Power supply question

Discussion in 'General Electronics Chat' started by yourownfree, Dec 5, 2014.

  1. yourownfree

    Thread Starter Active Member

    Jul 16, 2008
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    I have a power supply that is regulated, The voltage is fixed but can be changed if need be.

    Here is the question:
    The voltage at the output terminal is at 14.6 volts and will allow 15 amps to be drawn from it.

    I want to use it as a power supply for a Ham Radio Transceiver. Not sure which one, any one.
    I suppose 13.8 volt is the standard voltage, but is 14.6 still ok in your opinion?
    To me I think it is ok. I feel 15.5 volts is asking for trouble and 16 volts even more so. I seem to remember "some" alternators on cars going up to about 14.5- 14.8 volts "DC" at the output terminals, for you perfectionists. Why my pickup Ford F-250 diesel, goes even higher just after starting. near 18 volts then drops. Not saying that is right, but Lets just say The Ford is what it is.
    Ok back to the power supply, how do you feel about it, if you have proof with your answer even better, but I like opinions too. I just want to know how close am I to ruining the radio?
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,178
    1,799
    You have to look at the specs for the transceiver. Here is a sample

    Icom IC-756 ProIII; Icom IC-718; Icom IC-706: 13.8V ± 15%
    Elecraft K-3: 13.8V(nominal),11V(min), 15V(max)
    Elecraft KX3: 8V(min), 15V(max)

    14.6V is within the specified range for all of these transceivers.
     
  3. yourownfree

    Thread Starter Active Member

    Jul 16, 2008
    89
    0
    front_panel.jpg
    Thanks, I guess that's the best way. I built this supply to put out about 13.8 volts. the panel says 13.9 and I am sure I measured 13.9 volts maybe 14. But the person that has this power supply claims the panel says 13.9 but he measures 14.6. I asked if he would use two meters to check it in case one is off. I dont recall putting in 4 diodes in the regulator circuit only 3. Using a 12 volt regulator I attached 3 diodes on the common leg to bring up the voltage. This is a Kenwood ps30 power supply I rebuilt. I changed the circuitry to suit my idea of a power supply. It has an added front panel display, shows amps and voltage, now uses a regulator ic instead of old obsolete transistors. Has an over-voltage circuit so that when the voltage reaches a predetermined level it shuts the output off, uses a relay whereas other circuits burn out fuses and parts. Now in the pics you can still see my pencil marks used to cut out the meter etc., as it was not cleaned yet. front_panel.jpg fan.jpg
    The over-voltage is set for 15 volts. When that happens the power led light on the front panel comes on, as that is only being used for that reason. I replaced all the pass transistors and used Artic Silver for the compound. It has a cooling fan at the rear blowing on the transistors. It runs real cool, seems to be real hardy. I accidentally shorted the output and nothing happened. It just cut itself back from excessive draw. No blown fuses. I am pleased with it. Way too much time in this one. The problem with the old one is when the pass transistors blow, full voltage now makes it's way to the output and ruins your radio. The voltage is 22 volts dc. The engineer failed to do his or her part when they designed this one. That is just not right. It cant do that now, no way, no how. Here is a pic for all interested. Thanks for your comment, thought about that but sometimes you can fudge a bit, so just a thought I would like to hear from readers.
     
    Last edited: Dec 5, 2014
  4. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    I would have chosen to just leave the 12V regulator to output 12V.
     
  5. yourownfree

    Thread Starter Active Member

    Jul 16, 2008
    89
    0
    The person I built it for wanted more. 14 volts, and 13.8 volts is the standard. I did try other regulators ic's ie 5 volt plus a variable pot, but 12 seem to be the one that would output more current to the pass transistors and was more stable to use diodes in the common leg rather than a pot. There were a couple of ways to hook up the ic regulator in a regulator circuit, but I chose to wire it up with the output going to the base of the pass transistors and the input was through a small resistance. I removed the old base resistor that was original. so current could not flow if the circuit failed. It would kill the regulator ic first before the pass transistors shorted internally. I know as it happened to me on an ic that I tried earlier with less current rating. Anyhow, I doubt very much that the output is 14.6. I think his meter or whatever he is using is fouled. I designed it for 13.8 volts, the panel meter reads 13.8, and my meter when I designed it read 13.8 volts. I dont have the unit in front of me to resolve the question is it really 14.6 volts. If it is and the panel reads 13.8 then my panel display is wrong. It is actually measuring the output at the output in my circuit. Most electrolytic caps in a radio are 16 volts, I suppose most other parts are regulated in which case if I go over the standard voltage by too much, the internal radio regulators etc. could overheat and the only other thing I can see would be the final amplifiers, audio and rf would be overheating due to mismatching in the output, as the radio is designed with a certain specified voltage to maintain that swr match specified in their specs. I am told that the voltage on the electrolytic caps mean the running voltage and not the maximum voltage. This I do not know for a certainty but makes sense as in the old days the electrolytic power supply caps were rated at 150 volts in a cheezy direct power supply taking 110 volts ac and up-ing it to 150 to 160 volts dc. So I agree with the running voltage. but seriously I think 16 volts would be the limit for me, 11.5-14.5 a normal range. I am hoping to see this power supply again to know for sure what it is. I dont think my design failed. It's that some people will always question the unit since it wasn't a factory job. The person also stated that he wanted more current. Saying the amps on the panel doesnt read what he thinks he needs. Could I make it show more amps. I said No. That amps was something that is drawn from the power supply depending on the circuit. I said you cant push amps or have it sitting at 15 amps continuously, and the reason the meter doesn't show more is that it cannot change fast enough. It is not reading the peaks, but assured him it was working to potential. really useful for about 100 watts steady and maybe upwards to about 150 or so ssb. I just dont get it sometimes, do all you can do, put hours of effort into a project and the end result is, if the person doesn't know about electronics, they can somehow get the wrong ideas and try and trash the thing saying it doesn't work, when in fact it works better than the original. Why I would rather just build projects to satisfy me.


    As it turns out the person changed the battery in his meter as per my request and magically it reads 13.8 volts. Imagine that? The panel meter is right.
    Thanks for your comments.
     
    Last edited: Dec 6, 2014
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