Simple Lithium Battery Solar Charge Controller

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Even Keel
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Simple Lithium Battery Solar Charge Controller

Post by Even Keel » Oct 12th, '20, 17:06

I've got an 18Ah LifePO4 battery to run a LED light, VHF radio and charge the phones. I would like to connect my 20 Watt solar pannel. Without a controller the battery is meant to be smart enough to turn off, if the voltage is lower than 10 volts and higher than 14.7, but I'm thinking this is probably not a good idea, and I should be regulating it somewhere between 12 and 14 volts for longevity?. RTM has a nice controller for $90 which is heavy and bulky, and seems like a bit of overkill for such a simple task. Has anyone got any other ideas for me? Thanks

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zebedee
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Re: Simple Lithium Battery Solar Charge Controller

Post by zebedee » Oct 12th, '20, 19:49

The battery will have some electronics on board which is how it switches on and off.
Do you have any specs for the battery protection system? Specifically maximum input voltage it can protect from. If it's intended as a drop in replacement for a 12V lead acid battery it may only be designed to cope with about 15V, or they may have made it a bit more robust. If it will stand more than the Voc (open circuit voltage) of the panel (about 21V at a guess, check the label), then it should be fine.

BUT I have never worked with LiFePO4 batteries, so check with someone, ideally the battery supplier.
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Pand JR away
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Re: Simple Lithium Battery Solar Charge Controller

Post by Pand JR away » Oct 13th, '20, 08:24

Your battery is likely to be made up of lots of smaller cells inside its black box. They will look something like this.
LiFePO4  32650.png
LiFePO4 32650.png (11.28 KiB) Viewed 149 times
As Zebedee says there will also be some circuitry in there to manage the charge and discharge of all of these little batteries.

Unlike lead battery's Li ones don't discharge anywhere as much by themselves and they do not need a stepped charging profile like we are used to eg. trickle charging. The battery might look the same but it is quite a different animal inside. The job of the circuitry or BMS is to make it appear to function like the lead batteries we are used to.

Unfortunately there is not a lot of first hand experience with Li batteries on most sales floors and so seek your advice carefully. I would expect a controller to be required but if a lithium charging profile is needed in addition to the various lead profiles ( wet,AGM etc) I am not sure.
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Furstin
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Re: Simple Lithium Battery Solar Charge Controller

Post by Furstin » Oct 13th, '20, 11:09

Whether the controller will be able to pick up battery type, or care is a question.
Would an AGM\lead acid controller manage over voltage just not bang as much in as lithium could take?

Not sure sorry.

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Johny
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Re: Simple Lithium Battery Solar Charge Controller

Post by Johny » Oct 13th, '20, 13:22

I have a 100AH LiFePO4 (Lithium) battery on my boat. I also have a DIY Electric Car with a 12Kw/h Lithium battery pack. On the car the pack is divided into 12 sub-packs each of which have their own 58V charger. The chargers in the car limit current to 3A and voltage to 58.4 Volts - their is no other profile. It's called CVCC standing for Constant Voltage Constant Current. If you know the actual internal balancing system in the battery you can get a bit more complicated but it's usually not needed. (In my car I have modified the chargers to dial back the current to 200mA when the battery nears full charge but in retrospect I overdid it.)

On the boat I use an eBay PWM solar charger(cheapy) that allows me to set the actual charge voltage. It's often had to figure out if a solar charger will let you do this from the eBay descriptions though.
Yes, the battery protects itself but the overcharge protection is just that - it shouldn't be relied upon. The the battery cutting out at odd times is quite disconcerting.
My 2 cents worth is that any reasonably cheap solar charger will do the job. One thing to look out for is to make sure, with a small sized battery, that the solar panel can't put out more current than the battery can handle. The maximum charge current should be stated somewhere on the battery.
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Re: Simple Lithium Battery Solar Charge Controller

Post by Even Keel » Oct 13th, '20, 20:08

Thank you for the replies. Your information has been very helpful for someone who knows nothing about this sort of stuff. I'm not sure if I really need one but I've decided to go with a simple, sensibly priced Renogy Wanderer Li 30A PWM Charge Controller.

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Re: Simple Lithium Battery Solar Charge Controller

Post by Even Keel » Oct 14th, '20, 14:26

Just in case anyone is following this. There is a lot of miss information on charging lithium batteries. I've now been told a MPPT controller is required because they don't like being charged when they are very low or very high. Strange because there's a few PWM solar controllers for lithium batteries on the market. I'm now forking out the extra for 20amp MPPT controller.

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Re: Simple Lithium Battery Solar Charge Controller

Post by Slammin » Oct 15th, '20, 07:38

Yes smart battery needs a smart mppt controller. Make sure it has lithium option. For $20 more the Smartsolar has Bluetooth which allows reporting and controller options including turning on/off, limits etcetc

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