real oem states my car has a 90a/95amp rated alternator

would it cause me problems to fit a reconned 80amp alternator.

ive fitted this alternator as a used part 2 months back and its given up

thanks

The rating of the alternator will only affect its ability to cope with heavy loads. If you have the heater fan, headlights, HRW, etc, etc, you will need the higher output to keep some charge in the battery. It's very unlikely to affect the function of the alternator.

When you say 'reconned' do you really mean 'me conned'? My mate used to deal in recon electricals. He used to expect at least a 10% failure rate...

If the bearings and commutator are OK, a diode pack/regulator is all you would replace.

I buy my rebuilt gear from a proper Bosch agent who rebuilds them himself and gives a 12 month warranty.

i replaced the carbon brushes and the voltage regulator unit in the back for a new set from bmw for £6 and all is well.

"well" because the alternator is working again and i didnt have to spend £70!

The alternator is the generator that the whole system runs off of when the car is running. All the battery does is give you power when the engine isn't running for Cold Crank starting clock etc. I.e. when the car is running the battery is not used as the power source, all the elctricals will run off the output of the alternator with any surplus going to trickle charge the battery if it's needed. If you drop the overall amperage with a lower output alternator you may find that at peak draw times the alternator cannot supply enough current and the battery may have to be used to top up the system and that may end up ruining your battery if it is not given enough time to recharge once the load is reduced. This is also reliant on what extra electrical systems you have added to the car, extra brake lights, higher wattage lights, stereo power amps etc. I would get the minimum rating at least as a lower rating alternator may have to work at full output for longer to supply all the current that the car needs leading to a quicker burn out.

One to remember is a car's alternator is rated to run the car's electrical systems and not recharge the battery, it can only do this if there's surpus output that can then be diverted.

Rob

b318isp wrote: Madrab wrote: One to remember is a car's alternator is rated to run the car's electrical systems and not recharge the battery, it can only do this if there's surpus output that can then be diverted. Rob Yes, the rated at maximum expected demand. 80A is quite a lot though, nearly 1kW.

Agree with you there and BMW probably add headroom to their alternator output spec to allow for wear and variance depending on what the OEM spec of the car is in the way of electrical demand

I'd also venture a guess that the same alternator gets fitted irrespective of the amount of optional extras you may have. Eg, a fully equipped car may require 70A will all the kit on fully, a bottom spec car may require only 50A with all of it's bits on too, but the alternator will probably be the same. Obviously, iff both cars had all the kit switched off, they'd both draw a similar amount, just enough to run the engine, ecu etc.

So, if you've got lots of toys in your car, i'd make more of an effort to fit the higher spec alternator. If you've just got an interior light and windscreen washer, then 80A should be fine.

IMO I would always err on the side of caution, especially where the electrical system is concerned and would suggest that BMW quote the 90/95 amp alternator for a good reason. Unless you add up all the electrical endpoints and their theoretical maximum current draw to see what the max peak could be then I would always go with their OEM spec and would only go higher, not lower.

Rob