What to move to Aux Supply

[SteveS]

Hi Everyone,
 
I have installed my ELK-M1 Gold but haven't gone online yet.  I have the control panel, one M1DBHR, and the battery in a 14" elk can.  I have an ELK M1EXP currently plugged into a wall outlet but I would like to power off of the AUX supply.  I also have two M1KP off of the retro data bus hub, three Bosch Blue Line Gen 2 motion detectors and three System Sensor 2WT-B smoke detectors.
 
The current draw worksheet for this estimates 0.915A if I enter 0 for the number of M1XEP.
 
If I would like to increase the margin on the main power supply it seems like the only significant contributors to the current draw are the smoke detectors (when in alarm) and the two keypads.
 
Is there any issue with attaching the two data wires from the two keypads to the data bus module and attaching the power and ground over at another can with the AUX supply?  (I would tied the two power supply grounds together but keep the supply voltages isolated.)
 
Am I correct in thinking I can't move the power for the smokes as they are only two-wire?
 
thanks,
Steve

 

[RAL]

There's no problem with powering the keypads from the aux supply.  There's a wiring diagram in Appendix F (pg 67) of the M1 manual that shows the general method of how to connect things when using an aux power supply.
 
You could run the smokes off of aux power if you use a 2W-MOD2 to interface the smokes to the panel.   That essentially converts them to a 4-wire interface at the panel. You'd also need to run the aux power through a relay to allow you to reset the smokes.  I'm not sure the added complexity would be worth it, unless you also want to get the added benefit of the trouble indication that the 2W-MOD2 provides to the panel.
 
Hree are three ways you could divide up the load:
 
1. Power everything except the XEP from the M1.  This gives you the max of 0.91A that you calculated on the M1's power supply.  But that is in alarm state only.  In non-alarm state, the power draw would be about 0.52A.   Use the aux power supply for the XEP and any other devices you may add later.  The 0.91A in alarm state wouldn't worry me too much.  You still have about a 10% margin there. 
 
2. If you power the keypads from the aux supply, and put the smokes, motion detectors and the XEP on the M1's power, you'll be back up at a max current of 0.9A on the M1.  But again, that would be in alarm state only.  In non-alarm state, the draw would be about 0.5A. 
 
3. You could put one or both keypads plus the XEP on the aux supply.  That would get you down to 0.6A or 0.75A for max power on the M1.
 
 
One thing you need to take into consideration is that the battery on the aux supply should be large enough to power its devices for a longer time than the battery in the M1 will last.  You don't want the aux supply to go out first, taking the keypads and other devices off line while the M1 still has power. 

 

[Del91574]

Keep the pads powered off the panel. Loadshed the other devices first.
 
Smoke detectors are powered off the panel loop so their overall current doesn't factor into the equation here. (also draw micro-amps, so exceptionally trivial)

 

[SteveS]

At least for now (had to clean up the basement for the big Easter gathering!) I'm just going to power the XEP off of my AUX supply (Elk P1215K).  I was expecting to have to tie the grounds together but the XEP already received 12VDC from its own wall wart.  It doesn't really match the configuration in Appendix F.  Since the XEP already had an isolated 12VDC and GND I don't see the need to tie any grounds together -- until I add other devices.  Does that make sense?

 

[RAL]

At least for now (had to clean up the basement for the big Easter gathering!) I'm just going to power the XEP off of my AUX supply (Elk P1215K).  I was expecting to have to tie the grounds together but the XEP already received 12VDC from its own wall wart.  It doesn't really match the configuration in Appendix F.  Since the XEP already had an isolated 12VDC and GND I don't see the need to tie any grounds together -- until I add other devices.  Does that make sense?

 
Yes, that makes sense.  In general, when you have an aux power supply that powers devices that connect to the M1, you need a common ground reference between the two power sources.  The P1215K has a NEG/ground terminal on the circuit board that can be used to make that connection. 
 
In the case of the XEP, there is a ground connection through the serial port interface.  That's what allows you to power the XEP with just a simple wall wart, which doesn't provide a terminal to connect the grounds.  If you add other devices to the P1215K, you really should connect a  separate ground wire between the P1215K and the M1.  You don't want to depend on the ground connection through the XEP to make those additional devices work properly.