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Author Topic: Powering ham equipment safely  (Read 731 times)

Posts: 146

« on: December 14, 2001, 09:14:34 AM »

How do the rest of you power your ac powered ham gear?  Do you plug it directly into the wall plugs?  Or do you first plug it into some kind of surge suppressor, then into the wall plugs?  Should I be concerned about providing a "clean" source of power, free of line noise and surges?  If so, how?  I've read about the Tripplite Isobar surge protectors, but they are designed mainly for computers and other low current devices.  As a matter of fact, the Tripplite Isobar 8 Ultra has a 12 amp breaker that is well below the 15 to 25 amp power supplies my ham gear draws.  Any suggestions?  I currently live in an apartment, but I'm buying a house in the spring and I want to make sure my station is designed for safety.

Tom, N8EUI  

Posts: 20406

« Reply #1 on: December 17, 2001, 08:06:57 AM »

Commercially manufactured, AC-powered amateur station equipment is quite safe if operated directly from the 120V/240V mains in your home.  The "surge protectors" are, for the most part, unsliced baloney.  They (the inexpensive "protected" power strips, costing $5.99 to $29.99 or so) are just an outlet strip with one or more MOV's (metal oxide varistors) across the line to clamp huge transients that might occur under very unsual conditions.  Most ham gear doesn't need anything like this.

The expensive UPS's, which completely isolate your equipment from the AC mains, provide a much higher degree of "protection" from line transients and other baddies; however, they are large, heavy and expensive, since your equipment is essentially operated from a battery (or batteries), and the AC line is used only to charge that battery, and the battery drives a DC-to-AC power inverter to power your gear.  Typical cost per Watt of one of these devices, is in the $.30 range...thus, if you needed a 15A UPS for continuous operation, it would likely cost ~$540 or so (15A x 120V x $.30).  And, they are well worth it, if you live in an area prone to horrible power line conditions.

The problem with MOV "protected" power stips is that MOVs exhibit a well known failure mode that makes them prone to burning down the occasional residence.  It's happened many, many times (well documented in UL reports).  What happens is this:

An MOV is made of dozens, or hundreds, of grains of metal oxide (normally zinc based), in series to create the withstanding voltage needed, say 120V.  Since an MOV starts drawing current at its breakdown voltage, typically a ~180V MOV is used to protect a 120V line.

A transient comes along that causes the MOV to break down.  If that transient contains substantial energy (joules), as, for example, a lightning strike will, some of the oxide grains will fuse and become short circuits -- permanently.  Now, the "180V" MOV might only be a 90V MOV, after a strike.  That 90V MOV, which is based on the remaining good grains of oxide, draws continuous current and dissipates power as heat -- and gets hotter, and hotter, and hotter, until it starts smoking.

If it shorts altogether and causes the line fuse to blow or circuit breaker to trip (this would be a good thing), all's well, but you're off the air until you replace the MOV or the power strip.

However, if it fails slowly (this does happen) and just gets very hot, the MOV and any surrounding flammable materials can ignite and well...normally that does not lead to a happy ending.

Underwriters Laboratories (UL) and other consumer safety agencies periodically review listed products for safety, which includes fire avoidance, and they do a pretty fair job overall; however, it's exceedingly easy to "cheat" the system, and of course there's no law stipulating that products sold must be UL Listed.  Also, UL does not "guarantee" anything, and they have no liability whatever should a UL Listed product cause a fire, with damage and even death resulting.  So, the consumer must really be aware.

Having used, tested and reviewed many of the "protected" outlet strips on the market, I wouldn't use any of them, personally.  I use regular power outlet strips.  Regardless of what you use, you're never immune to EMP (electromagnetic pulse) damage, anyway.  The most damage I ever had to amateur equipment occurred when I lived in New Jersey and had a very near lightning strike (not direct), which blew out nearly all electronic devices in the house, whether those devices were plugged into the line or not!  I had an Astron RS35M sitting on a workbench, not connected to anything, nor plugged into the line, which blew its regulator by EMP caused by lightning.  Unbelievable.  Powerful stuff, that lightning.

73 de Steve, WB2WIK/6

Posts: 12354

« Reply #2 on: December 28, 2001, 09:20:46 PM »

Remember that a 13.8 volt, 25 amp power supply does not draw 25 amps from the 120 volt AC line. It likely draws more like 5 to 6 amps from the AC line. 13.8V x 25A = 345 Watts. If the supply is 50% efficient then it draws 690 watts from the AC line. 690W/120V = 5.75 amps.

I agree however that surge suppressor outlets with MOVs are pretty much a waste of money. I believe UL approval now requires a temperature sensitive fuse located near or as a part of the MOV (the result of smoke and fire caused by failing MOVs). That means that if the MOV fails and overheats then the fuse opens and (lacking any other circuitry or indicator device) you are now unknowingly running without any protection.

Posts: 12354

« Reply #3 on: December 28, 2001, 09:44:26 PM »

I have installed a surge protector at the electrical panel on the two circuits that feed my radio equipment. This is a solid state device that is designed to be mounted in a knock-out on the panel. One of the problems with all shunt type surge protectors is that they shunt the surge to the ground lead. If the device is on the end of a long line then the ground lead has resistance (and inductance) which can limit the protector's ability to function. By mounting the surge device on the panel, the ground lead resistance and inductance is greatly reduced. It can only protect against a surge coming in on the power line however.

Does it work? I have not had a surge related failure in 15 years so either it works or I have been lucky enough to not have had any surges large enough to damage the equipment. Who knows :-)

Posts: 18

« Reply #4 on: February 02, 2002, 02:20:40 AM »

I use a 500 VA UPS (APC Back-Ups ~$100) that allows about 15 minutes of SSB transmit or 60 minutes receive during an inverter run condition (Battery Power).  A standby UPS will protect your sensitive equipment from sags and surges.  When input voltage swings +/-X% from nominal, UPS automatically switches over to a battery that drives an inverter running at 60 Hz/120 VAC.  When the input voltage returns to nominal for a set period, the UPS returns to a standby state.

To size the UPS, simply calculate load requirements in watts then convert to VA and go hunting.  For single phase 120 volts, 1 watt = 1 VA.  Therefore, my 500 VA rated UPS is theoretically capable of supporting a 500-watt load (resistive).  Typically, a higher VA rating above what you calculate will provide a longer run time.

In addition to the UPS, I use a line filter with MOVs (home brew). A carefully selected line filter will help reduce AC line noise (common and differential mode) and MOV will clamp transients.  

A combination of the above hardware should cover about 99.9% of typical power disturbances.  


Posts: 1


« Reply #5 on: March 07, 2003, 12:48:50 PM »

I just plug a power-strip into the wall and run with it. The power-strip is used because it has multiple outlets, not because it has a breaker/MOV. I run AC to the 30A power supplies, then to a RigRunner 4012. Each piece of equipment that CAN run on 12V, does. And each RigRunner outlet is fused to as close a value as possible to the rated, average current draw of each piece of equipment. In the event of power failure, two 975AH Marine Batteries will take over (Simple NC Relay, Power Failure Switch) and disconnect when the PS is back up and running.

I have two power supplies, my cell-phone charger, RS Antenna Rotator and Laptop PS Supply plugged into the wall. If any of that stuff gets smoked, oh well.

Loren B. Cobb / KD7PLU
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