altronix al400 power supply standby

Can someone explain this standby time chart to me. I can't make any sense of it
 

The table is giving different examples of how much time the system can run with different sized batteries, assuming the system draws the currents shown when it is in standby and alarm modes.
 
The first row shows that:
 
If you have a 12V system with a 40Ah battery, it says that it can provide power for 4 hours with the system in standby, plus 5 minutes of the alarm sounding, assuming that it draws 4A of current in both modes.
 
Or, it can provide power for 24 hours in standby, plus 5 minutes of alarm time, if the system draws less current (just 1A) in standby mode and 4A in alarm mode.
 
And if it draws even less current in standby, just 300 mA, it can provide power for 60 hours.
 
Essentially, this table is providing the endpoints from 3 battery discharge curves, based on 3 different current loads.   It's not a great way to show the data, in my opinion, but I guess they thought it would give people an idea of what to expect.
 
I'm not sure if my explanation made things any clearer for you.

In the first example it seems to me that it should provide 4 amps for 10 hours given a 40ah battery. Why does it show only 4 hours?

Remember that the 40Ah rating is based on a C/20 discharge rate, which would be just 2A.   Drawing 4A would cut that by more than half, to about 9 hours.  Not sure why they went as low as 4 hours, unless they are being very conservative. 
 
[Edit]:
 
Moving on to the second column, where it draws only 1A, since that is less than the C/20 rate of 2A, it sure seems like then you should get close to the full 40 hours out of the battery, even with the 5 minutes of alarm time at 4A.  24 hours seems too low to me.
 
So you're right - the numbers here don't make good sense.
 
[Edit2]:
 
One other thought... a battery capacity needs to be de-rated for temperature effects, too. Although the table makes no mention of an assumed temperature, perhaps they built something other than normal room temperature into this.

RAL said:

Remember that the 40Ah rating is based on a C/20 discharge rate, which would be just 2A.   Drawing 4A would cut that by more than half, to about 9 hours.  Not sure why they went as low as 4 hours, unless they are being very conservative. 
 
[Edit]:
 
Moving on to the second column, where it draws only 1A, since that is less than the C/20 rate of 2A, it sure seems like then you should get close to the full 40 hours out of the battery, even with the 5 minutes of alarm time at 4A.  24 hours seems too low to me.
 
So you're right - the numbers here don't make good sense.
 
[Edit2]:
 
One other thought... a battery capacity needs to be de-rated for temperature effects, too. Although the table makes no mention of an assumed temperature, perhaps they built something other than normal room temperature into this.

Click to expand...

I was not aware or maybe forgot of the c/20 calc in rating the battery which I just learned means it assumes that the battery is fully discharged in 20 hours.....back to school for me.
 
Yes they must have calculated at temperatures and conditions of a worse case scenario. I looked at that chart for a long time on more than one occasion and just couldn't make any thing work in my head. Choosing a backup battery seems to me to involve some voodoo. It's a very inexact science.
 
To be safe I think that I will put the 8ah battery that I already have on the M1 control which by my calculations will yield about 13 hours backup. The altronix will be carrying about 1.6 amps load so I need to find a battery that will outlast 13 hour controller standby and still fit in the small altronix enclosure. Altronix tells me that the unit can take up to a 40ah battery so maybe they know of one that will fit.
 
Or maybe I will go with a 4ah on the controller which yields ~6.5 hours and a 12 -18 ah on the altronix. I'll have to shop for the largest capacity battery that I can fit in the Altronix box and then choose the controller battery based on that.
 
Can you recommend a good source for batteries? I've had good luck with batterymart.com in the past.
 
Mike.

mikefamig said:

Yes they must have calculated at temperatures and conditions of a worse case scenario. I looked at that chart for a long time on more than one occasion and just couldn't make any thing work in my head. Choosing a backup battery seems to me to involve some voodoo. It's a very inexact science.

Click to expand...

 
Looking at the numbers in the table some more, it really looks like they are more in line with a 28Ah battery than a 40Ah.  Even factoring in a low temperature, it would have to be extremely low for those number to be for 40Ah battery.  Or maybe I'm missing something here, too.
 
Recently, I've been buying Power Sonic batteries from Ecom Electronics via eBay.  For the batteries I was looking for, they had the best price when shipping was factored in.   All the batteries I received had recent manufacturing dates.
 
I think the largest battery you will find that will fit in the Altronix can is a 1290, which is 9Ah and the same size as a 1270 or 1280.  Above that, I think the batteries will be too tall or too deep to fit.
 
I would be tempted to put a pair of 1290s in parallel, which will fit side by side.  DEL may yell at me for suggesting this since Altronix doesn't explicitly state that parallel batteries are ok.
 
[Edit] Just saw your other post that says Altronix says parallel batteries are ok, up to a total of 40Ah.   So, yeah, that makes a pair of 1290s look like a nice solution.

Didn't say they weren't OK, there's specific items. The post regarding the Eflow supply is very specific, but compared to an AL400, they are night and day different boards.
 
I'm too lazy to look at the charts and do calcs, but battery calcs usually have at least a 20% safety on top of the absolute value in the calc.