hi I have a 1990 mini with a 65 amp alternator. All charges daily except when turning on lights etc If I run daily with out headlights and heater etc then no problem with charging or starting.
Alternator giving 14.3 volts. But only seems to be around 10-15 amps.
Turn on headlight then volts only 13.4
Turn on heater and lower volts
Turn on rear screen battery voltage lower than when turned off
My battery light shows before starting goes off when running but does not come on when not enough volts to charge
Tried replacing alternator no different
Headlight are around 8amp draw
Does all mini do this
I have checked earth cannot find any issue. I have even tried new earth from battery to alternator but no difference. Please help as winter coming so need lights heater etc
Measure the voltage at the alternator output terminal and the battery terminal when the alt is loaded. If they are significantly different you have resistance in the charging circuit. Use the voltage drop test method to isolate the point where the resitance is in the circuit. Replace all conneactions as required. Retest to confirm the fix.
Look up voltage drop tests for more info on youtube/google.
Thanks for that, have checked and voltage is same on large nut of solenoid and battery.
Although battery holds charge when no lights etc on I presume battery is ok? When start car starter turns over good does not seem sluggish so I again presume good supply from battery to starter. Should voltage at battery always be 14v+ when running as long as items turned on do not exceed amps of alternator i.e. 65amp. Modern cars stay at 14v but do mini’s with old style wiring?
Thanks for that, have checked and voltage is same on large nut of solenoid and battery.
Although battery holds charge when no lights etc on I presume battery is ok? When start car starter turns over good does not seem sluggish so I again presume good supply from battery to starter. Should voltage at battery always be 14v+ when running as long as items turned on do not exceed amps of alternator i.e. 65amp. Modern cars stay at 14v but do mini’s with old style wiring?
Yep 14.3 volts is the regulated voltage. The “new cars” copied the technology from the “old cars” !! Ha ha
Hi checked voltage off alternator, matches battery volts.
Have tried new earth from battery to alternator mount bolt to check earth and still no difference. Volts start at 14.3 and drop to 12.6 under load, i.e. no charge. Amp meter on alternator see to only show up to 12 amps max, could battery be faulty although never let me down all summer?
Your alternator should be able to power all the electrics after all thats what it does under normal running and nothing being supplied by the battery, your alternator cant keep the voltage above 13.7v it seems which is the minimum voltage to charge a 12v lead acid battery fully. You mention changing the alternator, wqs this for a new one or another you had access to?
The alternator circuit is pretty basic, as long as the alternator has exciter voltage going in and the out large brown is connected to the solenoid connnection and this is shared with the + cable going back to the battery, then if the earth connection is good then it will meet its voltage of the regulator of 13.7-14.3v assuming the fan belt is tight , if it wont and the above connections are good (please check all connection are clean and tight) then its inside the alternator where the fault lies
Alternator was fitted in May when bought car as old alternator did not give any volts. Since may not used blower lights rear screen etc so another new alternator sent from company for me to try. Incase may one was faulty. It is a 65 amp with 3 wires. Light bulb wire plus 2 wires to solenoid. New replacement received yesterday made no difference. May get battery load tested tomorrow. I have ran out of ideas. I have a lip on amp meter which only indicates around 12 amps on charge wire from alternator. Could battery be causing limited charge voltage?
Starter seems to crack well do don’t think power lead or earth from battery as starter would be sluggish.
Well then it points to at that point the meter was only detecting 12amps, you need to get the Alternator bench tested if you can’t see anything wrong as AC pointed out
