Battery Wont Charge

[Drewdown]

Hey guys I need a little help trying to figure out why my battery wont charge. Not sure if it matters but the car is a 91 318is.

The battery can be charged by a tender and will hold the charge until the car uses it up, but the alternator doesnt seem like it can charge the battery. Ive done some tests and checked for a drain, there was none. And then I checked the voltage. From what Ive heard its just at the lower limits of whats acceptable. I get 13.4 when at idle and 13.5 when revved. Any thoughts?

Could it be the exciter or a bad ground somewhere? I have a spare alternator too, so I could check that. Any thoughts?

[IminDiegoTriick]

You need to change the voltage regulator.

Make sure you know which part you need, whether it be Valeo or Bosch.

On your alternator facing the firewall there is two philip head bits you take out. The brand will be right there on the regulator. change it to start.

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=BMW&model=BE30&section=ELchrg&page=1&bookmark=3&part_number=12-31-1-726-022-M14

[Drewdown]

Ok Ill go see if its worn out. Should my two alternators be different brands I should be able to swap the whole thing out without any trouble, right?

[IminDiegoTriick]

what im saying is your alternator isnt worn out.. the voltage regulator most likely is the culprit. on an old e30 might as well change it out.. and there are two brands (VALEO/BOSCH) they arent interchangeble so check which one is for you.

A worn voltage regulator has two copper ends that are short... not long.

[Drewdown]

Yeah I got that. I was just asking if the regulator was worn out would I just be able to swap the alternator. Regardless both the alternators were bosch and both had somewhat worn regulators, but not to the extent that Ive seen others go out. I swapped the alternator just in case. Ill test it in a little bit

[AndrewBird]

Voltage at idle should be around 14v, so it is definitely the alternator or the regulator. I thought that if the regulator went out though, the voltage would be a lot higher then normal, not lower. Can someone confirm this?

[Eecen]

Its the carbon brushes that wear out, not the voltage regulator.
As the regulator/carbon brushes are a unit you just replace the voltage regulator. You could fit new brushes into your current regulator, but really why bother...easier to swap in a new one w/ good brushes.

[AndrewBird]

Ah, got ya. Didn't realize the brushes were part of the regulator.

[Drewdown]

Swapped out the alternator and it seems to have cleared up the issue. Thanks for the help guys :bow: