Dear enerwise

As my good friend Stalaslous says -
Yuh I luvs dis vheel ting - but vhill vhe akcjuile goes much fastur- den
vhe deed on sleds ?
Faster den dat hoars?
Laughing - he concludes - den vhe past hour shelves...:)

Regards

On Saturday, December 21, 2013, Keith Hughes wrote:

>
>  ------------------------------
>
>  Date:    Sat, 21 Dec 2013 20:56:20 -0800
>  From:    Stuart <ve3smf@YAHOO.COM <javascript:;>>
>  Subject: Re: Van Dies while in motion
>
>  Ref:=C2=A0
> http://ecmweb.com/design/highs-and-lows-motor-voltage=0A=C2=A0=
>  =0A"To drive a fixed mechanical load connected to the shaft,
>  a motor must d=
>  raw a fixed amount of power from the line. The amount of
>  power the motor dr=
>  aws has a rough correlation to the voltage 2current (amps).
>  Thus, when volt=
>  age gets low, the current must increase to provide the same
>  amount of power=
>  . "=0A=C2=A0=0A"The Highs and Lows of Motor Voltage=0AMay 1,
>  2000 12:00 PM,=
>   By Ed Cowern, P.E.=0AOperating a motor at the "outer
>  limits" of its voltag=
>  e requirements reduces its efficiency and causes premature
>  failure.=0AThe e=
>  conomic loss from premature motor failure is devastating. In
>  most cases, th=
>  e price of the motor itself is trivial compared to the cost
>  of unscheduled =
>  shutdowns of processes. Both high and low voltages can cause
>  premature moto=
>  r failure, as will voltage imbalance. Here, we'll look at
>  the effects of lo=
>  w and high voltage on motors and the related performance
>  changes you can ex=
>  pect when you use voltages other than those noted on the
>  nameplate.=0AEffec=
>  ts of low voltage. When you subject a motor to voltages
>  below the nameplate=
>   rating, some of the motor's characteristics will change
>  slightly and other=
>  s will change dramatically. To drive a fixed mechanical load
>  connected to t=
>  he shaft, a motor must draw a fixed amount of power from the
>  line. The amou=
>  nt of power the motor draws has a rough correlation to the
>  voltage 2current=
>   (amps). Thus, when voltage gets low, the current must
>  increase to provide =
>  the same amount of power. An increase in current is a danger
>  to the motor o=
>  nly if that current exceeds the motor's nameplate current
>  rating. When amps=
>   go above the nameplate rating, heat begins to build up in
>  the motor. Witho=
>  ut a timely correction, this heat will damage the motor. The
>  more heat and =
>  the longer the exposure to it, the more damage to the
>  motor."=0A=0AAnother =
>  source from the same author...=0A=0ARef:=C2=A0
> http://www.motorsanddrives.c=
>  om/cowern/motorterms12.html=0A=0A" =0ALOW VOLTAGE=0AWhen
>  electric motors ar=
>  e subjected to voltages, below the nameplate rating, some of
>  the characteri=
>  stics will change slightly and others will change more
>  dramatically. A basi=
>  c point is, to drive a fixed mechanical load connected to
>  the shaft, a moto=
>  r must draw a fixed amount of power from the power line. The
>  amount of powe=
>  r the motor draws is roughly related to the voltage times
>  current (amps). T=
>  hus, when voltage gets low, the current must get higher to
>  provide the same=
>   amount of power. The fact that current gets higher is not
>  alarming unless =
>  it exceeds the nameplate current rating of the motor. When
>  amps go above th=
>  e nameplate rating, it is safe to assume that the buildup of
>  heat within th=
>  e motor will become damaging if it is left unchecked. If a
>  motor is lightly=
>   loaded and the voltage drops, the current will increase in
>  roughly the sam=
>  e proportion that the voltage decreases.=0AFor example, a
>  10% voltage decre=
>  ase would cause a 10% amperage increase. This would not be
>  damaging if the =
>  motor current stays below the nameplate value. However, if a
>  motor is heavi=
>  ly loaded and a voltage reduction occurs, the current would
>  go up from a fa=
>  irly high value to a new value which might be in excess of
>  the full load ra=
>  ted amps. This could be damaging. It can be safely said that
>  low voltage in=
>   itself is not a problem unless the motor amperage is pushed
>  beyond the nam=
>  eplate rating.=0A=C2=A0=0AAside from the possibility of
>  over-temperature an=
>  d shortened life created by low voltage, some other
>  important items need to=
>   be understood. The first is that the starting torque,
>  pull-up torque, and =
>  pull-out torque of induction motors, all change based on the
>  applied voltag=
>  e squared . Thus, a 10% reduction from nameplate voltage
>  (100% to 90%, 230 =
>  volts to 207 volts) would reduce the starting torque,
>  pull-up torque, and p=
>  ull-out torque by a factor of .9 x .9. The resulting values
>  would be 81% of=
>   the full voltage values. At 80% voltage, the result would
>  be .8 x .8, or a=
>   value of 64% of the full voltage value.=0A=C2=A0=0AIn this
>  case, it is eas=
>  y to see why it would be difficult to start
>  =E2=80=9Chard-to-start=E2=80=9D=
>   loads if the voltage happens to be low. Similarly the
>  motor=E2=80=99s pull=
>  -out torque would be much lower than it would be under
>  normal voltage condi=
>  tions.=0A=C2=A0=0ATo summarize the situation, low voltage
>  can cause high cu=
>  rrents and overheating which will subsequently shorten motor
>  life. Low volt=
>  age can also reduce the motor=E2=80=99s ability to get
>  started and its valu=
>  es of pull-up and pull-out torque. On lightly loaded motors
>  with easy-to-st=
>  art loads, reducing the voltage will not have any
>  appreciable effect except=
>   that it might help reduce the light load losses and improve
>  the efficiency=
>   under this condition. This is the principle that is used in
>  the so-called =
>  Nola devices that are sold as efficiency improving add-on
>  equipment to moto=
>  rs."=C2=A0=0ALook at the digram in the article.=C2=A0 You
>  can see with a re=
>  duction in voltage, you get a corresponding increase in
>  current.=C2=A0 In t=
>  he given case, I suspect that the battery and/or the
>  alternator failed, wit=
>  h a resulting=C2=A0 voltage drop.=C2=A0 With several high
>  power devices, su=
>  ch as fans and lights, the current demands on the wiring
>  would have gone up=
>  .=C2=A0 Perhaps this caused overheating of the switch and
>  system failure.=
>  =C2=A0 This will only be answered when the original poster
>  tells what devic=
>  es failed.=C2=A0 State of the battery, alternator, switch
>  and other wirng.=
>  =0A=0AWhat do you think happened?=C2=A0 Your
>  thoughts......=0A=0ACheers!=0A=
>  Stuart=0A=0A________________________________=0AFrom: Larry
>  Alofs <lalofs@gm=
>  ail.com>=0ATo: Stuart <ve3smf@yahoo.com <javascript:;>>
>  =0ACc: vanagonlist a <vanagon@gerr=
>  y.vanagon.com> =0ASent: Saturday, December 21, 2013
>  10:33:59 PM=0ASubject: =
>  Re: Van Dies while in motion=0A=0A=0A=0AStuart, =0A=C2=A0
>  I'm afraid you ar=
>  e too far out on your limb. =C2=A0Your basic starting point
>  that any device=
>   will use a fixed amount of power is incorrect.=0AThat makes
>  the rest of yo=
>  ur argument and conclusions false.=0A=C2=A0 I am wondering
>  where you came u=
>  p with that premise.=0A=0ALarry A.
>
> Stuart, you are citing information for *A/C* motors.  DC motors, and other
> resistive loads do not have power factors, and operate under simple Ohm's
> Laws.  A DC motor has a fixed (abeit temperature variant to a degree)
> internal resistance, and when voltage drops, it will respond according to
> the relationship E=IR.  R is fixed, thus when E drops, I drops as well.
>  Power dissipation (Volt-Amps, i.e. E*I) decreases as voltage decreases. If
> DC power were invariant as you claim, then a headlamp bulb would glow with
> the same luminosity at 1 VDC as at 14VDC.
>
> Keith Hughes
> '86 Westy Tiico (Marvin)
>

--
roger whittaker 604.414.6266

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