Mep-002a Ammeter-Voltmeter transfer Switch

[RWG421]

I just picked up my first Mep 002A, and for the life of me I can’t quite get my head around the Ammeter-Voltmeter Transfer switch (AVTS) Function.

My Question is; with the Reconnection switch set to 120/240 1 PH, page 2-4 & 2-5 of the TM suggest that I set the AVTS to the "4 o’clock" setting ( Amps L3, Volts L3-L0 Phase 1) per table 2-2 on page 2-4 of TM5-6115-584-12

So if I measure across L3-L0 as the tables suggest I will read 120 volt, and I will wire L3 & L1 as my hot legs and L0 as neutral.

I know the AVTS setting contradicts a post on "MEP-003A hook up question” 9/12/2009
So this is where my confusion lies
Are Either Single Phase option on the AVTS (2 and 4 o'clock position) available to me as long as the Reconnection switch set to 120/240? If so how does this affect my connections at the load terminals?

Additionally does L1 become the neutral under 120v 1 phase 2 wire setting ”Figure 2-4 page 2-5” of the TM.

If so is this accomplished by the AVTS or the Reconnection switch position?

Thanks in advance for any insight into curing my brain damage.

 

[Speddmon]

You're thinking about that switch way too hard. The small switch on the front of the control panel does absolutely NOTHING to the large output lugs and the main reconnection switch located in the AC output box.

The small AVTS as you called it is only for the metering and gauges on the control panel. The 2 positions farthest in the clockwise rotation are the 2 you would be using when you have the main reconnection switch set for 120/240 single phase operation. One position (4 o'clock) will measure and display the amperage on L3, and voltage across L3 and L0 (120 volts). The other position (2 o'clock) will measure and display amps on L3 and voltage across L1 and L3 (240 volts).

 

[RWG421]

That clears up a lot for me, Thank you SOOO! Much.

Can this switch be moved during operation? And will the values be displayed on the panel, Volts on volt meter and amps as % of load?

I will be trying to fire it up this weekend, but I still have some "depreservation" to do. From the paper work I got with it looks like it has been in storage since 1983. I hope all goes well, 28 years of sitting oh my!

Thanks again for taking the time to share your expertise, not just on this question, but on other post I have read. They have really answered a lot for me about the Mep 002a.

 

[kipman]

Tom is our MEP pro, you only get one answer a day.

 

[Speddmon]

That clears up a lot for me, Thank you SOOO! Much.

Can this switch be moved during operation? And will the values be displayed on the panel, Volts on volt meter and amps as % of load?

I will be trying to fire it up this weekend, but I still have some "depreservation" to do. From the paper work I got with it looks like it has been in storage since 1983. I hope all goes well, 28 years of sitting oh my!

Thanks again for taking the time to share your expertise, not just on this question, but on other post I have read. They have really answered a lot for me about the Mep 002a.

Yes, you can change that switch while the set is running and under load. As long as you are running the set in 120/240 single phase operation, you'll see the displayed voltage in the 2 o'clock position go from 240 volts to 120 volts when you switch it to the 4 o'clock position. The % load shouldn't change at all since both positions measure the amperage from L3.

 

[RWG421]

Got it. Is it important to balance the loads between the two hot legs? What is the best way to do this if % load is measured off L3 only ?

thanks again,

 

[Speddmon]

Yes, it is kind of important to keep the loads in balance. Depending on what you are doing with it though, you may not need to worry about it too much.

If you are running it in 120/240 single phase mode, and have your house hooked to it. Any 240 volt loads are automatically balanced. The 120 volt loads are the only ones you need to worry about. Other than maybe a well pump or sump pumps, most of your 120 volt loads are going to be small loads such as light bulbs and possibly electronic devices with little current draw. It will take a lot of bulbs burning on just one leg of the generator to imbalance the phases bad enough to cause troubles. And the well pump and sump pumps, and intermittant loads and short ones at that, so I wouldn't be too concerned with them either.

Now, I wouldn't be running any larger single phase loads without doing some kind of load management. When I say that, I mean like working in your shop and running larger fans, or an air compressor or some 500 watt or larger quartz lights, circular saws or a grinder. But in my opinion, if your utility power is out and you are using the generator, I would think you have bigger things to deal with than to be working in your shop or garage.

 

[RWG421]

My plans are to back feed the panel for house and shop both.( both are in same panel) If it’s a short term outage the house (Refrig, freeze ect..) will be the primary concern, and our day temps are still over 100 here so depending on time of year A/C will be an issue also.

If it is a SHTF type deal the shop will be the primary concern (Inverter A/C there) so I can keep up with production.

Ideally I was thinking if I can manage the house draw to run the genset at 80%and the shop at an additional 20% ( no a/c's) this would give me the most fuel per hour bank for my buck, or is it really bad Juju to run at 100% for 8 out of 24 hours operation?

 

[doghead]

These generators were designed and built at 300% of their rating(output).

Running it for 40 hrs straight at 100% is no problem.

Also, the wattage rating was at 8000 ft above sea level. So in most cases, we get about 2000 extra watts out of them.

 

[RWG421]

So essentially these are 15 k (surge rating) generators by civi standards ??

 

[doghead]

Not exactly, but sort of!

Just look at the size of that generator head. Ever seen a 5k genset with a 300 lb head?

 

[Keith_J]

They are over-built for certain. Frequency is set by engine RPM, that massive 140 cubic inch IDI diesel is far more stable than any 600 CC gasoline twin used on most 10 kW commercial generators.

Output of the generator is based on the torque of the engine overcoming the back EMF of the load and the resistance of the windings (which increases with temperature, requiring more rotor current from the voltage regulator). If the frequency doesn't droop and the VR can compensate, all is fine. But if the windings over-heat and the VR maxes out, the insulation of the windings can be damaged. This is the nature of the "surge power" rating of most generators. Surge rating should only be relied to start motors, not continuous loading.

I have its little brother, the MEP 002A. I'm going to use it to drive my Miller 200 DX welder (3 phase). For all TIG welding, it will do fine but the welder draws 8.1 kW at 200 amps in stick (SMAW) so we shall see. 3 phase connection as that needs 14/4 wire instead of 12/3 for 240 volt single phase. Cheaper extension wire.

I just got back from doing some aluminum welding for TexAndy. I'm loving this welder, makes aluminum easy.

 

[derf]

So essentially these are 15 k (surge rating) generators by civi standards ??

Uh, no. I think you could drive 7.5kW load all day long, and maybe surge up to 10kW but a twin cylinder 1800RPM gen ain't gonna drive a 15kW load for any length of time.
The 003A is military rated 10kW and the civilian version doesn't have the oil cooler that the military version has and is rated at 15kW.

In my opinion you can drive loads of 1.5X military ratings near sea level at normal temps. If you try to drive 3X loads I think you will let the magic smoke out of something.

 

[derf]

They are over-built for certain. Frequency is set by engine RPM, that massive 140 cubic inch IDI diesel is far more stable than any 600 CC gasoline twin used on most 10 kW commercial generators.

Output of the generator is based on the torque of the engine overcoming the back EMF of the load and the resistance of the windings (which increases with temperature, requiring more rotor current from the voltage regulator). If the frequency doesn't droop and the VR can compensate, all is fine. But if the windings over-heat and the VR maxes out, the insulation of the windings can be damaged. This is the nature of the "surge power" rating of most generators. Surge rating should only be relied to start motors, not continuous loading.

I have its little brother, the MEP 002A. I'm going to use it to drive my Miller 200 DX welder (3 phase). For all TIG welding, it will do fine but the welder draws 8.1 kW at 200 amps in stick (SMAW) so we shall see. 3 phase connection as that needs 14/4 wire instead of 12/3 for 240 volt single phase. Cheaper extension wire.

I just got back from doing some aluminum welding for TexAndy. I'm loving this welder, makes aluminum easy.

I thought the OP was asking about an 002. Maybe I'm just confused but I'm positive that an 002 won't drive a 15kW load. An 003 will. But, before something goes POOF! we should make things clear. MEP-003A has 140 cu. in. displacement 4 cylinder Diesel motor and will drive 15kW load. MEP-002 has a similar but only 2 cylinder Diesel motor.

 

[RWG421]

MEP 002A is the unit I have,

So if I run at 120% I will be at 7.5 kw. The plan will be to manage the load less the A/C at about 80 %. The A/C will push it up to the 120% and could stay on for awhile ( its still 101 right now here in AZ)

Do you think it OK to run this way long term ( lets say 2 week outage?) or is it to much for a 002A?

This would defiantly meet all my power needs.

 

[derf]

I'm not a math wiz but I believe 7.5 is 150% of 5.0.
In my opinion you can probably run that gen at 7.5kW load till the cows come home.
Motors and compressors and such have different characteristics, though. Many have very high startup power draws.
If it were mine I would test it by gradually adding to the load. If a breaker trips or if the unit can't maintain output voltage and frequency then back off the load.
You don't want to find out the hard way that your gen stumbles when your AC compressor starts and that stumble fries your computer.

An AC that takes 20 Amps to run may require 40 Amps or more to start. Most central units have two fans, one outside cooling the condenser and one inside blowing across the coils to make cold air, and a compressor. If both fans and the compressor try to start at the same time you might have a big current draw for a few seconds.

 

[RWG421]

Doesn't the 002A get is 5kw (" maximum rated power........5KW (0.8 Power factor") ratting running at 80%?, or am I not understanding the whole Power factor thing?

That's great advice on the slow draw test, I never considered the " brown out affect' on my PC, scales etc .
That would not be fun, Thanks.

 

[derf]

Power factor is real vs. apparent power. You do not multiply power factor times rated output to get anything.

I think it is more like the gen has to make 10 Amps to deliver 8 Amps to the load. 8/10 is 0.8PF.

 

[RWG421]

Power factor definition is giving me a headache I like your approach "If it were mine I would test it by gradually adding to the
load." I think the only issue will be the house 3 ton 12 seer a/c. The shop has a 2.5 ton 18 seer inverter so i think that will run,so I
guess we could camp out there.We spent one weekend at 107 when the a/c went down , not fun at all.

 

[PeterD]

I love power factor, it confuses the heck out of almost everyone (the only more confusing thing is the 120/208 volts from three phase.)

Watts are (roughly) volts times amps with a 1.0 power factor.
VA are volts and amps, and take power factor into consideration.

In a perfectly resistive load, maximum current is drawn at maximum voltage. Both are timed or happen, at the same time. That is a power factor of 1.0. Watts equals VA (volt amps)

In a non-resistive load (almost always an inductive load) current lags voltage. That is maximum current happens not at peak voltage, but somewhat after (because of saturation). If you multiply amps at peak voltage, the watts reading would be lower than the true power delivered to the load. Same is true at peak current, because it happens at a time different from peak voltage, the apparent power is lower.

Instead what is done is that peak voltage is measured, and peak current is measured (without regard to when either happens) and that gives VA. And VA gives the best representation of the power required by the load.

So can the issues of power factor be corrected? Absolutely yes, and it is done all the time. Power companies use large capacitors on the AC lines to correct for the inductive power factor. The capacitors simply move the peak current demand to more closely match peak voltage. Can you do that with your generator set? Probably not worth the effort, as loads change too much.

Hint: for a capacitive load, the highest current occurs before the highest voltage. For an inductive load (motors!) peak current happens after the highest voltage.