# Method to switch between two loads in simple AC circuit?

#### dohnjoe

Joined Apr 14, 2021
11
Hi,
So I have lost all my knowledge of circuitry apparently and need some help.
I have a small bicycle lighting project: I have a lamp that is attached to an AC generator, producing between 1 and 10 V, and would like to attach a second lamp in parallel to the first. When this second lamp is turned on I would like the first one to go out (without a switch). Is there any simple method out there to do this...Triac, diode...etc. ?
Dave

#### AlbertHall

Joined Jun 4, 2014
11,218
Below is a circuit which will select between the two lights using a single pole double throw switch (SPDT).

#### djsfantasi

Joined Apr 11, 2010
7,626
Hi,
So I have lost all my knowledge of circuitry apparently and need some help.
I have a small bicycle lighting project: I have a lamp that is attached to an AC generator, producing between 1 and 10 V, and would like to attach a second lamp in parallel to the first. When this second lamp is turned on I would like the first one to go out (without a switch). Is there any simple method out there to do this...Triac, diode...etc. ?
Dave
How do you turn on the second lamp?

#### dohnjoe

Joined Apr 14, 2021
11
How do you turn on the second lamp?
It's actuallly a lamp on the trailer, and I would be attaching it to the bike in parallel to the first ligth (rear) in parallel. I would like the first one to turn off after attaching the second one. Not sure this is even possible without something complexer than I'm willing to build. Would like no switches at all. SO that's why I was thinking a triac or something, and source is a AC.

#### AlbertHall

Joined Jun 4, 2014
11,218
What is the wattage of the trailer lamp?

#### dohnjoe

Joined Apr 14, 2021
11
Something like 0.2 Watt at 6 Volt, can vary around that and be up to 0.6 Watt, depends on speed and the circuitry of the LED Lamp.

#### AlbertHall

Joined Jun 4, 2014
11,218
Something like 0.2 Watt at 6 Volt, can vary around that and be up to 0.6 Watt, depends on speed and the circuitry of the LED Lamp.
And this is AC?

#### AlbertHall

Joined Jun 4, 2014
11,218
You want the main light to turn off when the trailer is plugged in?
One way to do that would be to have a plug/socket with an extra pin. Then you have an extra plug with a link between the power and this extra pin and the main light is connected to the extra pin. When this second plug is plugged in the main light gets its power via the link on the plug. When that plug is removed and the trailer plug, which doesn't have that link, is plugged in the main light power is disconnected. Thus the switching is automatic.

#### dohnjoe

Joined Apr 14, 2021
11
Thought of this, but would like to use a 2-pin pogo magnet connection. And if there is no simple solution would probably go this route. For me the problem with that is that the female plug is in the elements and exposed to dirt/grime/rain, and will eventually corrode on the inside.

#### AlbertHall

Joined Jun 4, 2014
11,218
The extra plug could be sealed with a silicone sealant to protect it from the elements.

#### dohnjoe

Joined Apr 14, 2021
11
Water would likely still get in through the socket unless I had an extra pug for that. Thanks for the tip. Still looking to see if there might be an electronic solution. And if that fails, like I said I'd likely go the plug/socket route. Thanks for your help.

#### AlbertHall

Joined Jun 4, 2014
11,218
Is the bulb powered with AC or DC?

#### dohnjoe

Joined Apr 14, 2021
11
It's an LED lamp, AC goes in and the electronic converts it to DC

#### Ramussons

Joined May 3, 2013
940
Whatever "electronic" solution you work out, you are going to have an electric connector to feed the trailer. That is going to be a metal contact which takes you back to post #9.

#### dohnjoe

Joined Apr 14, 2021
11
Whatever "electronic" solution you work out, you are going to have an electric connector to feed the trailer. That is going to be a metal contact which takes you back to post #9.
Not if it's gold plated. And surface corrosion isn't the problem, it's the problem of a closed space and the corrosion taking place there

#### dohnjoe

Joined Apr 14, 2021
11
Thanks for all the tips, but I'm still looking for a solution to the original question and not a physical work-a-round. Anybody got an idea?

#### Yaakov

Joined Jan 27, 2019
2,902
There is no "simple" method to do what you want.

#### dohnjoe

Joined Apr 14, 2021
11
Thanks