Battery not charging light

[cpvh]

Hi All,

Back in the dark ages (60s,70s, 80s) cars had little bulbs that would come on to tell you your battery was no longer charging.

There have been a few people on the Peugeot?007 self Help FB group I?m on whose alternators have died, but their car?s not charging light hasn?t illuminated (despite its passing its POST before the problem and after its been rectified (see what I did there).

Got me to thinking, how were these bulbs driven in the past (i.e, what electrics / electronics / circuit lit them when charging stopped)?

And how are they supposed to work in ?modern? Cars?

On the ?007, I believe it?s an LED and I SUSPECT it?s fed from the ECU??

Anyone know?

[Chris Green]

Most alternators (and also dynamos as were used in 60s and before) had a specific terminal to drive the 'charging' lamp. It monitored the voltage between the alternator/dynamo output and the battery.

On modern 'all electronic' cars it needs to do exactly the same job but is presumably down to the designer exactly how it's driven.

[williamwright]

The bulb was connected between +12V after the ignition switch and the special terminal on the alternator or dynamo. If the latter was working there was 12V on that terminal so the light went out. If there was no output from the alternator or dynamo the terminal would drop to 0V (chassis). That would bring the bulb on.

This meant that a connection to the alternator/dynamo side of the bulb could be used to feed a relay that could connect a second battery so it got charged when the engine was running but was otherwise isolated.

Bill

[newshound]

In the good old days of dynamos, there was a sort of relay known as a cut-out that disconnected the dynamo output from the battery when the dynamo voltage was less than the battery. The bulb simply sat across the cut-out contacts. So if the dynamo was still working but its voltage was low and the contacts opened, the bulb would illuminate dimly. The later mods described for alternators in other posts were designed to give similar performance since, in those days, most people knew about the cutout. Everyone could change a plug, and most knew how to adjust points or change a capacitor too.

[Lee]

Fed via the BSI on most French things, do yourself a favour and don't look up Pug/citroen BSI/BCM failures...

Reset procedure (without the appropriate diag tool) is interesting* though ;)

*Almost Babel fish like :) :)

[ARW]

They don't.

You just wait until the battery is flat, the power steering does not work and it just stops running.

[newshound]

In the good old days of dynamos, there was a sort of relay known as a cut-out that disconnected the dynamo output from the battery when the dynamo voltage was less than the battery. The bulb simply sat across the cut-out contacts. So if the dynamo was still working but its voltage was low and the contacts opened, the bulb would illuminate dimly. The later mods described for alternators in other posts were designed to give similar performance since, in those days, most people knew about the cutout. Everyone could change a plug, and most knew how to adjust points or change a capacitor too.

[cpvh]

Adam,

I?ll bet it works on Toy Yodas, but then they are bullet proof, so I?ll probably never know (last one did 200,000 miles In 15 years (Petrol 2.0), and the alternator and the rest of the electrics bar a battery or two were as new.

Lee,

yes I know how awful / poor quality PSA cars are!

And know of lots of resets, though I?ve not had to do the BSI one so far.

[cpvh]

Bill,

12V on both sides in normal operation.

Clever!

[Steve Walker]

What? Place the satchel in front of the panel, with the junk mail inside it, hang your dressing-gown on the hook, place the towel over the drain and press the dispenser button?

SteveW

[Chris Bartram]

In the old days, the bulb fed the (field?) coil on the alternator from the battery, and the current through it was required to excite the alternator and start it charging- when it started to do so, the voltage both sides of the bulb became the same, so it went out. If the bulb wasn't connected or burnt out, the alternator wouldn't charge at low RPM- as RPM increased, it would self-excite.

I'd imagine you're right about the implementation now, but I don't know for sure. I know some cars have a charge control module.

[Brian Gaff (Sofa 2)]

Well a manual circuit should be pretty trivial as current will flow down a wire in one direction and in the other when its discharging. They used to fit meters with a centre 0 and you could then tell exactly what was going on and when. Brian

[Brian Gaff (Sofa 2)]

I'd imagine one could design a circuit with a two colour led, where its red one way and green the other and use an op amp and a low value resistor as a shunt and measure the polarity with the amp. Crude, but should work, but might need to be set up. Brian

[Brian Gaff (Sofa 2)]

Not really our old motor caravan had something like that but also a manual bypass if you wanted it.

Brian

[Harry Bloomfield, Esq.]

Brian Gaff (Sofa 2) has brought this to us :

A pair of back to back LED's, with the centre point connected to the point of polarity interest, and either end connected one to +ve, other to -ve makes a good simple indicator. A bypass diode would be needed in parallel with each LED, plus resistors to limit current.

[Lee]

I like this group :)

I had to reset a BSI recencently becuase the wipers were stuck on and the headlights wouldn't go out, after a battery change...

Just in case anyone is interested, the BSI reset is:

"Put the driver's window down, lift the bonnet and ensure all equipment is switched off.

Ensure all doors are closed and remove key from the ignition.

Wait for 3 minutes, disconnect the vehicle battery and wait 15 seconds.

Reconnect the vehicle battery, wait a further 10 seconds (do not open doors.).

Switch on the side lights through the driver's window.

Switch on the ignition and check system's functionality.

Hold lock button on key down for 10 seconds.

Remove key open & close door test central locking system.

Start the engine and complete the system's check.

Failure to follow this procedure could result in incorrect operation of many BSI related items."

[Dave Plowman (News)]

Depends how modern and complex. Some have alternators under the control of the engine ECU.

If a more basic self contained unit, the norm is 12v from the battery goes to the warning light, and the ground side of that to the alternator regulator. Without that 12v, the alternator won't start charging. Effectively that alternator connection supplies a ground to the warning light engine stopped, which moves to +12v as the alternator starts charging, so the light goes out.

[Steve Walker]

That makes HHGTTG seem almost sensible!

SteveW

[williamwright]

Yes it is. It was very useful for split charge relays as well. All you had to do was connect to the ignition warning light. Nowadays of course you use a voltage sensing relay, which has both advantages and disadvantages.

Bill

[williamwright]

What do you mean 'not really'? Not really what? I do wish you would put whatever it is you're answering at the top. You really are a very stubborn old man Brian.

Bill