alternator sizing

[chris240]

fellas

over the last month Ive been pulling my hair out trying to work out what could be slowly draining my battery.

I dropped in a carbed L28 last month and L28 alternator ..or so I thought..

We wired up the Alt to enable the removal of the external regulator and installed a diode etc as per previous postings...everthing appears spot-on.

But yesterday I had the alternator bench tested and was found to be fine, except, that we discovered its a friggin 35amp alternator ! could this be my problem ? I never got to speak to the auto-lecky as a mate passed the Alt onto to him (mates rates  )

any thoughts ?

[Scoota G]

35 amps will only do the basics... what else do you run?

[zed240au]

35 amp will only run basics i am running 80 amp on rx4 and was running 80 amp on old nissan v8 would suggest with stereos and other power hungry gear these days 80 amp would be on the money for you to use

 

at a minium 60 amp

[chris240]

Im actually running bugger all.....no cd player, no elec fuel pump, no interior light , although Im tempted to test the interior door light activator button on the door jamb..

 

Hey Mick, on another matter , did you recently have some distant relos stay with you, ....A guy called Mark + wife + kid from just out of canberra ??

[zed240au]

wasnt me havent had anyone staying over

 

mick

[chris240]

bit of a follow-up question....does a piddly 35amp Alternator have the grunt to even charge up a medium sized battery ?

[maddos]

I don't see why not. Your biggest current draw being your high beam, if you have 100w globes in, would make it 200w / 12v = 16A so that leaves a fair bit in reserve for whatever else is running and I assume driving through the day with no lights you would require very little current.

Plus if your battery is close to full charge won't draw much anyway.

[D.O.G]

My 280zx has a 45A Bosch alternator (fitted by a previous owner).

It, just, keeps up with all the electrics this has. I find at night, waiting at lights, with the wipers and demister on, the voltmeter swings back and forward in time with the blinkers.

I have a 65A alternator that I'll fit when time allows.

[Nacks]

What's your battery voltage with the engine running at a fast idle eg. 2000RPM? Anything between 13v and 14.4v is fine. This reading will depend on how flat your battery is and how much voltage drop you have across your charging circuit. 12v or below is not good.

 

35amps sounds pretty right on cars of that vintage. Bosch brought out a 55amp unit but they were mainly on cars that had A/C. some of the Japanese alternators were up around 45amp from memory.

 

You might have a crook battery or a leak that's draining the battery eg. glovebox light that stays on.

 

Do you have a voltmeter or a test light?

 

1. Turn everything off. Lights, ignition. close all doors.

2. Disconnect one battery terminal.

3. Put your voltmeter leads between the disconnected battery terminal and the battery post. If the voltmeter reads battery voltage ie. around 12v, you MIGHT have a big enough leak to drain the battery. Use your test light between the disconnected battery terminal and the battery post to see if there's enough of a leak to make the light glow. If the test light doesn't glow, you probably don't have a leak.

 

Testing an alternator on a test bench is one thing, fitting it to a car adds a whole pile of new ingredients that might be causing problems.

 

See how you go.