AIU current

The actual relays in the AIU are rated at 5 amps, and MTH states 4 amps for it's rating.  There were some old AIU models that apparently had higher ratings on the relays, this was discussed here previously and we all compared notes.  I took all three of mine apart and they all had the 5A relays.

I think the relays are marginal for track power.

George,

The AIU relays are rated at 4 amps maximum, as correctly stated in The DCS O Gauge Companion 2nd Edition. There's a section that describes how to connect external relays to the AIU to control track power.

Wow...that was fast. Thanks to both of you. 

George (G3)

External Relays used with an AIU

The photo shows my DCS system which uses external relays to control everything (track and turnouts). I use a dc voltage to operate each relay. The relays can be operated by a voltage anywhere from 9 volts to 14 volts. I supply a "common" connection to each relay using the AIU SW or ACC outputs.

 The relays are common heavy duty types. They include a socket with colored coded wires attached.

George,

I used to 'roll-my-own' relay modules to control track power ON/OFF and then found (thanks to gunrunnerJohn, above) these 8-relay modules on Ebay. These are available from this vendor for $10.28, shipped, and this vendor stocks them in the USA.

The modules have euro-style connectors for the track wires, and you would need a header connector to connect the input signals (through the AIU) to turn the relays ON/OFF, and a 5-volt power supply. I bought six-position (female) connectors from Jameco Electronics (need two per 8-relay module).

 This is how they look, and they don't take much room.

Good luck!

Alex

Alex,

Thanks...I may just go that route. Does the relay module come with the edge connector or do you have to purchase separately? Source?

Nice looking unit.

George (G3)

George,

In the picture below, the track wires just connect directly to the terminals (euro-style, very nice). The inputs (relay coils) are via pins that are spaced 0.1-inch. The easiest way is to use connectors made for these. The ones I found at Jameco were the cheapest (6-position), but servo-type connectors (3-position) also work.

Let me know if I can be or further help.

Alex

Here is another picture with the wiring more clearly shown. Please note that the relays will pick up (turn ON) with a negative signal. This means that the common to the AIU should be the negative side of the 5VDC supply, such that when the AIU ACC relay contacts close, the resulting signal from the AIU to the relay module is negative.

The connectors for the input signals and the 5VDC Gnd(-) and Vcc(+) are the ones from Jameco, and come as a harness* with a connector at each end. I cut the harness in half and get two connectors that way. The connectors have six positions or wires, for a total of 12 for two connectors. Since the module requires only 10; two for 5VDC power (+ & -), and eight for relay inputs, two wires from one connector are not used.

*Jameco part number 2174872 @ $1.95 each (so each 6-position connector ends up costing less than a dollar.)

Hope this helps.

Alex

Another wiring option is to google or ebay "Arduino jumper cable".  They come in various lengths, colors, male-male, female-male, etc.  I'd think a female-male jumper would work for you. The female-socket side would plug onto the pins of the relay module, and the male-pin side would plug into the AIU's screw terminals.  Arduino controllers are quite the rage now and they use the same 0.1" spaced pins so you might find the pricing of these cables attractive.

Thanks Alex and Stan,

I'll order today. I'll say it again, "This forum is awesome...such great help". I was going to go with the fast-blo 4A fuse, but this is better. I won't have to worry about current.

George (G3)

Alex,

I ordered the relay module. What size 5V power supply do you recommend? I have a .5A wall wort, but have also looked at Part No. 1955642 from Jameco. 

Recommendations?

George (G3)

The .5A is probably plenty.  The relays don't require much current to actuate.

Do you also run the 5V through the AIU to trigger the relay in addition to powering the board with the 5V? I am confused on the signal to the relay. Also, it looks like there are three terminals on each relay. Is that for NO and NC?

     John

Yep, the relays have both NO and NC contacts, as well as common.

From the eBay ad.

• 5V 8-Channel Relay interface board, and each one needs 50-60mA Driver Current.
• Equiped with high-current relay, AC250V 10A ; DC30V 10A.
• Standard interface that can be controlled directly by microcontroller (Arduino , 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic).
• Indication LED’s for Relay output status.

Looks like you supply 5V or ground to the inputs, depending on the jumper to pick the relays.

Are you sure about that?  As Alex points out for the relay module he used the inputs are activated by a "negative signal".  And the eBay link above also specifies "active low" inputs.  Alex's photos show this but I think the hookup might be as follows for, say, 4-channels:

Nope Stan, I'm not sure.  Very limited information, I don't have one to actually look at.   This one needs positive voltages.

However, this 8 Channel Arduino Relay Board seems to require a ground on the input to activate the relay.

At the risk of sounding like a broken record, are you sure about that?   Each relay is driven by a PNP transistor.  To forward bias or turn the transistor on, you must supply an "active low" input signal. 

But I do agree on the limited information.  They apparently specify the relay current (50-60mA) but that's after the transistor buffer.  They should also specify the input control current.  But like someone commented earlier, you can't even buy the parts for anywhere near the price of the completed module delivered to your door.

Thanks for the help. I think you have me close enough to figure it out so I will order one. It looks pretty useful even without an AIU.

          John

Well Stan, that's embarrassing, I just noticed the PNP transistors, didn't even look that far!   Ignore my comments, I need to read more carefully!