solid state 3ph converters

[news]

Do these inverters cancel out any reactive current requirement on the single phase feed?

AJH

[Andrew Mawson]

The input side of virtually all inverters are usually pretty similar in that they are a bridge rectifier feeding a large reservoir capacitor. The input current waveforms can be pretty nasty as the voltage on the capacitor varies with load, the rectifier starts to conduct at different parts of the sine wave.

However you need to specify a particular makes / model (and probably enquire from the maker) to fully answer your question.

Andrew

[Rob Graham]

I'm afraid, as so often here, a technical question without adequate informa tion of usage, etc. to be able to give a real answer.

If this is a high power system running 24/7, then such correction is requir ed. If, as I have, it is lower power (running a 1 hp motor) with a usage o f a few hour a week at the very most, then why the question as the impact o n the distribution system will be minimal.

[Bob Minchin]

OP mentions single phase input so that typically limits the power to the

3hp region. For higher powers, inverters are only available with three phase input. Most manufacturers have models with input filters which help reduce the interference sent back down the supply. I have some filters here surplus to requirements that can be had for the cost of P&P?

[Capitol]

Should do. IIRC the PSU is required to have power factor correction if over 80W or thereabouts.

[news]

I've not got that far yet. I do use variable frequency inverters for run induced draught fans but only 1 kVA.

The reason for my question is that 5 years ago I "rescued" a 1940s empire lathe from the scrap and I want to try it out but I don't have the correct motor. I was told it used to have a 5hp 3ph motor and I wanted to figure out what the biggest motor I could run from a single phase 30A ring.

I was thinking the slow start of the variable speed inverter could reduce the inrush current at start up.

The kVA rating of the supply with a 16A plug would be about 3.7 or around 5hp time power factor and subject to losses in the inverter.

AJH

[Bob Minchin]

Look at the range of inverters available. Very few will go over 3kw and run from single phase input as supplied. One supplier modifies new three phase input ones to run from 240v single phase - Drives Direct Nottingham. But even for those you will need a 32a feed from the CU and should not really be running them off a ring.

[tabbypurr]

13A 3.1kVA 2.6kW max if you fully control startup current 15A 3.6kVA 3kW " 16A 3.8kVA 2.1kW " 30A 7.2kVA 6kW " 32A 7.7kVA 6.5kW "

these are continuous figures, IRL 30/32A rings are routinely loaded well above 30/32A. And of course those loads apply iff all other loads are removed at the time. And iff your load is not near one end of the ring.

NT