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sam m
01-02-2005, 04:55 PM
Wondering if anyone could advise me what this (http://www.surplustronics.co.nz/shop/product-CR0500.html) would do.

I have a cheap solar powered garden light. I am troubleshooting one that doesnt work. It looks like the light sensor that switches the unit on when dark is not working. It is the type of sensor that 'open circuits' when dark.

I am keen to try and fix this myself but have no real knowledge of electronics so wondering whether the link I provided is what I am after.

thanks

godfather
01-02-2005, 05:05 PM
The LDR in the link has a resistance of 20 ohms (low resistance) when fully lit, and 1,000,000 ohms (high resistance, almost open circuit) when dark. Probably similar to the one in the solar light.

I notice that the solar lights I have seen lately use the output from the solar panel to trigger the light, and not a light dependent resistor (LDR) although the LDR window is still there, just unused.

A multimeter would easily test the one you have though.

Given the cost of solar lights (<$5 ) you would only fix one for experience, not economics.

sam m
01-02-2005, 05:19 PM
The LDR in the link has a resistance of 20 ohms (low resistance) when fully lit, and 1,000,000 ohms (high resistance, almost open circuit) when dark. Probably similar to the one in the solar light.

I notice that the solar lights I have seen lately use the output from the solar panel to trigger the light, and not a light dependent resistor (LDR) although the LDR window is still there, just unused.

A multimeter would easily test the one you have though.

Given the cost of solar lights (<$5 ) you would only fix one for experience, not economics.

Yes it is more for the experience than economics. I have a multimeter which I put across the resistor and it says 3.5 ohms (with the switch on 20k). Not sure what that means but I am guessing it must be faulty as when I cut the wire leading to it the LED works. Hence my 'open circuit' idea but obviously it isnt that but Light Dependant resistance.

If they only cost that much then I might look for local store for supply.



Thanks

Graham L
01-02-2005, 05:34 PM
Dick Smith and Jaycar both stock them ... but their prices are higher. Of course, the Surplustronics price + a courier charge would make a cheap one expensive.

Test it by measuring it facing the sun, then hidden from any light. The LDR is quite sensitive.

BTW, Surplustronics have a 3.5A selectable voltage laptop power supply for a good price --- $89-50.

sam m
01-02-2005, 05:48 PM
Dick Smith and Jaycar both stock them ... but their prices are higher. Of course, the Surplustronics price + a courier charge would make a cheap one expensive.

Test it by measuring it facing the sun, then hidden from any light. The LDR is quite sensitive.

BTW, Surplustronics have a 3.5A selectable voltage laptop power supply for a good price --- $89-50.

Have checked out DSE and they have this (http://www.dse.co.nz/cgi-bin/dse.storefront/41ff07ca03d05cf62741c0a87f9906eb/Product/View/Z4801) which is cheap enough to play with.

I checked the resistor and as it got darker the resistance went up to 17.3 before it got too dark to see the multimeter which is a bit of a catch 22, how can I tell what the full resistance will be in the dark when i cant see the meter? Not too worried as I just want to see if I can fix it with a new one.

Thanks for the advice.

godfather
01-02-2005, 06:04 PM
You simply put black electrical tape around the LDR head and measure that, it should equate to dark.

You have to measure it out of circuit though (disconnected one side from the circuit).