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Homemade 240W folding solar panels with 300W Turnigy Reaktor

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Bit of a ramble showing my experimental 120W solar panels driving a 300W Turnigy Reaktor charger and homemade 48V battery pack comprising 10 x 5.2Ah 6S LiPos, with balancing.

The charger works really well off the mains or 12-24V batteries, but running off solar panels directly reveals some room for improvement, and should only be a firmware fix.

It works well enough, but needs babysitting – I have to manually set the charge rate to just under the maximum power point current and hope that a cloud doesn’t come along, otherwise the voltage drops into a hole until restarted with a new current setting!

The charger can control the current draw, because it gradually ramps up demand at the start of a charge, but it doesn’t know about Maximum Power Point Tracking (MPPT), so it will continue to take whatever it can get, go right through the panels’ power curve, and if the current draw is too much, the voltage will drop to 10V and stay there.

This could be “easily” solved with a firmware modification to track the Maximum Power Point, but that’s a bit beyond my ability to break in, disassemble and recompile a new OS for it!

Turnigy could expand their market a lot if they could issue a firmware update to handle MPPT, or make a new solar-aware charger.

(I’m sure there are a lot of RC enthusiasts who would like to be able to charge their LiPos in the field, without needing to lug tens of kilos of car batteries around too!)

I tried to use a Victron MPPT charge controller, but it doesn’t do LiPos. won’t work without a lead acid battery connected, and won’t drive the Turnigy because it’s too capacitive! Oh well…
it will however keep a couple of batteries charged that I could use at home to charge the Lipos with, but the idea is to be able to charge the ebike battery on the fly with the panels on a trailer, or anywhere.
(The 7kg 48V LiPo pack contains as much energy as two 55Ah car batteries weighing 13kg each!)

So, I think to be able to make optimal use of the panels, I’m going to either need to find or make a solar MPPT BMS that’ll keep a 12S LiPo charged and balanced, or something simpler that will work as a simple MPPT power suppy of around 400W without any battery management to drive the Reaktor, and manually switch battery banks as necessary.

There are painfully few affordable options on the market with the power required, and believe me, I’ve searched high and low!

Perhaps the best option would be to roll my own using an Arduino Nano and a cannabilized 500W computer PSU, can’t be *that* difficult!

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2 Comments on "Homemade 240W folding solar panels with 300W Turnigy Reaktor"

  1. Adam Welch says:

    I found your video very interesting – I should have a bash at building a solar panel – I can't imagine it would look very pretty with my skills but I think it would be an interesting project to complete and I'm sure I'd learn a thing or two.

    I've been thinking about your issue here – having to manually track the power point and stop start your charge really does seem a chore. Perhaps I can suggest an alternative? Remember you have got a battery to power a solar charge controller – it's your lipo pack which needs to be charged.

    Have a look at this solar charge controller – http://www.ebay.co.uk/itm/141942470391
    It's claimed to be MPPT (I haven't tried one so can't comment) and is happy with battery banks of 48 volts (and more). Attach it straight to the main pos and neg of your lipo pack (lets start with charging one at a time, but perhaps you can run them in parallel later). Adjust the voltages within the charge controllers menu system to correctly charge your whole pack.

    You'll need to reconfigure your panels so that their MPPT point is higher than the battery voltage otherwise the whole system won't work! Now the lipo pack will power the MPPT charge controller and the panels will charge the pack.

    Get a separate BMS to balance the pack. So you're using an adjustable MPPT charge controller to charge the pack, and a BMS to manage the pack. Does that all sound like a sensible suggestion? If so, it could be the end of the road for your turnigy!

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