Soft start

Are there "Soft Start" units you could place between mains supply and a power tool?

I have a 2Kw 240v generator and its fine for most of my power tools, but my larger disc cutter (2000watt) will trip the generator on start up. If I spin the disc and quickly power it on, it all runs OK, so its close to the limit. The disc cutter is a "Hard start" tool - literally.
My home built circular saw with a 3/4 Hp also trips the generator (But I don't hand spin that one).

Any ideas out there which wouldn't break the bank?
BobH

If it's a brushed motor; you could, in principle, insert a "dimmer" circuit.

The simple ones are really intended for resistive loads, but I presume something suitable for motors will exist.

MichaelG.

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General principle here: http://www.pcbheaven.com/wikipages/Dimmer_Theory/

Edited By Michael Gilligan on 10/05/2018 19:21:16

The industrial soft starters are usually f expensive. Generally they use a phase controller to ramp in the voltage over a short period, so the suggestion of a dimmer type circuit isn't a million miles off. However, I doubt you'd want to be spinning knobs each time you start it up.

You can make up a sort of half way house / poor man's starter using a timer delay relay (perhaps 1/2 second or so) and a low-ish value resistor. I've got this arrangement on my giant TIG welder and it does the trick. The optimal value of resistor is a bit trial and error. Needs to be low enough to get things moving before you short out the resistor but high enough to limit the initial current surge below tripping level.

Murray

Plenty of cheap thyristor speed controllesr / dimmers on Ebay :

2Kw rated 192410752118 £1.23 delivered

4Kw rtaed 192410975598 £2.85 delivered

5Kw rated 192441295326 £4.69 delivered

I have used the 2Kw type to reduce the speed of pistol drills - put the module in a small diecast box wth a 13A plug on one end & a trailing socket on the other, so it could be put in circuit as required. Worked fine for my intended use, though for yours you would have to manually ramp up the speed with the pot.

Nigel B

Not tried it myself but powering up via a zero-crossing solid state relay like this might do the trick. They only switch when the AC voltage is zero, so the applied power comes up gently with the AC cycle, not at the peak. May not delay the onrush enough for this problem though - a full-blown soft-start is a more sophisticated and costly device.

Dave

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com.au%2Fulk%2Fitm%2F282957140944

Copy that link into your browser or  type in soft start for power tools on ebay , the seller appears to be U.K based .

We have kits you can buy here in Australia produced by an electronics magazine but they are abit expensive , i'm not sure if similar kits are available in the U.K but you could try some of the electronics stores .

Also check out on the net for units that have been built with arduino , i wouldn't be surprised if someone else has alread done this and you could copy what they have done .

Edited By XD 351 on 10/05/2018 21:02:47

I have a very large Lidl angle grinder with a thyristor soft start unit in it, so it can be done, and thyristors are the way to go, but dont do a lot of stop start or they overheat, thank the lord for Lidls 3 year warranty!

Everyone seems to be frantically agreeing that phase control / triac / thyristor soft start (they are all the same principle) is most appropriate and the ebay listings are probably the most cost effective way to implement them. A module from a hand power tool is obviously going to be more cost effective than an stand alone soft starter. And no need to make stuff if you can acquire it for peanuts.

Is your generator 2kW or 2kVA? Also is that its continuous rating or maximum with time rating?

If the tool is a true 2kW you may well be sailing close to the wind with the genny if the disc cutter is fully loaded when running.

Possibly the better way of not breaking the bank would be a larger generator or lower powered disc cutter. Generator rewinds can get expensive.

That said, if it is not an inverter generator, just upping the revs at start-up (of the disc cutter) may get it started without a trip. That was a trick I used with a 1.5kVA generator to start a 150W freezer motor (around 35 years ago). The freezer compressor’s thermal trip used to go out with the generator struggling for motor power. It was not long before the little genny was replaced by a 4kVA diesel.

I was going to suggest what ndiy has just said,ie. speed up the genny moter at switch on. Maybe a bit of wire, or a compliant wife. I have a 2.4 kw genny, 3kw max. Most tools run ok but one 9" grinder and a chainsaw do sometimes make it cut out without a bit of boost. Never any trouble running, or reliability problems. No doubt I will be told not to do it.

2Kw 240 v 50hz genny. I see that a soft start module is on the bay for not too much. I may have a punt, or use a smaller grinder. The circular saw is ‘out’ as it is a cap start. Thanks for the reply. Bobh

Today, my 'new bevel' saw arrived 6 days ahead of schedule - well done Evolution France. Another reason for researching Soft Start was to make sure that this new saw would not stall the generator, but to my delight, it has its own (un advertised) soft start and it starts and runs fine with the generator. The Rage 3S300 cuts through 300 x 60mm timber, 6mm steel etc etc. Looking forward to using it for making a timber garage over the coming months. It was 35 euro cheaper than other advertisers as it was a factory return (reason unknown). I expect other manufacturers do this and if you need a tool, perhaps see if the manufacturer has stock he wants to "off load".
BobH