Is this alternator?

saitrix

saitrix

saitrix

Soldato
Joined
2 Jun 2003
Posts
8,950
Location
Nottingham
Hi,

Right last 2 times coming to my car the battery has been dead. Both times I have started it with jump leads from another car. Initial thought was something draining it or battery is duff. But I noticed today when I drove it the voltage reading was fluctuating. In traffic it would drop down to 11-12v then when I was cruising with revs it would get up to 13v+. So does this sound like the alternator has gone on me?
 
Yes.

Quick test is flash a voltmeter across the battery terminals when the car's running - should read 13.5-14.5 volts or in that region. Any less (say 12v) and the alternator is not outputting a proper charge.

Fortunately not very difficult to change!
 
Voltage is nearly always somewhat lower at idle, but 11 volts is too low. What are you measuring the voltage with? If it's a dash gauge they can be very inaccurate, best to use a multimeter.

The problem could be down to the battery, the alternator or duff connections between them.
 
Awesome. Just thought though, remember hearing some belt squeel a few days ago. I best check the belt first, forgot about that.

Already looked at Canley, £24 for a recon exchange. Not bad and local enough.
 
Dogbreath said:
Voltage is nearly always somewhat lower at idle, but 11 volts is too low. What are you measuring the voltage with? If it's a dash gauge they can be very inaccurate, best to use a multimeter.

The problem could be down to the battery, the alternator or duff connections between them.
Click to expand...

Tis a dash one, but it is different to its usual though. Which before it would solidly hold above 13v.
 
Yea it's very rare to get a fault with the dash items in the Dolly and typically they are very accurate, unless the voltage regulator goes - but then that's not isolated to one gauge, so you'd see errors with the temp gauge and so on :)
 
xvivalve I think - not sure though - but he'll point you in the right direction. Should be in the club mag (all the details) by now - if ya a member :)
 
If you can, put another known good battery on the car and run the engine. It should go up higher than 13V, closer to 14V is best. It can well drop down to 11-12V at idle, mine does, but it flips up when the revs go up. Sounds like either the battery isn't holding charge or it's not being charged. Do you know how old the battery is?

If I remember I'll measure mine at idle and revs.
 
Jonny, a modern alternator (anything 1970~ onwards really) shouldn't show charging characteristics like that, if they do then it's failing or there's a fault in the system.

The charging system should show a good ~14.4v straight off the bat when at idle after switchon. I've not owned a car that doesn't hold anything less than a 14v+ charge at idle with the ancilleries off.

Older generators, which is what it sounds like your describing, do however show that effect :)
 
If you want to check for something draining the battery you can make a tool.

Take a blown fuse, wire it with 2 terminals that fit your multimeter. One by one replace the fuses in the fuse-box with it measuring Current, would tell you what circuit the fault is on.
 
Lashout_UK said:
Jonny, a modern alternator (anything 1970~ onwards really) shouldn't show charging characteristics like that, if they do then it's failing or there's a fault in the system.

The charging system should show a good ~14.4v straight off the bat when at idle after switchon. I've not owned a car that doesn't hold anything less than a 14v+ charge at idle with the ancilleries off.

Older generators, which is what it sounds like your describing, do however show that effect :)
Click to expand...
Mine drops off on idle but it might be because of the large pulley on the front. It's a brand new mk1/2 Fiesta one, old Lucas shape.
 
Check the connector on the back. The alternator on my GT wasn't charging the battery but the connectors had become, I dunno, corroded or something and were not passing power out. I took the connector off, cleaned things up a bit and stuck it back on. A nice 14.25 volts or so on idle. :D
 
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