Using a Relay Board With CAI Webcontrol

[apostolakisl]

Lou,

Thanks for pointing out the difference in how inputs are driven on the Electronics Salon Rly-2 board (described in your eBay link) from other popular relay boards like those from SainSmart (commonly used with Arduino).

If possible I'd like to avoid is two separate power supplies: one for the WebControl and another for the relay board. What I'd like to know is if the 8-relay board (Electronics Salon) can be powered by the WebControl's 5V output. If all 8 relays were to be activated, do you know if the current draw would exceed what the WebControl's 5V output can supply? The eBay page indicates 800mA with all relays activated. Is it simply a matter of ensuring the WebControl's 9VDC supply can supply sufficient current (say a 1A rating) or will its onboard regulator (I'm assuming it has something onboard to efficiently drop the 9VDC to 5VDC) be overtaxed?

No, CAI can't power the relays. There is no dry contact relay that will work on that little bit of current as far as I have ever seen. There are solid state relays that work with that small amount of power, but these aren't really suitable to switch a real load. I have some solid state relays that only draw a few milliamps but all they switch are Elk zones and only serve the purpose of signaling the Elk, not actually switching anything of substance on/off.

You can use a single wall wart to power both the relay board and the CAI, but you would have to pull the power to the relay board directly from the wall wart, not through the CAI. If the relay board isn't rated at the voltage of the wall wart, then you would need a voltage regulator in between.

 

[123]

Thanks, I suspected that might be the case. Maybe I'm looking in all the wrong places but 9VDC relay boards are hard to find. All the budget boards are 5V, 12V, and 24V. I wanted to avoid two power supplies but it looks like I may not have a choice.

 

[apostolakisl]

Thanks, I suspected that might be the case. Maybe I'm looking in all the wrong places but 9VDC relay boards are hard to find. All the budget boards are 5V, 12V, and 24V. I wanted to avoid two power supplies but it looks like I may not have a choice.

Consider a 12v power supply to power both the relay board and CAI. See if you can find a suitable voltage regulator to drop the 12 to 9 for the CAI part.

 

[fwd03]

I think if you could solder a copper heatsink to the big regulator on the WebControl board, it would take 12V directly. Without any heatsink, it gets too hot.

 

[Machineman]

I'm running those ebay "Electronic-Salon" 5V DPDT relay boards. The relay coil spec sheet says 100% over voltage which means it can run up to 10V. So Im using a 9V supply for the Webcontrol and the 5V relay boards without issue.

It was the board with the Black DPDT relays on ebay.

My first relay board was one of those other ebay "YWRobot" boards with the reverse logic. Total pain so I switched to 5V-On boards.

 

[apostolakisl]

I just ebay'd 5v ssr and there are some boards that can handle 240v 2 amps per relay. Trouble is that if all 8 are on it draws 160ma which exceeds cai spec's of 100ma total. So if you only had 5 relays on at once you would be ok. Solid state relays may not suit your purpose if you need dry contact, but maybe it will.

However, it is reverse logic which is a PITA as mentioned by machineman. EDIT: Oops, not reverse logic, output "on" means relay "on"

 

[123]

Thanks the "overvoltage" tip. I think I'll check the specs on the 12V relays and see if they can trigger on an "undervoltage" of 9v. Probably not but it's worth a look.

I looked at the SSR's but I just know, somewhere down the road, I may have a need to active the entire bank of 8 relays .... and I will forget about the current demand and toast the board!

 

[apostolakisl]

Thanks the "overvoltage" tip. I think I'll check the specs on the 12V relays and see if they can trigger on an "undervoltage" of 9v. Probably not but it's worth a look.

I looked at the SSR's but I just know, somewhere down the road, I may have a need to active the entire bank of 8 relays .... and I will forget about the current demand and toast the board!

There is a good chance that the coil will pull the arm at 9v, however, you will probably need a good quality transformer that doesn't peter-out as the current draw goes up or you may find that when several relays are activated it starts to lose it.

 

[123]

According to the specs for the 12v relay, if I've understood them correctly, the "pull-in voltage" is 75% of the rated voltage and it varies with temperature. I assume they mean 9v or a Relay rated for 12v. That's uncomfortably close to the threshold and, as you pointed out, the 9v supply may sag under load.

So I can either run the 5v relay board at 9v or get a 12vdc to 9vdc regulator board from Electronic Salon ($10) and use it with the 12v relay board. I might do the latter because I think I have a spare 12v wall wart. Otherwise I need to buy a 9v wall wart for the WebControl. New wall wart or a regulator, either way it's an unavoidable incremental expense.

 

[fwd03]

I just ebay'd 5v ssr and there are some boards that can handle 240v 2 amps per relay. Trouble is that if all 8 are on it draws 160ma which exceeds cai spec's of 100ma total. So if you only had 5 relays on at once you would be ok. Solid state relays may not suit your purpose if you need dry contact, but maybe it will.

However, it is reverse logic which is a PITA as mentioned by machineman. EDIT: Oops, not reverse logic, output "on" means relay "on"

I brought this SSR, which draws about 5mA when it turned on:
http://www.ebay.com/itm/200751812792

 

[apostolakisl]

I brought this SSR, which draws about 5mA when it turned on:
http://www.ebay.com/itm/200751812792

I actually believe I own one of those. I have it rigged up to a tiny toggle switch I tucked under the lip of the counter that turns the island garbage disposal on. It runs off a 9v battery. I was able to avoid drilling another hole in the granite to put one of those air buttons. It works great.

It lists the current as 3 to 25ma, so I guess it is at the low end since you are using only 5v.

 

[DigiDan]

I found that simply inverting the output in the IO control setup does get the 'ground = on' relay boards to work, but if you pull the power plug out of the webcontrol, you may find that this causes the relays to turn on (it did for me). Not really a desireable feature because I don't want to activate every device I have wired if the CAI fails.


Has anyone ever used a SN74HC14 inverter to invert the input to one of the 'ground = on' type of relay boards? I got it to work, but it's been a while since I was in school, and I can't really remember if the SN74HC14 can handle sinking current (around 2mA).

 

[fwd03]

You don't have to using IC to invert the input for those reverse logic relay board. You can just have a pull up resistor on each input. When the power lost on the webcontrol, the pull up resistor will keep the logic 1 to be feed into relay board input.

 

[Reederoo]

No, CAI can't power the relays. There is no dry contact relay that will work on that little bit of current as far as I have ever seen. There are solid state relays that work with that small amount of power, but these aren't really suitable to switch a real load. I have some solid state relays that only draw a few milliamps but all they switch are Elk zones and only serve the purpose of signaling the Elk, not actually switching anything of substance on/off.

You can use a single wall wart to power both the relay board and the CAI, but you would have to pull the power to the relay board directly from the wall wart, not through the CAI. If the relay board isn't rated at the voltage of the wall wart, then you would need a voltage regulator in between.

I am new here, but I am looking to do the same thing (power 5V relays from the CAI webcontrol). I have one here and I looked up the power regulator chip - it is LM2940S -5.0 (datasheet here: https://www.national.com/ds/LM/LM2940.pdf) According to the datasheet, it can handle 1.0 Amps. I am wondering if the 100mA total current spec for the CAI Webcontrol only applies to the digital outputs, not the +5V supply? If so, it may be that the microcontroller can't handle more than that, even though the power supply can handle 1A. The relays would be drawing almost all their current through the 5V supply, not the control inputs, so I think it would be fine to use the relays on the same +5V supply that comes off pin 3 on the temperature sensor screw terminal output. Any thoughts on that? I may try it out and see what happens unless you all can think of something I missed.

 

[fwd03]

It would work most the time. However, the relay switching could have spile from relay coil. If that spike feeds into processor's power line, it could cause PLC execution errors. It would be better off to have separate power regulator for your relays. I am using an old laptop 12V power supply, with two regulators, one regulate to 9V to power webcontrol, another regulate to 5V to power relays. The old laptop power adapter is really a good quality power supply, plus two regulators to reduce the interference between relays and webcontrol board, my setup running for over a year without any problem.