Cummins Generator RPM Goes Up and Down Sometime

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FAULT FINDING MANUAL - Cummins Generator Technologies

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thanks for this

really appreciate your feedback

How about a telephone call to Cummins' technical helpline? Try speaking to the representative who commissioned it!

At little or no load, even a very small variation in fuel delivery may result in noticeable rpm change. 1790-1800 doesn't seem abnormal under this condition. However, you could check the governor droop setting (if any), and whether it is controlling in isochronous vs. droop mode.

check the droop settings and fuel line/valves. May be not sensitive enough and need calibration. Taking too much time react to signals

I believe what you are presently encountering on your generator set is on the mechanical aspect of the equipment itself. More specifically, covering the engine governor system. As an overview, this component is the one that controls the engine rpm (revolution per minute) thus correspondingly, the generator output frequency in terms of frequency (hz).

Based on several years of experience with diesel engine, generator rpm are primarily controlled by the engine governor spring which balances and load & engine output. This is the part (the governor spring) that stabilizes engine rpm from ' no load ' to ' full load ' condition.

My suggestion is to have the engine fuel injection pump and governor assembly be pulled-out and subjected to bench testing (preferably to authorized manufacturer dealer within your area). From there, they will be able to accurately diagnose the present condition of your engine and at the same time recommend parts (if there are) to be replaced at lesser constraint on your part. Please consider that equipment dealers for generator sets (i.e. Cummins, Caterpillar, Komatsu, etc.) have competent technicians to perform such tasks and lesser problem on your parts.

Lastly, may I recommend that this undertaking be carried out as soon as possible, especially if your generator set are considered to be a prime mover (main source of electrical power) for your company. This will be advantageous for you to have lesser problem with your machine due to failures, in the future.

Looking forward in hearing from you. Thanks!

Thanks for the reply and the feedback

i have sent the fuel pumps and injectors to the supplier for this.

still waiting for a feedback from them

Don't <...wait...>. Get on the 'phone.

Hi

I have several trucks with Cummings engines. All of my 5.9L TDI when I first start them

they run perfect. After about 15 to 20 seconds the lights dim in the cab and there is a clunck sound in the engine area and the voltage drops from 15V down to 12 or a little less. It stays that way for from 4 to 10 seconds then the RPM goes back up and lights get bright and everything is fine. This will happen several times but ONLY if the engine has not been used and it is cold. I am in Beverly Hills so I should define cold. 55 Degrees for example if the engine has sat all night. IF it is down to like the low 40s ( Rare but it does happen ) then this happens several times before it quits.

I figured the requlator or batery or something was bad. Changed the Bats as I wanted Larger deep cycle Batteries anyway.

IT did not change a dam thing. Checked the system to see if there was any parasite

drain. Then I found what it was. On a cold day or when I first start for the fist time

and the engine Block and heads and water are all cold what happens is the stupid

computer is not hooked to the Glow Plugs. So until the dam thing gets warmed up

and since the computer is not involved in for example checking the RPM and exhaast gas temp the engines themistat although hooked to the computer ithe computer does not control the glow plugs. The Glow plugs on a cummings are very heavy duty as they have to be able to take a good beating so the filamint ( spelling sorry) is very think and make to last thus takes a lot of power and will take a ideling engine even as powerfull as these things are and the load on the Alternator is very high ( I messured it with a Clamp meeter and it is a lot of AMPs. More than all the lights all togther x 4 is about how much they take. Some engines have one glow plug for each cyclender.

My VW Passat Diesel only has one Glow plug and it warms up in at most 1 second as it is light and will have to be changed now and then.

What I am saying is if it all stops after the engine is warmed up then I bet that is the problem and it is not a problem. just a strange and or poor design by Dodge not Cummings as dodge is the one that provided the electical system and the goods to control it.

And if that generator is having the same problem as I am then it will be fine. I would let it warm up a bit before use unless it is a power backup deal.

But in short it will not hurt a thing.

Jim

Dear Mr. eddy boy,

The Speed Governor is TOO SENSITIVE. Pl. make it a liitle sluggish.

DHAYANANDHAN.S

In case of hydraulic governor droop is required to be adujusted. which is normally 2to 4% (36 to 72 rpm) with recovery time two seconds. In case of electronic governor electronic control required to be checked by temporary replacing the control pannel/governor with another gen set of same capacity.

10 rpm is well within spec. We are authorized Cummins Onan dealers. What is your concern related to? Please contact your installer or the rep. at Cummins.

1 fuel economy,

2 frequency variation

3 voltage variation

4 other mechanical issue

5 quicker response required. (you may need to create an uninterruptable power supply using a storage medium such as batteries and an inverter/charger)

How old generator is, how many hours it has been covered.

Dear friend you cannot run the generator without any load atleast as per cummins requirement for.any size of generator it must be 30% of load to be available after starting.of generator. Try and check as per recommended from my side.

There may well be nothing wrong.

How does the engine behave when loaded?

Your speculative repair attempts are a little worrying...

thanx wal for your reply

but the engine behave same if there is load or no load the rpm goes up & down for a second like if i start generator run good but sometime in 10 min or sometime after half n hour rpm 1793 or 1834 then in second coming 1800 or 1803

i mean to say for a second rpm goes up & down there is only 35% load on generator

i want to ask why this is happening i change fuel water seprator lifting pump but same problem

its new cummins generator running from 7 month

please reply if u have any idea for this problem

Dear Eddy,

I am wondering if you might have solved your problem as I am also experiencing the same problem as you have.

My generator is small at 125kva. Frequency 50 hz and engine rpm at 1,500.

Upon starting, ideal rpm is at 830rpm. This is maintained at 5mins to warm up the engine.

Once we engaged to rated speed, the rpm will increase to 1502 ~1504 rpm.

However, after 30 mins of operation. The rpm will drop to 1480 and will sometimes recover to 1502 within 4 secs. However there are times that the rpm stays at 1480 with no recovery back to 1500. As this generator is also running in parallel mode with another similar genset. This will result in a blackout of the entire ship. The problem is when the gensets are running in parallel operations. We are still able to run this genset on its own even with this intermittent problem.

I have changed, the fuel pump, hand priming pump, fuel filters, speed controller, magnetic pick up sensor, fuel return sensor, sensor control board. However, the problem seems to persist. Is this a configuration problem? I am trying to eliminate all potential factors before the cummins engineers arrive.

I look forward to hearing from any advise that you all might be able to share.

Thank you and please to hear.

hello friends,

I have the same issue here

Lately, just repaired the pistons but it seems to have the same issue when load kicks in it revs up and down.

Even the turbo gets burning hot so we have to shut after 15mins of operating.

please help!!!

Need to calibrate the speed sensors and fuel valves. May be time lagging in sensotivity resulting in fluctuation of speed. Fluctuation may be more at less or no loads than at full load. Setting of droop is next