ok guys i thought i would share this even though my vertex is dead and having issues with supplier and manufacturer maybe this will help some people out there.
so, the idea was not to use the vertex at all for a heated bed ( i was having reset issues of which i wanted to eliminate any interference from heated bed)
so i came up with this…
anyhow, components are:
large box clear front,
24v PSU
reprap power expander
reprap heater controller
power buck converter
fan,
various connectors
aluminium heatbed
anyhow, after some shuffling around and clever wiring, you use the buck to convert down to 12v, of which you use the 12v to power the (fan, heater controller, and your 5-24v from power expander)
i bought a reed style thermistor to replace the bulky one supplied and fitted this between the bed and glass (note to take out a little bit of the aluminium to account for it or you’ll crush the thermistor)
had it running last night, bed heated up to 50 degrees in just over a minute, and i have full control over the beds temp without touching the printer (NOTHING is hooked up to the printers mainboard!)
anyhow hope this helps, maybe giving an idea back may spur on velleman to get back to me 
lol or this will be getting used to power the 18’x18’ heatbed/monster build