Generators for charging battery banks.

[noenegdod]

That is for most generators where you will make the most power for the fuel you burn.

If you go have a look at the "operating hours @ a given load" for basically any commercially available generator you will see that as load increases to rated load, the efficiency of the generator will increase.

I think you have this confused with the internal combustion engine itself. Yes 60-80% load on the engine itself is in the most fuel efficient range for it, but the manufacturer has already done that work for you. They sized the engine to suite the alternator to be able to be operating in that 60-80% load on the engine, at the generators rated electrical capacity (or around it). That is part of why it has a rated capacity and a maximum capacity.

 

[ePowerBank]

I know this is from a long time ago but can you please explain the reasoning behind this.

If I understand this question and topic correctly, it has to do with having enough generator power to handle both Home Load + Charge Load.

For example, if your Home Load was 30A & your Charge Load was 10A, then make sure your generator can handle both (40A) combined (+ a safety margin?).

Please correct me anyone if I've got this wrong...

 

[ePowerBank]

Cats Meow for me was an open frame inverter with 240v and parallel. The 240 allows me to feed both legs of my panel while the parallel allows me to double down if it's a long outage.

I like they are quiet (compared to whole house generacs), portable/flexible, easy to work on and I can take with me if I ever move.

https://www.northerntool.com/shop/tools/product_200788693_200788693

I also converted to NG and set up a dual gas manifold in my garage so I'm ready and waiting for any problems.

Only issue I had was 5 months on back order (delivered last June) and the parallel box was junk - so I wired my own.

Here's side by side showing with & without NG kit.
> Add ons: NG kit, Wheel & Handle kit, Oil Drain line, Engine Hour gage.



> Fixes: Parallel box rewired from NEMA 10-50 to NEMA 14-50, plus added load meter




Extra Measure: Use set of Load Meters to monitor basic generator functions (V, Hz) including load house is pulling (A, W, Wh).
Also monitor balance to each of the legs in the 120V + 120V panel (yes, that's an old IPAD box, for now).
I keep this by Main panel to be sure I'm not over drawing overall, or have major imbalance between L1 & L2 legs.
Supposedly I can set an alarm for peak watts or amp, so my plan is to set about 90% of generator capacity.

 

[noenegdod]

If I understand this question and topic correctly, it has to do with having enough generator power to handle both Home Load + Charge Load.

For example, if your Home Load was 30A & your Charge Load was 10A, then make sure your generator can handle both (40A) combined (+ a safety margin?).

Please correct me anyone if I've got this wrong...

The OP was a lot simpler than that:

Is there a good solution for charging batteries with a generator? We have about 12v 300 aH on our battery bank. But occasionally, the solar doesn’t give us enough power. (winter usually) Is it alright to use a standard battery charger and a generator to fully charge our batteries?

But regardless, I was addressing one statement that based on 30 years of interest in ICE performance and 5 years getting paid to tune naturally asperated and forced induction vehicles as well as having read performance/efficency specs on numerous generators, is not correct:

You should get a generator that is at 60-80% load when producing the current you use to charge your batteries.

That is for most generators where you will make the most power for the fuel you burn.

 

[ePowerBank]

Curious: Does anyone know how to measure for THD, without a O-Scope?
I read on a generator review where someone reported their actuals THD's under various conditions.
Or is this a non-issue according to @50ShadesOfDirt experience? Is that for power case in US?

As an insurance buffer, I've added Costco $100 UPS setups in locations of things like Modem, Router, TV, Stereo, Projector.
I like that power to these devices is "filtered" in a sense, be it from generator or roller coaster Mid West weather events.

 

[noenegdod]

If I understand this question and topic correctly, it has to do with having enough generator power to handle both Home Load + Charge Load.

For example, if your Home Load was 30A & your Charge Load was 10A, then make sure your generator can handle both (40A) combined (+ a safety margin?).

Please correct me anyone if I've got this wrong...

As I said above, sizing a generator is actually a really simple procedure for anyone who has a substantial battery bank that is capable of running a house.

You simply get a generator that is capable of, on average, providing your days consumption. You want it to run at its rated capacity the whole time and ideally you want to not be converting from AC to DC and back to AC again. Therefor, having the ability to program an AC current limit and using an inverter/charger that has the ability to pass AC current straight through without conversion as well as supplement AC current when load exceeds the generators capacity is the best case scenario. Once the demand drops back to below the programed generators rated capacity the batteries receive the excess until the next high demand.

This way you can use the smallest generator that provides your average daily requirement instead of sizing it to provide your peak and suffering the fuel efficiency loss for the majority of its operation. The above does come with some loss though. You are converting from ac-dc-ac but generally speaking it is difficult/inconvenient to work around that.

 

[toms]

If you go have a look at the "operating hours @ a given load" for basically any commercially available generator you will see that as load increases to rated load, the efficiency of the generator will increase.

I think you have this confused with the internal combustion engine itself. Yes 60-80% load on the engine itself is in the most fuel efficient range for it, but the manufacturer has already done that work for you. They sized the engine to suite the alternator to be able to be operating in that 60-80% load on the engine, at the generators rated electrical capacity (or around it). That is part of why it has a rated capacity and a maximum capacity.

I’m not confused, i agree that in theory the maximum efficiency is at maximum rated output.

It may be true in some cases, but i have 3 generators, and all of them are most efficient at around 80% load.

I have attached a fuel use/load chart that shows actually a quite linear relationship between fuel use and power over 50%.

 

[noenegdod]

I’m not confused, i agree that in theory the maximum efficiency is at maximum rated output.

It may be true in some cases, but i have 3 generators, and all of them are most efficient at around 80% load.

I have attached a fuel use/load chart that shows actually a quite linear relationship between fuel use and power over 50%.

LOL, Ok Ok ya, but those are diesel, most likely turbocharged and you have to get up to an 80kw power plant to get proportional fuel consumption between 75 and 100% load. Everything under that uses 80-85% full load fuel to produce 3/4 output.

Because of AFR at different loads, combustion chamber temps, and the pumping loss difference between compression ignition and spark ignition, a small gasoline generator does not follow the same curve as in that chart.

 

[toms]

And yet in real life conditions, my Honda petrol generator (Eu20i) has a sweet spot closer to 60% rated output.

My 4.8kva Yanmar, and 8kva Kubota diesel are most efficient at around 80% load.

 

[tigerwillow1]

Sample waveforms to show a conventional generator doesn't necessarily produce a sine wave. These are voltage and current waveforms, voltage on top trace, current on bottom trace.

This is the eu2000i driving a PF 1 resistive load. Nice sine wave:


When the eu2000i drives a 0.7PF power converter (PD 9160A at full load), the sine wave distorts:


But it's a whole lot better than the conventional generator, in this case an Onan Microquiet 3600 watt:

 

[50ShadesOfDirt]

If OP is feeding the power from his genny to the inverter/charger to refill battery bank, then I submit that THD is mostly moot. This is exactly what we do, if the sun isn't cooperative. Inverter/chargers (magnum's, at least) don't care.

If one is using genny as a standby (no whole-house inverter), then THD becomes more important ... maybe, as we can't easily nail down the jelly ... is it your genny, or your devices in the house? I'm *still* digging into this ... wp's galore ... my eyeballs are bleeding.

Can the genny be load-limited to find the sweet-spot of (little to no) THD production, or it's governor tuned for same? An inverter/genny is probably doing this for you, but the cost ...

You could worry about all this THD FUD, and this might drive you to buy the EU or similar ... such sales tactics are good for (someone's) business.