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Old 09-09-2009, 15:08   #1
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Power Spikes from pto Generator - Help!

Have a pto driven generator that provides 120v at 800 rpm, but when pushed to 2200 rpm generator is producing 300v to 400v . I know this is a simple fix , but I am clueless as to the solution. Help!!!
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Old 09-09-2009, 21:14   #2
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I assume you mean 120V AC, right? In that case, you are supposed to set the engine rpm's so that the generator output is 60 Hz. You shave have 110-130V at that setting and keep it there. If not, your voltage regulation is broken. That can be either an AVR (Automatic Voltage Regulator, a circuit board) or a capacitor.

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Old 10-09-2009, 06:12   #3
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Thanks Nick, yes I did mean 120v ac. I will check out the voltage regulation today and see what it is doing. I am new to all this , and the learning curve on some of these systems can be long. I have just inherited the boat , and the electrical systems were put together with duct tape and bubble gum!!! Will post what I find.
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Old 10-09-2009, 06:45   #4
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It's likely just the revs

2200/800=2.75
2.75 * 120 = 330 volts

I have a 20 Kw PTO generator for my tractor, the RPMs to get the correct Hz/voltage are critical. My generator produces 120 VAC/60Hz at PTO speed which on this tractor is 2100 engine RPM, if I am off in my RPM by even 100 the Hz/Voltage is way wrong. If you get 120 Vac at 800 RPM then that's where it needs to run. I'm thinking that's all your problem is.
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Old 10-09-2009, 07:03   #5
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jdoe, This sounds like exactly what is happening. So what I need is to rig up a disconnect or bypass from the generator to the electrical system, when needing the extra power from the engine? When making the passage to the bahamas under power not sail, the problem came up and actually fried several systems. This generator is tied in directly with no clutch, disconnect, or regulation of any type that I have found as of yet.
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Old 10-09-2009, 07:46   #6
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768,

I think an electric clutch to enable/disable it is necessary and a nice AC multimeter with frequency display isn't too much luxury. I can recommend the Blue Sea Systems AC multimeter. It is panel/bulkhead mounted and shows AC voltage, current, frequency, and wattage consumed.

ciao!
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Old 10-09-2009, 12:51   #7
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I think this is why AC is usually made with a dedicated genset. If I wanted AC off a PTO it'd probably be better to make DC and convert it.
That said 800 rpm seems kinda slow. A freq meter would prove it up- correct rpm's is where the gen delivers the correct frequency(60 Hz)- then regulate to get the right voltage. I'll bet that the freq is way off at 800 rpm.

If it's 60 Hz @ 800 engine rpm I'll bet your pully ratios are way off.

Get a Blue Sea when it's set up. For now buy a hand held Fluke and test.
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