question

lnanne avatar image
lnanne asked

100/50 Smartsolar and Lithium

We are considering upgrading to Lithium and here is what we think we know based on the settings recommended by the manufacturer... We would set the absorption volts to 14.4 and the max time to 1.5 hours (because starting volts would be 13.6 which would result in 1/6th of 1.5 or 15 min). Float would be 13.6.

Our question is this... if the volts on lithium are generally a constant 13.6 until almost charged or almost discharged, and the controller is on float volts of 13.6, how do we utilize the excess solar to run our electric fridge and other loads during the day? Won't they run off the battery and the solar won't add to the battery because the volts are constant? Hope this makes sense and someone can tell me where my gap in knowledge is!

Thanks!

MPPT Controllers
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3 Answers
JohnC avatar image
JohnC answered ·

The effective V on Li's will drop under load. Mightn't be much, but will be enough.

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JohnC avatar image
JohnC answered ·

Hi Inanne. If you take loads from the dc battery bus or even ac via an inverter (fed from the dc bus), the mppt will simply continue on trying to achieve it's target V, whatever that is at the time. Ie. It will step up W from the pv to cover the loads too. Providing of course that W is available, it will continue to charge batts at the target V as well as supplying loads.

Tis the inherent simplistic beauty of dc-coupled pv.


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lnanne avatar image
lnanne answered ·

Thanks @Johnc but I think that's where my knowledge is slim. If the volts on the lithium don't drop (as I'm told), then how does the MPPT know to push more power? All the loads and the MPPT are wired to the battery bus.

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