All guru's welcome

[zemo]

I have a question.

I have a garage remote control. (Liftmaster 971LM)
It operates off a 3 volt battery.
I don't know anything more about this.

I have tried to modify this to to operate directly off a 12 volt battery but I'm afraid it will fry it.
I have two wires soldered to where the battery connects for the direct contact.

Now, how can I do this?
I want the cheapest and easiest way possible.
Can I solder some type of resistor in-line to drop the incoming voltage?

Let's see who can help!

Oh and gentlemen, please understand that I know nothing about electronics so please explain in detail.

Thanks Guru's!!!!

 

[Papabravo]

I have a question.

I have a garage remote control. (Liftmaster 971LM)
It operates off a 3 volt battery.
I don't know anything more about this.

I have tried to modify this to to operate directly off a 12 volt battery but I'm afraid it will fry it.
I have two wires soldered to where the battery connects for the direct contact.

Now, how can I do this?
I want the cheapest and easiest way possible.
Can I solder some type of resistor in-line to drop the incoming voltage?

Let's see who can help!

Oh and gentlemen, please understand that I know nothing about electronics so please explain in detail.

Thanks Guru's!!!!

Do you mean literally a 12VDC battery only, or are we talking about an automotive electrical system? If the overvoltage doesn't cause a problem then the alternator load dump certainly will. I recommend a 3-terminal regulator as a minimum. Even this may be unsatisfactory for your purposes without knowing some more about what you are trying to do.

 

[zemo]

Yes, this is automotive.
I would hook this into my headlight so there would not be a surge in volts.
It is not connected directly to the battery.
Basically, this is what I have.

I have a genie remote that operates off a 12 volt battery.
I have a liftmaster remote that operates off a 3 volt battery.

I want to be able to drop the volts down on the 3v Liftmaster, STILL using a 12 volt battery.

And wow! What a quick response!

 

[Sceadwian]

You'd actually prefer it being connected directly to the battery as it will absord most common voltage spikes. Considering it's a remote and it's 3.3 volts it was probably run from a coin cell which can't reliably source more than about 30ma's of current. Just use a zener regulator to drop the remaining voltage. Use a half watt zener just to be on the safe side.

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html

 

[Hero999]

I recommend a 3-terminal regulator as a minimum.

Yes, the trusty old LM317 or cost and space saving LM317L will both do here.

The circuit is on the datasheet.

 

[zemo]

Below is a copy and paste.
Will this work?

If it uses the same 2032 battery that my craftsman uses then a 45k ohm resistor inline with the power source will step down your voltage so that the remote only drops 3v. I looked up the specs for the battery and it's a .2mA battery, with 3v that comes to 15k ohms of resistance ( at the least) on the circuit board of the remote. Now apply 12v and the same current and you get a total of 60k ohms, we already know the remote is 15k ohms, so you need 45k ohms more. This will put the remote still getting .2mA at the most and the 45k ohm resistor drops 9v so 3v is all that's left for the remote.

If so, is there a certain way to put this resistor in line.
In other words, should I put the yellow stripe towards the 12v source or the gold stripe.
Does this matter????

 

[Sceadwian]

No, resistors have no 'end'
Wherever you got that tip from it's a decent one. At those current levels you can juggle voltages any way you want with cheap components.

 

[zemo]

Thanks Sceadwian!

I'm giving it a try.
I hope it works......

 

[zemo]

OK, with this resistor in place I am only getting .5 volts now.
Any suggestions?

 

[audioguru]

If it uses the same 2032 battery that my craftsman uses then a 45k ohm resistor inline with the power source will step down your voltage so that the remote only drops 3v. I looked up the specs for the battery and it's a .2mA battery, with 3v that comes to 15k ohms of resistance ( at the least) on the circuit board of the remote. Now apply 12v and the same current and you get a total of 60k ohms, we already know the remote is 15k ohms, so you need 45k ohms more. This will put the remote still getting .2mA at the most and the 45k ohm resistor drops 9v so 3v is all that's left for the remote.

Wrong! The recommended load for the CR2032 lithium battery cell is 15k for a current of 0.19mA and it lasts for about 1000 hours. Its internal resistance is only 20 ohms so it can supply up to 50mA for a few minutes.

How can you calculate a resistor to feed it when you don't know the current of the remote control?
The remote control unit needs a voltage regulator, not just a resistor that gives it 12V to fry it when it isn't transmitting and nearly no voltage when it is transmitting.

 

[chiba]

I'd guess 5.7K should work, or blow up something, either one or the other

 

[zemo]

Wrong! The recommended load for the CR2032 lithium battery cell is 15k for a current of 0.19mA and it lasts for about 1000 hours. Its internal resistance is only 20 ohms so it can supply up to 50mA for a few minutes.

How can you calculate a resistor to feed it when you don't know the current of the remote control?
The remote control unit needs a voltage regulator, not just a resistor that gives it 12V to fry it when it isn't transmitting and nearly no voltage when it is transmitting.

So what do you suggest?

 

[audioguru]

An LM317 set for a 3V output.

 

[Sceadwian]

For such a small project, a simple resistor and zener diode would be simplest. The link I posted above on the Hyperphysics web site has a zener regulator calculator, you just punch in your desired voltages and expected currents and it suggests resistor values and tells you the power dissipation required.

 

[zemo]

Well Sceadwian audioguru,

Like I said, I have zero experience in electronics. (I know what a battery is)

I thought it was more like sticking something in the line that would work.

I suppose I should find someone locally that could help me or if you think it is worth your time to give me a crash course in what "Exactly" what I need to do or how to make what you are talking about.

Thanks!

Ps. I'm glad this forum is anonymous cause I feel like an idiot...

 

[Sceadwian]

Lets make this simple then.

Use a 220ohm 1/4 watt resistor in series with the +voltage of your device.
Use a 3 volt 1/4 watt zener diode with it's anode on the +voltage and it's cathode on the -voltage. As long as the remote has a series resistance of about 50 ohms that will give you a minimum of 60ma's of current to the remote.

 

[chiba]

Just curious, If this remote when used with 12V and a 45k resistor had 0.5V accross it then that would show it's drawing 0.256mA and therefore it's internal R of is 1956ohms, So when running at 3V this would mean it's drawing 1.53mA, that's about 1/10th of a CR-2032's pulse current. If we tried running it at 12V with a 5.8k then wouldn't it work???

 

[Hero999]

I disagree, a zenner isn't the best way to do this because the quiescent current would be far higher than an LM317, therefore it's a waste of power.

 

[audioguru]

The remote draws 0.256mA with a 0.5V supply. I don't think it works properly with only 0.5V. Its current will be completely different when it is operating properly with a 3V supply.

The voltage regulation of some 3V zener diodes is crap and depends a lot on its part number and on its current. If the remote is not being used then the zener (and the remote) will have 3.5V. If the remote draws 50mA when it is working then the zener's (and the remote's) voltage will drop to 2V or less. Use the LM317 voltage regulator.

 

[zemo]

I don't know what the heck you guys are saying but, I thank you all for the great discussion.

Anyone else out there want to solve this?

I just may learn somethhing here!