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Author Topic: 12 V battery works fine - 12 VDC ac adapter sorta fails?  (Read 4674 times)

BoyntonStu

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12 V battery works fine - 12 VDC ac adapter sorta fails?
« on: February 25, 2012, 04:29:12 PM »

This is driving me nutz.

I am developing a hybrid circuit using X10 and non-X10 rf devices.  (315 MHZ and 433 MHZ)

I am testing a 12 v (non X10) 315 Mhz transmitter with a receiver/relay.

I trigger the transmitter with my water leak detector switch.

I wired across the transmit button and switch the 12 VDC on/off to control the transmitter.

Everything works fine and repeats using the battery.

I measure very low battery draw < 2 mA.

If I replace the battery with the wall adapter it works OK one time.

If I turn off the 12 VDC and  turn it back on again, the transmitter LED lights but no joy at the receiver. B:(

If I unplug the ac adapter and re-plug it in, it works fine again.

I am scratching my head.

Any ideas???

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dave w

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #1 on: February 25, 2012, 05:23:33 PM »

Is the wall adapter a battery charger or or a power supply? A charger may have a red/green LED to indicate "Charging" / "Charged" status and in the "Charged" status may not put out enough current to operate the transmitter. Only a guess.
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BoyntonStu

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #2 on: February 25, 2012, 06:14:03 PM »

Is the wall adapter a battery charger or or a power supply? A charger may have a red/green LED to indicate "Charging" / "Charged" status and in the "Charged" status may not put out enough current to operate the transmitter. Only a guess.

There is no LED on the Wally box.

AAMOF I tried 2 of them with identical results.

My guess is similar to yours, inrush current not sufficient with the adapters.

Even though the steady state current is minuscule, the battery inrush current could be substantial.

How can I work around this problem?

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Brian H

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #3 on: February 25, 2012, 07:12:36 PM »

Are you allowing the wall wart enough time to completely discharge.
If the circuit draws little current. It could take awhile for it to completely go to zero or real close to zero.
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BoyntonStu

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #4 on: February 25, 2012, 09:10:34 PM »

Are you allowing the wall wart enough time to completely discharge.
If the circuit draws little current. It could take awhile for it to completely go to zero or real close to zero.


Thanks Brian,

I am confused.

When the power to the wall wart is applied it must stay on for hours if necessary.

Does it need to discharge?

The relay is non-latching and for the circuit to function properly, the wall wart, once switched on, must stay on.

Perhaps I misunderstood.

Did you mean to say that the wall wart must be off for a period of time before functioning again in the short period test mode situation?

I will try doing that tomorrow.  Hmmmn.

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Brian H

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #5 on: February 26, 2012, 06:43:00 AM »

I have a feeling it is your transmitter circuitry. Keeping the trigger input On while switching the power to it is unconventional at best.

Maybe my thoughts where reversed. Maybe the battery momentarily dips enough for the always shorted trigger to again function.

Is the wall wart regulated? With a light load it could be putting out a much higher voltage if not regulated.
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BoyntonStu

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #6 on: February 26, 2012, 11:56:07 AM »

When you start your car and the radio immediately comes on, isn't that the same as the transmitter situation?
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Brian H

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #7 on: February 26, 2012, 12:22:31 PM »

When it is On does it send until turned Off or does it send a command and then stop?
If it is not continuous. It is using some sort of trigger to start it.
Maybe if you can give us a link to what you have it may help.
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BoyntonStu

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #8 on: February 26, 2012, 12:43:09 PM »

When it is On does it send until turned Off or does it send a command and then stop?
If it is not continuous. It is using some sort of trigger to start it.
Maybe if you can give us a link to what you have it may help.


When it is On does it send until turned Off?  Yes, when ON it becomes my 'latched' relay.

(I have no idea what the second smaller button does.)

http://tinyurl.com/88lu5yp

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Brian H

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Re: 12 V battery works fine - 12 VDC ac adapter sorta fails?
« Reply #9 on: February 26, 2012, 01:43:35 PM »

I saw your other post and will give that information a look.
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