Glort
" I have a device that does exactly that. Couple of them actually.
They are a voltage dependant relay.  I have one on my hot water system.  When the solar pushes the the mains voltage up to a programmed level which indicates sufficient power, the relay turns on the hot water. When the power  drops or can be set to work in reverse, it switches off.  They will run on AC or DC and are mains voltage rated."

Interesting device, do you have a picture or maybe an ebay link.
Rigging a generator to fire up on low battery voltage would be a nice feature.
I realize that many inverters have this feature, but it would be nice to have a separate device for project use.

You are correct Hugh, the fellow in Western Canada is Troy at Eco-Diesel.
I purchased my first Listeroid from him before bringing more from India.
He was carrying the "GTC" brand of listeroid which is a very reliable and well made version.
I believe he is still in business.
https://www.ecodieselcanada.com/?s=1&p=1

 Ok .... the Blend idea is cancelled until further notice 

Thanks, very useful information about WVO vs. WMO.
Being that I have lots of WVO and zero used engine oil, I feel comfortable building a
small burner for the WVO. I want to have some form of easy clean-out.
Perhaps placing the burn pot in a removable ash tray.

I assume you are burning used motor oil.
What is the typical by-product of burning WVO in these heaters?
I realize that motor oil leaves an ash residue, but what about WVO.
Can it burn quite clean if the combustion is hot enough.?
I suspect it would be a good idea to have a removable bottom in the burn chamber, or some sort of clean-out access.

So far this has proven to be a great design. It's very simple and straightforward to build, Cheap very, controllable and reliable and could be used for a Multitude of purposes. I think a slightly smaller dimensioned unit could be made to run at very low levels as evidenced by the downturn ratio this one has just by reducing the flue diameter. This actually seems more effective than fuel limiting as the thing will run over such a wide range of fuel in it but it does need to run hot.

Which burner is this?
Do you have a picture or a Ytube video link.
Sounds like a design I would be interested to learn about.
You say it operated stable at low output ?

I too recently dissmatled and scrapped my biodiesel processor.
Far too much work and mess in my opinion.
If I were running a more modern diesel vehicle with direct injection I may be more inclined to burn biodiesel.
But for my Lister and Changfa engines a blend of WVO and RUG is a much simpler way.
I was always concerned about handling/storing the biodiesel chemicals, disposing of the waste glycerin, and having to do a test titration to determine the fatty acid content of the oil in order to calculate the amount of catalyst to add.
Then there's mixing the caustic catalyst and introducing to the hot oil...
All to end up with a fuel for my stationary engines that is not much better than properly cleaned WVO.