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I use one of the blue relays from radio shack, sadly I don't have one of the little bags with the specs on it. I keep them all at school. Regardless, I power the coils with 9 volt batteries and they work very well.

Radio Shack does sell a 9v relay. And yes, its the blue one.

Just for my sake, anyone looking to get a relay should get this one. It's only 5 volts, so you can trigger it using your standard supply of four alkaline cells or a 6v lantern. I've had a very bad history with 9v batteries, since they last for all of two minutes. Swap them out if you can.

how can you trigger that relay with a radioshack photocell?How many are needed?

cypressfalls Robert wrote:how can you trigger that relay with a radioshack photocell?How many are needed?

By photocell, I'm going to assume that you mean a photoresistor. Using a photovoltaic cell (ie, a solar panel) and 10 volts of light doesn't generate enough current to shock a flea. Instead, you'll want to do something like what Dark Sabre did here. Basically, take two photoresistors, wire them up in parallel to the coil of the relay, and stick them next to a very bright light. You can easily get this to trigger with a standard flashlight lightbulb on 6 volts or more, just make sure the resistors are practically touching the lightbulb.

By the way, Radio Shack sells a nice pack of assorted photoresistors. They should be somewhere in the resistors drawer. I've only tried the kind pictured in Dark's photo, but I'm sure you could find a different arrangement that could maybe work without the need for the relay at all.

Edit: Out of curiosity, why do you need a relay at all?

we can't get the photoresistor to power anything major, and what we can is really really bad. We have a mini 3v motor that can't pull a switch closed after atatching string on it so it will wind and pull the lever on the switch. So maybe the relay should work.

cypressfalls Robert wrote:we can't get the photoresistor to power anything major, and what we can is really really bad. We have a mini 3v motor that can't pull a switch closed after atatching string on it so it will wind and pull the lever on the switch. So maybe the relay should work.

That might be an issue--if you can't get a 3v motor to work properly, I doubt that a 5v relay will trip. You can give it a shot (I'm running mine around 4.5v and it works just fine), but there's a good chance it's not gonna work. Are you just using one resistor? Two in parallel gave much better results for me, but I still had to put it less than a millimeter away from a bright lightbulb.

Are you using one of those halogen lightbulbs? if not what kind?

Primate wrote:

cypressfalls Robert wrote:we can't get the photoresistor to power anything major, and what we can is really really bad. We have a mini 3v motor that can't pull a switch closed after atatching string on it so it will wind and pull the lever on the switch. So maybe the relay should work.

That might be an issue--if you can't get a 3v motor to work properly, I doubt that a 5v relay will trip. You can give it a shot (I'm running mine around 4.5v and it works just fine), but there's a good chance it's not gonna work. Are you just using one resistor? Two in parallel gave much better results for me, but I still had to put it less than a millimeter away from a bright lightbulb.

When we could not get any of our motors to turn, we went to a 5v relay and it trips reliably with two photocells.

In order to get mine to work, I started with 10v in series and 1 photoresistor. Then I added more photoresistors in parallel, 1 at a time, until it started working consistently. I have a flashlight head shining on 4 photoresistors that trigger a fairly small motor (never had the specs for it) that triggers a switch that has had weight added to it so it will trigger easier. It was a bit tedious to figure out initially, but it is very consistent now.