Post by thread:[EE] Unusual alternator design?

On 10/3/05, Michael Rigby-Jones <spam_OUTMichael.Rigby-JonesTakeThisOuTbookham.com> wrote: > > > I managed to get it working (the rectifiers were toast), but I was > interested to know if this is a common or well known alternator > configuration? Does it have a name? Google isn't telling me anything, though > I'm probably not asking the right questions. > I think its called a dynamo. An alternator produces a DC current. Regards, Bob

Not in NZ. A dynamo is (usually - see below) DC, and alternator is AC, although it may be rectified to DC subsequently (as in a car). "Generator" is a more generic description which can encompass both although it seems more DC orientated in automotive use & AC orientated in power stations etc. (& Then there were the old wheel driven bycycle dynamos - which were AC, just to proove me wrong !) RP > I think its called a dynamo. An alternator produces a DC current. > > Regards, > Bob > -

At 04:40 PM 10/3/2005 -0500, you wrote: >On 10/3/05, Michael Rigby-Jones <.....Michael.Rigby-JonesKILLspam@spam@bookham.com> wrote: > > > > > > I managed to get it working (the rectifiers were toast), but I was > > interested to know if this is a common or well known alternator > > configuration? Does it have a name? Google isn't telling me anything, > though > > I'm probably not asking the right questions. > > > >I think its called a dynamo. An alternator produces a DC current. > >Regards, >Bob I don't see the original question. I think modern automotive 'alternators' typically include both a regulator (usually) to control the rotor current and a 3-phase bridge rectifier (6 diodes) connected to the stator windings. Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" speffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com ->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff

>-----Original Message----- >From: Spehro Pefhany [.....piclist-bouncesKILLspam.....mit.edu] >Sent: 04 October 2005 00:41 >To: Microcontroller discussion list - Public. >Subject: Re: [EE] Unusual alternator design? > > >I don't see the original question. I think modern automotive >'alternators' typically include both a regulator (usually) to >control the rotor current and a 3-phase bridge rectifier (6 >diodes) connected to the stator windings. Oddly enough I didn't receive my original question either, though clearly some people did. It was a bit of a long winded post on reflection so I'll shorten it: Single phase alternator with no direct electrical connection to rotor. Rotor has a coil, the ends of which are joined by a rectifier. Stator has two coils, one for the output, one to provide field. In this application (240v 50Hz 850W gas powered generator) the field was connected to the output coil via a simple current limiting capacitor. It simply not a configuration I have seen before, and I was curious if it had a name. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

> It simply not a configuration I have seen before, and I was curious if it had a name. FYI there seem to be a lot of these but without the wound rotor. That wound rotor should help with starting under load. It was probably fried by starting it under load. There is a schematic on the web where someone built exactly such a generator out of an old Briggs motor and a capacitor run ac motor (capacitor run ac is usually squirrel cage - your wound rotor is like a squirrell cage rotor but better). Peter

>From a purely technical standpoint yes you are correct. But I have yet to see an alternator without a bridge rectifier built into it. Regards, Bob On 10/3/05, Olin Lathrop <EraseMEolin_piclistspam_OUTTakeThisOuTembedinc.com> wrote: > > Bob J wrote: > > An alternator produces a DC current. > > No, it produces AC. That's why it's called an "alternator". > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com >

Mike, On Tue, 4 Oct 2005 10:36:26 +0100, Michael Rigby-Jones wrote: > Oddly enough I didn't receive my original question either Nor did I. > It was a bit of a long winded post on reflection so I'll shorten it: > > Single phase alternator with no direct electrical connection to rotor. Rotor has a coil, the ends of which are joined by a rectifier. Stator has two coils, one for the output, one to provide field. In this application (240v 50Hz 850W gas powered generator) the field was connected to the output coil via a simple current limiting capacitor. > > It simply not a configuration I have seen before, and I was curious if it had a name. I've certainly never seen or heard of it either - do you know how the coils are arranged (field on one side, output on the other, or interleaved, for example)? How many poles are there? I think the capacitor is probably for DC blocking rather than current limiting, or possibly give a bit of smoothing when the current / magnetic field reverses... I wonder if the rectifier is to provide a sort of reverse-commutation, so you get something like a sine wave rather than half-wave rectified (I know this sounds counter-intuitive, but it's that sort of arrangement! :-) Was there some base excitation? It must have either electrical feed or a permanent magnet somewhere, or it sould never get started. I don't suppose you put a 'scope on the output? I'd be fascinated to see if it manages a sine wave. Cheers, Howard Winter St.Albans, England

>>> An alternator produces a DC current. >> No, it produces AC. That's why it's called an "alternator". > From a purely technical standpoint yes you are correct. But I have > yet to see an alternator without a bridge rectifier built into it. Even with the (commonly 3-phase) bridge rectifier, alternator output varies to zero so frequently (more than once per revolution) that I would have to call it AC. At a minimum, I'd call it folded AC. The vehicle provides inductance (wiring harness) and capacitance (battery) to smooth it out to usable DC. Now an automotive generator(*) produced DC with some significant commutator noise superimposed on the output. Lee Jones (*) yes, I am (barely) that old; they had been phased out on new cars, but I had friends with older cars that still used them.

Lee writes: > Even with the (commonly 3-phase) bridge rectifier, alternator output > varies to zero so frequently (more than once per revolution) that > I would have to call it AC. At a minimum, I'd call it folded AC. > The vehicle provides inductance (wiring harness) and capacitance > (battery) to smooth it out to usable DC. Alternator output does not go to zero. The ripple current isn't even that big, about 15%. Remember, it's a three-phase generator. Ripple voltage is reduced by the battery and is much less than 15%. Inductance from wiring is negligible at operating frequencies. However if one or more diodes fail in the alternator, ripple shoots way up. Cheerful regards, Bob

>> Even with the (commonly 3-phase) bridge rectifier, alternator output >> varies to zero so frequently (more than once per revolution) that >> I would have to call it AC. At a minimum, I'd call it folded AC. > Alternator output does not go to zero. The ripple current isn't even > that big, about 15%. Remember, it's a three-phase generator. Oops. I was visualizing one phase in my head. I knew it was 3-phase but didn't overlap the outputs in my head. I stand corrected. Lee Jones

>From a purely technical standpoint yes you are correct. But I have >yet to see an alternator without a bridge rectifier built into it. Any alternator intended to produce AC output, as the one which started this discussion is, will not have any rectification in its main output. There may be rectification in control circuits for fields etc but these are auxiliary to the main intent. Alternator, as Olin says, is traditionally meant to refer to something which produces "Alternating Current" output = AC. Russell McMahon