Static converter?

[davebreeze]

Oct 24, 2009 9:33:39 GMT jackrae said:

Dave
Slightly off topic and probably obvious but,
when lifting high loads off a trailer or trying to get them under the garage door, letting the tyres down or even removing the wheels can often get you out of a bind.
Before you buy a rotary have you considered making your own? Fairly easy to do and requires minimal ziggy knowledge.
jack

Jack,

I did consider letting the tyres down but it isn't my trailer and we'd just had a discussion about how expensive the tyres were... also the Land Rover Discovery that was doing the towing blew it's head gasket on the way back to my house (turns out the fan wasn't working properly but it only showed up when it had to tow the trailer with 3/4 ton on it) so I didn't want to push my luck! The mill was on a pallet so for the first lift I blocked the crane up on half a railway sleeper and that gave me just enough lift to remove the pallet from under the mill and gain a few more inches. We'd already had to take the whole lot to the farm where the Discovery's owner lives in order to use a tractor front loader to lift the vertical head off the mill. But once I'd got it down to floor level it was plain sailing with the engine crane which even had enough height to put the vertical head back on.

I have considered making my own converter, especially since I found I had a copy of 'Electric Motors in the Home Workshop' which shows you how to do it. But I'm not sure I have enough electrical knowledge to get into that sort of stuff.

edit: having re-read the book mentioned above I see that the converter design in there is for 240v delta 3-phase. If the motors could run on that I'd just use inverters.

[drjohn]

Oct 24, 2009 16:49:49 GMT jackrae said:

Well if you don't give the full project specification what do you expect

This gets interesting

Exactly what are you trying to run on 50Hz that won't tolerate 60Hz and eats up 6KVA

Actually the battery doesn't need to be too large, just big enough to smooth out the AC ripple off the 6KVA charger, since it's the charger that would be providing the base power. But at that sort of load both charger and inverter would probably cost more than either a genny as suggested or changing the original equipment for 60Hz tolerant stuff.

Alternatively throw a wire across the transmission line and drag the county's generation system down to 50Hz

jack

A tumble drier which because of the 60Hz doesn't tumble - everything sticks to the side because it turns too fast - 3KVA on full power, an electronically controlled washing machine which just will not run at all - even the pump to empty it makes a diabolical noise - also almost 3KVA when heating the water and a combi-microwave oven whcih overheats because the cooling fan won't run properly 1.2KVA micro, 1.5KVA oven.

Replacement equipment will be the cheapest way out I think.

DJ

Sorry bringing your thread off topic Dave.

[pendembu]

I have been happily running an Elliot 00 Omnimill for years with a static converter without any problems. Any one of the motors can be run or all four together although the output has to be adjusted accordingly. I usually operate the vertical head and power the table and this is fine,I have never had any problems. I have been told a small motor (say half horsepower) wired in seies and used as a pilot motor will make for smoother starting but I have never bothered as I have no trouble starting. The only trouble was the mill cost £250 (a lucky bid!)and the converter £315 new. I have seen occasional second hand ones but they hold their price.

[davebreeze]

I did eventually get a Clarke 2hp static converter from my local Machine Mart. The mill starts up and runs no problem with this, and is very smooth running. It was £260, but I don't think I could have done any of the other options (like changing the motors for single phase) any cheaper. The biggest surprise was £23 in City Electrical Factors for the plug to fit the socket on the converter! The guy behind the counter must have seen the look on my face, as he knocked it down to £16.

The problem I now have is that I found the horizontal arbour is jammed in the spindle (3 morse taper) and I think the bearings are suffering from the effects of 45 years of people hammering on the end of the drawbar to knock the arbour out. I think I'll have to remove the spindle and arbour in one piece and replace the bearings. They seem to be off-the-shelf taper roller bearings so it should be an OK job, if one I could have done without! Hopefully the arbour will come out with a little bit of heat. I really wanted a mill without morse tapers, but this seems like such a good machine that I can live with it.

[pendembu]

I am glad you got fixed up OK as the mill is an excellent machine if a little too lightly built,especially the vertical head. There was a universal head which bolted to the horizontal arbour output but these are rare and much sought after.There was also a slotting head. Incidentally my horizontal motor is 2HP.
You can get a manual from Lathes UK. if you do not have one.
You can get some spares from North Cotswald Metals,including a horizontal spindle if you need one. Make and use a pair of wedges to remove tools,do not bash the ends of the drawbars,it ruins the bearings and is not very effective anyway.All too often the tool gets jammed in and is left to cold weld itself over the years.You can often pick up 3 phase plugs and sockets for pennies at boot sales.Does it matter to you if they are used?!!

[davebreeze]

I got 2 manuals with it, they contradict themselves on the power of the horizontal motor but mine is 1.25hp on the plate.

'Lightly built' is relative, it'll do me fine, it's solid as a rock compared to the X1 mill I had before!

Thanks for the pointer to North Cotswold Metals, I will have to see what state the spindle is when I get round to taking it out. I'd prefer not to hammer on the drawbar against the bearings but it looks like a few folk have been doing this already, judging by the dents around the pulley below the drawbar. I may try to come up with a design for a captive drawbar that pushes the arbour out again.

[69chop]

Oct 20, 2009 10:43:38 GMT davebreeze said:

I've just bought an Elliott Omnimill milling machine which I'm very pleased with (from Emtec Machine Tools in Basildon - great service, very helpful by the way). I'd planned to run it from inverter drives as I have with my Colchester lathe, but it turns out the 3-phase motors on the Elliott are not dual voltage, they're 400v only. So the options are: change all the motors to single-phase, or get a static converter.

So I'm just wondering what people's experiences are with static converters? I noted there was an earlier thread about VFDs where a couple of folks expressed satisfaction with running machines from static converters, but when you read the manufacturers websites they seem to be trying to put you off buying one rather than sell them!

I think I could change the motors for about the same cost as the cheapest converters, it's got 4 motors - one for the vertical spindle (0.75hp), one for the horizontal spindle (1.25hp) and two small ones for the suds pump and table power feed. It would be a big hassle though as I don't know how much of the switchgear would need changing too, so the converter is an attractive option.