Alternator voltage

[LarryK]

Hello all,

Been having some problems starting/getting the car start reliably. The battery seems to be fine and my mechanic was saying there's no parasitic draw happening, but somehow the alternator isn't putting enough power through to start things? Does that sound right? Anyway, I'm supposed to find out what kind of output/voltage the alternator is supposed to generate. It's a '74 Austin Marina, so I imagine to the Mk1 Morris version.

Thanks.

[locost_bryan]

Have a look at the Lucas test cards in this thread. Should tell your mechanic everything he needs to know.

[david painter]

With car at 2000 rpm with all consumers on you should be getting 13-14 volts output. Measured across the battery.
Dave

[Kilroy]

The alternator is responsible for charging the battery and supplying the electrics while the engine is running.
If the battery is not fully charged after a decent run then both battery and alternator plus all connections in between are under suspicion.
If you charge the battery fully using a battery charger does the engine then start happily.?

It is difficult to point the finger at any particular item without knowing a little about the behaviour of all of those parts.

[drinud]

If you fully charge the battery, does it turn over and start fine? If not, the alternator is most probably not your problem.

The starter could be tired internally, and also check all your grounding wires.

[IVOR DENNEY]

I had a similar problem where it was struggling to turn over even with a new battery , but I noticed the earth strap on the battery was getting hot when I was trying start it . It turned out to be the starter motor getting tired so I had it rebuilt and also had it uprated also which solved the problem , so it might be worth checking to see if the lead is getting hot when your trying to start it

[david painter]

If you follow the link Bryan has added relates to the Lucas test cards flow chart. How i approach non start / battery flat

1 Charge and test battery fully charged battery gives 13.8 volts
2 test battery under load lights on and cranking battery must not drop below 10 volts
3 Check earth under load test meter red lead on battery negative and black lead to body and engine block in turn ( actual battery post not the clamp) rank engine ( ignition disabled) volt drop must not be below 0.25 volts
4 do same test at starter with red meter lead on battery positive post and starter stud ( not the nut) again under cranking 0.25 volt drop must not be exceeded.
5 parasitic battery drain set meter to amps disconnect negative lead red lead to battery negative and black lead to battery negative lead with everything off draw must not exceed 40 mamp.
Dave

[LarryK]

If you fully charge the battery, does it turn over and start fine? If not, the alternator is most probably not your problem.

The starter could be tired internally, and also check all your grounding wires.

The starter is new, I believe. The battery appears fully charged and using a jump box (or whatever it's called) usually gets it turning over and starting at least once. I'll pass on the tip about grounding wires to the mechanic.

[LarryK]

If you follow the link Bryan has added relates to the Lucas test cards flow chart. How i approach non start / battery flat

1 Charge and test battery fully charged battery gives 13.8 volts
2 test battery under load lights on and cranking battery must not drop below 10 volts
3 Check earth under load test meter red lead on battery negative and black lead to body and engine block in turn ( actual battery post not the clamp) rank engine ( ignition disabled) volt drop must not be below 0.25 volts
4 do same test at starter with red meter lead on battery positive post and starter stud ( not the nut) again under cranking 0.25 volt drop must not be exceeded.
5 parasitic battery drain set meter to amps disconnect negative lead red lead to battery negative and black lead to battery negative lead with everything off draw must not exceed 40 mamp.
Dave

That seems to be how my mechanic was testing things but we'll try your suggestions. Thanks.