Advice, please - DC to AC conversion

[beaconterraone]

Hello all!

I'm seeking some friendly advice.

I have a weather station that just eats batteries. It takes two AAs, and doesn't like Eneloops, so I presume it is very demanding in that it wants constant current well above 2.4 volts.

Is there any reason I cannot convert the unit to a 3.0 volt DC output from an AC wall-wart? Would a 3.0 volt 1 amp adapter be too much power, or does the amperage only matter for maximum demand?

Thank you in advance!

 

[Mustang51js]

You could try rechargeable batteries with a small solar panel, otherwise you need a invertor to match what the batteries put out

 

[ddawg16]

1 Amp is way over kill....I doubt your using more than about 50ma at 3v.

If you have an outlet close and don't mind the cord...yea, it would work.

If it was me....find a dc wall wart that is close in voltage...say 5v (3v might be hard to find). What ever the voltage...use a zener to drop the voltage down close to what you want. I think I would also put a 3v zener inside along with a 20uf cap. Depending on the current draw...maybe a resistor and diode (1n4004) in series for protection. The diode prevents the voltage from being reversed....the resistor would limit the current in case you had a short.

 

[ishiboo]

3v warts are easy to find. I'll take a look but I think I actually have one or two here, for Wahl trimmers (pieces of **** BTW). I'll let you know. You need enough amperage to run the device. The trimmers warts are 500ma IIRC which will be plenty. Any "excess" is not an issue.

 

[exmaxima]

maximum[/I] demand?

Thank you in advance!

You can go to Radio Shack and buy a universal power supply for $20 that has various switchable voltages. I don't like them but they are readily available.

I would buy a regulated 3 vdc supply. Anything above 100mA is fine, such as this:

http://www.amazon.com/dp/B006QYQ0MG/?tag=atomicindus08-20

Good Luck

 

[beaconterraone]

Thank you to everyone who weighed in on this!

I decided to grab a 3V 400mA adapter off eBay for $4.00 including shipping. It's intended for an Evenflo breast pump, but we'll see how it works for a weather station.

I considered doing more "expert" work using zeners and capacitors, but I have very little experience to date doing that, so I'll go easy for now. I'll try that in the future after more study.

 

[bill in in]

Be advised that diodes have an inherent .7 volt drop in the forward direction, so your output would be reduced by that much. Dry cells are generally nominally 1.5 volts - actual voltage will be higher at first. Transformer type supplies might need a capacitor more than a regulator type.

 

[lametec]

Be careful with that breast pump adapter. It's probably an unregulated AC adapter, which means it puts out 3V at the expected load of the breast pump.

With your weather station, the load will be much smaller, and the output voltage will probably be much higher than 3V.

Put a voltmeter on the output of the adapter before connecting it to the weather station.

Here is a unit that would be much better suited.

 

[beaconterraone]

Be careful with that breast pump adapter. It's probably an unregulated AC adapter, which means it puts out 3V at the expected load of the breast pump.

With your weather station, the load will be much smaller, and the output voltage will probably be much higher than 3V.

Put a voltmeter on the output of the adapter before connecting it to the weather station.

Here is a unit that would be much better suited.

Thanks for the advice! I just went ahead and picked up an overstock Radio Shack regulated adapter for cheap (they rebranded them to "Enercell" so RS-branded are half price or better). I'll experiment with unregulated on a device I don't care about.

 

[beaconterraone]

An update: the conversion went perfectly. The adapter I got worked exactly as hoped.

And now the bad news...I discovered it wasn't a matter of low batteries. The weather station (a Meade TE278W) is inherently defective. It kept losing signal with the remote sensor, and the problem seemed to be remedied by replacing the batteries. However, after the problem reappeared after the AC conversion, I did much more digging, and found that several other customers have the same issue, that the unit just isn't designed well (the problem appears on a spectrum from "out of the box" to "just out of warranty"). Not a matter of interference or distance, either - it would just stop displaying no matter where it was located or how close the sensor was (including in the same room). The inside temperature and the atomic clock receiver work just fine.

I had fun doing the conversion, despite the ultimate failure of the project.