Alternator warning lamp

[purplerobbie]

I'm having trouble with the alternator warning lamp. It's old and doesn't always make a good contact.

Could I replace it with an led lamp? There is some on ebay the same size and the standard bulb type.

Or will it cause a problem?

 

[halcyon]

I'm having trouble with the alternator warning lamp. It's old and doesn't always make a good contact.

Could I replace it with an led lamp? There is some on ebay the same size and the standard bulb type.

Or will it cause a problem?

It provides initial rotor magnetic field to start the alternator charging, use a new filament bulb warning light with same wattage bulb.

Brian

 

[superheat6k]

It provides initial rotor magnetic field to start the alternator charging, use a new filament bulb warning light with same wattage bulb.

Brian

+1 The current flow through the filament bulb provides the field current required to excite the alternator to produce current. As it starts generating a small set of diodes provide the field current direct from the alternator's own output , which effectively provides an output voltage equal to the supply voltage to the warning lamp, but down circuit of the lamp, because both voltages become equal the bulb stops passing current and goes out.

If you were to use a very low current LED bulb the alternator will not have sufficient current to provide the initial field current require to get the alternator excited and producing current output. So this is the one application where a filament bulb albeit low wattage is necessary. An almost zero wattage LED just won't work.

 

[VicS]

+1 The current flow through the filament bulb provides the field current required to excite the alternator to produce current.

An almost zero wattage LED just won't work.

But presumably an LED with a resistor in parallel would work ...... but no real advantage over a simple filament bulb.

 

[ganter]

But presumably an LED with a resistor in parallel would work ...... but no real advantage over a simple filament bulb.

Correct.

 

[William_H]

The advantage of an LED with a resistor is that these can be soldered into the circuit meaning no contact problems. The lamp presumably was 12v 3 watt or 1/4 amp. This is equal to about 50 ohm resistor which at the most will dissipate 3 watts. So you need a 50 ohm (or 47 ohm) 5 watt resistor costing maybe half a squid. connect it in parallel with the LED. presumably one with a series resistor built in to operate on 12v. or an LED bulb or chip with about 330 ohm series resistor. good luck olewill

 

[purplerobbie]

The advantage of an LED with a resistor is that these can be soldered into the circuit meaning no contact problems. The lamp presumably was 12v 3 watt or 1/4 amp. This is equal to about 50 ohm resistor which at the most will dissipate 3 watts. So you need a 50 ohm (or 47 ohm) 5 watt resistor costing maybe half a squid. connect it in parallel with the LED. presumably one with a series resistor built in to operate on 12v. or an LED bulb or chip with about 330 ohm series resistor. good luck olewill

That sounds very complicated...

It was far easier to just buy a bulb and holder off ebay. £6 free postage.