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Amps
Aug 29, 2005 6:28:02 GMT
Post by Dmitri on Aug 29, 2005 6:28:02 GMT
It looks like a giant Light Bulb! ;D Just in case someone wants to use it as a light bulb: it emits a lot of UV rays . Thanks for posting that Dmitri, as I've only ever seen the 'glow' of them from the windows just below the substation roof. They seemed to 'glow' a lot brighter (and greener) than that when under load from trains starting-up, so perhaps that's a photo of a "dormant" mercury-arc rectifier!! Maybe (I wonder if everyone noticed a link to the bigger picture - it is here: www.starfury.demon.co.uk/uground/images/belsize03.jpg). And one more page about MARs (with photos): www.electricstuff.co.uk/mercarc.html.
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Amps
Aug 29, 2005 11:20:19 GMT
Post by igelkotten on Aug 29, 2005 11:20:19 GMT
736w?? Perhaps horses in the UK are stronger on average than those in the rest of Europe!! ;D You are actually on to something here, Pete. The horse James Watt used as a standard when he started experimenting with the idea of a standard measurment for work was a stonking big Clydesdale used to power a mine pump, if I remember correctly. In other words, about as big and strong as horses ever get. Thus, most horses in the world are not capable of delivering a full horsepower.
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Deleted
Deleted Member
Posts: 0
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Amps
Aug 29, 2005 13:13:03 GMT
Post by Deleted on Aug 29, 2005 13:13:03 GMT
Back E.M.F. is a flow of current produced by a motor as a direct result of the function it provides. Back EMF is a voltage, such that back EMF is proportional to speed: i.e. double motor speed, double back EMF. Nothing to do with design- it's fundamental physics This just goes to show how much I've forgotten Thanks for the info - I thought I understood Back E.M.F., but I certainly do now. back EMF is a voltage in the opposite direction to supply voltage (as ikea says, because spinning motor can't help but act as generator as well), and current depends on net voltage, so bigger back EMF = lower net voltage = lower current when back EMF gets big enough it (almost) equals supply voltage so by definition cannot get any bigger. Now the motor just cannot get any faster. Electromagnetic field strength has not changed at all up to this point That was what I tried to say - apparently I mis-confused the concept of equalised voltage with the use of weak field. Thanks for the clarification. weak field acts on the current to the electromagnets. Big field = big 'push' so lots of torque for starting (and lots of current). Once up to speed not nearly so much 'push' is needed to maintain speed. What weak field does is to reduce current to electromagnets (there is a choice of how this is done, one is by field divert) and so the strength of the field itself , so the motor acting as generator does not have to push so hard against this field. Result is it can go faster before back EMF = forward voltage. Precisely! Thanks for helping me understand
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