Posted By krs on 10/01/2008 4:03 PM
I picked the 1N914 diode and the 78L type 6 volt regulator on purpose to make a point.
A rectifier is not a rectifier is not a rectifier......if they were all the same why do you think there are thousands of different types?
The 1N914 dide can comfortably handle 100ma of current, the 78L type voltage regulator is already maxed out at 100ma - so I went looking for a 5 or 6 volt relay with contacts that can handle 3 amps or better at 24 VDC.
Radio Shack didn't show any on their web site, so I looked at All Electronics, a surplus place. Of the 46 diferent relays they have listed, only one meets the requirements of 3 amp or better DPDT contacts and a 5 or 6 volt coil. This one:
http://www.allelectronics.com/make-a-store/item/RLY-642/6VDC-DPDT-RELAY-PC.-MT./-/1.html
Trouble is that the coil has a resistance of 50 ohms, so the relay will draw 120 ma when operating and you exceed the rating of both the diode and the 6 volt regulator that I listed.
You could try Mouser and Digi-key or active Electronics or Future Electronics or any number of others to try to find a relay with a higher coil resistance, but moving 3+ amp contacts takes a certain amount of energy and you are not going to find a low-current relay that will do that.
My point is simply that you can't just throw a bunch of components together in a circuit and hope that everything will work out in the end.
Maybe you know how to select each one and which component parameters are important and which one are not in a specific circuit, but I'm sure many people who might want to build this unit, cannot.
As I noted, use 4000 series diodes.
The rectifiers I typically see are 1 amp or more. The 555 chip can handle up to 250 milliamps, and I've used them to directly driver BIG relays (10 contacts at 120 volts) that draw 150 milliamps with no problems. You could certainly use this relay (even has the reverse diode built right in) , (though I was getting 4pdt 5 amp, 6 volt relays from these guys @ $0.60/each and got about 20 at the time). Aromat S2EB-5 relay features a polarized 130ohm 5VDC coil and four separate sets of contacts giving the equivalent of DPDT contacts. Contacts are rated 4Amp @ 250VAC or 3Amp @ 30VDC. Has 12 PC pin terminals. Sealed case is 1.11" L x .48" W x .40" Tall. Worth about $15.00. Brand New! G15227 Don't like their stuff?
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This works out to 120 milliamps and is within the capacity of the 555 chip:
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Or, two of these could be used for a dpdt: Or two of these to make a dpdt: |