Battery light on ......

[waltraud]

Hi. Westy Joker 83 DG originally a DF with leisure battery and original split charger. The battery might comes on a bit / not too brightly sometimes during or at the end of a trip. I think it tends to happen when i've come to a standstill. Fan belt tension is ok. Battery cells are covered with battey water. Main feed from battery to rear of van is is newish. So I wondered about alternator brushes/regulator and swapped a new pack onto it see pics. [attachment=-1]uploadfromtaptalk1397563785062.jpg[/attachment][attachment=-1]uploadfromtaptalk1397563798645.jpg[/attachment]

[waltraud]

Left overnight the starter battery reads 12.42 volts. When running it shows 13.4v at increased revs and around 13 when lights heater etc are on. when started up today no battery light on after ignition seems like battery tends to stay around 12.9 when high demand then when lights heatwr etc off charges to 13.7 or so. Is tjis normal? Is it poss that the battery is struggling to hold charge adequately? Am I fussing about nothing......

[waltraud]

After changing brushpack it seems to turn over more quickly suggesting battery charging well. On test now with battery light on, not very brightly but clearly on it reads 13.6 fast idle then up to 15.10 v when at high revs and 13.4 when under heavy load idling. Does battery light on suggest anything?? Thanks for any tips.

[pirate-pete]

Since nobody else answering I'll take a go

With engine running the indicator light should get battery voltage at both terminals, one via ignition switch, the other from the alternator indicator terminal (blue wire)

As same voltage at both ends then no current flows and lamp should stay off. You know your alternator is charging so I'd guess there is some voltage drop over the wiring somewhere. Don't have any manual handy at the moment to see what the VW alternators use as regulators or wiring diagrams but the bit now confusing me is that the T25 has an LED for the alternator light doesn't it? So that would only work one way round - lit when battery voltage flows to ground via uncharging alternator. With older cars I learnt on the bulb was a normal one so would light with current in both directions. Try to compare voltage at each terminal of bulb if you can get to it to see which is higher. Think you will find ignition side higher to get led to light. In which case see if you can temporarily replace that blue lead from the alternator to the next connector to see if that makes a difference - it looks a bit corroded in your photo where it enters the crimp terminal.

[MidLifeCrisis]

Since nobody else answering I'll take a go

With engine running the indicator light should get battery voltage at both terminals, one via ignition switch, the other from the alternator indicator terminal (blue wire)
As same voltage at both ends then no current flows and lamp should stay off. You know your alternator is charging so I'd guess there is some voltage drop over the wiring somewhere.

^^^^WHS

It suggests that at standstill the alternator is not producing as high a voltage as the battery is producing;
Or alternatively, the alternator is producing sufficient voltage but there is a 'voltage drop' along the wire that runs from the alternator to the indicator light.
Can you measure the voltage on the indicator wire, at the alternator end, when engine is idle?
Then, can you measure the voltage on the indicator wire, at the dash end (at the dash connector thingy)?
Do they differ (they shouldn't)?
How do they compare to battery voltage....?
(Thinking about it - you might have to disconnect the connector to the dash once the engine is running otherwise I think that you might end up measuring the battery voltage when you think you're measuring the alternator voltage (remember that this circuit, when the engine is running, has 12v at both ends) so it can get a little confusing as to what you are actually measuring....)

[Jakemate]

You may have a warning light diode breaking down in the alternator.
Check voltage at alternator on warning light terminal, if it's low remove diode pack from the alternator and stator and check each diode with a multimeter on diode test.

[waltraud]

Thanks all, ill do some testing today.

[waltraud]

Ok so at 900rpm warm engine the warning light blue lead on the alternator terminal reads 14.08v when revs on it reads 14.15. All after I cleaned up the terminals. See pics. I found the blue wire to alternator was corroded and fraying where rubbing on sleeve so could potentially have been dodgy or even grounding occasionally? ?

[waltraud]

[attachment=-1]uploadfromtaptalk1398527049264.jpg[/attachment][attachment=-1]uploadfromtaptalk1398527066206.jpg[/attachment]

[colinthefox]

The connector on that blue wire looks like it has been overheating. Probably a poor crimp. It will need cutting back to bright wire, then a decent crimp connector, or much better, crimp and then solder. Crimps don't stand up to vibration very well unless really well done.

[waltraud]

Since nobody else answering I'll take a go

With engine running the indicator light should get battery voltage at both terminals, one via ignition switch, the other from the alternator indicator terminal (blue wire)

As same voltage at both ends then no current flows and lamp should stay off. You know your alternator is charging so I'd guess there is some voltage drop over the wiring somewhere. Don't have any manual handy at the moment to see what the VW alternators use as regulators or wiring diagrams but the bit now confusing me is that the T25 has an LED for the alternator light doesn't it? So that would only work one way round - lit when battery voltage flows to ground via uncharging alternator. With older cars I learnt on the bulb was a normal one so would light with current in both directions. Try to compare voltage at each terminal of bulb if you can get to it to see which is higher. Think you will find ignition side higher to get led to light. In which case see if you can temporarily replace that blue lead from the alternator to the next connector to see if that makes a difference - it looks a bit corroded in your photo where it enters the crimp terminal.

After changing brushpack it seems to turn over more quickly suggesting battery charging well. On test now with battery light on, not very brightly but clearly on it reads 13.6 fast idle then up to 15.10 v when at high revs and 13.4 when under heavy load idling. Does battery light on suggest anything?? Thanks for any tips.

Since nobody else answering I'll take a go

With engine running the indicator light should get battery voltage at both terminals, one via ignition switch, the other from the alternator indicator terminal (blue wire)
As same voltage at both ends then no current flows and lamp should stay off. You know your alternator is charging so I'd guess there is some voltage drop over the wiring somewhere.

^^^^WHS

It suggests that at standstill the alternator is not producing as high a voltage as the battery is producing;
Or alternatively, the alternator is producing sufficient voltage but there is a 'voltage drop' along the wire that runs from the alternator to the indicator light.
Can you measure the voltage on the indicator wire, at the alternator end, when engine is idle?
Then, can you measure the voltage on the indicator wire, at the dash end (at the dash connector thingy)?
Do they differ (they shouldn't)?
How do they compare to battery voltage....?
(Thinking about it - you might have to disconnect the connector to the dash once the engine is running otherwise I think that you might end up measuring the battery voltage when you think you're measuring the alternator voltage (remember that this circuit, when the engine is running, has 12v at both ends) so it can get a little confusing as to what you are actually measuring....)

[waltraud]

Oops. Ignore last post. Re done blue wire and cleaned up generally. Lets see if the lighg comes on again or not. Will try to test at light end.

[pirate-pete]

Some useful info here http://www.ratwell.com/technical/ChargingSystem.html

The 15.1V at battery with high revs seems high - could it be the regulator is faulty. Was todays test of the blue lead when you read 14.5V at the same revs? If so there is a .6V difference which could cause the lamp to come on.

(Thinking about it - you might have to disconnect the connector to the dash once the engine is running otherwise I think that you might end up measuring the battery voltage when you think you're measuring the alternator voltage (remember that this circuit, when the engine is running, has 12v at both ends) so it can get a little confusing as to what you are actually measuring....)

Not sure whether disconnecting the dash connector would help as I think you need this connection in place to get the alternator to charge. I know what you mean about confusing though. Whether it is a bulb or a led it should have a voltage drop over it if lit though. From Tim's tests today though I think we know the ignition side has the highest voltage.

You may have a warning light diode breaking down in the alternator.
Check voltage at alternator on warning light terminal, if it's low remove diode pack from the alternator and stator and check each diode with a multimeter on diode test.

Looking at the diagram in that link I just posted above, that is a possibility too. If that blue wire has been shorting where it is frayed it could have taken out a diode. Could that account for the 0.6V difference between the output and the indicator terminal as that is a common voltage drop over a diode?

[waltraud]

The original figures were two days ago before I did the wiring clean up. Will check battery v again now to see if it goes up to nearly 15 which was weird 2days ago. My little battery/alt tester says its charging adequately see pic

[waltraud]

Ok. So today after few days standing battery at 12.5 standing. When started at highish revs at battery it reads 13.6. With full beam and wipers on it drops to 13.1 then quickly 12.9 and gradually gets a bit less....revving makes no diffetence. This is after swapping a new brush pack into alt. Hmm. Luckily have a good 2nd altr coming from metal michael but wondeted if this sounds like diodes and if so where to buy n how to replace? Thanks folks. :idea: