Powering Large ELK install for reliability and uptime


New Member
I have built a large ELK install and my plans include further expansion.

Currently the system seems very stable (a couple of weeks of non-alarm state uptime without any problems), however I'm becoming concerned that I may be pushing current draw too close to the margin for 100+% reliability.

I did have some problems where over many weeks I received a few troubles that an output expander was missing but would restore itself after just a few minutes. I first tried swapping out the offending expander with no change.

Of course I suspected KEYBUS problems and I'm embarassed to say how many times I fully rewired keybus into different configurations using different combinations of daisychaining and homeruns using the DBHR. Each time I double, triple, and quadruple checked the terminations on the panel, DBHR, and devices to make sure that no more than two and only end devices were terminated on each run. I even replaced segments of wiring with fresh CAT6. I even tried doubling up the wire for VKP+/- to increase gauge all to make sure that my keybus comm was as reliable as possible.

The problem finally seems to have gone away with a combination of two changes.
1) Powering some of my KEYPADS and EXPANDERS from AUX power outputs of the M1G instead of the VKP of the DBHR
2) Removing some of the devices from the DBHR and wiring them into a parallel run with the DBHR directly into the M1G

I can't say that I know exactly what ameliorated, if not solved, the problem, but power draw, especially from VKP, may have been a factor. If not, I am still concerned because it probablly will become a factor as I hope to add more devices to my system in the near future. My current total system non-alarm state power draw is roughly 0.950 AMPS per System Diagnostics with no Relays activated and remember that the majority of my total power draw is through VKP.

I have spent many hours reading on the forum and believe I fully understand the method of placing devices onto aux power supplies and tying the negative terminals together to create a common reference. However, I'm not sure that would be my ideal solution given that majority my power draw is from KEYBUS devices that are critical for system operation and would thus limit my operating time to the lowest capacity battery. Also, I really do not like or see much benefit to the ELK panel remaining alive while it's expander devices drop off rending the system effectively inoperable anyway.

Placing power supplies and batteries in parallel would achieve the ideal solution of
1) greater available current
2) increased run-time
3) full and proper operation as long as battery capacity is available

I already upgraded the main battery to the maximum 18Ah supported by M1G.

However, If I use another power supply and the original 8Ah battery and tie the battery in paralled with the main battery
1) the system will no longer be able to load test the battery(s) properly since the second power supply would keep the voltage high
2) also, I'm not sure if it's a concern, but does it solve the problem on wether the M1G can distribute the high current draw, especially through VKP, on a continuous draw basis?

Instead, what would happen if I tied BOTH the (-) AND the (+) of the secondary power supply and battery right into the VKP outputs of the M1G. One theory is that it would certainly provide additional power for the KEYBUS and if the secondary power supply and battery should fail, the M1G should be able to shoulder the load alone on a temporary basis from the high capacity main battery as long as it lasts. However, how would the M1G actually respond?

Are the (+) inside the M1G tied together without diodes? Would it have an essentially identical effect to wiring the power supply in paralled with the main battery? Would it affect load test? Would power off of main switch work or would power from secondary power supply flow back into M1G and keep it powered? Likewise, would power flow from secondary power on VKP to AUX power?

If the VKP+ is internally protected by a diode that would not allow current to flow in reverse back into the M1G, then I can see no real downsides since I can also add a 912 relay triggered from M1G AUX to control the secondary power supply and battery's positive thereby achieving a perfect system startup and shutdown from the M1G main switch.

If there is no diode then all bets are off. Of course, you could add your own diode to keep current flowing back into the VKP+ but I am already exceeding my experience level and don't have the time or DESIRE to experiment on my M1G possibly blowing it up in the process.

Does anyone know how the M1G power distribution works? Does anyone know if the solution would work? If not, what diode or other method would make it work?

I would really appreciate it, and I'm sure this can be a very educational experience for many if those more knowledgeable would contribute.

Thanks in advance.


Senior Member
I'm not experienced enough to answer any questions for you, but I'm very interested in forthcoming answers.

What and how many devices do you have running on the RS485 Data Bus, off the DBH and and control?



New Member
I'm not experienced enough to answer any questions for you, but I'm very interested in forthcoming answers.

What and how many devices do you have running on the RS485 Data Bus, off the DBH and and control?


Thanks, I appreciate your chiming in on the interest. I spent a significant amount of time searching and reading but did not find this scenario covered.

Right now I don't remember exactly how I broke them up between RS485 Data Bus chains and how I powered each chain, either directly from control, DBHR, and from AUX but it is something like the following (I promise to update if it becomes relevant):

1 M1G
5 M1KPAS (2 powered from AUX)
1 M1XRF2G (powered from AUX)
1 M1XEP (powered from Wall Wart)
1 M1XSP (powered from AUX)
1 M1TWI (powered from AUX)
5 Interior Speakers w/ mics
1 Attic Speaker (Out 2)
1 Outdoor Siren (Out 2)
7 Motion DetectorS
3 Glass Break
6 4-Wire Smoke
2 CO Detectors
3 Water Sensors
2 Dozen or so contacts on separate zones
Several non-alarm zones for monitoring various things (future use)

PS: I elected to use EOL resistors only where necessary, i.e. 4-wire smokes, the rest of the non-alarm contact zones normally closed. Is there any difference in current draw between NC contacts and EOL supervised?

I think it should be useful to many.


Active Member
I am just beginning to install the Elk (and it is my first time, so take this all with several grains of NaCl), but here is my plan to limit power draw from the main board control's power supply:

The M1G's power supply and battery will power just output 2's speaker, not much else.

All (or most) other devices will be powered by an Altronix 6A power supply (like Ebay item 250449840952, $30.00) plugged into a big UPS I happen to have on hand. Should be beefy enough for a bunch of components and maybe some 12v cooling fans for other areas of the closet.

The whole closet will be on a circuit serviced by a 20kW generator, which should theoretically kick in shortly after utility failure.

I didn't think I needed to tie negative terminals together for DC power. . .

I also plan to monitor the genset's transfer switch so I can know the true state of the utility power, regardless of what is powering the various stuff in the closet (utility, battery, UPS, etc).

Of course, I'm sure there are flaws in this plan. . . (ducks for cover)