How do you regulate a 150 amp power supply.

[Enterprise312ok]

One of the locals I talk to every morning purchased a 150 amp transformer power supply to run his linear amplifiers.
The problem is this power supply puts out 20 volts and we need to get it regulated down to around 15 volts.
What is the best way to do this?

 

[sp5it]

Show us schematic of that PS

 

[AudioShockwav]

Show us schematic of that PS

If it is like the majority of unregulated CB style of supply it will be a big transformer, several bridge rectifiers on a heat sink and a couple large caps to filter out some of the ac ripple.
And no schematic included.
It will require building a regulator circuit with pass transistors to handle the current.
Most of them float about 19-20 volts unloaded and " pull down" to 15 or 16 volts under load.
I have seen these in class c base amps like x-force and the like.
This is why they are cheap compared to regulated supplies.
Here is a 30 amp circuit for reference.

73
Jeff

 

[Captain Kilowatt]

I despise and refuse to use an unregulated power supply.

 

[DoctorAudio]

20 volts DC, no-load doesn't give enough headroom to regulate to 15 volts. You would need a transformer that floats (rectified and filtered) around at least 25 volts DC with no load. (transformer that delivers 18 volts AC, RMS)

 

[Captain Kilowatt]

20 volts DC, no-load doesn't give enough headroom to regulate to 15 volts. You would need a transformer that floats (rectified and filtered) around at least 25 volts DC with no load. (transformer that delivers 18 volts AC, RMS)

And you do not want the unregulated voltage to be any higher than necessary because the pass transistors in the regulator circuit must dissipate heat based on voltage drop across them and total current thru them. My Tripp-Lite PR-40 is rated at 32 amps continuous and 40 amps peak. The pre-regulator voltage is about 22 volts. It is set at 13.8 volts output and runs quite cool. The upgraded filter capacitor I installed is 100,000 microfarads so it helps with voltage sag on the pre-regulated side as well.

 

[AudioShockwav]

It is set at 13.8 volts output and runs quite cool.

We always set our supplies at 13.8 per the service manual in base radios in the past, the trend now is everyone wants 15 volts.
Added stress and heat for very little gain IMHO.
I recently fixed a TRC 455 for a friend that had been turned up on the internal supply to 14.9 volts to try to get a extra watt.

73
Jeff

 

[Captain Kilowatt]

We always set our supplies at 13.8 per the service manual in base radios in the past, the trend now is everyone wants 15 volts.
Added stress and heat for very little gain IMHO.
I recently fixed a TRC 455 for a friend that had been turned up on the internal supply to 14.9 volts to try to get a extra watt.

73
Jeff

2N3055 pass transistors are a LOT cheaper than a pair of finals for a 100 watt amateur radio.

 

[Onelasttime]

I would never use an unregulated supply on a radio especially!!! 13.8 has been the standard on most supplies that are not server power supplies for decades.

Back in the old days like when I was in H.S. and you could buy Toshiba 2SC2879's for $9 to about $12 in bulk knowing that they could stand up to "volting" it was forgivable. Not true today!

You will definitely want to build a regulating circuit.

So cool someone had one handy to put up as an example.

Outside of tube amps I only use switcher's today mostly for servers for all my radio hobby needs.

 

[Naysayer]

And you do not want the unregulated voltage to be any higher than necessary because the pass transistors in the regulator circuit must dissipate heat based on voltage drop across them and total current thru them. My Tripp-Lite PR-40 is rated at 32 amps continuous and 40 amps peak. The pre-regulator voltage is about 22 volts. It is set at 13.8 volts output and runs quite cool. The upgraded filter capacitor I installed is 100,000 microfarads so it helps with voltage sag on the pre-regulated side as well.

Capt. KW,
I'm shopping for replacement caps for my PS running an Astron VLS-35m board (28v). Current caps are old & wrong value (from a HiFi filter Board). Astron diagram specifies 21k at 50v. 100k value improves? Turn-on surge with higher capacitance may need a step-start to reduce stress on components. typical surge exceeds 10A on start.
Most articles I find about filter caps are from HiFi land.
neil
NYC

 

[Dr. Frankenstein]

Don't know if this will help any:

Astron Power Supply Index Page

73

 

[Naysayer]

Hi thanks for Reply. Repeater-Builder webiste very good. Diagram for the VLS-35m states 21k which I presume is (21000uF). When I read 100k in the OP above, I noted the difference given my PSU rebuild effort. Been reading about filter cap selection process. Aside from the scary looking math formula I see other considerations. Full wave or Half wave rectifier.

Found website that states optimal capacitance for various voltages for Switched supplies of different capacity:

Amount of capacitance on the power supply's output

High frequency switch-mode power supplies, such as Magna-Power's MagnaDC power supply line, use large banks of electrolytic capacitors to filter output ripple. The amount of capacitance used varies by the unit's peak output voltage rating. Table 1 provides the standard amount of output…

magna-power.com

I'm going to follow that.
Shopping for 6 new caps now.
Cannot believe the price increases.

neil

 

[Naysayer]

Learned formula to determine best capacitance value for AC to DC power supply from YouTube video:

I watched many vids before I found this plain-spoken vid that explains it with examples.
Schematix is YouTube Username of Creator.

Anyone trying to figure out how much capacitance is needed on a home-built PS watch this video.
neil, NYC