Soldering motor windings

Gary

I would have used any kind of solder I had around for making the extensions to the windings. But, maybe this motor will get much hotter than I've expected. Still, if the wires are twisted together then soldered and shrink wrapped, there should be no problem with the motor even if the solder gets soft due to normal heat.

I assumed there would be some special need to phase the windings when they are re-connected. I'd like to hear more about how this project works out.

I'd give you a 1 or 2 HP 220vac 3 phase motor if you live close enough to Los Angeles (or pay shipping).

Jerry

If the motor gets hot enough to melt the solder, you've obviously got another serious problem with the motor.... I would think all the enamel on the fields would be charred at that temperature.... Regular electrical (rosin core) solder should be just fine... Ken.

The winding temperature in high temperature motors can reach about 155 C when the motor is running at full power. According to a catalogue I have in front of me, rosin-cored solder (Ersin Multicore brand) melts at 215 C, so you should be fine. Try to desolder the star point instead of cutting it off. If case anything goes wrong you want to have the maximum length of wire available. I once cut a star point for this reason and while bending the wires into a sutiable position for soldering one snapped, leaving me with a difficult job soldering a lead onto the remaining stub. So it's worthwhile keeping as much wire as you can, and try not to bend the wires more than necessary.

Best wishes,

Chris

155 deg C?? Wow... I think tho that those would be special-purpose motors. I've never seen *any* machine tool, elevator, or any other motor get so hot you couldn't comfortably put your hand on it. Altho I had a Seagate 225 20 mb (!) hard drive you fry on egg on... :)

Also, motor wire is insulated w/ varnish or sumpn, so you gotta scrape that off as well, if making a brand new joint. Sep flux (in addition to rosin core, etc) has always helped me.

I'm curious tho as to the reasons/benefits of changing to/from star/delta in a motor. Is this for a voltage change? Some other reason?

Is it clear how to do this on any three phase motor?

---------------------------- Mr. P.V.'d formerly Droll Troll

It is *very* common to see motors rated 100C nowadays. See how long you can put your hand in water at that temperature!

Jim

They are. I quoted that figure because it's the highest you're ever likely to see in a motor. Most motors wouldn't run with a winding temperature of more than 100 C. But the winding temperature can be quite a bit higher than the temperature of the casing. For a good discussion of this subject see the book "Electric Motors in the Home Workshop" by Jim Cox.

It's usually so you can adapt a three phase motor to run from a single phase supply. Each winding needs approximately 240 V across it. In the star configuration a 415 V supply is required as the windings are connected end-to-end (it doesn't require 480 V as the AC voltages across the windings are 120 degrees out of phase). In the delta configuration each winding is connected directly to a phase of the supply. To "fake" a three phase supply, connect a single phase supply to two nodes of the delta and a capacitor between the third node and one of the supply nodes. Usually two different capacitor values are required for starting and running. If you've got a motor which is wired in the delta configuration for 415 V operation, you can't do this.

It's not always clear but if you've got a motor you want to convert, tell me a bit more about the terminations and what the data plate says and I'll try to help.

Best wishes,

Chris

As Chris has stated, its for a voltage change.

3-phase induction motors have 3 windings to which the 3 input lines are attached. Here in UK the voltage between any 2 input lines of a 3-phase supply is approx. 415v. If one end of each of the 3 windings are connected together (to make like a Y or star) then the 415v between each line is sent through 2 windings (from the input to the star point to the output), and each winding experiences a little more than half of the 415v. It actually 'sees' approx. 415 divided by root3 = 240v, because the phases are 120 degrees apart.

A single phase supply (normal supply in a house) uses just one of the 3 lines, plus a neutral line. The voltage between the line and neutral is approx. 240v, which, strangely enough, is the same as that 'seen' by each winding in the motor above (well its not strange really, 'cos its for the same reason).

In order to run a 3-phase motor on a 1-phase supply you have to generate the other 2 phases, and for that you need either a converter or an inverter (there are pros and cons for each). Either way, you also have the problem of the voltage change. If you split the star point and reconnect the windings so that the end of each winding is connected to the start of the next one (to make a triangle, or delta format) then each winding will 'see' the full 240v and the motor will on 240 3-phase the same as it did on 415v.

Most modern 3-phase motors have both ends of each winding exposed on the terminal block. You can then easily join the 'output' ends together to make a star configuration, or join each output end to the next input to make a delta form. Some motors don't have this convenience and the star point is buried inside the motor somewhere. This makes it much harder to convert.

I hope this helps.

Gary

Have you ever done this "convert star to delta"? I'd be concerned with phasing the 3 windings when reconnected. I suppose you are prepared to properly re-connect the windings.. But, I'd like to know more about how critical it is to *properly* phase the windings when reconnected.

Also, I get stuck with my thinking that the current into this motor will be twice what it was with double the voltage. I think you have already figured all that out and, of coures you arent really halving the voltage.

Anyway, I do want to hear how this project works out.

Jerry

Hi Jerry, I've done it now. I cut 2 of the wires at the star point so that I could use what was the neutral as one winding end, and then extended the 2 cut ends by splice crimping additional bits of wire. Then, by using a continuity meter (ohm meter), I matched and marked each new end with the original input terminals: this showed that each winding had a resistance of barely 10 ohms. I then connected the end of winding 1 with the start of winding 2, the end of 2 with start of 3, and the end of 3 to start of 1. Then, to check that all connections were reasonable I measured the resistance across each pair of terminals and got about 6 ohms, which seemed acceptable 'cos it was equivalent to resistances of just under 10 and 20 ohms in parallel. I then reassembled the motor and tried it out. It works fine.

The only critical things are: the original input terminals are used as line inputs, each winding end is connected to a winding start that is not its own, and each terminal ends up with 1 winding start and 1 end attached. The order is not important: the worst that can happen is that the motor runs in reverse, and if that happens you just reverse any 2 input lines. You can change the run direction of any 3 phase motor by swapping any 2 input lines.

When switching from star to delta, the current would be twice IF the voltage remained at 415, but its now reduced to 240 so the current remains the same.

Great. Problem solved. Are you running off a 240 V three phase supply or a 240 V single phase supply with capacitors? I've been running a 1 3/4 hp mechanical hacksaw off a single phase supply with capacitors and it works fine. Only problem is that the relay which switches capacitors has been playing up recently. Maybe I need a beefier one...

Chris

I'm running off a 240v single phase supply via an inverter to give me control of the motor speed as its in a miller. It is variable from barely moving up to twice normal speed. The displayed frequency going from 1Hz to 100Hz.

Gary

I wonder if the current in the motor would be the same. I was thinking that a given power from the loaded motor would require twice the current with half the voltage. I dont say that this is going to be a problem. I just thought it should be considered.

I'm glad to hear that the phasing of the windings is something I can figure out when/if I try this someday. Thanks for the info.

Jerry

Although peak winding temperature may range as high as 150deg C in a high temperature motor winding this is only the temperature reached deep in the winding at full load at minimum rated input volts and maximum rated ambient temperature. The temperature at the outside of the end turns of the windings is much lower than this but can still be over 100 deg C.

With the wires twisted together (i.e. no mechanical strain on the solder) ordinary 60/40 soft solder is quite O.K. but the insulation is a bit iffy. In most motors the insulating sleeves, tapes and binding string are enveloped in an overall high temperature varnish which provides both electrical and mechanical protection. Without this protection care is needed in insulating and securing the remade joints.

Most black PVC insulating tapes are only rated at 80 deg C. Yellow polyester and fibreglass tapes have higher temperature ratings but are not easily available. The simplest solution is to wrap with multiple layers of plumbers teflon tape and finally secure to the winding with string. If necessary use a dab of epoxy resin to secure any loose ends but use the one hour or overnight cure variety as most of the fast cure 5 minute varieties soften at pretty low temperatures.

Phasing is very straightforward. Use an ohmmeter to sort the windings into start and finish pairs (starts are of course the three separated star points), Then produce a triangle of output connections by connecting the finish of one winding to the start of the another. It doesn't matter which winding is connected to which. The only thing that matters is that the finish of one winding must connect to the start of another.

Jim

Thanks Jim

A guy can learn alot, without even studdying, from information like your post.

Jerry