ammeter - 110v vs. 220v?
- Thread starter TRX
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Then what's neutral for?
Okay, power is (usually) generated in three phase. It comes out with three wires (legs), each carrying one phase, 120 degrees apart. It gets to town, the business district gets three phase to the breaker box; out here in the residential wasteland we only get two legs.
My box has two 110v legs, 120 degrees apart from the three-phase point of view, which is why 1+1 does not equal 2 when you're talking about alternating current, and I've seen math majors reduced to helpless confusion when confronted with the kind of equations used to describe what goes on down at the naughty bits, so don't try to explain it to me, I never got past trigonometry.
Each leg runs down one side of the breaker box; Code tells me to balance my loads on each side so the legs are evenly loaded. Each leg, and the outlet it services, is separate from the other, all the way back to the generator in the next county. Which is why you're not supposed to plug stereo components or computer equipment into outlets on different legs; you'll get hum or strange reboot problems sometimes.
So, I have a 220 socket, it has both legs, plus neutral and ground. Each leg of the 30A socket is on a *different* 15A breaker, though the handles are pinned together. The breakers are referenced to neutral, not tied together electrically. A load past 15A on either leg is going to trip a breaker; the handles are connected so they both disconnect together no matter which one trips.
I have no idea what's going on inside the motor; it could be mutant ninja squirrels for all I know.
[clickety] Here's something I should have looked at first; a chart showing the same motors wired either for 110 or 220. The 220 amp rating is half of the 110 rating at the same horsepower. https://cdn.automationdirect.com/static/specs/ironhorsesprs.pdf
So an 8.5 amp load on a 220 would be 8.5 on *each* leg, and I can measure either leg to neutral and assume (yes, that word) the other leg is also pulling 8.5 amps.
Maybe. I guess I'll find out when the meter gets here.
"That boy, he's about as sharp as a sack full of wet mice." - Foghorn Leghorn.
sberry
Banned
You are effectively using 2 wires instead of one as a supply. Its still 17 amps so to speak,,, just 8.5 down each wire at 240 There is no neutral here. The white wire in the 129 circuit is a grounded conductor till it gets back to service main and at that point the N carries any imballance. If there was equel load on the other 120V leg it would be zero and it would be 240 load.
sberry
Banned
Each leg is 30A on the breaker breaker.
The point is that 240 doubles the capacity of the wire.
We need some pictures or drawings here.
You don't measure current flow to neutral, voltage yes. There is no neutral in 240.
The point is that 240 doubles the capacity of the wire.
We need some pictures or drawings here.
You don't measure current flow to neutral, voltage yes. There is no neutral in 240.
FordTruckWench
Well-known member
Most residential wasteland gets only one of the three phases, not two.
Find a power pole that holds a residential transformer (and isn't some end-of-line partial hookup.) Going pole to pole, you'll typically see three or four high voltage wires. That's the three phases and an optional earthed/neutral conductor.
The primary side of the transformer will be fed by a dinky wire hooked to the anointed phase, and a second bare dinky wire running down the pole to a ground rod. If the high voltage has an earthed/neutral conductor, the second dinky wire also hooks to that.
The secondary side of the transformer will have three fat wires coming out - two hots and a center tap. The center tap will also be hooked to the wire running down the pole to ground. At your service entrance, you will think of the center tap as your neutral.
TRWham
Well-known member
Single phase service does get only one phase, but that still requires connection of the primary side of the transformer to either 2 lines (when a single phase or delta primary) or, sometimes, one line and a neutral, but even then to form that neutral we need connection to at least one more line (but usually if that's the case it's all three and the primary side is a wye).
Your 1 line system would be forced to use the earth as a return path to the power station, and the earth is a bad return path. When needed, neutrals throughout the distribution system return current to the 3 lines, and those then get it back home to mother alternator. There is no neutral that travels all the way back through distribution and transmission and back to the plant. If our houses only needed 240 V service, we would need no neutral anywhere in the system.
I think the confusion is rooted in our careless use of the terms phase and line (or leg). These things are not the same, but we use the terms interchangeably. A phase can only exist between 2 points at different potentials, thus single phase power requires connection to 2 lines at different potential over time.
ForceFed70
Well-known member
The meter you link to would work. Wire one of the hot legs through it.
Easier route would be to go with a cheap AC clamp style meter, plus you could use it for other purposes when needed. Something like this: https://www.ebay.com/itm/Digital-AC...m=152872713773&_trksid=p2045573.c100507.m3226
American Locomotive
Well-known member
The neutral is for 120v loads. 240v only loads don't need the neutral, and don't care about it. Some 240v loads (like clothes dryers and electric stoves) have a mix of 240v and 120v components inside them, so they need a neutral
No, this is not correct. The 3-phase power up on the poles is typically around ~14,000 volts +/- a few hundred volts. It's a "wye" configuration with 3 phases and a neutral. In residential areas, you have a pole transformer that's connected between a single phase on the pole and the neutral. This transformer has what's called a "center tapped" secondary. It has 3 connections to secondary low-voltage winding. One connection to each end of the winding, and one in the center. The secondary of this transformer has 240v across each end of the winding, and 120v from each end to the center tap point.
When you hook up a 240v load, there is nothing special going on. As far as the 240v load is concerned, that center tap point isn't even there. It's just seeing 240 VAC.
You can't measure current between a leg and neutral, because the motor isn't connected to neutral.
The power plant generator might be 3-wire 3-phase, but the 3-phase high-voltage power out on the poles (~14kv) is 4-wire 3 phase.
MikeF2316
Well-known member
I think the OP should take some of the early advise and get himself a cheap clamp on ammeter. Then all he needs to do is find a single hot wire somewhere and clamp it on.
And this is a valid way of measuring how hard you're working your machine. You may think you're at or near capacity, but it's hard to tell until you have some experience. The ammeter will tell you.
If you want more accuracy than a cheap clamp on, you can run the wire through the clamp multiple times. You just need to divide the current reading by the number of loops.
And this is a valid way of measuring how hard you're working your machine. You may think you're at or near capacity, but it's hard to tell until you have some experience. The ammeter will tell you.
If you want more accuracy than a cheap clamp on, you can run the wire through the clamp multiple times. You just need to divide the current reading by the number of loops.
TRWham
Well-known member
Exactly, but as I said, that neutral is on the distribution side and does not extend through transmission to the generating station. There are no neutrals on the towers carrying the transmission lines. There is no need for them.
ETA: Also, that distribution neutral only connects to the primary on the transformer to provide the incoming single phase power. It is not the same as the neutral that serves the house. That neutral is the center tap on the secondary of the transformer. It is possible to have electrical service with no neutral anywhere in the system until the last transformer serving the customer.
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Sure, except the only wires that aren't the armored cable to the lathe or inside the electrical box are the pigtails to the motor, which are both under the electrical box and behind the headstock, not visible from any position where I would be cranking on the tailstock handwheel.
Yeah, I would have to replace one of the motor leads to run it to a $5 permanent meter, but it doesn't seem nearly as sensible if I do it for a temporary $26 meter.
I'm pretty sure the small single phase ones don't use a starter and therefore rely only on the internal overload in the motor. Never had great faith in those. Even with a starter it seems like any motor that regularly gets overworked to the point of tripping overloads will have a short life.
Best to just keep from overworking the motor. Simplest way to do that is put a meter somewhere the operator can see it. Or know exactly what the machine is capable of and never exceed it, but again how do you know without some sort of feedback?
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Jim greengo
Well-known member
AntonLargiader
Well-known member
AntonLargiader
Well-known member
If you bog and stall the lathe, you risk breaking an expensive cutting bit and can ruin the workpiece (which could be worth more than the motor). Makes a lot of sense to be able to monitor this.
AntonLargiader
Well-known member
As for understanding the current draw at various voltages, it's worth clarifying that the motor doesn't just draw less when it's connected to 240. It's wired differently to do that. At its simplest (non-reversible motor):
Wired for 120: two 120V/8.5A windings in parallel. 8.5+8.5= 17.
Wired for 240: the same windings in series. 8.5=8.5.
Motors get a lot more complicated than that with more windings and direction changes, but the basic one is a simple one that's discussed on many sites.
https://www.eng-tips.com/viewthread.cfm?qid=423318
https://terrylove.com/forums/index.php?threads/electric-motor-wiring.25258/
Wired for 120: two 120V/8.5A windings in parallel. 8.5+8.5= 17.
Wired for 240: the same windings in series. 8.5=8.5.
Motors get a lot more complicated than that with more windings and direction changes, but the basic one is a simple one that's discussed on many sites.
https://www.eng-tips.com/viewthread.cfm?qid=423318
https://terrylove.com/forums/index.php?threads/electric-motor-wiring.25258/
sberry
Banned
I have a plug and cord for 120V to meter things and if it was really a deal would open the box or something to meter it for trouble shooting. This sounds like a hobby scheme to start with, is there really a reason to think we gonna run the snot out of it cutting till smoke rolls out the windows.
Plug it in and run it. This could be a concern for everything you own, the only stuff I really overloaded in my career was a couple grinders and a chop saw. Don't do that stupid,,, was the cure. I probably wouldn't have been watching the meter. Same for a couple grinders, changing brand helped.
I will agree there are lathes with meters and strict design parameters but is this something a guy has to run on the hairy edge. If its got a factory motor has enough power to run it like a sane man. Same for welding machines, they got a duty cycle but very few get truly cooked from it. I got a couple worked wayyyy wayyyy beyond rating and still work the same today as when I got them 30 years ago. Cant use them enough to burn them up or wear out.
Plug it in and run it. This could be a concern for everything you own, the only stuff I really overloaded in my career was a couple grinders and a chop saw. Don't do that stupid,,, was the cure. I probably wouldn't have been watching the meter. Same for a couple grinders, changing brand helped.
I will agree there are lathes with meters and strict design parameters but is this something a guy has to run on the hairy edge. If its got a factory motor has enough power to run it like a sane man. Same for welding machines, they got a duty cycle but very few get truly cooked from it. I got a couple worked wayyyy wayyyy beyond rating and still work the same today as when I got them 30 years ago. Cant use them enough to burn them up or wear out.
American Locomotive
Well-known member
There's more to it than that. It can be very easy to overload a lathe without intending to. Not all material cuts the same, and not all cutting tools cut the same. A 0.010" deep cut might seem to work just fine without any issue. Then you decide to go to 0.015" and the thing stalls, breaking an expensive carbide insert.
For example, carbide insert tooling requires much higher speeds and feeds to work well compared to traditional HSS manual lathe tooling. You work the machine much closer to its limits, and having an ammeter can be handy to indicate that you're getting close to the limit.
Is it a hundred percent necessary? No, but it's a useful item to add, and it requires very little effort to install and wire up. For someone just tinkering around cutting brass on an old southbend, it's probably not worth the effort. But if you're going to be doing some serious turning on tough steel, it can be very useful.
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