Hi mhutsby, Hi andrew,
This inverter circuit has cropped up a good few times.
Every time i see it, i cringe.
I consider it to be a poor circuit,
however, i have not constructed it.
Although i have constructed other low power inverters
most of which have worked adequately.
Here is a link to the thread on this forum where i first
saw this particular circuit:
https://www.electro-tech-online.com/threads/ip-core.2695/
I too thought the capacitors were the wrong way round,
but this is not the opinion of others who have examined
this circuit.
One point which was made clear is that the high ripple
current demanded of the capacitors in this configuration
means they have to be tantalum types. (or equiv)
Cheaper electrolytics will not stand the heavy demand
and will fail.
That earlier thread has many useful comments from other
constructors too.
One basic point is to check that the two 12volt windings
are correctly oriented.
Normally i don't reply to a post where the original poster
has only posted once.
There are too many that never post again.
Little home made inverter units are a favourite of mine,
i've made quite a few.
I favour the bridge type circuit with four Tr's or Ft's
which i originally started using because it has a single
winding as primary.
Best of luck finding a nice simple inverter Andrew,
Regards, John