power pack rated at 27 VA

Watts = Volts X Amps

We are missing info. I cannot solve for Amps without knowing Volts.

VA is Volt Amps for purpose of discussion = Watts

If you operating voltage is 12 volts.  The (maximum) amperage 2.25.

Hi Vernon,

This is a MRC 6200 operating in mode 2, 0-14v  at 27va. It is shutting down after running near an hour with amp draw under 1 amp. Thanks for replying,

Ray

OK, I am attempting to determine if this power pack, MRC 6200, is defective. The situation is, operating in mode 2 (rated 14 v, 27 va) potentiometer at half throttle ammeter on line reading .95 amps for approximately 1 hour the pack shuts down. Does this show the power pack to be defective or is this overloading the power pack?

I hope I am giving enough information for an answer.

Ray

This is a low wattage unit but is only half loaded based on provided data, you can do the math. From your symptoms, it appears to have some sort of thermal overload that eventually trips. Might be age, ventilation, or other causes.

Google search results in plenty of forum posts in various scales of that exact model failing.

So just call it- it's not meeting your needs now, go with something else with higher capacity.

Well, remember that the ratings of such supplies are probably rated at full voltage.  It's quite possible that running at half voltage you'll get considerably less than 27VA out of it.

@gunrunnerjohn posted:

Well, remember that the ratings of such supplies are probably rated at full voltage.  It's quite possible that running at half voltage you'll get considerably less than 27VA out of it.

John,

I am kind of a rookie, does what you are saying mean the power packs protection might shut it down at lower amperage?

Thanks for your input,

Ray

A few comments:

We're right at the edge of a 'duty cycle' discussion.  The power pack may be rated at 27VA, but a secondary question is if the power pack was designed for that usage for hours on end, or just a typical length of running time, say 30 minutes?  In the old days, power packs were over-designed to provide reliability (think of the people who claim you can weld with a ZW), but newer power packs are likely not as over-designed due to efforts at containing costs.

Secondly, there might be issues with a weak thermal overload breaker too.  Don't forget that all of these parts have design tolerances and your transformer may have a thermal breaker out of tolerance or at the edge of being out of tolerance.

Dale

@Rayin"S" posted:

I am kind of a rookie, does what you are saying mean the power packs protection might shut it down at lower amperage?

Depending on how they regulate the power, a lower than maximum voltage, many power control circuits don't have the same current handling capability as they do at full throttle.

I don't do much with DC supplies, but take an electronic AC transformer, say the CW-80.  If you run it at 18 volts, you'll be able to get close to 80 VA, the current limit is 5 amps.  However, if you're running it at six volts at 5 amps, that's only 30VA before you trip the over-current circuit.