Wet stacking generators

[bdog]

I have another thread about electrical consumption but had another question regarding generators. I am looking at diesel units in the 8-10kw range. The generator will run about 80 hours a week, two weeks a month. The thing is of an 80 hour week maybe 40 of those hours will be near the rated load and the other 40 hours I will be drawing 2,000 watts or less. The generator salesman I was talking to said that is not good for the generator and will cause wet stacking. Is this a real problem or a wives tale? I have heard of wet stacking before but have never seen firsthand damage from it and I have a dozen things with Diesel engines many of which idle quite a bit. I don't want to spend 7k on a new generator and mess it up though.

 

[Rock knocker]

The generator won't be idling, it'll be running full RPM, just not under a load.

 

[bdog]

I know that but the sales guy said it running that long under such a low load wasn't good for it? He wasn't trying to sell me something else heck if was almost trying to talk me out of buying it.

 

[bdog]

Google found this - maybe it is a real problem

Wet stacking - Wikipedia

 

[bigdeano]

If you're worried about it just hook a heater up to put a little more load on it. It would probably only be a problem in cold weather I would think.

 

[100 td]

40 hours full load, 40 hours 10~20% load. That a **** of a lot better than just about any hire generator gets! If it is a quality made generator I wouldn't be too concerned, if it a chinese engine, well, what's the difference in the scheme of things! If it's an 1800rpm set, (most likely) the engines are capable of a lot more hp if they were running up around 2800~3000rpm, so they are fueled accordingly, but realistically when the genset is running at full load, the engine is only at 65% of rated load at higher rpm, and should run for ever and a day. If it's a 3600 rpm unit, smaller, lighter, generally noisier but depends on deadening, and when it's running full load on the set, the engine is working at full load, probably less of these about, they generally cut out at about ~11/12kw.

 

[DieselBound]

Can't say I'm the sharpest tool in the shed when it comes to generators, but my understanding is that RPMs are to be fixed in order to match up with the generator head's required frequency. The only thing changing on a given engine's operation is fueling.

Diesel engines are good at managing load fluctuations because their torque curves are well suited for such. Most diesel engines' torque curves are at lower RPMs than other engines. And in general, diesel engines will last longer than others simply because of their fuel (oil-based means better wearing).

 

[Industrial Toys]

I mostly run an Onan/Kubota 7.5 for backup. That's not to say it gets a lot of hours, but in the summer, it is not impossible to have a house load of a couple hundred watts, A fridge, some wal warts and security stuff mostly. I have never seen evidence of wet stacking. It's probably more an issue with bigger sets. A customer has a new 100K unit that basically just runs fire pumps and emergency lighting. I'm guessing, they are going to have an issue, especially being new and computerized.

I often run 5K of load into a hot tub in the summer. Mostly for excercise under load. You in Texas could run some AC units!

 

[DieselBound]

IT, what is that genset that you have? Mine's a 7.5DKDFL (circa 1993). I picked it up about a year ago and am now closing in on finishing the setup for the installation. I have some concerns whether I might run into issues powering some of the computerized crap I have: (computers themselves are off of a UPS), washer, stove and fridge having circuit board stuff (also my water filter's head). Per my local utility's billing, my average electrical use comes out to about 14kW/day: only real electrical draw is my water heater (4,500W, I believe); probably will need to figure on some sort of sink.

 

[Industrial Toys]

7.5HDKAL. Came out of a book mobile. I had to get the stator rewound. I never had an issue with clean power. I have a 200 amp ASCO ATS, and basically you would never know you are on aux power. My computer is also on a UPS as is a phone system, but that's about it.

I have electric heat, so of course that mostly get's shut off in the winter during an outage and the stove gets fired up.

I rewired my hot water heater for 110V so the elements don't get calsified as quickly and when I run my smaller backup (Yanmar 3.7) I save a little power. Never noticed any lack of hot water.

Oh, I do run my gensets all only 240volts into a transformer and never have to worry about balancing loads.

 

[DieselBound]

You've got a newer unit. It might have better controlled electrical output than mine does. And you're running through a transformer. I'm patching into my service panel using a simple interlock: that's the plan- I'm all wired up; have not changed wiring on generator yet (have a receptacle plug due in shortly).

It is claimed that no one is aware of the generator head on the generator that I have ever going bad. Trade-off, I'm thinking, is that the power isn't as clean as newer units. Here's a link to a thread I put up on SmokStak. And this is my only reservation.

 

[Industrial Toys]

I'm learning about this stuff as I go. I thought the VR was something magic (for Onan prices it should be) and have a spare VR for my 7.5. I got a 12.5 Onan/Isuzu awhile ago and opted not to use the Onan computer/VR. I just bought a used, universal Basler VR! Works great.

I don't know where your ugly power could be coming from. I do think, some of the cheaper alternators have more harmonic distortion although I'm not going to pretend to understand this. Every one of my units is brushed, so that isn't a concern for power quality.

I had a friend who once had a brushless Winpower (I believe) 20KW set behind his Ford 5610. His lights flickered like crazy. I had to laugh (to myself) as the man was so wealthy, and yet had such crappy power. I thought it was on account of a pretty crooked driveline but he insisted not. I never did find out what it was.

As far as a transfer switch. Hey, at least you have connectors. I used to throw the main switch and clip booster type clamps into the splitter box.

 

[bdog]

These are the units I am looking at Perkins Diesel Generators* Made in USA with pride

 

[Industrial Toys]

NICE. That's what I like to see. Who makes the alternators? I notice they use the Dynagen controllers. I have a couple I have been meaning to install.

Surprised they use Paul SR for advertising. Apparently a fraudster and in some financial trouble. They even dragged poor little innocent Mikey into it!

 

[DieselBound]

I'm learning about this stuff as I go. I thought the VR was something magic (for Onan prices it should be) and have a spare VR for my 7.5. I got a 12.5 Onan/Isuzu awhile ago and opted not to use the Onan computer/VR. I just bought a used, universal Basler VR! Works great.

I don't know where your ugly power could be coming from. I do think, some of the cheaper alternators have more harmonic distortion although I'm not going to pretend to understand this.

I had a friend who once had a brushless Windpower (I believe)20KW set behind his Ford 5610. His lights flickered like crazy. I had to laugh (to myself) as the man was so wealthy, and yet had such crappy power. I thought it

LOL, yeah, Onan/Cumins prices ARE up there! I'm in need of tracking down a coolant sensor (torn between going through the hassle of taking it out and matching it up or just ordering one up).

I think that I'd read about the replacement VRs. I'm only proficient enough in this generator-speak to say that I recognize those two letters together No clue whether that applies to my genset or not.

bdog, just keep in mind all the other costs associated with plumbing up a generator. I went out on a limb and shelled out $2,500 for my 1993 unit. For me, I view this all as for emergency situations only: my wife is really good at dealing with lower-level living, so managing lower-down on the convenience scale is doable (so that has, in theory, saved us money)- it'll be all-manual (though there IS electric start on the generator).

 

[100 td]

Buy the larger 10 instead of the 8, even if you don't need it, (one day you will) depending on the design of the alternator, if your prime mover has more power than the rating of the alternator, the alternator can be overloaded and the engine keeps powering it and the alternator eventually burns out. If the engine is less powerful than the generator then when you try to overload the the alternator the engine bogs and can't produce the power so the engine feels it but the alternator can't overload and burn out.
At $380 more for the heavier alternator with the same prime mover, I would go the 10. YMMV

 

[TractorGuy]

These are the units I am looking at Perkins Diesel Generators* Made in USA with pride

Those are pretty good prices for the size in brand new. Looks like enclosures are kind of pricey but you could probably build your own enclosure.

I purchased a 10KW Tactical Quiet surplus generator this year. Wet stacking is a common discussion over on the Steel Soldiers Forum. Mine has 2600 hrs on it and no sign of wet stacking. I have only used it for 4 hours but I test run every month with a 40 amp load. When I actually used the unit for 4 hours it didn't see much time near the 40 amp load I test under. I think it got up to 32 with the AC, well and rest of the house running but I turned off the hot water heater and some other stuff to manage load.

Either way you will probably want a load bank to test run and exercise the unit. Here is a thread on the one I made to run mine.

 

[DieselBound]

I think the recommendation is to run once a month (or a frequent run) without* a load and to do a full-over switch quarterly. That's my plan. Doing a full switch over ensures that the entire system is able to do what it's supposed to do.

* For sure, if you can load it then do it. But, it's not necessary for brief/operational checks.

 

[Gcorron]

Wet stacking is a real problem. But NOT in yours. You have small units that will have load on/off of them, that will cure the problem. All will get warm enough.
As for your salesman, he is just that, a salesman. He wants you to purchase some sort of load bank thus increasing his profit.
Given those conditions, and the size of your units, you can skip the load bank.

George

 

[bdog]

My current generator is a military mep003A 10kw diesel. It has worked well but the frequency varies more than I like for the computers and it is super loud. I am not using this for my house it is strictly to power a mobile office type trailer. I often set my unit up fairly close to people's houses and the noise makes them mad. I thought about the tactical quiet but I think all the military units have manual frequency control. These other units are computer controlled frequency and voltage.