Today's mystery object

[Graham W]

I managed to tunnel out today and did some experiments with Torqeedo charging on the go. One disappointment was that I couldn't get the step-up controller to work with my 28v bike battery without blowing the 4A fuse. I also risked trying it with a 5A fuse, just in case it was on the edge, and it blew that too. The combination worked when topping up an almost fully-charged Torqeedo battery but not, it seems, when really needed. Anyone know of a cheap 12-36v current-limiting device (other than a fuse)?

Other results:
Direct connection to a 12v battery (with fuse and diode) - 25W
12v battery through step-up controller to charge at 30v - 65W
28v bike battery through step-down controller to charge at 14v - 25W. This could be increased (the current is adjustable) but even 25W generates quite a lot of heat.

So the weird-looking part of the mystery object turns out not to have been very useful, except perhaps for part-charging overnight. The fastest recharge at 65W is about the same as the standard (slow) mains charger that comes with the motor.

[Graham W]

I tested this step-up controller with a 12v battery and managed to get 109W out of it while the Torqeedo was on the move, the best range extender so far http://www.ebay.co.uk/itm/DC-DC-12V-to-32V-3-4A-Step-UP-Waterproof-Power-Voltage-Converter-Regulator-/321221379452

I also fooled my solar controller into charging the 12v battery at the same time, using a 28v lithium bike battery stepped down to 20v, giving approximately 40W and thereby mimicking a large solar panel.  So in theory, a 300W (12v, 24Ah) house battery could continue to boost the Torqeedo at 109W for about four hours before being completely discharged.

A word of caution - at these sort of currents, it is worth investing in plugs, cables and connectors that will not waste energy by causing resistance and generating heat or worse, melting.  Everything should also be appropriately fused and always test polarities with a multimeter before connecting up - it is easy to connect wires the wrong way around.  2.5mm diameter tinned cable and Bulgin Mini Buccaneer plugs and connectors can cope with these sort of loads.

[david]

WOW Graham. I am marveling how you have figured this all out. Even trying to follow your directions in the library, I feel that I am back in collage. Struggling at that. Trying and keep! My Hat is off to your Sir.
Looks like I will stick with the gas engine – Or my oars – until I graduate your class! 

Regards,

David.