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eHam Forums => Elmers => Topic started by: K5UNX on February 16, 2013, 05:41:02 PM



Title: Power Supply size?
Post by: K5UNX on February 16, 2013, 05:41:02 PM
I just bought a FT-857D. I am going to mount it in a portable case of some sort and need a power supply. I am looking at the MFJ-4125. It's 25 amps. According to the manual for the FT-857, it can consume 22 amps. I assume that's at a full 100 watts transmit level. I don't think I would run the radio at full power all the time . . . but I am new to HF.

I am also planning on possibly charging or powering my FT-60R. According to it's manual, that would take 1.6 amps. The only other things I can see using that power might be a small LED light. Not sure what else.

I am planning the following in the case. FT-857D, Power Supply, Antenna Tuner. Maybe the LDG FT-Meter.  I was thinking about a rig runner power dist panel but now I am thinking I might not need that, just a Power Pole spitter maybe.

Am I cutting the power too close with the 4125 at 25 amps??

Wayne



Title: RE: Power Supply size?
Post by: K8AXW on February 16, 2013, 05:46:49 PM
Wayne:  IMHO, yes.  I'd go for a 35A supply.  Even though you'll be using SSB and CW, I'd still go with a supply with a bit more headroom.  The 25A supply will work but....as I said, my opinion.


Title: RE: Power Supply size?
Post by: AA4PB on February 16, 2013, 05:59:21 PM
The MFJ-4125 is rated 25A intermittent and 22A continuous. My opinion is that you a cutting it pretty close.


Title: RE: Power Supply size?
Post by: W8JX on February 16, 2013, 06:53:28 PM
Wayne:  IMHO, yes.  I'd go for a 35A supply.  Even though you'll be using SSB and CW, I'd still go with a supply with a bit more headroom.  The 25A supply will work but....as I said, my opinion.

Bit of overkill here. I have a 20 Astron that I used as a main supply for many years and now is a backup. I replaced it several years ago with a light weight Astron SS 30.


Title: RE: Power Supply size?
Post by: AF5C on February 16, 2013, 07:59:19 PM
Jetstream makes a 28 amp supply I have that isn't much bigger than the MFJ one. Still small and lightweight.  I would check the QST review on the FT857D.  It will tell exactly how much current it consumes at full power. I am guessing it is less than 22 amps. Probably more like 17 to 18 or so.

John AF5CC


Title: RE: Power Supply size?
Post by: G4IJE on February 17, 2013, 02:42:00 AM
IMHO a 25 amp supply would be fine. After all, that's what they are made for - powering a typical 100 watt transceiver. I've owned several 100 watt HF rigs over the years and don't recall any of them taking more than about 18 amps "key down".


Title: RE: Power Supply size?
Post by: K2DC on February 17, 2013, 03:51:32 AM
I've never had a problem using a supply rated at 25A peak.  However, I didn't have much luck with the MFJ-4125.  Mine lasted about 6 months before the power switch failed, so I bypassed it (not worth replacing).  Then after another 6 months it died altogether.  You mileage may vary.

73,

Don, K2DC


Title: RE: Power Supply size?
Post by: K1CJS on February 17, 2013, 05:57:43 AM
A good rule of thumb to follow is to use a power supply that will deliver twenty percent more than the required constant draw on it.  If your system will use 23.6 amps (the total of the two rigs) you should use a power supply that will deliver not less than 28.3 amps--or a thirty amp power supply.

If this is done you will never run your supply at full output, will have a comfortable margin for overdraw if it ever happens, and the power supply should last you a lifetime.  Scrimping on the power supply may be the worst thing you can do, especially with some of the rigs today that just may be adversely affected by any undervoltage that may occur.

If you do use a twenty five amp supply to supply that 23.6 amps, there is a possibility of overdrawing it--possibly causing premature failure, especially with economy supplies that just may be too closely rated, not to mention possible damage to your equipment.  The question is this:  Do you want to spend a little more now--or spend a lot more later?


Title: RE: Power Supply size?
Post by: AA4HA on February 17, 2013, 06:02:16 AM
I think that the 25A supply is cutting it a bit close as well. You also stated that you are going to be using a portable charger and a tuner as well. I am assuming that your portable case is something you can use for field days or EMCOMM. You will end up finding something else you want power for, like a small LED light for night operations or a TNC or maybe to float charge a backup battery for when you do not have AC hookup.

An unspoken thing about electronic specifications is "duty cycle". Any manufacturer (not just MFJ) will give you an intermittent rating but it almost always has been tainted by sales and marketing types who would happily say "25 amps intermittent duty", even if that intermittent duty cycle was 5-10%. Consider what a radio amateur who does data modes would have for a duty cycle (as high as 30-50% of the time they are transmitting). Also that power supplies are rated in a nice environment at 20C (68F) with plenty of air flow to keep things from overheating. You on the other hand are going to pack this up in a box, probably use it where the outdoor temperature may be 30-35C (80-95F) and possibly with an incoming electrical service that is not rated right at utility specifications. You should mentally derate any product specification by another 20%. (wow K1CJS, we were thinking the same thing)

I deal with electronics specifications all the time when pulling together designs for communications systems in less than desirable environments. (too hot, too cold, locked in a cabinet on a utility pole somewhere, maybe a fan but not allot of airflow) It is embarrassing to install a 12 volt, 5 amp supply in 30-50 sites where you know the load is only 12 volts, 3 amps and then to find out that in the months of June, July and August that they had to replace 2/3 of those supplies because they burned up. Naturally the client wants you to credit them for the replacement supply and their tech labor to go out there and swap those things out. Also they justifiably left with a sense that this half a million dollar priced system is less than reliable because they cannot go a week without something failing. Now I just spec in a 10 amp supply from the same manufacturer and seldom have a problem unless it is caused by lightning. BTW, these are not cheap supplies either; they are industrial rated and cost a few hundred $ each.


Title: RE: Power Supply size?
Post by: KE3WD on February 17, 2013, 06:44:44 AM
Switching Supplies are good, lightweight and can solve the portability problem well. 

The one thing that I encounter on the testbench all the time when switching supplies fail is the fact that people don't realize the effects of powerline transients on the Switchmode supplies. 

Very common that the supply as purchased has little to no transient protection built in, also very common to see various supplies used in the field, such as the switchmode supplies used in pro audio gear, to take a transient hit that typically will take out the rectifier(s) that are usually rectifying the AC line current before chopping it up and presenting it to the smaller transformers or autoformer coils involved. 

Therefore, if you are contemplating a Go Kit for Emcomm and contemplating use of a Switchmode supply, I recommend adding Powerline Transient Supression to the kit for the AC input line. 

This problem will be greatly exacerbated by the sometimes necessary use of generator power, auxiliary power sources, etc. that EmComm operations necessarily may throw your way. 

Even just a good quality powerstrip that includes good quality MOV transient protection can go a long way towards keeping your switchmode supply running. 

I also have my suspicions that many of the reports of premature switcher failures, even when plugged in at home in the shack, become victims of powerline transients and thus get the bad name.  Transient Surge Protector strips are cheap insurance, not only for the switchmode supply as a separate, but for many of the appliances and accessories found in the modern ham shack as well.  Like the ubiquitous computers, etc.


73


Title: RE: Power Supply size?
Post by: W8JX on February 17, 2013, 07:03:20 AM
A good rule of thumb to follow is to use a power supply that will deliver twenty percent more than the required constant draw on it.  If your system will use 23.6 amps (the total of the two rigs) you should use a power supply that will deliver not less than 28.3 amps--or a thirty amp power supply.

If this is done you will never run your supply at full output, will have a comfortable margin for overdraw if it ever happens, and the power supply should last you a lifetime.  Scrimping on the power supply may be the worst thing you can do, especially with some of the rigs today that just may be adversely affected by any undervoltage that may occur.

If you do use a twenty five amp supply to supply that 23.6 amps, there is a possibility of overdrawing it--possibly causing premature failure, especially with economy supplies that just may be too closely rated, not to mention possible damage to your equipment.  The question is this:  Do you want to spend a little more now--or spend a lot more later?


The big problem with this logic is there is NEVER a high constant load. The only constant load is a few amps or so with rig in receive mode. The is not commercial 100% key down with high current draw operation. When using SSB your average load is around 8 to 10 amps max when transmitting. When digital you may have I higher load at times but it is NOT constant and is intermittent in nature with a duty cycle of 50% or less typically. Also I have never tested a rig that actually drew the amount of power that it was rated at. It is typically 10% or more less and the nominal figures in spec's are more of a "never will exceed figure" than a actual consumption. 


Title: RE: Power Supply size?
Post by: N4NYY on February 17, 2013, 07:18:30 AM
25A with 30-35 amp surge will be more than enough. I know people that have used Astron 20A with no problem


Title: RE: Power Supply size?
Post by: K5UNX on February 17, 2013, 08:08:07 AM
To answer or confirm a couple thought. Yes I am planning on this being a portable rig for emcomm, field day, comm volunteering at local events and such.  This being my only rig, I want it portable. I can see running a small LED light, and possibly something else that I don't know about now. A guy in my club recommended a MightyLIte Supply. I just now realized what he was talking about  . . http://www.mfjenterprises.com/Product.php?productid=MFJ-4235MV   This one is 35A.



Title: RE: Power Supply size?
Post by: AA4PB on February 17, 2013, 10:03:52 AM
25A with 30-35 amp surge will be more than enough. I know people that have used Astron 20A with no problem

An Astron RS20A is rated for 20A intermittent and only 16A continuous. Thats not good for a radio that is specified at 22A key down plus the addition of some other accessories.


Title: RE: Power Supply size?
Post by: AC5UP on February 17, 2013, 03:16:41 PM
Lest we forget, each mode has a duty cycle that affects the current drawn from the radio. There's also the RF power adjustment to consider.

If you're running RTTY bulletins at full power you will be very close to the maximum rating for the radio.  You should also realize that dropping power from 100 to 80 watts for a mode like RTTY could avoid a premature equipment failure with little affect at the other end of the Q.  SSB at 100 watts PEP is like FM at maybe 60-ish watts unless you're James Earl Jones and have the speech compression cranked to the max.  The duty cycle of CW depends on the speed and to some extent on the fist sending it.

Point being that for normal SSB @ 100 watts PEP a 20 amp Astron is more than adequate.  Especially for a temporary / portable setup when size, cost and weight are considerations.  If you think you have to run full rated power to make Q's you're either new at this or have a G5RV in your attic.  With a halfway decent antenna and normal band conditions 50 watts of RF is more than enough to do business.

OTOH, there are Hams who wouldn't dream of calling CQ at less than 400 watts because they have a linear and it makes no sense not to use it for every Q........  Part 97 be damned.   :P


Title: RE: Power Supply size?
Post by: W8JX on February 17, 2013, 03:18:36 PM
25A with 30-35 amp surge will be more than enough. I know people that have used Astron 20A with no problem

An Astron RS20A is rated for 20A intermittent and only 16A continuous. Thats not good for a radio that is specified at 22A key down plus the addition of some other accessories.


It is rated at 20 amps at a 50% duty cycle. It will actually do more as it does not cut off at 20 amps. As I have side before, I used one nearly 15 years before replacing it with a SS30. Even had a VHF/UHF mobile on at same time a lot but only actually transmitted on one at a time.  Again I have never tested a HF rig that actually drew what it was rated at. It was always less.


Title: RE: Power Supply size?
Post by: N4NYY on February 17, 2013, 03:19:10 PM
25A with 30-35 amp surge will be more than enough. I know people that have used Astron 20A with no problem

An Astron RS20A is rated for 20A intermittent and only 16A continuous. Thats not good for a radio that is specified at 22A key down plus the addition of some other accessories.


I have a RS-35m. I said I know people that use a 20 amp Astron.  I suggested 25A continuous.


Title: RE: Power Supply size?
Post by: N8NSN on February 17, 2013, 04:17:19 PM
Many good replies.

One easy way to make any piece in a station last (provided no accidental damages happen):

Leave head room.

It's been the typical experience that most gear lasts much longer if not pushed to it's specified limits of operation on a regular basis.

The last place you want to experience a failure in em comm equipment is in the field.

I agree a 35 amp PS is the best answer.
Answer #1A as a subpart to the 35 Amp answer is transient voltage protection. Furman makes some nice 1/2 rack width and full 19 & 1/4 inch standard width - line conditioners. Some of them are pr icy, but a conditioner that can take 84<145 VAC and keep her steady at 115 VAC has some "meat" to it. Could easily be considered money well spent if it runs the go-box for many years and/or "gets the job done" when under critical demand.


Title: RE: Power Supply size?
Post by: KE3WD on February 17, 2013, 05:21:08 PM
The term for specifying a power supply that can deliver higher amperage than needed is: 

Derate 


Derating a power supply *by a reasonable amount* is always a good thing for the power supply's MTBF. 


73


Title: RE: Power Supply size?
Post by: AA4PB on February 17, 2013, 05:51:25 PM
Well, if a power supply is rated at 20A peak then the current limiter will probably fold back if you exceed 20A, even momentarily. If his radio really draws 22A on voice peaks then the supply voltage will drop every time he hits a voice peak. He's likely to have a distorted SSB signal unless he keeps the audio drive level low.

Much better to purchase a little larger power supply IMHO.


Title: RE: Power Supply size?
Post by: W8JX on February 17, 2013, 09:08:14 PM
Well, if a power supply is rated at 20A peak then the current limiter will probably fold back if you exceed 20A, even momentarily. If his radio really draws 22A on voice peaks then the supply voltage will drop every time he hits a voice peak. He's likely to have a distorted SSB signal unless he keeps the audio drive level low.

Much better to purchase a little larger power supply IMHO.


A RS 20 is rated at 20 amps @ 50% duty cycle not 20 amps peak. Most HF modes are far less than 50% too at full draw too. I NEVER had any problems with mine and again never saw a rig that draws its rated amount either when checked. It is always less. Bigger is not always needed nor is it always better either.


Title: RE: Power Supply size?
Post by: AF5C on February 17, 2013, 09:28:38 PM
According to the QST review, the 857 draws 16A at full output.

John AF5CC


Title: RE: Power Supply size?
Post by: W5LZ on February 17, 2013, 10:03:43 PM
I'm not going to argue about how much current a particular radio draws.  I will say that having a larger than needed power supply always comes in handy.  Tell me you never added some little do-dad to that power supply later, or never wished the @#$ thing was just a little bit bigger so that you could power something else from it too.  How much is 'too much' is something you will have to decide though.
 -Paul


Title: RE: Power Supply size?
Post by: W8JX on February 18, 2013, 08:39:54 AM
I'm not going to argue about how much current a particular radio draws.  I will say that having a larger than needed power supply always comes in handy.  Tell me you never added some little do-dad to that power supply later, or never wished the @#$ thing was just a little bit bigger so that you could power something else from it too.  How much is 'too much' is something you will have to decide though.
 -Paul


With that logic better buy a 1 ton pickup and trailer too as you might need to haul something one day too.


Title: RE: Power Supply size?
Post by: WH7DX on February 18, 2013, 02:16:04 PM
Get the astron rs 35m.    It's 25a continuous and 35a peak.   It's only $40 extra for the higher power.    With cw and 100w the lights still dim but it's fine.   

I wouldn't go less than 25a continuous. 


Title: RE: Power Supply size?
Post by: KE3WD on February 18, 2013, 04:00:09 PM
A 35m for use in an EmComm Go Kit.


right. 


Um, would the wheelbarrow be optional?





Title: RE: Power Supply size?
Post by: AC5UP on February 18, 2013, 04:41:39 PM

We should cut N4NYY some slack. He's been working on a job application all weekend.

Dude is interested in a position that opened up late last week at the Vatican.

 :P


Title: RE: Power Supply size?
Post by: WH7DX on February 18, 2013, 05:08:46 PM
Use the 35m for home and a small car battery for portable... Either on the car or extra.

True portable would be the internal 897 which I own as a potable second radio and also hooked up to my 600ft beverage.   

Get a small solar kit to charge battery or just run the vehicle with jumpers.


Title: RE: Power Supply size?
Post by: WH7DX on February 18, 2013, 05:42:04 PM
Here you go. 

This is a portable 857 with small battery..   Will need to trade off battery size and weight for output watts etc....

I wired my 897 with connectors and fuse already on the radio and on the Astron RS-35M power supply at the house with connectors on that side and with an extra set for a battery. 

All I need to do is pull the connectors apart on the home power, put the battery connectors on and plug the radio in.  I figured I'd always have a battery and didn't want to spend the money for the Internal battery for the 897.

My 35M also connects to the Kenwood TS-570, Diawa Meter and FTL Meter.  There is also something to add

http://www.youtube.com/watch?v=jLSzSeajr7U



Title: RE: Power Supply size?
Post by: N4NYY on February 18, 2013, 06:37:57 PM
A 35m for use in an EmComm Go Kit.


right. 


Um, would the wheelbarrow be optional?





I have a 35M. I did not suggest that. I suggested a 25 amp continuous. There are a ton of those switchers around for portable operation, which is why I did not specify a brand. Why do you have to be condescending?


Title: RE: Power Supply size?
Post by: N4NYY on February 18, 2013, 06:43:24 PM
If you need a small footprint switcher for portable use, this is about as small as you can get for 25 amp continuous. I work at HRO on Saturdays and sell a lot of these. These are hugely popular for ecom because of their size. And it has powerpoles. The Astron 35M if perfect for a base but too big for portable use. I have that as my base PS.


http://www.powerwerx.com/power-supplies/powerwerx-30-amp-desktop-switching-power-supply-powerpoles.html (http://www.powerwerx.com/power-supplies/powerwerx-30-amp-desktop-switching-power-supply-powerpoles.html)



Title: RE: Power Supply size?
Post by: K1CJS on February 19, 2013, 01:59:40 AM
Those who say a twenty or a twenty five amp supply would be plenty aren't remembering that supplies used to their capacity get warm--sometimes very warm.  For use in an emcomm box where air circulation may well be problematic, that is asking for trouble--and one thing you do not need is a failure right in the middle of an activation.

Excess heat is the cause of most power supply failures, not electric line transients (although the cheaper switching supplies sometimes don't have sufficient protection against them) and heat is what has to be protected against.  You do this by making sure you never draw a full rated load from the supply.  Taking the maximum amperage rating 'pull' of the radios and adding twenty percent more as a cushion almost always insures that the power supply will never get so hot that it's mounting in an enclosed space will hurt it.

As I said before, Do you want to spend a LITTLE MORE NOW, or a LOT MORE LATER?


Title: RE: Power Supply size?
Post by: K8GU on February 19, 2013, 05:06:40 AM
Buy the biggest power supply you can afford, lift, or tolerate in your shack.


Title: RE: Power Supply size?
Post by: K8AXW on February 19, 2013, 07:32:41 AM
Quote
Buy the biggest power supply you can afford, lift, or tolerate in your shack.

 ;D  You're my kinda guy!  I also feel a kinship to Tim, the Toolman, Taylor of TV fame. 


Title: RE: Power Supply size?
Post by: W8JX on February 19, 2013, 10:47:34 AM
As I said before, Do you want to spend a LITTLE MORE NOW, or a LOT MORE LATER?

There is another way of looking at this too. A big oversized linear supply draws a lot more power when idle and under load than a modern compact switch so you can pay more now to buy that big door stop and pay even more later over its life span to feed it with its lower efficiency.


Title: RE: Power Supply size?
Post by: K1CJS on February 20, 2013, 07:55:26 AM
There is another way of looking at this too. A big oversized linear supply draws a lot more power when idle and under load than a modern compact switch so you can pay more now to buy that big door stop and pay even more later over its life span to feed it with its lower efficiency.

I'm not arguing linear vs. switching, I'm arguing having a supply with extra capacity to prevent overheating and/or failure.  Please stop reading more into posts made than are there.