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Power supply suggestions?




 
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WQ9E
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« on: March 14, 2009, 09:43:37 PM »

Spring is coming and I would like to get my PRC-47 outside for some use without putting a pair of 12 volt batteries in series like I did last year.  According to Collins specs, it draws a maximum of 320 watts on transmit high with a 24 volt supply (100 watts out CW or SB) working out to 13.3 amps.  12.5 amp 24V switching supplies are light and can be had for very low cost; moving beyond this current capability and the price goes up rapidly.

Has anyone had any experience slightly overloading one of these switchers?  Or other suggestions?  Hopefully I will be able to use the same supply with the DY-88 dynamotor pack for my AN/GRC-9  We will see how long my 5 year old can provide hand cranked generator power for my Chinese copy of the Angry 9-definitely no "old buzzard" transmissions.

Thanks!
Rodger WQ9E
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Rodger WQ9E
WA1GFZ
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« Reply #1 on: March 14, 2009, 10:05:51 PM »

Take a variac core and wind a secondary over the core to get the voltage you need. 3-#12 in parallel should do it just fine. Just count the turns on the variac. They are usually set up for 130 volts full winding. a little math will tell you how many turns you need. Put a few extra on just to be sure so you can remove them if necessary. Get a 25 amp bridge and a few big caps and there you go. 
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WQ9E
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« Reply #2 on: March 15, 2009, 09:17:55 PM »

Thanks for the idea!  I am going to see if one of the little 24 volt 12.5 amp switching supplies will suffice and if not it will be time to try this as plan B.  Since the rest of the PRC-47 and AN/GRC-9 setups are pretty heavy it would be nice to have one light weight component for my "dxpeditions" to the gazebo.

Rodger WQ9E
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Rodger WQ9E
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Patrick J. / KD5OEI
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« Reply #3 on: March 15, 2009, 10:24:58 PM »

possibly use two of the supplies in parallel, but isolated from each other by diodes. Some do not play well like that, and it can be gotten around by putting a 100 Ohm resistor across each diode so the supplies 'feel' the load together. The downside is having to buy towo and lash it up to find out.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
WQ9E
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« Reply #4 on: March 16, 2009, 10:01:06 AM »

Patrick,

I thought about trying two in parallel the way you described but if the one doesn't work then I will "bite the bullet" and build a big 24 to 28V adjustable supply.  The PRC-47 should run OK on the one switching supply since the peak current should be within 1/2 amp of rated and the average will be pretty low.  The Angry 9 might work depending upon how the switching supply reacts to the dynamotor  in the DY-88.  At some point I am likely to look for a T-195 to go with my R-392 and at that point a big 28 volt supply will be necessary.

Rodger WQ9E
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Rodger WQ9E
Jerry-n5ugw
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« Reply #5 on: March 16, 2009, 01:04:01 PM »

Lmbda makes some realy heavey duty 24 and 28vdc powersupplies and can be had fair on the used market. I used one with my ART-13 Power supply.
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WD5JKO
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« Reply #6 on: March 16, 2009, 02:46:32 PM »



Roger,

   My suggestion would be to use that supply you have, and place a large electrolytic in parallel with it, such as 50,000 MFD or more. This way the cap will supply the peaks and the voltage will hold steady so long as the switcher average current stays below current limit. This should work for SSB, but not full power tune ups at 100 watts carrier.

   Since the PRC-47 has a receiver as well, I fear that the switcher noise will make it's way into your receiver causing QRN. One way around this is to also provide power from something like a 24v 1.5 A linear current limited supply (enough for receive), and put that in parallel with the switcher output. Then set the switcher output to something less, like 23.5 vdc (with linear supply OFF).  Done this way, the switcher will stay OFF (no noise) until the voltage drops below setpoint (23.5). The reservoir capacitor will be key to make this dual supply scheme work.

The MFJ battery booster 12v -> 13.8v) works this way (keeping switcher off during receive).

Jim
WD5JKO





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WQ9E
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« Reply #7 on: March 21, 2009, 06:34:35 PM »

First, thanks for all of the information and suggestions from the list.  I decided to give the 12.5 Amp 24 volt switching supply from Marlin P. Jones a try.  It arrived Friday and I attached the cables up today and took the PRC-47 out in the yard for a test run using its 15 foot whip on 40 meters.  It tuned up fine and the supply seems to power it OK in both the low and high power positions; according to the PRC-47 meter it is maintaining regulation OK in the high power transmit position.

I made a couple of SSB contacts on 40 meters into FL and called CQ a couple of times on CW but no response.   That was the first time I used a straight key clamped to my leg and I can't really blame people for not coming back to my CQ.   I put ferrite sleeves on all of the leads from the switching supply and it doesn't seem to be too noisy although I have not checked every possible frequency since the PRC-47 isn't exactly a great band cruiser. 

The PRC-47 has been modified for LSB and I added the variable tuning modification so it can tune between 1 Khz. steps.  Audio reports were OK but one of the stations I contacted was former military and recognized the audio as coming from a mil type set.  I was using the telephone handset with it and I will try the separate hand mic later.  I need to either undo the setup for VOX or do it correctly, whoever had it before has it set up where you have to press the PTT switch and talk to activate the VOX.  Being the simple type I plan to just set it up for regular PTT operation.  At first I thought I had power supply troubles because when I pushed the PTT it would go into transmit for a second and then drop out again until I realized I had to talk to make it work.

The only thing I need now is the proper sized connector for attaching a wire antenna to the output of the transceiver.  It came with all other accessories in its transit case including the pack frame if I ever lose my mind and try to take it for a longer walk.  One of the neighboring farmers stopped by to see what I was up to and he remembered the radio from his time in S.E. Asia; he enjoyed trying to tune in some stations without dealing with heat, humidity, and VC.

Rodger WQ9E
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Rodger WQ9E
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