DIY EV DC/DC converter?
 

Switching power supply
Perhaps the design could be modified for use as an EV DC/DC converter? At 40A continuous, an auxiliary battery might not even be necessary. Just a large car audio cap or two to assist the supply with load transients.

Modifications needed:
* If an auxiliary battery is used, the supply must not draw any significant current when off. Putting the controller on its own rectifier is an easy way to solve it. Then the only draw when off will be the feedback voltage divider and (insignificant) leakage current of the components.
* The supply (generally) needs to operate from a lower voltage. Use transistors with lower voltage ratings but higher current ratings and scale transformer turn ratios and component values as appropriate.
* Since devices like digital meters and the MOSFET drive circuit of some EV controllers need isolated supplies, add auxiliary outputs to supply those voltages.
* Replace the current-based fan controller with a temperature-based fan controller. Or leave the fan running whenever the supply is on since the power usage is insignificant.

Thats way above my head, but I can definitely see where that would be incredibly useful.

You can just buy any old 13.8V SMPS and stick 150...300VDC into it (rated voltage is normally 110...240VAC, take that times sqrt(2))

And then out comes your 13.8V :-) I switch mine on+off together with the main battery contactor (which is operated from the 12V aux battery)

But what about for voltages lower than 150v?

And I realized that an ordinary 13.8v supply will probably not work with an auxiliary battery unless it is modified. First off, 13.8v is not enough voltage to get much charge for short trips. A timer needs to be added to put it up to 14.4v for a few minutes. Then a current limit circuit must be added so the supply will never overload. (And tie that into the timer so it starts timing once the current limit is out.) And the supply must be tolerant of voltage remaining on its output when the input is disconnected. Most supplies will discharge the battery or even be damaged by that. Then add a circuit that will light up a warning light if the voltage drops below 13v and flash it whenever it is in current limit.

I found a basic DIY DC-DC converter, complete with instructions...but it only goes to like 60volts...DC-to-DC Converter I'm probably going to figure out how to modify that one up to whatever my pack will be running...plenty of time to figure that out, though...still looking for a glider and funding >.< real bad time to work in the auto industry lol

I don't know if this will help but Instructables have a DC-DC-HV-Boost-Converter which shows how you can boost the voltage to 500V.