10 replies to this topic

[sddwalker]

Hi All,

 

When i'm pootling round town then my battery charges ok and all is fine. However on the motorway my lights start to go dim after a little while along with the fan and wipers slowing. So i have to stop at a service station, switch off all electrics and leave the car running. After a few minutes then i have enough charge for the lights to go bright again and continue with my journey.

 

Since my journey to work is mainly along the motorway with a couple of minutes at either end going slower, then I often run out of charge and need to be jump started, which is getting a little tiresome.

 

I've checked the voltage...

engine off: 12.5V

engine idling: 13.7V

revving the engine to high revs (i don't have a rev counter, but I made sure it was >2500rpm at least) doesn't seem to change the voltage.

unfortunately i can't check the voltage very easily when bombing down the motorway when i have a fault condition.

 

I haven't noticed the battery symbol lighting up on the dash-board when i have the fault condition.

 

Obvious culprits are battery / alternator (probably the latter), but I'd like to double check.

 

Has anyone had this problem before? if so, what did you do to fix it?

Any ideas on how to diagnose it? I don't want to just guess and spend lots of money replacing things needlessly.

 

Thanks

Stu

[Dusky]

Dodgy voltage regulator maybe, or fanbelt slipping at higher rpm.

[brad-the-bear]

as above, check the tension of the belt first

[Icey]

unfortunately i can't check the voltage very easily when bombing down the motorway when i have a fault condition.

 

Why not? Find a +ve connection inside the car (interior light circuit for example) and tape a multimeter to your dash.

[KernowCooper]

If the belts tight then carry out a charging test on the alternator its in the FAQs Electrical

[bmcecosse]

I too would suspect belt slipping - try a new one.   But it may be the alternator has lost a phase (or two) - and can only provide a limited charge - I'm guessing in town/when idling the headlights/heater/wiper are not all on...so then it can maybe pump out say 8amps charge to the battery. But that's it's limit - so no hope of it matching lights etc.  

[sddwalker]

Thanks for your feedback guys. Sorry for the poor form in not following up sooner - I've been struggling for day-light hours when I'm free :)

 

Dusky/Brad - Indeed my fanbelt was slack (i could easily spin the alternator slipping on the belt). I have tightened it as much as I could, but there's still more than 1/2 inch movement on the long side. To tighten I pulled it up as hard as I could with one hand, and tightened the nut with the spanner in my other hand ( and another spanner wedged the bolt side of the adjustment bracket to stop it spinning)... is this a two person job to get it extra tight? any special techniques you guys use? I couldn't see any obvious signs of wear, but perhaps it is just worn and sitting too low in the pulleys.

 

Kernow - After that I checked the alternator per the advice in the FAQ - all reassuringly normal.

 

Where is the voltage regulator located? Rain has stopped play at the moment, but hopefully I can get back out to check that too.

 

Icey - true... I shall invest in some crocodile clips for my multimeter ;)

 

 

 

Ta!

[Icey]

 

 is this a two person job to get it extra tight? any special techniques you guys use? I couldn't see any obvious signs of wear, but perhaps it is just worn and sitting too low in the pulleys.

 

Careful! It's not supposed to be monstered, there should be some deflection on the belt. There should be around 1/2" deflection on the length between the alternator and the crank pulley.

 

If it still slips when the belt is the proper tension, it'll want replacing.

[brad-the-bear]

Normally a pry bar or crow bar does the job. Wedge it in between the block and alternator (at the top). Don't go too tight tho. You want about 90 degrees of "twist" between the alternator and crank pulley. Seen an old timer judge the right tension by seeing if he can turn the engine over by turning the alternator pulley with a spanner or moving the fan with his hand. If it all moves its about right. 

[KernowCooper]

Voltage regulator in in the alternator attached to the case and brush gear in behind the black cover on the ACR series on the A127 type its bolted on the back, with a volt meter on the battery and everything turned on you use on the motorway, then see if the alternator can keep the voltage up if it does not then its faulty, your looking at 13.7v minimum to charge the battery, if you have a clamp  meter you  can also test the alternators amperage output on the + cable

Edited by KernowCooper, 14 December 2014 - 08:56 PM.

[sddwalker]

Thanks to all for the advice... it turned out to be the simplest of the possible causes - the alternator belt was slack. I think the symptoms (charging at around town with low revs but not on motorway) came about because there was just about enough traction to turn the alternator at low speed, but when at high revs the belt will bulge out a bit, reducing the contact length with the pulley, hence less traction to turn the alternator.

 

Thanks again