Generator fuel usage gph??

Wdeertz · May 21, 2020

I have a Phasor K3-6.5kW generator (Kubota 3 cylinder Diesel engine) and have been unsuccessful in finding Specs on the fuel usage for this generator. I’ve been using 0.5gph as my estimate of fuel consumption under normal load but this gives me an unusually low gph rate for my primary engine. I have the fuel burn specs for my primary engine and if I use a gph rate that corresponds to my normal rpm I get About .25-.35gph fuel rate for this generator. I recognize that there is a degree of inaccuracy in reading the sight gauge but this is over about 600 gallons of fuel burn so should be fairly accurate.

Does a .25-.35gph fuel burn rate for this generator sound reasonable? Seems to low to me.

Jeff F · May 21, 2020

Sounds reasonable. That's what my generator uses putting out about 3 kw. Fuel consumption is load dependent.

Stout · May 21, 2020

Our 9kw Onan MDKBL manual says .5 gph at half load an .8 gph at full load. This is with a 3 cylinder Kubota, 68 cu in engine.

High Wire · May 21, 2020

About 0.8-1.0 gph for 8Kw fully loaded.

caltexflanc · May 21, 2020

I think Phasor is still around, have you tried contacting them?
https://www.phasormarine.com/contact.htm
The numbers you came up with sound about right. I'd round up to be safe. It is very load dependent as already mentioned.

GFC · May 21, 2020

I must be the odd man out on this forum. Do you guys really keep that close track of your fuel burn?

I've never even tried to keep track of my fuel except to watch the gauges to see about how much is left in each tank.. I have 3 tanks and 700 gallon capacity and have never been concerned until my tanks all get down to about 1/4 capacity.

What am I missing here? The fun of crunching numbers?

Comodave · May 21, 2020

GFC said:
I must be the odd man out on this forum. Do you guys really keep that close track of your fuel burn?

I've never even tried to keep track of my fuel except to watch the gauges to see about how much is left in each tank.. I have 3 tanks and 700 gallon capacity and have never been concerned until my tanks all get down to about 1/4 capacity.

What am I missing here? The fun of crunching numbers?

We do the same pretty much. Fuel isn’t the big cost in boating, we spend more on other things for the boat. As long as I can afford the fuel we will buy it. When it starts putting a crimp in our budget then I may rethink my attitude.

caltexflanc · May 21, 2020

I personally just like to measure things. Old saying goes, "if you can measure it, you can manage it". I liked to figure out about what the engines were burning, and needed to subtract genset usage to do that.

rslifkin · May 21, 2020

For me, the primary reason to keep track of fuel burn is to have good numbers for trip planning as far as for stops, etc.

Ken E. · May 21, 2020

I'm about .3 -> .4 gph at about half load with a NL 5 kw. I use a separate tank for the genset, so I keep an eye on it for fuel dock purposes. I'd rather know than not know.

Wdeertz · May 21, 2020

rslifkin said:
For me, the primary reason to keep track of fuel burn is to have good numbers for trip planning as far as for stops, etc.

Thanks for all the responses. I guess given an average load of 50% my fuel burn rate is inline with others. My least concern is the cost of the fuel but as the last 2 replies mentioned without measuring and knowing your burn rate how can you properly plan, particularly a long passage. Besides I’m a number geek and like doing computations and such :socool:

tiltrider1 · May 21, 2020

If you are making 5k then you will burn 1/3 a gallon per hour.

fractalphreak · May 22, 2020

My old Onan generator manual calls out its output in the manual. One thing I've come to find out is it takes a specific amount of diesel fuel to do given work - so comparing your generator size and output to others should give you a close idea. If you don't have anything as detailed, here's a link to a manual for the engine in your generator, I <think>. It lists the same model as the Phasor literature, but shows it can go up to 3000 or 3200 RPM, depending on the version. I'm guessing those engines are set to 1800 rpm for life and vibration(noise?) It has performance charts for the engine, and depending on which version of the engine it looks like around .8 gph at max output at 1800 rpm....(they give their burn in g/KwHr of engine output...then you have to convert to diesel gallons) That's what their performance chart for that engine shows the engine SHOULD be using if it was making all of the HP it could at 1800 rpm...

http://products.jacobsen.com/img/manuals/05e4bg_en_v.pdf

My figure above - computing from the engine performance curve - seems a touch high. I don't have my big genset manual here at home but I believe it says .5 gph at 50% load and .8 gph at full load...for a 7.5 KW genset. I haven't the detailed ways to verify how much load I'm actually putting on it and my actual burn rate, but I know I'm not always fully loading it and go with .6 gph.

For the group - do Kw of generated power translate directly to hp the engine is using, or is there a known loss/correction?

jleonard · May 22, 2020

When I cruise the boat uses 1.7-2 gallons per hour and that includes "normal" generator use.
I don't see a need to go into more detail.

Ski in NC · May 22, 2020

It really depends on the load. More load burns more fuel, but it is not linear. It takes some fuel to spin the machine, and then more fuel if you use power.

For a 6.5kW at 1800rpm (which I think this Phasor is), I'd figure 0.2gph running with zero load, 0.3gph at 25% load and about 0.4gph at 50% load. Unusual for a pleasure boat with small gennie to average over 50% load.

On my 5kW a typical load is 25-50% and it works out to 0.3-0.4gph.

Your numbers of 0.25-0.35gph make good sense.

Codger2 · May 22, 2020

GFC said:
I must be the odd man out on this forum. Do you guys really keep that close track of your fuel burn?

What am I missing here? The fun of crunching numbers?

I feel the same way but I have the Maretron Fuel Management system and can read the burn at any rpm instantly. (I don't bother trying to know exactly what the NL 12W generator is burning.) This is probably the best electronic feature I have on the boat!

Wdeertz · May 22, 2020

fractalphreak said:
My old Onan generator manual calls out its output in the manual. One thing I've come to find out is it takes a specific amount of diesel fuel to do given work - so comparing your generator size and output to others should give you a close idea. If you don't have anything as detailed, here's a link to a manual for the engine in your generator, I <think>. It lists the same model as the Phasor literature, but shows it can go up to 3000 or 3200 RPM, depending on the version. I'm guessing those engines are set to 1800 rpm for life and vibration(noise?) It has performance charts for the engine, and depending on which version of the engine it looks like around .8 gph at max output at 1800 rpm....(they give their burn in g/KwHr of engine output...then you have to convert to diesel gallons) That's what their performance chart for that engine shows the engine SHOULD be using if it was making all of the HP it could at 1800 rpm...

http://products.jacobsen.com/img/manuals/05e4bg_en_v.pdf

Thanks for the links, that Kubota manual will be a good addition to my library.

Wdeertz · May 22, 2020

Codger2 said:
I feel the same way but I have the Maretron Fuel Management system and can read the burn at any rpm instantly. (I don't bother trying to know exactly what the NL 12W generator is burning.) This is probably the best electronic feature I have on the boat!

Nice on a planing or semi-planing boat but on a full displacement trawler it’s a bit of overkill. Manual calculation will suffice for me while based on some of the replies it seems others are ok with sticking their finger in the air. :whistling:

rslifkin · May 22, 2020

Wdeertz said:
Nice on a planing or semi-planing boat but on a full displacement trawler it’s a bit of overkill. Manual calculation will suffice for me while based on some of the replies it seems others are ok with sticking their finger in the air.

Interesting thought. I tend to go the other way with it. I have a pretty good idea of what I burn running on plane, as I go through fuel fast enough that it's easy to calculate good burn numbers. It's harder to estimate at low speed where it takes longer between fillups and a 0.5 gph error can be 10 or 20 percent off rather than being insignificant.

sunchaser · May 22, 2020

Wdeertz said:
Nice on a planing or semi-planing boat but on a full displacement trawler it’s a bit of overkill. Manual calculation will suffice for me while based on some of the replies it seems others are ok with sticking their finger in the air.

With most newer engines the algorithms for fuel burn are part of the electronics. The data can be presented on a neat Maretron system like Codger's or the engine builder's "smart view." Very nice to have that data, for many reasons, whether on a trawler or planing vessel.

Wdeertz · May 22, 2020

rslifkin said:
Interesting thought. I tend to go the other way with it. I have a pretty good idea of what I burn running on plane, as I go through fuel fast enough that it's easy to calculate good burn numbers. It's harder to estimate at low speed where it takes longer between fillups and a 0.5 gph error can be 10 or 20 percent off rather than being insignificant.

Good point, I guess it depends on your perspective. On my full displacement hull the fuel burn rate is fairly static until you try to push it beyond displacement speeds. On a “go fast” boat I guess the burn rate is so high you never pass up a fuel dock without refilling :banghead:

Wdeertz · May 22, 2020

sunchaser said:
With most newer engines the algorithms for fuel burn are part of the electronics. The data can be presented on a neat Maretron system like Codger's or the engine builder's "smart view." Very nice to have that data, for many reasons, whether on a trawler or planing vessel.

Don’t disagree it is nice to have but to add to an older analog trawler provides limited benefit (cost > benefit).

PPandE · May 22, 2020

Since generator fuel burn is a function of load, I wonder if fuel consumption could be calibrated to a totalizing watt-hour meter? I would think that under normal usage there would be an easy kWhr/gal conversion. I’ve seen meters for about 20bucks including sensor on Amazon.

mickand · May 29, 2020

Being a Scotsman with short arms and long pockets I do keep an eye on fuel burn.
Seriously, travelling between 6-7000 miles each year, fuel is my major cost, so worthy of my attention.
A prop pitch change 3 years ago, allowed me to reduce rpm's by 300 or so for the same speed and my fuel consumption went up from 2.75mpg to 3.4mpg.
This is not inconsiderable when you do a lot of miles.

reeltime · May 30, 2020

Gfc

GFC I'm with you , my boat holds 5000 ltrs , what the 3 cyl Kabota 12 kva uses doesn't worry me to much , its just part of the overall costs in cruising. :socool:

ksanders · May 30, 2020

GFC said:
I must be the odd man out on this forum. Do you guys really keep that close track of your fuel burn?

I've never even tried to keep track of my fuel except to watch the gauges to see about how much is left in each tank.. I have 3 tanks and 700 gallon capacity and have never been concerned until my tanks all get down to about 1/4 capacity.

What am I missing here? The fun of crunching numbers?

I’m with you.

I only keep track of fuel burn to an extent that it affects my boats range significantly.

catalinajack · May 30, 2020

The speed of a generator is set to 1,800 or 3,600 RPM in order to derive current at 60 cycles.

fractalphreak said:
My old Onan generator manual calls out its output in the manual. One thing I've come to find out is it takes a specific amount of diesel fuel to do given work - so comparing your generator size and output to others should give you a close idea. If you don't have anything as detailed, here's a link to a manual for the engine in your generator, I <think>. It lists the same model as the Phasor literature, but shows it can go up to 3000 or 3200 RPM, depending on the version. I'm guessing those engines are set to 1800 rpm for life and vibration(noise?) It has performance charts for the engine, and depending on which version of the engine it looks like around .8 gph at max output at 1800 rpm....(they give their burn in g/KwHr of engine output...then you have to convert to diesel gallons) That's what their performance chart for that engine shows the engine SHOULD be using if it was making all of the HP it could at 1800 rpm...

http://products.jacobsen.com/img/manuals/05e4bg_en_v.pdf

My figure above - computing from the engine performance curve - seems a touch high. I don't have my big genset manual here at home but I believe it says .5 gph at 50% load and .8 gph at full load...for a 7.5 KW genset. I haven't the detailed ways to verify how much load I'm actually putting on it and my actual burn rate, but I know I'm not always fully loading it and go with .6 gph.

For the group - do Kw of generated power translate directly to hp the engine is using, or is there a known loss/correction?

fractalphreak · May 30, 2020

catalinajack said:
The speed of a generator is set to 1,800 or 3,600 RPM in order to derive current at 60 cycles.

that makes too much sense to not have thought of, especially considering I followed my manual to adjust the RPM/governor on mine last year to get it as close to 60 Hz as possible!

OldDan1943 · May 30, 2020

Just my opinion but, if you figure 1 gph, you would be wrong and pleasantly surprised if it doesn’t burn that much.

syjos · May 30, 2020

I had a Westerbeke 4.0 that the manual claimed .5 gal/hr

Switched to a 5.5 Westerbeke and the manual claimed .5 gal/hr

Both generators burned less than .5 gal/hr average.

I think the manufacturers guess the burn rate.

Generator fuel usage gph??

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