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Old 06-29-2017, 09:54 AM   #1
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Generator Question

How long do you run your generator prior switching over to it with a minor load? I suspect it would be based on how large the generator is and based on an adequate warm up period. The generator on Bay Tripper is 5kw so it's relatively small. I switch to it within a couple of minutes of starting. Am I doing it wrong?
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Old 06-29-2017, 10:03 AM   #2
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Assuming it is a diesel genset I put a load on it immediately of about 10% or so and go to whatever demand I have once it warms up - typically less than a couple of minutes.
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Old 06-29-2017, 10:04 AM   #3
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Regarding your genny "warm up". I usually start the genny with no load and let it run until it smooths out (typically less than 20-30 seconds) then apply loads sequentially.
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Old 06-29-2017, 10:04 AM   #4
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I switch within seconds. as soon as the oil pressure gets high enough for me to let go of the preheat switch, I start applying load.
If the genset is cold, I'll get a little "hunting" and if that happens I turn off my water heater for a minute until the genny warms up, then it won't hunt.
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Old 06-29-2017, 10:05 AM   #5
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Depends on the generator. The coolant temperature on mine rises quickly, even without a load. When I see 100 degrees, I add some load. Add the balance of the load when it reaches operating temperature.

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Old 06-29-2017, 10:13 AM   #6
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I turn on my main breaker within maybe 30-60 seconds of startup. But initial load is never more than about 25%. Then maybe a minute later the inverter/charger switches over its loads and ramps up charging. That brings load up to 50-60%.
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Old 06-29-2017, 10:41 AM   #7
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I start my small NextGen 3.5KW unit with the genset's breaker off. I let it run for a minute or so. Then I turn the breaker on and the Freedom inverter/charger slowly ramps up its charging over a minute or so. It can put a 10 amp AC load on the generator if the batteries are down. That warms up the generator and after a few minutes of high current charging the charger ramps down to about 5 amps AC. I then add any big loads like the water heater or stove top.

So like my propulsion engine I wouldn't put big loads on the generator until it is well warmed up. I don't try to plane my boat until the engine is at operating temp for example. A generator being a smaller engine takes less time, but probably 3-5 minutes if it has a light load on it.

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Old 06-29-2017, 10:54 AM   #8
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I have a 5kW and switch it over probably ten seconds after start- how long it takes to walk back and check that it is pumping water. But load is small, like charger and fridge. Big loads like AC I wait like five minutes for it to warm up.
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Old 06-29-2017, 11:30 AM   #9
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Sometimes I start it with the breaker on and sometimes with the breaker off. Depends on what I'm doing at the time. I always preheat about 20 seconds. Knock on wood, I have not had any significant issue with it except a minor leaking seal which I replaced as soon as I was able. My gen is large and likes to handle larger loads. During the christmas parade, Just powering the 5000 or so leds was not enough to keep it happy for a 4 hour period of time. I had to turn on more cabin lighting, (also leds).

I think it depends on the generator. I am also still learning what all of my systems like and are capable of doing. Trial and error if you will.
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Old 06-29-2017, 11:45 AM   #10
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The NEC mandate for required backup power generation is not to exceed 10 seconds from power outage to power restoration.

Because of this I have no problem immediately loading a generator. Never seen one hurt by that practice over a several decade career. Granted many of these unts are kept warm with block heaters, but they also go from a dead stop to full load in one step, something a recreational marine generator never really sees.

An interesting note... At my shop we go from power outage to fully loading our generators in 3.7 seconds. That includes detection, crank, and load transfer. We also have a two generator system. If the primary generator fails to pick up the load, the secondary unit will come online, all in under the 10 second NEC requirement.

I know the above has nothing to do with "marine" generators, but the insite is relevant since for every marine generator there are probably a thosand land based units in service.
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Old 06-29-2017, 12:53 PM   #11
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Generally about 5 minutes. My Carver came with one of those stupid auto switching "selectors" that threw the load onto the generator the very second it started. Nothing you could do to stop it other than make sure there were no AC loads available. So what that meant, in the heat of the summer I had to sit and wait as the boat heated up to the tune of about 1 degree a minute as the generator warmed up. Also cool down was the same way. No way to select what I wanted. If the generator was running, all household AC loads were on it. Soooooooo....I installed a "barrel switch". Not a cheap little Mfer. But the auto switch drove me crazy. Pilots are control freaks ya know....

And I let it cool down for the same amount of time....about 5 minutes.
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Old 06-29-2017, 01:15 PM   #12
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Have put small load on my Westerbeke 8kw immediately as the refrigeration and water heater are fed with 110 v ac as soon as the ac is present. The inverter passes through the AC to the house outlets immediately. The two inverter/chargers which are the major 110v load take perhaps thirty seconds to cycle to bulk charge after the 110 ac is present.

This has been going on for 18 years. Little late for me to start worrying about it.
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Old 06-29-2017, 01:28 PM   #13
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I put between a 10-20% load on mine within about 30 seconds of starting. Beyond that, I try to wait a couple of minutes if I plan to say switch on all 3 air conditioners.

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Old 06-29-2017, 01:33 PM   #14
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We have westerbeke 7.5 diesel and I load it immediately. We have a roof top air, and small refrigerator. I have a 2nd alternator that keeps everything up while underway so I turn the charger off .
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Old 06-29-2017, 01:36 PM   #15
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I let it run a couple minutes under a light load, like fridge and battery charger, just to hear and watch it run, make sure water is pumping, then switch on whatever I want. What is the hurry?

Mine has an autostart on demand feature, which I never use. It can start and stop on demand, but with a fridge and a PC and lights, it is going to want to run most of the time.

I removed the charger circuit from the autostart side, otherwise it wants to run all the time. I just leave the charger switch on all the time, that way I wont be forgetting to turn it on.
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Old 06-29-2017, 01:49 PM   #16
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Quote:
Originally Posted by ksanders View Post
The NEC mandate for required backup power generation is not to exceed 10 seconds from power outage to power restoration.

Because of this I have no problem immediately loading a generator. Never seen one hurt by that practice over a several decade career. Granted many of these unts are kept warm with block heaters, but they also go from a dead stop to full load in one step, something a recreational marine generator never really sees.

An interesting note... At my shop we go from power outage to fully loading our generators in 3.7 seconds. That includes detection, crank, and load transfer. We also have a two generator system. If the primary generator fails to pick up the load, the secondary unit will come online, all in under the 10 second NEC requirement.

I know the above has nothing to do with "marine" generators, but the insite is relevant since for every marine generator there are probably a thosand land based units in service.
I too worked in industry where we had backup gennies that had to get on line in 10sec. Big old Nordbergs and it was a challenge to meet that spec.

But if there was no rule requiring 10sec, I think most engineers would prefer some warmup, especially on big machines. That thermal stress issue..

When testing, we would start with gov set low, then sync and gradually add load over like 15min. We were gentle with them when we could.

Also, those backup machines usually don't log a lot of hours. Testing and an occasional outage. So there may be issues that are not seen.
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Old 06-29-2017, 02:08 PM   #17
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Quote:
Originally Posted by Ski in NC View Post
I too worked in industry where we had backup gennies that had to get on line in 10sec. Big old Nordbergs and it was a challenge to meet that spec.

But if there was no rule requiring 10sec, I think most engineers would prefer some warmup, especially on big machines. That thermal stress issue..

When testing, we would start with gov set low, then sync and gradually add load over like 15min. We were gentle with them when we could.

Also, those backup machines usually don't log a lot of hours. Testing and an occasional outage. So there may be issues that are not seen.
The "average" recreational marine generator probably dies from lack of use or corrosion related issues I would believe, but that is defered to you, since I don't deal much in the recreational side.

Again, I have never seen or heard of a generator failure that was even thoght of being attributed to immediate loading. I live in a world where standby generators are immediatly loaded to near full load once a week during the weekly generator test cycle. These units frequently are in service for decades. The Automatic Transfer Switch initiates a transfer, which applies full load in one step. This is even aggrivated by the fact that many installers do not turn on the "in phase monitor" function which makes the intial loading a pottentially 180 degree out of phase transfer with a 30 milisecond break before make. (in my opinion not a good idea).

I do see a number of generator end failures, but when you look at the installation, they are situations where where high ambient temperatures, mixed with high loading levels exceed the manufacturers operating specifications. That and the occasional end bearing failure.
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Old 06-29-2017, 02:29 PM   #18
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If its hot out I go to full load in 30 seconds. :O
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Old 06-29-2017, 04:36 PM   #19
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I never thought about the question. Takes but a moment after starting for the Northern Lights to sound 'normal'. Takes more than that for me to get over to the panel. I leave all the 110v panel breakers off so switching stuff on is sequential. The AC is on a separate panel and is therefore switched later as well.

I can certainly hear the genset change sound with varying loads, but very seldom does the rpm dip even for a moment.
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Old 06-29-2017, 05:11 PM   #20
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This is what my Westerbeke 8BTD manual says:

Once the engine starts, check instruments for proper oil pressure and battery charging voltage. Never attempt to engage the starter while the engine is running. Apply a light load to the generator and allow the engine's operating temperature is reached (170 - 190 F) and when a load is applied to the generator.

My interpretation:
-Start it.
-Close the breaker/transfer switch.
-Light load until normal coolant temp on the gauge.
-Apply large loads like AC, water heater, battery charger, etc.

Even at full rated electrical load, a marine gen engine is not at full engine load. My 8 BTD is a 21hp (16Kw) diesel engine.

The key to the wear is the oil temperature. If it is a cold engine room start, let it warm up with light load first. If it is warm from running a few hours ago, or the engine room has been warm from the days run, go ahead and load it up.
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