Onan MDL4 High Hertz

[Sadey]

I’m not sure when my 20KW generator started producing high hertz but it is, around 65hz. I’ve always looked at the voltage before switching over power sources, but never paid much attention to the hertz. My clocks were running fast at times and for whatever reason I looked at the Hertz the other day while shutting down the 20KW and discovered the issue. Mystery solved on the clocks. I’ve done a search on this site and the internet but cannot find how exactly to adjust the RPMs on this generator. I understand that it needs to run at 1800 RPMs to produce 60 Hz, but I’ve scoured the parts manual, operator manual, and an online service manuals and can’t find instructions on how to adjust it.

I don’t have a way to check rpm’s but obviously I have volts, hertz and amp gauges on my power distribution page.

 

[Captain Ralph]

Do not give the original analog panel meter any credit for accuracy.
You need a real hertz meter.
I not recall the rotary Stanadyne governor adjustment or has one.
I did find this electronic htz adjustment bit the manual states Do Not Touch.
Single pdf page to large to upload.

I'm about to head off shore. I'll look deeper tonight.
In the mean time, find a DVM with htz ability.

 

[Sadey]

I did see the cautionary note about adjusting voltage in the manual, but I can fine nothing that speaks to hertz adjustment. The reason I suspect the gauge is right is it works correctly on the shore, power side that and the fact that my plug-in clocks are running fast when that generator is powering the vessel. I saw a post by Sky about a Digital volt/hertz meter. I’ll search Amazon and find one for verification purposes. Thanks for the help Ralph. I really appreciate it.

 

[nor'easter]

I did see the cautionary note about adjusting voltage in the manual, but I can fine nothing that speaks to hertz adjustment. The reason I suspect the gauge is right is it works correctly on the shore, power side that and the fact that my plug-in clocks are running fast when that generator is powering the vessel. I saw a post by Sky about a Digital volt/hertz meter. I’ll search Amazon and find one for verification purposes. Thanks for the help Ralph. I really appreciate it.

Don't know about the hertz, but you can verify the RPM by phototach. Might be a place to start.

 

[Pascal]

This one measures Hz and is pretty cheap.

Klein Tools MM420 Digital Multimeter, Auto-Ranging TRMS Multimeter, 600V AC/DC Voltage, 10A AC/DC Current, 50 MOhms*Resistance,Orange/Black https://a.co/d/3GAhg4J

When I redid the panel on my 53 I installed BlueSeas multimeters. They cycle between volts, Amps and Hz with big red displays. Easy to read

If your clocks are fast then you are indeed running too high / fast. There will be some frequency variations depending on load, usually up to 62 hz no load is fine and will give you 60hz under typical load.

Your manual should give you instructions on how to adjust RPM/frequency. The 2004 45 Onans on the boat i run have electronic controller and can be adjusted.

 

[Sadey]

That’s just it, Pascal I can’t find in any of the three manuals the procedure for adjusting RPMs.

 

[Pascal]

How old is it? Maybe it has a mechanical adjustment on the governor instead of electronic. The 45 manuals show the electronic regulator was optional in 2004

 

[Sadey]

It’s original to the boat so a 1988-1989 MDL4 20KW. I’m sure it’s a mechanical adjustment. I suspect I know which screws are the adjustment ones but would love to be sure before I start monkeying around. After I’m done being naughty at the bakery I’ll post a picture of what might be the adjustment.

 

[Captain Ralph]

O K, I'm back on the hook. What a great day off shore.
So, My data with me is thin. Back at the compound a lil better,, Where the new DB is getting built back up.
Thanks to many in sending stuff to me.

I remember one thing, my poor notes show some other ideas.
Really need a pic of the side of your pump. Older MD* had a throttle lever on the side. Easy/pezey.
Newer Stanadyne pumps it got weird.
Is there an electrical wire to the pump?

 

[Captain Ralph]

More cud to chew on while shopping for a Htz meter;

What htz do you read under a good gen-set load?

1800 RPM makes the HTZ but the governor has a challenge keeping it there within a few RPM because of varying loads.
A lightly loaded gen-set may run a couple RPM over 1800.
A loaded set may run just under 1800 RPM.

I recall there is(was) a RPM droop adjustment also to these injector pumps.
It was only good for just a few RPMs also.

Yes, older (cheap) clocks use 60Htz to sync by.
Later clocks (not so cheap) have their own crystal tank oscillator and do not rely on the 60Htz to sync by.
I can not tell you these differences from clock to the other clock but I know I've gone thru this.

 

[Avenger]

Frequency is all about RPM. Voltage will be effected by RPM, but if the frequency is right, incorrect voltage is a "back end" problem. Either the generator itself, or the voltage regulator.

If it's a Stanadyne, the RPM adjustment is on the throttle lever. There is a Droop adjustment involved as well. I can send you the service bulletin about how to adjust it if you need.

 

[Sadey]

Okay back at the boat. I ran the gen for about 20 minutes. Started out a 62hz and slowly over the run time it creeped up to almost 65hz. I loaded and unloaded the gen with about 20 or less amps. Under load it dropped to around 62-3 but went right back up to 64-5. I could hear the gen take the load as well as see it but it didn’t struggle and it’s hard to tell if the rpm’s are increasing with the increase in hertz’s or not, maybe? Voltage varied between 230-240s load no load. On shore power I get 61hz steady.

Not sure why it came out sideways. Please just turn your monitor 90 degrees starboard

 

[Sadey]

The manual would be most helpful, thank you!!

 

[Captain Ralph]

Your picture shows the good-ole-standard governor throttle lever.
For 3 HTZ I would not bother but if you need more grey hair or in my case, loose what hair is left;

Imagine a regular boat engine throttle; That lever in your picture connected to a Morse cable and throttle lever on the dash. Imagine holding that throttle lever in place, forever, so the engines runs only at one speed.
Just hold that lil lever in place at an exact position,, forever..

Those screws lock that throttle lever in place from both travel directions. The lock nuts keep the screws from moving.
From there the governor is told what to spin,, forever..

While the engine is running under load, you are going to make these VERY, Very fine screw adjustments.

Probably 10mm or 3/8" wrench. Two wrenches will be used to slightly unlock the lock nut while holding the machine screw in place. Only talking 1/32 or less of turn at a try on the machine screws. Just to barely move that lever an micro amount. I can not tell you now witch direction, it's a try one way or the other.
Loosen one screw and tighten the other screw. if that speeds up the engine, then reverse. All in micro fractions at a time screw turns.
For 3 Htz, your going to work on this for a while.

You are working around hot and running machinery.
Please be careful..

Or, when close to 32189, I'll knock it out for you..

 

[Avenger]

Okay, once again. Frequency is directly related to RPM.

It concerns me a bit that that it drifts so much with temperature, but for now I would.just reset ii and see how it behaves. I would also try to verify that the frequency meter is accurate. Utility power should be bang-on at 60Hz. I also agree the manual would help, but as a general rule mechanical governors for generators are approximately 2-3% variation, so they tend to be set 1.5 - 2 Hz over 60 when unloaded so they will droop into the correct frequency under load.

Have the frequency meter visible when you make the adjustments. You're going to be lowering RPM, so you're going to loosen the jam nut on the screw on the throttle lever closest to the drive end of the pump. Keeping pressure on the lever toward the drive end, gradually back out the screw until your frequency is where you want it. Then snug the jam nut. Then loosen the jam nut on the other screw and run the screw in to lock the throttle lever.

There's a more involved procedure for settings the droop adjustment, but for a 1 or 2 Hz I'd just reset the speed and see how it behaves.

 

[Captain Ralph]

There's a more involved procedure for settings the droop adjustment, but for a 1 or 2 Hz I'd just reset the speed and see how it behaves.

The droop adjustment is covered in the service manual, not the speed adjustment.
F M
You are correct, You don't want to mess with it.

 

[Sadey]

Thank you all for the help. I ordered a meter so once it’s here I’ll follow the above directions and see how it goes. I too am a little concerned about the increase as the unit warms up. Trouble up here is no professionals close by if it comes to that sort of an issue.

 

[Avenger]

The droop adjustment is covered in the service manual, not the speed adjustment.

The droop adjustment involves resetting the speed. It must be in there somewhere.

It's not rocket surgery, but for a couple o' hertz it's probably not necessary to mess with it. If you find the governor response is poor, or if the RPM hunts you may have to reset it. Jump off that bridge when you get to it. Again, I can send you the S.B. from Stanadyne if necessary.

 

[Sadey]

So I plugged a Hertz meter into my system and purchased a laser RPM reader. These are my findings:
At start up I’m turning 1806RPMs 61hz
After 9 minutes under load 1858RPMs 62hz
Fluctuations during run under load of up to 1866rpms and up to 62.2hz
Unloaded for cool down 1900rpms and the power panel meter reads 64hz but I’m a little suspect on that gauge other than trend.

Any ideas on why the generator seems to increase in RPMs, which bumps the Hertz up? I decided not to adjust the throttle since at start up and under initial load it’s running fairly accurately. Should I have adjusted it down six or 10 RPMs? My great concern is not necessarily the clocks running fast although my CDO kicks in and it is annoying but more importantly, am I doing any damage to other appliances or airconditioning systems.