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I need to convert 12VDC solar power source to produce -51 VDC. I have searched on the Internet trying to find a DC to DC converter or the schematics to build one. Anyone know how to achieve this?

Thanks

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How much output current do you need?

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Normal telephone line power runs around 224 K ohms @ -51 DC volts. The current, not sure how to measure it...but its around 1 amp...I guess, not sure. I'm trying to produce my own phone system with 12 call stations. I have watch a lot of youtube vides...but so far, nothings clear that I can get to work. I've been working on this close to a year! When you connect your tester on a hot phone line, it reads -51.9v and when you go off the hook, it drops to -8v. I have tried many things to get 2 phones to talk to no avail. Connecting a 12V Batt to 2 phones connected will turn on....but will not talk. Watching a youtube video show a guy doing just that and they worked! Perhaps new Wal-Mart \$5 digital phones won't work? I'm a loss!

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The current in a telephone line is no where near 1A, if you are close to the exchange it is about 50mA and if you are far it is maybe 10mA.

The power that feeds a telephone has a 300 ohm resistor (a relay coil) on each of the two wires so the phone transmits into 600 ohms and receives from 600 ohms.

Two telephones will work from a 12V battery if you connect 300 ohms to the +12V and another 300 ohms to the 0V. Then connect both phones to the free ends of the two resistors.

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To to be clear I got this right...using a 12V battery, as long as I connect a 300 ohm resistor to the +12V power IN and a 300 ohm to the 0V (or negative) then connect both phones to the + and - sources...they will work. Do I have that right? You mentioned a "Relay Coil"....is that the same as the resistor? Going to give it a shot.

Thanks audioguru

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I connected a 300 ohm resistor to the red wire and 300 ohm to the green wire, using an altered phone "Y", connected +12V (Red) and 0V (Green) and nothing.

Tried to download a picture of how I have it rigged...wont let me.

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I connected a 300 ohm resistor to the red wire and 300 ohm to the green wire, using an altered phone "Y", connected +12V (Red) and 0V (Green) and nothing.

Tried to download a picture of how I have it rigged...wont let me.

Do you have an issue uploading a photo on the forum? What's the problem?

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On the photo, I tried to use the INSERT OTHER MEDIA....is there a different way to attach a photo? I've been a member of this group before and its format has changed. I did, in the past, post photos. This is a really great Group...I have learned so much on practical electronics, and still learning!

Audioguru, I did figure it out. The phones work fine...thank you! I also now understand that the RINGER circuit has to be on a separate current from the SIGNAL circuit. Having the resistor inline doesn't allow the other ringer components to function. I'm going to use the same power source (+12V) but split it into two currents. I have to re-design my circuit board in my CAD program. The 3 channel prototype circuit board I am currently using will have to be altered.

My goal is a 13 channel system with operator panel.

Again, thanks so much!

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CoryD, you should normally see the "Drag files here to attach, or choose files.." as you can see on the attachment below. If you can't see it, please report your browser and operating system and also if you have javascript enabled or any antivirus is blocking parts of a webpage such as cookies.

Normal telephone line power runs around 224 K ohms @ -51 DC volts. The current, not sure how to measure it...but its around 1 amp...I guess, not sure. I'm trying to produce my own phone system with 12 call stations. I have watch a lot of youtube vides...but so far, nothings clear that I can get to work. I've been working on this close to a year! When you connect your tester on a hot phone line, it reads -51.9v and when you go off the hook, it drops to -8v. I have tried many things to get 2 phones to talk to no avail. Connecting a 12V Batt to 2 phones connected will turn on....but will not talk. Watching a youtube video show a guy doing just that and they worked! Perhaps new Wal-Mart \$5 digital phones won't work? I'm a loss!

I am attaching here 5 different telephone intercommunication schematics that was published on the old version of electronics-lab.com. They are old designs but may still be useful to help you with what you are trying to accomplish. I also have a telephone intercom system based on PIC microcontroller. If you are interested on this also, just tell me.

t_tink.zip

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I do not know which planet you live on but here in Canada the ringing is a 90VAC/20Hz signal on the telephone line. The 52VDC is still there during ringing and when a phone goes off hook it draws current from the 52VDC which is sensed and stops the ringing and connects the audio from two phones.

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"A solar charging system is not complete without an appropriate charge controller. Most units include a charge controller to charge 12-volt lead acid batteries and inverter for drawing power. Charge controllers are also available for lithium-ion to charge 10.8V packs (3 sells in series)."

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