diy solar

diy solar

Small solar battery / charger

RyanAK

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Mar 25, 2021
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I had a random thought last night to use a small solar panel I've owned for years (and rarely use) and mate it with some batteries.

I have a SunTactic sCharger-5 thats been sitting in a bug out bag for too long. I also have some extra 4400mah 3.7v pouch cells. Came up with this idea to match them together with a little charging board and a wood frame.

Traced out the panel outline, measured thickness of the panel and batteries so I could router out the battery holder section behind the panel.

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Cut out with the jigsaw. Lightly sanded and a couple coats of poly.

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Wired 5x 4400mah 3.7v cells in parallel. The board has a micro usb, usb-c inputs, and 2x usb outputs
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Works well! I think I will use this camping more often. The sun was never out when I needed to charge something. Now I can leave this out during the day, and charge my phone at night in my tent. Used all parts I had laying around my garage.

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Just plug the solar panel into the micro usb input in the board to charge with solar. You can also still plug the panel directly into a phone to charge and access the battery to charge also! The panel still pops out incase I want to use it separately.
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I’d be worried about sun heating the pouches.

very cool project though.

I have a few tiny power banks that have a 150W inverter built in. Tying in a small solar pan makes for a compact true solar generator!
 
I’d be worried about sun heating the pouches.

very cool project though.

I have a few tiny power banks that have a 150W inverter built in. Tying in a small solar pan makes for a compact true solar generator!

Ahh good catch, yes heat is a thing isnt it! At the very least, the cells lifespan would lower from the heat.

I do have an extra little inverter laying around, maybe I will add some cells and make a new case. How many AH do you have powering your little setups?
 
Well, they are phone power banks, so not much. I think they are 10,000 and 22000 mah rated, at 3.7V even though they are 14 or 16V banks in there...

Ahh good catch, yes heat is a thing isnt it! At the very least, the cells lifespan would lower from the heat.

I do have an extra little inverter laying around, maybe I will add some cells and make a new case. How many AH do you have powering your little setups?
 
Ryan, amazing idea and set-up. Also very handy for portable use. About the heating problems, I think that a layer of insulating material could help you prevent overheating. Normally foam, cotton, wool or materials that trap air are good at that; though not very firm. Placing the batteries on a bed of cotton for instance may not help at heat dissipation but may reduce the surface contact temperature. Good to check however the flammability of these materials, not an expert on this topic.

I like your model so much that I may copy it. I will make some calculations about weight and power and see If I can turn my small 20W solar panel into a portable setup. If the power I can add for the space and weight is too low I will abort. What are you expecting to power with this battery build?
 
Ryan, amazing idea and set-up. Also very handy for portable use. About the heating problems, I think that a layer of insulating material could help you prevent overheating. Normally foam, cotton, wool or materials that trap air are good at that; though not very firm. Placing the batteries on a bed of cotton for instance may not help at heat dissipation but may reduce the surface contact temperature. Good to check however the flammability of these materials, not an expert on this topic.

I like your model so much that I may copy it. I will make some calculations about weight and power and see If I can turn my small 20W solar panel into a portable setup. If the power I can add for the space and weight is too low I will abort. What are you expecting to power with this battery build?
Thank you! Using the 5 watt panel, it charged from 3% to 60% in about 3 hrs, and that was sitting on my table behind a foggy window on a cloudy day. I think it should be 15ah useable power. Using it to charge phones when camping mainly. I have a portable solar bt speaker, but its only a 3000mah battery. Barely enough to power the speaker all night let alone charge multiple phones.

Please post pics and details of your setup you build, very interested to see what you come up with. Im gonna see how this performs with the current setup. I have a device to measure total ah during a discharge. Going to charge it in the sun and discharge and see how it performs. I am in Alaska so its usually about 60-70 degrees here, not too warm.
 
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Hi Ryan, here my initial design maximizing the use of components I already have in stock, If I had to buy new components my design would be very different. The design is far from ideal, also because my knowledge in the matter is poor.
+ 8S2P 18650 2,55Ah spread in 4 battery holders = 33,6 - 25,6V (5,1Ah)
- no battery level indicator available at this voltage; possibility to use one 4S unit as representative indication for the whole battery set-up
- 12V solar panel connected to DC-DC step-up buck to 32V (sold as 30W panel, expected max. 10W and real 5-10W)
# Expected that XL4015 buck has PWM function to avoid backfeed battery to solar panel (is that correct?)
# 32V allows battery maximum charge of 70-75% (4V per cell) too low!
Reason for 8S instead of 4S = 1) nominal discharge current 18650 available = 5 A; at 12-14V low power limitation (60W); 2) Two loads desired (AC) 220V max. 60W and (DC) 5V 20-max. 40W
+ No BMS = No intensive use; expected manual balancing once every 2-3 months with Litokala 18650 charger (but BMS in stock 4S 40ampere max.)
+ DC switch in battery circuit to avoid passive drain of battery
+ DC-DC Step-down from 32V battery to 12V DC (max. 5 A; max power output = 60W) to feed DC-AC inverter at 12V
+ DC-AC inverter (max. 150W) + plug to connect devices.
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+ 5Amp fuse between DC-DC buck and DC-AC buck to protect bucks.

Remarks:
- Significant battery capacity reduction due to insufficiently high charging voltage 32V max., 34V required.
- Desired max. use: charge laptop (50-55W)
- Many inefficiencies (each buck 92-95% efficiency)
- Low battery capacity; at 50W max. 1hour.
- Expected weight = 1,25Kg
- Bigger battery 8S3P adding additional 400g (too heavy for portable?)

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That's a great idea for using spare / unused panels. I made one out of two 40 watt panels that were given to me in a purchase for larger cells with a cheap PWM controller.
 

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