Test Bench Circuitry

How many motors; how many total amps? The 16 AWG wire is good for about 10A, depending on what it is adjacent to, ambient temp, etc.

Are the outputs of the transformers also in parallel? If so, make sure you have not connected any of the transformers in 'reverse' with respect to the others. That would make the wire quite warm.

Now how would one know that unless they'd done it themselves?

Voice of experience. Ever put one battery cell in backwards in a four cell flashlight (torch).

Actually, reversing one or more transformers would only make the transformers (and the wires joining the transformers) quite warm (to say it mildly). The wires going to the relay and distribution block and motors would actually run cooler, because the reversed transformer(s) would pull down the output voltage of the correctly wired transformers.

Your point is still correct! A reverse-connected output will sooner or later release the magic smoke!

Is there a drawing of the circuit?

You say "assorted shaded pole motors", which would suggest that some carry more current than others, yet you say they are "rated at 1.7A locked rotor", which would indicate that they are all identical. Are they "assorted", or just "several"?

Apparently you have 11 small transformers connected in parallel at both the inputs and outputs, supplying current to a single relay, which supplies current to a single distribution block, and then to the motors.

There is always some variation from one transformer to the next, even when all of them were produced in the same batch. The transformer with the lowest voltage output won't contribute any current until the output voltage of all the others have been lowered by current demand to that low voltage. The transformer with the highest output voltage will be supplying the highest current, and will be the first to overheat, and possibly fail.

In fact, if there is more than a very tiny variation in the output voltages of the various transformers, at light load, those transformers having a lower output voltage will actually be using current from those having higher voltage, rather than supplying current. This translates to heat and wasted energy...

Larger transformers are nearly always more efficient than smaller ones of similar design. You'd be way better off getting a single larger transformer having the combined output current of the set of 11 small ones.

If you are doing this because you already had a bunch of small transformers on hand, then watch the temperature of every transformer individually, to be sure they don't overheat.

Interesting, you could well be right. No argument from me....

I was (wrongly) taking it that the transformers only had their primaries in parallel, but not the secondaries!

If it is as you say, then the smoke will get released shortly!!! Problem solved!!

I find running transformer secondaries in parallel, even if phased correctly, to be a really bad, bad choice. And seeming unnecessary too....

But, assuming all are phased correctly, if some are actually outputting even a tiny amount of voltage higher than the others, even say only 0.25 volts. These transformers will "grab" more load and could run hotter.....

Naturally, the more significant the voltage difference (measured solo, unloaded and using a digital voltmeter, not analog, would possibly help to see any small differences better), the larger the "share" of the load will be grabbed....

This could also easily be checked using say a clamp AC ammeter when running, to see what the exact currents are actually running through through each transformer secondary. Naturally, at a point before they are paralleled to the others....

A check at each transformer primary would also be a good idea too I feel. That might show a load at saturation for some....it may also bring some interesting readings too....

I guarantee a shock! (Pun intended!!)

Whats your take on my theory?

Something like this maybe, will surely help further and is being sold for under US$30:-

As I indicated, it would be much clearer if we had a circuit diagram of some sort, but since he says "...a relay switch and powers a distribution block..." (both singular, and "distribution" indicates multiple connections to a single point), I have to assume the transformers are paralleled at both input and output.

Yes, monitoring the output (and input) currents would indeed be wise. I paid a lot more than $30 for my clamp meter, but I don't doubt that it's possible to get one for that price, and it would definitely be a good investment for Drew if he doesn't already have one.

To Drew: If you are going to use a single relay, it would be much better to put the relay on the input side of the transformers. The current there is only 1/5 of the output current, so you can use a lighter duty relay, or the one you use will last much longer. Also, putting the relay on the inputs will turn everything off. If the relay is on the output side, when it is in the open position, the transformers are still connected to power and are wasting energy. This is especially true due to variances between transformers, so it would be entirely possible for one or more transformers to burn out if the system was left plugged in with the relay in the open position.

I forgot to address another issue: He says "a daisy chain of quick connects". This implies a series connection of the motors (doesn't it?). If the motors are in series, then each motor gets a fraction of the total voltage, so they would have to be 24/11= 2.2V motors, and all 11 would have to be identical and have have identical loads. Increasing the load on any one motor would slow it down, reduce its back EMF, and increase the voltage applied to the rest of the motors. Since shaded pole motors are single-speed motors (AFAIK), even a relatively small increase in the load could completely stop the motor. Increasing the load on several of the motors, but not on others, could easily exceed the voltage rating of the lightly loaded motor(s). I've never seen a shaded pole motor that ran on such a low voltage, but that doesn't mean they don't exist. I suspect that "daisy chain: was a poor choice of words, and the motors are really in parallel. In parallel, the size of the motors and the amount of load can vary, with one motor having very little effect on the others.

Drew K, you need to answer some of the questions you get asked.

I agree, that clarifications are in order. And I also agree with Andy Germany, and DK Warner that having all these transformers in parallel connect is a bad idea. Who came up with that? A predecessor? Put them back as individual feeds to each individual motor with each motor having its own switch, OR if the motors all need to be tested at the same applied voltage, put in ONE over sized transformer, but supply each motor with its own switch. Do away with the distribution block unless needed for terminating leads to the motors. Over size the motor leads, as you do not want variable potential drops under load that results in some motors being tested with lower voltage, some with higher, based on lead resistance variations.

I don't have a good way to draw the circuit so here is a picture of the transformer block and the motors. I will try to answer the other questions when I am back on the computer.

Itonly let me choose one picture.

Yep. It appears these are all parallel, including the transformers, and the concurrent (forgive the pun) output of the transformers feeds the "concurrent" to the motors. There will be a weak link in the electrical supply chain "upstream" of the motors. Not good. You need something better than this Rube Goldberg setup (or a new job).

Suggestion: Regulated AC power supplies. These should be able to supply the same voltage, frequency, and current, within tight specified tolerances, and not break the bank purchasing them. Each one would then independently supply its own motor.

The way it is now is just BS, and if your boss designed it, tell him I said he is a boob.

I can put in a request for one larger transformer, but it is not likely that I will be able to use one transformer per motor (there are 27 motors in this test and often 30 or 40).

This is my design with the only available parts on hand. I had it set up previously with only 6 transformers but suffered a significant voltage drop.

Drew K

Oops. Then you have my apology for the boob remark, and condolences on availability of the best test equipment. I like the idea of one larger transformer, especially if it had some sort of controls associated with it to limit voltage droop, and constant current ability to each motor.

Meh, I resemble the boob remark. I have let the smoke out of circuits in the past and burned off a few quick connect terminals by forgetting to shut off a circuit when changing it around.

Electricity is not the best field to be self taught in, but I do what I can.

Drew K

Beautiful and SO simple. GA.

Your only error was to forget the heat shrink tubing over each mains connection!!

Just funning with you!!!

Be sure to use color-coded heat shrink also!

Can't you see that I did! ...and I shrank the tubing with a proper heat gun, not the soldering gun.

I only used black and red at the output to more closely agree with Drew's wire. I used the European input colors, partly because the drawing was started using part of a previous drawing, but mostly because it's a pain trying to make white wires visible.

The wire was left over from a previous DC project I prefer to use white and black wires for AC, or just duplicate the colour scheme I am repairing (I have done more repairs than creations).

Drew K

Actually, I don't like the idea of one larger transformer! Accidentally shorting out a 24V transformer capable of putting out 68 Amps could do serious damage to the transformer, wires, operator, etc.

If each small transformer supplies current to only a few motors, then accidents are less likely to be dangerous.

Drew: If you do get one large transformer, make sure you use eye protection when working near this. Sparks from high current can send droplets of molten metal flying pretty far!

Fuses or breakers could be included....as could an RCD.......that wiring is just "lying in wait" to kill someone!!

I just now noticed your quote at the bottom of your post. I like it!

Thanks.

I am on some other forums where Trolls abound, it keeps most of them quieter, if not fully quiet!!

Here also!!

I also find it to be very true as well.....

I changed it about 4 weeks ago.....but I forgot to have a trumpet fanfare!!

I forgot to say, if you wish to use it simply go ahead, no problems.....

For a second I thought you liked my quote :-/

I added it a long time ago, I think it was after Obama was elected while I read Atlas Shrugged by Ayn Rand, I think the quote is just as valid today for a whole different set of terrifying reasons.

I do agree with Andy Germany's quote :-p

Drew K

Sorry! I've looked up John Galt at least once in the last year or two, after seeing it quoted, either in your posts or elsewhere, but I don't remember what I found.

Virtually all of my (very slow) reading is of scientific/technical nature. When I do try to read political or sociological stuff, I can't keep track of who said what... The fact that I rarely watch TV may contribute to that weakness.

Ayn Rand wrote the story a very long time ago, there is a made for tv movie I had to download that tries to convey what the story says.

The basic plot is the government is going socialist and forcing companies to give smaller companies a fair chance to grow by matching bids (no matter quality or quantity). John Galt is an engineer who disappeared but had been experimenting on a fantastic new motor that would make internal combustion and steam obsolete (the author describes what we would call an over-unity device but it is part of the plot and you have to accept it to enjoy the book) Many inventive, resourceful and hard working business leaders are also disappearing and you get hints that they are electing to remove themselves from the society that is turning into lemmings following the socialist movement.

It is a good read if you just hit the 'I believe' button on the science fiction the author uses to demonstrate the difference between the two ideals. The story is set when the transcontinental railroad was still the biggest technological achievement of the time so it will seem a bit dated today and the movie gives a modern take with mobile phones mixed with some classic styles.

There is a common saying in the book when someone asks a question without a clear answer the reply is "who is John Galt?"

The really strange thing for me is I am kinda liking that Sanders guy who claims to be a socialist but I don't hear him saying take from one and give to another, I hear him say pay the workers what they are worth. That I can get behind because all over the world I see people working hard to make products or services that only seem to get the people at the top profits.

Drew K

Sanders also is promising all the free stuff - free medical care, free college tuition, free lunch. He never seems to mention how to pay for all this, except by saying he wants to majorly increase taxes on the "rich". To cover his plan, anyone making over $75,000/year will wind up falling into the "rich" category, although NOW, he only wants to tax the "super-rich" 1% folks, but they already pay like 35% of all taxes paid. The bottom 45% pay less than 10% of all taxes paid. I like Bernie as much as the next guy, and standing next to H. Clinton, he stands honest and almost gigantic in his demeanor, some people could trust. But I would not vote for him for even a $1,000,000 payoff.

A Democracy will always vote itself a pay raise, and spend itself out of existence (loose paraphrase of comments from John Adams.) "Gentlemen, we have given you a Republic if you can keep her."-Benjamin Franklin. Americans: Your Liberty is once again being usurped by an overly powerful central government, it is time to bring power back to the people. Take back your birthright, get out and vote!

I like what he says about raising wages, that is the tide that raises all boats because if you give the common people more money they will spend it. Give the 1% more money and they will hoard more than they spend because they can't spend what they already have. If the industry won't self-regulate then someone needs to pry the pennies from the 1%.

Everyone likes to parade Bill Gates with how much money he gives to charity and such. I support giving money to research that can pay back with results, but if Gates had just paid his company workers more then they would have spent it and he wouldn't have to complain about taxes.

Follow the money, do CEO's deserve this big of a share of the profits?

Drew K

I'm not as much concerned about the 1% as I am about huge corporations. When huge companies like GE can figure out ways to pay NO taxes whatever, something is wrong!

My other complaint is the IRS. If we had a consumption tax and/or a VAT, we could get rid of the IRS, and (hopefully) force all those accountants and lawyers to do something useful.

I agree with making tax lawyers find better work, but not sure VAT is the best solution. Costs are just passed to the consumer directly. What about that Fair Tax they keep talking about?

Drew K

Who determines what is "Fair"?

The guy / girl with the most authority.

In a side note, what is wrong with my amp meter?

This isn't a side note! It's getting back to the main topic!

Unfortunately, I can't read the text on any of the devices, so I'm not sure, but here are several possibilities:

1. Clamp type Ammeters commonly do not make any connection to the red and black leads when using the clamp, so I usually remove the leads when using the clamp. I'm assuming your leads are dangling below and are not currently used. If the clamp does have a scale for measuring current through those leads, it is usually a separate scale (switch position) from the one that uses the clamp probe. You do correctly have a single wire feeding through the clamp.

2. The clamp probes I have, and have used, are very inaccurate at less than a few Amps. The gap in the clamp must be fully closed, and yours does appear to be so.

3. Are you attempting to measure the current through the field winding, or is that motor field just acting as a weight holding the alligator clips in position?

4. Since that analog meter has a scale going from 0-10, and you are working with 24V motors, I suspect that it is an Ammeter. Ammeters (except clamp-type Ammeters) must always be connected in series with the device whose current is to be measured. I can't see the motor leads, but if you are trying to measure the motor current, and one motor lead goes to each side of the analog meter, then you have the meter in parallel with the motor. That is the correct way to connect a Voltmeter, NOT an Ammeter.

5. That looks like a pretty husky power supply, capable of putting out quite a bit of power. I don't know what the n nor the 196 indicate. If, as I suspect, you connected a 10Amp meter in parallel with the motor, then turned on 24VAC from that big of a power source, that analog meter will have gone to full scale for a tiny fraction of a second, then returned to zero as soon as something in the meter melted and broke the connection. If that is what happened, that analog meter is kaput! There MUST always be something in series with a current meter to limit the current. That something is usually the load (in this case the motor winding).

If you would like, I can quickly make a diagram of the correct arrangement for measuring the motor current.

Whoops, I didn't check the picture before loading. The clamp read about 2 amps and the red digital should say 24 volts and 1.95 amps. The leads are dangling.

The circuit was correct, the analog meter was in series. The load was a 24 volt motor in locked rotor (offscreen).

The analog meter bumped a bit when I energized the circuit then dropped to a fraction of an amp and stayed until I switched off and on again.

It's all moot now anyway because today was my last day. I have been doing a background investigation for a law enforcement job and they told me today that they were contacted for the background check and have hired my replacement already. :-/

I hope he is competent and doesn't electrocute himself.

Drew K

OK.

I'm at a loss to explain why the Analog meter reads so low. One thought was that you might have had the power source set to DC instead of AC, but that couldn't be, because all the clamp meters I've ever used measured only AC. The only other thing I can imagine is a defective analog AC Ammeter, especially when the clamp and the power supply indicators agree.

Good luck on your next endeavor!

That power supply was ac only, I figured the analog meter was faulty.

Even if I stay in law enforcement I will keep a passion for engineering and will work on my own projects.

Drew K

Good luck out there Drew! I sincerely hope you have a great career in law enforcement. Stay safe, and stick with procedure!

The Amp meter is lying on top of the magnetic field emitted by the transformer inside that test device.

I would not have expected digital meters to be affected.....

If yes, why?

The reading is determined by the magnetic field created by the current into the clamping coil. Phase differences between the magnetic field from the transformer inside may oppose, amplify or distort the size and shape of the magnetic field being measured. Try it by introducing a moving permanent magnet while reading current.

I highly doubt that is a problem.

The test device is identified as a digital AC power supply. It may or may not include a transformer. If it does have a transformer, there is a high probability that the transformer is near the rear of the unit since the controls and display occupy the front.

The unit clearly has a metal case, which will act as a pretty decent Faraday Cage, keeping most magnetic fields inside.

Even if a magnetic field should somehow reach the meter, the chances of it being of the right strength and phase to cancel out the internal fields of the meter are really low.

It's pretty easy to burn out meters like that. I've done it more than once myself, and I've seen others do it several times. I'm willing to bet its just a defective meter.

The device is a power convertor and as being in a steel cage is an assumption, but I will abide by your superior knowledge. Thank you for setting me right, highly appreciated. It still stay a bad habit to use test equipment on top of other test Equipment. Enlarging the photo and the blank screen is a sure indication that the meter is probably destroyed.

Thanks. I didn't say steel; I said metal. It is most likely aluminum.

I definitely agree that it would be a wise practice to have the meters down on the (presumably non-conducting) bench, instead of on a metal surface, even though the metal is painted.

I think I had only put it on top for the picture. I had tested it on the table. That power supply had a steel case (had a magnet stuck to it for awhile).

I thought this type of amp gauge didn't burn out easily and if it did it would have an open circuit. It is placed in series and the circuit worked so it was not burned out.

Drew K

"It is placed in series and the circuit worked so it was not burned out."

Most common Ammeters either include or are attached to a shunt. A quick pulse of very high current could easily burn out the meter movement while leaving the shunt intact. The shunt inherently has a much larger mass, so can take short pulses without melting, while the fine wire in the movement heats up very quickly, usually melting at the point of contact between the fine wire and its connecting terminals.

Of course there do exist thermal current meters that don't use shunts, but they are very slow acting, so are not normally used in testing.

Whoa! You never said there might be up to 40 motors! Now your locked rotor current is up to 68 Amps! While it is unlikely that you will have 40 locked rotors at once, the unit should be able to handle that current for at least a few seconds. You need much larger wire, if all motors are to be connected in parallel.

120V shaded pole motors of that size are commonly impedance protected, meaning that locked rotors will not cause harm to the motor, even if left that way indefinitely. Since 24V motors must have significantly larger wire and fewer turns in their windings, I suspect they may not enjoy the same protection.

You would be much better off if you connected 2-4 motors to each transformer, with no connection from one transformer secondary to any other. Move the switch and relay (if there is a need for the relay) to the primary (120V side) of the circuit.

I'm guessing these transformers are around 2 inches across. I would expect a transformer of that size to be rated at 2-3 Amps at 24V. I can't read the labels. What is their rating?

Good idea!

That works for the test circuit - Though a single large transformer would probably be less expensive in the final assembly - then run fused secondary wires to small groups (or single) motors. The fuses will protect your wire runs. The motors are probably self protected.

No problem running the motors in parallel, but the transformers in parallel is a no go.

Use one transformer per motor, parallel the primaries, and switch the primary feed.

The red and black pair with the blue butt connectors are the 24 V out that are connected to the top of the transformers. The pair next to them are the 115 V (ish) supply, and the red and black twisted pair on the back left are clipped in parallel to the top of one of the transformers.

I am using a very durable relay that has multiple tabs to connect on either side.

Drew K

Thanks. That helps a little, but if you can post a picture of the transformers, you can also post a picture of a hand-drawn sketch of the circuit!

Those appear to be center-tapped transformers, commonly intended for full-wave rectification, or possibly transformers made to be used on either of two supply voltages.

I can't quite tell from the photo, but it appears that all three output terminals (assuming that the top terminals [opposite the mounting screws] are the output terminals), are used, but I can't follow the wires to see how they are connected. If they are 120V to 24VCT transformers, then the center output terminal should not be used.

It looks like I can see the two wires coming in from the right as connecting to the bottom terminals of the two rightmost transformers. I'm assuming those are the 120V input terminals. But it also appears that I can see wires connecting the bottom terminals to at least one of the top terminals of each transformer. There should be no connection from the 120V side of the transformers to the 24V side.

If the two wires from the right are the 120V input, then I assume that the other pairs go to the switch, the relay inputs and the relay outputs, but I certainly can't tell how they are connected.

The 5 motors shown are clearly connected in parallel with each other, so they all get the same voltage (minus a bit of drop due to the wires, so the last motor has the lowest voltage). If the wires are getting hot, then the voltage drop may not be trivial.

Please add either a circuit diagram (preferred), or views of the transformers from other angles and distances, so we can see where the wires go.

They are center tap transformers (had to google that last week before I started to know what a center tap was). I am not using the center terminal on the top because it is 12 volts as per the diagram and my preliminary tests with the multi-meter.

I tested the system thoroughly with my multi-meter before applying voltage to the bottom and I soldered all the terminals; there are no shorts between the top and bottom.

The 24 V wires leaving the transformers did get quite hot within a few minutes of the first motor test before I shut it down and added the twisted pair of wires (clipped to the #4 transformer on the left).

Currently, when it is powered I can feel a slight hum from the transformers and they are only slightly warm to the touch (infared thermometer shows only a few degrees above ambient) and the wires are about the same. I won't show how I am temporarily backfeeding a power strip to distribute the power (because AndyGermany will yell at me :) but the amps are too high to go through the circuit breaker switch on the power strip.

The wires going to the motors on the 3 parallel rigs are not warming in any detectable way.

Drew K

A closer image of one of the transformers and a motor (stator) in the background. That motor is not 24 volts.
Some of our motors have thermal cut out breakers under the tape, but most are designed to hold locked rotor below 100° C without a fan.

Drew K

Thanks. At least in this view I can indeed see that the center taps are unused. We still need to get away from wiring those transformer outputs in parallel!

After this test cycle is complete I will rewire the outputs for the 3 test shelves to power them individually and put the relay on the 115 side. I am also working on a cover for the entire rig then I will monitor the temp inside to see if it needs a fan.

I appreciate your drawing, wish I had access to the software to make my own.

Drew K

Use a spreadsheet program such as Excel, and make use of the insert objects functionality. make something that looks like what you want, then group it into a single object and save that as an object, you can build those up until you can diagram all the circuits you need to.

I will have to try that, I did make one in powerpoint, but didn't like the way it looked.

Drew K

Good. BTW, I know that electrical devices intended for use in a standard US power socket are commonly labelled 115V or 117V. I've even seen several from Japan that were labelled 100V. But standard wiring for homes in the US is 120/240V. I've measured socket voltages hundreds of times over the years, both in homes and in industrial settings. My home has consistently been around 123V for many years (as I've posted on CR4 at least a couple of times in the past), although I just measured it, and today it is 121.4V ±0.1V. Anyway, that's why I labelled the inputs as 120V, rather than 115V.

I'd really have a hard time getting by without CAD software. I've been using it, in one form or another, for 32 years. If you'd like, I can easily modify that drawing to suit your preferences, and if you'd like a higher quality copy, PM me with your email address, and I'll send a PDF of whatever size you prefer.

This difference is not a difference between peak AC and RMS AC, it is due to actual difference in the RMS values. RMS is 1/√2 (0.707106781...)of peak value. For 121.4 volts RMS, the peak is 171.68

Virtually every AC voltage metering device on the market is going to report the RMS value of voltage.

Apparently, there are different standards for "line" voltage 1P power in Japan, America, and other places, for example Britain uses 240 VAC 1P, as does (I suppose most of the EU).

I agree with your first two paragraphs, keeping in mind that there can be huge differences in the precision with which that RMS value is measured and/or displayed.

I also agree with your third paragraph, as long as for the US, you are referring to 120V line voltage.

For my point of view regarding 240V domestic voltage in the US, see my post #31 of this morning in the "Induction Oven..." Thread.

Thanks for both.