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Forum Index : Electronics : Transformer help
| Author | Message | ||||
rustyrod Senior Member  Joined: 08/11/2014 Location: AustraliaPosts: 121 |
Hi, Please, Could someone point me in the direction of a suitable transformer to run - Say 100 watt bulb at 240 v from one phase of 415/480 ? This is for a work light on a lathe and there is only 3 phase (no neutral) on that side of the shed I have 3 phase switch avalible I don't want extension cords dangling everywhere, A new 5 core wire, power point/plug and sparky is prohibitive. It is also not as simple as running another wire for neutral to this point OR do I get it wired from a phase and earth ? This works but seems wrong Any suggestions will be appreciated, Thanks Always Thinking |
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oztules Guru  Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
I am not a fan of 240v on a lathe light.... water and bits of swath going all over the place.... So first I would check to see how the lathe electrics work. If there is a relay there ( and I suspect there is), then this will probably have a 24v supply already via an internal transformer, and you can piggy back this for a 24v light. If HV is not a problem you could use a 240v incandescent light and a capacitor, to step the 415 down to run the light between phases if desperate. If you have a few microwave transformers around, they can be split, and use two of the primaries in series on a single core, and wind a 24v secondary. Or ( this is an anathema to me ) you could just buy one of these: https://www.ebay.com.au/itm/Radameta-Transformer-60VA-415-0-15-to-48V-1-25Amp/322194159073?hash=item4b0444b5e1:m:mtt7t4E w4gWPuEGAmXXVLLw This 48v can then be used to drive cree leds or similar, or you could rewind the secondary to 24v and use 24v leds etc. True 415:240v trannies at the 150w range seem very expensive, and I really don't like the 240v on the saddle. I really think you will find a decent tranny in your lathe already though, and just use leds in the light ( thats how I run mine too ). .........oztules Village idiot...or... just another hack out of his depth |
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| Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 181 |
Correct, there is normally a 24v control circuit. 24v LED lamps are common place now and would be less of a load for the control ckt than a halogen or incandescent. Cheers Pete'. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
You beat me to it Pete. A great many switchboards and machinery use 24v ac internally for control of lamps, relays, timers, and all kinds of things. You may have much more luck finding a 380v-415v to 24v transformer. Then use 24v incandescent bulbs. Hint, large trucks and busses often have a 24v battery, so stop, turn, side clearance and indicator bulbs will all be 24v. An incandescent lamp is the safest for a lathe because it does not flicker on and off at mains frequency, and act like a strobe. A cluster of bulbs will produce a softer shadow than a single bulb, which produces less eye strain. Just had a look on e-bay, several available from both Germany and USA, but the postage is ridiculous. But these are the types of transformer to be looking out for. They almost invariably have screw terminal blocks fitted. They come up fairly regularly, something from Oz will definitely show up if you are a bit patient. https://www.ebay.com.au/itm/190150-CONTROL-TRANSFORMER-75VA-400-380-24V-50-60HZ/161507508006?ssPageName=STRK%3AMEBIDX%3A IT&_trksid=p2060353.m1438.l2649 https://www.ebay.com.au/itm/SBA-Trafo-EGS-075-092-Transformer-192-W-In-380-400-420V-Out-24V-8A/371873812484?ssPageName=S TRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 Cheers, Tony. |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
You don't get the strobe effect if you use filtering on the dc input for leds. https://www.aliexpress.com/item/Three-phase-AC-380V-input-24V-5A-output-120W-Explosion-proof-power-supply-of-high-reliab ility/32832506241.html?spm=2114.search0104.3.59.BuvGYo&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10065_10151_10344 _10068_10130_10345_10342_10547_10343_10340_10341_10548_10541_10562_10084_10083_10307_5680011_10175_10060_10131_10155_101 32_10133_10154_10056_10055_10539_10537_10312_10059_10313_10314_10534_10533_100031_10103_10073_10102_10557_10142_10107,se archweb201603_25,ppcSwitch_7&btsid=61575ce7-90bf-46f9-b811-914456b1580b&algo_expid=5b395467-9344-455a-afbe-194a56631315- 11&algo_pvid=5b395467-9344-455a-afbe-194a56631315 wow thats an address  but $36 is pretty good.It provides a better more stark contrast than a filament type. ......oztules Village idiot...or... just another hack out of his depth |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Thats a much better solution Oz. Cheers, Tony. |
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| rustyrod Senior Member Joined: 08/11/2014 Location: AustraliaPosts: 121 |
Thanks Gentlemen for these suggestions I also am not a fan of 240 v incandescent bulbs as work lights, Should the glass get broken there is only the remains of the filament support to hold on to in order to unplug the deceased bulb! Hopefully it is switched off and the switch is in the active wire. Below is picture of inside my main switch (cover removed for photograph)  Not a transformer anywhere. However primed with your combined suggestions I found this Transformer Multi voltage 6.3V 24V 36V 110V or this one multi voltages 6.3 12 24 and 36 v My next question : Will either of these be happy on my 415 volts ? Always Thinking |
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| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
Yes, if the utility transformer has a neutral tap. And does your machine have a fourth wire for neutral coming in? Not, if it is delta. If you can find two identical small 240V transformers the primary can be wired in series and the output in parallel. Phasing them right or it is a big short. Too bad you are not closer, I get a lot of these small control transformers free from a commercial HVAC company. They are in all the old units they replace, just scrap for metal recycling to them. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That is a rather interesting question, the answer is "probably". The most important thing is that a prospective transformer designed to work at 50Hz. A 60Hz transformer will have either 20% less iron or 20% less turns, and is very likely to suffer if the incoming voltage is also a bit high. Voltages around the world are mostly 220v, 230v, or 240v. The corresponding phase to phase voltages are, 380v, 400v, and 415v. The difference between 220v and 240v is only 9% The actual incoming supply variation may reach +/- 10% Now the guy that designed the transformer will build in some margin into his design, but how much we do not know, and can only guess. I have replaced several burned out transformers over the years that were rated for 220v 60Hz (American) that ran for a while in Oz, but those were running at 29% more than the original design voltage and frequency, and possibly up to 39% more than originally intended. Hardly surprising that the smoke eventually came out. Now both of those transformers you linked to are o/k for 50Hz and are said to work up to 380v. The designer will have already allowed for an incoming mains variation of 10% more than that, plus some safety margin above that again. Pushing that up from 380v to 415v 50Hz will only add an extra 9% which should be ok. Cheers, Tony. |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
I would still go for the pwm for $36. .......oztules Village idiot...or... just another hack out of his depth |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1026 |
That picture of the switch. I would bet that is a Star Delta Starter BY A.I.E. Engineering. 20Hp? Nice to see some old gear still in use.  Cheers Aaron Cheers Aaron Off The Grid |
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| hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120 |
One thing to remember is a transformer turns into a resistor once the core saturates. This is what causes transformer burn out. The sine wave turns into a flat top one. I figure a 10W LED would be sufficient for your lighting needs. That would be approximately .03A at 440V. With a 380V transformer, place a 220 ohm 5W resistor in series with the transformer primary. If the 380V transformer doesn't saturate, the resistor will barely get warm. If saturation begins that rise in current will be dissipated in the resistor instead of the transformer, saving it. |
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| rustyrod Senior Member Joined: 08/11/2014 Location: AustraliaPosts: 121 |
Thanks all, The switch has been upgraded to more modern with reverse  A friend brought me some lights and voltage doublers along with 2 cartons of spare bulbs. The lights are around 400mm square. He said these will light up your lathe!   The doubler ballast transformers - each are seriously heavy Sylvania Lighting Constant wattage ballast 1500w 500v 3.3a MHL1500/240  These output 500 v at 1500 watts, so one was wired up in reverse. Holy shades batman - a 60 watt bulb was a bit bright So a voltage was taken to find 320 v Maybe a single smaller capacitor is required In the meantime a transformer with a 50 w down light has been set up Always Thinking |
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