mcramsay
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| posted on 12/5/16 at 09:19 PM |
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Alternator wiring
I have a Lucas a127 60a alternator fitted on my marlin but I am struggling to get it to work with the dash lamp. With the lamp connected up to the
alt, it does not charge and the lamp says lit it is a 4w lamp (30 ohms resistance). If I disconnect the warning lamp connection and connect up a
switched +12v supply instead the alternator works as intended and gives out 14v on idle. It just will not start to charge through the warning light. I
have by passed the wiring in the car and went straight from the lamp to the alternator with the same issue
It's all a new build so it has never worked previously. And the alt is brand new. Any ideas?
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britishtrident
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| posted on 13/5/16 at 06:37 AM |
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I think the next line of investigation is to do a sanity check on the cars wiring,
Wth the Key On Engine Off (KOEO)
(1) If you disconnect the alternator plug does the bulb go out?
(2) Reconnect the alternator plug and measure the voltage between the Warning Light terminnal on the alternator and a good ground on the engine. As
the field coil on the rotor has a ressistance of about 3 ohms should expect a voltage reading of more than 10 percent of battery voltage.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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02GF74
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| posted on 13/5/16 at 06:56 AM |
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When you unplug warning lamp connection from alternator, does the lamp go off?
Also 4 w bulb would be about 3 ohm, not 30.
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JoelP
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| posted on 13/5/16 at 08:11 AM |
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When i had similar problems, it was because my bulb was too small. I hid a larger one behind the dash. A resistor soldiered across the light
terminals is a tidier solution.
Beware! Bourettes is binfectious.
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prawnabie
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| posted on 13/5/16 at 08:40 AM |
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Also the bulb will need to be a filament type, I had this problem with I had an LED as the warning lamp, I had to fit a standard bulb behind the dash!
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britishtrident
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| posted on 13/5/16 at 11:22 AM |
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I checked on the the smaller versions of A127 you would normally see about 5 volt on the Warning Light terminnal key on engine off.
The larger 100 amp version of the A127 will show about 4 volts
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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mcramsay
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| posted on 13/5/16 at 01:04 PM |
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The light goes out when disconnected from the alt. I will take a few readings this afternoon and see what's actually being fed into the
alternator from the charge light. I am using a lamp not led.
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mcramsay
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| posted on 13/5/16 at 01:52 PM |
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Ok so if I disconnect the warning lamp connection, and ignition on engine not running I get just under 12v. If I plug in the connection from the lamp
and read voltage again I am only getting 1.3 volts when connected up to the alternator so that's the problem, but why is that happening? I tried
the same test with seperate leads from the warning light again with the same results. When the light is plugged into the ind connection on the alt
plug voltage drops to 1.3 Volts going in
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Oddified
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| posted on 13/5/16 at 02:49 PM |
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Not sure about the other suggested voltages of 4 or 5v on the terminal (the ign light would be a bit dim...) but i have a 127 alternator on my own
car, just tested the voltage on the alternator ign terminal (ign on/engine off) and i have 0v65. I have a 2.2w bulb.
Ian
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mcramsay
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| posted on 13/5/16 at 03:25 PM |
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Managed to sort it. I put a 30 ohm resistor in parallel with a test bulb of the same size, and it instantly worked. But the resistor got bloody hot
when the ignition was on and not running, so I tried again with the standard car wiring through the dash lamp, the only difference this time was I
gave the engine a little light Rev, and the light went out and stayed out and all worked as it should, I can live with that for now.
The only outstanding issue is that if the rad fan comes on and you put the main beams on the fan dies unless you Rev the car, I'm guessing
I'm maxing out the alt output at idle, I suspect the battery has an issue aswell and is majorly dropping volts under load.... It is a small
pc680 battery I have had for 3 years and have not kept on trickle charge. And I have a massive kenlowe fan to power aswell
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Oddified
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| posted on 13/5/16 at 05:36 PM |
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Have you got an oversize pulley on the alternator? (used on high rev engines to stop the alternator being over speed), that would explain the blip
needed to extinguish the ign light and low output at idle.
Ian
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mcramsay
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| posted on 13/5/16 at 05:55 PM |
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I did change the pulley size, and was maybe a bit conservative, I can't remember what diameter I put on in the end. I could go a little smaller
it seems, max rpm for my alternator is 16000 I believe. It works for now, but it is something I may look at in the future
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