Need help with 21kw genset

[GameRV]

Out of curiosity, who said anything about extension cords ? Or where you making a point?
Thsnks

[joestue]

how long is your neutral? as in physical length in feet.


if all your loads are 120vac and patched out from a junction box or what not, then that extra current in the neutral is only costing you wasted power in the cable between the junction box and the generator.
changing the generator to output 120vac at 190 amps wouldn't make any difference.

4 ac units at 11 amps each isn't but 25% of what that generator is capable of.

[bob g]

the extra current due to poor power factor doesn't cost you anything (or very little in theory)
however it cost the generator in reduced output.

even though the reactive current circulates, and produces no useful work, it does take up capacity of the generator.

that generator is a single phase 120/240 vac unit rated at 21kva with a power factor of 1.0

this means it can deliver in theory 21kwatts into a purely resistive load, however it cannot deliver 21 kwatts into a load with poor power factor. my bet is the aggregate load power factor is likely around .7 lagging which means the generator can only support about 15kwatts of load,  the balance is taken up by the reactive components which do nothing but take up generator head space and burn a bit more fuel in doing so.

had the generator been rated at 21kva with a powerfactor of .80 a .70 pf load would present less of a problem with the head and you could probably get 19kva out of the generator in useful work driving loads.

so what do you do now?

have someone check the power factor of the loads, all of them that are running at the time of the generator faulting and armed with that info you will have a pretty clear picture what the hell is going on.

if if were me i would simply order an electronic meterhead from austin international, and mount it between the generator and the breaker panel, just like on the side of your house.
they can set it up to read out power factor of the loads very easily.

i would bet a dollar to a dog turd this is exactly what the problem is with your setup.

bob g

[joestue]

I understand that but he's only loading it to ~30-40% nameplate, even factoring in a power factor of ~0.7

[GameRV]

If I understand you right (this is a stretch), with the gen having a power factor of 1, it would work best with equipment with a power factor of 1. I have no idea what the PF is for a tv , xbox 360, Duotherm rooftop ac or fluorescent lighting. So if they are all different or Duotherm's are problem..... Then what? Shop for rooftop ac with PF of 1? Obviously money is an object and I bought the bus due to 4 ac's and 21kw generator. This was a bookmobile in Denver and ac's and gen came with. All I did was add tvs and 360's.

[bob g]

all i  can tell you is this

florescent lights can have horrible power factors, as can some consumer puter products, also the roof mount ac units can also have very poor power factors.

you could buy a "kilawatt" meter and check the power factors of any 120vac load that is under about 1800watts or so (maybe its 1500 i don't recall for sure), they are cheap and you can check each individual load and see what adds up?

my bet is those 4 airconditioners are probably running at some powerfactor less than optimum, mainly because consumer gear generally has no concern for poor power factor because you don't have to pay a premium for it. so oem's knowing this will generally not worry about adding powerfactor correction cap's because they add cost, in a cost conscience markets they will cut a nickle let alone a few dollars without a second thought.

bob g

[joestue]

I think you need to take a look at that generator again, specifically the engine.

btw, poor power factor may increase the electrical losses, but it doesn't significantly increase the mechanical horsepower input to the generator.
the fact that it runs for 30 minutes means there's nothing wrong with the electrical side (assuming its putting out 120/240vac 60hz) there's no way you're actually pulling 34 hp from the engine yet only 7kw worth of electricity. that missing 18KW worth of heat would be going somewhere, and you'd know where in about.. 1-3 minutes.

[bob g]

what did i miss?

7kwatts of power to run 4 rooftop airconditioners, plus all the video/puter stuff, plus all the lights?

if that is the total load, i agree the engine is the problem

all i have read so far is the OP looking for more amperage to power loads with.
which leads me to conclude he has far more than 7kwatts of load applied to the generator.

bob g

[GameRV]

Maybe I can shed some light. The other day we ran like 4 xbox's and tv's and 3 ac's for couple hours no problem. I could run all 16 systems for an hour with all 4 ac's in max cool. Thought there was being on max cool would eliminate spike in amps when compressor goes off, then comes back on. I killed the gen (it died) when I threw the a breaker for an electrical heater (double breaker connected to each leg). Thought process was that the extra amp pull from the heaters put it over the max. We had the bus since September and have run the ac's with no problem and lights on. My novice opinion is that I am at the limit of the generator. That's what bugged me, at 21 kw I shouldn't be. Only thing I could think of was 240 vs 120.

Also, gamerbus and xbus are running 13kw gens and identical setup, just they have only 3 ac's. Gamerbus says he is maxed out at 13 kw (110 amps)

[GameRV]

Here are some test results. Ran for 2 hours, no shutdown. Removed gas cap which clearly states non vented after first 30 minutes. Not sure where to look for clogs in vent if there is a vent other than gas cap option.

No ac's
Tvs on standby and xbox's on standby
Leg 1 = 2.1
leg 2 = 1.8
common = 0

Dashboard
Leg 1 = 10.2
Leg 2 = 11.4
common =1.2

15 systems in game 1 dash
Leg 1 = 13.0
Leg 2 = 13.0
common = 0.1

1 ac fan only
Leg 1 =14.6
Leg 2 = 12.8
common = 1.5

Compressor high
Leg 1 = 23.1 spiked as high as 63
leg 2 = 13.0
common = 9.7

2 ac's
Leg 1 = 16
leg 2 = 13.0
common = 3.0
 
Ac 2 compressor
Leg 1 = 16 spiked as high 63.4
leg 2 = 12.8 spiked as high 13.5
Common 12.2

4 ac's max cool
Leg 1 = 33.5
Leg 2 = 33.2
Common = 2.4

30 minute mark
Dropped ac's to med cool

Leg 1 = 15.7
leg 2 = 15.4
common = 0.1

Removed gas cap, no hiss

[GameRV]

Today's test not good. Same setup as yesterday just with gas cap removed from the get go. Shut down after 1 hour 43 minutes. My plan is take it to pros tomorrow morning.

[dnix71]

Your ac spiked as high as 63 amps? That's gives away what the problem is. Short cycling the ac is basically a dead short. "locked rotor amps" is another word for it.

If two ac's short cycle your rig will fail. There is no fix for that except a lockout relay. The local Taco Bells have those to save money on peak power charges. You need to wire all the ac's to a relay that allows only 3 compressors to run at a time. The lockout rotating relays run one ac less than all and shut down the compressor on one a time in sequence for 15 minutes each. After a 15 minute shoutdown there is no short cycle because the system has had a chance to equalize pressure. Forcing each unit to rest makes them last much longer, too, because it gives the oil time to return to the bottom of the compressor.

For this to work correctly you must set the thermostats low enough that they will not shut off with 3 cooling.

[GameRV]

How much to install a lockout relay?

[dnix71]

The guy I met who did the work at TBell didn't say where he got the stuff, but any ac guy could put a time delay restart on each ac. Set the delay at 5 minutes and you can be reasonably sure that no ac will short cycle and hang up.

http://www.johnstonesupply.com/corp/tabid/1783/default.aspx?product_group=1205  This page shows one model, with different operating voltages.

They would not be wired the usual way, which is to prevent restart after power failure, but rather restart after compressor cycling. Most larger commercial units have intelligent delay relays built-in, but older home units like you have didn't have them.

On commercial split systems the thermostat feeds are all sent to the lockout relay. If you know what an electric zone sprinkler system timer looks like you can visualize what happens.
Lets say you have 4 ac's. You get a 4 zone timer and run the low voltage thermostat leads to each zone relay. Zone 1 is 1-2-3, Zone 2 is 1-2-4, Zone 3 is 2-3-4, Zone 4 is 1-3-4.
In each case only 3 ac's operate at a time and the length of time each zone is on is adjustable. No matter which zone is on, one ac is locked out. This type of relay must be "make before break" to prevent all the ac's from going off between zone changes.

You could even do it yourself with a 120v 4-zone electronic sprinkler timer if you had access to each low voltage thermostat wire.

[GameRV]

Maybe it doesn't matter but this is not a residence. These are 4 duotherm rooftop ac's on a bus. GameRV.com Also, the ac itself didn't spike to 63, the total amp draw on that leg spiked to 63. So you can see that after spike, amps rested about 23 so that means ac spiked 40 amps taking draw from 23 to 63.

[joestue]

at this point i would get/build a big resistive load and see if the generator can deliver the rated power of 21 kw.

[dnix71]

40 amps must still be locked rotor short cycling. The normal ac pull is only 11. That genset can't handle that with all the other stuff on it. 21KW is enough to run two normal residences.

When you run more than one ac at a time one will cut off first when they cool down the bus enough. If that one doesn't stay off for 5 minutes it will hang trying to restart. When it does it pulls 4 times the usual amount of power. That's just too much for your genset.

You might consider putting the ac's on a different panel and carry a second generator to power those.

[joestue]

40 amps must still be locked rotor short cycling. [...]That's just too much for your genset.

 its not anywhere close, unless the engine is only 15 HP
63 amps on one leg is ~7.5kw

[GameRV]

I'm not sure these ac's are short cycling. I gave tried to manually get the compressor to refire after reaching temp and failed. I didn't know why it did that until u mentioned short cycling. I think these ac's are new enough to not have that issue. There are two legs of 120 in panel and ac's evenly balanced. So there is no possibility of 3 ac's firing/spiking on one leg.

[None54]

   I'm concerned with the unusually high voltage in the neutral under higher loads. Sounds like a parctialy cut neutral return line or a bad connection. I've been following this thread,,,I've experianced the same symptoms in the past and it turned out to be the neutral line causeing the problem. I am not an electrican by trade.
  Becareful, not haveing a proper neutral can be deadly.
.....none54

[GameRV]

I have come to the conclusion this being in an rv that this is a floating neutral and the load is equal to the difference between leg 1 and leg 2. Evidence above shows numbers support this theory.

[GameRV]

Rv pros finally found a part we (myself and mechanic) were unable to find. The oil pressure switch. We had already replaced the thermostat switch but never located the oil pressure switch. We convinced ourselves the oil pressure sender was Aldo the switch (with 1 wire I was stumped). Rv pros were stumped until they got a "contortionist" with a double jointed elbow to locate the oil pressure switch "buried" on the backside. He removed the wires to simulate no low oil pressure signal being sent and he said it ran for 4 1/2 hours.

[GameRV]

Update. They replaced the oil pressure switch and said it was running for an hour without fail so come and pick up. On my way, they called and said after an additional 45 minutes, it failed. I picked it up friday due to a get together saturday. They left the new oil pressure switch connected and then chose to disconnect the control panle to test if that was part of the problem. I drove the GameRV home with the gen running to test their new theory out. Got home, put a load on it, ac's and xbox's and then it died......not the control panel. Cool weather around time of tests. Saturday was hot (90 degrees). Friends over and fired up systems. Died quickly this time (45 minutes) and would not stay on longer than minute or two after that. I then disconnected the temperature switch and it ran for 4 and 1/2 hours without fail. Laser temp gun on hoses read about 177 degrees. Back to RV shop monday and they are still working on it.

[GameRV]

Update. Just got off the phone. They stated new oil and oil filter along with new radiator cap. They said radiator cap had some seepage. They ran for 4 hours no shutdown, then 1 1/2 hours and still running to ensure stability with success. I had read somewhere that too much oil in generator engine could cause incorrect readings and shutoff. Party tomorrow night so I will update Saturday with results. Cross your fingers yall and pray for us!

:-)

Mike

[GameRV]

Don't know if anyone still following....hope so. Leaving thermostat shutoff switch disconnected has let us run without shutdowns for a while now. However, on Saturday we had a 2 hour party and the generator quit (i'll explain in a bit) with one minute to go in the party. Parents and kids pleased with party and understanding. Some time ago, my mechanic called because generator was running, but providing no power. Weird. Shut all down and moved switch in bus from gen to off to shore and back to gen again. Also thew main breaker (looks like 4 20 amp breakers with one handle labeled 150amps). When I say main beaker I mean in the bus at the top of the panel with all the individual breakers below. Somehow the gen began producing power that time. Now this summer has been hot and temp like 108-112 common. Gen temp running as high as 230-240 near max of 250. Shutting off one ac could bring temp down 20 degrees or so. Still no shutdowns. One other time we had gen run on stratup with no power. Again, switching input and resetting breaker was able to produce power again. Now, for last Saturday, gen never stopped running, just power quit after 1 hour and 59 minutes......weird. We shut gen down and attempted to restart, no luck. Would not even attempt to turn over. Left off while drove back home (20 minutes). Then tried again, no sign of any attempt to turn over. A few minutes later.......gen started up....yay....but....no power. Tried switches and breaker but to no avail. Top breaker on panel does not seem "engaged". Does not seem to "lock in" to the on position. Going to bus with mechanic today to attempt to fix. Is there a breaker on the gen head itself? Maybe that got thrown and thus pevents main breaker from being thrown "on"?

Great feedback last time and hoping for some knowledge,
Thanks in advance to all.

[thirteen]

Possible you could have a breaker that is going bad or partly bad. It heats up because of a weak connection and kick out the supply inside the breaker. And sometimes the breaker will not trip. Once it totally cools down it works right. I would suggest that you take a ohms reading on the breaker with nothing attached to it. You might have an area that causes heat to build up thus causeing an open circuit. Just a few ideas to start to play with .

[GameRV]

All signs point to bad breaker. Met mechanic out there and I went to show him how breaker would not engage and just like previous post said, it had cooled down enough and engaged. Ran for a few mInutes under load and breaker tripped when mechanic lightly touched it. Then it refused to engage again. New breaker/breakers 150 amp to be installed tomorrow.
Thanks!

[David HK]

Just an idea.

Does your generator have brushes?

If Yes, how many hours has the generator run in its life? And, if its a lot, have the brushes ever been changed?

I once had this experience on a Gin Palace in the middle of the China Sea.

David in HK

[GameRV]

Isuzu engine with Norpro generator model 4LE1 I believe is "brushless".

[GameRV]

From Norpro site:

The Power Max Isuzu or PMI Series diesel generator uses the powerful and durable Isuzu diesel engine and a brushless generator featuring AVR (Automatic Voltage Regulator). These units which also include automatic shutdowns, radiator cooling, industrial grade muffler, rubber isolation mounts, oil drain kit, skid base, battery charger, battery tray, battery hold down and battery cables. This engine series is able to produce power ratings from 12-375 kW at 60 Hz. The Digitec 300 Controller, with auto start capability, is now standard on all Power Max Isuzu generator units

[equiluxe]

Pull the fuel uptake pipe out of the tank, I had a very similar problem, engine would run for so long or until a heavy load went on, after a lot af chasing things and even sending the injection pump for overhaul all to no effect, I pulled the fuel take up out and found a leaf in the pipe that acted like a valve if the flow went over a certain rate it closed and the engine died.

[Frank S]

If there is a flexible hose in the fuel system check to see that it does not have a perforated liner causing it to suck closed. 

[GameRV]

New breaker solved it. Just gotta figure out how to keep gen cool when 116 degrees in summer. Gen running hot, 230 and up.