Thread: Speaking of 300Tdi alternators, 100a vs 75a

So why change?

My auto electrician told me to put in what I need, the more amps the more they heat up, the more they heat up, the quicker they die and the more strain on wallet and other parts.
Older alternators that produced say 35-50amps would live for long tome, due to heat mainly.

That was his way of clarifying and I put in a brand new bosch from memory at $480 plus labour and works great. 75amps.

Originally Posted by big guy

So why change?

My auto electrician told me to put in what I need, the more amps the more they heat up, the more they heat up, the quicker they die and the more strain on wallet and other parts.
Older alternators that produced say 35-50amps would live for long tome, due to heat mainly.

That was his way of clarifying and I put in a brand new bosch from memory at $480 plus labour and works great. 75amps.

THis may be a good point, however the fitment of a 100amp D1 alternator in place of the std def item does seem to be a popular course of action.....particularly when you are running extra electricals, eg a winch

I don't have a winch. Just a Versalite and a 40 litre Engel. No spotties either.

I think perhaps if I put in a 100a I'll get the benefits of a faster charge (not that I seemed to have suffered) but the car is old enough that the downside of longevity will not effect me (I may be in a D4 having sold the Defender! God that will be a sad day, and an expensive one $80000 sheesh!)

But the stick with the 75a argument resonates with me. I guess price difference needs to be factored in too.

Not sure of the efficiency of automotive alternators but they also produce heat while producing electricity. A good way to blow them up. or diodes in them for a start is to not get rid of the heat fast enough. Mainly a problem with heavy electrical load in hot weather.

After reading that Magneti Marelli alternators have a needle roller rear bearing that needs periodic cleaning and repacking, pulled mine (65 amp on 300Tdi) apart and did this. Also with a bit of trial and error, found an O ring to act as a seal, which should be a lot better than nothing for keeping the dust out.

Noticed something about these alternators, which I gather are a design from Joseph Lucas, the Prince of Darkness, in England where the temperature is on average cooler than Australia: Compared with Australian made Bosch alternators, they have a very small area of holes in the housing to let air in. Yet the fan behind the pulley that sucks it in is similar size.

So I drilled several holes in the housing to allow more air to pass through. Some looking and thinking necessary regarding where to bore them, including that they are not blocked off when alternator is assembled.

Should be less likely to have overheating problems than standard alternator with shortage of air holes, even though housing design does not allow as much open area as Bosch alternators have.

When did Landrover move to 100amp alternators as stock in the Discos (and Defenders for that matter)? Are the 100amp versions typically made by Bosch?

Just to clarify a few things.

1. The heat generated depends on the current actually taken from the alternator, not its rated output. In fact, if the same current is output, the higher rated alternator will run cooler (or at least be less stressed; sometimes the higher rating is gained by using more heat tolerant materials and just allowing it to run hotter). The difference in engine load and hence fuel consumption will be negligible, as you will be drawing the same current except when boosting the battery from a low state, and you will be doing this for a proportionately shorter time.

2. Unless you are using more power (extra lights, fridges, gadgets) than the original alternator provides, so that you keep running the battery flat, the only advantage of the higher output is that it charges your battery or batteries faster. Now this may be an advantage if you are doing only short runs, particularly if you have two or more batteries. But a higher charge rate on any battery will reduce its life, so it is not all plus.

3. In practice the difference between 75 and 100A is pretty minimal, and I doubt you would find any real difference unless you are having trouble keeping your battery fully charged. Remember that in reality, the maximum output will rarely if ever be reached, so the difference between the two is a lot less than it appears.

John

i fitted a disco alternator to my defender......i couldn't be bothered changing the pulley over so now i have to remember i am running a longer? serpentine belt

My MM 100amp realy went over 30amp whilst charging.
went to 60amp if the batteries were flat.
So I would so having an 100amp ALT it would not draw a lot of heat be cause it is running under 50% most of the time.

BUT after killing 3 MM I'm now runnning a Bosch

http://www.aulro.com/afvb/discovery-...r-300-tdi.html