem. I cleaned the starter motor’s earth, and replaced the bare metal battery earth and the earthing strap under the gearbox with better protected insulated earth cables, as I thought corrosion might’ve caused them to no longer work. I also cleaned the nuts, bolts and washers, as well as the areas they made contact with the body, but still no luck.

With a battery fully charged the light on the speedo is sometimes dim straight from the start, and the other day whilst on a roundabout the speedo lights went just about as dim as they could go without being fully extinguished, and the car lost all power – I was just able to roll to a safe place in a layby, where the car made a miraculous recovery and kept going, with the lights nearly at their full brightness.

I, being of very limited car knowledge, and with only the most basic understanding of electricity and such, am now under the impression I should be looking for a loose connection that is getting jolted in and out of place, which would explain why sometimes the car plays ball, and why other times it gives up before miraculously curing itself.
Any advice, suggestions on what to check, or what wires are most likely to be causing me jip?

Thanks!

[oliver90owner]

If it ain't the battery or the alternator, it must be something in between or current going somewhere it shouldn't. Does the battery hold charge if the car is not run for several days?

So far, the best advice I can offer is to ascertain which of the above (most likely not charging the battery). Buy a cheap meter and check voltages while checking for breakages in the circuit. I once had a Corsa (which had clearly received a front end repair) and eventually found a cracked conductor within the bent protective shrouding.

Alternators used to be battery sensed but now almost universally machine sensed, so they stop charging if disconnected from the battery. If there is 14.4V at the alternator and less at the battery, it is likely that lead which is the culprit.

I've also come across so called 'refurbished' alternators which have not had the slip ring replaced or have sticking brushes.

Bypassing the heavy spade connection to the battery is one possible fix, but it would only fix it if there is a break or high resistance.

You cannot (easily) damage a digital meter, if set to 20 DC volts range, for this type of use.

[beero]

I would check the wires at your control box, or if this has been removed check where it was sited on the bulkhead. You are likely to have connections there where the control box was bypassed.

[StillGotMy1stCar]

I will assume you’re not confusing dynamo’s with alternator’s.
An alternator is easier to fault find.
The alternator has an inbuilt regulator which gets its reference voltage from the ignition light, so if the red ignition light doesn’t come on when you turn the ignition on then it won’t charge. Easily tested by removing the small wire from the alternator and shorting it to earth with the ignition on it should light.
The large wire on the alternator should be live whether the ignition is on or off and is unfused so be careful not to ground this wire as it will quickly burn. It can be tested for voltage with a simple test light.
Regards John.

[michaelbrown1995]

Yes, it's an alternator not a dynamo, fresh from ESM.

Control box is in place, but the brown and yellow cable from the alternator is not connected to anything - it used to be attached to the bulkhead regulator box but I disconnected it when a mechanic suggested having it connected to the alternator with its own regulator might be the cause of the problem.

[Nickol]

O dear, what People tell you.

Look at the alternator wiring Diagramme in the Electrical section of this Forum and check that your alternator is wired like it should be.

There is not a lot to go wrong with an alternator except for sticking brushes. ( famous last words - I did have to replace the diodes on mine at one stage) To check with the engine at a fast idle , look for over 14 V at the battery Connections and if less, work back along the System from there. The control box, is no more than a connecting Piece, as its intended functionality when using a Dynamo is bypassed when connected to an alternator