8 replies to this topic

[TMW.Racing]

Hi, am interested find out if there is any extra performance to gain from doing the big alternator n battery change, or is it just to help starting and being able to load the car up with toys? Mine is an almost standard 998 with a radio, but it can feel sluggish when everything electric is turned on... Also, as there are not many electrical toys on it at the moment, would it damage the battery to have the higher output alternator with not much to run?

Thanks in advance!

[danie garry]

doubt it'd make any difference to the performance but could be corrected on that. the bigger battery and alternator will help if u have problems with cold starting or have alot of electrical stuff in the car, spots, radio, amp etc

[daemonchild]

If anything, I'd have said that the Pug battery is marginally heavier...

There will be no performance gain, but at least you'll be able to use your lights, rear heated screen, fan heater, windscreen wipers AND as a bonus listen to the radio in the winter.

[Dan]

Man people seem to have such a hard time understanding electricity!

A 75 amp alternator doesn't have to produce 75 amps, it simply can do if it needs to. If the electrical load on the car is the same then the power drawn through the alternator will be the same. Adding a bigger alternator won't mean there is more power in the electrical system, just that there is more available if needed. It can't harm the battery, the battery will still only draw as much as it needs to charge. The real benefit is that there is more power available so it will charge quicker. The load on the engine from any alternator producing a certain output is more or less the same nomatter how much the alternator is capable of producing, it's what it is producing at any given time that makes a difference not what it can produce. It will probably have a marginally noticable negative effect on your performance because as said above the battery is heavier and the alternator will be loaded more heavily by the battery charging which the engine will feel. It will as I said charge quicker though so the battery load will come off the alternator earlier and in that repesct you might notice a slight improvement after a few minutes driving. The idea that because it's a 75 amp alternator it can give more power more freely and so will feel less of the load and in turn load the engine more lightly is quite misguided unfortunately. If the car was using around 40 amps previously once the battery was charged, it will still use around 40 amps now ignoring the battery current. So the engine will still need to supply the same amount of energy to the alternator to generate the power.

[TMW.Racing]

Man people seem to have such a hard time understanding electricity!

A 75 amp alternator doesn't have to produce 75 amps, it simply can do if it needs to. If the electrical load on the car is the same then the power drawn through the alternator will be the same. Adding a bigger alternator won't mean there is more power in the electrical system, just that there is more available if needed. It can't harm the battery, the battery will still only draw as much as it needs to charge. The real benefit is that there is more power available so it will charge quicker. The load on the engine from any alternator producing a certain output is more or less the same nomatter how much the alternator is capable of producing, it's what it is producing at any given time that makes a difference not what it can produce. It will probably have a marginally noticable negative effect on your performance because as said above the battery is heavier and the alternator will be loaded more heavily by the battery charging which the engine will feel. It will as I said charge quicker though so the battery load will come off the alternator earlier and in that repesct you might notice a slight improvement after a few minutes driving. The idea that because it's a 75 amp alternator it can give more power more freely and so will feel less of the load and in turn load the engine more lightly is quite misguided unfortunately. If the car was using around 40 amps previously once the battery was charged, it will still use around 40 amps now ignoring the battery current. So the engine will still need to supply the same amount of energy to the alternator to generate the power.

Cheers dan, has backed up my understanding of it. The reason I asked was there were a few other threads worrying about the alternator damaging the battery which seemed odd to me so I wanted to throw the idea out to see what peoples thoughts were! Am planning a fairly major overhaul of the engine and I.C.E over the summer so I think I shall go with the upgrade.

Ta for the help people!!

[Dan]

there were a few other threads worrying about the alternator damaging the battery which seemed odd to me

Yeah people do ask some odd things!

[MRA]

If you do fit a higher output alternator please make sure your wiring can actually take the higher current........ thermal events are things you only want to read about

[icklemini]

^^^ what he said... have mentioned it before (and mildly flamed) : the standard wiring between alt and solenoid could do with beefing up.

on the performance side of things: the 'bigger' alternators have heavier rotors, so with the electrical load aside, just spinning them takes more power from the engine and loads up the bottom pully... which is held together by rubber....

[Dan]

what he said... have mentioned it before (and mildly flamed) : the standard wiring between alt and solenoid could do with beefing up.

I too know this pain. I've given up! It's easy to do though as the 75 amp units have a power output stud as well as the connector block.