Low voltage can solve small generator problems

[Opera House]

I have a small quiet 400W 4.7A generator I like to use but it won't run my 5.6A shop vacuum or 15A Ryobi miter saw.  I solved this problem with a discarded computer UPS.  These have a high current transformer which is approximately 20 volts center tapped.  Connected as a buck transformer, it not only drops the voltage to about 100V but boosts the available current by about 15%.  For example the vacuum with no load draws 4.7A with a generator load of 4.1 amps.  At full load it draws about 4.7A from the generator.   The miter saw draws a lot more current and the motor needs to be "bumped" a couple of time till it gets up to speed.  Then it will easily cut a 2X6 if you go slow.  The slightly reduced speed doesn't affect a lot of applications.   This works with any brushed motor.  It should not be used on any induction motor as these draw more current as the voltage is lowered.  

In the example shown, the UPS has two sets of three outlet strips. I set up one strip for 110V and the other three for 100V.  

[hydrosun]

I've also read that brushed motors have more torque on 120 volts dc. So the ac output of the generator could be rectified and will start with less current.
Chris

[OperaHouse]

Somewhat true.  Without the inductance of the motor to lower current it would have more power but the generator doesn't have more power and it will just die quicker.  I do run a 220V router on the 120V AC line rectified and filtered DC. 

[Xan]

Ahhh that might explain why my Sabre Saw actually seems to be slightly gruntier running from an MSW inverter than it used to from the grid!