Max current on 1-wire

[DavidB]

Anyone have a more definite answer on the max current. I ask cause on the relay board the 12v is jumpered to the regulator. But says this on the info page:

The relay board requires supplemental power. Due to the current it draws, which is high for a 1-Wire circuit, it should be powered locally and not over the CAT-5 cable.

I have a 1amp transformer supplying the Master Hub board and the powering the temp sensors. If I remember correct the coil current on these relays is 40mA each @ 5v. So it would depend on how many relays your turning on at time, mine would have max of 3 on. The contact voltage is from another source, so was wondering if that perhaps is what the warning was about or if was about the Coil current. I can supply it with another transformer and remove the jumper. But was wondering what others are doing.

 

[ericvic]

There are two problems with running the power to the relay on the CAT5. First is the voltage drop from the resistance of the cable but that will probably not be that much of a problem unless the run is really long. The second potential problem is noise on the 1-Wire data line. There is no formula to use for the second issue, it is more of a trial and error effort.

Eric

 

[DavidB]

My run was going to be about 10ft. Too bad I don't have an o'scope, was thinking about noise on the line, that is why was going to be on separate channel on the hub. Thought that might be enough, since I access each channel at a different time. But Owfs keeps a virtual filesystem on the devices and reads periodically so that would present a problem cause I never know when it would be reading and I might be switching a relay. Oh well, I had another transformer reading to power it anyway.

 

[sda]

The second potential problem is noise on the 1-Wire data line.

I assume activating the relays would cause the noise?
Wouldn't the voltage regulator provide some isolation?
And even if external power is used, the grounds would be common.

 

[DavidB]

The second potential problem is noise on the 1-Wire data line.

I assume activating the relays would cause the noise?
Wouldn't the voltage regulator provide some isolation?
And even if external power is used, the grounds would be common.

Due to the back emf wouldn't it be more likely to cause a spike or noise on the line when you deactivate the relay instead of when activating? The supression diode should take care of most of it but I would still think that would be the time most likely to introduce some noise. Wish I had a scope to check it out.

Anyone with a scope care to test it?

 

[ericvic]

There are suppression diodes on the relays. I haven't looked at it on a scope though.

Eric