Got a Honda gx390 with a 7500 /9350 power head. I bought it untested and with only 5 hour run time I know why it was at the auction. It was only producing 50hz and 105 volts. Engine was to slow. Dialed it up to 62.8 and 122v with 3000 watts load. Is this good or should this be adjusted differently?
How to dial in generator rpm?
- Thread starter Fordiesel69
- Start date
IIRC they're supposed to run @ 3,600 rpm while under any load. On construction sites some machines idle down when no one is using electric lighting or tools. What is the rpms it's running at?
the voltage is good but try to get closer to 60hz this could cause motors to run a little harder. I am sure with an oscilloscope this would be more accurate and there is probably a +/- a few % on whatever your test equipment is. I use a mastech circuit analyzer to dial my generator in under the cover there is a potentiometer which I never had to play with I just make slight carb adjustments. this is the analyzer I use.
https://www.mastech-group.com/global/en/ms5908a.html
https://www.mastech-group.com/global/en/ms5908a.html
yes 3600 RPM is correct
Thx. I figured it was just a 2 pole setup.
How did you “dial it up” exactly? It should be 60Hz.
I would personally dial in the voltage and frequency at the most common load on the generator. Who cares what it runs with no load on it unless you just like hearing it run without putting a load on it.
If that 3000 watt load is common I would dial in the frequency as close to 60 as you can. Don't concern yourself as much with voltage as you do the correct 60 Hz frequency.
governors will allow rpm ti decay a little with load so that's why it does you no good to dial it in with no load.
If that 3000 watt load is common I would dial in the frequency as close to 60 as you can. Don't concern yourself as much with voltage as you do the correct 60 Hz frequency.
governors will allow rpm ti decay a little with load so that's why it does you no good to dial it in with no load.
Grid voltages can vary a lot, but frequency is pretty tight - like 59.7 to 60.3 tight.
In the end it will depend on what your running. An electric motor may not care. An IC will.
If it were mine I would try to get it to run at 60 Hz under load and let the voltage be what it be, and I likely wouldn't run anything sensitive.
In the end it will depend on what your running. An electric motor may not care. An IC will.
If it were mine I would try to get it to run at 60 Hz under load and let the voltage be what it be, and I likely wouldn't run anything sensitive.
dnewton3
Staff member
We'll assume you're speaking of a typical simple generator and not an inverter type (which should self adjust). And that, typically, you'll not need all that power, you'll only use it to 50% rated load.
Many folks adjust for rpm under no load; that's not a good method.
Always use the expected typical load and then adjust for 120V; err a tad on the high side so that if you get a larger load, it's still acceptable. (You should load it to the most common expected load + maybe 20%).
This is adequate and should serve you well.
Many folks adjust for rpm under no load; that's not a good method.
Always use the expected typical load and then adjust for 120V; err a tad on the high side so that if you get a larger load, it's still acceptable. (You should load it to the most common expected load + maybe 20%).
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I would dig up the user / service manual and have a read through.
In general we usually set mechanical governors to ~62.5Hz / 3750rpm with the engine warmed up, no load. Ideally you would set it to 59-60Hz when under your maximal load but that's often difficult as most of the heavy loads are usually cyclic (AC, furnace, fridge, sump pump, etc).
Coming from the electrical world working with motors and controls +/- voltage not as much of an issue like hz. Either one can hurt and stress a motor you wouldn’t want an ac compressor motor or refrigerator compressor working 3% or more harder than it has to especially if some units are nearing end of life. Yes even grid voltage varies but as mentioned it’s tight at or around 60hz. Proper voltage and hz is what provides the right start up torque and running efficiency. As for sensitive, electronics a good ground separated from the neutral and steady voltage is key many logic boards and sensitive equipment failures due to sagging and spiked voltages
I have a larger Briggs generator, and the manual gives a Hz range while running unloaded. I think the range is something like 61.5 Hz to 62.5 Hz. The voltage is higher in that state too, around 126v. But of course, under load this comes down closer to 120/60.
No idea what rpm it’s turning, but I’m more concerned with the power output. Briggs seems to take the same approach.
No idea what rpm it’s turning, but I’m more concerned with the power output. Briggs seems to take the same approach.
I learned to never buy a flathead tecumseh genset as the gov is not accurate or fast enough. Briggs ohv are pretty goos. But the best I have read is the genuine honda and the Subaru Robin engines. So with my gx390 the gov recovers the load pretty well.
I dialed it in notbwith engine rpm, but rather a kill a watt meter and got it close. Now I need to find more heaters to load it more.
I dialed it in notbwith engine rpm, but rather a kill a watt meter and got it close. Now I need to find more heaters to load it more.
For a traditional generator, you don’t set engine speed. You set hz at the power head under load. You’ll need a multimeter set to hz. You verify voltage at the same time. Most have automatic voltage regulators now but if it doesn’t and the voltage goes above 125v you’ll want to adjust it back down.
60HZ at 50% load. This is the way.
