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Old 18-08-2021, 10:05 AM   #1
alan s4
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Solar power for lithium battery?

I don't have power in my shed so I use solar power battery chargers on my bikes - works surprisingly well even in Scotland!

Looking to change to Lithium for both my S4 and 996 (more for cold weather cranking than weight saving). S4 fitted with MOSFET and 996 about to be.

Question is whether a solar charger is compatible with Lithium?
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Old 18-08-2021, 11:43 AM   #2
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So lithium batteries should be charged (read that as have to be) by first applying a constant charging voltage and current until the battery has almost reached its full charge state (80ish%). Once you get close to full charge (80-90%)you should maintain the voltage but taper off the charging current.
Once it's charged then you need to stop the charge, lithiums don't like being float charged. Instead you need to run a scheduled charge.

Options would be to run a standard PWM (Pulse Width Modulation) solar cell controller, that's what they normally come with and they're really cheap. Not ideal as it would effectively be trickle charging BUT as I assume it's a dedicated bike battery you're using it should have the charge control and battery protection circuits built in. Or you could use the panel to charge a leisure type battery (better and designed for use with constant float charging) to power a cheap inverter which powers your real smart battery charger.

Best would be to use a MPPT (Maximum Power Point Tracking) solar controller which is more of a smart DC-DC converter. The advantage in these is that they'll keep the voltage closer to constant and remember a lithium batteries charge at slightly higher voltages than wet cells, up to 14v isn't uncommon. PWM's often won't deliver this consistently, the MPPT's will maintain the volts by dropping current, PWMS drop both. The MPPT controllers are more expensive but not by too much.

In either case a timer to let the battery get charge once a week or so would be a good idea. As long as the lithium battery capacity gets to 80% capacity it's going to be optimal for long life, always charging to 100% gives you a slightly lower life span.

So Yes you can
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Old 18-08-2021, 11:52 AM   #3
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Funny you should post this - five minutes before I read it, I'd been leafing through today's MCN and there was a mention of Optimate's Duo solar charger, which they specifically said can charge both standard and lithium batteries. Not cheap though.

https://www.optimate.co.uk/products/optimate-solar

I see Optimate do just sell the controller, which presumably could be used with your existing solar panel.

https://www.optimate.co.uk/products/optimate-solar-duo
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Old 18-08-2021, 12:04 PM   #4
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Excellent response

At least I now know I'm not going to end up with an explosion and a ball of flames.......
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Old 18-08-2021, 12:06 PM   #5
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Luddite - didn't see your post - thanks for that. That looks an even safer option.
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Old 18-08-2021, 03:34 PM   #6
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Have a look at Victron energy blue solar pro PWM regulators, they are settable and can be programmed with an equilibrium voltage.

We aim for 14.2v float but use nickel metal hydride types.

For mains charging we use nickel cadmium at 14.4v float.
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Old 18-08-2021, 05:12 PM   #7
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Lithium floats about 14.3

I assume that they are taking the **** with their cell prices ??
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Old 06-09-2021, 11:10 PM   #8
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Quote:
Originally Posted by alan s4 View Post
Question is whether a solar charger is compatible with Lithium?
I question why you'd need it? I switched to a Shido at the same time as I replaced the (duff) RR because the Yuasa didn't seem to hold a charge anymore (and I'm so tired of lead-acid batteries generally; I've replaced more in the last 10 years than the previous 30). The S4 would sit outside in winter for 4-5 weeks or longer (sometimes with snow on it) between the infrequent dry day rides, and it was fine.

Without a parasitic draw, LiFePo4 voltage drops about 1% a month, even in cold weather, compared to 10+% for lead-acid. Seem to recall the Shido is rated 40% more CCA than the stock battery - so a lot more in reserve.

The only trick is that you have to "wake" them up if they're really cold; draw enough juice to warm them up and get the chemical reaction started. Turn the headlight on for 30 seconds, or kick the fuel pump prime with the key 5-6 times does it for me.

In fact, I haven't charged the Shido since I fitted it, well over a year ago; only thing I've used the tender cable for is checking the voltage without diving under the tank...

It was a bit of a nail-biter in the winter until I learnt to trust it/the manufacturers instructions. Pulling significant current before starting when it'd been sitting for weeks and weeks in freezing conditions seemed really counter-intuitive at first. But it was obviously right, because it wouldn't engage the starter or go over compression if you didn't... In warmer weather, you don't need any of that.
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Old 07-09-2021, 09:34 AM   #9
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Quote:
Originally Posted by alan s4 View Post
Excellent response

At least I now know I'm not going to end up with an explosion and a ball of flames.......
Never underestimate the power in an energy dense battery system

Most current generation batteries should have multiple safety circuits inbuilt, the older ones just assumed you knew what you were doing and as a lot didn't ....
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