HP ESP 120 Power Supply

HP ESP120 Power Supply

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:

 

 

HP ESP120 Output Specifications

 

My ever growing supply of supplies…any time I see these in the $20-30 range, shipped, I can’t resist..

Comments

51 responses to “HP ESP 120 Power Supply”

  1. Phil Lohiser Avatar
    Phil Lohiser

    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

    1. N4GA - Rob Avatar
      N4GA – Rob

      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!

      1. Robert Dale Avatar
        Robert Dale

        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

        1. N4GA - Rob Avatar
          N4GA – Rob

          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.

  2. Phil Lohiser Avatar
    Phil Lohiser

    Thanks Rob, W8KLK

  3. Slava, VE7LWW Avatar

    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 🙂 )

    1. N4GA - Rob Avatar
      N4GA – Rob

      Roger all that. I’ve sen that mod somewhere before on the internets. I just live with the 51.4V.

      1. Bill Avatar
        Bill

        message me and i will send you a video K4KYB
        k4kyb@hoperadio.us

    2. Bill Avatar
      Bill

      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.

    3. Nigel Tegg Avatar
      Nigel Tegg

      Hi Slava,

      Do you have a diagram/procedure on how to get into these ESP120’s ?
      I have seen it splits into 2 halves with one large and one small face each.

      Regards, Nigel.

  4. Michael R Owen Avatar
    Michael R Owen

    Hi, Rob – Have you ever measured the ripple on the ESP-120? I’m curious.
    73,
    W9IP

    1. N4GA - Rob Avatar
      N4GA – Rob

      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. 🙂

  5. Gregr Avatar
    Gregr

    Can you turn the output voltage down any? I need 48 volts dc to power a twt high voltage supply.

    1. N4GA - Rob Avatar
      N4GA – Rob

      Maybe. I’ve seen web sites talking about a pot in there somewhere that has an effect.

      1. Bob Stout Avatar
        Bob Stout

        Does anyone know how to move birdies with these supplies? I have a birdies that starts out cold on 1.905 mhz and gradually creeps up to 1.906 mhz. Right where I want to operate. I can get it down using my notch filter but it’s still pretty annoying.

        I know there are a couple of pots in the 253232 but I haven’t tried turning them.

        Anyone know how to move the birdie?

        Thank you,

        Bob

        1. N4GA - Rob Avatar
          N4GA – Rob

          Bob,

          Don’t know how to change the switching frequencies of the SMPS but you might have some luck with the right capacitor across the output. Try the good ole .01uF, or even better parallel like .01, 0.047, 0.1, 1.0.

          Might work! 73s

          1. Bob Stout Avatar
            Bob Stout

            Hi Rob,

            I tried using a variety of caps and toroids (43 mix) to no avail. It’s my understanding MFJ has a control on one of there smps just for this purpose. In the event a birdie ends up exactly where you don’t want it.

            Bob

          2. N4GA - Rob Avatar
            N4GA – Rob

            Bob,

            This is definitely interesting! I just took a look at 1.906 here and strangely enough, I do not have anything there. However, I do have them at ~1.863 & ~1.962.

  6. Bob Stout Avatar
    Bob Stout

    Rob, that’s interesting alright and thank you for checking. I have two of these 253232’s and they both have the birdie on 1.906 mhz. I hope someone will chime in with more info.

    Bob

    1. Bob Stout Avatar
      Bob Stout

      Has anyone found a schematic for these? I have to say I’m very impressed with these supplies. Especially after slowing the fans down with Rob’s 15 ohm resistor mod. These supplies rock!

      Bob

      1. N4GA - Rob Avatar
        N4GA – Rob

        Bob – I’ve never seen a schematic for them. I agree, these things are impressive. I’ve also found that they will deliver much more than 50A with zero issues. Not sure how much more but I can peg my 50A Simpson and it sounds like it’s delivering 10A. Zero difference. Impressive!

  7. Rick Tyre Avatar
    Rick Tyre

    The birdies Exist especially on 80….every 97Khz and i`ve tried every trick in my bag to shut it up to no avail …One gets real close to where I normally operate (centered on 3620)..There HAS to be a way but so far no amount of filtering i`ve come up with has worked…S9+ and about 2kc wide with either DC lead connected.

    1. N4GA - Rob Avatar
      N4GA – Rob

      Mine is at 3628. Very faint and has no power. My noise floor is S5 and if I go over this faint signal its not above S5. But it is noisy and if I operated right there that would be a pain. I also have a 10 year old 12v SMPS Astron that makes the same signal in the exact same place. I have a FLEX here so easy to see these things.

  8. Phil Desrosiers Avatar
    Phil Desrosiers

    Nice! Is there a version for 120V mains?

    1. N4GA - Rob Avatar
      N4GA – Rob

      Phil,

      Not that I’m aware of. Would be nice though.

      1. Bob Stout Avatar
        Bob Stout

        As I’ve been using my power supply over the last several months, my birdie that was on 1.906 mhz has been slowly migrating south. It is now on 1.901 mhz where it is out of my way thankfully.

        Bob

        1. N4GA - Rob Avatar
          N4GA – Rob

          Mysterious little buggers these SMPS! I’ve seen my faint birdies drifting around as well. I wonder what the purpose would be for them to vary at all!

          1. Bob Stout Avatar
            Bob Stout

            I may have spoken too soon. Much to my dismay, my 160 meter birdie has changed direction and is slowly heading back up the band.

            None the less, I am so impressed with the performance of these power supplies, I can easily live with their idiosyncrasies.

  9. Gary Johnson Avatar

    Are there any special precautions when paralleling two ESP120’s. I thought I saw a link talking about a choke to eliminate the two supplies bucking one another.

    1. N4GA - Rob Avatar
      N4GA – Rob

      Gary – I’ve never had the need to parallel two of them. But my bud KF8OD has and you can see it here.

      1. Nigel Tegg Avatar
        Nigel Tegg

        What I need is a procedure/diagrams on how to get into these ESP120 PSU’s to make the modification to the voltage adjust board! (and the fan speed reduction at the same time)

  10. Gary Johnson Avatar

    Thanks for the information. Built a remote box to control the power to the power supplies and a switch to enable the supplies.

    Regards
    Gary
    K0GWA

    1. N4GA - Rob Avatar
      N4GA – Rob

      Sweet! I never seem to get around to any power supply related improvements. I keep working on the pallets.

    2. Roger Klein VE3MVL Avatar
      Roger Klein VE3MVL

      Gary, saw your pictures, so I am grovelling for some suggestions for safe controlling of the amperage down to about 25 or 30 amps from the 48a or so using a fet or a direct switch or variable pot of some kind. Wondered if you might be attempting the same kind of thing? I don’t have a PS yet but also wondered if you had a peek inside on the big caps, i wouldn’t expect there might be bleed resistors.?

      1. N4GA - Rob Avatar
        N4GA – Rob

        Roger,

        The PS won’t deliver more current than demanded by the pallet. So if you want to do current limiting, I would put that on the pallet. Lots of people have done this in lots of different ways.

        I don’t do it at all..

        Rob

  11. Glen K4KV Avatar
    Glen K4KV

    Question: is there a way, through the control pins, to shut off the input power to the power supply? I just tried the 3 pin thing, and it only shuts off the voltage. I bought a Meanwell SE-1500-48 for my home brew 2M LDMOS amp, and the fans are noisy, and the Meanwell puts broad-band noise on the 2M receiver. The Meanwell has control pins, but, alas, only turns off the output voltage as well. With the HP supply powered up near the 2M receiver, I hear NOTHING!
    What I did on the Meanwell was to add two opto-block AC relays and a 240 wall wart so I could run tiny little lines to the amp and use a front-panel on/off switch…
    73
    Glen K4KV

    1. N4GA - Rob Avatar
      N4GA – Rob

      Glen,

      Can’t speak about the Meanwell, but as far as I know, there’s no way to basically completely shut off the ESP120 using the control pins. Some have talked about turning it on and off with like a solid state relay, but it takes too long to boot up and come on. Mine takes 7 seconds.

      I chose to quiet the fans and leave it on while I’m operating.

  12. Glen K4KV Avatar
    Glen K4KV

    Rob,
    Just put the modified (fan) HP supply on the 2M LDMOS amp. It is unusable because of
    rx noise, S6. The Meanwell is below S0, but still noticeable.
    I wrapped the power leads in a Type 31 core, then a Type 43 core (5T) and did not help
    the noise at all.
    Funny, since the HP supply running next to the amp makes zero noise, plugging it in
    makes it BAD!
    🙁
    73
    Glen K4KV

    1. N4GA - Rob Avatar
      N4GA – Rob

      Well that no bueno!!

      I don’t have 2M here so I’ve never “heard” the ESP up on 144Mhz.

      Did you try different caps to ground on the positive lead? If it’s really really bad that prob won’t fix it, but may as well experiment.

      1. Glen K4KV Avatar
        Glen K4KV

        Rob,

        Ordered a bag of 100 Type 31 beads, 1/4″ ID and 3/4″ OD perhaps 3/4″ long.
        Put beads on both positive and negative leads inside the 2M amp. I have a number of 1000pf caps to ground various places. I was reading about a ham in Sweden who claimed two 470pf 1kv caps on the Line inputs to ground might help. Have not tried that yet.
        The beads did not help the Meanwell noise at all, even though it was already low.
        I will check HP supply soon. I also plan on putting beads on Line input to both power supplies. The HP will be worth it, anything I can do to quiet it.
        I do not have an HF LDMOS amp yet…I would surely like to hear from someone using the HP on 2M.
        73
        Glen K4KV

        1. N4GA - Rob Avatar
          N4GA – Rob

          Good luck Glen – sorry you’re having to chase down these birds.

          Cool callsign by the way!

  13. Glen K4KV Avatar
    Glen K4KV

    Rob,
    Found a solution!
    Modified the amplifier first. Took type 31 beads and wrapped all power leads, both positive and negative in the amp with three turns through the beads. I took my spectrum analyzer and made a jig to test various beads, and amount of turns.
    Both type 31 and 43 were effective. One bead on a wire had 5db of noise suppression at 2M. Two beads had nine. It took 5 beads in a row to get 16db. So, started winding turns on one bead. It looks like to me that 3T is very good. More turns means more suppression below 60Mhz.
    Funny how the tests worked: the type 31 had it’s best suppression at 60Mhz regardless of turns, kind of like a ‘natural’ frequency. Type 43’s frequency was a little over 100Mhz.
    So…went from S5-6 noise to S0 now. I can still hear the increase in noise, but it does not register on the S meter. The Meanwell power supply has NO noise now.
    But the HP is so much more powerful!
    73
    Glen K4KV

    1. Glen K4KV Avatar
      Glen K4KV

      Ooops, forgot to say that the 3T through a bead had a suppression of 20db on 2M
      Glen

    2. N4GA - Rob Avatar
      N4GA – Rob

      Glen,

      Thanks for posting this information. Hopefully this helps people that are having these issues.

      73s

      Rob

  14. Glen K4KV Avatar
    Glen K4KV

    I have been corresponding with John G4SWX about SMPS noise problems.
    Apparently he has done way more work on this than I have ever seen before.
    Anyone interested in conquering the noise on SMPS should send him some notes.

    He told me that one should quiet the supply on HF first. His best solution was to
    wind a 15uH choke on the output of the supply, then filter that with two low ESR
    electrolytics. He said, then, add your vhf suppression.
    I have not tried this on the HP server supply yet, just added the vhf suppression only.
    73
    Glen K4KV

  15. Bill Carver, W7AAZ Avatar
    Bill Carver, W7AAZ

    With the fans unplugged my supplies 5V and fan voltage would come on but the 50V was disabled.

    The black negative power lead of each fan passes through a bank of sixteen 1 ohm resistors on the edge of the PCB right next to the 8-pin fan connector. They put four in parallel, creating four 1/4 ohm resistors. No schematic, but evidently they are looking for commutation pulses in the fan current and without those they refuse to allow the 50V.

    I pulled all 16 resistors from the board…..hard because you can’t get to the back side, but it can be done. Then paralleled the four pins that go to fan black leads. Now with one 1 ohm resistor between any black lead and ground one super-quiet Arctic P12 fan develops enough commutation signal to keep the four detector circuits happy.

    And they evidently also require some fan DC to be drawn to enable +50V. I’m generating +12V from the fan voltage using cheapie little boost boards (approx $2) to run two P12s, and that current draw satisfies the current-draw requirement of the supply.

    1. N4GA - Rob Avatar
      N4GA – Rob

      Bill,

      Really good info, thank you! We slowly pick apart the details of the ESP120!

      For now, I’ve just really slowed down the fans by putting series resistors inline with each one. Not sure how slow I can make them, but currently they are maybe 1/10th as loud and quite acceptable.

      I like the way you did it though.

      Some day, I will gut one of these and put it in another case and try to completely eliminate the fans. Would be a nice challenge and I bet it would still run cool.

  16. Robin Midgett Avatar

    Hello,
    I’ve just discovered this treasure trove of info…thank you!
    I’d like to hear from anyone who has knowledge of the Flextronics switching power supply, model CIS-S1600ADE00. This is a 240VAC input model rated to 133 amps at +12VDC. I’ve looked around the web and can find this SMPSU for sale and listed as discontinued, but haven’t found any documented hacks for enabling the supply to turn on without being in a server. I have access to several of these supplies but no info on how to light them up…

    https://www.radwell.com/en-US/Buy/FLEXTRONICS/FLEXTRONICS/CIS-S1600ADE00/

    Cisco part number for this supply is: 341-0732-03 A0
    Another part number on the label: CIS-S-1600ADE00-301

    1. N4GA - Rob Avatar
      N4GA – Rob

      Hi Robin and welcome to the site. Posting this for you so if anyone is familair with this power supply, they might chime in.

  17. Marek, SQ3HTX Avatar
    Marek, SQ3HTX

    I’m starting to collect components for my PA project, and this PSU would be ideal, yet it’s becoming a scarce compared to 12V ones, also shipping from USA to Europe would kill me. Most offers seem to pop up in USA. I found a similar candidate, Power Supply 2000W for Brocade DXC 8510 23-0000067-01. Looks promising.

    1. N4GA - Rob Avatar
      N4GA – Rob

      Marek,

      Over the years I’ve seen these server supplies come and go. This makes since as they get obsoleted and removed from server farms. Right now it seems there are some good Korean ones, but those are hard to get in the US!

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