Flat battery, jump starts, then dies when disconnect SOLVED!

Sun Dec 11, 2011 11:22 am

I've been fiddling with the electrics a bit http://www.e30zone.net/modules.php?name ... c&t=209098

Last night all was fine - fired up after a jump start. This morning it's fired up 3 times but dies when you disconnect the donor battery! Any ideas what to check?

Sun Dec 11, 2011 11:30 am

Condition of battery. Try another one.

Sun Dec 11, 2011 11:36 am

fit the donor battery ! it sounds like the cells in the one on the car are fubbered

Sun Dec 11, 2011 11:45 am

Cheers. It's been jump started a few times, could that be why? Is it possible I've fried my alternator?

Thanks!

Sun Dec 11, 2011 11:48 am

Jump starting can have adverse affects on a battery so it would be my first port of call! Then check your getting around 13/14 v charge from alternator then .

Sun Dec 11, 2011 12:03 pm

I get 10.9 Volts from the battery, I'll try joining the good battery starting up, and measuring the volts then.

...

Just measured 12.3 from the donor good battery, when the car is running the measurement is about 11.8 - 12. Just to clarify, that's with the old and donor battery joined up, as I don't want to take the new battery out the other car.

Does that confirm the old battery is knackered, not the alternator?

Sun Dec 11, 2011 12:40 pm

Should be 14v when running, unless you have an alternator problem which it sounds like you do

Sun Dec 11, 2011 12:47 pm

sounds like the rectifier pack has died you can replace this a company called durite do them for pennies if you fancy a challenge will get pt nos if you can post the long bosch nos on your alternater

starts with 0 192 ect

Sun Dec 11, 2011 6:19 pm

One of these?

http://www.ebay.co.uk/itm/DURITE-RECTIF ... 6&x=29&y=5

Some challenge! Does that mean taking the alternator apart? My electrical skills might not stretch that far, is there a decent how to guide?

Cheers!

Sun Dec 11, 2011 7:34 pm

not that thats for a lucas alt you will have bosch or valeo mate

Sun Dec 11, 2011 7:41 pm

To be honest I'm not even sure what one of these is! Appreciate the help, will look for the part no tomorrow. Much work to replace? I'll have to take the alternator off yeah?

Sun Dec 11, 2011 9:54 pm

FAR more likely to be the brushes (part of the regulator pack) than the rectifier pack.
Assuming a Bosch alternator, unscrew the two screws on the back of the alternator, remove the pack and check the condition of the carbon brushes.
If one is very short, and has signs of arcing on the end, that's very likely to be your problem.
Gently pull on the brush to stretch the copper braid holding it in place slightly, and it'll be good to go again for a week or two, while you source a replacement.

Mon Dec 12, 2011 12:44 pm

I'll take it out next weekend for a look and post what I find. Is it a big job to take these out? Any specialist tools required? Any top tips? I have my trusty Haynes at home I'll take a look at that but anything else would be much appreciated.

It's no problem off road as it's a track project.

Mon Dec 12, 2011 1:01 pm

milescook wrote:Any specialist tools required?

10mm spanner and a 6mm hex socket to remove the air filter/AFM assembly for access, then a #2 cross head screw driver to remove the regulator pack. A true five minute job.

Tue Dec 13, 2011 9:20 pm

Got my alternator out. Possibly not needed but I thought may as well while I'm there, in case the whole lot needs replacing.

Took off what I think is the regulator...

Look okay guys? One is *slightly* shorter than the other, and there's black carbon that seems to wipe off at the ends.

Thanks!

Tue Dec 13, 2011 10:08 pm

that looks ok to me what about the slip ring no cracks

Tue Dec 13, 2011 10:10 pm

Sorry whats the slip ring?

Tue Dec 13, 2011 10:27 pm

That's the regulator pack, and unfortunately there's nothing wrong with those brushes, so the search goes on!
What I can see from your pic., however, is that your alternator is of the type mounted on rubber bushes, and so has a separate earth strap. Check that both ends of this is making good contact to clean metal.
Slip rings are what the ends of the brushes rub against, but I doubt if there's anything wrong with them.

Tue Dec 13, 2011 10:32 pm

Thanks Brian. The metal contacts seem to be tidy?

Anything I can do with a multimeter with it off the car? Otherwise, what's the next step please!

Cheers for the help.

Tue Dec 13, 2011 10:59 pm

Next step is to put it all back together and see if it works now.
A volt meter between the alternator case and the battery negative would have shown up the fault before things were disturbed (should read very close to zero) if the earth strap was the problem, but the chances are you will have cured that now, simply by removing and replacing it.

Tue Dec 13, 2011 11:04 pm

Will give it a go. I have to think of the possilibty I've cocked something up here:

http://www.e30zone.net/modules.php?name ... c&t=209098

Also maybe the current battery is buggered. It ran lovely with the donor battery connected in parralel!

Will put it all back together (hopefuly!) tomorrow.

Wed Dec 14, 2011 8:43 pm

All back together now, and no different

Just with the donor battery connected and the engine running I get about 11.8 volts at the good battery. Switching on headlights and revving the engine doesn't jump the volts up.

I have to consider the fact I have been a bit of a spaner, so I've been racking my brains what I could have done to cock things up. See the below picture:

This is where the live battery feed from the cut off joins the car electrics properly, the more I think about the more I'm wondering is that connection up to the job?

I somehow think looking at it again I know the answer......!

Curiously though I checked the volts coming direct from the alternator and this started off about 12.4 volts, as i took more readings the figure seemed to come down to about 12.1 either at the terminals or before my junction box.

Wed Dec 14, 2011 10:54 pm

The alternator does spin, but the belt does seem quite loose to me. You can push it a few inches. Could this be an issue?

Wed Dec 14, 2011 10:58 pm

12.4 is still fat too low for an alternator output voltage. Needs to be close to 14 volts minimum.
Is the battery warning light circuit still connected up?
If so, I think it's time to try a fresh alternator.
As long as all the terminals in your joint are bolted tightly together ( the bottom cable with the red showing looks like it could do with being the other way up) that joint is OK from a continuity point of view, if being a bit dodgy on the left from an insulation viewpoint. It's a way I frequently join 400 volt cables at a couple of 100 amps together, before filling the (purpose made) box with potting compound.

Wed Dec 14, 2011 11:18 pm

Haven't put the dash clocks back in,please don't tell me there's some sort of circuitry on board that that tells the alt to charge the battery!

it worked fine with them out before so I thought....

Anyway I'm glad the joint looks okay ill sort it out plus I want to get the connectors that seal up both sides.its only a b and q junction box!

My belt seems loose I think,that can't help with charging I guess? You can spin the alt it doesn't move the belt but it works vice versa.

Wed Dec 14, 2011 11:30 pm

According to some research,a blown battery warning bulb n the dash is enough to stop the alternator charging.I guess not having the dash clocks in might also do the same trick....will try plugging this in tomorrow can't wait!

Wed Dec 14, 2011 11:55 pm

m42club.com/forums/showthread.php?t=150

Hmm! Think ill definitely be trying it with the dash clocks plugged in!

Happy that this might be the answer.

Thu Dec 15, 2011 9:05 am

Instrument cluster is part of the charging circuit! The reference voltage for the regulator is fed to the small
er terminal on the alternator via the battery warning light and/or a bypass resistor connected across it.
Belt should deflect about 1/2" under moderate pressure on its longest run. If you tighten it, onlt slacken the 13mm nut by the adjuster cog a small amount, or the cog will slide off of the side of the adjuster rack and chew up the teeth.

Thu Dec 15, 2011 10:54 am

Cheers Brian you're a legend!

Not quite obvious how to tighten the alternator belt though, can someone advise? The bolt with the teeth seems all the way up the scale and can't pull the alternator any tighter.

BTW: Donated some notes to the e30zone - this is such a great place with some genuinely very experienced very helpful people!

Thu Dec 15, 2011 1:52 pm

Slacken the alternator pivot bolt very slightly, and the inner end of the adjuster arm. Slacken the 13mm nut that clamps the adjuster cog in place slightly, then turn the adjuster with a 19mm (17mm?) spanner. Hold the belt at the correct tension with the spanner and tighten the 13mm nut, followed by the other fasteners you loosened.
If the adjuster is fully out, then you'll need a new belt - 9.5mm X 965mm for M20 engines, 9.5mm X 1013mm for the M40 and 9.5mm X 1025mm for the M42.
You'll need to remove the power steering belt first (similar method, just less accessible), so it may be a good idea to get a new one of those as well.

Thu Dec 15, 2011 9:40 pm

Put the cluster in - can only find blue and white plugs I take it mine doesn't have the yellow plug - at least I can't find it...?

Battery light comes on and stays on. Even without the flat battery connected at all that light stays on. As far as the ignition is concerned, I only need green and purple connected up to red?

I'll look at the alternator belt to tighten it up in case that's what's stopping my alternator kicking out enough charge - though it does spin.

One other thing, the indicators don't seem to work anymore - not sure if that's related? Though the lights do as the flick off when I turn the alarm off.

Cheers!

Sun Dec 18, 2011 5:08 pm

Ha! Long story short, replaced the alternator for a reliable sourced Bosch one from a 325 touring - current one was a recon'd unknown make that I don't have much faith in anyway. Replaced PAS and alternator belt while I was there, turned out I'd re-fitted the belt when I took the alt out originally - before I knew about the dashboard needing to be in, on the adjacent cog wheel from the engine. A smaller one!

This was why everything was so slack... Half inch of travel now, when I did a volts read and saw 13.9 then over 14.4 with some revs I could have cried!

Very happy cheers for the help!

Hope this helps out someone as mechanically dim as me!

The full story here - as it made me chuckle I thought I'd write it up!

http://racing.cookieonline.net/e30-320- ... tor-racing

Wed Feb 04, 2026 1:31 pm

Brianmoooore wrote: ↑
Thu Dec 15, 2011 9:05 am
Instrument cluster is part of the charging circuit! The reference voltage for the regulator is fed to the small
er terminal on the alternator via the battery warning light and/or a bypass resistor connected across it.
Belt should deflect about 1/2" under moderate pressure on its longest run. If you tighten it, onlt slacken the 13mm nut by the adjuster cog a small amount, or the cog will slide off of the side of the adjuster rack and chew up the teeth.

Thanks again, Brian

https://www.youtube.com/shorts/xd72H03N4IM