MEP-002A and -003A main breaker

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ashwood486

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I will talk with a couple of industry HVAC friends tomorrow they have first hand information on these soft starts .
I checked my 4 ton heat pump with a true RMS amp meter. Its starting amps was 39 and levelled out at 11 -12 . During 90 degree heat.
I'm still planning on checking the r3 reistor adjustment before I make any changes
 

Speddmon

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Not sure if you have any kind of hard start kit/ soft stater on your heat pump, but starting current typically is about 6 times the motor full load current. Your meter may not be fast enough to catch the peak current reading on startup. At 11 - 12 running amps, the starting current should be in the neighborhood of at least 70 or more since I'm sure the full load rating is more than 12 amps.

My 5 year old 3 ton geothermal heat pump pulled about 75 amps on startup and about 42 or so after I installed the hard start kit.
 

Speddmon

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That is what I would have figured too, but the parts TMs list them as having the same NSN, so I thought it was controlled by R-3 setting. Is the TM wrong? (would not be the first time). Is there a way to change set point? Others seem to have agreed it is the same. I really don't know.
That was my bad...I looked cross eyed at the TM and saw two different NSN's. They are the same breaker for the 002a and 003a. I verified this with a spare output box I have for an 002a sitting in my garage and the new 003a breakers I ordered. They are the same.

There must be something going on with your control box, either the R3 itself or the CT/CVT assembly if you can't get the R3 adjustment to 0.6 amps as stated in the TM.
 

ashwood486

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Thanks for the information . My top priority now is to get serious about the r3 adjustment .
I'm actually happy with just 39 amps at start up. A few years ago it was a lot more from the older units. I believe this number should be easily overcame with the mep002 , considering it falls so fast to 12 amps .
 
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Triple Jim

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You may have read it already, but back on the 2nd page, Speddmon posted a PDF file from the manufacturer of the breaker, that tells how it works. Large overloads will trip it immediately. It doesn't sound like 39 amps would fall into the "large" category, but there has been some mention of breakers that somehow lose the fluid damping feature (leaking fluid?), so they lose their time delay feature and trip even at small overloads quickly.
 

Speddmon

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Thanks for the information . My top priority now is to get serious about the r3 adjustment .
I'm actually happy with just 39 amps at start up. A few years ago it was a lot more from the older units. I believe this number should be easily overcame with the mep002 , considering it falls so fast to 12 amps .
I think you may have missed the point of what I posted above. New or old compressor doesn't change the physics of the motor. I don't think your meter is catching it as it's peak. 39 amps at start-up is way too low for a motor or compresor that has a running load of 12 amps without some kind of soft starter already installed.
 

F18hornetM

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Well my MEP-003a will run my whole shop. Mill, lathe and many other pieces of equipment. I even turned a bunch on and hit the sub feed breaker, No problem. But....It would not start my 5hp, 2 stage compressor. but after doing some checking found my compressor has one of two start capacitors bad. I have noticed cold start issues this winter with it, had to be very warm to start. Checking the amps on one leg while trying to start spiked at 100 amps momentarily. The main on the generator never tripped. So I am pretty convinced the MEP-003a will run motor loads. No problem. Must be breaker issues maybe. When I repair the motor on the compressor I'll try it again.
thanks for the great info here
 

Triple Jim

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I bet you'll be OK when you replace the bad capacitor. My 003A starts my industrial 5hp 2-stage compressor OK. It has a 1725 RPM Baldor motor, I assume something like what you have.
 

F18hornetM

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I believe that's the same. Mine is also a Baldor 1725 motor. Its about 30 years old been a great compressor. Seems to me the breakers, at least on mine are fine and will start a motor load.
I am very impressed with the MEP-003a so far compared to my gas engine civilian models. Although I do have a 8.5 kw Miller diesel welder that does pretty well to. Its just high speed and loud.
 

ashwood486

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I really want to thank everyone that have helped and given experience and knowledge on this subject.
I have a few observations about the breaker on this generator as well as the new HVAC units on the market.
First off,
If I came to service your a/c unit and it was running 11-12 amps.< photo included> It was starting 3-5 times the running amps at 39.
The factory manual says the running amps will reflect the outside weather conditions because Freon pressure and temperature are directly related. They also say this is normal amps for a unit to use with a scroll compressor and an equalizing valve in the system. I have said all this to explain that in our home when a breaker was installed almost 30 years ago, after being checked with any amp meter , or in my case a calibrated amp meter from the power company, not mention my own HVAC meter,
I wouldn't hesitate to change the breaker out and call it a day.

I also think another style breaker would be better in this unit for the main 3 phase power.
A molded case thermal magnetic breaker that has an adjustable trip mechanism would be a better choice in my personal situation. I have used these and they work great for many industrial situations. Ebay is full of them.

All of this is my opinion only and should never be taken as anything more. I'm not asking this machine to go above it potential, its should handle this situation with out breaking a sweat. I think the breakers are set to trip way to soon and if a brand new power company issued amp meter won't or can't read the starting amps because it doesn't last long enough, then the breaker has some major problems.

I think some parts of this machine could benefit from the new technology that has came along in the last 30 years since it was built in 1984,,,,,,. lol , when this machine was built we didn't have the internet and was just moving from 8 track tapes in our cars to this new thing called cassettes. All of our pickups came with mostly am radios and a CB antenna was mounted somewhere. We sure didn't have A/C or cruise control with carpet on the floor and the Dukes of Hazard was still cool.

Thanks guys
 

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Speddmon

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Nobody is doubting your knowledge, ability or skill with AC systems. But you are just not paying attention to what I am saying about starting current. Starting current is the same as the motor rated Locked Rotor Current (LRA) which is minimum 5 to 6 times or more of the motor rated Full Load Current (FLA) and is only present for about 100 to 300 milliseconds (mS). Your scroll compressors still have an AC induction motor that runs the compressor. The advantage of the scroll compressor is that it allows the pressures to equalize so the motor is not starting with any "head" pressure. The scroll design does not change the characteristics of an induction motor. When you are measuring 12 amps of running current that is still not the rated full load current of your compressor, it is mearly what your compressor is pulling at that point in time. Which in an AC system will vary with temperatures and refrigerant pressures. The manufacturer lists a motor FLA rating for every compressor and motor built and it will be listed on the tag on the compressor. And if you dig deep enough your scroll compressor manufacturer will also list in the design specs of the compressor the LRA for that compressor.

As I said in an earlier post, let us assume that the 12 amps you are measuring is the actual full load rating of that compressor (which it is not)

If the full load rating was 12 amps, the starting current or LRA is minimum 5 to 6 times that rating or 60 to 72 amps. Your meter is not fast enough to catch the peak LRA that is only present for 100 to 300 mS, what you are seeing at 39 amps is the LRA coming back down to the normal running load. If you finally follow what I am saying you will see, on an MEP-002a that has a breaker rated to trip somewhere in the neighborhood of 50 amps, why starting a motor with an inrush of 70, 80 or even 90 amps the breaker will trip. Even though the current is only there for a split second, the breaker only sees a very large current spike and tries to do it's job and trips out to protect the machine.

You don't have to take my word for this, although motors and motor controls are what I do for a living. Research motor LRA yourself and you will see almost everywhere that it is 5 to 6 times FLA.
 

F18hornetM

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I know one thing, I saw a 100 amp draw on my meter :razz:
I've enjoyed this post. Thanks for all the info on motors Speddmon!
 

ashwood486

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I have been fully understanding you statement and facts about FLA , LRA , and RLA for motors.
I'm surely not listening or not grasping all this information . I was being taught the same stuff all through school . Lol.
I just have changed my opinion and am looking at motors with a whole different concept than most . I wasn't going to get into it and fully respect your position on these subjects but, please allow me to say a few opinions.
Manufacturers have to make the tag for every motor based on testing performance from more than one motor , ending with worst case scenarios . Every motor doesn't start and run exactly the same as the next . If you lined up 20 of them they will all have different readings under exactly the same conditions . Just like the stickers on new cars about mpg. Even if a motor is locked up everyone will show different readings . The motor manufacturers have a chart also showing the different amp draws based on voltages and hertz being applied from high to low and the results , because they fluctuate and are definitely not the same in every city.

Just these things alone make the tags on motors and compressors just a general guideline and not an absolute .
If you rebuilt 5 motors every motor would give different readings in the same environment.
And every person is always boasting about how their generator is running at 130% capacities and doing great , so I think the breakers should also have the same capability of starting 30 % more than rated . I've always been taught the military equipment is built way better than anything else in its class.
Again all this is my opinion only . I fully respect yours.
Don't take offence please .
These breakers are also 30 years old. Things get weak.
 

Speddmon

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I wasn't going to get into it and fully respect your position on these subjects but, please allow me to say a few opinions.
No offence taken, I love a good discussion and hopefully the other members can gain some knowledge from the things said here. Not arguing, but the next statements you made are just that, your opinion. Let me give you some facts.


Manufacturers have to make the tag for every motor based on testing performance from more than one motor , ending with worst case scenarios . Every motor doesn't start and run exactly the same as the next . If you lined up 20 of them they will all have different readings under exactly the same conditions. Just like the stickers on new cars about mpg. Even if a motor is locked up everyone will show different readings.
If you lined up 20 motors from the same manufacturer you'll find almost all of them to be dead on with one another under the same running conditions. There are a few minor external factors that will effect them such as bearing friction, but the effects will be minimal. There will be a difference if you lined up 20 motors from 20 different manufactures, but we need to compare apples to apples. Now, there are the manufacturing irregularities that will pop out an oddball every now and then and typically this shows up as a bad motor right out of the crate.

When a manufacturer makes a motor, they are all made the same. Using the same materials and the exact same length of wire in the windings and the same amount of iron in the cores. And since the electrical resistance of a certain gauge of copper wire is fairly constant, each motor would have almost the exact same amount of resistance in the windings. And since the amperage draw is Ohms Law, being I = V/R or Current equals Voltage divided by the Resistance, the current draw will be almost exactly the same in each motor. And again, the electrical theory behind locked rotor current is always the same. When the rotor is not spinning the inductive resistance is not present, so the circuit looks just like a standard resistive load and will have very high current draw because of the very low resistance of a motor winding. As the rotor begins to spin, inductance comes into play and the apparent resistance of the windings goes up thereby lowering the current.

You can take that to the bank. In the industry when we change a motor out we expect to have the same current draws. If they were different every time as you suggest, we would be constantly changing and recalculating motor overload protection. That is why there is NEMA, or the National Electrical Manufacturers Association. They set the standards that all manufacturers who want a NEMA certification must follow and be within specs. And trust me, nobody buys non-NEMA equipment if they want to get any kind of consistency and longevity out of their equipment.


The motor manufacturers have a chart also showing the different amp draws based on voltages and hertz being applied from high to low and the results , because they fluctuate and are definitely not the same in every city.
Actually, that doesn't change hardly at all. I challenge every member here to go out and check the Hz reading coming into your house all over this country and you'll find them all to be at 60 Hz and voltages to be relatively close as well. For the power grid to work, this is an absolute, the frequency needs to be exactly the same throughout and the voltage generated needs to be very close. If it is not, one power station would take all of the load and another one running at a lower Hz would not take any (or very little)

Just these things alone make the tags on motors and compressors just a general guideline and not an absolute .
If you rebuilt 5 motors every motor would give different readings in the same environment.
And every person is always boasting about how their generator is running at 130% capacities and doing great , so I think the breakers should also have the same capability of starting 30 % more than rated . I've always been taught the military equipment is built way better than anything else in its class.
Again all this is my opinion only . I fully respect yours.
Don't take offence please .
These breakers are also 30 years old. Things get weak.
As I said above, your 5 rebuild motors being the same manufacturer and rewind shop (compare apples to apples), would be almost exactly the same. If you took a Baldor motor rewind from XYZ armature shop and a Leeson motor rewind from Homewindingshop.com and a US Motors rewind from 3D electric, yes, they would give you different readings under the same conditions. But they would still be pretty close since they have a NEMA standard to follow.
 

F18hornetM

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To verify the main breaker will hold on a motor load. I replaced the bad capacitor on my 5hp 2 stage compressor. Hooked up shop to the gen and with just a small grunt it started the compressor fine. Had lights, fans etc and compressor running at 50% load on the generator. So as far as I am concerned. The main breaker will hold a 5hp motor load on a compressor. I even ran my T.I.G on it for awhile.
 
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1000eemonarch

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I just got my MEP-002A running (nice clean unit that didn't need anything besides filters, oil and a couple of gauges, but I did tear all the sheet metal off and go over everything with a fine tooth comb) and decided to try it on a 3HP air compressor. Same thing as a lot of the previous posts on this thread!

The air compressor is a very compact but heavy duty industrial 3HP, 3phase 208Vac unit from the early 80's (Toshiba Toscon). With the MEP-002A in 208V 3-phase mode, putting out exactly 208Vac at 60 HZ flipping the breaker with the compressor connected pegs the loadmeter and trips the breaker instantly, without the engine bogging down.

By dropping the frequency to 50HZ and the voltage to 190V it will start, and then increasing voltage and frequency to normal the loadmeter sits around 30% with the compressor chugging away. Engine doesn't sound labored at all.

That tells me the breaker in this unit, just like a lot of people have complained, is overly sensitive to motor starting inrush currents. OK, I might just hold out for a good deal on a MEP-803A, but I'm pretty sure I can make this MEP-002A do a little better. Here's some ideas:

R-3 adjustment, which I have not tried, but it seems no one as had much luck with that route.

Add shunt resistance to the low-current side of the breaker (3 resistors in between each pair or six small terminals on the breaker) was thinking of using resistors equal to the breaker's internal resistance across those terminals. That would divert half the current away from the breaker doubling the trip point. Just an idea, not sure if it would work.

Bypass the breaker and run an external breaker (probably the easiest).

Part if the problem is that box with the breaker is very crammed with stuff and not easy to work inside of, and besides I don't want to butcher it. Part of the beauty (at least to me) of these units is the insane complexity and high quality components inside. I could gut that box with the crazy drum switch and the current transformer, wire the 12-lead alternator for 3-phase and use a modern voltage regulator and circuit breaker but it just wouldn't be the same....

I spent about half an hour trying to understand the electrical schematic of this unit (and I'm used to dealing with complicated electrical schematics) and gave up trying to understand it!

What's the opinions on an MEP-803A's ability to deal with 3-phase motor starting? I might just try to get one of those and sell the -002A.

Another (possibly unrelated) question.... What's the black plastic box behind the current transformer to the left in the high voltage box? The field rectifier board is on the right of it. On mine the plastic is cracked in a few places, but it's hard to get a good look at it without pulling stuff apart.
 
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