9 replies to this topic

[blacksheep1990]

I just purchased this sweet 1990 Mini Saloon.



Being a lifelong gear head (petrol head according to Jeremy Clarkson) the urge to make changes is incessant. I was told that the alternator is only a 45 amp model and as I want to add an electric fan, electric fuel pump, and an aftermarket (MSD) ignition. There items make me think the original alternator won't be up to the task.

So, I guess all that was to ask what are some swap alternator solutions that would give me a good electrical foundation on which to build?

Thanks
Eric

[RooBoonix]

An upgraded alternator is a good upgrade, maybe you could fit one of the 60A or 70A alternators fitted to some Mini's. (I think the MPI used the 70A version, which may fit).

 

Someone else will be able to confirm whether it will fit but there are 2 possible options. I know some people have fitted alternators from other cars with even higher charging abilities but I'm not sure if they needed modified brackets or not.

 

Good luck!

Cam.

 

PS: Love the car, nice and clean

[KernowCooper]

Those items you listed are within the standards car 45a alternators range. the fan wont be going all the time, Ignitions draw very little current and the fuel pump wont be a issue. If you Battery and Alternators up to scratch then you wont have any issues, your current Alternator wont be charging flat out, as soon as you have started up the Alternator will be monitoring battery voltage and load and will decrease it charge accordingly.

[BlackPlates]

http://m.ebay.com/it...4222?nav=SEARCH

That fits in!! And you can get a 120A version!!

The pulley will need machining to fit the shaft and to line up with the belt though... I used the pulley off the old alternator and made it work! You do have to turn the bottom bracket around though, or it wont adjust correctly

[A-Cell]

Also if you increase the output of the alternator from 45 to 60 or more amps then you will have to increase the carrying capacity of the wire from the alternator to the solenoid where it connects to the main battery cable, or risk the failure of the fusible link.
You may as well follow KernowCooper's advice and keep it standard.

[Cerberus]

Won't you be using more of the engines power to run a bigger rated alternator too?

[KernowCooper]

Only the the power reserves are used so if you driving around and the batteries fully charged then its putting in the same 5amps as the smaller one would.

 

A bigger alternator will only charge the battery as fast as the regulators see's the voltage and requirement. The bigger alternator will come into its own with 4 Cibies on and a 1000w amp in the boot, while you use the inverter as your driving to toast a few tea cakes in your in-dash toaster.

A bigger Alternator gives you more reserve amperage to run power hungry circuits, thats all. I cant see a normal road going mini needing a 120a Alternator?

[blacksheep1990]

Thanks to everyone for the advice.

 

I will ensure my stock charging system is up to par before I do any alterations.

 

Eric

[Cooperman]

Do a 'power load chart'.

This involves listing every electrical item which can be switched on at any one time. The total will be in watts.

Now divide the total watts by 12 and this gives the figure of power drawn in amps. Add 20% as a safety over-ride and that is the size of alternator you need.

So, for example, if the maximum possible current drawn is 360 watts, that is 30 amps. Add 20% that gives 36 amps, so any alternator giving 36 amps or more will be fine.

[Captain Mainwaring]

Do a 'power load chart'.

This involves listing every electrical item which can be switched on at any one time. The total will be in watts.

Now divide the total watts by 12 and this gives the figure of power drawn in amps. Add 20% as a safety over-ride and that is the size of alternator you need.

So, for example, if the maximum possible current drawn is 360 watts, that is 30 amps. Add 20% that gives 36 amps, so any alternator giving 36 amps or more will be fine.

 

20%? Not enough by miles given UK climatic conditions - you've assumed that the current output is constant. After a few cold cranking cycles in winter conditions then an hour sat with accessories on at night in traffic, you'll be needing your RAC membership.

 

Given your example there is just about enough left over to give a trickle charge to the battery with all accessories on and at rated alternator RPM, not idle.