Dynamo vs Alternator

[ianf]

I have just had an interesting conversation with a friend who is considering fitting a lightweight starter and an alternator to his car (an MGA twink). I was consulted for my opinion (silly boy) and in the case of his car think it would be a good idea. I have shied away from the alternator route on my elan as I have believed the stories that one of the reasons the water pump fails is due to excessive water pump bearing side load. I have the fan belt so loose it could probably be changed without adjusting the dynamo and apart from an occasional squeal (normally when on hols in France - this could just be the car's sense of humour though) everything works ok. I understand that an alternator would need a tighter belt to drive it hence my reluctance to change (& a preference to keep the car standardish).

The question: The company who may sell my friend an alternator reckon that the bearings on a modern alternator would cause less drag than on an old dynamo - this I can believe - but surely if the output is higher the electrical resistance produced ( don't know the correct term but it causes a modern car engine to slow if you turn the heated window on etc) would be greater requiring a tighter belt?

Any thoughts anyone?

Many thanks,

Ian

[Emma-Knight]

I have just seen an S3 with a toothed-belt driven alternator. The owner said it is very reliable - no pump failure since (he owns his car since '71
and is frequently racing the car).And easy to convert - just change the pulleys, fit belt and go. (also suitable for dynos)

Limora also offers an alternator in a mocked dyno-lookalike housing.


Anna

[cliveyboy]

Water pumps fail when people get frightened of the belt slipping and so overtighten it. If you take an alternator you should be able to turn it very easily by hand. Therefore all you need is enough tension in the belt to rotate the pulley with out slipping which is not a lot.
Be careful having the belt too loose as I had some charging problems recently and it was because the belt was too loose.
Toothed belts are good for the water pump as they do not rely on friction so they can be quite slack.

Cliveyboy

[carrierdave]

Hi Ian,
Its actually round the other way. You need to have a tight fan belt for the dynamo because of its much lower out put, whereas with the alternator you can afford to have a slacker fan belt because of its higher output characteristics.

I?ve just converted my car to an alternator and the change is quite dramatic. No longer do I have to worry about keeping the rev?s up at a set of traffic lights, in order to stop the lights from dimming.

regards
David

[stuartgb100]

Yep,

I agree with David.
I just cannot believe just how loose the belt can be, and still the alternator works fine and charges the battery.

Definitely the way to go IMHO.

Regards,

Stuart.

[JJDraper]

Ditto above experience. I have an early +2 with an alternator conversion. Belt is quite loose - when the engine is off (of course!) you can turn the alternator pully quite easily by hand. No water pump problems so far in the last 40k miles/5 years and the battery is always well charged. My only problem was when the metal spring clip holding the plug in place was lost (I don't know how) and the resulting arcing destroyed the plug, but not the alternator fortunately. Local auto electrical specialist soldered new plug & supplied new clip on for ?20. He stressed that the plug must be soldered to the wiring as the high current can cause overheating of plain crimped joints.

My only problem is knowing what fan belt to ask for - any ideas?

Jeremy

[chicagojeff]

in my opinion, generators are horrible. you must have an alternator. I have a racing set up for a street car that works quite well. One belt, toothed, for the alternator. A second belt, gilmer, for the water pump. That way, tension is not that great, and neither slips.

[chrishewett]

I envy yor friend with the MGA twincam, What a great car!
Chris

[alaric]

A conversion involving a toothed belt and matching cogs would be good; this should avoid the thing slipping when the lights and screen heaters are on.

Sean.

[stuartgb100]

Jeremy,

In my notes from PO, I found as follows:

Fan Belt ? Dynamo Belaco R547 or RH789
Fan Belt - Alternator Belaco RH 684

and

RING: RFBC 785 Toothed belt for Alternator on a +2
MOTAQUIP: VFB 111 V type belt for alternator on a +2

Don't take these as gospel, but they may be a useful start.

Regards,
Stuart.

[JJDraper]

Thanks for the info Stuart.

Jeremy