Hi all,

Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.

Thanks!

writes:
Hi all,

Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.


What you're saying is: You want to build a 20A 13.8V power supply with
OVP. That it happens to take 24Vdc instead of 120Vac is trivial.

Your options are -- design a nice switching converter (which based on
the tenor of your question is beyond your mettle at the moment) or
build an enormous linear regulator and dissipate a couple hundred
watts making a very nice place for the cat to nap Best to set that
24V supply on the shelf, hope some day to find a good use for it, and
either buy or build a 13.8V supply from scratch.

Thanks!


--
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Lawrence Statton - m s/aba/c/g
Computer software consists of only two components: ones and
zeros, in roughly equal proportions. All that is required is to
sort them into the correct order.

Lawrence Statton N1GAK/XE1 writes:
What you're saying is: You want to build a 20A 13.8V power supply with
OVP. That it happens to take 24Vdc instead of 120Vac is trivial.

Oops, just noticed the .co.uk in the OP - replace that 120 with a 240
73 N1GAK

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Lawrence Statton - m s/aba/c/g
Computer software consists of only two components: ones and
zeros, in roughly equal proportions. All that is required is to
sort them into the correct order.

wrote:
Hi all,

Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.

Thanks!

Sell the 24 VDC power supply,Boatanchor people still use 24V supplies..
Buy a used 13.8 VDC @20 A for less than $100 ,maybe even $75.00
...Old timer

Light aircraft switched over to 24 volt electrical systems sometime in the
mid 1970s. You can sell that thing for a pretty penny to an avionics repair
shop and get what you wanted in the first place.

If there is a small civilian airport near you, inquire about where they get
their radios fixed and take a trip to the one that seems most viable.

Jim



wrote in message
oups.com...
Hi all,

Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.

Thanks!

"Lawrence Statton N1GAK/XE1" wrote in message
-did-not-set--mail-host-address--so-shoot-me...
writes:
Hi all,

Just bought this power supply ... 24V ...It's a heafty beast ...
... if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. ...Any pointers, please.


What you're saying is: You want to build a 20A 13.8V power supply with
OVP. That it happens to take 24Vdc instead of 120Vac is trivial.

Your options are -- design a nice switching converter (which based on
the tenor of your question is beyond your mettle at the moment) or
build an enormous linear regulator and dissipate a couple hundred
watts making a very nice place for the cat to nap Best to set that
24V supply on the shelf, hope some day to find a good use for it, and
either buy or build a 13.8V supply from scratch.


OR...OR...how about ... Unwind about half of the transformer secondary
and fiddle with the regulator (appropriately). You should maintain the
current level it originally had. The potential (sorry for the pun) for a
fault causing a disastrous overvoltage is less as well.
However be aware of the overhead voltage-- that is the difference in filter
output voltage relative to 13.8, so you have enough room for the regulators,
the ripple and mains dips. I did something like this with a 24V 5A supply
long ago to get 5V 25A (5V. TTL logic was big then). I actually rewound the
secondary with bigger wire to get the higher current capacity. ( also a
slight tweek on the regulator topology for improved overhead). It had the
common 723 regulator topology, so changing voltage was simply changing a
zener and I must have beefed up the series pass transistors.
Of course not knowing what your regulator topology is, this could be hard.
I also have a 15 amp., Kepco, rack-mount linear hernia generator. Then,
recently, a $99 MFJ 25 amp, hold-it-in-one-hand switcher. The ham fund had
it and it took a lot less time than the re-wind.

73, Steve, K9DCI

Just bought this power supply and it turns out to be 24V as opposed to
12 as I'd hoped. It's a heafty beast and should be good for running my
HF mobile if I can drop the voltage down to 13.8 whilst retaining about
20 amps for the rig's TX current draw. I know I can buy a commercial
dropper, but that'd be cheating, so can anyone suggest how I might
acheive such a device through HB-ing? Which active devices would be
best for this purpose? I'd like over-voltage protection built-into any
design put forward if possible. Any pointers, please.
====================================
Perhaps the transformer secondary winding has some lower voltage taps
which would enable you to use for 13.8 V operation ,having to waste less
energy and coping with the heat sinks and pass transistors fitted.

Another possibility is to connect the PSU transformer's primary 230/240
winding to a step down transformer's 115 V or similar lower voltage
winding ,provided the step down transformer has the same or higher power
rating than the one of the PSU
In principle the stepdown transformer could be an auto-transformer
(including a variac set in fixed position) ,obviously of adequate power
rating.
Some variacs (like the 8 Amperes unit I have) also have a fixed centre
tap , meaning that with 230V input they give a variable output as well
as a fixed 115 V output.

A stepdown transformer could also be a high voltage transformer say 230
to 500 V or similar but reverse connected (again : of adequate power
rating).

In all cases you would have to change the voltage control circuit ,such
that the voltage can be set to 13.8 V . The latter 'might' only involve
changing some resistors and/or a zener diode .


Frank GM0CSZ/KN6WH