Kohler 12RES or RESL?

Bigwooo · August 2009

I'm finally ready to purchase a backup generator. I've settled on a 12kw propane powered Kohler .

Now, I've discovered that there's a 12RES and a 12RESL. It appears the 12RES has an electronic governor, and the RESL has a mechanical governor. The RESL also comes with a 12 circuit transfer switch.

From what I understand, I don't need the 12 circuit transfer switch, just a 2 wire relay between the generator and my outback charge controller for the auto start feature.

Can anyone tell me if the 12RES, or the 12RESL is a better match for my pair of FX2012 (off grid) inverters?

Is an electronic governor better than a mechanical governor?

Thanks

Dave Angelini · August 2009

Re: Kohler 12RES or RESL?

Take a look at the 6500 watt Honda inverter generator. It may not have the power you want but it will be quiet and never give you issues with voltage quality.
I buy mine thru a dealer in Maine who has done 3 for me now (propane mod) with
no problems at altitude.

To your question, buy the most expensive one!

mike95490 · August 2009

Re: Kohler 12RES or RESL?

What will the genset be powering ? AC loads only, Battery charger only, or a mix of both. Govener is only RPM's so if you are battery charging only, who cares about 58 hz or 62 hz, the microwave will still run. Gensets ran houses fine before electronic goveners came to be.

icarus · August 2009

Re: Kohler 12RES or RESL?

Personally, before the Honda EU series came along, I would have voted for the mechanical gov. every time, since I could field repair it, but the honda puts out perfect voltage under all load conditions.

Having said that, I have no clue about modern Kohlers.

Tony

BB. · August 2009

Re: Kohler 12RES or RESL?

Looking at charge rates for your battery bank (12 volt batteries assumed) and the 5-13% rule of thumb (AGM's can accept somewhat higher charge rates):

212 amp*hours * 6 batteries * 12 volts * 0.05 = 763 watts
212 amp*hours * 6 batteries * 12 volts * 0.13 = 1,984 watts

At 50% generator load (and a compatible charge controller) -- a 4-5kWatt genset would seem to meet your charging requirements.

Of course--if you need more power (and who doesn't), then the larger genset may make sense for you.

In general, keeping the genset at 50% minimum power loading will increase the fuel efficiency.

The nice thing about the Inverter/Generators (Honda's, Yamaha's and such) is that the engine can throttle back when loads are less--and the inverter keeps the frequency rock solid (on the smaller units, this is controlled by the "eco throttle" mode--but, when throttled back, there is less surge output for motor starting loads and such).

The Honda eu2000i (1,600 watts rated) is a good example of one that can run down to 25% of rated load with near linear fuel flow reduction... One way to look at this (from Honda's specifications):

1.6 kWatts * 1.00 * 4 hours / 1.1 gallons = 5.81 kWhrs per gallon of fuel
1.6 kWatts * 0.25 * 15 hours / 1.1 gallons =5.45 kWhrs per gallon of fuel

You can review the fuel flows here for the RES (PDF):

[FONT=Fixedsys]Fuel Consumption at % rated load
% Load

8.5RES [B]12RES[/B]
60 Hz 50 Hz [B]60 Hz[/B] 50 Hz

Natural Gas, m3/hr. (cfh)
100% 3.7 (132) 3.3 (118)[/FONT] 5.4 (193) 4.8[FONT=Fixedsys] (173)
75% 3.2 (113) 2.9 (101) 4.7 (163) 4.2 (148)
50% 2.6 (93) 2.3 (83) 3.5 (124) 3.1 (108)
25% 2.2 (77) 1.9 (69) 2.6 (93) 2.4 (84)

LP Vapor, m3/hr. (cfh)
100% 2.0 (72) 1.7 (61) 2.3 (81) 2.1 (74)
75% 1.3 (45) 1.1 (38) 2.1 (75) 1.9 (68)
50% 1.0 (36) 0.9 (31) 1.8 (60) 1.5 (53)
25% 0.8 (29) 0.7 (25) 1.2 (45) 1.1 (40)

LP Vapor, kg/hr. (lb./hr.)
100% 3.7 (8.4) 3.2 (7.1) [B]4.3 (9.4)[/B] 3.9 (8.6)
75% 2.4 (5.2) 2.1 (4.4) [B]3.9 (8.7)[/B] 3.6 (7.9)
50% 1.9 (4.2) 1.7 (3.6) [B]3.4 (7.0)[/B] 2.8 (6.2)
25% 1.5 (3.4) 1.3 (2.9) [B]2.2 (5.2)[/B] 2.1 (4.7)

LP vapor conversion factors:
8.58 ft.
3 =1lb.
0.535 m3 =1kg
36.39 ft.
3 = 1 gal.

Nominal fuel rating:
Natural gas: 37 MJ/m3 (1000 Btu/ft.3)
LP vapor: 93 MJ/m3 (2500 Btu/ft.3)[/FONT]

The RESL (PDF) fuel flow appears to be identical to the RES:

LP Vapor, kg/hr. (lb./hr.)

100% 4.3 (9.4)
75% 3.9 (8.7)
50% 3.4 (7.0)
25% 2.2 (5.2)

Make all of your purchases justify their usage...

-Bill

Bigwooo · August 2009

Re: Kohler 12RES or RESL?

BB. wrote: »

Looking at charge rates for your battery bank (12 volt batteries assumed) and the 5-13% rule of thumb (AGM's can accept somewhat higher charge rates):

212 amp*hours * 6 batteries * 12 volts * 0.05 = 763 watts
212 amp*hours * 6 batteries * 12 volts * 0.13 = 1,984 watts

At 50% generator load (and a compatible charge controller) -- a 4-5kWatt genset would seem to meet your charging requirements.

Of course--if you need more power (and who doesn't), then the larger genset may make sense for you.

In general, keeping the genset at 50% minimum power loading will increase the fuel efficiency.

-Bill

Thank you for all the information Bill. Yes, under the confines of the system I've posted in my signature a 4-5 watt would be fine (and less expensive!), but we're off grid in Mexico and on some of the really hot/humid summer nights I'd like to run a mini-split AC for a few hours a night to cool down the bedroom a bit, and I've got a welder I'd like to fire up and tinker with once in a while. The welder needs 8kw to run smoothly, so I figure with 12kw I should be able to cover all my bases comfortably.

I found someone at Kohler to talk to and they said the RES provides clean power for electronics etc. and the RESL isn't as clean of power and is only recommended for lights/AC/fridge but not for computers, wide screen tv's etc.

Vic · August 2009

Re: Kohler 12RES or RESL?

Regarding the Honda EU 6500 isa, I've seen voltage regulation problems with 240 VAC output, when the current drawn on each leg is not identical.

For example, using stacked Xantrex/Trace SW+ 5548's to charge my batts, since the inverters are ascnychronous to each other, one inverter takes a gulp of current to charge bhe batts, and the other leg is yanked out of regulation, causing the inverter on that leg to drop out due to Overvoltage. The only solution for my application is to switch the output of the Honda to 120 VAC, which limits my max charge I (one inverter only) to about 75 Amps DC.

Generally, I do likke the Honda EU series generators -- have four of them here, but the 6500 is not a good solution for non-PFC inverter/chargers when stacked.

This experience dictated the larger Kubota diesel genset, which is unphased by the action of the inverters.

It is possible that the Honda simply cannot supply the peak demand of the charger which might have a very large peak for a half-cycle or so.

The other thing about the 6500 is that it "idles" @ 2450 RPM with no load. I had hoped that the 6500 would have been 2X the EU 3000 -- which is the finest EU generator in the Honda line IMHO. I still do run the 6500 on occasion to charge batts, and to run two small window A/C units. THe 6500 was unhappy when one A/C unit was on one leg of the output AC and the other A/C on the other leg -- the same thing. One A/C's compressor kicks on, and the other leg goes over limit on AAC out. The Honda 6500 has only 21 hours on it, but it might have been defective, but have nothing to compare it to.

Anyone here have any experience with the Honda EU6500 isa on 240 VAC with asnychronous leg/leg AC loads ?? Thanks, good luck, Vic

Kohler 12RES or RESL?

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