Optimizing load when running generator (minimizing fuel waste)

[randalkoene]

Hi all!

So, I realize that generators are able to adjust their throttle somewhat to a given load. So, for example, a 2.7kW max generator won't always be producing 2.7kW regardless of the load (e.g. you connect just a single LED lamp).

That said, I'm pretty sure that these generators can't perfectly match their fuel consumption to the load, in fact, it may be near-fixed.

(Will a generator of a given type - pretty much - use the same amount of fuel per hour regardless of the load attached?)

I'm wondering how to optimize this and minimize fuel wastage. After all, I don't want to have a very small generator, because then it's impossible to meet the need when a big load comes along. But I don't want to be wasting fuel on a gigantic generator either when the load is small.

I actually bought a 2.7kW generator based on the approximate max load I was considering.

Of course, I also got some deep cycle house batteries.

How to minimize wastage?

Do you buy 2 or 3 separate 25 Amp battery chargers, so that you can draw a nice 600-900 W while recharging the batteries simultaneously in pairs (if you have 4 or 6 deep cycle batteries)? (Does recharging deep cycle batteries at 25 Amp wear them out more than recharging them at 10 Amp?)

Any other tips on how to match load as much as possible to generator output at optimal fuel consumption while the generator is running... and not to need the generator at other times?

Thanks for any insights! I admit that I'm totally new to gasoline generator management.

Cheers,
Randal

[o1marc]

There are active threads here discussing wiring your batteries for equalizing the charge to each battery.

[TJones]

Originally Posted by o1marc

There are active threads here discussing wiring your batteries for equalizing the charge to each battery.

Inverting type generators like a Honda will adjust the rpm to match the load. The currant is internally inverted to 60 hz. These are the most efficient for loads that will vary.

The non inverting generators must maintain a specific rpm usually either 1800 or 3600 rpm to maintain the 60 hz. They adjust the throttle or fueling to maintain this rpm as load changes. These are most efficient for loads close to their continous rated output.

Charging rates for the batteries will depend on the type of batteries and the total capacity. It is best to use the manufactures recommended rate.

Ted

[TheHubbardBus]

No matter what the load, you're still having to turn the same amount of engine, if that makes sense. So while you'll see some diff in fuel consumption depending on what you're powering, the best thing you can do to achieve max efficiency is match your generator to your load. In other words, don't use more generator than you need.


The way that we achieve that goal is to use 2 small generators (parallel capable inverter-type) instead of 1 large. Use 1 when you can, 2 when you have to. Not only do you save on fuel, you save on noise, and if one goes tits up, you always have a spare.

[E450Shorty]

I designed hybrid generator systems in a previous life... your best option is an auto start setup with a battery bank. So you are basically running off of batteries until they draw down to the trigger voltage for the generator to start and run at near full load to recharge the battery bank. Once the batteries reach a pre-programmed state of charge, the generator shuts down and you eliminate all of that wasted low/no load running time. there are a few good controllers that are pretty easy to set up as a DIY'er. let me see if i can dig up some of my old info.

[Sleddgracer]

Originally Posted by E450Shorty

I designed hybrid generator systems in a previous life... your best option is an auto start setup with a battery bank. So you are basically running off of batteries until they draw down to the trigger voltage for the generator to start and run at near full load to recharge the battery bank. Once the batteries reach a pre-programmed state of charge, the generator shuts down and you eliminate all of that wasted low/no load running time. there are a few good controllers that are pretty easy to set up as a DIY'er. let me see if i can dig up some of my old info.

sounds like a great idea - similar set up to emergency generators in a hospital

[Iqinsanity]

I am designing my own inverter generator setup, I’ve been documenting it in a thread called “ac vs dc based system” or something like that.

Really, one of the best ways to get max efficiency is to use a liquid cooled generator. 1/3 of your output (every internal combustion engine) is waste heat out of the exhaust. 1/3 is the electricity. The last 1/3 is normally wasted heat from cooling the motor. If you can harness that heat in winter at least to heat the bus you effectively double your efficiency without touching the electrical portion.

Think radiant floor heat or a heater core and blower.

The beauty of my system is that I’m not going to be limited to a low charge rate from chargers because I’ll have high amp alternators charging the batteries. I own a 48v (56v if I change the regulator) alternator that puts out about 100 amps. And I can easily hook up another alternator to charge another 48v battery bank or a 12v alternator for a 12v battery bank. Whatever.

There’s also the possibility of using an automotive compressor and running air conditioning off the motor in summer. So that means charging the batteries with full electric output and still cooling the bus, the main goal obviously is to pump as much electricity into batteries as fast as possible (without exceeding the max recommended battery charging rate)

When building a bus we need to make as many things dual purpose as possible, well why do people take the single most energy consumptive device (generator) and only get one use out of it? Why watch all that heat go away then pay more money to make more heat? Why run the air conditioning off electricity as yore trying to store as much electricity as possible as fast as possible so you can shut down the generator and stop using fuel?

Please understand that this is all my theory, I have not finished building an actual setup. But the concept is sound. Use alternators to charge batteries and don’t waste the extra heat. Don’t put a heavy load on the electrical system whether it’s the ac or dc side by using a electrical air conditioner while the generator is on let the electrical system charge, that’s the whole point of turning the generator on.

[Dem0072]

The quick answer: Go solar if you plan on full-timing.

If you don't, and its just a weekend rig, generators are fine.

Harbor Freight has stores just about everywhere and they sell a generator for just a little over $300 that has a rough consumption rate of 0.20gal/hour, with a runtime of 16hrs @ 50% load. Which is pretty good, for a cheap generator. Plus being Harbor Freight if it ever breaks you lug it back and they give you a new one. So an efficient generator is your first way of minimizing waste. The mentioned generator will do 3500w continuous, its half-load (sweet spot) is 1750w, which is sufficient to recharge batteries and run your lights, fridge and so on. And it'll kick up its duty cycle for heat & air.

Second, think outside the generator. It eats fuel, keep jerry cans around. Making special trips just to get fuel can get costly quick.

Third, if you're going to hook it up to batteries, use efficient batteries. Deep Cycle lead acids aren't a great value, it takes 5 times the battery (and 5 times the weight) to get the same output of them that you could with LiFePo4 (Lithium Iron Phosphate). They're spendy, but they pack a punch in a smaller physical footprint and they last 20 years instead of 3 years, and are far more forgiving on imperfect conditions.

Fourth, if you're going to spend serious away time where you've foregone the need to keep it 72o inside (going on a hike?) you can get more modest solar setups to keep batteries topped off, so that things like the fridge stay running and the primary duty of the generator is to support rapid recharging off grid and really hungry loads (AC, heat, water heater if electric).