Ham/CB/other transmitter radios... linear vs switching PSU?

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

^^ Post 18 has all I changed.

I wonder if a whole bunch of hams and CB'ers are now going out buying a 36K resistor to hack their xbox psus to (near) 13.8V if they find this post... now is this novel? I don't think so, this is at least the third SMPS I've hacked to a different voltage... but useful? seems like it?

BTW, R318 should be marked "79B" ... if it's not, all bets are off... If it is, go ahead and stack that 36K resistor on top and have at it.

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Ugh, annoyances with the Xbox PSU:

I'm not sure yet if it's UVP or OCP but it seems if a heavy load is presented, it likes to shutdown. I'm not sure if it's a problem with my PSU or just how UVP/OCP is designed. If, however, the load is present during power on, it will happily run the load. It may well be charging capacitors or the lamp cold resistance, but either way, not liking them.

I tried this:

Xbox PSU 175W -> 325W inverter -> 100W incandescent light bulb.

If I have it all hooked up, I can flip the switch on the Xbox PSU and it powers up just fine.

However:

- turning the 325W inverter on with no load after the PSU is turned on: Causes shutdown. Powering up the PSU with the inverter turned on is fine.
- Plugging in the 100W light bulb when the inverter is powered up causes shutdown. If the lamp is plugged in and turned on with the inverter and the PSU, it lights up just fine.

Haven't tried it with a 100W radio, because I don't have one... may have to loosen up UVP/OCP a little, for my use a little (big?) 3V droop is just fine.

[stj]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

it could be tripping on a surge, or it can shutdown if it gets hot - there is a thermal sensor in it.

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Definitely not heat related because it's instant shutdown, too much thermal mass to explain the sudden event.

Surge == OCP protection ...

[CapLeaker]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

SUCCESS! With some risk of the OVP failing... at least it worked for me luckily!

I have: Microsoft XBox PSU Model HP-AW175EF3 (HiPro made in China)

Noting that the resistors on the board are all glued and soldered, I figured the best way is to parallel a resistor.

I paralleled a 36K resistor (it's what I had in my junk box...) to the existing R318 on the board. I got a resultant voltage of ...

13.73 volts (unloaded)!

Close enough! This should be excellent for a car battery eliminator. Now I need to have a connector on the output that's actually usable...

I need to work on my SMT rework skills... or actually have some good flux or something.

BTW: Yes, my noise floor in my house for 2m/70cm is pretty awful... all my computer gear it appears *sigh* In fact it seems when I have BCN loaded one of my monitors, it causes tremendous noise picked up on 70cm. It's kind of hilarious, I can hear it when I move a window off one display to the other...

Tradeoffs...

With older ham gear it is possible to get more RF out, by adjusting the output voltage of the PSU. The new ham gear doesn't do that anymore.

[CapLeaker]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Ugh, annoyances with the Xbox PSU:

I'm not sure yet if it's UVP or OCP but it seems if a heavy load is presented, it likes to shutdown. I'm not sure if it's a problem with my PSU or just how UVP/OCP is designed. If, however, the load is present during power on, it will happily run the load. It may well be charging capacitors or the lamp cold resistance, but either way, not liking them.

I tried this:

Xbox PSU 175W -> 325W inverter -> 100W incandescent light bulb.

If I have it all hooked up, I can flip the switch on the Xbox PSU and it powers up just fine.

However:

- turning the 325W inverter on with no load after the PSU is turned on: Causes shutdown. Powering up the PSU with the inverter turned on is fine.
- Plugging in the 100W light bulb when the inverter is powered up causes shutdown. If the lamp is plugged in and turned on with the inverter and the PSU, it lights up just fine.

Haven't tried it with a 100W radio, because I don't have one... may have to loosen up UVP/OCP a little, for my use a little (big?) 3V droop is just fine.

Try putting a large capacitor between the PSU and the inverter?

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

I don't know why there was even an obsession with 13.8V, though that extra RF output with higher voltage being a possible reason on older equipment (do newer equipment have SMPS to stabilize the voltage or does it limit the final drive if the voltage is high?)

12V = Nominal voltage of a 6-cell lead acid battery when not charging.
13.2V = typical open circuit voltage for fully charged 6-cell lead acid batteries.
13.8V = typical standby/float charge voltage for a 6-cell lead acid battery.
14.4V = typical cyclic/rapid charge voltage for a 6-cell lead acid battery.
15V = 6-cell lead acid battery killer, unless it was sulfated and needs that voltage to pass current.

At least I can use this PSU to charge batteries now, at 12V it won't charge.

Do typical ham radio switching power supplies actually have a large capacitor in them to deal with the key up burst power, or does it allow for a temporary droop? I haven't looked at the insides of such to see how it deals with sudden power draw...

[CapLeaker]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

A lot of a bit older ham gear was able to produce more than lets say 100W. The 100W was rated at 13.8V. However one put 15V into it, well you had more power.

Times change and so do transistors and PA's. Some RF transistors are driven at 24 or 48V. Some can do "Class A". These days the new gear stays at 100W, regardless if you overvolt the PA or not. Motorola liked their stuff back in the days at 14.2V.

As far as power supplies go, there are different kinds. I've got a large linear PSU made for an audio wall at a store, which is double filtered. So you got power, transformer, rectifier, a huge capacitor bank, regulator and another large capacitor. It makes an Astron linear look like garbage.

As for switchers in ham gear, most of them have more amperage than the radio actually needs. Alinco does 32A, most HF gear only uses 20A. No there isn't any thing meaning full dropping in volts once you put a good load on it. Often they will even put more out than they are rated for, before they go into protection mode.
Sometimes RFI can get into the control circuit of the switching PSU and there will be some fireworks and smoke signals. Most of the time that is caused by tuning a bad antenna, nothing is grounded correctly and the HF radio sits on top or under the PSU.

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Hence they will lose power when running at 12V... got it... hah.

I need to do some more accurate monitoring to see why this Xbox PSU goes into shutdown protection, but I don't know if these typical ham switchers have giant output caps to reduce the droop and causing protection to kick in, or if their switching frequency is faster and can detect these droops quicker and respond to them...

[stj]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

maybe the ocp is dampened with a small cap at the sense pin.

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

The datasheet has a 0.1uF (appears to be C27 I *think*) as a damper capacitor for Isense in the reference design. Maybe I should up it a few uF ...

Actually it looks like it also has a 10uF capacitor as a damper with a 100Ω resistor in series... HMM... However in the real circuit (C8) it looks like it's a MLCC SMT capacitor.

Unfortunately I may have to remove the capacitor to check its capacitance...

---

I stuck in another 10uF capacitor in parallel with C8, whatever it is... hmm...did not help much.

[stj]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

the resistor is probably the limiter here - try putting something in parallel to let the cap charge faster.

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Actually want to let it charge slower - increase resistance - as it's measuring the voltage across the capacitor to determine current draw.

I really need to simply take a look at the waveform/droop and ensure this is indeed what's happening, I'm just guessing at this point. The odd thing after experimenting a bit last night, after some warm up, I was able to turn the inverter on and off without tripping the PSU where initially it had always tripped... so something changed...

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Okay...this PSU seems to at least happily power my icom 35W transceiver. It's drawing about 7A on transmit, about 96W, which is quite possible for transmitting 35W... now this opens another question which is not relevant to this thread...

[Longbow]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

Citing the frequencies of some generic switching supply and assuming that broad band interference will be transmitted and create interference with surrounding equipment is just ignorance. There are all kinds of linear and switching supplies. You get what you pay for. A typical output spec for a high quality 12 volt switcher is 150mv of noise at rated output.

Look at how many of our devices are powered by cord mounted switching supplies and somehow these rarely cause problems with computer peripherals, etc. Have a look at your precious linear supply on the scope and be amazed at the unexpected noise that is present there also. It just is not switching noise. Especially for 2 way radio, keep in mind that the current demand will vary from minimal (<1 ampere) to significant (>15 amps) at the touch of a button. Switching supplies are adept at coping with that kind of quickly varying load. As usual, there is a lot more to the story than Mr. Reader's Digest believes.

If you are fine with something that weighs 100 pounds and makes a groaning noise every time you turn it on or draw massive current, then by all means avail yourself of an Astron or other linear supply. A well designed switcher on the other hand will work perfectly, and often better than the anchor weight, AND will likely be easier and less expensive to fix down the line if repair becomes necessary.

That's the way it is.
Longbow

[eccerr0r]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

I think that this xbox PSU has bad caps in it now... it works better when warmed up...

[SpaceToast]

Re: Ham/CB/other transmitter radios... linear vs switching PSU?

I have an Icom 7100 in my shack that draws 23A *max* when I transmit 100W on the HF bands, and I power it with a TekPower 30A SMPS.

The extra current capacity means that even with the 7100 occasionally drawing 23A, I still have a little power in reserve for other gear. It has an adjustable output with a detent at the 13.8V position, and it lets me adjust the switching frequency to help reduce EMI in the form of harmonics produced by the switcing process.

Of course, changing the switching freq doesn't really reduce the harmonics, but it can shift the noise away from a frequency you are trying to receive.

I have a solid ground system, and I use ferrite chokes on my power, USB, and audio cables at my home shack so I haven't needed that function there, but when operating in remote areas on generator power, it has come in handy.

I'm playing with an X360 psu that I got at Gamestop for $5. If I can get it to power my ID-5100 at 35 - 50W on the VHF & UHF bands, I'll use it for my go-box. Otherwise, I have several decent PC PSU units that I should be able to 'crank up' to 14V or so.