wet stacking or idling my Mep-003a

[Wolfe]

Hi,
new member here with a question on running my Mep-003A. Is it ok to idle these units to warm them up and cool them down or will that do harm to the electronics? Also, is it ok to run the generator without a load on it as long as the breaker switch is turned off? What does the term wet-stacking mean when taking about a generator? Thanks for your advice and this site has been a great help to a new guy trying to take care of my new, used 003a.

 

[doghead]

Never idle it, it will destroy the voltage regulator(This is in the operators manual and has been covered here before).

An advanced search in the axillary equipment forum for, "wet stacking", "idling", and any other things you question, should help you easily answer your questions.

 

[Isaac-1]

Like Doghead said, never idle these, I personally think the biggest mistake they made in designing these generators is to include a user accessible speed control knob, on first start up set it to about 61.5 -62 Hz no load so it will droop to about 60 Hz fully loaded then never touch the knob again.

As to wet stacking, this is the effect of running a diesel engine at less than peak operating temperature, which can result in cylinder glazing, and thereby increased blow by, as well as partially complete combustion and build up in the exhaust system. Running unloaded will generally lead to low engine temperatures in diesel engines, however the MEP-003a is an air cooled diesel, so tends to run hotter even at no load than a comparable water cooled engine design, and therefore wet stacking is much less of an issue than it is in say the water cooled MEP-004a. This does not mean a MEP-003a can not wet stack, just that it is much less prone to.

Ike

 

[Wolfe]

Thanks so much for your help. I will make sure to not idle the unit. Going to take a little time getting used to hearing a cold diesel rev up when its still cold. But, based upon the information on this site, its the way the motor was designed. Thanks again for your help,
Mark

 

[Isaac-1]

I am just glad you checked here first, all too often we get people here after they have killed the AVR's by idling

 

[Wolfe]

If you dont ever idle the motor is the voltage regulator still a weak spot in the system? Just wondering if its something that should be updated to head off any problems down the road. Is there a thread where all the 003A's weakness are addressed or are the machines so over built that they dont really have too many things to worry about if maintained properly.

 

[steelandcanvas]

Also, is it ok to run the generator without a load on it as long as the breaker switch is turned off?

You can run it unloaded with the breaker opened or closed, makes no difference. Just make sure the little door is closed to avoid contact with the output lugs.

 

[Triple Jim]

After all my testing, it's still being said that running an 002A or 003A under speed will hurt the AC regulator? The regulator has less work to do when the engine is running under 1800 rpm in these two generators, not more. I've measured the regulator output current below 1800, at 1800, and above 1800, and the greatest control current occurs above 1800, not below. I even installed an ammeter on the control panel of my 003A so I can easily monitor the regulator current supplied to CVT1 by Q3 on the regulator board. The greatest stress on the regulator occurs above 1800 rpm when it has to supply extra control current to CVT1 to keep the generator output voltage down. Running my 003a at the slowest speed it will go for 15 minutes resulted in Q3 being cool to the touch.

I'm not promoting running these generators below 1800, because there is no reason to do so, and there may be other reasons it's not a good idea, like reduced engine cooling.

 

[doghead]

Says the guy selling voltage regulators.

Here's the exact verbage from the TM. Read it any way you like.

STARTING GENERATOR SET (SEE FIGURE 2-3).

CAUTION

Do not idle engine.

Operate generator set only at rated RPM.

Do not use either to aid starting generator set.

Do not operate in excess of 200 hours continuous

with JP-4, MIL-J-5624 bulk fuel.

 

[Triple Jim]

Yes, I understand, and I did say that I don't recommend running it under 1800 rpm because there may be reasons like reduced engine cooling, and there's no good reason to do it. I'm just saying that everything I've done to test the regulator in the 002A and 003A has proven that no extra stress is placed on it by running the engine below 1800.

Note that this warning in the 002A TM does not mention the regulator. Also note that the 003A TM does not have the do not idle warning in it, even though they use the same regulators. I wonder if this warning is a holdover from other manuals to other generators that actually do put extra stress on their regulators at low engine speed. Or maybe it's just because if someone runs the generator at reduced speed with loads connected, bad things could happen to the devices connected.

As far as making and selling regulators, I sincerely hope you don't think I'm sharing my test results in an attempt to make people damage their equipment. You can examine the schematic of the regulator in the TM and plainly see that the way it works it to supply current to CVT1 to reduce generator output. You can also put an ammeter in the control loop like I did and see that I haven't fabricated this for profit.

 

[doghead]

Truly a mystery we may never solve.

 

[Isaac-1]

There really are no shortcomings to the MEP-002a / MEP-003a design that make them in need of any updating, they do however have a few common issues that are not critical to their operation.

1, Some argue that the voltage regulation system is overly complex, it is certainly esoteric compared to modern commercial AVR's.To put it in simple terms most commercial AVR's work by boosting the excitation field to the desired level, whereby a complete failure of the AVR circuit board generally results in no voltage being produced by the generator, by contrast the AVR's on the MEP-002a / MEP-003a work by dampening a full voltage output which is produced by a type of transformer, meaning its most common failure mode causes the voltage to go high. (about 150VAC instead of 120VAC). Having said that the standard AVR circuit is well built, and fairly reliable, it is also economically repairable with the most common failure component a $5 transistor that can be replaced by anyone with basic soldering skills. (3 legs to solder and one screw to remove). Personally I see no benefit in replacing a working or economically repairable AVR system with a commercial drop in product.

2, The other most common problems with these generators when they are in running condition has to do with the instrumentation, this is due to multiple issues, the gauges themselves tend to fail or go out of calibration due to vibration and moisture, and the frequency transducer that drives the frequency meter is failure prone due to aging components. Having said that none of these gauges are critical to the operation of the unit, some people choose to retrofit modern digital gauges to their generators, but this usually involves some metal work on the part of the front panel holes, etc. as original style gauges can by hard to locate and prohibitively expensive. It is always a good idea to double check the panel meter accuracy with a known good meter, the cheap ($20 from Amazon, etc) Kill-A-Watt P4400 is nearly ideal for this.

3, I do not mention injector pumps here as failure of those are often attributed to long term improper storage and are therefore not relevant to the topic at hand.

Overall it is rare to see failures in these generators once people have them up and running, and when we do it is not any one specific component, but instead random failure like you might find with any mechanical device.

Ike

p.s. I might add DC charging regulators as a age / wear prone component, while I probably would not replace a working one, it might be smart to have a spare on hand, much like having a spare or two of those $5 transistors.

 

[Munchies]

Triple jim is spot on.

 

[johnray13]

A while back there was a post about the transistors in the VR. I meant to pick one up to have on hand as cheap insurance but never got around to it. If anyone have a part number for the transistor, I probably ought to pick one up.

Thanks, John

 

[Isaac-1]

To recycle a PM I sent:

I bought mine from Newark Electronics (not my favorite electronics parts place, but they had the low price at the time) The original transistor has a JAN or JANX2N3584 , the JAN prefix is just saying that the part is mil-spec certified, in this case a certain percentage of the production lot would be tested to failure, you of course pay a LOT MORE for these, and they are functionally no different than the standard commercial version 2N3584 These can sometimes also be found on ebay. Be aware these are heat sensitive when soldering, and should be held with pliers as a heat sink, and allowed to cool between each joint that is soldered.

Ike

 

[Triple Jim]

Ike, agree with all, except I've had recent horrible experience buying electronic components from eBay. Specifically, there are counterfeit parts floating around, and you can't tell until you're really counting on one and it fails. I strongly recommend paying a couple bucks more to buy it from a seller who has a reputation to uphold, like Newark, or Mouser, or Digi-Key, or Allied, or Farnell (etc).