Generator voltage mystery

[SV__Grace]

My Nextgen 5.5kw generator (1700 hours, 4 years old) is misbehaving in a mysterious way and I'd appreciate any ideas for addressing this.

Upon startup, with no load, voltage/hz averages 124/63, which is a tad higher than normal for this unit. Normal is 122/62 or so at first.

I have Mastervolt electrical components installed during our refit 4 years ago.

If I turn on my MV 100amp AC charger AND the MV combi inverter charger (set for 100amps) the voltage spikes to 129-131- scary!

I called my electronics guy (a MV expert) that did the install and he says the AC charger can handle voltage that high, but not the inverter charger.

OK, so if I turn on the AC charger the voltage spikes from 124 to 130 and stays there for some minutes then starts dropping to 128 or so.

At that point I learned that I can turn on the inverter charger and within a few seconds it will drop further to 125 or so and continue to drop until settling into normal charging voltage/hz of 120-122/59-61.

While it's charging at full 200amps if I turn off the inverter charger (to run an appliance, for example) it spikes back up to 128-130, then back to normal if I turn the inverter charger back on. Behaves badly with partial load, behaves normal under full load.

Whew! At least I found a workaround, so my current routine is to start the generator, let it warm up for a minute or so, turn on the AC charger, and @5 minutes later turn on the inverter charger and it reliably follows the pattern above.

Some clues:

- The capacitor quit before all this and I replaced it with the exact same thing.

- It's a bit harder starting than before but starts pretty easily and seems to run smoothly enough.

- Changing fuel and air filters made no difference.

- Eight months ago we swapped our AGMs for Lithium and most of the generator hours were partial load to charge those damn AGMs in absorption and float modes, and now full load continuously for the Lithiums.

A mystery. While I can live with this I'd love it to work as normal and worry there's a problem that will get worse- any ideas?

[more]

The United States and Canada use a supply voltage of 120 volts ± 6%
your mastervolt combi have an Input voltage range 90-140 V

what is your problem?
how you measure. what Power Quality Analysis equipment you use
i suggest use rent something like this

https://www.youtube.com/watch?v=xWdW8PYlGUU

overvoltage is an event where the rms voltage rises above 110% of the nominal rms voltage and stays there for more than one minute.
Sags occur when the rms voltage decreases between 10% and 90% for a duration of a half-cycle to one minute. In a 60Hz power system, a complete sine wave lasts approximately 16 milliseconds, a half cycle is approximately 8 milliseconds.
Swells are defined as an increase in the rms voltage to over 110% for a duration of a half-cycle to one minute.

read more

https://testguy.net/content/361-Powe...d#undervoltage

[SV__Grace]

Originally Posted by more

The United States and Canada use a supply voltage of 120 volts ± 6% your mastervolt combi have an Input voltage range 90-140 V what is your problem?
how you measure. what Power Quality Analysis equipment you use

Thanks much for your response. I have a dual helm boat and use the inside MFD to monitor the electrical system via cPanel. Mastervolt has great data/monitoring features.

If the voltage stays at 129 or above for more than a few seconds the inverter charger will cut off and then kick on again if voltage drops below that. This may be a setting that my electronics guy established, but he insists that the combi can't handle high voltages and I trust him on that.

I've been a boat owner for 35 years and have never seen voltage from shore power over 122 or a generator above 124 or so. You may be right but I can't imagine my expensive combi handling such high voltage for hours at a time.

If I let it run from the start that way, the charge current will trip on and off for 5 minutes or so before stabilizing (another clue), which is worrisome and not normal.

So the mystery is, after 4 years of established, normal charging behavior, what might be causing the voltage spike above 129v at startup and partial load, while stabilizing under full load after 5 minutes or so?

[tkeithlu]

I think I can emember enough of Electrical Engineering 101 to simplify more's explanation to: Measuring AC voltage is tricky. Theoretically you should use the root mean square of the sine curve, which is about 0.7 of the peak voltage. Your meter can mess that up, and your inverter, for that matter, likely doesn'r even send out a sine curve.

Simplifying even further: You probably don't have a problem.

[more]

Originally Posted by SV__Grace

Thanks much for your response. I have a dual helm boat and use the inside MFD to monitor the electrical system via cPanel. Mastervolt has great data/monitoring features.

If the voltage stays at 129 or above for more than a few seconds the inverter charger will cut off and then kick on again if voltage drops below that. This may be a setting that my electronics guy established, but he insists that the combi can't handle high voltages and I trust him on that.

I've been a boat owner for 35 years and have never seen voltage from shore power over 122 or a generator above 124 or so. You may be right but I can't imagine my expensive combi handling such high voltage for hours at a time.

If I let it run from the start that way, the charge current will trip on and off for 5 minutes or so before stabilizing (another clue), which is worrisome and not normal.

So the mystery is, after 4 years of established, normal charging behavior, what might be causing the voltage spike above 129v at startup and partial load, while stabilizing under full load after 5 minutes or so?

buy minimum this
https://www.amazon.com/UNI-T-Multime.../dp/B087BL3XKX

and check voltage on input mastervolt
but in real life your eletrician guy need this minimum
https://www.aliexpress.com/item/32504139301.html
easy fix if your mastervolt suck 10A 120V
30 meter cable 2.5mm2 betven generator and mastervolt.
Or buy new generator voltage regulator

[HeywoodJ]

Well, the spec for the generator voltage regulation is +/- 5%, so the generator is out of spec regardless of anything else. I would vote for two options, and they both get pointed to by recent changes/observations:

1. The new capacitor - The capacitor is the voltage regulation on these generators, and most of these can capacitors are +/- 20% of rated capacitance. If you used a 40μF/400V cap then you could be anywhere from 32 to 48μF actual capacitance. Your voltage won't vary as much as the capacitance (i.e. it's not 1:1 change in capacitance vs. change in voltage) but it will vary, and 5-6V isn't a huge leap. Presuming you don't have the tools to accurately measure a big capacitor, and given that they aren't too expensive, I'd try a different cap. You can get double- or triple-capacitor cans (such as a 40/40/40μF can) that allow you to try three different units for about the same price as a single (and sort of carry an in-place spare, although all units will be subject to the same heat). If you can find a friendly appliance repair person you might even be able to borrow a couple of caps in the 35-45μF range and try them out.
2. Engine speed - Engine speed can also affect voltage, and you say it has recently been a little harder to start. There's a chance that the governor setting is a bit off. If you have a decent frequency meter in the system or a really good tach you might be able to tell straight off, otherwise a strobe would be a great tool to have anyway. You should be at 60Hz loaded, and probably a little bit higher unloaded. If your frequency/tach are dipping then I'd start to look at the governor (and fuel, air, etc. - but you already said those are OK).

[more]

Generator output voltage may be changed slightly by adjusting the engine speed up or down.
This is done at the speed screw voltage is in the acceptable range between 115 and 130 volts A.C., you may begin to test
load. Start by turning on one breaker at a time on the vessels panel beginning with non critical
loads such as a toaster, stove element etc. All devices should be checked one at a time at first
for correct function and then in groups to determine what may be run together without overload.
The UCM2-5.5 will provide up to 46 amps of current at 120 volts. If this is exceeded, overload will
result and unit will lose speed, frequency and voltage. A sure sign of overload is black smoke
coming out of the exhaust.

http://www.nextgenerationpower.com/I...rt/UCM2-55.pdf

[phorvati]

102V to 132V is what UL classifies as range for nominal 120V AC mains. Any appliance with UL label was tested for full operation at its maximum and minimum rated temperature at 102V, 120V and 132V. Beyond 132, you need to check input rating for whatever appliance you are using on the AC mains.



I am not sure how capacitance regulates voltage. Capacitance smooths out the ripple. And usually if one cap dies device still functions just fine and its not like a diode failing in an alternator. The way voltage regulation works in a generator....Some sort of feedback is used to regulate output voltage. Output voltage is rectified to a DC value (max output peak )and divided down to a smaller proportional voltage and fed into comparator circuit. Comparator circuit turns ON or OFF power to the Field Winding. Filed winding, just like an alternator, is used to provide more or less magnetism on the rotor and increase/decrease output voltage.

Basically the AVR(automatic voltage regulator) is pricey and if you suspect its failing its typically ~500-1000+$. Its a potted little box with bunch of through-hole components. If you can see the model number on it, its a great spare to have on board.

But based on what you said, I would find a way to double check your measuring equipment and perhaps if you can run the same test on someone else's generator that is known to work good that would be helpful.

[HeywoodJ]

Originally Posted by phorvati

...I am not sure how capacitance regulates voltage. ...

Not all generators have an expensive AVR, some just use a capacitor in the excitation winding to "regulate" output voltage. Not nearly as precise as a good AVR, but also not nearly as expensive or fickle. Mastervolt has an OK explanation, see 7. THE THEORY OF CAPACITOR REGULATED ALTERNATORS

In the excitation circuit a capacitor is mounted. The capacitive value determines the strength of the magnetic field and therefore the output voltage. Since this is a fixed value, the output voltage is not automatically readjusted under load.

For the OP, a couple of different tech notes on troubleshooting capacitor-regulated generators:

Trouble Shooting Capacitor Regulated Pancake Light Tower Generators

ELECTRICAL TESTING AND TROUBLESHOOTING GUIDE, LOW PROFILE CAPACITOR EXCITED AC GASOLINE GENERATORS

The OP's NexGen uses a Markon BL105 head-end, which is a capacitor excited brushless alternator. Its more expensive brother, the SL105 is almost the same equipment, but with an AVR. The manual for both is here. Note that the manual says:

The main stator winding is designed for series/parallel connection to give a dual voltage output and no voltage adjustment is possible.

This is generally true, but small adjustments to voltage output can be made by changing capacitance slightly.

One more small point, capacitor regulated generators really prefer to run near power factor = 1, they don't do well with reactive power. Since you say it all used to work fine I wouldn't necessarily go down this road. For the Mastervolt gear I'm not as familiar with settings, do they have a power factor correction setting that might have gotten turned off? Or power factor correction circuits that might be having problems? One way to test this would be to try to load the generator to 80-90% of full load with a purely resistive device. Can you borrow 3-4 1500W electric heaters from folks around you?

[smac999]

you won't hurt the inverter charger. if the voltage is out of range it will just shut itself off (charger and ac passthrough). and start inverting instead if the inverter is on.

the mastervolt charger is probably good for 120-240v

[Wandering1]

What happens when you turn on a resistive load like your immersion heater?

[SV__Grace]

Thanks for all your ideas and feedback guys! I swapped out the capacitor for another brand/manufacturer that I had in my spares and read in the manual (thanks to a download link from user 'more') that reducing the governor speed corrects some high voltage problems (makes sense- faster speed, higher hz), tried it out and initial results look promising. (RTFM, right? my favorite acronym that I remind other people to do! ).


I'll post an update after more testing and use in real world conditions (cold start, launching both chargers at the same time, etc). With my newly upgraded solar panels and lithium batteries that could be awhile!

[more]

Originally Posted by SV__Grace

. (RTFM, right? my favorite acronym that I remind other people to do! ).

yes 99% read-the--fuucccckingggg-manual help

[Bycrick]

Voltage too high? My old Westerbeke has essentially no electronic voltage regulation. You adjust motor speed for about 60 Hz and hope that it outputs a usable voltage. If it doesn’t, you take the generator head apart and adjust shims in the magnetic gap. Really.

The result is that to have the Genset put out close to 60hz and about 120 v RMS when the inverter charger is running at max, the No-load output is about 132v RMS at 62 Hz. My Outback inverter charger didn’t like that at all until I changed the default settings. But it works just fine that way.

[SV__Grace]

OK, tweaked the governor by slowing the RPM a tad and swapped out the capacitor for a different manufacturers.

Upon a cold start with batteries at 35% (gotta love lithium) flipped the switch as normal to activate BOTH chargers (200amps) and after an initial spike to 129v it quickly settled within normal range of 120-122/59-61.

Success!

One thing I noticed is a drop of 20 charging amps or so around 70-80% SOC where it would usually stay at or near 200amps until 90% or so. Usual pattern is very reliably 20% per hour- 3.5 hours to go from 30% to 100% and this would add @ 30 minutes to the charging time to get to 100%.

We'll see how it goes. If this is permanent I can live with it as it is much better than the 8 hours it would take to get my AGMs to 100%, half of that time in float mode! (which might have built up carbon on the cylinder heads of the generator, changing the performance and RPMs). And the Lithums don't need to go to 100% so I can turn the generator off whenever I want.