Author Topic: portable telephone (Read 3626 times)

Fiddlehead44 · « **on:** May 19, 2006, 12:22:43 AM »

My portable phone has a wallwart charger 9V 210 Ma(DC) input

that keeps it charged-up.

My small solar panel is 12V 18 watt.

Could this be used to charge my phone? If

so, how would I hook it up? My solar panel

is hooked up to a charge controller

and a small 12V garden tractor battery.

Fiddlehead44

RP · « **Reply #1 on:** May 18, 2006, 06:38:13 PM »

A simple non-technical solution would be to get a car charger for the phone and connect it to the battery.

ghurd · « **Reply #2 on:** May 18, 2006, 08:00:21 PM »

I figure this is a cordless land line phone. Not a mobile or cell phone?

Should work for a cell phone too, if it doesn't have so many connections you can't tell what is what.

Google LM7809 voltage regulator, maybe add a 5 ohm resistor in the positive line.

G-

drdongle · « **Reply #3 on:** May 19, 2006, 05:49:04 AM »

A LM 7809 or a DC to DC converter salvaged from some other piece of equipment or bought surplus.

drdongle · « **Reply #4 on:** May 19, 2006, 05:56:37 AM »

Just thought of something, measure the actual output of the power pack. More than likely it will be about 12 volts, if so just wire directly to the phone with a fuse in line 315 or 500Ma or so depending on the wall wart rating. The phone will have an internal regulator, that may make the use of another regulator or converter redundant.

dinges · « **Reply #5 on:** May 19, 2006, 06:28:39 AM »

In car shops they sell those little cigarette-lighter gadgets that you plug in the cig.lighter and that can output several voltages 3-5-6-9V, usually. That should do the trick, if you can connect a cig. lighter socket to your battery.

Seems the easiest & cheapest solution to me. Unless you love building stuff & know about electronics, in that case Ghurd's LM7809 (09, not 05) should do the trick even better.

There are many options other than these. You figure out what's easiest/best for you.

Peter.

dinges · « **Reply #6 on:** May 19, 2006, 06:31:10 AM »

These gadgets already have a fuse built in. If you decide to homebrew something else, do NOT forget the fuse. Anything that connects to a battery should be fused, IMO. A short circuit can make a wire glow like a lightbulb.

Slingshot · « **Reply #7 on:** May 19, 2006, 07:36:50 AM »

That's possibly the cheapest solution, as well as the most power-efficient. Nowadays most of the little "car chargers" use switching regulators, and waste very little power. Around here (Dallas), the "99-cent stores" have them available for most phones for ... you guessed it ... 99 cents.

ghurd · « **Reply #8 on:** May 19, 2006, 08:26:36 AM »

Be careful with the 99 cent chargers. Around here, they are not switchers, just a resistor.

One of my 4.5V (3 cell) phones had the batteries cooked in one short charge with the 99 cent charger.

Some have a sticker saying "just because the package says cell phone model #1234 and the plug fits, make sure the voltage matches your phone". Sounds like they know about the problem.

G-

ghurd · « **Reply #9 on:** May 19, 2006, 08:30:26 AM »

Google "7809T". 30 cents at hit #1. TO-220, 1.5A.

G-

Slingshot · « **Reply #10 on:** May 19, 2006, 02:45:48 PM »

That's interesting. I had not taken one of them apart, but now I think I will since I lost the phone that mates with one of the 99-cent chargers. I'll post back with the results!

Fiddlehead44 · « **Reply #11 on:** May 20, 2006, 03:32:45 AM »

Thanks for all your suggestions. Yes it is a land phone.

I tested the output of the 9V wall wart and found 13.68V

This plugs into the phone stand and the stand has a couple

of spring loaded contacts that the phone sets on when not in

use. I measured these terminals and found 11.72V's.I would

guess that I could connect directly to the battery with a fuse

in the pos line? I also found an old cell phone cig. lighter

charger and hooked it to my battert that was showing 12.72V.

The output of this convertor was 8.16v. Would this be safer?

BTW, I plan to use my solar panel for other devices also. Such

as a small floresent light for my bathroom. Someone used a bulb

out of an old scanner and I'd like to try that, but can't find

the post now.

Thanks again

fungus · « **Reply #12 on:** May 20, 2006, 03:40:52 AM »

Heres the link to that story:http://www.fieldlines.com/story/2006/4/8/2412/41855

ghurd · « **Reply #13 on:** May 20, 2006, 06:15:24 AM »

The open volts of a transformer like that drop quick under a small load.

The solar charging battery can go past 14V, and there is no impedance in the battery line. Thats going to be 60% overvoltage sometimes. So I certainly wouldn't do it direct. Especially since the parts to do it regulated only cost $2.

G-

terry5732 · « **Reply #14 on:** May 20, 2006, 05:29:05 PM »

Probably a zener diode. A resistor wouldn't drop the voltage so much as the power (amps). There are many simple zener diode regulators for small power apps.

ghurd · « **Reply #15 on:** May 20, 2006, 10:07:30 PM »

That is my point. They were resistors. Period. Not even a reverse protection diode. Battery killers.

Ever open a cordless charger for a $10 HF drill? Transformer, bridge, resistor.

I guess it is OK, because they say not to let them overcharge. LOL

G-

drdongle · « **Reply #16 on:** May 21, 2006, 07:19:12 AM »

Just hook it streight to the 12 volts with a fuse, it will work fine.

elvin1949 · « **Reply #17 on:** May 22, 2006, 10:34:39 PM »

I can't find that post either BUT that is

a cold cathode sp? bulb.

Others can tell you more about it.

later

elvin

hvirtane · « **Reply #18 on:** May 23, 2006, 10:35:26 AM »

There are even hand operated generator chargers available for mobile phones.

Never seen them in Finland, but in India.

Something similar is available here:

http://www.ambientweather.com/maemhageflan.html

http://www.newenergyshop.com/

There are ready made solar cell chargers for mobile phones as well.

http://www.cetsolar.com/sc150.htm

- Hannu

dinges · « **Reply #19 on:** May 23, 2006, 12:12:56 PM »

Another very simple solution would simply be to put 5 or 6 diodes in series (e.g. a 1N4007 or similar) and put it in the positive line, together with a fuse. The diodes drop about .7-.8V each, five of them drop about 4 V; your 13.8V will become 9.8V at the phone, which is good enough. The fuse prevents fires.

battery +13.8V --|>|---|>|---|>|---|>|---|>|---|FUSE|--- +9V to phone

the ground wire has no components in it, goes straight to ground of the phone.

--|>|-- = diode (e.g. 1N4007)

Peter.

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Author Topic: portable telephone (Read 3626 times)