 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / BMW Cars / April 2004Batteries and alternators - advice please
I bought a new battery for my 1995 model M3 in February. Using the "secret" OBC function to monitor voltage, I found that it's somewhat lower than I expected. If I don't drive the car for a few days, it will read around 11.4 to 11.7 volts in first key position (engine off), although the car will still start ok. I had the battery supplier check it, and he told me the battery was quite flat and that the alternator was at fault. Although it produced the expected 14 volts, his instruments showed under it could deliver only 30 amps. He would expect at least twice that figure. So I ring the mechanic, and they say it's unlikely to be the alternator. Apparently they hardly ever go wrong, and if they do they either work or they don't. End result - I'm not sure what's going on! Even if 30A is low, it seems plenty to keep the battery charged. I'd have thought the charging current would be no more than an amp or two, probably a lot less. On the other hand, in the back of the owner's handbook under "Electrical system", it says "alternator 105A", lending support to the "30A is too low" argument. I'd appreciate any insights from anyone who knows more about this than I do. Thanks, Andreas. > I had the battery supplier check it, and he told me the battery was quite > flat and that the alternator was at fault. Although it produced the > expected 14 volts, his instruments showed under it could deliver only 30 > amps. He would expect at least twice that figure. It varies its output according to the load (from things like lights) and the condition of the battery. If it's giving 14 volts, this means the battery is (near) fully charged. Alternators are designed not to dump their full output into the battery - a maximum charge of around 30 amps would seem about right. The rest of the output is 'reserved' for running the car's electrical system.  Signature*Two wrongs are only the beginning * Dave Plowman dave.sound@argonet.co.uk London SW 12 RIP Acorn >> I had the battery supplier check it, and he told me the battery was quite >> flat and that the alternator was at fault. Although it produced the [quoted text clipped - 7 lines] >would seem about right. The rest of the output is 'reserved' for running >the car's electrical system. The alternator regulator and brush set are available as a replacement unit (rather than buy an entire new alternator) for about £20ukp. Well worth a try. Easy - 2 screws to change. However you should check why the battery is running down. Do a "no load" test Switch everything off and measure the current drain from the battery - it should only be a few mA. Remember (if batt in boot) the boot light takes a few 10's of mA. Press the boot switch in to turn it off. DO NOT START THE CAR WITH AMMETER IN CIRCUIT. I had a "brand new battery running flat", prob. Turned out to be a couple of things - one of which was a faulty control unit for the heated door lock drawing 5.5*A* at random times. The other was a faulty clamp on the main cable from boot to engine bay. HTH > >> I had the battery supplier check it, and he told me the battery was quite > >> flat and that the alternator was at fault. Although it produced the [quoted text clipped - 4 lines] > >the condition of the battery. If it's giving 14 volts, this means the > >battery is (near) fully charged. I think the alternator is supposed to deliver round about 14 volts no matter the state of the battery, though I could be wrong. He tested the battery with the engine off to determine that it was not fully charged. > The alternator regulator and brush set are available as a replacement unit > (rather than buy an entire new alternator) for about £20ukp. Well worth a try. > Easy - 2 screws to change. Maybe for someone who knows they're doing mechanically - sadly that doesn't really apply to me! > I had a "brand new battery running flat", prob. Turned out to be a couple of > things - one of which was a faulty control unit for the heated door lock drawing > 5.5*A* at random times. The other was a faulty clamp on the main cable from boot > to engine bay. Yes, I'm starting to believe there maybe something like this going on. I'm going down to Southampton to see my brother-in-law next week-end and I know he has an ammeter, so I'll try to borrow it and do a check. Thanks for all the feedback, Andreas. Hello Just browsing and found your post. I have a 525i with battery probs - how do I find the secret Voltmeter via the OBC please? Mine is reading as low as 11.7 volts but starts daily but if left for 2+ days it goes flat. Thanks Chris > I bought a new battery for my 1995 model M3 in February. Using the > "secret" OBC function to monitor voltage, I found that it's somewhat lower [quoted text clipped - 22 lines] > Thanks, > Andreas. > Hello > Just browsing and found your post. I have a 525i with battery probs - how > do I find the secret Voltmeter via the OBC please? Mine is reading as low > as 11.7 volts but starts daily but if left for 2+ days it goes flat. I don't know if it works the same on a 5 series. On both my M3 and the 328i I had previously (both E36 models), the secret OBC functions were accessed by pressing the 100's and 1000's buttons on the extreme left simultaneously. It should respond by prompting for a test number; enter 9 for the voltmeter (press the 1 button 9 times and press Set). Hope that works for you. I got this information from this newsgroup originally. Andreas. > On both my M3 and the > 328i I had previously (both E36 models), the > secret OBC functions were accessed by pressing the 100's and 1000's > buttons on the extreme left simultaneously. I wrote this from memory and got it wrong. The two buttons you need to press are the 1000's and 10's. Andreas. > I bought a new battery for my 1995 model M3 in February. Using the > "secret" OBC function to monitor voltage, I found that it's somewhat lower > than I expected. If I don't drive the car for a few days, it will read > around 11.4 to 11.7 volts in first key position (engine off), although the > car will still start ok. If it starts the car & it's not *overcharging* the battery then don't worry about it. > > I bought a new battery for my 1995 model M3 in February. Using the > > "secret" OBC function to monitor voltage, I found that it's somewhat lower [quoted text clipped - 4 lines] > If it starts the car & it's not *overcharging* the battery then don't > worry about it. I've read that lead-acid batteries should be kept near to fully charged otherwise their life is shortened considerably. I was inclined not to worry, but at 115 pounds a time, I don't really want to replace the battery every few months... Andreas. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.