Electrical help needed..

[decca]

I am trying to wire up an alternator to charge a battery. The ignition warning light I have does not draw enough current to activate the coil in the alternator so I thought put a higher wattage bulb in the circuit (20w this does activate the alternator) but I really want the nice warning light that I have already drilled a hole for in my control panal. When I connect them only one bulb will light and it doesn't work the alternator

Hope you can see from this pic. I would have thought both bulbs would light up.
I have also tried a 10w resistor that was supposed to work but it doesn't.
Were am I going wrong?

 

[WorkshopChris]

Both will light up if you wire them in parallel but you have them is series so the small indicator light must be limiting the power to the light bulb preventing it from illuminating.

 

[dobbslc]

Does the bulb actually work?

 

[Seadog]

Have you wired them in series? I can't tell from the photo.

Beaten to it

 

[Seadog]

Wire the resistor and smaller bulb in parallel.

 

[dobbslc]

Looking at the wiring if they are in series they should both light up or nothing!
Maybe that bulb has failed and sorted out inside so it flows a current but doesn't work.

 

[Seadog]

Looking at the wiring if they are in series they should both light up or nothing!

Not if one is significantly larger in wattage than the other. there will be a faint glow from the filament of the higher wattage lamp which could easily be missed.

 

[brightspark]

Not if one is significantly larger in wattage than the other. there will be a faint glow from the filament of the higher wattage lamp which could easily be missed.

yup both would need to be the same wattage

 

[Cobbler]

Can't understand why it won't start charging with just a warning light though, that's all there is on a car to complete the circuit.

 

[500e]

http://www.gomog.com/allmorgan/LucasFault.pdf
Lucas publication Page 36 on for 17\18 ACR type others as well a good read if you are not sure of lectrik.
And much to big Cobller

 

[2tpmafia]

Can not tell from the picture but is the bulb connected to the positive of battery to the terminal on back of alternator

 

[rtbcomp]

The bulb forms part of the control circuit and is connected between the small terminal on the alternator and the battery +ve. The battery +ve must be connected to the big terminal, this provides the initial power for the field and the power output once the alternator is running. Obviously the battery -ve should be connected to the alternator frame. Don't run the alternator if its output isn't connected to the battery.

The bulb is only a few watts, again from memory about 5. When the alternator gives an output 12v appears on both sides of the bulb and it goes out. If the warning bulb blows, the alternator won't give an output.

 

[decca]

Looking at the wiring if they are in series they should both light up or nothing!
Maybe that bulb has failed and sorted out inside so it flows a current but doesn't work.

No, both bulbs work.

 

[decca]

Can not tell from the picture but is the bulb connected to the positive of battery to the terminal on back of alternator

If i connect the little lead from the alternator to the small bulb in the warning light and then connect that to the + on the battery the bulb lights but the alternator doesn't energize. If i do the same with the 20w larger bulb it works as it should and energises the alternator. I need to fool the alternator into thinking the warning light is a larger wattage. (I think) but don't know how to do that.

I think the key is in the series or parallel wiring so i will google it.

Cheers for the help.

 

[rtbcomp]

Does the small bulb light up? and go out when you run the alternator with the big wire connected to the battery? There's no way you need a 20w bulb in the ignition circuit. It is a 12v alternator?

 

[Seadog]

Read post 8 again.

 

[decca]

Does the small bulb light up? and go out when you run the alternator with the big wire connected to the battery? There's no way you need a 20w bulb in the ignition circuit. It is a 12v alternator?

The bulb lights up but doesn't go out when the alternator runs so i turned the pully by hand and connected the small wire from the alternator direct to the + on the battery with everything else connected and I could feel resistance when I turned it. With the small bulb connected there is no resistance. With the 12v 20w bulb in the alternator works and the bulb goes out when it runs.

 

[decca]

Read post 8 again.

Your right there, there is a very faint glow.

 

[Seadog]

Apologies, I meant post 5

 

[rtbcomp]

The bulb lights up but doesn't go out when the alternator runs so i turned the pully by hand and connected the small wire from the alternator direct to the + on the battery with everything else connected and I could feel resistance when I turned it. With the small bulb connected there is no resistance. With the 12v 20w bulb in the alternator works and the bulb goes out when it runs.

I suspect you may have damaged the regulator circuit, the 20w bulb may be feeding the field directly with about 2amps, IIRC the field takes a maximum of 4 amps so 2Amp will be enough for you to feel resistance, whereas a 6 watt bulb will only pass 0.5 amps. You will be getting an output but it will not be regulated, so you risk damaging the battery. Can you measure the output voltage with the alternator running at different speeds and maybe a load such as a couple of headlights connected to the circuit.