Wednesday, 5 February 2014

Solar Charging for Electric Bike

Thanks to absolute bargain I found from gumtree, now I can charge my electric bike battery using solar panel. Unfortunately, I can’t find any suitable charger system off-the-shelf. My requirement:

  1. MPPT (with booster) to charge e-bike battery directly from the solar panel. In my case, 12V solar panel to charge 36V lithium battery (Panasonic cells).
  2. Cost of the total system (solar panel plus chargers). If the whole system cost way too high ($/kWh of its lifetime), I’d rather charge them from the grid.

The closest one I got so far is but the price is a bit steep for me (must order the custom voltage for me). I'll put this on the back-burner when everything else fails :).

So, my idea #1 so far:

1. Solar Panel, 12V 80W (it only cost me AUD110!!);
2. DC-DC converter, CVCC (constant voltage constant current) (Ref #1 below);
3. Ah and Wh meter (Ref #2 below);
4. eBike battery (mine is 36V 11.6Ah with Panasonic cells)

Reasoning behind my selection:

  1. There is no MPPT in the DC-DC converter above. However, considering the cheap as chips unit, and plenty of 'oomph' in my solar panel, me think this should be OK.
  2. It's not a dedicated lithium charger. Although I can set the CV (Constant Voltage) to 42V, I'm not sure what is the degrading effect of leaving 'trickle' (float) charge at 42V. Reading many articles regarding 'float' charge of lithium batteries, I've come to conclusion "simply don't do it". Although, from my experience with the supplied charger, once it's topped up to 42V, it stays in this state for a long time. When I left the battery unused (after full top-up) for almost 2 days, the voltage is still 41-ish volt.
  3. Due to unknown risk above, I've decided to use the Ah (complete with Wh) meter. So I can monitor the charging accurately.

My idea #2 is to buy el-cheapo 12V to 240V inverter and use my supplied charger. However, I like the idea setting the charging current of idea #1 :).

Cost so far:

Not too bad. Definitely comparable to my grid-connected charger. Figures maybe optimistic (as in, the ability to charge everyday) :).

Results? Well, I need to wait until I get the converter first!


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