Hi CompMan2020,
I was about to post a new thread, when the server listed this thread as being related to the title I had in mind...
Unaware of your experiments, I've recently started using what I suspect is the same DC-to-DC convertor you are using, rated for 12V input and 24V output at 10A (240W), the equivalent of pulling 20A at 12V:
You've made no mention of any difficulties getting the 24V output of the convertor connected to your Bluetti EB240, but I had to jump through a lot of hoops to get around the fact that the EB240 expects to see "+" polarity at both the inner sleeve of the 7.9mm power plug
and at the center pin. Most cables that can be purchased with a 7.9mm plug already attached at one end have an unpowered center pin. That's the case with this iGreely cable, for example.
https://www.amazon.com/gp/product/B07WP4696G/
This can be confirmed by testing continuity between the inner sleeve of the unenergized 7.9mm plug of the Bluetti AC charger and the center pin. Those two poles of the three-pole plug are electrically connected within the cable. Try checking that continuity with your choice of several aftermarket cables that come with a 7.9mm plug and you'll find no continuity between the inner sleeve and the center pin. Indeed, there are several such cables at Amazon, made for various purposes other than use with the EB240, where reviewers are complaining that the center pin is not engergized.
This requirement that the centerpin and the inner sleeve both soldered for "+" prevents use of a Jackery cable with the Bluetti EB240, for example.
I could only find one one solderable 7.9mm plug online. Note within the data sheet PDF, that it has 3 poles (center pin, inner sleeve and outer sleeve):
Can you please tell me how you built the cable that goes from your DC-to-DC convertor to the Bluetti EB240's 7.9mm charging jack?
I probably overcame the problem the hard way, but I did get it working:
View attachment 27625
With a 3-liter V6 at idle, it loses some RPM when the alternator kicks in under the 20-Amp load - which, by the way, is too great a load for the 15A fuses and, most likely, 14AWG wire that feeds the 12V accessory jacks inside my vehicle.
Input voltage to the 12V-to-24V 10A convertor drops from 14.1 to 11.0, when the 7.9mm plug is inserted into the EB240's charging jack. (Output voltage drops from 24.0 to 23.8.)
I'm using 12AWG cables for the entire circuit, with clamps on the battery posts and a 35A inline blade fuse, near the battery. In addition to the convertor itself and the two voltmeters, the project box contains a 40x40x20mm 0.03A 12V fan that pumps air into the box, across the heat sink fins and out through holes drilled in the opposite side. It never gets above ambient temperatures, that I can tell by handling the box.
https://www.amazon.com/gp/product/B07V4GGPW3/