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Old 25-02-2010, 16:42   #16
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Originally Posted by chala View Post
do you idle your generator.
The generator is governed to run at a constant speed of 3000rpm. I do let it run a few minutes before applying a load and after the loads are shut off.

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Old 25-02-2010, 16:54   #17
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Originally Posted by s/v Jedi View Post
With all those fans and the first 7 years without trouble I don't think it's heat. I think it's time to get a geek with a scope and check out the wave forms coming from the windings and on every wire connected to the AVR.

AVR repair: ah, I couldn't see it was potted on the photo.

cheers,
Nick.
Yes, that is what I was thinking. I have suspicions that the waveform has been dirty for a while. When I measure the frequency, it shows 180hz (60hz system) under inductive loads until I put a resistive load on it - then it shows a constant 60hz. It is strange that it is 3x the nominal frequency. I suspect that there are harmonics or regular voltage spikes that are averaging on my frequency meter, but the meter doesn't have the resolution to show what is happening in real time.

Ideally, I would remove the head and take it somewhere. Is it realistic to expect that the head could be diagnosed removed from the engine? We are in Puerto Rico right now, so might have good options for getting it fixed (compared to the Bahamas).

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Old 25-02-2010, 17:40   #18
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Been pretty frustrated with the no-load output from my NextGen 3.5KW genset, too. BTW, this has the optional "high stability voltage regulator". Hah!

Here are a couple of screen shots from a Digital Storage Oscilliscope (DSO) taken a few months ago:

The first is with practically no load, just a fan on the A/C unit. The second is with a 20A load. Note that in the first the line frequency was 86.4Hz; with a load applied, it kicked back to about 63.6Hz.

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Haven't had much chance to get back to this problem, yet. Mainly, it's an annoyance, since the easy fix is to switch in a load. But it would be nice to have a cleaner output at low loads, and I'm sure the frequency can be adjusted down to 60Hz where it belongs.

Bill
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Old 25-02-2010, 18:46   #19
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Bill,

Does it make a difference whether the load is inductive or resistive? For mine, the inductive loads result in the the dirty frequency measurements, while the resistive loads seem to make it cleaner. Also, do you have the big capacitor to regulate voltage?

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Old 25-02-2010, 19:57   #20
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Mark,

Good question.

Insofar as I can tell, the resistive loads make for a cleaner output. There is a slight advantage also on frequency.

Here's a shot with one of the A/Cs running...about 18A or so load....and as you can see the frequency is about one Hz higher but the output is still not clean. Compared this to the second pic in the above post, which was a 20A pure resistive load.

Re: a big capacitor, I don't know. Have a stock NextGen 3.5KW model installed by the dealer, with a brand new AVR.

Bill

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Old 22-05-2010, 10:03   #21
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This is driving me nuts

Here is the update on the generator problem:

I found a person with the exact generator as ours whose engine was kaput. So I got their generator head and swapped it out with ours, thinking that there was something wrong with our head. I also removed the original voltage regulator on the replacement head and replaced it with a brand new one.

The new regulator blew in 4 weeks (~10 runs). Thinking these non-OEM replacement regulators I have been buying are not up to snuff, I installed the original equipment regulator that was originally on the replacement head. It almost immediately started giving high voltages. It will run OK for a while (up to 1hr), then the voltage will spike up high. After shutting it down and starting again, the same thing happens.

So, I don't think this is a generator head problem, but something to do with the engine or post generator wiring. The engine starts and runs fine and I don't detect any surging or stalling or other change in rpm. The post generator wiring is pretty straight forward, sized generously and wired professionally. It is also pretty simple - generator to panel. There is an Outback inverter/charge with transfer switch on the leg controlling the outlets and low-load stuff, and the generator is connected directly to the high load stuff.

Does anybody have any ideas? Answers from Phasor have been along the lines of too much heat and don't shut down while under load. I have massive amounts of forced air cooling running through the head and never shut it down under load. Could it have to do with the type of load? When the Outback battery charger is running, the frequency I measure on a multimeter changes from 60hz to 180hz, but drops back to 60hz when a resistive load is added. I have always contributed this to a dirty waveform (like Bill shows) that just gets averaged or perverted in a multimeter reading (I don't have a scope to see what is really happening). Could the charger somehow be causing this problem?

This is driving me nuts.

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Old 22-05-2010, 22:51   #22
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I will assume that your generator is an alternator, (produce alternative current, voltage). An alternator is basically a pretty simple thing. The Frequency of the alternator is related to the RPM of the “prime mower” in this case your diesel 3000 rpm. The frequency will drop under load if the diesel as a mechanical governor or be pretty accurate if the governor is of the electronic type. The current (Amps) that the alternator can supply is limited by the carrying current capacity of the main wiring of the alternator. The voltage produced by the alternator is related to the excitation of its field by the DC supply of a voltage regulator. There is a multitude of different voltage regulator, yours seems to be an electronic Automatic Voltage Regulator. It is always possible to check and to run in an emergency an alternator by supplying a suitable DC voltage straight from a battery. Normally a 6 to 12 volts battery does the job. If manufacturer information is not available it is possible to measure the voltage at the field terminal to get an idea of what will be acceptable. A test will be successful if the supply voltage is stable even with a small load. If not various test of insulation, checking of surge suppression diode etc will be required.
Loading of an alternator. Best load is resistive, then inductive corrected, then inductive. Worse load are capacitive load that produce a leading power factor they will destabilise most AVR. I am wondering if the inductive load that you put on your alternator as been over corrected by the addition of to many capacitor, just a guess or if to much RF from your electronic load is feed back to your AVR and is getting spiked. To find out is just to run your alternator with know safe load and progressively find out which appliance your AVR does not like. Hope this help.
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Old 05-06-2010, 08:48   #23
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Originally Posted by colemj View Post
the commutator is clean and shiny
Mark
I would assume that you meant to say the slip ring(s) is, are clean and shiny. Commutator normally implies dynamo. Alternators who include a dynamo for the production of the field excitation DC are quiet rare since the advent of silicon rectifier. Due to vibration and dust, slip ring can become oval making the brush to jump slightly. This can also affect proper voltage regulation. Brushes jumping can be best observed in the dark, a slight jumping of a brush will be indicated by increased arcing where the brush jump. The best rectification of the problem is to remove the rotor and have it rectified on a lathe if the ovalization is not too great.

Quote:
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The generator is governed to run at a constant speed of 3000rpm
Mark
So you must have a two poles alternator running at 50 Hz. Now you have not mentioned the voltage. If it was 110-120 Vac then it will be quiet odd because most 110-120 Vac alternator does run at 60 Hz or 3600 rpm in direct drive. The point is that some AVR will be happy to work in both frequency but not all of them; the same apply to the alternator.
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Old 05-06-2010, 11:20   #24
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Hi Chala,

Thank you for your help with this.

I said commutator, because that is what it looks like to me. The brushes ride on a segmented rotor like I'm used to seeing with electric motors. Could be slip rings, I will check further. The generator head is a Stamford head, if that helps.

It is a 120/240V 60Hz head that is wired for 120. The engine runs at 3000rpm, as per the manual. It is belt-driven, so I always assumed the extra 600rpm was generated by the pulley size difference between the engine and the head.

Your suggestion to turn off all loads and look for the one causing trouble is a good one. In fact, I know it misbehaves with one specific load - the battery charger. The Outback inverter/charger comes on automatically when I turn on the generator, so is always on when the voltage regulators go bad. Doesn't mean it is causing the problem, but I will try running without the charger on and see if the problem remains. The inverter/charger is a line-frequency type (big heavy transformer), so it might have a big capacitance and leading power factor. Although Outback is a very good engineering company and I would suspect that they would have seen this problem a long time ago.

Could there be a problem with the internal transfer switch on the inverter and how it connects/disconnects neutral to ground?

I want to restate that this problem has occurred with two separate generator heads. So I suspect the engine (don't know how this could be a problem) or boat wiring (although the generator ran fine for 6 years without a problem).

Thanks for your continued help - I need it.

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Old 05-06-2010, 20:40   #25
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(although the generator ran fine for 6 years without a problem).
Rule one of faultfinding. “ If the appliance has been running OK in the past what could have been done recently that could affect its present running” a process of elimination.

Quote:
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(big heavy transformer)
Transformers are normally inductive and produce a lagging power factor.
Capacitors are normally capacitive and produce a leading power factor and are used to correct a lagging power factor. Over correcting is not recommended.

Can you be more precise about what type of Stamford alternator you have?
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Old 05-06-2010, 22:48   #26
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May be this could help. More information is available at http://www.cumminsgeneratortechnolog...5%20Manual.pdf.
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Old 10-06-2010, 14:56   #27
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I have written previously on this thread, but have had a new development. I had sent my freedom 30 to an authorized repair facility in Orlando. Since my presenting problem was the ac buzz in my VHF radio during charging, I asked them specifically to put an oscilloscope on both the inverter and charger output.
This thread could be of value.
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Old 11-06-2010, 05:24   #28
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Thanks Chala,

I am not ignoring your help - I'm not a a place where I can do a lot of troubleshooting right now. But I will be in a couple of weeks and will be back trying to solve this problem. Stay tuned!

Mark
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