Replacing 15kw diesel Gen with Propane - Recommendation & Important Considerations?

muirhouse · April 2015

My over 10 year old china diesel genset is knocking horridly and on its way out. Looking for a propane replacement that requires no babysitting. Can you please recommend? And are there any expensive diesel to propane replacement issues? Current generator is in its own shed, large underground propane tank about 20 feet away and basement of house with inverters and batteries about 20 feet away from that. The 15kw was oversized to charge my 16 surrete/48 volt system alternating with 8 panel with PV, so looking for propane 8KW, I think. Any discussions around this would be much appreciated!

mike95490 · April 2015

Wait before you dump it. When was the last time you de-carboned the head ? Or tried a water sprayer and spritzing a mist of water into the intake manifold (remove the air cleaner first) ?

I was having a heavy knock in my lister, and did not have the time to open it up and so I used a hand held spritz bottle and while running at hot temp, sprayed some water in. As it flashes to steam it cleans carbon out.

For converting diesel to propane, you cant. You have to keep some diesel as pilot ignition, and can not go too far past 70% propane. To convert a diesel engine to propane, you have to install a spark plug, adjust timing and reduce combustion ratio to at least 11:1 or lower.
here's a LONG thread about the issues of converting diesel to 100% propane
http://listerengine.com/smf/index.php?topic=7344.0

muirhouse · April 2015

Thank you Mike95 for the carbon cleaning suggestion, I will try this, it does sound like a thrown rod however, but keeps on running. I don't want to convert to propane, just replace the diesel generator with a propane generator, and am unsure about what propane generator to get and what changes/additions I might have make in the infrastructure, wiring, etc.

Mangas · April 2015

I have a CumminsOnan 20 kw propane, water cooled, 1800 rpm unit.

A little larger than what you are looking for but a good choice for larger off grid applications. Not sure if they make the lower rpm propane models below 20 kw but try their website.

In my opinion, CumminsOnan manufacture well engineered and reliable gensets.

muirhouse · November 2015

Thank You Mangas, I am in NH and have a PV setup which has cut the runtime of the generator in half. So really, the generator is now backup to the PV, used to charge the batteries in bad weather. 20 KW seems like overkill for this, am I wrong? But I am really having trouble getting the right recommendation for a new generator, as it must be correct size for my series stacked Xantrex inverters to handle. I am being recommended an 8.5kw Kohler air cooled. One supplier says this is too small, another installer says it is just fine, not sure who to believe. I know the water cooled and 1800 rpm is way to go but too expensive for me right now. So with my two Xantrex 4kw inverters and my PV doing lots of work on sunny days, can I manage with the 8.5kw? Thanks guys ~ Jan

vtmaps · November 2015

muirhouse said:

But I am really having trouble getting the right recommendation for a new generator, as it must be correct size for my series stacked Xantrex inverters to handle. I am being recommended an 8.5kw Kohler air cooled. One supplier says this is too small, another installer says it is just fine, not sure who to believe.

Who to believe depends on data you haven't provided to us.

What is the ah capacity of your battery bank? If I know the ah capacity I can calculate how many generator watts it will take to charge the batteries at a reasonable rate. What other loads will the generator handle while it is charging the batteries? Those loads, plus the charging load will be the generator capacity that you need.

--vtMaps

muirhouse · November 2015

VTMaps: 16 Rolls Surette 6 V 350 amp hour batteries. My useage is small. 240 well pump, radiant floor heat, w/d, refrigerator, 1 computer, radios, sometimes TV flat screen, lights, normal household: toaster, microwave, hairdryer.

inMichigan · November 2015

Personally, I lust after this one...(48VDC)
http://http//www.altendc.com/diesel-battery-charging-dc-generators
http://static1.squarespace.com/static/555b260ee4b07f48c9a7bdac/t/555f8df8e4b08654c670dad3/1432325624979/ALTEN+Duke+Diesel+DC+Generator+eBrochure.pdf
but I have no experience other than admiring it on the internet...

inMichigan

vtmaps · November 2015

muirhouse said:

VTMaps: 16 Rolls Surette 6 V 350 amp hour batteries. My usage is small. 240 well pump, radiant floor heat, w/d, refrigerator, 1 computer, radios, sometimes TV flat screen, lights, normal household: toaster, microwave, hairdryer.

So that's a 48 volt, 700 ah battery bank. Charging at 10% of the ah rating is 70 amps. If your absorb voltage is 60 volts and 70 amps are going into the battery, that's 4200 watts.   There are some losses in the inverter/charger, so add another 10-15%... so that means the generator must put out almost 5000 watts to achieve a 10% charge rate.

If you are also running loads while charging, you may want a larger generator than 5000 watts.

I believe that your inverters can limit their charging to prevent overloading a generator... i.e. if you have a 5000 watt generator and are charging the battery, and then you switch on the 1500 watt central vac, the inverter will drop the battery charging down to 3500 watts so as to not draw more than 5000 watts from the generator.

By the way, I based the generator size on giving the batteries a 10% charge rate. You don't need that high a rate... it's just a rule of thumb.   It is especially useful for solar charging because using higher current (like a 10% charge rate) allows the battery to be charged in less time (and in the winter there is not much time).

If you are using a generator to charge the batteries, you don't have to worry about the sun setting, so you can charge at a slower rate (and the batteries are probably better off being charged at a somewhat lower rate).

--vtMaps

Mangas · November 2015

Based on your battery bank description, I'd research 10 - 15 KW units. Personally, I like to have lots of KW headroom when my batteries are being charged by the genset simultaneous with running the house, wells etc.

In addition to Cummins Onan, Kholer makes a very good genset.

Most 1,800 rpm, water cooled propane units are 15 KW or more. My opinion is higher rpm, air cooled units will probably be your best bet. I prefer propane fueled gensets. If you search the forum, you can get a good feel about the back and forth between gas, diesel and propane generators. Everyone has their own opinion based on their set up and fuel availability.

BB. · November 2015

One issue--How cold does it get in your area... You may need to pre-heat the motor on cold winter days. And if you have smaller propane tanks, they may run cold and you lose your propane pressure. Unless you get a liquid propane fueled genset (need vaporizer at engine to turn fuel into liquid).

-Bill

muirhouse · November 2015

Hi BB - I am in NH, and babying the 15kw diesel all winter is why I am switching to propane. My propane tank is 500 gallons, is buried underground. The genset I am set to get is a used 2007 Kohler 8.5/12 RES, LP vapor, natural gas rated.

muirhouse · November 2015

And wondering about issues re the change from 1800 rpm (my old diesel) to the 3600 rpm Kohler propane. Looks like the two wire start is the only electronics that has to be done (no transfer switch, off grid). So the rest of this is going to be negotiated via settings on the SW 4048. I think I should call Xantrex perhaps.

Anawa · November 2015

Muirhouse: I installed the same Kohler 8.5 (propane) and due to the current weather conditions in my area, I've been using it every day for the last 2 weeks. My battery bank is 804ah at 48 volts. The charging amps start out at 80+ at 58 volts, but drops fairly quickly. At this rate, I do not think the gen efficiency is nothing to rave about.

The only downside I've discovered is it uses a fair amount of fuel, so take that into consideration when sizing your tank.

Paul
In Georgia

BB. · November 2015

Here is a nice PDF from Generac on sizing for propane:

http://www.probuilder.com/showvillage/2013/products/pdf/Generac_SizingGuide.pdf

Down to Zero F, it appears that a 500 gallon tank is OK for 15 kWatt load.

Of course, if you run your tank towards empty before refilling it--Then there is less heat transfer from the outside to vaporize the fuel--And you could still lose propane pressure (cold weather, tank less than 1/2 full, heavy load on genset).

As always, get confirmation from your local propane supplier about tank/genset sizing for your area/installation (above/under ground, etc.).

-Bill

notes · November 2015

Try this place. Great service and a 3 year warranty. http://www.genconnexdirect.net/
Moderators, if I am not supposed add a link please delete post. Sorry in advance.

BB. · November 2015

Not a problem. On topic links are fine. Always nice to hear good things about a supplier.

-Bill

inetdog · November 2015

muirhouse said:

And wondering about issues re the change from 1800 rpm (my old diesel) to the 3600 rpm Kohler propane. ...

The conventional wisdom is that 3600 RPM generators, regardless of the fuel, are not really well suited to prime mover use with several hundreds of hours per year. The higher engine speed just produces too much wear, even when under low load. There are, of course, always exceptions and there are ways of improving the like of 3600 RMP engines by careful (and more expensive) design.

From http://www.generatorjoe.net/html/stepxstepgenerator.html :

To produce 60 Hz electricity, most engines operate at 1800 or 3600 RPM. Each has its advantages and drawbacks. 1800 RPM, four pole sets are the most common and least expensive in large generators. They offer the best balance of noise, efficiency, cost and engine life. 3600 RPM, two pole sets are smaller and lightweight, best suited for portable, light-duty applications. 3600 RPM sets are considered "Standby Generators" and can never be considered for prime power use.

In simple terms it’s like operating your car at 90 mph, versus 45mph – at 45mph your car will last longer, is quieter, less maintenance and longer life. Most 3600 rpm units are twin cylinder air cooled lawn mower engines, while the water cooled 1800 rpm units are comparable to those found in forklift and tractor engines. The bottom line is the 1800 rpm water cooled units will last longer, offer less maintenance problems and be more fuel efficient. In addition, 1800 RPM generators are designed to be rebuilt, 3600 RPM units are designed to replaced and are much lower in cost (most of the time). Some 3600 RPM stationary units and most RV and commercial power units can be rebuilt at least one or more times but this process is not inexpensive.

muirhouse · November 2015

The concern is what size generator to get, given the confusing input from suppliers making site visits - One supplier says that my two Xantrex inverters each pull 18 amps, and an 8.5 kw generator is too small, only puts out 30 amps. I am confused by the 18 amps, don't know where he is getting that as it says max charge amps is 30 amps right on the Inverter. Please help me get this straight.
Here are the specs on my Xantrex units, stacked, 240 volt system, batteries are 16 Rolls Surrette 350 ah, wired series/parallel.

Generator Model Numbers SW4048 and 4048 Plus
Inverter 4000 Watts each Stacked.

Top Inverter S/N 445428 4048 7/2002

Inverter System -
Nominal Battery Bank Voltage 48 Volts
Nominal DC Operating Voltage 59 Volts
Range of Operating Voltage 44-64
Max op DC current 100 Amps
Nominal AC output 120 0 ~
Nominal frequency 60 H
Max continuous output current 33 amps
Max output overcurrent protection 35 amps AC
Max output fault AC current 78 amps AC rms

Battery Charging System -
Nominal AC input voltage 120 Volts
Operating Frequency 60 hz
Max continuous battery charger AC current 30 Amps AC
Max continuous battery charger DC current 60 amps DC
Max continuous battery charger input VA 3600VA
Max AC Transfer switch Input current 60 amps AC
--------

***Also, when I have had down time for repairs to the old china diesel, I have in the past plugged in to an AC outlet, a gas driven Honda generator I think it was 6.5kw. That was backfeeding I know, but Was that going straight to the batteries, bypassing the inverters?

MarkC · November 2015

I've always gravitated toward this supplier - have NO EXPERIENCE - simply the combination of supplier choices of build parts and price for 240 volt split phase designs in the sizes appropriate for relatively small KWH usage designs (small compared to "whole house" generators).
http://www.centralmainediesel.com/order/Honda-5kw-Propane-Generator.asp?page=H04585

Did I miss something about your number of PV panels? Seems you might have inverter/battery capacity for almost double your PV panel count - further possible reduction in generator demands? Would you consider a MPPT CC to further unload the generator - more effective battery charging via solar? I use the SPS of the SMA Sunny Boy as emergency off-grid charging for a 48 volt system, but realize it is not that effective.

muirhouse · November 2015

I only have room on the roof for 8 panels, and MPPT CC SPS SMA, whoa, need translating.

muirhouse · November 2015

Here's another question. I will be decoupling the old two wire start from the diesel wiring, can I just hook the new generator's two wire start right into that same wire set? the change from 1800 rpm to 3600rpm won't be an issue?

MarkC · November 2015

muirhouse said:

I only have room on the roof for 8 panels, and MPPT CC SPS SMA, whoa, need translating.

Maximizing the PV panels to match the battery charging requirements (say 70 amps minimum @ 50 volts - likely 4000+ panel nameplate watts), combined with an efficient solar charge controller (MPPT type) could more adequately "fill" the batteries via solar power daily - and depending on patterns of energy usage, could reduce generator usage substantially - may allow you to go to a much less expensive generator system that "fits" the needs. Just a thought!

On the other hand I use what is called a "secure power supply" (SPS) that comes with the SMA SunnyBoy on-grid inverter to charge the 48 volt battery system with the OEM golf cart battery charger (110 volt AC powered by the SPS). The SPS only works when the grid is down. Not the most efficient by any means, but it is only for emergency - not really "off-grid".

arby · November 2015

<<Max continuous battery charger AC current 30 Amps AC
Max continuous battery charger DC current 60 amps DC
Max continuous battery charger input VA 3600VA>>

I have one SW 5548, so I don't have this question, but will each inverter put 60 amps into the bank , boosting the charge rate to a theoretical 120 amps?
It appears that one inverter will only accept 30 amps AC, or 3600 watts. If both inverters were putting out full charge , that would require a maximum input of 7200 watts by my thinking.
To get 7200 watts continuous I would guess that you would need probably something like a 10,000 watt genny.
Propane seems to give trouble starting in very cold temperatures.
That's how I would read those ratings, but I'm a neophyte in these things.

Vic · November 2015

arby said:

<<Max continuous battery charger AC current 30 Amps AC
Max continuous battery charger DC current 60 amps DC
Max continuous battery charger input VA 3600VA>>

I have one SW 5548, so I don't have this question, but will each inverter put 60 amps into the bank , boosting the charge rate to a theoretical 120 amps?
It appears that one inverter will only accept 30 amps AC, or 3600 watts. If both inverters were putting out full charge , that would require a maximum input of 7200 watts by my thinking.
To get 7200 watts continuous I would guess that you would need probably something like a 10,000 watt genny.
Propane seems to give trouble starting in very cold temperatures.
That's how I would read those ratings, but I'm a neophyte in these things.
<<

arby, you are basically correct, in all regards.   But I have been told that a pair of venerable SW inverters will NOT stack well, as one of muirhouse's inverters appears to be an SW, Stacked with an SW Plus ... I have never tried stacking a combo like this.

Regarding just how much genset that one needs, if does depend upon the amount of battery charge current needed, plus the amount of AC loads on the inverters, as the genset needs to supply these ...   AND, there are latitude and high temperature deratings, as well as a 10 - 15% derating from Standby rated power to Prime power, and so on.

OOOPPPppssss looks like I have erred again, as this all looks like it is a Quote, with no added Comment!    Gotta love it!   FWIW, Vic

muirhouse · November 2015

HI Vic, That's OK, thanks for weighing in. I hear alot about inadvisability of stacking my 4048s - they have been stacked for a over ten years now without a problem. - Arby: that's the question I was not understanding. If I was running my system all these years with the 15kw diesel was putting out 60amps, and an 8.5 propane would put out 30amps, there's a big gap in my understanding of electricity that needs filling. Yes I can adjust settings on the Inverters, but 30 amps is a big differential.

arby · November 2015

You will just have to adjust the input amps down until it no longer pops the genny's breaker. You will probably still get the at least the 70 amp input to the bank with the 8500.

muirhouse · November 2015

Right, so simple! Thank you alot for confirming.

Anawa · November 2015

Muir: my 8.5w Kohler (propane) will easily output a max of 90+ amps through my 2 stacked Outback 3648's (off-grid) and when the SG is low at 1.24.

Paul
in Georgia

Anawa · November 2015

Muir: if you decide to go with the Kohler, don't forget to run a 110v AC circuit to the unit that is used to power the built-in charger for the starting battery.

muirhouse · November 2015

The SG? and your 3648's are 36 amps?

Replacing 15kw diesel Gen with Propane - Recommendation & Important Considerations?

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Replacing 15kw diesel Gen with Propane - Recommendation &amp; Important Considerations?

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Replacing 15kw diesel Gen with Propane - Recommendation & Important Considerations?