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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
Comments: To: Keith Hughes <keithahughes@yahoo.com>
In-Reply-To:  <1387692527.3678.YahooMailBasic@web160401.mail.bf1.yahoo.com>
Content-Type: text/plain; charset=ISO-8859-1

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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