240v 45amp off grid power. Suggestions? 2

[LukePots]

I am a ceramic artist building a pottery studio that will be off grid, and mobile (inside a large utility trailer, refitted as my studio/classroom) and I am looking for help solving the issue of supplying power to my Kiln and studio. The kiln uses resistor heating elements, with no fan or motor. It will be fired approximately once every two weeks. A firing requires between 8 and 10 hours of continuous power supply.

Kiln power demand:
- 10,800 watts
- 45 amps
- 240 volts

I need to minimize:
- Weight
- Noise
- Size

And maximize:
- Fuel Efficiency
- Portability (easy to load/unload from trailer)

A large 240v 50amp portable generator would meet the kiln’s power demand but does poorly in all other respects. They’re too heavy, loud, inefficient for general use, and difficult to load and unload from my trailer to be a good option.

I need help finding an alternative option. One that I’m working with right now is a bank of paralleled inverter generators that I could disconnect when not firing the kiln to save fuel. This is where I’m looking for help. Is that possible with the power I need?

* First question: is it possible to get a 240 V power supply out of paralleled 120 V inverter generators?

* Follow up question: Low wattage units supply 120v. In parallel, amps go up but voltage does not. I know that putting the units in series would raise the voltage. Is it possible to put inverters into series and then parallel them?

* Second question, is it possible to parallel more than two inverter generators?

* Third, is there an other alternative option out there?

Any answers, suggestions, or guidance welcome! Thanks!


 

[waross]

Rethink the generator.

I just bought this for $950 Canadian ($681 USD).
It is fairly quiet and puts out up to 20 KW.
You don't have to unload, just park it near and plug in the cable.
I need a 40 HP diesel engine for another project.
When I am done I will have a utility trailer as a bonus.

Inverters:
Some models have a sync cable available that allows them to be operated in parallel.

They’re too heavy, loud, inefficient for general use, and difficult to load and unload from my trailer to be a good option.

10800 Watts for about 20 hours per month.
That's over 100 Kilo-Watt-Hours per use.
For 12 Volt batteries that is over 9,000 Amp hours.
One 8D battery I looked at does about 250 Amp hours. You would need 36 8D batteries with that spec.
Weight: 161 Lbs. With cables about 3 tons of batteries.
Price from $500 to $1,000 .... $18,000 to $36,000.
Now add the price and weight of the inverters.
$25,000 to over $40,000 for 20 hours a month?
Really, re-think the generator.
By the way, on the way to the studio pass by the service station and fill the fuel tank.
Much easier than fueling up on site from Jerry cans.
I expect the fuel consumption at 10.8 KW to be about one gallon per hour. Possibly slightly more.
At 40 KW output it would use about 3 Gallons per hour but fuel consumption is not linear with load.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Compositepro]

If you are off-grid you would do far better in meeting your requirements with a propane fired kiln. It will be far lighter, quieter and more fuel efficient than using a generator. Burn fuel to make heat rather than turn a generator to make electricity the make heat.

 

[waross]

Good call Compositpro.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FacEngrPE]

Please DO not try hooking AC generators in series (Inverter or mechanical). it is a surefire method to seeing what happens when two sign waves with slightly different frequencies beat against each other. (SMOKE)

Fred

 

[waross]

Actually, with generators, the voltage will slowly drop to zero and then rise again to the expected voltage.
Cycle time may be measured in seconds or major fractions of a second.
This won't hurt the generators but some loads may not like it.
For generators this is probably moot. You won't find a 10 kW generator that produces only 120 Volts.
Good quality inverters have an accessory cable that will sync them to allow then to run together.
For generators in parallel, we used to use light bulbs and watch the sign waves beat across the light buld.
When the light went out we would close the switch.
Once connected the generators will lock together electrically and stay in step.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LukePots]

Thanks All! Given me lots to think about. I'm not off grid, as in off-[in the wilderness], I'm operating out of a refitted utility trailer. I'm switching to electric from a gas fired kiln, actually. It presented it's own problems (I live out west and firing gas kilns outdoors can pose a wildfire hazard).
I'm going to switch to a lower wattage (6400 watt) electric kiln to address the issues that you guys have pointed out with the former beast. Thanks again! I'll keep checking back incase any one else has some extra input.
Take care
Luke

 

[LittleInch]

So what is your power demand "normally". Then people can see what is required to fill the gap.

Are you using a solar array and batteries or a smaller invertor generator? One and one spare or??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[che12345]

Dear Messrs LukePots , waross, Compositepro

I have nothing new to offer except agreed with the proposal/advice by the learned Mr. Compositepro; by using propane/gas fired kiln. You may have a small cylinder of gas plus a spare cylinder if deem essential (total two)in less than 100kg. They occupy very little room. No special tools, spare parts needed.
It may not be economical to tug along a generator plus a spare generator if deem essential (total two) with battery maintenance tools, spark-plugs, lubrication oil, air and oil filters etc.; not to mention the noise and smoke pollution.
Che Kuan Yau (Singapore)

 

[waross]

My 6 kW diesel gen-set has about 18,000 hours and still running well.
I haven't yet had to replace spark plugs.
The battery was old when I got it.
Seven years later it is still starting reliably on the same battery.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

Is a gas fired kiln a bigger fire concern than a 12kW to 15kW genset running? That size of genset will produce lots of heat and hot exhaust gasses.

Bill - your diesel genset has spark plugs????

 

[waross]

Lionel; No, that's why I have never had to change them.
Those light towers are everywhere here.
The sound level is quite low.
Lots of heat, yes, but not at the temperature of a kiln.
With the trailer mounted units the heat is outside the studio.
By the way, I am not against a propane fired kiln but the OP has concerns.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mfgenggear]

ever thought about combination , wind generator, solar, and propane generator.
diesel generator is a very good choice.
it will depend on the budget.

 

[mfgenggear]

bummer about solar systems id the up front cost to buy and install it. mainly the batteries.
15k SYSTEM IS VERY EXPENSIVE.

 

[stevenal]

Parallel 120 v sources get you 120 v.

 

[itsmoked]

I was party to an 8ft x 6ft x 6ft high wood fired kiln run. It took 3 guys 24 hours of feeding about 2 cords of wood thru it. I didn't see any sparks leaving it so hi doubt that's a propane issue.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[che12345]

Dear Mr. Compositepro (Chemical)7 Jun 20 20:51
" If you are off-grid you would do far better in meeting your requirements with a propane fired kiln. It will be far lighter, quieter and more fuel efficient than using a generator ".
You are a much respected contributor of the Eng-tips forums. Welcome to the electrical/electronic engineers forum, Sir.
We are from different branch of engineering. Our team/group (who are mainly electrical/electronic by training) may have had inevitably missed out some "blind spots" without realizing it. Your learned and invaluable guidance/advice by looking on the problem at a different angle is greatly appreciated. Thank you.
Che Kuan Yau (Singapore)