Power consumtion

shrtcirkt

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I'm working on a new pir circuit and power consumption seems a bit high.
At idle the circuit is drawing 5.0ma and during a trigger it is reaching as high as 15.0 ma.
is it just me or do you think this is a bit excessive? I added in an opto coupler to lower the consumption, but I think the voltage regulators I am using may be drawing most of the idle current.
Any thoughts?
 

Archilochus

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Hi shrtcirkt,
I've seen some PIRs that run at idle around 15 to 20 mA.  Is this your own design - or a store bought?  Can you read the part#s on the regulator and op-amps??
If you suspect your regs - measure the current AFTER the reg - if it's lower, then you know it's your reg wasting the power.

Archilochus
 

shrtcirkt

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Arch,
this is a hybrid of my design and the amazon module. The amazon module is supposed to draw 400ua at idle.
I've been searching the Duracell and Engergizer sites for useful info to determine battery life and did not find much. What I did find tells me I should get about 40 days out if it the way it is.
I did find another regulator that boasts 1.2ua power consumption. Thats about a 1/3 of the current regulator.
I'm gonna try a couple of those and see how they work as well.
 

Archilochus

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If the sensor is drawing ~.4mA - and the reg specs at ~.005mA - I wonder what's pulling the rest of the current??  Strange....

Archilochus
 

shrtcirkt

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The voltage reg that I currently have in the circuit is an 78L06 in a TO 92 case. I use two of them, one toregulate the voltage to the micro controller and the other to clean up the input power to the PIR module.
I have not been able to find any spec sheets for this regulator so I am not sure what the actual current draw is supposed to be.

Arch, is there an online resource that you are aware of for specing out or cros referencing components?
 

Archilochus

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Hi shrtcirkt,
Ohhh... 78xx regs... That's where the power is going! Toss those beasties in the rubbish - or just save them for use in a line-powered project.  6 volts might be high for the microcontrollers - I think MAX supply is around 5.5 volts.

I use http://www.freetradezone.com to spec unknown parts.  If you can tell the manufacturer - the best info is usually found from their site.

Tinhorn had sent me an address for the site he uses to spec parts - but I can't seem to find it off-hand. I'll post it if I come across it.

Archilochus
 

shrtcirkt

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I've got a couple more regulators, they are Seiko S81250SG, are you familiar with this one? It's rated at 1.2ua with a 50ma output current.
Thanks for the info :)
 

coyotebandit

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shrtcirkt,
I had problems with a circuit of mine using a v-reg that was using too much current. I took it out and just ran it off 3 AAA's and it's running fine now. Still get more false pics with the Amazon than the RS PIR. But on a digital setup, it works ok. Did you ever tap into the sensitivity circuit built into the main chip?

I have heard good things about the Seiko regulators, but I haven't tried them yet.

CB
 

Archilochus

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The various Seiko regs work fine - and the price can't be beat!  Make sure to read the data sheets - particularly the section relating to Input / Output capacitors.

Archilochus
 

shrtcirkt

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I just finished swapping out the 78L Voltage reg for the seiko S81250SG. WOW !! What a difference.
At idle the entire pir now draws 350ua and about 7.5ma during a trigger cycle.

Arch, I've done some searching on the threads and I cant find the formula for figuring out battery life. I want to run this with 4 c cells. Did you or Tinhorn post that info at one time ?
Thanks again !!
 

Tinhorn

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Hi shrtcirkt,

Wow, that teaches us a lesson about those voltage regulators, thanx for the comparison figures......


The formula you're looking for is:

Batt Life = Batter capacity (ampacity) / Current

be sure to use the same units in the formula (amps or ma's or ua's)


"C" cell ampacity (alkaline) = 6000 ma's
350 ua's = .35 ma's

6000 / .35 = 17143 hrs or 23.8 months

Wow, almost a lifetime  he he

(AA = 2000 ma's which is 7.9 months or AAA's = 1000 ma's or 4 months)

Tinhorn
 

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