I live in a solar powered house up in the mountains. We have a backup generator, 11K derated for altitude to 9K), which is set up to provide 240v for my power tools.
With great excitement I bought a 20in Powermatic planer, 5hp. It should draw 760×5= 3800 watts. BUT, the sucker draws 63 amps when it starts. The genny runs it for about 3 seconds, and then shuts down. It has a 50amp breaker, but that does NOT trip. It just overloads the machine and its internals shut it down.
Now, a 20K diesel generator is pretty pricey to just run this planer. But, I traded my little Delta 12in away when I got this big hummer. (Boy, if you haven’t seen one of these, Hy yourself down to the local big tool place and look at it. Its beautiful)
Does anyone have any ideas how to wire the genny,( house) to deal with this problem, or how to wire in some sort of hugh capacitor to carry it over the startup draw?
Thaks for the help
Stef
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What I did to be able to start the 2 Hp Unisaw on a 30 amp 120 volt service is to spin it up using an electric drill as a pony motor. I made a starting cam like for hand crank starting an old time car engine. Get it spinning before you hit the switch, and there's much less starting surge.
-- J.S.
The electrical experts should chime in, but being around equipment enough I think there are magnetic starters and even a simple disconnect that can be wired between the generator and equipment that can soften it's initial draw. we had the same issue once and for the life of me can't remember the engineering beind the strategy but wiring in a disconnect solved the problem. the designer described something about how the power was going into the windings, etc.
also, are you never going to add more equipment or square footage such that a larger generator would never be needed otherwise?
Dave
One very strange way to handle this is with another relatively large motor in "parallel" with the generator, one with a large flywheel. Even an induction motor, spinning a flywheel, will act like a generator when the voltage drops, but a brush-type "AC/DC" motor is much better in this duty.
But simply spinning the thing up with a smaller motor, as suggested, is likely a better (and certainly simpler) approach.
happy?
A very simple way to start the planer (assuming it lugs or trips due to its inertia) is to pulse width modulate (PWM) the start current by hand - this uses the inertia of the generator to advantage and also the time delay response of a breaker to advantage. Turn on the planer for 1 second and then turn it off, leave off for 1 second and turn it on for 1-1/2 second, off for 1 second, on for 2 seconds, etc. repeat till it comes up to speed. In the power electronics world this is called 'soft start'.
An addition to the statement 'Even an induction motor, spinning a flywheel, will act like a generator when the voltage drops'
3 phase yes, but think the respondent is probably on single phase? When the frequency drops, yes also for single phase, understand (been wrong before though) that for a single phase induction motor to be a generator the slip has to be positive, meaning the RPM has to be high enough to be above line frequency for the number of poles (e.g 4 pole induction motor above 1800 RPM if 60 Hz maintained). What this says is that if the engine is stalling out cause it cant drive the generator, a single phase induction motor with flywheel will help (cause the gen frequency drops way below 60 Hz). If the engine isnt apprecaibly lugging down to a slower speed and the trip is due to overcurrent, then a single phase motor with flywheel wont help.
There are also other factors that are beneficial for having other single phase motors on the line, such as power factor not dropping to near zero during single motor start, etc. but probably beyond the scope of this discussion.
Edited 2/28/2006 10:13 pm ET by junkhound
Excellent tip Junkhound. I'll use that someday when were trying to get a compressor started.
blue
perhaps you can find a smaller VFD to start the thing..
.but those may not function too well on your generator output either.., since it can't maintain the frequency under a big load
Thanks a lot guys. If I understand correctly, sounds like the electronic device to simulate a soft start is the solution. But, before that, I'll try the pulsing technique. That sounds sufficiently low tech for my feebel brain to handle.
I sure appreciate all the answeres
Stef
"It should draw 760x5= 3800 watts. BUT, the sucker draws 63 amps when it starts. The genny runs it for about 3 seconds, and then shuts down."
The 5 hp 3600 rpm motors Baldor shows in their catalog have a nominal full-load efficiency of .83, and a power factor of .99 (they obviously have a run capacitor), so full load current would be (5 x 746)/(.83 x .99 x 230) = 19.7A, and 4531 volt-amps (VA) at 230V (or 4486W at .99 PF).
They also have a locked-rotor Code letter "G", which translates to 122A to 134A at 230V. No wonder you can't start it. The low current reading you're getting may be the highest intermittent (or surge) current the genset can produce, and probably at very severe voltage drop, or your meter is slow.
I'd suggest rigging a mechanism to slacken the belts, then tension the belts after the motor starts, perhaps with a hinged motor mount. The genset will probably be able to start the motor alone, with no connected load, then run the planer after a few seconds recovery time from motor starting. You could also start a small motor, then use it to spin up the main motor and cutterhead.
Be seeing you...
Edited 3/1/2006 2:45 pm ET by TKanzler
Your response led me to sorta remember some thing from the past. Can't/wouldn't you be able to get a better start if there was another motor already running, say a 2HP motor. Doesn't this tend to balance out the initial draw. Or, is my memory going/ getting all mixed up again??? Or can't he increase the overload protection setting on the mag starter?
Thanks,
I'm going to check out the motor mount, cause that sounds like a good idea. Your watts calc pretty much jibes with mine. I think if I can just get it running the genny will keep up.
I'm also going to contact Powermatic and see what they have to say.
It is possible the high amp draw is because the machine is new, belts stiff, lubricant cold, etc. If I can get it running and sort of 'break it in', it may do better.
I knew I could count on your guys to come up with some good ideas.
Thanks again
Stef
First just make sure it starts without the belt on.
If ignorance is bliss why aren't more people
happy?
"It is possible the high amp draw is because the machine is new, belts stiff, lubricant cold, etc. If I can get it running and sort of 'break it in', it may do better."
Actually, current draw depends on the rotor speed, which in turn depends on applied load and voltage (lower voltage causes greater slip [percent speed reduction from synchronous] which in turn causes higher current draw). Since the motor starts at zero speed, the current draw will be maxed no matter what, and if the voltage is low while it's starting (which it will be with a small generator), it will take longer to get up to speed, causing high current draw for a longer period of time. Since that generator will not be able to deliver 120+A, the voltage will be pulled way down, the motor's torque curve will be severely depressed (as the square of the voltage), and with the cutter head belted to the motor, it will start slowly, if at all.
As the previous poster suggested, pop off the belts - if the motor starts, you're golden. Full load current for that motor should be well within the capabilities of the genset, and it would only pull that much if you work it hard. For edge jointing, very little power is needed, so very little current will be demanded of the genset. Be seeing you...
Do I understand you to say, if I can get the motor up and running to speed, and then ease in the belts it should work?
I tried the intermittent start up; motor on, motor off, motor on, motor off, etc, with no apprciable difference.
I guess I could rig a motor suspension system with an external lever, allowing me to ease the motor down on the belts.
Is that what you suggest?
Stef
That's what I'm suggesting. As another poster also suggested, take off the belts and see if the motor starts - if it does, you should be golden. The motor has a locked-rotor (or inrush) current of 120 to 130+ amps, which the generator will not be able to supply, but it might start alright with the load totally removed. I've started air compressors this way with my little 4k generator - causes a burp, but once running, no problem.
The motor in question, if I have the right one, requires about 4.5kW at full load, which is about one half of what your generator is rated for, and if the motor control is set up correctly, and you're careful not to overwork it, it should run without a problem (as long as you don't have voltage drop issues, which compounds the problem). You should be careful not to overload the motor even if powered off the grid, so using a gen set shouldn't force you to operate any differently.
I might suggest, if the motor starts fine with no belts, that you try planing material for a while with an ammeter attached (or a clamp-on), to get a feel for how hard you're working it. Some big wide-belt/drum sanders come with ammeters installed just for this reason. Be seeing you...
That's a good point about voltage drop. He should make sure he's got good beefy cables all the way between the two units, and keep it as short as reasonably possible. Not the place to be using a WalMart extension cord.
If ignorance is bliss why aren't more people
happy?
Thanks, guys
We brought the genny into the house panel with 6ga wire, and the 30amp circuit is wired with 10ga. There are no extension cords, and the cable off the machine appears to be 8ga, although its stranded, of course, so a little hard to tell.
I'll be trying all the experiments this weekend, so any more ideas you have, please keep them coming.
BTW, any thoughts on a lever, pivot arrangement to allow slowly lowering the motor on to the belts without going into the housing?
Stef
The simplest arrangement is to have the motor itself on a pivoted mount -- basically a board with a hinge at one end. A cam under the board can adjust the tension. But check out what's there for adjusting belt tension already. If, eg, the motor is on a slide, you could set up a couple of those toggle clamps used for jigs so they'd hold it in place -- release the toggles and slide motor forward to start, then slide back and activate the toggles to tighten the belt.
If ignorance is bliss why aren't more people
happy?
How about 290 dozen hamsters in exercise wheels, all linked to the outboard end of the motor shaft via pulleys& belts? Don't forget the centrifugal clutch so that the poor critters are disengaged when the motor itself gets going.
Iff'n I remember my power engineering right, there's 762 watts/horsepower and 1740 standard hmp ("hamsterpower") per hp. That's if they're fed Purina hamster chow (the hamsters, not the horses).
Cliff
.....but since the generator has been re-rated to 9Kw ......he is still about 3.5Kw short of being able to start that motor. even if he gets it running without a load, and trying to manually connect something turning at 1725 to a dead high - inertia load is not a good idea ...unless replacing parts often is an option.. the genny is to small to provide any surge adequate to get this equipment turning quick enough ...it is too small, even at sea level, to start this machine ....the only option that may work ...is limiting the current during start-up its 746 watts but who's counting.....:>)
.
What you are looking for is a magnetic starter with a "soft start" circuit built into it.
real quick,
how did you break-in this generator ?
what size was that load ?
did you run it at full load for at least 24 hrs? 48hrs.
are you burning oil at full load?
what is the normal load.......
does it have an exerciser or do you decide when to run it ? what is the load when it is just exercising?
A generator won'thandle an overload as well as a transformer does anyway
so, if you don't break it in at FULL load and do not run it periodically at full load, it will, in all probability not run well when you try to start some large load
Maddog,
It runs at full capacity, speed anytime it starts. It has about 400 hours on it.
Now I am getting depressed.
Stef
It doesn't burn oil. I'm not sure what an exercisor is, but it is controlled by the inverter. When the batteries get to 45 volts, it turns on, and runs full speed until they reach 55 volts.
S
Edited 3/10/2006 11:01 am ET by fatboy2
So this is actually a UPS??
If ignorance is bliss why aren't more people
happy?
No.
I must have failed to mention we are a solar home, off the grid.
When there is insufficient electricity in the batteries, the inverter senses that and takes control of the generator.
But your planer is running directly off the generator, right?
If ignorance is bliss why aren't more people
happy?
thats right. It has a complete separate setup from the panel the generator feeds. After that, for the house, there is a transformer steping it down to 120v and thence into the charge controller of the solar system.
Stef
All I'm trying to say is that an 11Kw generator is still a bit small
even if you were at sea level .....but you would likely have good luck trying to start it by pulsing as was mentioned early on......and since your de-rated gens surge capacity is not enough for that planer the best solution is to limit the amount of current going to the motor during start-up......which is what a VFD or a soft start motor starter can do for a couple hundred $.....also,adding a second set of pulleys between the motor and load and experimenting with pulley diameters... may allow you to keep the load light (this is sort of what was done on old lathes) and is similar to the suggestions hereThe questions about break-in and oil consumption would point to a unit that had never been installed or run correctly .....but 400 hours of running ....answers them