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Author Topic: An amperage question  (Read 1440 times)

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Offline Quebecnewf

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An amperage question
« on: November 05, 2018, 05:15:21 PM »
The three hp (old ) electric motor that came with this old planer I bought says 13.5 amps. 

Ran it today with my 6500 watt Honda generator . Seemed to run ok but just wondering how many amps I would be pulling . I have no clue about this type of thing. .

Quebecnewf

Offline sawguy21

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Re: An amperage question
« Reply #1 on: November 05, 2018, 05:57:35 PM »
The motor will only use what it needs, in this case 13.5A. Startup draw will be considerably higher, probably 16-18A, which the generator will comfortably handle.
old age and treachery will always overcome youth and enthusiasm

Offline Quebecnewf

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Re: An amperage question
« Reply #2 on: November 05, 2018, 06:45:19 PM »
That's what I was thinking but not sure. When I throw on the motor which is starting the planer at the same time of course , the generator staggers but quickly come up and runs .

So I guess I will see in the spring if I leave it electric and run it with generator or switch this one to gas like my other 2 .

Like the idea of the generator at the mill site because it gives me electricity for other tools . 

Quebecnewf 

Offline beav

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Re: An amperage question
« Reply #3 on: November 05, 2018, 07:09:50 PM »
Volts x amps = watts
Probably 120v?
13.5 x 120 = 1620 watts
13.5 x 240 =3240 watts
The startup surge is significantly higher.
1 hp. Is roughly 750 watts

Offline muggs

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Re: An amperage question
« Reply #4 on: November 05, 2018, 07:44:27 PM »
The start up amps is about 5-8 times higher than full load amps. If the motor is not fully loaded it will not pull the 13.5 amps. It will pull less.  Muggs

Offline Quebecnewf

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Re: An amperage question
« Reply #5 on: November 05, 2018, 08:12:08 PM »
The motor is wired 240 so if I'm reading the post above correctly I should be pulling 3240 watts .?

So about half the output of my 6500 watt generator?

Quebecnewf


Offline Ianab

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Re: An amperage question
« Reply #6 on: November 05, 2018, 08:30:59 PM »
So about half the output of my 6500 watt generator?


Roughly yes. 

It will probably take all the generators power, for a second or so, to start the motor, but once it's running it should only be under about 1/2 load. 
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Offline muggs

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Re: An amperage question
« Reply #7 on: November 05, 2018, 08:35:03 PM »
I am surprised by your amperage. My book says a 3 hp  single phase is about 17 amps on 240 V. The 3 hp on my compressor is 19 amps.    Muggs

Offline Quebecnewf

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Re: An amperage question
« Reply #8 on: November 05, 2018, 08:43:40 PM »
It says 13.5 at 220 I think about double that if wired 110 .

Quebecnewf 

Offline esteadle

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Re: An amperage question
« Reply #9 on: November 06, 2018, 07:52:28 PM »
You could put a voltmeter on the generator and measure your voltage. That would make your current and power calculation more accurate. 

With motors, I use higher voltage wiring if I can. Lower voltages mean higher currents to produce similar power. Motors fail due to heat that melts conductors. Motors heat up due to resistances in the motor windings. Low, but non-zero. The heat produced is a function of the resistance times the current times the current, again (Pl - R * I^2).  Doubling (x2) the current produces 2 x 2 = 4 times the amount of heat in the motor. Best to keep it wired at 220/240 unless you have no option. 

With generators (constant Voltage, limited current), it's best to load the generator with the most demanding load first (anything with a surge current, like motors) and then add lower loads in descending order (heaters, lights, etc). This is called sequencing the workload. Avoids overload. 

It's also best to unload it the reverse way. taking away a large load from a power source can cause an imbalance that feeds back to source / motor that results in a stall. if not, it can surge voltage to the the remaining loads. this is called load shedding. Better to take away a couple lower loads first, and anything sensitive to surge (incandescent light bulbs, for one) then disconnect the main load.

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Offline 00frick

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Re: An amperage question
« Reply #10 on: November 06, 2018, 08:42:58 PM »
You haven't said how old this motor is or if it is a capacitor start motor. the old rule of thumb on the old motors was 3 times the amperage for starting. Starting load is a very short time. It is very hard to detect starting voltage with a voltmeter unless it is a good one. It would probably be easier on an older motor than a newer one. You seem to have a very nice generator since most Hondas produce a pure sine wave and are very reliable. Many regular generators without the extra filters (for lack of a better word) are hard on capacitor start electric motors (and anything electronic). Your Honda laboring for a moment should not be that big of a deal as long as it is not under any sort of load other than starting. If it is an old motor, I would bet that it would outlive the generator. What everyone else said is accurate.

Offline beav

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Re: An amperage question
« Reply #11 on: November 06, 2018, 08:55:01 PM »
The planer won't pull rated amps until a load is applied. When you try to hog 3/16 off that wide oak board you will exceed rated amps.
However you have a comfortable margin with your honda (best generator available).
The Honda will only surge to 6500 watts, they do print the constant watts on it, prolly around 5800 watts.
Compressors are a tougher load to start, quite often against the low air pressure set point

Offline Runningalucas

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Re: An amperage question
« Reply #12 on: November 06, 2018, 09:18:26 PM »
I don't have my '17 code book in front of me, but you always figure off of rated HP; rather than stated amps.  There are a lot of particulars from there; all electric motor design specific.   

There are a number of applications, or design, that allow for start up amps in excess of several hundred %.  I would easily think with a rated FLA of 13.5 amps under normal use, would see double the amps at inrush. 

Offline Satamax

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Re: An amperage question
« Reply #13 on: November 07, 2018, 12:53:11 PM »
Well, the last few years, i have researched bout big generators and load etc. 

The rule of thumb is,  3X the power of your load for the generator is best practice. So if you're pulling 

13.5 amps, X 220 volts, = 2970 watts. /0.89 (the cos phi)  3337 watts 

X3 10011 watts.  A 10kw generator should be perfect.  (not 10KVA) 

But if you use X2 the load, this is not too bad. 

A HP is 736 watts, and a KW is 1.36 HP. 

3337 /736= 4.53 hp. 
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Offline Quebecnewf

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Re: An amperage question
« Reply #14 on: November 07, 2018, 08:42:26 PM »
This is the motor we are talking about . It's an old motor but runs real smooth


 




And here is a pic of the motor tag 

Quebecnewf

Offline 00frick

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Re: An amperage question
« Reply #15 on: November 07, 2018, 09:59:40 PM »
The tag was what was needed to be seen.   

Offline 00frick

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Re: An amperage question
« Reply #16 on: November 07, 2018, 10:11:35 PM »
You will have to check your voltage that the generator is making as this will effect the wattage used. As stated by someone else, volts times amps equals watts. There is a difference in wattage if the Honda is making 108 or 123 volts or 215 or 241. Regardless, that is a PRETTY old motor. It is probably able to make 8 or 9 horsepower for short periods of time (yes, amperage will increase). These motors are no longer common like they used to be.  

Offline Runningalucas

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Re: An amperage question
« Reply #17 on: November 07, 2018, 11:51:41 PM »
You will have to check your voltage that the generator is making as this will effect the wattage used. As stated by someone else, volts times amps equals watts. There is a difference in wattage if the Honda is making 108 or 123 volts or 215 or 241. Regardless, that is a PRETTY old motor. It is probably able to make 8 or 9 horsepower for short periods of time (yes, amperage will increase). These motors are no longer common like they used to be.  
Not trying to school you, promise, but watts are a product of pure resistance.  Volt-amps, or Kilo volt amp is what motors are measured in to to comprehend their draw.  A Volt Amp is what's used for reactive loads; capacitive, or inductive.   The reason this distinction is made, is that 'apparent power'(think service factor), will show more apparent power used, than actual true-watt power.   You can adjust the load by incorporating capacitive reactance using VA calcs.

Offline mike_belben

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Re: An amperage question
« Reply #18 on: November 08, 2018, 11:59:19 AM »
Im not trying to school either of you, sincerely.. i mean it.  But to be purely scientific about it, empiracle evidence has proven that flipping on that motor contactor and apply a start load to the generator is like having the neighborhood fat kid jump into the radio flyer wagon hooked to your bike JUST as you are about to start up the bottom of that big hill to chase the ice cream truck that didnt see you waving your arms across the front lawn.  Hence why the governor says "ughh" outloud.  I mean, who can blame it under such circumstances?   

Not I sir.  Not I. 
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Offline Runningalucas

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Re: An amperage question
« Reply #19 on: November 08, 2018, 01:23:41 PM »
Im not trying to school either of you, sincerely.. i mean it.  But to be purely scientific about it, empiracle evidence has proven that flipping on that motor contactor and apply a start load to the generator is like having the neighborhood fat kid jump into the radio flyer wagon hooked to your bike JUST as you are about to start up the bottom of that big hill to chase the ice cream truck that didnt see you waving your arms across the front lawn.  Hence why the governor says "ughh" outloud.  I mean, who can blame it under such circumstances?  

Not I sir.  Not I.
crack me up!!!! lollollollol

Offline 00frick

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Re: An amperage question
« Reply #20 on: November 08, 2018, 08:05:13 PM »
 I do enjoy being schooled. That is why I am here. I truly do appreciate your comment on KVA. It is rarely spoken about as it is usually a utility company reference. My point was to calculate the amperage being used or needed vs. the capacity available.             


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