Elk M1G and power - finding reality - spreadsheet vs. measure

[Linwood]

I'm worried if I have enough current capacity without extra power supply.

How is the right way to do it?

I did the spreadsheet thing. I did it twice, once with max draw and once with idle. My idle I can compare to the Elk-measured value, and I get 0.523 (calculated) vs. 0.320 (measured), so I am not all that sure of the spreadsheet numbers. BUt they come from the spec sheets.

My calcualted total is a whopping 2.254A, but that's with all smokes sounding together. With the smokes at idle, and removing the siren (so I don't PO the neighbors) the spreadsheet says I should be at 1.558. So I
set off the alarm and it then showed 0.405A on the keypad (and I had both keypads in use, one to set the alarm, one to view, so both were active). That's quite different from 1.558 calculated. I did it twice, got about the same value each time.

My multimeter only does 400ma, so I would need to buy another to measure separately from the Elk. Is the Elk's measurement usually accurate? During an alarm state?

And what's the real target I am aiming for. It has a 2.5A power supply, a 1A continuous rating. The spreadsheet recommends a new power supply if the alarm condition current exceeds 1A (all the amounts on it appear to be maximums, so I assume that is alarm condition not standby). Is that right, or is it 1A standby and 2.5A in max alarm draw?

Basically I have conflicting info -- calculations for a given configuration are different by a factor of 3 from the spreadsheet. Most of this is probably in the M1TWa, which is rated at 1A. Since that is the primary thing drawing in an alarm condition (with no siren or smokes sounding) one would thing it is drawing about .1 (the difference in the 0.320 measured idle vs. 0.405 sounding). That's a huge difference from the 1A rated amount, which may be if you have a ton of really low impedence speakers? But I'm off even further than the .9 difference there in the calculation.

Should I trust the keypad measurement?

Should I go buy a bigger multimeter?

 

[ecborgoyn]

I don't have my M1 installed yet (not even ordered yet....). But Elk tells me this (paraphrasing): The M1 p/s can supply a continuous 1A current for the entire system. It can supply a maximum of 2.5A 12VDC power. The difference is drawn from the battery. You can manage it as you like. But you need to be aware of the battery draw-down if you use more than 1A of 12VDC.

I can't comment on the accuracy of the internal current measurement. Buying a bigger multimeter might be a good investment. BUT you will most likely never see the calculated max current draw. Simply summing the spec'd max consumption of the devices is an absolutely worst-case. I'm not sure if you can get EVERY device simultaneously into a worst-case power consumption state.

 

[Linwood]

That last comment is true, but then again I can get every device into a "normal alarmed state". Which is why I wonder if in that state I can trust the Elk measurement, and whether others have seen such divergence from the specs? (IN a good way I hasten to add -- drawing less power than expected).

 

[Del91574]

When designing a system, you never want to do an "actual" or idle current as the spec, you want to figure the current draw for every device in alarm condition. The number that the M1 supports is the 1A continous.

You need a secondary power supply, no doubt about it. You have to figure at the worst possible case scenario, otherwise the system will fail, and at the worst point possible.

The system will provide 1A continous with a short term availability of 2.5A, however that affects other items, and the statement regarding where the extra current comes from is accurate.

Elk's calculator spreadsheet is what you need to go by, not what you're seeing as an actual value on a meter or via a keypad.