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I wanted to share what I used for a power supply for my freshly minted uBitx.? Just completed today and made my first contact SSB on 20M - 1200 Miles using 1/4 WL Vertical!
For power supply I used an ATX power supply from an old desktop PC case.? You can wire the green wire off of the 24 pin atx connector to ground to power on the supply.? You get 12V from the yellow wire.
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Dear James,
I tried with my old PC power supply. I am getting 11.6 between Yellow and Black .? On load it drops down to 11.3V.? Any info to modify to get 13.8V ...73 Rajendran,VU2SMM
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Rajendran,VU2SMM
If you look at the schematic of most older PC power supply units you will find that they almost
all use the same PWM IC to control output voltage.? There should be two resistors (one from +12V
and one from +5V, that join with a third resistor to ground at a pin on the PWM chip.? The combination
of the 12V and 5V inputs generate usually 2.5 volt potential at this PWM input pin-1.? That is matched
with a 5V / 2 = 2.5V reference connected to the opposite input of the error amplifier at pin-2.?
Matching of these two input voltages is used to regulate the PWM output and thus the 12V and 5V
levels.?
The PWM chip is usually a TL494 or something very similar.? The three resistors connect to pin-1
and control output voltages.?  By re-computing the value of the 12-volt resistor and disconnecting the 5V resistor it is usually
possible to make the 12V output be close to 13.8 or something similar and remove regulation
of the +5V.
You may notice that the 5V AC windings and the 12V AC windings on the transformer are in series.
This means that your total current output can be close to the original 5V rating as long as the 12V
rectifier diodes will stand that amount of current.? In some cases it is possible to interchange the
5V diodes with the 12V diodes to provide more current handling capacity.? Info from the diode
datasheet will tell you what the maximum current and PIV might be for your particular diodes.
It may be necessary to add more filter capacitance to this new 13.8 volt output in order to minimize
switching transients and LF ripple.??
PLEASE BE VERY CAREFUL WHEN WORKING WITH PC POWER SUPPLIES.? THE AC LINE
INPUT IS RECTIFIED TO 360 VOLTS DC WITH NO GROUND ISOLATION FROM THE AC MAINS.
IF NOT VERY CAREFUL YOU COULD EASILY ELECTROCUTE YOURSELF.
Arv? K7HKL
_._
On Sat, Jan 20, 2018 at 11:32 PM, Rajendran Mayilsamy <mrajsuba@...> wrote: Dear James,
I tried with my old PC power supply. I am getting 11.6 between Yellow and Black .? On load it drops down to 11.3V.? Any info to modify to get 13.8V ...73 Rajendran,VU2SMM
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Già visto e messo da parte, ma i switching creano disturbi nello "shak" dei radioamanti. Per questo li ho messi a riposo!
Il 21 gennaio 2018 alle 8.16 Arv Evans <arvid.evans@...> ha scritto:
Rajendran,VU2SMM
If you look at the schematic of most older PC power supply units you will find that they almost
all use the same PWM IC to control output voltage.? There should be two resistors (one from +12V
and one from +5V, that join with a third resistor to ground at a pin on the PWM chip.? The combination
of the 12V and 5V inputs generate usually 2.5 volt potential at this PWM input pin-1.? That is matched
with a 5V / 2 = 2.5V reference connected to the opposite input of the error amplifier at pin-2.?
Matching of these two input voltages is used to regulate the PWM output and thus the 12V and 5V
levels.?
The PWM chip is usually a TL494 or something very similar.? The three resistors connect to pin-1
and control output voltages.?  By re-computing the value of the 12-volt resistor and disconnecting the 5V resistor it is usually
possible to make the 12V output be close to 13.8 or something similar and remove regulation
of the +5V.
You may notice that the 5V AC windings and the 12V AC windings on the transformer are in series.
This means that your total current output can be close to the original 5V rating as long as the 12V
rectifier diodes will stand that amount of current.? In some cases it is possible to interchange the
5V diodes with the 12V diodes to provide more current handling capacity.? Info from the diode
datasheet will tell you what the maximum current and PIV might be for your particular diodes.
It may be necessary to add more filter capacitance to this new 13.8 volt output in order to minimize
switching transients and LF ripple.??
PLEASE BE VERY CAREFUL WHEN WORKING WITH PC POWER SUPPLIES.? THE AC LINE
INPUT IS RECTIFIED TO 360 VOLTS DC WITH NO GROUND ISOLATION FROM THE AC MAINS.
IF NOT VERY CAREFUL YOU COULD EASILY ELECTROCUTE YOURSELF.
Arv? K7HKL
_._
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I'm looking at this 12v 30a/360w power supply that was suggested by someone recently.? It has adustable output and runs a whopping $21.49 delivered from Amazon.? If it doesn't suck, it'll be handy to have around.
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I bought something that looks pretty much exactly the same.? Be advised, as soon as you put any load on it, the fan will come on.? I just moments ago put a load on mine (a CB radio under TX), and the fan noise increased substantially.? I used the CB to test it as I recall previously using the PS and having it go to 16-18V under load (hence the CB- didn't want to risk my good stuff....).? This time it stayed at 12.8 or so.? YMMV.? Aloha, Steve WH6ST
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There is a company MegaWatt in Santa Clarita California that markets a very similar looking line of power supplies, but they are heavily filtered and regulated. They are twice the price as what you link, but I can personally attest to their quality. There are many knock-off clones marketed from China that are junk from a radio use standpoint.
Thomas Noel
KF7RSF
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Make sure the brand is mega watt and not the cheap Chinese knockoff. The cheap ones don’t have proper RF filtering and they use cheap fans.?
The fan on my mega watt 26amp was noticeable too and I complained. They sent me a fan that was quieter, less cfm’s but it did the trick. And I’ve been using it with a 100W radio doing digital modes and it hardly works up a sweat.?
Joe
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On Jan 21, 2018, at 1:10 PM, Rob Snow < rsnow@...> wrote: I'm looking at this 12v 30a/360w power supply that was suggested by someone recently.? It has adustable output and runs a whopping $21.49 delivered from Amazon.? If it doesn't suck, it'll be handy to have around.
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Dirty DC made for striplights (led`s) noisy as hell I would guess !
Dave
On 21/01/2018 18:10, Rob Snow wrote:
toggle quoted message
Show quoted text
I'm looking at this 12v 30a/360w power supply that
was suggested by someone recently.? It has adustable output and
runs a whopping $21.49 delivered from Amazon.? If it doesn't
suck, it'll be handy to have around.
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I HIGHLY suggest one of these:?
I put one into a box with volt and amp meters. I also added a dual USB port to it for charging stuff.? The ONLY noise I get from it is actually from the switching regulator in USB module I used and that only happens when the port is in use. 73 de AA9GG
On Sun, Jan 21, 2018 at 2:13 PM, David Lacey via Groups.Io <g4jbe@...> wrote:
Dirty DC made for striplights (led`s) noisy as hell I would guess !
Dave
On 21/01/2018 18:10, Rob Snow wrote:
I'm looking at this 12v 30a/360w power supply that
was suggested by someone recently.? It has adustable output and
runs a whopping $21.49 delivered from Amazon.? If it doesn't
suck, it'll be handy to have around.
-- Paul Mateer, AA9GG
Elan Engineering Corp.
NAQCC 3123, SKCC 4628
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I'm a bit confused over operating voltage for BTX40.? Understanding that the PA can be run up to higher voltages, and the main board is spec'd at "12V", is it proper and safe to run the main at 12.6V- typical battery voltage?? How about 13.8V if, say, plugged into a running automobile system?? Thanks, Aloha, Steve WH6ST
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Many here run it at 13v and more.
But at 12v R141 is already cooking, over its 1/4W rating.
Q13 is also running hot.
Going above 12v makes it worse.
Several reports of having R141 open up, if it does then replace it with a 1/2W 10 ohm resistor.
Q13 could be replaced with a leaded version of the 2n3904, which can dissipate more power than the mmbt3904 that is normally stuffed.
I'd recommend a low dropout 12v linear regulator, such as the LT2940CT-12,
power to the IRF510 kept separate.?
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On Thu, Jan 25, 2018 at 01:14 pm, Steve Thatcher wrote:
I'm a bit confused over operating voltage for BTX40.? Understanding that the PA can be run up to higher voltages, and the main board is spec'd at "12V", is it proper and safe to run the main at 12.6V- typical battery voltage?? How about 13.8V if, say, plugged into a running automobile system?? Thanks, Aloha, Steve WH6ST
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There should be some tolerance like 10% +/- ?on the voltage applied that shouldn’t hurt or hinder it. My Yaesu takes 13.8v by t 12v on the line works just as well?
Joe
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On Jan 25, 2018, at 4:14 PM, Steve Thatcher < stevep2p@...> wrote: I'm a bit confused over operating voltage for BTX40.? Understanding that the PA can be run up to higher voltages, and the main board is spec'd at "12V", is it proper and safe to run the main at 12.6V- typical battery voltage?? How about 13.8V if, say, plugged into a running automobile system?? Thanks, Aloha, Steve WH6ST
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Good to know your Yaesu is fine with 13.8v.
Unfortunately, R141 on a stock Bitx40v3 is not.
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On Thu, Jan 25, 2018 at 01:44 pm, Joe Puma wrote:
There should be some tolerance like 10% +/- ?on the voltage applied that shouldn’t hurt or hinder it. My Yaesu takes 13.8v by t 12v on the line works just as well?
?
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Well that definitely is the power requirement for the Yaesu but I was running my bitX40 On a computer power supply that I tweaked to 13.8 V And it was running fine, no issues. I even was doing digital modes with it, FT8 specifically. I’ll make sure I use the proper power requirement for my micro bitx but as a real world example the bitx40 did run on 13.8v and finals really didn’t feel hot at all. Maybe I was lucky.?
Joe, KD2NFC?
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On Jan 25, 2018, at 4:51 PM, Jerry Gaffke via Groups.Io < jgaffke@...> wrote: Good to know your Yaesu is fine with 13.8v. Unfortunately, R141 on a stock Bitx40v3 is not. On Thu, Jan 25, 2018 at 01:44 pm, Joe Puma wrote:
There should be some tolerance like 10% +/- ?on the voltage applied that shouldn’t hurt or hinder it. My Yaesu takes 13.8v by t 12v on the line works just as well?
?
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I have 3 bitx 40 v3 and all run at 13.8 v
I run them almost all the time with ft8 or jt65
I have oversize heat sinks on each.
Output around 8watts
Powersupply is well filtered plus extra filters inside the rig
Joe
VE1BWV
On Thu, Jan 25, 2018, 6:09 PM Joe Puma < kd2nfc@...> wrote: Well that definitely is the power requirement for the Yaesu but I was running my bitX40 On a computer power supply that I tweaked to 13.8 V And it was running fine, no issues. I even was doing digital modes with it, FT8 specifically. I’ll make sure I use the proper power requirement for my micro bitx but as a real world example the bitx40 did run on 13.8v and finals really didn’t feel hot at all. Maybe I was lucky.?
Joe, KD2NFC? On Jan 25, 2018, at 4:51 PM, Jerry Gaffke via Groups.Io < jgaffke@...> wrote: Good to know your Yaesu is fine with 13.8v. Unfortunately, R141 on a stock Bitx40v3 is not. On Thu, Jan 25, 2018 at 01:44 pm, Joe Puma wrote:
There should be some tolerance like 10% +/- ?on the voltage applied that shouldn’t hurt or hinder it. My Yaesu takes 13.8v by t 12v on the line works just as well?
?
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Steve
AA9GG
