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Pressures seen for tough woods

Post in 'The Gear' started by DennisR, Dec 20, 2007.

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  1. DennisR

    DennisR Member

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    If any of you have a pressure gauge on your log splitter, then could you tell me what pressure you get when you split the following types of wood that is 16" long minimum:

    Hickory
    Black Walnut
    White Oak
    Northern Red Oak
    Water Oak
    Elm

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  2. computeruser

    computeruser Feeling the Heat

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    I'd think it would have more to do with the particular piece at issue than the species. I've seen ash with knots that was a bear to split and box elder or elm that popped right apart...
  3. DennisR

    DennisR Member

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    What I was getting at with this, is calculating appropriate horsepower demand for different species of wood to come up with RMS horsepower in a program I am making. So if someone wants an electric log splitter, rather than going out and buying a Ryobi or DR, they instead can simply replace their gas engine on their current log splitter they already have with the appropriate horsepower single phase induction motor. It's not as simple as saying: "All I have to do is replace my 5 horsepower gas with a 5 horsepower electric." NO! A 5 horsepower single phase induction motor can ruin the log splitter components because although it says 5 horsepower, it's meaning is CONTINUOUS. It can actually put out up to 10 horsepower while the pump may only be rated to take up to 8 gasoline engine horsepower for example.
  4. triptester

    triptester Feeling the Heat

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    The only calculation that needs to be made is matching the electric motor to the rated max. output of the pump. The hydraulic systems normally should have built-in relief valves. An oversize motor will not harm the pump as long as rpms and psi do not exceed pump specs.
  5. DennisR

    DennisR Member

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    "The only calculation that needs to be made is matching the electric motor to the rated max. output of the pump."



    Not quite. Its true for gas powered, not for single phase induction motors. You have to find the RMS horsepower.



    Here is a good explanation written by Ed Cowern:

    There are a great many applications especially in hydraulics and hydraulically-driven machines that have
    greatly fluctuating load requirements. In some cases, the peak loads last for relatively short periods
    during the normal cycle of the machine. At first glance, it might seem that a motor would have to be
    sized to handle the worst part of the load cycle. For example, if a cycle included a period of time where
    18 HP is required, then the natural approach would be to utilize a 20 HP motor. A more practical
    approach to these types of “duty cycle loads” takes advantage of an electric motor’s ability to handle
    substantial overload conditions as long as the period of overload is relatively short compared to the total
    time involved in the cycle.

    The method of calculating whether or not the motor will be suitable for a particular cycling application is
    called the RMS (root mean squared) horsepower loading method. The calculations required to properly
    size a motor for this type of application are relatively simple and are presented in this paper.
    The RMS calculations take into account the fact that heat buildup within the motor is very much greater
    at a 50% overload than it is under normal operating conditions. Thus, the weighted average horsepower
    is what is significant. RMS calculations determine the weighted average horsepower.

    In addition to reducing the size and cost of a motor for a particular application, RMS loading also offers
    the advantage of being able to improve the overall efficiency and power factor on a duty cycle type of
    load. For example, when an oversized motor is operated on a light load, the efficiency is generally fairly
    low, so working the motor harder (with a higher average horsepower), will generally result in improved
    overall efficiency and reduced operating cost.


    The rest of the article is here: www.motorsanddrives.com/cowern/motorterms9.html

    As the saying goes: "You cannot compare an apple to an orange".
  6. triptester

    triptester Feeling the Heat

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    Unfortunately with wood splitters the duration and horsepower requirements are unpredictable. What been used as a common comparison between gas engine and electric motors is to figure 1 hp. electric = 2 1/2 hp. gas.
    So when replacing a 5 hp. gas engine you would use a 2 hp. electric motor.
  7. DennisR

    DennisR Member

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    "comparison between gas engine and electric motors is to figure 1 hp. electric = 2 1/2 hp. gas.
    So when replacing a 5 hp. gas engine you would use a 2 hp. electric motor."




    It is approximate and is only useful for 3-phase NEMA Design B motors (NEMA design A would be 4 times) , NOT electric motors like you said meaning any kind whether it's AC or DC which is false. It really depends on the motor type, not some fancy approximation. I have come up with a particular single phase motor that meets the breakdown torque requirements, even under 25% voltage drop. It's 3 horsepower, and its number is 120341 from electricmotorwarehouse.com. It's a 240 volt only motor, but that saves on weight since it does not have windings for the low voltage of 120 volts (its not dual voltage compatible as already stated). So if anyone wants to replace their 6 horsepower or less gasoline engine, then this motor will be a good replacement.
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