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Forum Index : Electronics : Soft start 3kva transformer
| Author | Message | ||||
Haxby Guru  Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Hi all, I have a 3 kVA isolation transformer that trips the circuit breaker on switch on. What's the usual way to stop that happening? NTC thermistor? Or resistor "precharge"? |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 961 |
What style of transformer is it? Been using a 2kva in the house no problems starting, its Double C Core I think. Its runs from a HF Inverter, just plug in and it works. Cheers Aaron Off The Grid |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
It's a toroidal transformer. It trips a C curve RCBO about once every 3 times I plug it in. I got it off eBay so I'm not sure of its history. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Pretty typical for commercial toroidal transformers that run at a fairly high flux density. All you can do is soft start it through a series resistor for a second or two. How about a three position switch ? off/soft start/on Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 792 |
I occasionally work on gear that has a pretty gutsy NTC thermistor in series with the mains input. One I replaced was on a decent sized switch mode power supply (27V 22A) and the replacement I found was from element14 ... part number 2113008 It's 2.5 ohm and good for 15 amps. Resistance @ 100% Max Current: 0.03 ohms Resistance @ 50% Max Current: 0.07 ohms Datasheet here ... http://www.farnell.com/datasheets/1598322.pdf I've often wondered if they would be useful for some of this work where we worry about toroid windings or capacitor charging inrush blowing fuses and circuit breakers all the time. This link shows their offering up to 50 amps max steady state current ... https://au.element14.com/c/circuit-protection/thermistors/inrush-current-limiting-icl-ntc-thermistors Cheers, Roger |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Ok NTC thermistor sounds like the easiest solution. Thanks all! |
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InPhase Senior Member  Joined: 15/12/2020 Location: United StatesPosts: 178 |
Light bulb in series with the line and a switch to bypass it? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Thermistors work fine for a fixed occasionally switched heavy load, but may have issues with a general purpose workshop type isolation transformer used for testing purposes. See how it goes, but a thermistor need time to cool before the protection fully resets. Rapid cycling of the on/off switch with a hot thermistor will not provide the expected surge protection. Still, a very big step in the right direction. Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1122 |
Jaycar sell a kit for "Soft Start" anti surge applications, see Kitset , based on an article from silicon chip mag, july 2012. I have built two and they work well, when powering things like drop saw's with inverter AC supply; no reason it wont work with a transformer, noted that the kit rating is 10 amps. Cheers Mike Edited 2021-03-30 09:50 by Solar Mike |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1387 |
why not? cheap. easy to do. wronger than a phone book full of wrong phone numbers |
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| Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 178 |
The humble incandescent lamp has served me well in the industry as a fuse when repairing things. It will show you when something isn't right, and not blow anything else up in the process. Apart from real estate it may take, it's a brilliant....oh crap, unintended pun....anti surge/fuse option. Cheers Pete'. |
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