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Old 30-04-2019, 17:03   #1
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Overheating NextGen generator head

I have a NextGen 3.5, new unit professionally installed last year. Runs great, but the thing will only do a little over 2kW (20 amps at 110V) continuously, anything more and after about 5 min the thermal circuit breaker mounted on the generator head trips and won't reset for about 10 min because it is overheated. It's in a sound box with the recommended exhaust fan. I figured that air flow might be the issue so hooked up an additional 4" duct with a fan of twice the recommended CFM in addition to the regular fan on a 3" duct, but it still tripped after a few minutes at around 24 amps. And this was with the engine off (it draws from the engine room) and 65 degree F outside air temp. The engine isn't overheating, it's got good water flow and coolant level is good. The fans are definitely working because they're exhausting very hot air.
Any ideas on why the generator electrical portion is getting so hot? I would expect a 3.5 kW system to at least be able to do 3kW continuously, and especially baffling is the fact that the NextGen uses the same electrical gen portion for both their 3.5 and 5.0 so it's actually a 5kW generator electrically. One wonders if you're also limited to just over 2kW continuously on their 5kW model since only the diesel engine is different? Any ideas?
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Old 30-04-2019, 17:17   #2
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Overheating NextGen generator head

What kind of hose are you using?
Mine did that when I had the cheap supplied drier hose, what was happening was when the hose got hot, the blower would suck it flat and really reduce the airflow.
I replaced it with 3Ē aircraft Scat hose and no problems since.
Scat hose is smooth bore, wire supported and very high temp hose, it doesnít suck flat and being smooth bore will flow way more air, and of course can handle much higher temps than the generator runs at.
I was shocked at the cheap junk hose my Nexgen came with.
https://www.aircraftspruce.com/catal...p?recfer=13568
SCEET hose is even better, and more expensive of course
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Old 30-04-2019, 17:28   #3
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Re: Overheating NextGen generator head

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What kind of hose are you using?
Mine did that when I had the cheap supplied drier hose, what was happening was when the hose got hot, the blower would suck it flat and really reduce the airflow.
I replaced it with 3Ē aircraft Scat hose and no problems since.
Scat hose is smooth bore, wire supported and very high temp hose, it doesnít suck flat and being smooth bore will flow way more air, and of course can handle much higher temps than the generator runs at.
I was shocked at the cheap junk hose my Nexgen came with.
https://www.aircraftspruce.com/catal...p?recfer=13568
SCEET hose is even better, and more expensive of course
Will definitely check that, expensive stuff though isn't it!
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Old 30-04-2019, 18:36   #4
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Overheating NextGen generator head

How long is your hose run?
Iím just running the supplied blower with no issues, the generator is good for about 27 or 28 amps continuously, the limit is engine output, when you get higher amps, the RPM of the engine begins to droop, this causes the voltage to drop. So to get the same number of Watts output, the amperage increases, so you will see higher amperage, but no more real output due to voltage drop.
Mine seems happy at around 25 amps continuously, much more than that and the engine begins to slow down.
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Old 30-04-2019, 18:43   #5
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Overheating NextGen generator head

The engine is passively cooled of course, itís cooled by convection, no fresh water pump. If you use a high concentrate of coolant, it will overheat. Water cools better than antifreeze, so run only about a 25% mix, not a 50/50 mix like usual.

Also on mine, the water pump began to leak and spray salt water all over the entire thing and did so until the water pump finally seized and threw the belt off, and then the engine overheated and shut down.
Only then did I see I had a salt water leak inside of the enclosure.

I really didnít like that, so Iím now using a March air conditioner pump that is of course AC powered, once the generator beings to make AC power the pump runs. This means I have no rubber impeller to worry about, canít fill the exhaust from over cranking, and the pump canít leak water inside of the enclosure, cause the pump is in the bilge.
The March pump must be mounted below waterline.

I also had issues with the little Racor filter clogging, and the screw on cartridges were harder to find, so I put that little Racor on my outboard in the dinghy and put a Racor 500 on the generator. The filters are far easier to find as everybody uses a Racor 500, plus they are cheaper too.
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Old 01-05-2019, 03:53   #6
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Re: Overheating NextGen generator head

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The engine is passively cooled of course, itís cooled by convection, no fresh water pump. If you use a high concentrate of coolant, it will overheat. Water cools better than antifreeze, so run only about a 25% mix, not a 50/50 mix like usual.

Also on mine, the water pump began to leak and spray salt water all over the entire thing and did so until the water pump finally seized and threw the belt off, and then the engine overheated and shut down.
Only then did I see I had a salt water leak inside of the enclosure.

I really didnít like that, so Iím now using a March air conditioner pump that is of course AC powered, once the generator beings to make AC power the pump runs. This means I have no rubber impeller to worry about, canít fill the exhaust from over cranking, and the pump canít leak water inside of the enclosure, cause the pump is in the bilge.
The March pump must be mounted below waterline.

I also had issues with the little Racor filter clogging, and the screw on cartridges were harder to find, so I put that little Racor on my outboard in the dinghy and put a Racor 500 on the generator. The filters are far easier to find as everybody uses a Racor 500, plus they are cheaper too.
Good to know going forward, although at least at this point my engine is fine, it's the electrical section that's overheating.
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Old 01-05-2019, 04:49   #7
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Overheating NextGen generator head

Just tid bits Iíve learned over four years and 1000 hours of using the thing.
I need to adjust my valves, havenít done it yet.
The pencil zinc in the heat exchanger last a long time, but itís easy to check, and I have never, ever gotten anything in the oil screen, so Iíve gone to pulling it and cleaning it every other oil change, which is 100 hours of course.

It seems to be a pretty robust and simple generator, you can change capacitance of the capacitor to vary output voltage if needed and you adjust the Governor arm to adjust the Hz rate of the generator. Mine needed both to stay where I wanted it to be, I had to turn the speed up to get to 62 Hz when unloaded cold so that it was 60 Hz under load and hot.

When you get enough cooling air through it, it should be a pretty trouble free machine, so far mine has been.

Iím pretty sure the motor was originally designed to be a stationary motor to run things like mobile sign generators for extended periods, so the motor ought to last a very long time if the oil is kept changed.
Iím still astonished by a ball bearing crankshaft, thatís not cheap, but gives insane long service life.
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Old 01-05-2019, 05:31   #8
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Re: Overheating NextGen generator head

I bought a 5 kw last November and have run it at 30+ amps for a about 2 hours with no issues. I was however quite disappointed in the fact that the parts shipped were not the parts advertised in their brochure nor in the documentation provided with the unit. The documentation says it has a Markon alternator head, but in reality it has a Linz. It says it has an Oberdorfer water pump but it really has a Jabsco. It says it has this heavy duty drive belt used in motorcycle drive trains but it really has a nine rib serpentine belt. The Jabsco shaft seal leaked at less than 50 hours of use. It was then I discovered that the pump was a Jabsco. I was looking to buy spare impellers at about that time and am glad I looked because the Oberdorfer impellers were about $80 each and I would have really been pissed if I had purchased them and found the pump was a Jabsco in the middle of nowhere when I needed to replace the impeller. About the only thing that was as advertised was the Kubota engine.

The enclosure for the 5.5 has a baffle that directs the cooling/combustion air over the alternator head before it goes anywhere else in the enclosure so the alternator always gets the coolest air. Does the 3.5 enclosure have such a baffle?
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Old 01-05-2019, 05:46   #9
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Re: Overheating NextGen generator head

The 3.5 doesnít have a baffle for that, however its vents are designed so that air is directed over the generator head first.
My generator head is a Syncro, the Markon Head was the old head that had a rep for dirty power I believe.
Reason I was given for the switch was the newer Kubota motors didnít have the drive for the water pump anymore and that forced a switch
Ditch the raw water pump and go to electric, mine failed just as yours did, one reason claimed is if the belt is too tight, it can cause the seal to fail.

First Kevlar belt ribbed drive motorcycle Iím aware of was a Kawasaki 440 way back when, and it used a belt that looks like this generator has.

If your ever in Jacksonville, drop by and see the Nexgen facility, itís actually a small shop and these little Marine generators donít seem to be their major business, bigger ones are.
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Old 01-05-2019, 05:55   #10
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Re: Overheating NextGen generator head

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Originally Posted by a64pilot View Post
The 3.5 doesnít have a baffle for that, however its vents are designed so that air is directed over the generator head first.
My generator head is a Syncro, the Markon Head was the old head that had a rep for dirty power I believe.
Reason I was given for the switch was the newer Kubota motors didnít have the drive for the water pump anymore and that forced a switch
Ditch the raw water pump and go to electric, mine failed just as yours did, one reason claimed is if the belt is too tight, it can cause the seal to fail.

First Kevlar belt ribbed drive motorcycle Iím aware of was a Kawasaki 440 way back when, and it used a belt that looks like this generator has.

If your ever in Jacksonville, drop by and see the Nexgen facility, itís actually a small shop and these little Marine generators donít seem to be their major business, bigger ones are.
I had heard there was an issue with the pump drive on the Kubotas as well yet my pump is direct drive off of the engine, not belt driven.
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Old 01-05-2019, 06:42   #11
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Overheating NextGen generator head

That is a difference between the 5.5 and the 3.5 then, the pump on the 3.5 is belt driven.

However ditch the mechanical pump, plumb in a March air conditioner pump, wire it direct to the generator, no downside that I can find and many upsides, like you canít fill the exhaust by over cranking, and the exhaust is blown dry on shut down cause the pump quits just before the engine stops.
Now the engine will run for about 4 or 5 sec with no water flow on start up, but that short of time causes no harm.
Plus a March pump will run for years and tens of thousands of hours, they rarely fail, and if you have AC in the boat one spare can cover both applications.

The March pump must be mounted below waterline, they will not prime, not even one inch.
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Old 01-05-2019, 10:21   #12
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Re: Overheating NextGen generator head

I am no expert. A couple of items that come to mind are:
1. check the output voltage under load. Make sure your RPM drop isn't causing the AMP load to increase as voltage drops. I adjusted my RPM while running the hot water tank. It gave a constant amp load and the RPM was adjusted under load.
2. Does your hot air have a place to go? The blower may direct air on the head but how does the air leave. Mine blows on the gen head then out a hole that is higher (hot air rises) into the engine bay. Then I installed an engine room blower to blow air out of boat. The blower is A/C driven from generator and the engine blower is D/C. (my Nextgen 5kw charges my batteries).
3. Bad breaker- salt water environment has destroyed many connections on boats. You said it was the temperature breaker but is it the overload breaker?
4. Is the Air conditioning kicking off the overload breaker. Maybe install a start up capacitor to help startup.
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Old 01-05-2019, 13:45   #13
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Re: Overheating NextGen generator head

I went through a long process correcting an overheating problem on my NexGen. The previous owners did not do a good job changing the zinc often enough and they broke apart clogging the heat exchanger. This was not obvious as the waterflow appeared more than adequate. We tried ultrasonically cleaning the heat exchanger with no success. We determined that the ultrasonic cleaning was unsuccessful by cutting the heat exchanger open after replacing it. The heat exchanger that comes with the NexGen does not have removable endcaps. I replaced the heat exchanger with one made for a Phazer Generator which is nearly identical to the NexGen. This solved the problem. Then I bought a Honda 2000 as a back-up to the NexGen. I am a belt and suspenders guy when it come to my boat.
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Old 01-05-2019, 19:15   #14
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Re: Overheating NextGen generator head

Try calling Nextgen. They are very helpful and provide excellent customer support. We have a 5.5, circa 1999 and still running!
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Old 02-05-2019, 03:51   #15
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Re: Overheating NextGen generator head

No matter which type or color your antifreeze is, it will transfer heat most efficiently when blended with the proper amount of water. The specific heat capacity of ethylene glycol is only about 65% that of water, at the temperatures seen in a cooling system.
If pure antifreeze-coolant (ethylene glycol) is used in a cooling system, the system loses about 35 percent of the heat-transfer capabilities it otherwise would have, when antifreeze is mixed with the proper amount of water.
It is only when pure antifreeze-coolant is mixed with water that its freezing point is lowered. So if you need protection below the zero mark, you had best mix the antifreeze with water, in the proportions suggested.
Water must be mixed with the antifreeze-coolant in order to keep the performance additives (silicates, phosphates and nitrates) suspended. Without water, these important additives tend to settle. If they do that, you lose anti-corrosion and other additive protection.
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