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How to power small off grid three phase machines?

stoneaxe

Stainless
Joined
Mar 2, 2010
Location
pacific northwest
We have a 3 phase 3hp lathe and 2hp mill. They do not run at the same time. Right now they are powered through a 10hp RPC. on grid power.
We are at the very end of a dead end with sketchy reliability when the wind blows hard. Every time it goes out I wonder if it is ever coming back on....

What is the best way to power up these machines when grid power is gone?
Buy a three phase generator and power them up directly?
Buy a big single phase generator to start the RPC?
Use a smaller RPC?
What sort of output would we need?
 
You might look into a surplus military diesel generator that outputs both 120/240VAC single phase and 208VAC 3 phase such as the MEP-803A. They are quite common, but may need some TLC to get fully functional. Diesel fuel would be preferable for a remote location. You would directly power the equipment, Solar, battery backup with an Inverter would be a much more expensive proposition, I would use a VFD to power the 3 phase motors vs. an RPC in that scenario. I wouldn't use the RPC.
 
Can 240v three phase be run off 208V?
Depends on the equipment, really. If you get something that will not accept 208V and insists on 230/240, you can get a buck/boost transformer without much trouble.
Do you know if both single and three phase power can be run at once?
Yes, but you might not be able to run both at full load simultaneously. This is a case where you check the generator manual.
 
My power goes out every time the wind blows hard as well. It is never more than 2 or 3 days at a time though. I just start picking away at other projects like repairs, organization, or 2nd op stuff that I don't need much power for.

If and when I do get to the point that production cannot be interrupted, I will be be going with the military surplus diesel generator.
 
If you have solar and batteries, there are some inverters that can be interconnected to produce 3 phase. I am trying to recall the brand, but I did a demo setup back at the Consulting Co for a customer. You connected the outputs, of course, and there was a control cable harness as well to get them in sync.

Worked well.
 
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I have several friends who just bought big gas drive miller welders that also generate 3 phase. Much higher resale value than a cheap generator, and of course, you can weld with them too...
 
I would recommend a propane fueled generator rather than diesel should you wish to go the standby generator route, unless you have something else that consumes diesel. Diesel doesn’t keep indefinitely like propane does. It’s best to have diesel fuel used up within a year or so.
 
We have both- a spare 60 gallon propane tank and a hundred gallons of of fuel oil.
Nice thing about fuel oil- and I am presuming a diesel gen-set will run on home heating oil- is it does not take a special delivery truck to fill.
 
Toss a bit of marine fuel stabilizer into the tank ,and it will never get fungus in it,...............also best to have large fuel strainers ,water traps and filters ......which you may already have for your boiler ................Before I quit the refinery,I got enough drums of diesel to last me over five years ,bit of stabilizer/biocide in each drum and the last was clear as the first.
 
I would recommend a propane fueled generator rather than diesel should you wish to go the standby generator route, unless you have something else that consumes diesel. Diesel doesn’t keep indefinitely like propane does. It’s best to have diesel fuel used up within a year or so.
That advice is wrong. Diesel fuel is the same as heating oil, but with anti-waxing and metallic lubrication additives and it is road tax free. Diesel fuel and heating fuel will last indefinitely. Heating fuel will require a can of anti-waxing additive if the fuel is exposed to temperatures below about 4 C. Propane on the other hand will not vaporize in very cold temperatures. I use heating oil with additives successfully in my my generator and forklift and have been be for many years
 
That advice is wrong. Diesel fuel is the same as heating oil, but with anti-waxing and metallic lubrication additives and it is road tax free. Diesel fuel and heating fuel will last indefinitely. Heating fuel will require a can of anti-waxing additive if the fuel is exposed to temperatures below about 4 C. Propane on the other hand will not vaporize in very cold temperatures. I use heating oil with additives successfully in my my generator and forklift and have been been for many years
Diesel fuel will certainly not last indefinitely. I’ve seen it. It get pretty rank smelling and doesn’t burn clean at all. Lots of carbon formation. And long term stored diesel is vulnerable to algae formation in it, which is another whole form of purgatory. Propane stops vaporizing at -40C/F so really not a concern unless you are Santa Claus living at the North Pole.
 
Recommendation for diesel is more for burn rate/cost, propane fuel consumption is about 2X or more than a diesel generator. LPG requires a larger more expensive tank, as well as fuel availability/delivery in rural setting. Diesel fuel is considered safer than LPG. Durability and continuous run duration of a diesel powered generator is typically better than LPG. Military surplus generators would be expected to be able to last much longer than most of the light duty LPG generators. Assuming that the power outages occur frequently the fuel would be used and replenished, some of these diesel generator have built in fuel tanks either in the skid or on a trailer, so something like a 75 gallon diesel tank should get you around 150 hours of run time with mixed load.

Other common surplus military generator models MEP-1040, MEP-804A as well as others. Larger kW military generators tend to be 3 phase only, and have higher fuel consumption. I do not know if both 3 phase and single phase are are available simultaneously (depends on the model), total output kW is typically combined/total output which is a function of the Hp rating of the power source. If your machines were run on single phase input VFD's this would mitigate the need for 3 phase power generation. Parts may be an issue, but one could get another generator for replacement parts for not much, filters and consumables seem to be commonly available for these military generators.

Diesel generator fuel consumption at 25, 50 and 100%
10kW0.53 gal/hr0.65 gal/hr0.88 gal/hr
 
We have a 3 phase 3hp lathe and 2hp mill. They do not run at the same time. Right now they are powered through a 10hp RPC. on grid power.
We are at the very end of a dead end with sketchy reliability when the wind blows hard. Every time it goes out I wonder if it is ever coming back on....

What is the best way to power up these machines when grid power is gone?
Buy a three phase generator and power them up directly?
Buy a big single phase generator to start the RPC?
Use a smaller RPC?
What sort of output would we need?
It doesn’t take that much of a generator to start a 10hp RPC .If you plan to use it regularly an expensive diesel generator could be worth while, otherwise gas or propane for now and then.
Good luck
 
Diesel fuel will certainly not last indefinitely. I’ve seen it. It get pretty rank smelling and doesn’t burn clean at all. Lots of carbon formation. And long term stored diesel is vulnerable to algae formation in it, which is another whole form of purgatory. Propane stops vaporizing at -40C/F so really not a concern unless you are Santa Claus living at the North Pole.
Yes, contamination of diesel fuel does happen, but the fuel itself does not go bad. Contamination is usually caused by the ingress of water. Without water nothing grows in it.
 
It doesn’t take that much of a generator to start a 10hp RPC .If you plan to use it regularly an expensive diesel generator could be worth while, otherwise gas or propane for now and then.
Good luck
No RPC is required if the gen set is 3 phase in the first place. Yes you can use a 3 phase gen set to power single phase loads as long as you do not exceed the max current limit of any of the three phases of the alternator. In that light, you should size the gen set accordingly. My 25 kva diesel genset powers my entire house and my 3 phase machine shop without issues.
 








 
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