12 replies to this topic

[oliver122]

hi all , what it is is my alternator is nakerd , anyway i have seen an 80 amp alternator i was going to get , but i know my battery is 60 amps , with 600 cranking amps , would the 80 amp alternator have a bad affect on the 60 amp battery ?

[lrostoke]

No alternators only provide what is being asked of them, it won't be pumping out a constant 80amp

[oliver122]

i thought that , but thought id best ask , because i don't fancy having to replace the battery again as well

[Wil_h]

Surely it's a 60Ah battery, not a 60A battery?

The cranking Amps is the maximum it will supply, owing to internal resistance of the battery. But as above it won't damage the battery no matter what current rating your alternator is.

[oliver122]

yurp it will be ah more than likely just me being stupid XD

[bmcecosse]

But why fit such a big alternator?? The wiring is not designed to take anything like that current. A standard alternator is all you require..... In any case - what's wrong with your alternator? Would a set of brushes fix it??

[Dan]

You may well need to increase the amount of copper between the alternator and the solenoid if you fit that.

[tommy boy]

Why would he need to increase the amount of copper (up grade to wiring ) from alternator to solenoid? As i see it , The car will only draw the current it actually needs, to a max of " everything on". Unless fitting half a dozen spot lights and massive sound system then the mini wiring is up to the job. A standard 45a alternator will take just a bit longer to replenish the battery after normal starting. 80a will do it a bit quicker is all. If you want to spend money wisely, then buy a new battery with the largest ah number that will fit into the hole. Cold weather reduces the efficency of all batteries. Winters on the way!!!!

[Dan]

The amount of power drawn by the electrical system will not increase no. That's why I haven't said anything else will need to change. A battery will draw as much power as can be supplied when it's flat, if the car is drawing say 35 amps total and the alternator is capable of supplying 80 at the speed its being driven, the battery will take as much of that as it can before its resistance stops it. It will charge the battery more quickly but in a Mini the battery and alternator are not coupled directly together by one large cable as they are in most cars. There is a much smaller pair of cables from the alternator to the solenoid as we all know, designed on most Minis to be just about able to cope with the standard alternator and a little more due to the use of standard wire sizes. I would suggest these are not up to an 80 amp alternator charging a heavily discharged battery on most Minis. And as you say, winter is coming.

[tommy boy]

Point taken. Mini`s are fun arn`t they

[Cooperman]

Mine has a 70 amp alternator and the alternator feed cable is duplicated to prevent damage.

[bmcecosse]

If it were to charge the battery at 80 amps = the battery won't last long!!!!!!!!!!! And - there really is NO need for a large battery. My TR7 (2 litre ) starts easily with a far from new size 38 battery - and I used a tiny Varley on my Rally Elf - but I did use jump leads from another car for a cold start...... A large battery is just unnecessary weight to lug about - as is an over size alternator.

Edited by bmcecosse, 26 August 2011 - 09:18 PM.

[Dan]

A lead acid battery given the correct DC supply voltage regulates its own charging current because as it reaches capacity its internal resistance increases. Given access to a potential 80 amps a 60 Ah battery would start off drawing all of that, and then the current would decrease exponentially. When a conventional lead acid battery has been at float (zero current) and 'gassing freely' for a certain period (which depends on details of its construction I believe, largely to do with how much paste is in it) it is fully charged. The alternator cannot force the battery to take 80 amps once the internal resistance in the battery is too high. There is nothing wrong (except a slight increase in weight and in engine loading while charging a low battery) with running a high output alternator. It will charge your battery faster which can only be a good thing.