Construction details of A Complete 13.8 Volt, 50 Amp Power Supply

cathead

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Another thing about SMPS, the electrolytic capacitors have a definite life so don't expect them to last forever.
A regular transformer supply will out live most of us if cared for properly and easier to repair should
something go wrong.
 

charles.hardt

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Not to rain on the parade, but more about offering alternatives: If you're building one for fun/education/a hobby, fine, otherwise, a switcher supply with the same specs is $35 on Amazon.
I am an amateur radio operator and own a 30 watt switching amplifier, which I paid a lot more than $35.00 for, but that is really not my point. SWPS are very noisy RF sources, interfering with everything. You can do a lot to quiet them down, toroid suppressors on every wire going in and out of the SWPS, but never totally get rid of the interfering noise, especially when you are trying to hear that weak one. The SWPS technology will get better with time, but it is not there yet. I am going back to an analog power supply. I ran an analog PS for better than 20 years, before it gave up the ghost. Replacement parts not available, ICs unidentifiable (Chinese). I replaced it with my present day SWPS. I am in the process of ordering parts for this analog PS design. It looks good on paper. I enjoy building and I have not seen a high current analog PS for sale, but then again I really haven't done much searching.

73 all,
Charlie, N2PKW
 

charles.hardt

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I am an amateur radio operator and own a 30 watt switching amplifier, which I paid a lot more than $35.00 for, but that is really not my point. SWPS are very noisy RF sources, interfering with everything. You can do a lot to quiet them down, toroid suppressors on every wire going in and out of the SWPS, but never totally get rid of the interfering noise, especially when you are trying to hear that weak one. The SWPS technology will get better with time, but it is not there yet. I am going back to an analog power supply. I ran an analog PS for better than 20 years, before it gave up the ghost. Replacement parts not available, ICs unidentifiable (Chinese). I replaced it with my present day SWPS. I am in the process of ordering parts for this analog PS design. It looks good on paper. I enjoy building and I have not seen a high current analog PS for sale, but then again I really haven't done much searching.

73 all,
Charlie, N2PKW
Correction: I.....own a 13.8 Volt 30 Amp......
73,
Charlie,N2PKW
 

tq60

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Poor man's clean power supply can be very simple.

Regulation is a must.

High current for intermittent duty also.

A 30 amp power supply cansuppy 30 amps but usually normal output with a transmitter preset is maybe 1 amp at full receive volume with say 30 amps when transmitting.

One can build a small power supply using a simple 12 volt regulator in a 3 leg package, 7812?

These are goid for maybe 1 amp, parallel them to get more for maybe 2 or 3.

Next add a couple diodes in series with the ground pin to elevate the ground to about 1.3 above ground.

Output now 12 plus the 1.3, 13.3 volts.

Now get a couple VRLA batteries and connect them to the power supply with proper fuses.

Now battery backed output capable of additional output for intermittent duty of the transmitter and power very clean.

The regulators can be isolated with chokes and a shield if additional cleaning needed but not likely.

Output loads and duty cycle determine battery size.

Neumar and Astron both have power supplies with internal batteries that work on this principal, sold as battery backed power supply but battery allows for surges in excess of power supply output.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

charles.hardt

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My friend you bring back memories. When I first became a ham I bought a 2 meter FM transceiver kit, back in early 90s, about 25 watts out, requiring 12 volts with about 3 amps. I spent my money on the kit, which was cheaper than new assembled radio. I did not have money for a higher current output power supply. I had a wife and three young kids at the time. I still have the wife (She is a keeper), but my kids are now married, on their own and providing grand kids (Hoping to get at least one ham out of the crew). Not a whole lot of excess money for my hobby back then. I had an old regulated radio shack 12 Volt 1 amp supply. I had a 12 Volt Lead Acid battery. I do not remember where I got the battery from, but used that in parallel to my regulated power supply. The battery/Power Supply worked great for years, even as I transitioned to 100 watt HF gear. Lead Acid Batteries handle the shock of loafing along at less than an amp when receiving to the instantaneous requirement of 10 amps when transmitting at 100 watts very well. But here is the problem with modern HF RF Power Out amps. To my knowledge all Japanese and US Ham radio manufacturers use the same basic FET RF output designs, with FETs that are deigned to normally operated at 50 v0lts in "12 Volt" portable gear. Like most ham operators all my gear is 12 volts, so as to be used in a portable operation. Only the top of the line desk style Ham Gear have built in 120/240 Volt Power Supplies biased for there finals at 50 volts DC. 12 volts is at the bottom end bias for the FET's to produce linear outputs with no unwanted RF products. Even though our gear is by convention called 12 Volt devices, their cleanest output is around 13.5 volts while transmitting. Getting below 13 volts can be problematic and with lead acid you will be around 12 volts at best. I have Lithium Iron Phosphate batteries that have higher cell voltages than lead acid, they are expensive, but they are an option and I am considering your design. It will come down to cost. I already have two transformers with secondary's at 18 Volts at 50 amps and one at 30 amps. I do need to ensure they are good. Both are probably 20 years old. I am pricing out the rest of the components as we speak. Sorry for being so wordy, but it helps for you to see where I am coming from. I will let you know my final decision. I am an experienced builder and have done a number of scratch builds. I enjoy the build process, including scratch building the frame and cabinet.
73,
Charlie, N2PKW
 

charles.hardt

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Continued comment to above concerning floating the power supply above ground with diodes in series I really have to analyze your comment closer. Diodes typically for small signal have a .7 volt drop and for higher current diode's have over a volt drop. I don't see the voltage source for the additional 1.3 volts. We frequently use diode isolation between our VRLA batteries at our solar powered emergency communication sites in support of our state's FEMA Hurricane response. The diode isolation between batteries causes unusable voltage drops, but necessary to prevent current flow between batteries. So we use DC to DC Buck Converters to bring voltages up to 14 volts. They tend to be somewhat inefficient and RF noisy. But this world is all about compromise.
 

brino

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Continued comment to above concerning floating the power supply above ground with diodes in series I really have to analyze your comment closer. Diodes typically for small signal have a .7 volt drop and for higher current diode's have over a volt drop. I don't see the voltage source for the additional 1.3 volts.

Hi Charles,

I believe @tq60 was talking about the ability to apply a voltage offset to the ground pin (and therefore the internal voltage reference of) the ubiquitous 7812 family of fixed voltage regulators.

ScreenShot210.jpg

In fact these "fixed" voltage regulators can be used as variable regulators by applying a variable bias voltage to the ground pin.

ScreenShot211.jpg

ScreenShot212.jpg

The first two images above are straight from the ST datasheet here:
https://www.st.com/resource/en/datasheet/l78l.pdf
The third one is from here:
https://www.st.com/resource/en/datasheet/l78m.pdf

-brino
 
Last edited:

tq60

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Exactly...

The diodes usually bias at 0.6 volts.

Stack 2 and now 1.2 ish.

Raises the ground reference 1.2 so output is 12 volts above reference.

Float voltage for lead acid is 2.25 per cell.

12 volt battery is happy at 13.5.

If higher is needed stack them up.

Or build a good filter


Sent from my SAMSUNG-SM-G930A using Tapatalk
 

slmnklyc

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Hi, I really didn't understand this relay connection..
Does the "Live In" connected to "NC" pin of the relay?
Live In>>NC
COM >>SW2 & R15 & Line out to T1
NO pin not conected to anything
??
Thank you!
 

petcnc

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Hi, I really didn't understand this relay connection..
Does the "Live In" connected to "NC" pin of the relay?
Live In>>NC
COM >>SW2 & R15 & Line out to T1
NO pin not conected to anything
??
Thank you!
Follow the connection diagrams below and it will be clear
 

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