Date: Sun, 22 Dec 2013 00:36:29 -0800
Reply-To: Roger Whittaker <rogerwhitt1@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Roger Whittaker <rogerwhitt1@GMAIL.COM>
Subject: Re: Van Dies while in motion
In-Reply-To: <1387692527.3678.YahooMailBasic@web160401.mail.bf1.yahoo.com>
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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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