240V to 110V Transformer Switching: Managing Inrush Current and Voltage Spikes

Hi,

(I am new to this forum so apologies if this is not in the correct forum)

Background - the control signalling from an electric vehicle charge point to a car has a minimum current specification. To reduce the minimum charging power a 240-110v transformer is being considered to be automatically switched in to reduce the power when low power is only available.

However, I don't have much experience in high power/electromechanical and am concerned that voltage spikes might be present and their effect on the electric vehicle (switched-mode) charging circuit.

My questions are

a) when switching-in/out a 240v-110v transformer are there expected to be voltage spikes and if so what devices do people recommend to reduce these spikes?

b) from experience switching the transformer in manually (with no load connected) can cause the MCB to trip and I want to understand the overload mechanism and it's impact on the electric vehicle. (my understanding is that a transformer is inductive and should prohibit rapid current change that would trip the MCB)

Any help gratefully received,
Regards,
Rob

Hi Rob,

All i can gave you are reference notes about transformers:

1. Transformer Basics
2. Transformer Design

Hope it helps,

Why does the electric vehicle community think that 110 V is a common voltage in NA?
More often one might see 120 to 125 V.
A transformer designed for a 110 V input will be very unhappy with 120 to 125 V.

Kevin
aka Speedskater

Thanks for your reply Kevin.

In fact I am in UK. The 240v-to-110v transformer is being used to reduce the supply voltage to the EV.

Rob

Thanks to everyone for their comments.

Some more googling found the following useful article.

http://licn.typepad.com/my_weblog/2012/03/to-...ross-john-dunn-consultant-ambertec-pe-pc.html

so to answer my own questions

a) if tx switched in with V at max and switching out with I at zero then there should be minimum spikes.
b) the MCB is tripped when tx switched in when V is near zero