Hi all,

 

First off, i know there are already a lot of threads about these things, but they were all on the Felicia so wasnt sure how relevant it was to a mk1 favorit 1990 (carbed) hence yet another thread.

 

Symtoms are when i start the car the battery light remains very dim but gets brighter the more load i introduce, wipers are slow etc. then after a few km the light slowly fades to off and then wipers go a bit quicker.

 

Tests:

 

Car not running across battery: 12.4V

 

When light is dim and car running (no gadgets switched on) across battery: 11.2V (stays constant at any revs)

When light is dim and car running (no gadgets switched on) from Alternator to Battery -ve: 13.8-14.4 (higher with revs)

 

When light is OFF and car running (no gadgets switched on) across battery: 12.6V (stays constant at any revs)

When light is OFF and car running (no gadgets switched on) from Alternator to Battery -ve: 13.8-14.4 (higher with revs)

 

My question is a simple one i hope. What needs replacing, the alternator itself, or just the little regulator thing on the side? I was pretty sure it was the whole alternator until i saw it putting out 14.4 from the B+ to the battery through a multimeter.

 

Cheers in advance!

 I was pretty sure it was the whole alternator until i saw it putting out 14.4 from the B+ to the battery through a multimeter.

You didn't measure the voltage FROM alternator TO battery. You measured the voltage ON alternator, which is a different thing. 

 

I advice you to measure the voltage drop between alternator B+ and battery positive pole, then the voltage drop between alternator housing and battery negative pole. Both measurements should be less than 0.1-0.2 Volt. If not, clean thoroughly all contact points and/or replace thick wires in between.

Edited 13 December, 201312 yr by adurer

Hi adurer,

 

Sorry took so long to get back.

 

From Alt housing to battery negative there was a 0.7v reading, but after i repositioned to a non rusty nut the body earth lead it went down to 0.2v so that ok now.

 

From Alt B post to battery positive there was a 3v reading on the meter. I cleaned all battery connections etc and any wires connections i could see but this drop remained :( .. The wire from the b post on the alternator isnt that big really, only a 2/3mm wire.

 

I guess this means that the alternator and regulator are actually ok? but i got some dodgy wiring?

 

Thanks very much

 

Courior

 

EDIT:

After checking some wiring diagrams its seems from the B+ post there should be a single wire to the battery. I have 2 wires! ... So.. If i remove these 2 wires (i presume one or both is damages and shorting to the body), and just put a brand new wire from here, around the engine bay, to the batt +ve terminal, this should solve things?

 

Thanks again, grateful for your time mate.

Edited 16 December, 201312 yr by Courior

No problem.

The cable from alternator B+ to battery positive should have 10 mm2 in section. That corresponds roughly to minimum 3.5 mm in diameter. Remove those two cables and install a single tinned copper cable 3.5 - 4 mm in diameter. A 3 Volt drop is huge. Present cable(s) don't short to ground, you would have used a fire extinguisher by now. It's just corrosion inside.

The 3v drop was with no gadgets turned on, i suppose would be worse if i put the fog/head lights on etc... I will replace the cable as you said and mark this as solved hopefully!

 

Sort of makes sense that its this, for ages the wipers have been slow etc (months, even a year i suppose) but now after driving through a LOT of water it rapidly got worse to the point of seeing the red warning light and then seeing voltages low.

 

Fingers crossed its this! and if your ever in malta let me know and i owe u a pint

 

Courior

You're on.

Figuring it out is not big deal, it's Kirchhoff's 2nd Law. If we're talking Ohm's law, the rusted cable that normally has some milli-ohms, has now some 0.5 ohms, which is a lot. I would definitely have a look at starter cable too.

Well, when you first mentioned to test the voltage drop, i had to google what that was and how to do it lol... in my search i found some great sites and one of them recommended i test:

 

Typical voltage drop maximums:

• starter circuit (including starter solenoid) = 0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame = 0.30
• battery positive post to alternator b+ stud= 0.5 volt with maximum charging load applied (all accessories turned on)
• battery negative post to alternator metal frame = 0.20 volt

Of course your 2 tests are here as well. But apart from that 3V drop, and the other one i fixed, all other voltage drops were within the above guidelines.

IF that voltage drop of .6 is across the solenoid contacts, I'd be looking at either replacing the solenoid / stripping out the solenoid and cleaning  all the contacts.

IF that voltage drop of .6 is across the solenoid contacts, I'd be looking at either replacing the solenoid / stripping out the solenoid and cleaning  all the contacts.

 

Typical voltage drop maximums:

• starter circuit (including starter solenoid) = 0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame = 0.30
• battery positive post to alternator b+ stud= 0.5 volt with maximum charging load applied (all accessories turned on)
• battery negative post to alternator metal frame = 0.20 volt

Just a follow up.

 

I have done as Adurer said and removed the 2 wires (taped them up good for now) and put a new wire from B+ to the + on the battery. Now i have a healthy 13.9 Volts across the battery!

 

Im so happy that i didnt buy a new alternator/regulator!! just €3 worth of wire and 10 minutes was all it took to fix it!

 

On a seperate note.. Im my excitement of fixing this issue. I decided to cut the rust out of my bonnet and weld in a new bit of steel... after finishing this job as well.. I have noticed that i forgot to protect the windscreen from the angle grinder sparks and now i have a very scratched/pitted front window. Is there anything i can do to get this off/make it less visible?

Jewlers Rouge?

i used a stanley blade to scrape off the bits sticking up and then some very light polish to smoothen it out as not to damage the wipers. Still can see the marks but only just.

Once again, adurer states the obvious. It's all about Ohms law. .6 Vdrop at start up means a very low level of tarnish, but 0.6v drop can drop a low battery to one not capable of turning engine over. At 0.6v drop, as i said, it's case of polishing the contact faces, or replacing the solenoid,. Ohms law stated voltage drop = current  x resistance. At starting currents ( 80+Amps) , it only takes a minute .0075Ohm of tarnish to do this.

Hi all,

 

This is back to haunt me! Not exactly the same, but here goes. Here are my new symptoms (I have installed a digital voltmeter on the dash):

 

1) when its coldish 8-12C and I start the engine from cold, I get readings that seems to fluctuate randomly from 12.9-14.9 volts regardless of rpm

2) during (1) the digital meter seems to be flickering/dimer as if 1 of the 3 phases on the alternator was damaged maybe. although voltage is high.

3) Once motor is a bit warmer the voltmeter is brighter/more stable and at 1000 rpm I have 13.8V (no lights etc)

4) my dip beam circuit knocks it down to 12.9V idle and 13.2V driving (2000 rpm +)

5) if I use anything else that's a bit heavy on electricity (fog lamps / indicators / wipers etc.. ) I can get it down to 12.5v driving and this activates the Dim warning lamp.

 

There is no voltage drop as I had before. is it time for a new alternator/battery? :(

 

Cheers,

 

Courior

the same scenario happens every time: we keep the battery on car even if it is very old and weak.

then in turn the alternator gets damaged: fried regulator, diodes, windings, etc.

judging by the symptoms, both the battery and the alternator must go.

Just a follow up.

Sorry took so long. But today I found a Guy breaking a skoda in the street so I parked up next to it and swapped out the alternator. Got a healthy 14.2v at 2k rpm and 13.5 with all lights etc on.

Well chuffed with that... All for 20 euro. Brilliant

Courior

Sent from my MB526 using Tapatalk 2

Edited 2 May, 201412 yr by Courior