| Author |
Message |
    
Tracker293
New member
Username: Tracker293
Post Number: 5
Registered: 9-2007
| | Posted on Saturday, October 24, 2009 - 2:48 am: | 
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I have an unregulated competition power supply that has an output of 18 volts. My question is, can I use a competition voltage regulator to regulate the voltage in the supply down to about 13.8 or so and regulate it there so that I could possible run my 16 in the house instead? Or should I order another Astron RS70 supply
Thanks |
Joey_migs
Junior Member
Username: Joey_migs
Post Number: 34
Registered: 9-2009
| | Posted on Saturday, October 24, 2009 - 12:24 pm: |
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It depends on whether the power supply you have is already rectified and filtered.
If it is already rectified and filtered, you can simply use a LM 723 IC chip to regulate voltage to 13.8 VDC.
If it is not already rectified with smoothing caps, you will need to add a diode bridge and some filtering capacitors(to flatten out ripple) to yield an output voltage of 13.8 VDC with a minimum AC hum.
Let me know, I can provide a schematic, parts list and parts sourcing. |
Tech237
Moderator
Username: Tech237
Post Number: 1239
Registered: 4-2004
| | Posted on Saturday, October 24, 2009 - 12:20 pm: |
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You can certainly regulate it down BUT 18v down to 13.8 is not really leaving enough leeway for regulation. Usually if I am looking at 13.8VDC regulated I will usually start with 24 or more as the input voltage.
Also if you add and external regulator you have to make sure it can handle the current drawn and has adequate heatsinking.
MY suggestion is buy another supply designed for `13.8vdc..
Having said the "negatives" experimentation is always worthwhile.
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
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Tracker293
New member
Username: Tracker293
Post Number: 6
Registered: 9-2007
| | Posted on Saturday, October 24, 2009 - 2:53 pm: |
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The supply already has 2 filtering caps. and I believe 2 rectifiers between the transformers and the output lugs. That would be great if you could possibly send me that information. The supply is capable of about 300 amps output. Thanks |
Joey_migs
Junior Member
Username: Joey_migs
Post Number: 35
Registered: 9-2009
| | Posted on Saturday, October 24, 2009 - 9:08 pm: |
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If the output is already clean DC (Rectified and filtered) you can use a simple voltage divider circuit to reduce the voltage from 18 to 13.8. The 300 A output concerns me - what is the voltage and current of the service? I am sure you will not be drawing that sort of current for the radio.
Voltage Divider:
Vout = R2/(R1+R2)* Vin
Vout = 76.8/ (76.8 + 24.3)* 18
13.67 VDC= 76.8 ohm/(76.8 ohms + 24.3 ohms)* 18VDC
You will have to use resistors that can handle the power you require, power resistor will be needed:
(www.resistorsonline.com/housed-chassis-mounted-wire.html)
You can find the power by multiplying Voltage (18 VDC)by Current(?A).
 |
Tech833
Moderator
Username: Tech833
Post Number: 1767
Registered: 8-2002
| | Posted on Sunday, October 25, 2009 - 10:08 am: |
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In order to build a voltage divider to run your equipment, you need to know what the current drain of the equipment will be.
Good thinking, but in this case, maybe not the best way to go.
Best bet- Buy a power supply that is the appropriate size and be done with it. Much less chance of damaging expensive radio equipment that way. |
Tech237
Moderator
Username: Tech237
Post Number: 1240
Registered: 4-2004
| | Posted on Sunday, October 25, 2009 - 11:46 am: |
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What Joeymigs didn't tell you was to allow full current capability the resistors would have to be able to dissapate 1000W each.
At 20 Amp draw, they would not to handle 360W
At 10 Amp 180W
Not really practicable ratings for a Power Supply, but a great way to heat the shack during winter.
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
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Joey_migs
Junior Member
Username: Joey_migs
Post Number: 35
Registered: 9-2009
| | Posted on Sunday, October 25, 2009 - 11:38 am: |
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I am going to back-peddle and agree with Tech833, Even with a small current draw of 5A, resistor power rating will be pretty high.
(5A)^2 * 76.8 ohms = 1920 Watts
(5A)^2 * 24.3 ohms = 607.3 Watts
Myself, I enjoy tackling this sort of thing so I would get it to work ultimately but I wouldn't want you to damage any of your equipment using my advise.
If you shop around, you can get a good no frills 25 A switching power supply for as little as $75 - $100
I have a Samlex SEC 1223 that 12VDC @ 23 A that I picked up around ten years ago for like 70 bucks.
Joe |
Tech237
Moderator
Username: Tech237
Post Number: 1241
Registered: 4-2004
| | Posted on Sunday, October 25, 2009 - 12:09 pm: |
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OOps - teach me to do it in my head
300A - 6912000 watts
20A 30720 watts
10A 7680 watts
Even worse values
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
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Tracker293
New member
Username: Tracker293
Post Number: 7
Registered: 9-2007
| | Posted on Wednesday, November 18, 2009 - 11:45 pm: |
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Thanks for everyones input on this. I guess I need to back up and start over again. Thanks |
