I have just ordered the one myles mentioned above. I had installed the original 'Neddy' one, but one of the electrolytic caps blew up when I left the output open circuit. The input voltage was only about 20v, but the output went up to above 40v. The capacitors are only rated at 35v. I will test the new one and might have to put a high value resistor across the output to stop it happening again if the 24v are disconnected.
NZMCA member, 2005 Canter 3.6l. 370w solar. 220AH Gel house,195l Fresh/150l grey. VSR,12v Equaliser charger, 7 stage 240v charger, 1000w mod sine inverter, 300w pure sine inverter, 12v Vitrfrigo 90l fridge. Webasto diesel heater. Thetford WC.