Battery Size
- Thread starter jmed999
- Start date
jmed999
Active Member
I assume it has to do with the required length of time needed and the required amps or wattage of the devices connected to it. They will each be connected to an ELK-965 so they don't get drained too low...I'm thinking that will factor into the selection process as well.
Maybe there are guidelines or tables to go by.
Any ideas?
Maybe there are guidelines or tables to go by.
Any ideas?
BraveSirRobbin
Moderator
I would calculate how much DC current is being drawn from your system. Look up the current each device is drawing, including the siren in alarm mode, plus the draw of the security system itself (it's DC current draw). Add those up and that is your total DC amperage.
Select the number of hours you want the system to be backed up and multiply by the DC amps. This is your amp-hour rating that is needed for that amount of time.
Double this value and that should be the battery size you select. The reason of doubling the value is to insure the battery will not get to far below 50% of its discharge level (so you can guarantee it will charge back up), and also leave some room for error in the initial calculation.
Of course if this size isn't feasible, you can adjust the calculation parameters above by say assuming you will only have the siren on for xxx minutes, or you can risk battery draw below 50% capacity, etc...
I'm sure others have their own way of doing this and will chime in as well.
Select the number of hours you want the system to be backed up and multiply by the DC amps. This is your amp-hour rating that is needed for that amount of time.
Double this value and that should be the battery size you select. The reason of doubling the value is to insure the battery will not get to far below 50% of its discharge level (so you can guarantee it will charge back up), and also leave some room for error in the initial calculation.
Of course if this size isn't feasible, you can adjust the calculation parameters above by say assuming you will only have the siren on for xxx minutes, or you can risk battery draw below 50% capacity, etc...
I'm sure others have their own way of doing this and will chime in as well.
:hesaid:
BUT, I would caution against three batteries. That's three times the expense, three times the maintenance, three times the lead sent to the recycling center, etc. Try to figure out how to get the job done with one battery charged from one source. If you are short on capacity with one battery, even two in parallel is better than three scattered about. In any case, make sure that each battery is only charged from one source.
BUT, I would caution against three batteries. That's three times the expense, three times the maintenance, three times the lead sent to the recycling center, etc. Try to figure out how to get the job done with one battery charged from one source. If you are short on capacity with one battery, even two in parallel is better than three scattered about. In any case, make sure that each battery is only charged from one source.
Not entirely the case. The OP sounds like they are using remote power supplies.
In the case of sizing batteries, for example, in a standard structured wiring cabinet, you can fit 7 Ah batteries easily and have space to spare. Now, if I need to provide <24 Ah of power, I'm not going to be able to put a 26 Ah battery inside the can, but 4 batteries will fit easily. Also, if you price out batteries, a common 7 Ah is going to be cheaper than a larger 10 or higher Ah and typically, they are going to be easier to find and also have the stock rotated more compared to an "odd" sized Ah when considering the typical trade sizes. A lot of times, the price of 7 Ah's as a commodity are going to be significantly cheaper than the larger Ah sizes, much so to the point that you can buy 2 of the smaller batteries for the cost of a single 10 or 12 Ah battery.
The typical reason to not use multiple batteries in parallel is it increases failure points or if the batteries aren't "matched" then a push/pull on the charging circuit or standby is going to be the result.
If you were looking at a single panel and power supply, then appropriately sizing the batteries is part of the equation, the other part is by upsizing the battery, are you going to need to install a battery can to facilitate a single larger battery rather than 2 smaller ones.
jmed999
Active Member
Using a Kill a Watt meter I was able to determine my M1G console uses 0.08 Amps and 6.7 watts when armed and 0.22 amps and 22 watts when the alarm is triggered/siren blasting & using AC..
So does this mean the 8Ah battery it's connected to would run for 8/(0.22*2) = over 18 hours? That's assuming the system is alarming the entire time too. And that's only using half the battery.
Seems like that is too long. Am I missing something in my calculation?
Thanks!
So does this mean the 8Ah battery it's connected to would run for 8/(0.22*2) = over 18 hours? That's assuming the system is alarming the entire time too. And that's only using half the battery.
Seems like that is too long. Am I missing something in my calculation?
Thanks!
No.
The system will only run until there's not enough voltage to physically run it, not until the battery is stone dead. You also need to figure off the posted alarm currents of the components and not what they're actually drawing, as that can vary.
Can't remember the exact voltage cutoff, but other panels have a LBC at 10.5 VDC. The M1's data bus starts all sorts of rebooting and havoc when dropped below 12V.
Have you downloaded the spreadsheet that Elk has and plug your values into it?
There's variable formulas for calculating the standby time and alarm time, for example, a fire alarm requires 24H of standby followed 5 minutes of alarm time.
To simplify standby calcs:
(Standby draw * hours standby required) + (Alarm draw of all attached components * .084 hours) = C
C =amp-hours * 1.2 = battery size required.
You can also plug in for the second set of variables a derating factor by multiplying those values by .0012
The system will only run until there's not enough voltage to physically run it, not until the battery is stone dead. You also need to figure off the posted alarm currents of the components and not what they're actually drawing, as that can vary.
Can't remember the exact voltage cutoff, but other panels have a LBC at 10.5 VDC. The M1's data bus starts all sorts of rebooting and havoc when dropped below 12V.
Have you downloaded the spreadsheet that Elk has and plug your values into it?
There's variable formulas for calculating the standby time and alarm time, for example, a fire alarm requires 24H of standby followed 5 minutes of alarm time.
To simplify standby calcs:
(Standby draw * hours standby required) + (Alarm draw of all attached components * .084 hours) = C
C =amp-hours * 1.2 = battery size required.
You can also plug in for the second set of variables a derating factor by multiplying those values by .0012
BraveSirRobbin
Moderator
FYI, the killowat is measuring 'AC' current draw.
jmed999
Active Member
Isn't that what I'm interested in?
jmed999
Active Member
Thanks for all the info DEL! I didn't know a spreadsheet existed...I'm going to look for it now.
jmed999
Active Member
The M1 Current Draw spreadsheet is here...http://www.elkproducts.com/Owner_support_tools.html
It's very helpful and solidified my Kill-a-Watt findings as they were VERY close.
Kill-a-Watt : http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1358691369&sr=8-1&keywords=killawatt
It's very helpful and solidified my Kill-a-Watt findings as they were VERY close.
Kill-a-Watt : http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1358691369&sr=8-1&keywords=killawatt