Battery Backups - What should die first?
- Thread starter Smcross03
- Start date
Smcross03 said:
The M1 should run out of power first. If the aux power runs out before the M1, the M1 will notice the loss. That might be keypads or input expanders disappearing, or powered sensors, such as motion detectors, going open and creating false alarms.
As the M1's battery discharges, the M1 will gracefully shut down due to low battery voltage.
Thank you RAL.
In previous posts you mentioned balancing out the load and how difficult it can be. I've been using the Elk spread sheet and looked up as many idle and active loads that I can. The issue I am having is when I try to balance the loads the M1's standby current draw is higher than my aux power standby by current. However, the aux power alarm current draw is much higher than the M1's current draw. I've been pulling my hair out over this. Should I just be looking at alarm current or standby current to make my battery choice? Any suggestions you may have would be great.
In previous posts you mentioned balancing out the load and how difficult it can be. I've been using the Elk spread sheet and looked up as many idle and active loads that I can. The issue I am having is when I try to balance the loads the M1's standby current draw is higher than my aux power standby by current. However, the aux power alarm current draw is much higher than the M1's current draw. I've been pulling my hair out over this. Should I just be looking at alarm current or standby current to make my battery choice? Any suggestions you may have would be great.
tmbrown97
Senior Member
I think you'd need your crystal ball to know what condition your house would be in when the power goes out... that said, I'd go with standby power, not alarm power to make the choice... my reasoning is that hopefully if you're in an alarm state, the signal gets out that there's an alarm before the unit dies... and in an alarm state, it's not as big of a deal if the loss of sensors triggers the alarm - as it'd already be in an alarm state and would've already appropriately notified people. It's when it hasn't alarmed yet that you want it to be on the lookout as long as possible.
Smcross03 said:
You need to look at two numbers: the alarm state current and the non-alarm, armed state current.
The alarm state current will be higher the the non-alarm current because it will be powering things like sirens, other sounders, cellular communicators and keypads, etc. Both the M1 and the aux power supply must be able to supply enough current for the devices that are connected to each power supply. It's really a worst case, maximum current number. So when you look at the specs for things like a cellular communicator, use the higher "transmit" current, which is often around 500mA or so.
The non-alarm, armed state current will be lower since the sirens aren't sounding, and the cellular communicator isn't transmitting. So the current draw from a cellular communicator might be more like 30 mA. And an M1 keypad will probably be drawing 50mA rather than 160mA.
In calculating the amount of time each battery will last, I use the non-alarm current along with a few minutes of alarm current time. For example, if I have an 8Ah battery on the M1 supply, and the non-alarm current is 250 mA, and the alarm current is 1.5A, then I come out with:
Non alarm only calculation: 8Ah at 0.25A = 32 hours
5 minutes of alarm current: 5 minutes = 0.083 hours at 5.2 times the non-alarm current (0.25A vs 1.5A), so subtract 0.5 hours (~0.083 x 6)
Total expected run time: 32 - 0.5 = 31.5 hours.
Do a similar calculation on aux power supply battery and then pick a battery size to ensure that the aux power supply lasts longer.
The Elk current draw worksheet helps to add these numbers up, but it doesn't tell you all the extra current that the M1 draws during alarm state. The original purpose of the spreadsheet was to tell you if you need an aux power supply or not, so it doesn't worry about alarm current vs non-alarm current. It's just calculating the current that all the add-ons draw while in non-alarm state. It assumes the highest current for the keypads, but doesn't count the Out2 current used to drive a siren or speaker, which can draw another 1.0A. So you need to unlock the spreadsheet and modify the numbers a bit to calculate the results as I have.
