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!

Why not just use relays with 24VDC coils and skip all the other electronics?

Dale H

George,

Each of the 5-volt relays draws between 0.065 and 0.070 amps. I would allow 1/2-amp per 8-relay module just in case all the relays are energized at the same time.

Stan,

Your diagram is correct - use the (-) of the power supply to pick up the relay.

Dale,

That's what I did, except I used 12-v relays. I built five such 6-relay modules with the 12-V coil relays, but the next three will be the 8-relay modules even though I will have an extra two relays. Still, the cost of the modules I built was around $20 (relays, terminal strips, connectors, etc.) and about two to three hours of building time.

The 'other' 8-relay modules, with the 5-volt relays, are ready to go as purchased for about $10. They have fly-back diodes (as my home made ones do) but they also have the  optically isolated relay inputs, which mine do not. (I used Form-C contact relays for my modules as they were about as cheap. The 5-volt relays also have Form-C contacts.)

Here are  both home made and purchased:

  (Click for larger size)

Good thread, BTW.

Alex

Alex

I use a lot of NAIS SP-2-P type relays. These are DPDT 15 amp contact with 480 ohm 12VDC coils. So they only use about 1/3 watt each. They have a unique fulcrum design. Best relay I ever used for what I do. I wire them here in series for a 24 volt DC 4PDT application. For single relays I use a resistor.

This board is for 2 loops and routes trains so they run one a a time in conventional.  3 trains on each loop. Also a brief soft stop in the block and switching for block signals. Click to enlarge

This board routes 3 trolley,one at a time and provides station stops along the way. Also provides reduced and increased voltage for uphill and down hill. also a 1 step soft start.

I admire your layout progress have been doing mine also.

Dale H

I've read everything that all of you wrote. Even though I had experience with PNP and NPN transistors in my Air Force days 25 years ago, I opted for the relay modules that Alex recommended. I couldn't be happier. I connected my first two relays to their track segments today and it worked perfectly. If you're using DCS and an AIU for track power, this is the only way to go. I ordered the jumper cables recommended by Stan and they're perfect for this setup. 

Stan also submitted a simple schematic diagram for wiring of the relay module. Thanks Stan and Alex, for your input. If I had not asked this question, I would never have known how to do this correctly. P L U S...the lights on the module are an operational feedback that is extremely helpful. 

All new new track...new cork...new benches...new sound-proofing...I feel I'm on the right "track" this time. The 3 Gs are having a blast with this hobby. To think we're all sitting under the train table today wiring up power to the yard...was great fun.

Thank you all for what you do in this forum. I am a member of many forums and this is by far the best...for help, fun and interesting reading, not to mention forum operation.

Soon I'll be submitting photos. There is a virtual theatre pipe organ that is an integral part of this entire project. Also built by the 3 Gs.  So far we have one level with two more in design. No scenery but plenty in stock once we make some decisions. 

I also have some MTH Realtrax I'll sell in another more appropriate post. 

Again...thanks to all.

George (G3)

Hello,

This is an excellent thread and I would like to thank all those that contributed.  I have tried the suggestions and it works great.  Not trying to hi-jack the thread but, am curious to know what type of wire you found to work best with the relays from transformer to track power.  I use 16AWG stranded on my layout but, find this to be a bit of a tight fit in the relays.  Any suggestions on connectors or perhaps using solid core wire?  Thanks, Alex

Since I will only have 1 engine in a siding/or parked at a turntable siding.I am going to use a Quick blow 4 amp fuses per siding that will power the siding.

I had 2 MTH Premier engines running at 25 SMPH and was only drawing 1.7 to 1.9 amps pulling 5 0f my old 027 cars on my Z4000's gauges.So I hope I should be safe.

I'm looking at using one of these relay modules (SainSmart?) to switch power to my 8 whisker spurs, but am looking at using a 16 channel version to also simultaneously switch an MTH DCSRC to the spur being accessed to send a watchdog signal only to that spur.  I think that would allow me to only have one DCSRC to use with the 8 spurs, without shorting spurs together unless I intended it.

Question:  Although many of you are using the AIU to switch the relays, since they appear to be gnd actuated, can I just use a toggle switch at a control panel to switch the ground to actuate the relay?  I assume this ground contact is continuous rather than momentary?

Thanks,

Tom

No reason at all you can't use a toggle, the relay boards are just looking for a logic level.