2
If that doesn't work for you, you can make your own for a couple dollars if you are handy with a soldering iron. I've made and use four with the included schematic.
See pics below:
![]()
![]()
See pics below:
Reversing Controller
1 - 9 of 27 Posts
2
Posted By Torby on 09/30/2008 7:00 PM
You want the diode across the coil, not the contacts
![]()
" src="http://www.mylargescale.com/DesktopModules/NTForums/themes/mls/emoticons/wink.gif" align="absMiddle" border="0" />
Correct. Sometimes I also find it helps to put a capacitor here or/also. In the case of a capacitor, I usually find the value is not critical, and can be on the order of 20 - 100 mfd. In this case you need to be sure that you have the correct + and - in accordance with the relay coil (not reversed like the diode) and that the capacitor voltage is higher than the relay voltage.
There is actually about a 1.5 volt drop from the chip to the relay so the relay really gets about 4.5 volts. This is enough for most 6 volt relays. (I've used literally a couple dozen driven off 555/556 chips). If you can find them you could even use a 4.5 or 5 volt relay, providing the contacts can handle the current of the trains.
You want the diode across the coil, not the contacts
Correct. Sometimes I also find it helps to put a capacitor here or/also. In the case of a capacitor, I usually find the value is not critical, and can be on the order of 20 - 100 mfd. In this case you need to be sure that you have the correct + and - in accordance with the relay coil (not reversed like the diode) and that the capacitor voltage is higher than the relay voltage.
There is actually about a 1.5 volt drop from the chip to the relay so the relay really gets about 4.5 volts. This is enough for most 6 volt relays. (I've used literally a couple dozen driven off 555/556 chips). If you can find them you could even use a 4.5 or 5 volt relay, providing the contacts can handle the current of the trains.
Posted By krs on 09/30/2008 10:10 PM
Toddalin -
I must admit I didn't realize that was your circuit - I thoght it was the schematic of the Aristo unit. I just looked at the diagram - didn't read the text.
But as a former commercial designer, I'm curious about a few things.
1. Why do you think a back-emf diode is not required across the relay coil? The 555-type timers I'm familiar with don't provide an internal protection diode and without back-emf protection and the inductive load, the output transistor won't survive for long.
2. Pin 4 and 5 in your circuit are not connected. If not used, pin 4 should be connected to the positive supply and pin 5 should be connected to ground through a 0.01 mf (microfarad) capacitor to eliminate electrical noise.
3. I think a 220 mf capacitor would be more appropriate for the timing capacitor simply because 220 mf is a standard value where as 200 mf is not.
And finally - since it looks as if people want to build this circuit for their own railroad, it would be helpful if you took the time to list the specific components required with the appropriate RS part numbers.
1) Of the literally 2 dozen of these I've made, only a couple have required me to add the back-emf diodes for proper, long-term operations. If it ain't broke, why fix it?
2) Of the literally 2 dozen of these I've made, I've only found it necessary to add the 0.01 cap on pin 5 in one case and that was for an occasional glitch problem. About 8 out of 10 schematics I've reviewed omit these parts too.
3) As I noted, the part values aren't critical. I use parts from cannabilized VCRs, TV sets, DVD players, etc., and Internet surplus sales, so I gets what I gets.
All component values (except the relay which is obviously 6 volts as mentioned) are included in the schematic. If the named part is not in RS stock, use the next "bigger" value and that should do the trick.
These are the circuits that drive my module for the Del Oro Pacific. They use 9 556s and one 555. None have the reverse diodes or 0.01 mfd caps. These drive 10 of the 6 volt relays.
![]()
Toddalin -
I must admit I didn't realize that was your circuit - I thoght it was the schematic of the Aristo unit. I just looked at the diagram - didn't read the text.
But as a former commercial designer, I'm curious about a few things.
1. Why do you think a back-emf diode is not required across the relay coil? The 555-type timers I'm familiar with don't provide an internal protection diode and without back-emf protection and the inductive load, the output transistor won't survive for long.
2. Pin 4 and 5 in your circuit are not connected. If not used, pin 4 should be connected to the positive supply and pin 5 should be connected to ground through a 0.01 mf (microfarad) capacitor to eliminate electrical noise.
3. I think a 220 mf capacitor would be more appropriate for the timing capacitor simply because 220 mf is a standard value where as 200 mf is not.
And finally - since it looks as if people want to build this circuit for their own railroad, it would be helpful if you took the time to list the specific components required with the appropriate RS part numbers.
1) Of the literally 2 dozen of these I've made, only a couple have required me to add the back-emf diodes for proper, long-term operations. If it ain't broke, why fix it?
2) Of the literally 2 dozen of these I've made, I've only found it necessary to add the 0.01 cap on pin 5 in one case and that was for an occasional glitch problem. About 8 out of 10 schematics I've reviewed omit these parts too.
3) As I noted, the part values aren't critical. I use parts from cannabilized VCRs, TV sets, DVD players, etc., and Internet surplus sales, so I gets what I gets.
All component values (except the relay which is obviously 6 volts as mentioned) are included in the schematic. If the named part is not in RS stock, use the next "bigger" value and that should do the trick.
These are the circuits that drive my module for the Del Oro Pacific. They use 9 556s and one 555. None have the reverse diodes or 0.01 mfd caps. These drive 10 of the 6 volt relays.
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
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
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.
![]()
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.
1 - 9 of 27 Posts
