With the lamp in? Sounds fun 
Supply size
- Thread starter RF Lighting
- Start date
Do I need to stand well back? 
As an aside, but slightly related ...
A while ago along with a mate we acquired a nice 4 post lift. 16ft long, 4ton, ideal for working on Land Rovers
Trouble was, it came with a 3 phase motor.
Anyway, Dad rummaged in boxes of what Mum calls "rubbish" and another "big" motor and a selection of caps appeared - plus an old Ford Excort (or the rear wheel drive) variety flywheel and a taperlock bush to mount it on the motor. So then began a number of experiments in getting the thing running - the first being to wind some rope round the shaft, pull hard, and after the rope has cleared the shaft - apply power. The plan was to make a 3 phase supply we could DOL start the lift pump onto.
But, the technique relevant to this thread is I tried using the heater element out of an old washing machine as a series resistor to limit current while the motor ran up. It did "sort of" work, but when it was about half up to speed, there was obviously some "interesting" effects going on as the motor began some violent "hunting"
Abandoned that idea, adapted a 220/440 transformer to get 415V and added an old manual star-delta starter. Got that bit going nicely - then my mate got diverced and we no longer had anywhere to put the lift
A while ago along with a mate we acquired a nice 4 post lift. 16ft long, 4ton, ideal for working on Land Rovers
Trouble was, it came with a 3 phase motor.Anyway, Dad rummaged in boxes of what Mum calls "rubbish" and another "big" motor and a selection of caps appeared - plus an old Ford Excort (or the rear wheel drive) variety flywheel and a taperlock bush to mount it on the motor. So then began a number of experiments in getting the thing running - the first being to wind some rope round the shaft, pull hard, and after the rope has cleared the shaft - apply power. The plan was to make a 3 phase supply we could DOL start the lift pump onto.
But, the technique relevant to this thread is I tried using the heater element out of an old washing machine as a series resistor to limit current while the motor ran up. It did "sort of" work, but when it was about half up to speed, there was obviously some "interesting" effects going on as the motor began some violent "hunting"
Abandoned that idea, adapted a 220/440 transformer to get 415V and added an old manual star-delta starter. Got that bit going nicely - then my mate got diverced and we no longer had anywhere to put the lift
Thought you were going to say you built a single to three phase motor generator using car tyres for power transfer 
I've certainly used that approach in much more modest situations, but (assuming you mean to leave it permanently 'in circuit', rather than bypassing it after start-up) can one actually get (at all, or for a sensible price) NTC thermistors with a low enough resistance and high enough power dissipating capacity to be used with a 10kW tranny? Even a 0.1Ω (at operating temperature) device would have to dissipate around 160W at full operating current. Maybe such devices are easy to find - I haven't got a clue!
Kind Regards, John
I had the opportunity to ask my brother today ...
The protection is designed to discriminate for switch on surges - where they have circuit breakers. Bear in mind that the breakers of the sizes they use have clever electronics and often programmable response curves - a far cry from the basic thermo-magnetic trips in our tiddly little MCBs.
I assume that where fuses are involved, they are naturally slower acting.
He did add that the noise from a big transformer when first switched on did alarm him at first. Apparently they can start off very loud, and then quieten down over the next couple of minutes - which I suspect will be the initial surge saturating the core and then it taking a little while to work the "DC magnetism" out of it. Apparently the newer low loss transformers are very quiet.
Thanks. So, in terms of the question I asked, are you saying that they 'just accept' the very high start-up current (simply taking measures to stop it operating protective devices), rather than taking any measures to 'mitigate' (i.e. reduce) that start-up current?
Kind Regards, John
AIUI, yes - they just accept the currents and mitigate the effects on protection systems.
In their favour are several factors. Firstly, it's not a frequent action - we are used to switching everything off when we leave the workshop, their stuff only gets turned off for maintenance or a fault. And then the supply upstream tends to be "fairly robust".
In their favour are several factors. Firstly, it's not a frequent action - we are used to switching everything off when we leave the workshop, their stuff only gets turned off for maintenance or a fault. And then the supply upstream tends to be "fairly robust".
Fair enough. I guess that exactly the same concept as using a Type D MCB in a more 'modest' situation!
Kind Regards, John
That's about it, yes. I imagine they have people doing a few more calcs than for an average domestic install though !
I have a friend who works in a well known installation up the coast near Workington, where there used to be a power station. He says that for some of the main supplies, they have blast rooms they have to retreat to before operating breakers. Having a direct 132kV connection (or rather, several - and when this was put in place, a direct connection to the power station), the Zs and hence potential fault current is such that the risk when operating a breaker is not insignificant.
I have a friend who works in a well known installation up the coast near Workington, where there used to be a power station. He says that for some of the main supplies, they have blast rooms they have to retreat to before operating breakers. Having a direct 132kV connection (or rather, several - and when this was put in place, a direct connection to the power station), the Zs and hence potential fault current is such that the risk when operating a breaker is not insignificant.
There are two 132,000 to 32,000 transformers in a town near me which are extremely old. They only use one, but leave the other energised, but off load. During some maintenance, they deliberately announced they were going to be turning one on, as they new the noise would cause some questions! The sound was quite scary for several minutes, but the first few seconds sounded like it was on it's last legs!
There was a tranny in sub station in South Wales that "groaned" when the economy 7 period started, a lot of houses all switched on their Off Peak at the same instance. This might have been one of the first TeleSwitch areas and I believe it led to staggering the on time over a few minutes.
And ? You've had a whole weekendGoing to try a couple of different sized heaters first and see if that works as I can cobble it together out of stuff I've knocking around the workshop.
We want to know if it worked, or if you blew the workshop up 
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