More questions about electric sawmill's power options

[Glenn1]

I did not want to hijack a thread so here is a new one.  Let's say I want an electric mill running 25HP and it will be set up inside a building with a large overhead door and a blower sending the dust to the great outdoors.  Not sue if a LT40 electric will only run on 240V or could it possible run on 48V?  I do not have 3 phase in my area so I am left between a rotary converter and a 20kw genset.  I can probably put together a 3 phase converter for around $500.  It will run as 240V or 480V power so I am guessing that I will still have a decent sized electric bill. 

The other option is to purchase a 20kw genset.  I don't have access to natural gas so I am also guessing that the next best option would be diesel.  Would it be more cost effective to find a 20kw genset that is 480V verses 240V?   Where can I find one at less than $10,000?

How about the difference in cost to run a genset vs using electricity for a 3 phase converter.

Thanks,
Glenn

[PC-Urban-Sawyer]

One difference between 240 vac and 480 vac three phase is that the wiring from the converter to the motor can be smaller for the higher voltage if the load size (hp of motor) remains the same. This makes that portion of the installation cheaper and easier...

Herb

[Glenn1]

That is good to know.  I see that the LT40 can accept 460V power.  Now to decide between a converter and a genset    ??? ??? ???

[PC-Urban-Sawyer]

Without getting into specifics (because I don't have any  :D :D :D ) I think you'll find a converter is cheaper to buy/build and operate, with less maintenance than a genset. On the other hand, a genset could be portable...

Herb

[boscojmb]

An electric motor requires at least twice the KW to start as it does to run.
I think you need at least 40KW to start a 25 HP motor.

[ozarkgem]

How much electricity will 10 grand buy? Then figure in oil change, diesel and so one. Phase converter would be my choice. I run my mill on a gen set now but have already ran another service to get rid of the genset. Mine is a 20 KW Detroit . I run my 20 hp motor with it. Works really well and pretty fuel efficient. It would not be to hard to figure the KW hrs that you would use and multiply it by your electric rate.
  One gal per hr is 8gal per day is 40 gal per week is 160 gal a month x diesel price.

[Dave Shepard]

As mentioned, you need a bigger genset than 20kw. Playing with 480v requires experience. Google arc flash. To run a converter you need to have enough amperage in your service to run it. I don't think you are going to run a 25HP off of an RPC from a 100 amp house service. Running a genset is not the cheapest way to go, unless it is the only way to go. By that I mean that if having 3 phase service installed will cost you  $10-20k, then a genset is cheaper. To have enough juice to run the RPC big enough to start a 25HP motor, I bet you will need a commercial meter. That will be an upfront cost plus demand charges. You will have to run you motor a consistent amount every month to make it work. Start that motor just one time in a billing cycle, and you've set your demand.

[Glenn1]

I read about arc flash and wonder how common it is with 240V?  We have 200 amp breaker boxes so hopefully that will be sufficient to run a 40-50 hp phase converter.  What do you think?

[dean herring]

This may a bit off the exact subject ,but I was wondering I you had a lt-15 electric mill, could a hydraulic chain turner and clamp be put on it. I think it would work. Can you buy a turner kit and clamp or get it piece at a time. Thanks for any info. FAILURE IS NOT AN OPTION.
Dean

[boscojmb]

Max you can get out of the 200 amp service is 24KW.
Not enough to start a 25HP motor.

It is possible to "soft start" an electric motor. This may work. Hopefully someone else knows more about it than I do.

[sandsawmill14]

I read about arc flash and wonder how common it is with 240V?  We have 200 amp breaker boxes so hopefully that will be sufficient to run a 40-50 hp phase converter.  What do you think?

arc flash can happen at any voltage with higher voltage  more likely to happen 480 volt can be high as 35,000 F I have only personally seen 2 in the last 20+ years but when my daughter was in the burn center at vanderbuilt for 9 days the man in room next to her was involved in arc flash lost his ear lobes and over 1/2 of his nose 3rd degree burns on 40% of his body. I met his wife in the hall and she was telling me what had happened when told her I was electrician she tried for 3 days to get me to go meet him because he was doing same job as me, but I couldnt do it(he was still knocked out).  Both flashes I was in (1 my fault 1 just happened) I was lucky only lost hair and looked like a real bad sunburn. I can name 6 off the top of my head that were hospitalized by arc flash.  This is one of the reasons i am now a full time sawyer.


far as the phase converter i have never seen a rotary phase converter that would make 480 without transformer but im not saying you cant. I do know a static converter will do it. but if i was doing it i would make a rotary converter out of electric motor and run on 240v .

if you go with genset   1 hp=.745 kw       25 hp=18.625 kw x 2 =37.25 kw  so 40 kw would be minimum size genset for that motor
dont forget any other loads you will be running as well. to properly size genset take highest fla x 2  then calculate total fla for everything hooked to genset (dust blower, edger...) then use which ever is larger  and that will be MINIMUM size genset kw       hope this helps

[schmism]

if you go with genset   1 hp=.745 kw       25 hp=18.625 kw x 2 =37.25 kw  so 40 kw would be minimum size genset for that motor

I disagree with this assesment.   an electric motor labeled 25hp does not draw 37.25kW     As with the other tread,  check the name plate and look for the full load amps listed for the voltage stated.   (current goes down as volts go up)  You'll likely find the 25hp labeled motor draws 30amps at 460v which is 13,800vA.    Most motors in this rateing either use VFD soft starts or motor starters that have large capacitors that offset high starting currents

As to the original question,  were can you find a 25kW genset.... check your local craigslist.   mine has a 45kW 3ph  for $9k  onan no less.
http://peoria.craigslist.org/for/4913841016.html
most gensets in this range have roughly the same performance meaning a 25kW genset at 80% load  = 16kw might use 2gal/hr.   a 45kW genset running at 35% output would likely use close to the same amount of fuel per hr.

a rotory phase converter is unlikely for that size power demand.   generally you have to spin the 3ph motor with a single phase of 20% larger,  and your unlikely to find a 30hp single phase motor.

[ozarkgem]

According to the electrical shop that built my RPC I can run a 25 hp off a 50 hp RPC on a 200 amp service. I can run a total of 80 HP(if I remember) on the same converter. You can't start them all at once.Than is what I plan to do. He will also build a phase converter using 460 volt single phase. I didn't know that existed but it does. There was a sawmill in Neosho using a 40 HP motor on his mill using single phase. Maybe Dboyt has been to his mill and seen it. I just remember there were some big ash wires going to that thing.

[WoodenHead]

Here's a link to an article about sizing the genset for a soft-start.

http://www.sprecherschuh.com/library/techdocs/tips/pf-pcs-generator-size.html

This vendor recommends no less than 3 x FLA.

"While taking the application considerations above into account can help reduce start-up issues, the best recommendation is to size the generator so what the motor could be started across the line (approximately 600%). This practice ensures that the generator has sufficient capacity and if there is ever a problem with the PCS/PF Softstarter, the customer would be able to use a bypass contactor to start and run the motor. In applications where the motor is completely unloaded at start-up or very lightly loaded (oversized motor) it may be possible to size the generator smaller. In general a designer should avoid sizing the generator less than 3 times the FLA of the motor."

For those interested, here's a link that describes some of the issues with using soft-starts and generators (i.e. make sure your genset is designed for it or you will have problems over time):

http://static.schneider-electric.us/docs/Motor%20Control/Soft%20Starters/ATS48%20Soft%20Starters/8638PD9606R198.pdf

[Dave Shepard]

I wouldn't run 480 just to save $100 in wire. ;)

[Glenn1]

Dave,

That's the exact feeling that I now have.  I'd rather not have an arc flash and loose my eye brows.     ;D  220V seems just fine to use.

[Ohio_Bill]

https://forestryforum.com/board/index.php/topic,680.msg7377.html#msg7377

Bibbyman did a nice writeup on his phase converter in this post.

[sandsawmill14]

schmism  the way me and woodenhead are sizing gensets are for heavy industrial use where they are running 10+ hrs a day 5+ days a week  a sawmill is as heavy as it gets. even a bandsaw will peak a 25 hp motor. but the  x 2 rating i was giving is to cover start load not fla. this was for the MINIMUM size genset to run motor
the fla on the 25hp would be 18.625 kw then you have to add 25% to cover the 1.25 sf rating which is 23.28 kw to get peak fla then determine the voltage genset is making, going from 480 to 440 is almost 10% not huge but must be considered if try to max out a genset .  So instead of spending hours doing math we just use 2x the fla on biggest start load or total load which ever is bigger as the MINIMUM. 3x or more is better but with used equipment you have to use what you can get.  I personally would not use less than 100 kw genset for 3 phase that sounds like over kill but 25 hp is 1/4 what it will pull add a 15 hp blower you at 40%  then add a 25 hp edger your at about 70-75% plus add another 10-12% for 1ph transformer and dont use electric service for mill, your making the electricity might as well use it.  another way to look at it is it takes roughly 2 engine hp to produce 1 kw of electricity so if you are used to sawing with a 25 hp gas mill the genset would have to have 50 hp engine to get roughly a 50% increase on mill power (1 hp electric = approx 1.5 hp gas) so a 35-40 hp engine on mill would burn less fuel but would only pull the one load. but you (at least I) dont want to run 4 -5 gas engines to power all equip so that is where the genset proves to be best option. I hope to have my mill converted in the next 2-3 months.

glenn1 schmism is right about it running on the smaller genset it will cut good in 4-6" lumber but when you get to 12"+ you wont be happy it would really slow down.  we used a 40 hp power electric motor to start a 250 hp chipper years ago because the 900 lb disc made start load to high for genset to start so there's always a way to get by  but why start out that way when it will cost very little if any more to get the bigger genset and the fuel would be less than a gal an hour difference unless you added more load which you cannot do if you start out to small.   the are alot of good used gensets out there hospitals are a good soure as they update every so many years. we got 4 250 kw gensets a few years back they were late 1980s yr models with less than 200 hrs on them. but the smaller they are the harder they are to find.  good luck with whatever you decide on

[Joe Hillmann]

25 hp on 240 volt will draw 72 amps running and more than that on start up.  If you use a phase converter figure 20% loss in the convertor which.

When you figure it all out you would at least a 178 amp service to run just the 25 hp motor with no other loads at all.  I also think the national electric code calls for having 250% percent service for the size of the 3 phase load which for 25 hp would be 180 amp service.

So with a 200 amp service you could run the mill but you would be pushing it to run anything else at the same time.