A/C voltage spikes?

[jt11791]

I need some advice and a sanity check. The problem started when I was at anchor with my generator running. I turned on my two A/C units, which started up normally but then there was a “bang” and both units went dead.

I took a quick glance at the boat's electric panel and nothing was amiss, the volt meters showed 120V on each leg and no breakers were tripped. The only other thing running from the generator was my battery charger and that was still charging the batteries.

I took the boat into a marina and had an AC tech take a look. He found the circuit boards fried in both AC units and in one the start cap was also blown up. He replaced the boards and cap and both units started up and ran normally (on shore power). In fact, I ran the AC for a week at the dock with no problems, but I did not think to test them on the generator. Once I left the dock and turned on the AC (one unit) with the generator running it instantly blew out again.

So it looks like the generator (a Kohler 10EZ) is putting out bad power. The thing that worries me is that I can’t see a problem other than the dead AC. The generator appears to run normally, RPM is constant. It works fine making hot water and charging the house batteries. The volt meters on the panel always show 120V on each leg and when I test with a handheld meter I get the same. As I can think of nothing else to try, I installed a new voltage regulator in the generator but I’m not certain the problem is solved and I don’t want to blow up another expensive AC circuit board. My handheld meter shows 120V on each leg, but that’s what it showed with the original regulator. Has anyone else ever seen voltage spikes from their generator? How would you proceed?

[Sailmonkey]

Look at the power with an oscilloscope. There may be something in then waveform that can give you a direction to look in.

[Corvidae]

Voltage drop when the AC kicks in can spike the amperage, blowing the cap, and melting the relays on the controller board. One way or another electric motors draw enough wattage to start moving. When the voltage goes down, they pull more amperage, until there are no more amps, or something melts.

It's probably not any one thing, it's all the things at once putting a large enough load on the generator.

Now that it's happened though, check for burnt connections, and wires that seem to be working, but are stiff or brittle.

[goboatingnow]

Is this a 3 phase generator

[Jammer]

I try to stay out of these electrical threads.. hard to diagnose via internet.

If it were my boat the way I would diagnose it is connect large loads, ideally while watching the voltage waveform with an oscilloscope. If you do not have an oscilloscope you can purchase inexpensive software ones with USB probes that run on a tablet or laptop. Or just look at voltage.

Making hot water is all good but you want to see what the genny does when loaded all the way to its rated capacity. Use your water heater, add kitchen appliances. One other way to do this is to buy small space heaters and connect them being mindful of circuit capacity. 1500 watt heaters are easy to buy and inexpensive. Your genny is 10,000 watts, you want to get close to that.

Chances are your problem will show up when it is loaded up that way, you'll get overvoltage, undervoltage, erratic voltage, or dropouts or harmonics or something in the waveform.

You could also try starting a large motor and see if that recreates the problem without the attendant cost. Use an air compressor or something, and just be quick on the switch to disconnect it if it doesn't start right away and it will be fine.

[wsmurdoch]

I will assume your air conditioner is 120V and your generator is 120V/120V/240V. If you have an open neutral or a neutral with a significant resistance between your loads and the generator, the voltages between the two hot wires will remain 240V, but the voltages between either of hot wires and the neutral will depend on the loads. While disconnected from shore power, you might try running your generator with a 120V/1600W heater plugged in and operating normally between one hot wire and the neutral and a 120V/100W light bulb between the other hot wire and the neutral, and while they are in operation measure the voltages between each of the hot wires and the neutral.

[OzeLouie]

As above but could also be a faulty IC unit in the generator. AC gen sets have to create their own sine wave (Pulse width, frequency, peak voltages etc) and if the IC unit is faulty you can get some very strange output. This would be noticed by items like a motor that requires alternating supply to function and not effecting things like heaters etc.
As suggested, check that it is supplying the correct voltage to the aircon, then the outputs' wave pattern etc with a CRO.

Cheers Louie

[Frankly]

If the system is 120/240 and the ACs are 120V the floating neutral would be the first place to look. Easy test to perform. Get your meter and play around with resistive loads (water heater, coffee pot, toaster, incandescent lights). Check that both phases stay close to 120 volts under various loads. A lot of DVOM have a max voltage capture mode might be easier than O scope.

Also check that the neutral to ground voltage stays at 0.

Capacitors often sound like fire crackers/ gun shot when the fail from overvoltage.


Frankly

[jt11791]

Thanks for the thoughts, here are a few more details.



The generator is single phase.
The AC units are 230V, so they use both legs.
I don't have an oscilloscope, just a basic multimeter, but maybe I can hire someone to bring one out.


The damaged circuit boards all had blown MOVs (varistors).


OzeLouie, what do you mean by IC in the generator? Is that the voltage regulator unit? My generator has the "voltage regulator" which is a potted circuit board and not much else.

[Frankly]

I would take a serious look at neutral to ground / phase to ground voltages (should be same and neutral to ground should be zero). Your AC controllers may have some filtering connected between phase conductors and ground. Also check the line to line voltage. Varistors, depending on size, can absorb significant spikes/ surges (thats the reason they are there).


Frankly

[OzeLouie]

Originally Posted by jt11791

Thanks for the thoughts, here are a few more details.



The generator is single phase.
The AC units are 230V, so they use both legs.
I don't have an oscilloscope, just a basic multimeter, but maybe I can hire someone to bring one out.



The damaged circuit boards all had blown MOVs (varistors).


OzeLouie, what do you mean by IC in the generator? Is that the voltage regulator unit? My generator has the "voltage regulator" which is a potted circuit board and not much else.

Hi jt, Firstly refrigeration is my trade not electronics so there must be members who can explain this better, but here is what I have 'gleaned' from others:

An alternating generator has to have its current oscilated (pulsed, sine wave) to the required frequency and that means a pulse width and voltage peak of the pulse to suit the alternating voltage. In the case of your 240VAC gen set it will most likely have a 50 cycles per second frequency and each peak voltage to approx 330V. is required.

As i understand, it is like the brains of the gen set and if that goes crazy (and they can) then the generator can put out some very damaging current / voltage.
Note again that such a problem will most likely only effect loads that require oscilating supply (AC) and not items like heaters etc. that don't.

Suggest finding an electronics expert who could test your IC unit or maybe you could remove the IC unit and take it in for testing.

This may help also: https://www.manualslib.com/products/...z-3564195.html

Cheers Louie

[Sailmonkey]

Originally Posted by OzeLouie

Hi jt, Firstly refrigeration is my trade not electronics so there must be members who can explain this better, but here is what I have 'gleaned' from others:

An alternating generator has to have its current oscilated (pulsed, sine wave) to the required frequency and that means a pulse width and voltage peak of the pulse to suit the alternating voltage. In the case of your 240VAC gen set it will most likely have a 50 cycles per second frequency and each peak voltage to approx 330V. is required.

As i understand, it is like the brains of the gen set and if that goes crazy (and they can) then the generator can put out some very damaging current / voltage.
Note again that such a problem will most likely only effect loads that require oscilating supply (AC) and not items like heaters etc. that don't.

Suggest finding an electronics expert who could test your IC unit or maybe you could remove the IC unit and take it in for testing.

This may help also: https://www.manualslib.com/products/...z-3564195.html

Cheers Louie

Louie,

You really shouldn’t offer generator advice. A generator has no IC’s to control the “pulsing” that’s all done by non adjustable windings and rotational spacing. No magic circuitry here.

[skipperpete]

[Sailmonkey]

Originally Posted by skipperpete

Attachment 246567

What help are frequency converters to the OP?

[Corvidae]

240/120 circuits are almost always 60hz, because that's the US standard. 50hz countries don't usually have a 110volt circuit, or a neutral, they're just 230 volts at 50hz. There are probably exceptions, if I knew I probably couldn't call them Euro trash any more.

Either way, the easiest test is to stick a volt meter on the AC circuit while the AC kicks on, and watch the voltage. If it drops more than about 20%, bad things are likely to happen. Any multimeter might work, I'd say get a cheap one with a fast needle gauge, or an expensive one with data logging. Some decent meters do have a Min option as well for this exact purpose.