Thread: Drill Sharpener

Originally Posted by GSRocket

I take it that voltage step down is the steel chunk to the left of the switch?

Yep. It looks a little dodgy but at least the former part is earthed. The reason this particular treadmill had a 110V transformer is because it was made in the U.S. It came from a Lifefitness 9100 treadmill, an old but very good commercial treadmill that would have been seen in many gyms in the early 1990's.

Simon

Again guys, just want to thankyou for helping me reach a decision.
Besides the sharpener, I'm going to buy one of these -2.25 Horsepower
$_12.JPG
So will this stepdown be adequate?
http://www.ebay.com.au/itm/4000W-240...1cbff1d&_uhb=1

$_57.JPG

Originally Posted by GSRocket

Again guys, just want to thankyou for helping me reach a decision.
Besides the sharpener, I'm going to buy one of these -2.25 Horsepower
$_12.JPG
So will this stepdown be adequate?
http://www.ebay.com.au/itm/4000W-240...1cbff1d&_uhb=1

$_57.JPG

How many drill sharpeners are you planning on running at the same time?

Simon

Originally Posted by GSRocket

Again guys, just want to thankyou for helping me reach a decision.
Besides the sharpener, I'm going to buy one of these -2.25 Horsepower
$_12.JPG
So will this stepdown be adequate?
http://www.ebay.com.au/itm/4000W-240...1cbff1d&_uhb=1

$_57.JPG

That is a DeWalt DW618M, rated 110V 12A. With Electronic variable speed and soft start. DeWalt claims it has "2.25 HP maximum motor HP". Whatever that means.

110V x 12A is only 1320W input power. Even if we assume parts of the US have 120V, 120 x 12 is only 1440W going into that router.

1320W / 745 = 1.77HP
1440W / 745 = 1.93HP

I am sorry, but there is no way this Router can put out 2.25HP if only 1.77 or 1.93HP go in. It would be against all laws of physics. Also keep in mind these are "universal" type motors, whith an effciency barely above 50%. Meaning you get just a tad more than half the power that goes in at the shaft, the rest is wasted in heat and to move air for cooling. Sorry if this is not you wanted to hear.

To your question: the proposed step down transformer can put out 20A at 110v, that is 2200W (not 4000 as claimed). Also, it has a 10A fuse at its input, that limits the input power to 240V x 10A = 2400W. Which seems to confirm the max 2200W at the output. Maximum output of 2200W / 745 = max 2.95HP and max 20A. Given that the router is rated 12A and fitted with soft start, I would not expect the inrush current to be more than 20 A. All considered, I would say this 2200W step down transformer is marginally suitable, it would be better if it was rated genuine 3000W or 4000W.

I hope the above shows that is is not that easy to select a suitable transformer. You need to carefully read specs. The transformer seller does not quote the continuous power, but either a fantasy value or maybe a peak inrush power that can only be sustained for a very short time (seconds). Equally, the router does not specify a shaft power (nor a duty cycle for that matter), but again some fantasy inrush peak value akin to power specs given for home vacuum cleaners and consumer air compressors. You always get what you pay for.

Originally Posted by cba_melbourne

That is a DeWalt DW618M, rated 110V 12A. With Electronic variable speed and soft start.

Well I'm glad you knew what it was. lol

I had the same thoughts re the 4kW supply.
The only other thing I would ask is what socket this would use in the US? If it plugs into a 10A? socket then I think we know what the rest of their numbers are.

Stuart

Thanks cba. You are really helping me.
These are Australian made stepdowns that seem to be the real deal.

http://www.ebay.com.au/itm/2400-WATT...=item3a7ebc6ed

also here http://www.tortech.com.au/step-down-...wn-transformer
2400_watt_step_down_transformer.jpg
Considering these seem to be vastly superior the 2400w would probably do it whilst taking into account a decent buffer and that's the maximum they suggest for a 10amp outlet.
They do two models, the 'economy' one is $250 and the 'Isolated' one is $600. Quite a difference although I have no idea how this affects the practicality in day to day use.
I'd appreciate your opinion.

Hi Guys,

If its just a matter of dropping a couple of hundred watts at 120 volts you could use a pair of 100 Watt light bulbs in parallel but in series with the drill grinder.
Reduced Voltage.jpg
Like this. You will have roughly half the incoming mains voltage at the junction of the light bulbs and the drill grinder or use a suitable transformer with a pair of 110/120 volt primary windings. On 240 volts the primary windings will be in series, again the centre tap will be half the incoming voltage.
Its important to make sure that the transformer body is securely earthed. Also make sure that all wires are properly insulated and secure.

Sorry forgot to include this interesting link to drill grinding jigs and techniques.

http://www.modelenginemaker.com/inde...88.0;topicseen

Originally Posted by GSRocket

Thanks cba. You are really helping me.
These are Australian made stepdowns that seem to be the real deal.

http://www.ebay.com.au/itm/2400-WATT...=item3a7ebc6ed

also here http://www.tortech.com.au/step-down-...wn-transformer
2400_watt_step_down_transformer.jpg
Considering these seem to be vastly superior the 2400w would probably do it whilst taking into account a decent buffer and that's the maximum they suggest for a 10amp outlet.
They do two models, the 'economy' one is $250 and the 'Isolated' one is $600. Quite a difference although I have no idea how this affects the practicality in day to day use.
I'd appreciate your opinion.

What they call "economy model" is an autotransformator. An autotransformator has only a primary winding with tappings, no secondary winding (see also here: http://en.wikipedia.org/wiki/Autotransformer). This is what is normally used for a step-up or step-down transformator, because it is cheaper to manufacture and also somewhat lighter.

What they call "isolated" uses a transformator (and not an autotransformator). It has a primary and a secondary winding, and the two are galvanically insulated from each other. See also here: http://en.wikipedia.org/wiki/Isolation_transformer

For the purpose of just running a grinder or a router in a workshop, you certainly do not need an isolated transformator.

$250 for the "economy" is IMO a lot of money just to run a 110V router worth $150 in Australia. Yes a toroidal autotransformator has less losses and it is probably quieter (less audible hum) but I doubt that matters - you do not run the router 24hours7days nonstop so efficiency gains are very small, and I am sure when running the router makes more noise than a cheap humming transformer ever could. I personally would either use a low cost (or recycled for free) step down transformer, or buy a new 240V router.

For Stu, yes that DW router model uses the common small US 10A power connector, with earth pin, this one:
http://www.ereplacementparts.com/ima..._399063-02.gif

You're quite right cba. It was reaching the point that the router as such would not be worth importing.
But I thank you for your superior knowledge and the trouble you went to to explain things, I learn't a lot.

Originally Posted by BaronJ

Hi Guys,

If its just a matter of dropping a couple of hundred watts at 120 volts you could use a pair of 100 Watt light bulbs in parallel but in series with the drill grinder.
Reduced Voltage.jpg
Like this. You will have roughly half the incoming mains voltage at the junction of the light bulbs and the drill grinder or use a suitable transformer with a pair of 110/120 volt primary windings. On 240 volts the primary windings will be in series, again the centre tap will be half the incoming voltage.
Its important to make sure that the transformer body is securely earthed. Also make sure that all wires are properly insulated and secure.

And for a bonus, you would have all the lighting you need to do the job.

Actually this is becoming harder to do in Australia. The govt want to get rid of all incandescent globes. We had a guy come around recently and on behalf of the Victorian Govt gave us a number of power saving items including 40 14w CFL's. I am thinking of selling them on EBay as we are already converting to LED B22 globes which make the CFL's look like birthday candles, and only 10w. So you would need 20 to get 100w to drop the voltage to 110. Problem is you would need to wear a welding mask with all that light.

Dean

Originally Posted by BaronJ

Hi Guys,

If its just a matter of dropping a couple of hundred watts at 120 volts you could use a pair of 100 Watt light bulbs in parallel but in series with the drill grinder.
Reduced Voltage.jpg
Like this. You will have roughly half the incoming mains voltage at the junction of the light bulbs and the drill grinder or use a suitable transformer with a pair of 110/120 volt primary windings. On 240 volts the primary windings will be in series, again the centre tap will be half the incoming voltage.
Its important to make sure that the transformer body is securely earthed. Also make sure that all wires are properly insulated and secure.

I can not recommend the idea with the light bulbs. At least not in the context of hooking up a 110V Drill Doctor. The DD uses a DC motor.

- with an incandescent lamp, when its off the cold filament has a very low resistance. Once the filament get hot and begins to glow, its resistance is much higher. It is said a light bulb has a positive temperature coefficient, it is a PTC resistor. In practice, this means in our case that when the motor is turned on, it will initially be hit with the full 240V, resulting in a very high inrush current. The excessive current is unlikely to damage the motor, as DC motors can support high currents for a short time (think a servo motor, or a car engine starter motor). But the very substantial overvoltage (initially 240V into a device designed for 110V) is possibly not ideal for the rectifier, the power switch and the overall insulation.

- As the motor accellerates the light bulb warms up and limits the voltage as intended. But now, as the motor is on speed and not loaded by grinding, the current drops. The lamp gets again cooler, and causes the voltage to the motor to rise. This is not good. On a DC motor, the motor speed is proportional to the applied voltage. Double the voltage means almost double the rpm. So with the lamp cooling the motor rpm rises in an uncontrolled manner whilst idling.

- Now we load the motor by grinding a drill. The current rises, and the lamp gets hotter. Thereby limiting the current and reducing the voltage to the motor to well below 110V.

This behaviour is exactly the opposite of one would expect a motor controller to do. Instead of limiting top rpm at idle, it increases rpm at idle. And instead of increasing the current when the motor is loaded to keep rpm constant, it decreases the rpm and with it the power output.

Sorry BarronJ, but in the case of a DrillDoctor, it's got to be either a step down transformer, or pay the price for a 240V export model.

Im wondering why these are so cheap?




It would be worth while getting one just to see if they are compliant with Australian Safety standards.... They might be auto-transformer style, in which case that would be illegal... Refer to the latest SAA wiring rules.. Or they could be SMPS.. then into an inverter, that would be an interesting design, they could do a 60Hz output version from 50Hz in, or even 3 phase out



In the United Kingdom they mandate the use of 110V power tools on construction sites for safety reasons. Further, these are usually 110V secondary winding with center tapped earth, so either side is only 55V above ground. So as a consequence there are a number of firms who supply 240 to 110V rugged duty transformers for power tools. And the prices compare favourably with 240-110 isolated transformers. You need to watch the duty cycle specs, mostly they will not be rated for continous usage. But a router is not going to be buzzing away for hours on end? Is it?

UK 110V Site Transformers look like this.. But they use special plugs.. You'd need to find one with US style plugs. Or perhaps modify one by changing the plugs.



http://www.ebay.com.au/itm/3-3-Kva-S...item3377c403ba

Here is a google image search for "Site Transformer 110V" https://www.google.com.au/search?q=s...w=1549&bih=922



In the workshop here I have a 2KW 240 to 110 isolating transformer permanently wired to a couple of US style wall outlets. Easy enough to do.

Ray

PS..
Reading the advertising blurb on this one, which looks identical to the 2KW version of the black one above, except for the color.. they say it's solid state switching, and what's more
it is fully compliant with Australian and New Zealand Safety standards.. ( without specifying an approval number or standard )

Originally Posted by RayG

......................................................
It would be worth while getting one just to see if they are compliant with Australian Safety standards.... They might be auto-transformer style, in which case that would be illegal... .....................................

Ray, autotransformers illegal? Can you elaborate on that? There have been Aussie made autotransformers since there is electricity... and they still are made today.

Australian safety standards? As far as I know, Australia recognises IEC standards. If it was not so, Australia could shut down whatever electical exoprt industry is still left. Because the rest of the world could then request by reciprocity that each item made in Australia is tested in the country where it is to be sold. Did you know that for that reason, Australian line voltage is now officially 230V, to bring our country in line with the EC?

The yellow thing that you show is a safety insulation transformer used on certain high risk building sites. As far as I am aware, nobody would use such a special and expensive piece of safety equipment at home or in a workshop, unless it was a wet area workshop or a mine.



Edit: I just see that the yellow thing is actually quite reasonably priced.... not like the ones in the RS catalog.... so yes it may be a valid alternative.