Related to my previous post about geophysics resistivity I am looking to get several hundred volts from a battery supply. I have successfully tested the approach with one of these units https://www.ebay.co.uk/itm/336230507336

I would like to get more current, given that these are cheap and readily available it seems easiest to use several of them rather than building a higher power unit. I know its not ideal but could I connect two or more via high voltage diodes (e.g. 1N5408 ) and rely on them balancing due to voltage sag?

 

You should be able to. But beware! If you have just two of those in parallel and you're running a 100W load, if one gives out for any reason the second will collapse because it's being overloaded. Now, imagine seven of them in parallel and you're running 450W. If one fails then a second will fail. Then a third, then a 4th, 5th, and quickly all of them will cascade in failure faster than you can react to shut them off.

 

but could I connect two or more via high voltage diodes (e.g. 1N5408 ) and rely on them balancing due to voltage sag?

Resistors are actually better for load balancing because the voltage drops more with increased current than a diode, which tends to keep the voltage drop in a small range.

 

From the testing I've done, these things seem to be current limited so if I keep cranking up the voltage into a fixed resistance then it just hits a point where the current stays the same despite increasing the voltage. My concern was more around if one of the units was at a slightly higher voltage and started driving the others in reverse, hence the diode.