Commission - Power Supply Current

[Smith.gf09]

Hi I am hoping someone can help me. When completing commissioning paperwork it asks for PSU current in alarm and normal. Now I've heard multiple ways of obtaining the current readings, can anyone point me in the right direction. The ways of obtaining these readings are as follows....

 

- Step down side of transformer in series with PCB (however this obviously gives a DC reading)

- Take current readings for all devices then add these together (however this doesn't take into account the draw of the panel)

- Use battery current readings (however there is a separate section on the paperwork for battery current)

 

Now ACT meters state that this should be obtained using the first method. However in the NSI code of practice handover checklist it states "log the normal DC current loadings of all power supplies".

 

http://www.nsi.org.uk/wp-content/uploads/2012/10/NACP-11-1-Code-of-Practice-Intruder.pdf&ved=2ahUKEwicm7Kdnb3rAhVCXxoKHSMeA6YQFjAAegQIBBAC&usg=AOvVaw2_ErP3wXi-6ScPSJbZc2wI

Edited August 28, 2020 by Smith.gf09
Additional info

[MrHappy]

connect meter to pos of battery & pos battery lead

 

turn off mains power (normal current reading)

 

set alarm, trigger alarm (alarm current reading)

 

apply mains remove meter plug battery back on

 

 

 

[james.wilson]

As above

[sixwheeledbeast]

To play devils advocate that doesn't include the battery charging current so wouldn't be "the normal DC current loadings".

A lot of panels for a while now you don't have a point where you can test the full DC current of everything in series. There is no separate PSU board. They have AC onto the board or molex connectors that you wouldn't be able to test in series with.

Your left with testing system current via the battery terminals, some panel current test pad points or the readings off the keypad however accurate they are.... 

In reality I have never seen an inspection where the method of test was questioned, as long as your all testing the same way with a meter for the same thing you'll get the same results each time.

 

[Andyha]

Interesting

The quiescent current of the system is the load off the battery when there is no mains power noting that in systems with multiple distributed PSU's the load is in fact taken for each PSU (it is not aggregated)

The alarm load is similarly taken for each PSU with the alarm activated (i.e. sounders and strobes, any relays and other alarm loads being driven

I don't believe the recharge load to the battery, while very important, counts in this calculation

The calculation is for establishing the simple battery autonomy. For each battery you take the quiescent current and a number of alarm event current values for defined periods (say the 20min statutory alarm cutoff period) add them up and work out how long each battery in the system will last for. With a requirement for 12 or 24hr battery autonomy you then work out whether the fixed size battery will last long enough, whether a larger battery or battery array in required or whether to shed load from a PSU to another to get the battery to last

 

The recharge current and recharge time is specified in EN 50131 and is an important property of the PSU capability but is not part of the alarm and normal (quiescent) load calculation as far as I am aware

[james.wilson]

4 minutes ago, Andyha said:

say the 20min statutory alarm cutoff period

15min cutoff now and 30 min iirc for battery calc

 

5 minutes ago, Andyha said:

The recharge current and recharge time is specified in EN 50131 and is an important property of the PSU capability but is not part of the alarm and normal (quiescent) load calculation as far as I am aware

only in as much as the psu has enough capacity to run the system and recharge the battery in the recharge time required. ie leaving 100mA isnt enough unless it a 1.2 A/h

[Andyha]

2 minutes ago, james.wilson said:

15min cutoff now and 30 min iirc for battery calc

 

only in as much as the psu has enough capacity to run the system and recharge the battery in the recharge time required. ie leaving 100mA isnt enough unless it a 1.2 A/h

 

Agreed the capacity of the PSU must be adequate to support quiescent current and recharge of battery at the same time.

 

Thus I specify PSU load to be not greater than 50% PSU capacity.

 

What seems like a simple question has quite a complex set of answers 

[james.wilson]

Agreed but still needs caution

a 1A psu supplying 500mA would need a 6 A/h battery to last 12 hours.

then the same to recharge but if you factor a 10% derate for age over 3+ years it would take you over. 

 

Some would still run a 1A psu at 0.95A anyway

 

 

[Andyha]

Good point well made on 6A/H battery and caution

 

Must admit I had not done the load to amp/hour calculation while writing that post

 

Hopefully useful to the original post

 

and yes, far to many will run a 1A PSU at 950mA load or more cos it can so it must be right

 

[james.wilson]

Probably 1.5A cos an old 1A linear could