Reversing Controller

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.

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).



http://www.goldmine-elec-products.com/prodinfo.asp?number=G15227

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?
>


This works out to 120 milliamps and is within the capacity of the 555 chip:

http://www.allelectronics.com/make-a-store/item/RLY-642/6VDC-DPDT-RELAY-PC.-MT./-/1.html




Or, two of these could be used for a dpdt:

http://www.allelectronics.com/make-a-store/item/RLY-499/5VDC-SPDT-6A-RELAY/1.html


Or two of these to make a dpdt:

http://www.allelectronics.com/make-a-store/item/RLY-501/6VDC-SPDT-10A-RELAY/1.html

Posted By krs on 10/01/2008 4:03 PM

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.






Actually, no it will only draw ~90 ma.

Remember that you only get about 4.5 volts out of the chip. (4.5 x 4.5)/50/4.5 = 90 ma

Furthermore, ANY rectifier or RECTIFIER diode or 6 volt regulator purchased at Rat Shack has the necessary capacity. Switching diodes (that you selected) are not typically used as rectifiers.

If anyone wishes to build a reverser and is having trouble finding a suitable relay, the included schematic will allow you to use the A/C tap on your power pack or any dc source of ~14-22 volts to power the electronics. This costs no more and does have advantages. First, you are not limited to the 7-8 volt minimum on the track as you would be using the prior diagram. Next, it gives you access to a much wider variety of relays so you can more easily find what you need. Use a 12 volt relay (very common) and a 12 volt regulator, and you probably can get all the these parts at Rat Shack without problem. Or, get them surplus and save even more money.

Again, you may need to put the reversed diode across the relay coil to prevent eratic behavior. Use a 1 amp (4000 series) diode for this.

I put the below list together. For the items with a question mark, is more description needed to go into RS pick up all or most of the parts?
Please edit the list as needed. Is a pot a resistor? Thanks.

bridge rectifier ?
capacitor 100 mfd 35 volt
capacitor 10 mfd 16 volt
capacitor 200 mfd 16 volt
regulator positive 6 volt
resistor 1 k ohm
resistor 47 k ohm
pot 500 k ?
555 chip ?
relay coil ?
relay armature ?

Posted By chrisb on 10/03/2008 5:52 PM

I put the below list together. For the items with a question mark, is more description needed to go into RS pick up all or most of the parts?
Please edit the list as needed. Is a pot a resistor? Thanks.


bridge rectifier ?
capacitor 100 mfd 35 volt
capacitor 10 mfd 16 volt
capacitor 200 mfd 16 volt
regulator positive 6 volt
resistor 1 k ohm
resistor 47 k ohm
pot 500 k ?
555 chip ?
relay coil ?
relay armature ?

Lets hook it up using the a/c tap as I showed in the second diagram. Then you can get all the parts at Rat Shack.

The bridge rectifier at link:
http://www.radioshack.com/product/index.jsp?productId=2062581&cp=2032058.2032230.2032269&parentPage=family

Because we are going to use the a/c tap, we would like a little more filtering on the power supply so the relay doesn't "chatter." Instead of using the 100 mfg 35 volt cap, use this 470 mfd cap:

http://www.radioshack.com/product/index.jsp?productId=2103624&cp=2032058.2032230.2032267&pg=3&parentPage=family

And instead of the 10 mfd 16 volt cap, use this 47 mfd cap:
http://www.radioshack.com/product/index.jsp?productId=2102512&cp=2032058.2032230.2032267&pg=3&parentPage=family

Use this diode to go across the relay coil if necessary:
http://www.radioshack.com/product/index.jsp?productId=2036270&cp=2032058.2032230.2032269&parentPage=family

Lets use a 12 volt relay. This includes the coil and armature and can switch 5 amps so should be plenty for a single engine to go back and forth:
http://www.radioshack.com/product/index.jsp?productId=2062483&cp=2032058.2032230.2032277&parentPage=family

With a 12 volt regulator:
http://www.radioshack.com/product/index.jsp?productId=2062600&cp=2032058.2032230.2032279&parentPage=family

The 555 chip:
http://www.radioshack.com/product/index.jsp?productId=2062596&cp=2032058.2032230.2032279&parentPage=family

Lets use a 1 meg pot as they have it and this will increase the total time up to about ~2.5 minutes:
http://www.radioshack.com/product/index.jsp?productId=2062297&cp=2032058.2032230.2032275&parentPage=family

And you can use this 220 mfd instead of a 200 mfd cap. This should take cycle time from anywhere from a minimum of about 8 seconds up to about 3 minutes:
http://www.radioshack.com/product/index.jsp?productId=2103623&cp=2032058.2032230.2032267&pg=3&parentPage=family

Questions? Just ask.

Todd