alternator

[green123]

hello i put an alternator on today the man i got it of adured me it works i connected it up put wires on and put the tester across to find the dredded no charging at 12.6 volts the same as when the engine is not running i took the leads of the alternator to find the alternator is putting out 3 volts does anybody know what is wrong with the alternator ?

[mike.perry]

Never run an alternator on an open circuit, ie with the battery disconnected, you will knacker it.
Have you rewired the control box correctly?

[bmcecosse]

First off -is the car -ve earth??? And yes - open circuit running can ruin an alternator.......... Connect it up as per the diagram at the head of this section - and then measure the volts again.

[green123]

i have its till12 .6 volts and when engine revved dosent changed so im going to take it of and have a look at it

[Alec]

Hello Green123,

does the warning light work, if it doesn't that could be your problem?

Alec

[green123]

hello warning light goes out when started do dont know what problem is alternator works as i took it to a auto electrition and he said it works so any ideas?

[Alec]

Hello Green123,

if the light goes out then it's putting out more than battery voltage. Is the meter you are using accurate, an easy rough check is battery voltage before and after starting, if it's about 2 to 3 volts difference your meter would seem to be reading low?

Alec

[green123]

i will buy a new tester and see

[bmcecosse]

I asked already and had no answer - IS THE CAR NEGATIVE EARTH ????
If so - it's your wiring that's faulty!

[green123]

yes the car is negatice earth thats how its suppose to be for an alternator aint it

[kennatt]

don't bother with the meter simply get the car close to a wall start it switch headlights on rev it if the lights get brighter its working if not then there is a fault somewhere,even with a full battery the lights should get brighter.

[bmcecosse]

The meter obviously works - the wiring is wrong.....

[Alec]

Hello BMCE,

he's already stated that it's negative earth, what other wiring is wrong?

Alec

[green123]

hello so what wiring is wrong then for it not to be working

[bmcecosse]

Although the car is supposedly -ve earth - it's just possible the battery has been removed for charging - and refitted wrong way round? The alternator has been tested and is fine - ergo - it must be the wiring in the car that is wrong if it's now not charging in the car.......
Is it wired up EXACTLY as in this thread ? http://www.mmoc.org.uk/viewtopic.php?f=11&t=39514

[Alec]

Hello BMCE,

connecting the alternator with crossed polarity will blow the diodes. Green says the warning light goes out so it is charging, it's just his voltage reading that seems low?

Alec

[bmcecosse]

The diodes should hold ok , after all - that's what diodes DO - but it's certainly not an ideal way to treat it. The warning light may not be wired correctly - this is the most likely scenario.......

[Alec]

Hello BMCE,

thinking about it you are probably correct, not so sure about the regulator and the transistors in there though. It's not good practice to connect electronics to reverse polarity?

Alec

[bmcecosse]

It certainly is not - but there is no suggestion of this from the OP - I was just suggesting a check - as a means of determining why a seemingly working alternator does not work on this car.......

[green123]

yes it is wired up like the diagram light goes out so should be charging put a tester across 12 volts when not started started 12 volts the same i was thinking its something to do with the car electrics now will it affect the alternator if i dont have a wire from the alternator to the solenoid as i havent done that yet? many thanks