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MG Midget and Sprite Technical - Alternator query - NOT the usual question!

Hi all.
Delighted to say I converted my Mk III midget to alternator power this weekend, thanks to all who gave me help especially Graeme Jackson & MGMike! ( cheers both )
We did the conversion using a gutted rb340 regulator technique.
When we started the car afterwards , the ignition lamp went out pretty much instantaneously, is there a way an automative idiot like me can find out if the alternator is doing what it should? or is this good enough?
i.e an alternator health check ?
thanks all
colin frowen

Hi Colin, a good weekends work - did the same thing a week or so ago and not looked back.

I had previously fitted a double power socket from Halfords (to power the sat nav) which had red-amber-green battery condition indicator lights.

Running on the dynamo, the green would light OK when running, when idling with lights and music on, the green would flicker to amber.

With the alternator, the green light stays on at all times, whatever is on.

In addition, the alternator makes an audible whistle, quite different to the old dynamo.

Regards Tony
Tony G

Unless you want to monitor either the output voltage or the current flow, the lamp going out is good enough.

I like gauges, so I have a ammeter (queue big debate re pros/cons volt meter vs ammeter), but in truth you don't need one, when you consider that most people survive their entire driving career without either of them. :)
Lawrence Slater

I you want to do an initial check, whilst running at say 2000 revs the voltage should be about 13.7 ish.

At rest when left to settle for say an hour I would expect a battery to be about 12.3 ish.

richard boobier

Anything over 13.4vdc when running is normal.

And the usual resting voltage is about what Richard says 12.2 -12.4vdc

And if you dont have a multitmeter to check with I bet a handy neighbour does, and a basic one is fairly cheap anyway. Which will be handy in future, so treat yourself.

You shouldn't need to rev the engine to get those voltage outputs. The alternator on my 1275 Midget produces over 14 volts at idle speed, providing the lights etc are off. Simply measure the voltage across the battery terminals with the engine off and then idling. A perfectly reasonable multimeter is less than £10 so why not invest in one?
Mike Howlett

as others have said, the best way to check is with a meter but if one isn't available the old methods still apply.
The warning light will go out when the alternator output is above battery voltage, therefore if you have a good battery, its safe to say its working (in terms of voltage output) if the light is off at tick over. As Lawrence notes an ammeter is needed to confirm the output is a net feed or net drain ie amps out of the alternator or amps from the battery. Putting the lights on high beam, heater blower on and wipers running whilst watching brightness of the lights when the engine is run from idle and slightly above will confirm if the alternator is delivering the required amps.
After that just drive and forget for about 100k miles (my modern ran 120k before needing a replacement).

(Lawrence, I won't start the debate on ammeters as that's more personal choice than necessity, oops perhaps I have after all ;0)
M McAndrew

Nah, there's no fish biting here today mike. lol. ;)
Lawrence Slater

Ammeters... "Flame on" sparky !!!!

Oh that did it... Now the debate begins... lol.

Basically... Anything over 14.4 volts is bad and anything under 12 is least thats my understanding... So between 12 and 14.4 and your golden

I personally belive you should have a gauge or two or 14

The pros of a volt gauge are there cheap, simple and idiot proof and will tell you if there is a charging issue

I like ammeters but i just dont have the courage to hook up the really better know what your doing, these are not to idiot proof.
Prop and the Blackhole Midget

This thread was discussed between 02/12/2012 and 04/12/2012

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