Kubota D1005 Volt/Freq Adjustment Issues

[Jay L]

Hi All,

I have a Kubota D1005-E3BG with a Mecc Alte NPE 32-B/4 10.5kVA generator head with a S.R.7/2 regulator put together by Central Maine Diesel in 2012.

The frequency has always been a little bit high, approx 63.5 since new - maybe since it was set up in Maine and I'm using it in Hawaii - but it never caused any issues so I left it alone. 

I got a new UPS last month and it doesn't like the high frequency (limit is 63) so it beeps constantly on generator power - very annoying. 

I decided to adjust to ~62 no-load Hz which is within tolerance for the UPS and from what I've read it's what many people recommend.

I was easily able to adjust engine speed to get ~62 Hz by by loosening/tightening the two set screws that pinch the throttle lever located on the outside of the governor assembly after loosening the lock nut on each screw.

Of course I had to adjust voltage using the voltage pot on the regulator - pretty easy to set.

Unfortunately voltage now droops by up to 40 volts as load is increased, so of course I stopped testing until I get some advice.  Hz remains steady.  Hopefully someone can explain how I should be adjusting everything as I am obviously doing something wrong.  I see there is also a Stab pot and a Hz pot on the AVR, but it seems like the governor isn't doing it's thing now rather than the need for other regulator adjustments.

Thanks in advance for your help!
Jay L.
Mililani, Hawaii

[mike90045]

...... Hz remains steady. 
....... but it seems like the governor isn't doing it's thing now rather than the need for other regulator adjustments.

If the Hz remains steady no-load - full load ,  your governor is doing fine.  I don't understand how reducing RPM's to dial in 62Hz from 63Hz, could also result in a 40v drop.  (I don't see how it could even cause a 4v drop, but maybe 2V)  It smells like the AVR is not doing it's job properly.

On a side note,  anyone know of a strobe wheel, like used to be on record players, that would fit on our genset pulley ?  That would solve a lot of issues of odd ball harmonics or distortion causing frequency meters to be way off.

[Thob]

Let's start with: How are you measuring Hz?  Do you have a kill-a-watt or similar digital meter that you're measuring the output of the generator?

Also, did you adjust the Hz control on the regulator?

The frequency output by the generator is determined by the number of poles in the generator and the RPM of the generator rotor.  A four pole generator will produce 60 Hz when operating at exactly 1800 RPM.  Since you can't (easily) change the design of the generator, the only way to change the frequency is to change the generator RPM.

The "Hz" control on the regulator is probably designed to cut off the generator when the engine is operating too slowly.  This helps prevent damage to connected equipment and prevent loosing the field "flash" in slow engine operation, especially during an unexpected event (like running out of fuel).  Normally it is set to something like 57 Hz, when the generator is below that point it will cut the output voltage considerably.  It could be that this control was adjusted too high to start with, and by lowering the RPM slightly you may be tripping this.

Let us know what you find!

[mobile_bob]

harbor freight sells an optical tachometer iirc, anyway i think that is where i got mine.

it somes with a roll of reflective tape and has proven to be quite accurate in my opinion.

very useful tool for sorting out odd problems

bob g

[Jay L]

Thanks for your replies!

Scratch most of my initial findings after I adjusted the RPMs to get ~62 Hz.

Here's what's going on:

Adjusting the generator's RPM to control Hertz, and adjusting the voltage pot is straight forward.  I have a Sperry meter that does frequency and of course a/c voltage.

I'm pretty sure Thob is right with the Hz pot adjustment.  This pot had sealant on it from the factory but really easy to peel off to reset it.  I have the Mecc Alte SR7-2G manual so I worked through the instructions to reset everything (except the AMP pot which is also sealed) from scratch.  Instructions say voltage and STAB pots fully CCW, and Hz pot fully CW to start.  Crazy thing is that the Hz pot seems like it could be damaged inside because it doesn't hit it's left/right limits solidly like the other two - hope not :-(.  Moving on, I set the voltage to 240 with the gen producing 62 Hz, then the STAB pot gets moved CW until an incandescent lamp begins to fluctuate, then backed off slightly until stable.  For the Hz pot adjustment, the generator is taken to 10% lower than nominal speed (I used 54 Hz based on math since I don't have a tach), and the pot is rotated CCW until voltage drops 5V.  After those settings, RPMs are restored to normal.  After all that, the gen seems pretty normal with no load with only a volt or two of fluctuation and a little instability, about .5 up and down (fast) for Hz.

The new symptom of a problems is that when I add load, the voltage creeps UP.  I started with a 1000W heat gun and voltage increased by about 5V, and it gets worse from there as more test load is added.

My main suspicion is the Hz pot - it just doesn't feel normal and I assume if it's not making solid contact inside it could screw up everything.  Also, not sure if 10% lower than nominal speed translates to what I did by lowering speed from what should be 1800 for 60 Hz to X RPM for 54 Hz.  The math is 1800 - 10% = 1620, and then the ratio of 60/1800 = x/1620 which is 54.  Clever, but maybe non-proportional or something else weird.

Unless anyone has suggestions, I really want to change this pot.  Anyone know it's rating?  It looks like a 3386P but I'm not sure of the resistance and wattage ratings.  I wrote to a Mecc Alte support but got an out of office, lol, and I'm not sure if they'd give that info anyway.  I can likely see the rating on the side of the pot if I take the AVR out of it's housing - or maybe I'll need to remove it from the board if the marking is on the side next to another one :-(.

Hope someone has some theories...

Thanks!
Jay

[Jay L]

Decided to go ahead and remove the hz pot.

It was no joke to get it off the regulator board without damaging anything because the plastic surround on the SR7-2G is filled with resin top and bottom.  I used a dremel, hot #11 knife, and a soldering iron and sucker and with a lot of patience no harm was done.

Turns out the pot is a bourns or similar 3362P-104, 100K ohms, .5 watts.  Have a replacement on order so hopefully by next weekend I can post the results after installing it and attempting to adjust the regulator again.

I tested the pot after I removed it, and it seems that in some spots of the (over) rotation it does give normal readings, but it's totally jumpy or open at most points.  I'm pretty confident that with generator vibration it wasn't holding steady and causing the adjustment problems.

Jay.

[Jay L]

Replaced the hz pot and it seemed like all was going to be well, but still having some issues.  Had no issues adjusting voltage, stability, and hertz threshold - but now voltage is dropping unacceptably as load is added, like from 240 no-load down into the 220's at less than 1/4 load :-(.

I assume that the original damaged hz pot may have damaged other components, or maybe physical damage just from replacing it.

Anyway, I've got one of the SR7-2G Chinese knockoff regulators on the way to confirm/deny that my mecc alte SR7-2G regulator is good/bad.

I'll post later, comments welcome about dropping voltage as load is added.  Oh, and I think the kubota governor is working fine because frequency remains stable and you can hear the engine handling sudden load well like my air compressor motor.

Thanks!
Jay