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Author Topic: 12 volt power supply transformer,diodes  (Read 5032 times)
KC9VZB
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Posts: 48




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« on: December 26, 2012, 03:59:06 PM »

I just got a kenwood 450sat thinking power supply was no big deal,I'd build one.when I looked on this site for schematic what I found was regulated supplies.  The specks for the radio says it will operate on 12 to 16 volts so why all the fuss to regulate? Is there a voltage bounce going from transmit to rec?



 
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KE3WD
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Posts: 5689




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« Reply #1 on: December 26, 2012, 04:01:19 PM »

Yes indeed, with an unregulated supply, the shift from Receive, which may draw around 2 Amperes tops, to Transmit, which suddenly demands 20 Amperes for the 100W rig, is indeed enough to cause big problems. 

Your rig should be run using a regulated 13.8VDC supply. 


73
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KC9VZB
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« Reply #2 on: December 26, 2012, 04:21:21 PM »

My computer posted before I was done!I ordered parts I didn't have.I can put parts together but my knowledge slowed down when integrated circuits came out.I wasted allot of time years ago blowing up mosfets when 50 amp versions came on the market building power inverter by turning mosfets on and off with a 555 timer set at 60 cycles. It always worked for a little while then the magic smoke.I have a pair of 4-400c tubes and all the parts for amp .I'm taking my time on this one. 
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WB6BYU
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« Reply #3 on: December 26, 2012, 04:36:40 PM »

Regulated supplies are certainly the norm for base station use, though when
operating mobile the output of the car electrical system will vary considerably
more than that.  I don't see any reason why you couldn't run it from a stiff
enough unregulated supply.  You'd probably want the following functions:

1) protection for the rig in case of supply failures.  In a regulated supply this
takes the form of a "crowbar" circuit to short the output and blow the fuse
should the output exceed +15V or so.  (One advantage of an unregulated
power supply is that you aren't starting with +18 to +20V out of the filter
caps, so there less of a chance of the rig seeing an over-voltage condition
unless your power lines fluctuate a lot.)

2) protection from reverse voltage, in case of rectifier failure.  A reversed
shunt diode to blow the fuse should work.

3) reasonably good dynamic regulation.  If the voltage varies as you modulate
on SSB, the distortion products may be worse.  So while the radio might work
a constant +12V or +16V, having the voltage vary between those limits as
you speak isn't a good thing.


I have a power supply that I've used with my TS-450 (and the TS-430 before
that.)  It has a relatively high internal resistance along with pretty wimpy pass
transistors for a 20A rating:  basically the supply can JUST provide +12V at
20A, and the regulator keeps it below about 13.2V at low load currents.
(This saves money on the transformer, transistors, etc.)  A supply, regulated
or unregulated, that has less than 1V difference between no load and 20A
should be adequate, though I'd try for half that drop if possible.  That may
require a transformer that is rated at somewhat over 20A to keep the
series resistance low, but it is easy to measure.

Oh, and I don't use that power supply any more at 20A SSB unless it is
the only one that I can find.  Works fine for a 50W 2m rig, though.
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KE3WD
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« Reply #4 on: December 26, 2012, 06:49:25 PM »

...when operating mobile the output of the car electrical system will vary considerably
more than that.  

I don't see that in modern car electrical systems.  At. All.

My Ford with the rigs installed, I also installed my own DC voltmeter, and it is indeed rather well regulated.  So well, in fact, that slight changes have proven to indicate time for alternator with built in regulator be rebuilt or replaced. 

Think about how much of the electronics in the car are now also solid state and would not like the variances of an unregulated system, too. 

As for operating a modern rig on an unregulated DC supply, just because something lights up the rig and it appears to be operating at the time is not an indication that such is a good way to do things. 

Then there are modern rigs, like the TS-870 series as one example, that, if the power supply sags below 13.5V, output power drops by a rather astounding figure, like as far down as one half.  And as little as a 0.5 volt can raise Cain with that radio. 

Just not worth the hassle.  Not when good and well regulated switching suppllies are available for much less than linear.  And really, a linear supply is not all that expensive either, when you consider the expense of possible rig damage, not to mention a lousy sig out there.


73
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K8AXW
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Posts: 3823




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« Reply #5 on: December 26, 2012, 09:13:23 PM »

The Kenwood 930 had a notoriously weak power supply which had to be either repaired or replaced in many radios.

Suggest you Google TS-930 power supplies and you'll find that a PCB from FAR Circuits is available for a suitable internal power supply which can be built for around $50.00.  The circuit design information is available online.

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KA4POL
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Posts: 1975




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« Reply #6 on: December 26, 2012, 11:33:17 PM »

The answer to your question is called Ohms Law. Unless you got zero resistance you'll always find a voltage drop along a line.
The 450 requires 2 A in receive and 20.5 A in transmit according to the manual. To keep it simple let's assume we have .1 Ohm resistance. This will result in a voltage drop of .2 V against 2.05 V.
There are lots of simple circuits to be found in the internet for achieving what you need. Try to be on the save side by designing for about 30 A at 13.8 V which is a reference value.
To just give you some links:

http://electronics-diy.com/12v-power-supply.php
http://www.eleccircuit.com/high-current-12v-30a25a20a15a-ham-radio-power-supply/

These are very simple sample circuits using conventional techniques. You also might consider switching power supplies. Those, however, are a bit more critical for the inherent RF noise they produce when built without proper filtering.

Whichever way you go, study how commercial power supply circuits are built. You can search and download manuals of those.
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K5LXP
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« Reply #7 on: December 27, 2012, 06:05:22 AM »

The hardest part of any linear supply is coming up with the power transformer.  Once you've got that it's only a few more dollar's worth of parts to make it regulated and filtered.  There's no practical reason to not build or buy a regulated and filtered supply.

Mark K5LXP
Albuquerque, NM

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AA4PB
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Posts: 12832




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« Reply #8 on: December 27, 2012, 06:26:40 AM »

Unless you have a well stocked junk box you'll probably find that the cost of individual parts for a regulated linear supply approaches the cost of an Astron or similar off-the-shelf supply. Don't forget, you also need a case, heat sink, etc. Unless you are exactly duplicating someone else's proven design, the design of a linear supply can be a bit more involved than you would think by just looking at a schematic. For example, how large does your heat sink need to be? That depends in part on the maximum continuous current rating and the voltage differential across the pass transistors.

Building a supply for a 1-2 amps is one thing. Building a *reliable* supply to handle 20-25 amps can be a lot more complex.
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AC2EU
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« Reply #9 on: December 27, 2012, 06:41:19 AM »

Linear supplies are very "old school" but very straight forward.
However, linear regulation is extremely inefficient , that's one of the reasons why they have fallen out of favor to the new switch mode supplies.
They are light weight and efficient.  A well designed unit with good rf suppression works fine for me! I have been using one for two years and have yet to find any band where I get "hash" from the supply.
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WB6BYU
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Posts: 13230




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« Reply #10 on: December 27, 2012, 07:21:46 AM »

Quote from: KA4POL
The answer to your question is called Ohms Law. Unless you got zero resistance you'll always find a voltage drop along a line.


If it was just resistance it would be much easier to build a supply with good regulation.

The other major component of the output voltage variation is the rectified sine wave
used to charge the output capacitor.  With a very light load the output capacitor will
charge to the peak of the input, but that peak voltage is only delivered over a small
portion of the AC cycle.  As you increase the current draw you have to use more
of the cycle to deliver enough current, and the average voltage gets lower as you
do so.

If you have a transformer rated at 12VAC (RMS) then the peak voltage will be
( 1.4 * 12 = ) 16.8V, and this is what the capacitor will charge to with no load.
But at full load it will drop down closer to the nominal 12VAC, for a change of
4.8V.  This voltage change is in addition to any voltage drop due to resistance
in the circuit.

That's why regulated supplies are generally used.  An unregulated supply works OK
for a relatively constant current load.  In this case, if you design the power supply
(transformer voltage and capacitor size) so that there is plenty of reserve
capacity, you may be able to get a low enough voltage drop under load, but it
isn't a trivial exercise.
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AA4PB
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Posts: 12832




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« Reply #11 on: December 27, 2012, 07:46:35 AM »

Linear supplies are very "old school" but very straight forward.

Very straight forward but at 20+ amps the design is not trivial if you want it to work reliably. Make a mistake and your radio can be "toast". If you are going to design a linear supply then you need to test it under full continuous load BEFORE you start using it with your radio.
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KC9VZB
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Posts: 48




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« Reply #12 on: December 27, 2012, 01:02:25 PM »

I haden't thought of test first,I would feel like crap if radio was toasted.schematic I'm looking at has a diode placed so fuse will blow if there's a rectifier failure.$65-75 isn't much more to spend,on the other hand for switching supply.
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KC9VZB
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Posts: 48




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« Reply #13 on: December 27, 2012, 01:13:32 PM »

theres a 33 amp S-350-12 on e bay for $56 post paid,Any one use one.HuhHuhHuh
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KK4MYT
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Posts: 14




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« Reply #14 on: December 27, 2012, 03:52:23 PM »

I use a smaller version for my rig now. It is only 12v but its rock solid at 12v I have built a box with amp and volt meters and watch to make sure no issues.

http://www.ebay.com/itm/New-High-Quality-360W-DC-12V-30A-Regulated-Switching-Power-Supply-Metal-Silver-/180906108285?pt=LH_DefaultDomain_0&hash=item2a1ed8257d
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