Batteries / Power Systems: August 2008 Archives

Here are some pics of the low-voltage converter that I created using the National Semiconductor LM2576HVT-12-ND buck-converter. The chip pretty much did everything for me -- all I had to do was to add two power-smoothing caps, a blocking diode, and a RF choke (which I mistaking undersized; promptly blew up and which I jerry rigged a loop of wire).

In the top left of the photo above, you will also note my premade, off the shelf 12VDC to 5VDC converter. This powers my LED headlights.

The following photo is the back side. Please note that I am a really lousy solderer. The LM2576HVT-12-ND will take any input from 16-75VDC and output a steady 12VDC @ 3A continuous but they mention that with active cooling it could do 5A continuous. That's 36-60 watts, plenty for me.

This is the wiring schematic that I used:

Top side again. The setup is small enough that my ESC and UBEC still fit in the project case with plenty of space for airflow -- and for another DC-DC converter to fit in there in case 3~5A is not enough.

The resulting low-voltage converter and ESC "mounted" on my bike with duct tape. This is an older photo, I've reduced some of the wiring and since changed the SB50 connector to a PowerPole 45.

Some miscellaneous notes that are bouncing around my head.

• The Phoenix HV-110 has a listed max volts of 50 volts, which I thought would mean I could use 40 NiMH cells, with a nominal voltage of 48 Volts. However, you are limited to 36 cells NiCd/NiMH which gives a max nominal voltage of 43.2V. This is a little bit of a bummer since I had planned on doing 5S packs of 9.6V which would have given me 48V. I think this is because although the nominal voltage is 48V in that case, the peak voltage (fresh off the charger) can be in excess of 60V and the FETs most probably aren't rated that high.

• It turns out that I could've bought the 180 kV motor instead of the 130 kV motor. As it stands, I'll either have to get a smaller V-belt or a larger front pulley if I want a max speed of 45 kph (30 mph). No worries.

• I'm wondering what the best way to charge my NiMHs is. They don't sell many 38.4 V chargers, so I may just stick with 2 x 19.2 volt chargers and charge 2 packs at a time. I may want to get even more chargers so I can do the entire megapack at the same time.