I have been playing with other ideas on this topic, here is my latest success.
I use Libreoffice impress to make a an xml ppt file out of my slideshow.
Here is whats needed to have success.
Make your slides
Click Slide Transition button on far right on my screen
Set Advance Slide Automatically After to the time you want the slides to show
Click apply to all slides
Next on the top menu click Slideshow
Then in the sub menu click Slideshow Settings
Set the type to Auto
Set the time below auto to "00:00:00" this means loop forever
Click ok
On top menu click File
In sub menu ckick Save As
Chang the "save as type" to "open office xml presentation .pptx"
Change the file name and location and save
<br>
Now you can run the file NOT in OpenLP but just in windows via the powerpoint viewer full screen on your projector
Use the show desktop button in OpenLP to show or hide the slideshow.