Nice 28V PSU 1200W no fans

[radiogareth]

This has popped up https://www.ebay.nl/itm/1PC-Power-Suppl ... SwcHRdCUkX. He also has other radio related bargains, check out his shop especially 'Radio Communication' section.
Yes he will ship to the UK (I asked him).
I have no need of such a beast but for the money, even if it got clobbered by duty, it's still a bargain. Maybe someone knows how to knobble the Voltage up a bit, like 32 would be handy....
Gareth

[g0mjw]

I bought a pair last time this came up. They are good but they do need fans to circulate air through them if you are going to use them to their full capability. The 27.2V can be adjusted by fooling the measurement. I think I posted something on how but I forget where. I set mine to 28V, don't know the limits.

Mike

[G8GKQ]

Hi

I have just received one of these power supplies and would appreciate details of the modification for 28V if anyone has been able to find it.

Thanks

Dave, G8GKQ

[g8gtz]

Mike has now posted the original

Put a 100k across the marked resistor.

Mine is on order.... but apparantly they won't go to 32v

Noel

[g0mjw]

Nobody said they won't go to 28V. The patch I showed was just to get to 28V which is where I wanted it to be. I worked out the circuit more or less and gave the voltage feedback a minor tweak. 32V may be possible with more tweaking. If you want 32V without tweaking you could always add an isolated 5V PSU in series with protection diode. However...

We assume output power scales approximately with the drain supply squared. 28x28 / (32 * 32) = 76.5%. Linearity though does not scale in the same way. It is unknown how much more power you will get on DVB-T with 32V vs 28V with acceptable shoulders. Also device proximity to self destruction scales very rapidly with supply voltage.

Here is a version of the image not sent via QO100 and photographed.

PSUMod.jpg (197.02 KiB) Viewed 1671 times

Here is a wider view. Look up the IL300 and all will become slightly less opaque.

1.jpg (757.53 KiB) Viewed 1671 times

The resistor is part of an op-amp circuit feeding that linear opto-isolator.

Mike

[radiogareth]

Interesting point about supply voltage. I only mentioned 'might go to 32V' it as the latest crop of Nokia pallets were built for 32V on the finals.
If people require a range of voltages (like 12VDC for a Stealth unit, 13.8. 24, 28 and 32) then a pair of hacked HP Server units can be configured to give up 16V (and beyond probably IF you change the output caps. https://www.youtube.com/watch?v=9--g63ew9HU The second PSU needs two of the case mounts isolating from ground by virtue of nylon screws and suitable insulating washers. Be aware the heatsink inside these units seems to be at 400VDC with the reservoir capacitors behind it....
Whether or not you trust your PAs to such an arrangement is up to you.....
Gareth