Ok, I’ll come right out and say it: I think the HP ESP120 is one of the best 50V power supplies you can get for home brew LDMOS RF Amplifiers. There, I said it.
First, there’s the price. If you stalk eBay and wait for a seller that has a bunch of these to sell, you can get these for $20-$40 each, shipped. So, the price is right.
With that checkmark out of the way, here are some of the good things about the ESP120.
The ESP120 is made like a tank and designed to produce 51.4V at up to 57A, continuously, 24/7.
Given that, almost no Amateur Radio mode, other than AM, even begins to exercise the ESP120 at all. It just sits there, basically idling, 95% of the time.
Rated at 2950W maximum output, even if your amp has a lousy 70% efficiency and you are outputting legal limit 1500W, you’re only using 72.6% of the maximum output of the ESP120, on peaks.
The ESP120 is easy to enable and turn on.
Probably enough said, but with a simple jumper and 240v AC, you’re up and running. Here’s how to enable.
You can silence the fans!
In case you have not experienced it, 50V server farm power supplies are as loud as a vacuum cleaner, and the pitch of the whine is way more irritating. In most cases, you can do very little about this because most server supplies us PWM to control the fans so the fan speed is reported back to the MCU. So if you slow them down, the supply will switch into standby mode to protect itself. If your fans have more than two wires, it’s a PWM fan.
The ESP120 uses a good ole 2-wire fan so you can slow them down with resistors to near-silent and the supply keeps on supplying. It also continues to run cold in Amateur use. You could probably replace the fans altogether with resistors and be fine.
The ESP120 is fully regulated and “smart.”
Let’s face it, fully regulated power supplies capable of 2950W are pretty rare. And having full regulation while doing things like SSB and CW is a great benefit for linearity and IMD, as the supply is not sagging all over the place.
Also, I call this supply “smart” and what I mean by that is it’s always saving your butt. If it detects arcing, extreme load changes (like a short), or takes on too much RF, and who knows what else, it instantly and silently moves into standby mode. I once had a loose 50V line with the screw on my terminal strip not fully tightened. The ESP120 kept kicking out because it “knew” that load it was seeing was just too erratic.
Here are some photos:
Hello Rob , I have been on facebook for some time and just found your page , good info. for us amateur builders , I have 2 new ESP 120 supplies and am wondering if I should hook AC gnd. , DC neg and case together , have had them running and looks like very little potential between all 3 , much interested in your 50v step down circuit for bias. etc. Thanks , Phil W8KLK
Phil,
Nice to meet you!
I did not hook AC Ground and DC Ground together. But as you noted, perhaps all three are already together.
Here’s my 50V to 14V regulator.
Super simple and reliable little regulator for this specific purpose.
I need to get the schematic up and I’ll try to do that this weekend.
Thanks!
Hi Rob,
Nice job, great site – I just bought two PSU to use with my amplifier. I also want to make the little regulator board. What software did you use to design it?
73,
Robert VE7ZN
Robert,
Thanks for the comment. I used Altium Designer which is way overkill for this tiny board. But I work for Altium and have access.
Let me know if I can help.
Thanks Rob, W8KLK
Hello, Phil.
I also have the ESP120, and I like how it works. Excellent power, good quality and “smooth start”.
But I want to try to increase the output voltage. From 50.5 to 53.5 V, you can change the small trimmer of the resistor near the “+” output. The trimmer is placed on a small “SEC CTRL BRD”. More than 57.5 V you can increase by updating “SEC CTRL BRD” (replace the resistor that is next to the trimmer), but after 57,5 V the overvoltage protection is activated. Maybe someone knows how to increase the level of overvoltage protection? ( I know that I need to change the filter capacitors if I want more than 60 V 🙂 )
Roger all that. I’ve sen that mod somewhere before on the internets. I just live with the 51.4V.
you have to adjust the reference voltage in the crowbar part of the protection circuit.
I disable to reference voltage on one supply and let one supply do it for both supplies.
Less issues with fluctuation this way.
Hi, Rob – Have you ever measured the ripple on the ESP-120? I’m curious.
73,
W9IP
I have not. That would be an interesting measurement but I’ll be the first to admit that I’m not a SMPS designer.
I instead spend all my spare cycles on TLT design and testing.
So for now, in the power supply department, I just take what the ESP gives me. 🙂
Can you turn the output voltage down any? I need 48 volts dc to power a twt high voltage supply.
Maybe. I’ve seen web sites talking about a pot in there somewhere that has an effect.