Auxiliary Fuel Tank for Generator

Question

If this question has been answered somewhere before, please point me to the link. I've searched everywhere and can't seem to find an answer.

I bought a used fiver that had a Onan 4000 watt genset that was mounted in this monstrosity of a cabinet that attached to the fiver rear hitch. Appeared to be way too much weight and besides it looked UGLY on the back.

So, I cut the mount down, removed the battery and fuel tank and now I have a small, compact removable generator on the back. Of course this brings me to the question that prompted this post:

I want to mount a gas tank way forward under the fifth wheel. Moeller makes a wide range of permanent mount marine tanks that are ABYC and NMMA compliant. Is there any issue with building a bracket and putting this tank under the fiver? I have confidence that my friend and I can build a bracket with a weight safety margin of at least double the weight of the tank, gasoline, and mount. This mount would be permanently attached to the side frame rails with grade 8 hardware.

Also, are there any other tanks that I should consider? RDS makes a whole line of tanks but most of them are auxiliary tanks for diesel and do not allow gasoline in them (at least according to the web site.)

So, what am I missing?

Thanks,
Paul.

ckwizard777 · Answer

I think the Moeller tanks would be as good as any as long as it's properly supported.They put fuel holding talks in toy haulers so I dont see a problem.

b_o__plenty · Answer

Why not get rid of the noisy Onan and replace it with a more portable, quieter and way more fuel efficient Honda. You can easily hook up a outboard motor fuel tank and live happily ever after. A lot less expensive over the long run...

B.O.

paulb1310 · Answer

B.O. Plenty,That is actually a good idea.  I plan on using a three tier approach.  I own both a 2000 watt Honda and a 1000 watt Honda.  I love both these dearly for a whole multitude of reasons.  I was planning on only using the Onan for high altitude hot environments.  As you likely already know, generator output drops dramatically with higher elevations.  And even gets lower at these elevations when the temperatures are extreme.  When the temperatures get hot on the Western high desert, it takes quite a bit of power to run everything.  The 4000 Onan only produces 2800 watts at 9000 feet.  So, on a hot, desert day, the Honda generators will struggle to run the AC.Now, the "tier" approach:  For less electricity demand, I will use either the 2000 watt for medium loads or the 1000 watt for light loads.I will use a Mercury boat quick disconnect for the fuel input to the Onan.  Additionally, I will equip each of the Honda generators with an externally fed fuel cap and a fuel hose from my large tank to hook onto the Mercury connector.  This way, I don't have to mess with any fuel cans and I can run any of the three generators any time I want, depending on the power needed.

paulb1310 · Answer

Here is the altitude and temperature information from the Onan RV Generator handbook:

If you travel at high altitudes or in extreme temperatures, your generator can lose power. In such lower-density air conditions, you can’t operate as many electrical devices as you could under normal operating conditions. Power decreases 3.5% for each 1,000 feet above an altitude of 500 feet. For example, to operate at 4,500 feet (4,000 feet above rated generator altitude) multiply 3.5% x 4 (4,000 ft) = 14% power loss. Then multiply .14 x your generator’s power rating: 4,000 watts x .14 = a loss of 560 watts at that altitude.

Power decreases in extreme temperatures by 1% for each 10° F (5.5° C) above 85° F (29.4°C).

So, in the extreme Western high desert, a 100° day at 9000 feet the generator would only put out about 2800 watts. Of course, I DO understand this is the absolute extreme conditions that are pretty atypical.

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