controlling 250V DC/AC with solid state

[Simon]

I already pointed out that we could spend just £500 on some batteries as we don't have any and we need 10 to carry out tests but that was too much. Our customer will be buying a power supply that runs off the mains which will be all the access we have to power for testing, I know, I know, but apparently times are hard and I don't know what excuse they will make up when times are not hard. Of course we'd need to put the batteries in a box to stop some idiot killing themselves with them. and we have no kind of approval or training on high (lethal) voltages, not even me.

I have run a drill motor off rectified mains before and it worked fine, no more sparking than on AC (it was not a speed controlled one).

[oldway]

I have read that paper now several times.

Very good!
I'm sure you have learned something about the DC motors and I am pleased with this.

But this document does not allow you to know all about it.

Some of your statements are true, others are not.

I obviously can not develop it here because this is not what Simon expected and it does not answer to his question.

I don't believe this is will happen when a vacuum motor starts on a DC current with no inrush protection.

This is not right.

The series motors are better protected against flashover that separately excited motors due to the existence of an inductance in series with the armature which limit the di / dt.

But contrary to what you think, they are not safe from flahover.

Indeed, the independent excitation motors works with saturated field or nearby saturation.
Armature reaction also occur with universal motors.
For this reason, traction series motors have auxiliary poles and compensation windings to offset the armature reaction.
Universal motors are DC motors adapted (laminated frame to avoid losses by eddy current) to operate with alternating current but they are not designed to be started directly from a battery.
PWM soft start is far better, avoidind risks of flashover and high current surges in dc bus.
With a weak battery, starting dc motor without current limiting can also induce a voltage dip and undervoltage fault in others equipments.

@Simon: ...staggering...
I have worked in foreign countries, in project management and development in power electronics.
I never see such a thing....It is better to say "no comment" for not being rude.

[Zero999]

How about using an NTC resistor?

I know they're not designed for starting motors and I certainly wouldn't recommend it for a motor driving a load with a lot of inertia, but this motor reaches full speed within second and the surge will be lower than a rectifier and capacitor, which is what they're designed for.

[Simon]

Interesting, I didn't know they had NTC's specifically for inrush current control.

[Zero999]

Interesting, I didn't know they had NTC's specifically for inrush current control.

Yes, the cold resistance, when no current is flowing, is relatively high when it heats up due to the surge, the resistance dramatically drops. They're normally used for rectifiers in switched mode power supplies, rather than motors but the surge is short lived in this case.

Here's an example:
http://www.digikey.co.uk/product-detail/en/AS35%2020010/570-1116-ND/2614399
http://media.digikey.com/PDF/Data%20Sheets/Ametherm%20PDFs/AS3520010.pdf