When converting voltage from 110 to 220 with a power converter, is 3 to 1 a decently safe ratio for available to required wattage? I need to get 220 to my spindle and really don’t want to run a dedicated line.
The wattage will be similar, the maximum available current will change.
P [power in Watts] = U [Voltage in V] * I [Current in A]. We are not in ideal world and there is some energy waste, but you can assume for 1kW:
I=1000/230=4.35A for 220-230v
or
I=1000/110=9.1A
What is important is the wire diameter and insulation, more Amperage need larger wire diameter. I would use 2.5mm2 wire (cable cross section) up to 16-18A, which is close to 2kW.
Not worried about wire size, know how to do that (Degree in Electrical Control Engineering) More worried about power spikes on startup overloading the converter.
Some manufacturers are recommending a 1.5 ratio, I like to err on the side of caution, so I thought a ratio of 3 should do it. Just wanted to see what others thought of the ratio.
I never used a power converter, as we’re 230 in Europe and don’t have 110V devices. I think power converters should have some filters, like what you have in the UPS. I would add 20-25% of the spindle wattage and choose converter based on that number.
That is fine for running wattage, however I am still afraid of startup spikes overloading the converter. I think I will just be safe and go for a 3 to 1 ratio. The price of the converter is almost the same as a lower wattage one. But thanks for your input, it is appreciated.
Why don’t you want to run a dedicated line? I just ran 2 220v lines in my garage. I’m now proficient in EMT bending and box offsets 
was easier than I thought it’d be.
I am out of room in my panel after wiring up the hot tub, swimming pool, outdoor lights and my business workshop (i work from home repairing clocks). Will be a pain in the ass to try and free up a circuit.
What about using those tandem breakers for your 110 stuff? http://mobileimages.lowes.com/product/converted/047569/047569071065_07681554.jpg
Already loaded it up with those…lol
Do they make a dual pole hex breaker?
You could always put in a sub-panel below your existing one; sounds like you need the room.
Might do that if I can find a reasonably priced one.
Is your spindle on a soft start? That will strongly limit the spikes. But, you’ll have to make sure you’re not taking heavy cuts if you’re limited on wattage.
Remember that you can share circuits too. If you need 220v, wire into an existing 220v circuit where you’re unlikely to run both at the same time. It’s within the NEC.
I decided on just that, I am going to piggy back it on my hot tub line…if I am in the tub, I am not using the spindle, and the tub without the jets running leaves enough current for the spindle. Thanks everyone for your input, it made me think about all the options.