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Charging a LiO Battery with a solar panel for Ebike

Oliver O'Neill

Dec 6, 2015
2
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Dec 6, 2015
Messages
2
Hi everyone,

This is a project I've been working on for some time. As a bit of background I got a job in an electric bike shop. I live in Australia where there is plenty of sun and I want to do long distance touring with my bike. So for this project I need to have the solar panels charging while the motor is running.

The electric motor runs at 36V which gets its juice from a controller, which in turn gets its juice from a lithium ion battery. This battery is charged at about 42V. My biggest concern is what circuits to use between the panels and the battery.

One issue I forsee is that charging the battery and discharging it at the same time might cause problems. Lithium Ion batteries require a specific charge cycle and if you deplete it while it is charging it may damage the battery. One way around this would be to get a second battery and charge/use them separately. Another option would be to bypass the battery when the motor is running.

The other issue is the best way to power from the panels to the battery. For this project I need to use light weight flexible panels which I can only find in 12V. The battery needs 42V but the battery charger runs on mains voltage. What I'm wondering is how I can get the voltage up high enough while retaining efficiency. Three options come to mind.

1. Use a step up circuit to boost the voltage to the 42V and feed it directly into the battery.
2. Use a different curcuit to raise the voltage to mains level and use the mains charger.
3. Run several panels in series to increase the voltage.

I'm very keen to see wha tother people would do to get this working.
 

Alec_t

Jul 7, 2015
3,650
Joined
Jul 7, 2015
Messages
3,650
G'day. Welcome to EP.
What is the panel spec (open and short circuit current, watts)? Methinks you will need a pretty big panel area to get any useful amount of charge into the battery.
Option 2 would have the advantage of proper/safe charging of the battery. You don't want to be the cause of a bush fire :).
 

Oliver O'Neill

Dec 6, 2015
2
Joined
Dec 6, 2015
Messages
2
The current panel I have for testing is 54V open and I think 42V closed. I don't have the specs but I did test it in the sun and got 52V open. The motor runs on about 200W if you pedal enough. Thats feasible for my purposes. The issue I have with the second option is its charging voltage a lot. will this have the worst efficiency?
 

GPG

Sep 18, 2015
452
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Sep 18, 2015
Messages
452
Last edited:

alsmith

Aug 18, 2015
7
Joined
Aug 18, 2015
Messages
7
This isn't a new dream, many have tried. Can I suggest that you check out the ebike group at endless sphere? Please read the existing subjects before reposting old ground covered, but these guys are good with all kinds of self built ebike stuff, you'll struggle to find better help and experience.
 
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