AC motors

[Anonymous]

QUOTE: Originally posted by flee307

AC is a sign wave. DCC is pulsed DC that has a positive and negative component that is phase shifted. It's like a pulsed DC power pack that has pos and neg leads and ground. The pos is +12v from ground, the neg is -12v from ground, and they are 24v apart from each other. But they are still DC.

Now we get into similarities and differences between these terms, and pulsed DC and AC can look very similar. AC is not necessarily sine wave, any waveform (including rectangular pulses) that is one polarity for 1/2 its cycle and then reverses polarity for the other 1/2 cycle is AC. This is the type of pulses used for LANs (Ethernet etc) and is chosen so it will pass through transformers at computer interfaces without distortion. Pulsed DC alternates between one polarity only, then completely off, and has an average DC value that makes DC motors run in one or the other direction. DC pulses can also be sine shaped (MRC power packs) as well as square. It is also the type of signalling used for digital logic (TTL, CMOS etc) that does not have to pass through transformers. The bridge rectifier in a DCC decoder converts the AC pulses to DC to operate the decoder logic.

But a 50% pulsed DC wave will pass through a capacitor with some distortion, and if no DC offset is added afterwards it becomes AC since it becomes centered about 0 volts and has true positive and negative reversals. If a DC offset is added it stays pulsed DC. If it is not 50% duty cycle, it becomes AC with a DC offset (one polarity is a higher voltage than the other) so in effect it becomes both together.

The main difference between AC and DC is that if you filter pulsed DC with a large capacitor, you will still get a DC voltage at the average value of the pulses. But if you filter AC the same way, you get 0 volts.

If you look at AC or DC pulses on an oscilloscope they can look identical. The only way to know what you are seeing is if you know where ground (0 volts) is in relation to the waveform.

[Anonymous]

QUOTE: Originally posted by flee307

AC is a sign wave. DCC is pulsed DC that has a positive and negative component that is phase shifted. It's like a pulsed DC power pack that has pos and neg leads and ground. The pos is +12v from ground, the neg is -12v from ground, and they are 24v apart from each other. But they are still DC.

Now we get into similarities and differences between these terms, and pulsed DC and AC can look very similar. AC is not necessarily sine wave, any waveform (including rectangular pulses) that is one polarity for 1/2 its cycle and then reverses polarity for the other 1/2 cycle is AC. This is the type of pulses used for LANs (Ethernet etc) and is chosen so it will pass through transformers at computer interfaces without distortion. Pulsed DC alternates between one polarity only, then completely off, and has an average DC value that makes DC motors run in one or the other direction. DC pulses can also be sine shaped (MRC power packs) as well as square. It is also the type of signalling used for digital logic (TTL, CMOS etc) that does not have to pass through transformers. The bridge rectifier in a DCC decoder converts the AC pulses to DC to operate the decoder logic.

But a 50% pulsed DC wave will pass through a capacitor with some distortion, and if no DC offset is added afterwards it becomes AC since it becomes centered about 0 volts and has true positive and negative reversals. If a DC offset is added it stays pulsed DC. If it is not 50% duty cycle, it becomes AC with a DC offset (one polarity is a higher voltage than the other) so in effect it becomes both together.

The main difference between AC and DC is that if you filter pulsed DC with a large capacitor, you will still get a DC voltage at the average value of the pulses. But if you filter AC the same way, you get 0 volts.

If you look at AC or DC pulses on an oscilloscope they can look identical. The only way to know what you are seeing is if you know where ground (0 volts) is in relation to the waveform.

[Anonymous]

QUOTE: Originally posted by flee307

I see you live in AU, so before I can answer that I need to know if the water swirls clockwise or anticlockwise in your toliet?

Actually, the water does go down counterclockwise, and then gets shot back out again when one of us yanks flushes up here on top of the world. You know how water pressure works. Everything runs down hill, Thats why there's so much water down there.[;)]

[Anonymous]

QUOTE: Originally posted by flee307

I see you live in AU, so before I can answer that I need to know if the water swirls clockwise or anticlockwise in your toliet?

Actually, the water does go down counterclockwise, and then gets shot back out again when one of us yanks flushes up here on top of the world. You know how water pressure works. Everything runs down hill, Thats why there's so much water down there.[;)]

[GDRMCo]

QUOTE: Originally posted by emeraldisle

QUOTE: Originally posted by flee307

I see you live in AU, so before I can answer that I need to know if the water swirls clockwise or anticlockwise in your toliet?

Actually, the water does go down counterclockwise, and then gets shot back out again when one of us yanks flushes up here on top of the world. You know how water pressure works. Everything runs down hill, Thats why there's so much water down there.[;)]

It goes clockwise you dofus

[GDRMCo]

QUOTE: Originally posted by emeraldisle

QUOTE: Originally posted by flee307

I see you live in AU, so before I can answer that I need to know if the water swirls clockwise or anticlockwise in your toliet?

Actually, the water does go down counterclockwise, and then gets shot back out again when one of us yanks flushes up here on top of the world. You know how water pressure works. Everything runs down hill, Thats why there's so much water down there.[;)]

It goes clockwise you dofus

[Anonymous]

Actually it goes counterclockwise in the Northern hemisphere and clockwise in the southern hemisphere. So what's it do at the equator?

[Anonymous]

Actually it goes counterclockwise in the Northern hemisphere and clockwise in the southern hemisphere. So what's it do at the equator?

[Anonymous]

I've seen the little Tenshodo SPUDs (it stands for Self Propelled Universal Drive), but these are powered trucks with a motor driving both axles through a worm drive system - If anyone's seen the old Tri-Ang mechanisms the design is very similar. SPUDs are handy when you want to motorize something without intruding into the bodywork - in the UK they're often used to power diesel and electric multiple units as they allow you to fit an interior. However, SPUDs have no flywheel and I suspect they wouldn't last long before burning out if you added the amount of ballast you would need to haul a decent length train!

[Anonymous]

I've seen the little Tenshodo SPUDs (it stands for Self Propelled Universal Drive), but these are powered trucks with a motor driving both axles through a worm drive system - If anyone's seen the old Tri-Ang mechanisms the design is very similar. SPUDs are handy when you want to motorize something without intruding into the bodywork - in the UK they're often used to power diesel and electric multiple units as they allow you to fit an interior. However, SPUDs have no flywheel and I suspect they wouldn't last long before burning out if you added the amount of ballast you would need to haul a decent length train!

[Anonymous]

Hey Railroading_Brit I've been looking for them, where do you get them?

[Anonymous]

Hey Railroading_Brit I've been looking for them, where do you get them?

[Anonymous]

Well, I know of a few suppliers in the UK, but I'm not sure if they'll ship to the States. there's a supplier named Branchlines (email [e-mail]), who also offer the Black Beetle units which are very similar (these offer different wheelbases/wheel sizes to the SPUDs). There's also www.dckits.co.uk (Their main speciality is plastic kits for multiple units, but they also sell SPUDs/Black Beetles). I'd advise trying the latter first as they have a website - Branchlines only appear to have an email address!

[Anonymous]

Well, I know of a few suppliers in the UK, but I'm not sure if they'll ship to the States. there's a supplier named Branchlines (email [e-mail]), who also offer the Black Beetle units which are very similar (these offer different wheelbases/wheel sizes to the SPUDs). There's also www.dckits.co.uk (Their main speciality is plastic kits for multiple units, but they also sell SPUDs/Black Beetles). I'd advise trying the latter first as they have a website - Branchlines only appear to have an email address!

[Anonymous]

It is true, AC motors run at essentially one speed, determined by the number of electrical poles ususally on the stator, but this is true only for three phase synchronous motors. Straight poly phase induction motor's rpm will vary as the load is increased, difference in RPM called "slip". A commercial DC motor's speed is varied by changing the armature (ususally the rotating part) current, i.e., the magnetic field. Any wave form other than DC (none) is AC, even a lighting strike (fast time rise). AC locomotives generate AC which is rectified to DC and then "reconverted" to AC usually using a PWM (pulse width modulating) system quit similar to DCC systems. The motor RPM is controlled by the width (therefore the number of "pulses/second) of the pulses. The "frequency" of the number of cycles creates the singing noise heard in the earlier DCC systems. To be authentic, you'd need three phase on your "track" to use a straight AC motor (or a convertor in the loco).

[Anonymous]

It is true, AC motors run at essentially one speed, determined by the number of electrical poles ususally on the stator, but this is true only for three phase synchronous motors. Straight poly phase induction motor's rpm will vary as the load is increased, difference in RPM called "slip". A commercial DC motor's speed is varied by changing the armature (ususally the rotating part) current, i.e., the magnetic field. Any wave form other than DC (none) is AC, even a lighting strike (fast time rise). AC locomotives generate AC which is rectified to DC and then "reconverted" to AC usually using a PWM (pulse width modulating) system quit similar to DCC systems. The motor RPM is controlled by the width (therefore the number of "pulses/second) of the pulses. The "frequency" of the number of cycles creates the singing noise heard in the earlier DCC systems. To be authentic, you'd need three phase on your "track" to use a straight AC motor (or a convertor in the loco).

[Anonymous]

i stand corrected...thats what i get for answering questions when im half asleep...99% of my experience was in 3 phase repair and that is what my answer was based on but FLEE pointed out my error...sorry for the bogus answer i see there are several people that have more elec. engineering knowledge than me and i will leave this to them.....scott

[Anonymous]

i stand corrected...thats what i get for answering questions when im half asleep...99% of my experience was in 3 phase repair and that is what my answer was based on but FLEE pointed out my error...sorry for the bogus answer i see there are several people that have more elec. engineering knowledge than me and i will leave this to them.....scott