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Author Topic: Linear Power Supply Wanted  (Read 6665 times)
W5ZZT
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Posts: 70




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« Reply #15 on: December 27, 2013, 03:23:13 AM »

The great majority of power supplies being manufactured are the switching type. Besides the Astron RS-35M who else manufactures linear power supplies?



I have 2 of the Zurich DPS-2512M.  It's basically the exact same power supply as the MFJ-4035MV.  People complain about the fans being too noisy but mine don't bother me at all.  But then again I don't have then right next to my ear.

I had the Astron 35M before and had RFI problems with it.  When I had my amp at legal power it would get into the supply and shut it down.

All that said I have not actually listened to the MFJ but it appears to be a copy of the Zurich.
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K9MHZ
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Posts: 406




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« Reply #16 on: December 27, 2013, 04:23:41 AM »

linear power supplies?


DSP...(great call, BTW!),

One thing I've noticed locally is when hams are trying to decide on what size of supply they think they need, they're doing just some quick power formula calcs and getting a supply based upon what current figure they come up with....generally calculated from the transmitter power levels.  That's just about always going to result in an undersized supply, since you're not also figuring in the rig's circuit inefficiencies, which get dramatically worse the higher you go in frequency.  Also, Astron tends to name their models based upon On/Off (50%?) duty cycles, ie the continuous value will be quite a bit less in a given model.  So....definitely research a model's continuous current handling capability, and you'll end up going up in size.

   
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W8JX
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« Reply #17 on: December 27, 2013, 05:24:16 AM »

Funny thing is we live in a switching supply world be it your phone chargers, HDTV's, blue ray players to name a few are powered by them today. trying to hang on to old boat anchor linear supplies is like trying to hang on to 14 year old XP that will no longer be supported in a few months.

Linear power supplies will never go away!  They are just to easy to build and they meet one major requirement, Reliability!

If you repair a switcher it's kind of frightening to realize that the only thing standing between your Radio being Fed 300Vdc versus 13.8Vdc is a $5 Chinese IC and a Zener diode, either of which faulting can cause big problems.

BTW someone said switchers handle large input voltages.  Yes that's true but they also have no form of input isolation. You get a lot of isolation when your going through a nice beefy transformer.

I remember when I was learning about how to repair switchers that the guy explaining their operation to me said from an engineering stand point its like balancing a Fridge on a mop stick.  It typically requires ten years of SPS experience before an engineer can design a proper low noise reliable switching supply.

Never seen a switch go crazy on output voltage. The just go to zero when they fail. Linear on other hand can go wild and needed a crowbar to protect equipment. Then there is effiecncy, why hang on to a design thatuses more energy and costs more to use?
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N4DSP
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Posts: 148




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« Reply #18 on: December 28, 2013, 12:29:11 PM »

Efficiency,,,,give me some figures on the cost of running a Linear compared to a switching supply and tell me how they are more efficient than a Linear.


[/quote]

Never seen a switch go crazy on output voltage. The just go to zero when they fail. Linear on other hand can go wild and needed a crowbar to protect equipment. Then there is effiecncy, why hang on to a design thatuses more energy and costs more to use?
[/quote]
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K5TR
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« Reply #19 on: December 28, 2013, 12:56:16 PM »

The great majority of power supplies being manufactured are the switching type. Besides the Astron RS-35M who else manufactures linear power supplies?

MFJ has one - I am happy with it so far aside from it having a noisy fan.  The fan comes on whenever you draw
any real current from it.  I was thinking I might open it up and make the fan run slower all the time instead of
coming on when I transmit.

MFJ-4035MV

It can be had for about $130 - from the various ham places.  Do some shopping.
I got mine with free shipping - and since it is not light that was a good thing.
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George
K5TR
W8JX
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Posts: 5794




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« Reply #20 on: December 28, 2013, 03:27:09 PM »

Efficiency,,,,give me some figures on the cost of running a Linear compared to a switching supply and tell me how they are more efficient than a Linear.

http://www.eham.net/ehamforum/smf/index.php/topic,73501.0.html
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N4DSP
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Posts: 148




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« Reply #21 on: December 28, 2013, 05:28:00 PM »

Great research and interesting. Thanks for the link. However as Trish stated earlier the rf component on the ham bands is troubling due to the nature of the switchers. I do thank you for your thoughtful replies.

john

Efficiency,,,,give me some figures on the cost of running a Linear compared to a switching supply and tell me how they are more efficient than a Linear.

http://www.eham.net/ehamforum/smf/index.php/topic,73501.0.html
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N4DSP
Member

Posts: 148




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« Reply #22 on: December 29, 2013, 11:39:34 AM »

W8JX,
with that in mind and your experience with switchers what manufacturer and model number would you
recommend keeping in mind the efficiency and no rf hash.

thanks


Efficiency,,,,give me some figures on the cost of running a Linear compared to a switching supply and tell me how they are more efficient than a Linear.

http://www.eham.net/ehamforum/smf/index.php/topic,73501.0.html
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KD8MJR
Member

Posts: 2291




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« Reply #23 on: December 29, 2013, 07:05:33 PM »

Never seen a switch go crazy on output voltage. The just go to zero when they fail. Linear on other hand can go wild and needed a crowbar to protect equipment. Then there is effiecncy, why hang on to a design thatuses more energy and costs more to use?

I have a Yaesu FT-1000MP Mark V on my bench right now that would totally disagree with you.  Grin
The FP-29 power supply went south and took most of the radio with it.

In the old days when I use to repair tracker V's, VIII's and X satellite receivers I found that almost 80% of dead units had bad Switchers.  When they came in I would check for shorts and then just slap a brand new supply in and pray.  About 75% of the time they would come back on and the others.... well lets just say after a few attempts at fixing these units I found out it was not worth it because most of the chips were fried!

You might want to take a look at this
http://cd.textfiles.com/group42/ELECT/REPAIR/F_SMPS.HTM#SMPS_008

or gulp even this

http://en.wikipedia.org/wiki/Switched-mode_power_supply#Failure_modes

Needles to say, if the feedback circuit has an issue and sends back a lower relative voltage than whats really on the output then the chopper circuit will ramp up to compensate and your equipment will have a bad day.

If the Capacitors on the output start to fail you stand a chance of having really wild Oscillations on the output followed by shorted mosfet's and a blown fuse. If your equipment survives the oscillations consider yourself lucky.

 I am not saying that all of this is very common in a well designed modern SMPS but it is something I have seen many times in older supplies and still happens occasionally in newer supplies.  Would I trust my Icom 7600 on a modern switching power supply, yes but I would prefer not to if I had another option

As for linear supplies like Astrons, I have never seen one fail.  I know it happens but it's such a rare event and honestly I have never seen or heard of one damaging equipment.



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W8JX
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Posts: 5794




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« Reply #24 on: December 30, 2013, 06:05:07 AM »

As for linear supplies like Astrons, I have never seen one fail.  I know it happens but it's such a rare event and honestly I have never seen or heard of one damaging equipment.

I had one once. I bought it at a flea market and voltage was high and unstable as it had a flakey regulator.
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KD8MJR
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Posts: 2291




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« Reply #25 on: December 30, 2013, 10:26:52 AM »

One of the points I was making that maybe got lost was that the output capacitors will always die at some point.  It may take 3 years or it can be 10.  When that happens watch out because your rig may go with them.  Just ask PC techs how many times they get bad PS and they will tell you a lot!  Then ask how often they found dead Mobo with the dead PS and I bet they will tell you that it happens from time to time.  I guess my point is that I don't want to take that kind of chance with my Rig.
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W8JX
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Posts: 5794




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« Reply #26 on: December 30, 2013, 01:55:00 PM »

One of the points I was making that maybe got lost was that the output capacitors will always die at some point.  It may take 3 years or it can be 10.  When that happens watch out because your rig may go with them.  Just ask PC techs how many times they get bad PS and they will tell you a lot!  Then ask how often they found dead Mobo with the dead PS and I bet they will tell you that it happens from time to time.  I guess my point is that I don't want to take that kind of chance with my Rig.


I have a 20 year old Astron 20 amp that I now use as a backup the last 4 years. When I got it I slipped/fit two 10,000ufd caps in parallel inside case that are paralleled with output terminals. I also used 100,000 ufd of external capacitance with it and never had any problems and it still works. When I changed over to switch I am still using 100,000 of external capacitance. While I have no science to support it I do believe that the added capacitance reduces peak PEP surge loads on power supply and extends the life of its own capacitors.
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KD8MJR
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« Reply #27 on: December 30, 2013, 02:04:54 PM »

While I have no science to support it I do believe that the added capacitance reduces peak PEP surge loads on power supply and extends the life of its own capacitors.

Interesting Idea, I wonder if anybody has some data on this.
My off the cuff thinking is that it won't help because the bad caps will have a High ESR and the good ones are not going to help with that.
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W8JX
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Posts: 5794




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« Reply #28 on: December 30, 2013, 05:05:12 PM »

While I have no science to support it I do believe that the added capacitance reduces peak PEP surge loads on power supply and extends the life of its own capacitors.

Interesting Idea, I wonder if anybody has some data on this.
My off the cuff thinking is that it won't help because the bad caps will have a High ESR and the good ones are not going to help with that.


Well all caps have like "x" number of cycles in them depending on their load cycle or charge/discharge rate and depth of this cycling. The problem is determining the value of "x".  It stands to reason that the less or shallower they are cycled, the longer their life should be. External caps take the surge loads of internal ones.
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