Another Electronics Question: Atl Charge Light

[MrOizo]

Hey people that know what you're talking about.

I have converted all my dash warning lights to LED and have been reading that LED's are not ideal for the dash warning light as there is not enough load to get the Alternator excited and to start doing its business.

What are acceptable ways to do this?
I was thinking something along the lines of a big enought resistor, relay or something else?

[Jonno2002]

just put a bulb behind the dash somewhere and leave the led in view

[Dell'Orto]

Narva to a resistor for LED tail/indicator lights, so I would think thats the best way to go.

[matt dunn]

Narva to a resistor for LED tail/indicator lights, so I would think thats the best way to go.

Too much wattage for most alternator circuits, Toyota's anyway.
It may burn out the regulator. Indicator bulbs are 21W, Most alternator bulbs are 5W max.

[Dell'Orto]

Hah, yeah wasn't meaning the actual Narva one Just a resistor in general

[MrOizo]

So a 5W resistor and a suitable LED?

- 12V circuit
- 2V LED Voltage
- 20mA LED Current

= ~500 Ohm Resistor. Needs to be a 5W one?

[matt dunn]

So a 5W resistor and a suitable LED?

- 12V circuit
- 2V LED Voltage
- 20mA LED Current

= ~500 Ohm Resistor. Needs to be a 5W one?

500 Ohm? where does that come from?

A 5 watt alt light is a (I = V/W) 0.4 A at 12.5V.
and ( R = V/I) 12.5V / 0.4A is a 31.25 ohm reststor,
or 33 ohm as that is what would be available.

and so yes will have to be a 5W one at 33 ohm,
and is wired in parrallel with the LED.

What resistor you need to run in series with the LED,
or if you need to run one will depend on the LED.

[MrOizo]

So a 5W resistor and a suitable LED?

- 12V circuit
- 2V LED Voltage
- 20mA LED Current

= ~500 Ohm Resistor. Needs to be a 5W one?

500 Ohm? where does that come from?

A 5 watt alt light is a (I = V/W) 0.4 A at 12.5V.
and ( R = V/I) 12.5V / 0.4A is a 31.25 ohm reststor,
or 33 ohm as that is what would be available.

and so yes will have to be a 5W one at 33 ohm,
and is wired in parrallel with the LED.

What resistor you need to run in series with the LED,
or if you need to run one will depend on the LED.

Shame on me! Was V=IR only. Been too long since i worked with this stuff..

Thanks for formulas - will use these when working out something suitable.

[sergei]

The problem with LED you will find that if there is voltage of ~1.8V across it, it will lit up (even though it will be behind a resistor, as it is a non-linear device), as all it needs is a few hundred microamps to be visible that is on (it will be faint). The regulator probably has more than few hundred microamps pulling from the warning lamp circuit. To prevent that, the simplest way is to put it in series behind of a zener diode (say 6V to 10V), like so:

Code: Select all

               //
+12V ---www--|>|---Z<|--- ALT



where --www-- is LED resistor (you will probably end up using 680Ohm),
The (anode)--|>|-- (cathode) is LED and (cathode) --Z<|-- (anode) is a zener.

Edit: and in parallel to that is 5W resistor. Also leave OEM diode in place.

[matt dunn]

Actually this whole thing depends on the alternator that you are using,

as some will work with just the LED as they dont need currrent to kick off,
and some wont.

Usually ( but not always ) an alternator that has an ign feed to it as well as a warning light won't need the current,

where one that has just warning light and a sensing wire will need the current in the WL circuit.

Most toyota denso alternatots that are S + I + L
will work with the LED warning light.