Hello,
I have the below circuit but it drains the batteries over about a 6-8 hrs even with the led's off. What could cause this?

 

Hi Gary,
What are the battery types and ratings?
E

 

Additionally:
Use the 555’s CMOS version

 

Yea, use a CMOS 555 and a transistor to buffer the LEDs.

That might help.

 

I believe that the 555 timer draws a standby current at all times, not just when it is timing. But certainly the CMOS version should draw less current.

 

The NE555 draws appx 6ma at 9 volts on standby.
The cmos version can only source 10ma.
Adding a mosfet to drive the LEDs is required.
Depending on the LED type it might also be possible to wire the LEDs in series to reduce the current when activated.

 

Let me add to my post #5 comment: Standby current is not something that should be ignored. It is quite capable of depleting a battery charge.

 

Hello,
I have the below circuit but it drains the batteries over about a 6-8 hrs even with the led's off. What could cause this?

View attachment 361094

Let's see what the expected battery life would be.

You don't give the relevant details, so I'm having to guess. Please correct my if either of these assumptions are incorrect.

Assumption #1) You are using a typical Alkaline 9 V battery.
Assumption #2) You are using the basic 555 timer IC (i.e., the TTL version (e.g. NE555 or LM555) and not a CMOS version (e.g. LMC555))

The LM555 data sheet shows that the quiescent current draw is fairly linear with supply voltage:



At room temperature it is typically 5.5 mA at 9 V. From the specs at 5 V and 15 V, however, it could be more than 10 mA and still meet spec.

The Energizer 522 data sheet shows the typical capacity as follows:



So you should expect at least 600 mAh at currents below 10 mA. At 6 mA, you would therefore expect it to last around 100 hours. If you are only getting 6 to 8 hours when the timer is static with the output LO, then something else is causing the problem. To drain this battery in 8 hr would need a current draw of about 50 mA.

You need to measure the actual current draw. If it is less than 10 mA when the output is LO and your batteries are draining that fast, you might need to focus on the batteries. Are they alkaline? Are they new? Are they reputable?

 

If you want to use a standard, bipolar 555 with essentially no standby quiescent power, below is the LTspice sim of a 555 one-shot circuit with an added CMOS CD4050 hex buffer IC to power the circuit only when active (output high):
The quiescent current is essentially just the static leakage current of U2.

 

Instead of just the idle current, there may also be leakage current thru that 470 mFd capacitor. So that could be one cause, based on no additional information.
Of course, since we have no information about "the batteries", nor what is meant by "drained", nor what part of the world the TS is located in, we are all guessing. ( Previous threads have commented that in some parts of the world batteries are very poor quality.)

 

Instead of just the idle current, there may also be leakage current thru that 470 mFd capacitor. So that could be one cause, based on no additional information.
Of course, since we have no information about "the batteries", nor what is meant by "drained", nor what part of the world the TS is located in, we are all guessing. ( Previous threads have commented that in some parts of the world batteries are very poor quality.)

One my first thoughts, after seeing what the expect lifetime should be with a bipolar 555 and an alkaline battery, as the leakage in that cap. But 50+ mA of leakage? Even if that were the case, the 68 kΩ resistor would limit it to little more than 0.1 mA.

Either there's something else drawing current, or the batteries are old or poor quality, or the 555 is a functional low-quality counterfeit.

Until and unless the TS deigns to provide more information, I don't know that much else can be offered.