Robin RGD3300 Diesel Genset

Re: Robin RGD3300 Diesel Genset

Sort of an update for folks who wonder about the long term viability of a small diesel prime power genset for off-grid:

I'm satisfied that it works as advertised, and it's pretty cheap. 94 degrees here today, 72 degrees in the house. Our solar has been running our AC and other normal loads, plus bulk charging the batteries (they haven't been absorbed yet this week) most of the time during the peak of the day. About this time of day (6:00 PM) the power from the solar starts to drop off enough that it doesn't keep up with loads anymore. So this is the time of day that I start the little Robin diesel so it can help out.

The 2-ton AC unit easily consumes 60 kWh/day in hot weather. We can produce about 33-34 kWh with solar, and about 8-10 kWh with wind power on the average. We're using ~80-85 kWh/day right now with the AC running. The wind picked up some this afternoon and it's supposed to blow up to 30 mph tomorrow. If it does that we probably won't have to run the diesel at all tomorrow because we can get 75 kWh in a day pretty easy from the turbines if the wind is 20 mph. But that doesn't happen that often in the summer. So on the average the other 35-40 kWh/day has to come from the diesel prime generator in order to enjoy our new air-conditioned lifestyle

The Robin diesel has been producing that 35-40 kWh on 4.6 gallons of diesel fuel per day for most of the week. So as the weather got hotter, the cost to run it, per day, has gone up. I'm using the AC2 input on the inverter for it this week because I can easily adjust the load on the generator by adjusting the Gen Support Amps. I set it to the lowest possible value to maximize solar harvest, and only use from the generator what is required to get the batteries bulked (but not absorbed) by the end of the day. The batteries are actually liking it - they're nice and cool and haven't used a single drop of water. So the cost to run the diesel has to be subtracted off the cost in batteries long term. I don't know what that cost is, but I know this is drastically increasing the life of the batteries by doing it - they basically haven't been worked all week, pretty much floating back and forth from about 65-80% SOC.

So, again, this is not the setup for everybody. Most off-grid folks won't a run a generator until the last possible watt-hour has been pulled from the batteries and life as they know it is gonna end unless they start it up. I don't look at it that way. We REALLY like our new air-conditioned lifestyle. And this is what's it's going to take to do it. It's seasonal. And the hottest part of the summer is yet to come. But I think me, my wife and our batteries are liking our new diesel prime power addition to our off-grid system.
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Chris

Re: Robin RGD3300 Diesel Genset

The compressor has never stopped running today. The RH was 88% and now as the temp has dropped after sundown the RH has gone up to 92%. The RH in the house is 39% and 72 degrees temp. It's REALLY comfortable in here tonight. The air outside is so heavy that you can almost chop it with an axe. Here, we call it "muggy". It's what happens when we get a warm air mass that evaporates millions of tons of water off Lake Superior. We'll have fog here so thick after midnight that we won't be able to see 100 yards.
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Chris

Re: Robin RGD3300 Diesel Genset

Ours didn't use that much power either when the temp was in the 80's and the humidity around 65%. But yesterday water was running out of the condenser like from a faucet.

With the AC we don't even have to run a dehumidifier in the basement now - the basement floor is not "sweating" at all. And we're saving on how much the 'fridge is running too. Our unit pulls 2.5 kW for the compressor and fan on the condenser. And then the air handler in the house draws about 180-200 watts. The air handler blows the air thru all the heating ducts for our wood furnace, so it goes to every room. It works really good. We only got 2-ton capacity cooling 2,000 sq ft. The installers that put it in, when they came to evaluate the "heat load" of our house, said it's better to size a hair too small than too big because it will be more efficient in normal mid-80's conditions, even though it runs steady with the temp in the 90's and really high humidity. They did not recommend a mini-split unit for whole house cooling, including dehumidifying the basement.
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Chris

Re: Robin RGD3300 Diesel Genset

You know, sometimes things are so obvious that you don't see 'em. I've been fighting with improving the ventilation in my new powerhouse because I was seeing temps up to 110-115 degrees F in there in hot weather. In the old enclosure I built last fall for the Honda, the genset ran cooler in that enclosure in hot weather than it did standing in free air.

You know why? I had to regroup. The theory that heat rises is a good one. But it don't work in this application. In the old enclosure I was forcing fresh air in the top and out the end of the enclosure. It worked because it enhanced the natural airflow over the genset produced by the engine's cooling fan. So far I've been fighting that natural airflow in the new powerhouse. After the lightbulb came on over my head I hung some shop rags in there on a string and ran each genset one at a time with no ventilation fans running to see how the air wants to flow. And then I enhanced it with the fans. And I got immediate and drastically better results.

[video=youtube_share;q1KJSwf1GKU]http://youtu.be/q1KJSwf1GKU[/video]

The heat basically exits on the control panel side of the Robin and heads right out the exhaust fan. On the Honda the heat exits the end facing the door, turns the corner and heads right out the exhaust fan. The air intake fan provides a higher pressure area of cooler up near the ceiling because it's considerably more powerful than the exhaust fan. That prevents any heat from the gensets from rising as it heads out the exhaust fan. The circulation fan grabs air from the air intake fan and forces it down towards the floor to the cooling fan intakes on both engines, and the cooling fans on the engines do the rest of the work.

It works. Not like I expected in my first "design", though.
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Chris

Re: Robin RGD3300 Diesel Genset

Well, yeah. It's got chrome fuel cap, chrome switches, chrome exhaust and a few chrome bolts. I should probably pick up a chrome valve cover and some chrome cylinder stud nuts for it. A valve cover from a Yanmar L70 fits it and you can get those in chrome Plus maybe a stick-on chrome mudflap babe for it.

With all that chrome stuff, it's bound to put out more power :cool:
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Chris

Re: Robin RGD3300 Diesel Genset

I've been running it 100 hours between oil changes (it's got a pressure lube system with a filter) and it's on its third oil change since I bought it. The little thing holds just about two quarts of oil. Even running at 115 degrees inside the powerhouse in really hot weather, it has never required any add-oil between changes. I'm running Cenex Superlube 518 SAE30 diesel oil in it.

One of the unexpected side effects of adding the Big Chrome Exhaust was that it made the exhaust note deeper and louder. So I had to make a baffle for the end of the 2" exhaust tube inside the big one to quiet it back down.





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Chris

Re: Robin RGD3300 Diesel Genset

SkiDoo55 wrote: »

Have you thought about adjusting the placement of the small exhaust pipe inside the large outer and having the large outer open on the shed side to created an argumented exhaust which will pull air out of the shed to aid in keeping it cool.

Yeah, that's the way I got the Honda. But it took a lot of fiddling with it to get the exhaust pulse to create a negative pressure in the vent pipe. The diesel smokes a lot, especially at full load the way I got the pump adjusted for minimum "droop" to hold a constant frequency. I'm afraid if it's not perfect it would pull smoke into the powerhouse.
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Chris

Re: Robin RGD3300 Diesel Genset

It takes proper size and length of the secondary tube as well as proper placement of the primary (usually called the "stinger") to get it to work. I stumbled on the correct combination with the Honda in my other smaller generator enclosure I had built for it. The sound wave can't be allowed to expand until it hits open air, and the expansion of the sound wave at that point creates a vacuum on the secondary tube.

Diesels are unthrottled so they move a lot a more air (exhaust flow volume) than gasoline engines do (except when a gasoline engine is at wide open throttle). It would be a bit more tricky with a diesel.
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Chris

Re: Robin RGD3300 Diesel Genset

mike95490 wrote: »

My shoulders are both shot, so the electric start is important for me. The listeroid has a great flywheel, which helps it fire off.

Any cold starting advice - preheating the air with a propane torch at the inlet ? I see they have a glow plug option - anyone with experience with that ? Coldest I'm expecting is 15F (-10c) in this area on a rare occasion.

Is it easy to let it idle for a moment to warm up, or does it slam the governor right to 3600 rpm (60Hz) at start up ?

As long as the engine will crank at normal speed, pre-heating the intake air is usually sufficient to get most direct injection diesels to start.

Most small generators go right to rated speed when started up. You'd have to hack the throttle linkage like I did on my Robin to get it to idle for a few minutes for warmup.
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Chris

Re: Robin RGD3300 Diesel Genset

keyturbocars wrote: »

Is there any risk of damaging the AVR if the generator is run at lower than rated RPM?

Absolutely none as long as you don't try to load it during warmup. The AVR is powered by the exciter winding in the gen head and a diode. It will attempt to full-field the rotor but with limited voltage input from the exciter it can't do much.
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Chris

Re: Robin RGD3300 Diesel Genset

keyturbocars wrote: »

OK. That's good to know. I remember reading in the past about some older military gensets (MEP-002A and -003A) that people said they fried the AVR because they ran it at lower RPM. Apparently, they just started it up and ran it at low RPM with no load, and something failed on the AVR board.

The AVR tries to full-field the rotor if the voltage is low. But it takes a lot longer than just a couple minute warmup to burn it out at low voltage. I should take a photo of the throttle "hack" I did on the Robin. I put an aluminum arm on the throttle lever with two notches in it. One for dead idle, and an intermediate notch for warmup. It has the same latch mechanism as the Yanmar for rated speed operation.

Basically, when you first start it you'll let idle for about 30 seconds to get oil pressure and make sure everything has lube. Then you'll push it up to about 2,800 - 3,000 rpm under no load and let it warm up until warm air is blowing off the cylinder fins. At that point you can take it up to rated speed and put load on it. This is way easier on the engine than starting it cold and having it misfire and smoke from incomplete combustion and being over-fueled when it's cold.

It takes a lot longer than the couple minutes required for warmup to overheat the AVR from trying to full-field the rotor.
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Chris