DIY solar power bank 5V 230Wh - Page 2

Daox · 08-04-19, 05:36 PM

I went ahead and ordered two of the ebay dc-dc converters listed above. These are also from China. I searched for a lot of alternatives, but I was unable to find one here in the US that had the power I wanted plus the undervoltage protection that this board has.

Daox · 08-04-19, 06:20 PM

I am looking for one final piece before I continue with the mechanical part of this project. I would like some sort of state of charge meter. I'd like to keep it simple to eliminate phantom load on the power bank. I think something that activates with a push button would be good so it completely disconnects when not in use. It doesn't need to be an active system. However, the only other type of system I'm aware of is a voltmeter. This really isn't the greatest way of measuring state of charge, especially with LiFePo4 batteries. You guys got any suggestions for this?

NiHaoMike · 08-04-19, 07:43 PM

Just build a dual comparator circuit with one output to trigger around 3.15V and another around 3.45V. That will give an easy indication of low and high charge. If you want more accuracy, you'll have to use a BMS with that feature which is hard to find for one cell LiFePO4.

Daox · 08-05-19, 08:07 AM

Thats pretty much what I was thinking. Thanks for confirming Mike! You've been quite helpful on this project and I appreciate it.

I was able to find a nice LM3914 board which drives an LED bar graph with a push button right on it. It seems pretty perfect for the job. They have two pots, one to adjust the 'full' voltage, and one to adjust the 'empty' voltage. That is also ordered and now on its way from China.

https://www.ebay.com/itm/LM3914-3-7-...02d0%7Ciid%3A1

Daox · 08-06-19, 01:19 PM

Here is a rough electrical diagram of the power bank. It's pretty simple and we have talked about lost of the parts thus far. The one we haven't yet is the switch. I'm not confident that the dc-dc converters will not suck power while not in use, so I added the switch to power them off when not in use. I imagine the charge controller is made to not drawn down the battery it is made to charge.

I think it would be nice to probably put a led on the dc-dc output as well just to make sure it is actually charging. I'll probably add that.

Daox · 08-07-19, 04:38 PM

With the electrical stuff mostly figured out for now, I am going to switch over to making the enclosure for the power bank. Thankfully, my 3d printer is big enough to handle this task. Here is my initial design. It still needs some work, but I think it looks pretty nice.

Here is an exterior shot. The USB plugs are on the right with the LED meter on the left. Still going to have to stick a switch in there somewhere.

Here is an inside shot. The larger grey boxy thing is the charge controller, and the two other smaller ones are the dc-dc converters.

Daox · 08-09-19, 06:49 AM

To keep things moving, and be able to print items before I get the electronics I had to change the design a little. I added a bunch of mounting holes to the main housing for flexibility. Once I get the electronics, I'll make up some small brackets to hold them to the housing. This will allow me to get the housing printed up. Its going to take approximately 17 hours, so I'd like to get it done sooner than later. This also allows future changes and upgrades or parts replacement with something other than the original parts without having to reprint the large housing.

Here is a picture.

Daox · 08-09-19, 07:29 PM

I also ordered my solar panel for this project the other day. I went with a 20W 12V panel from Newpowa. I got it on Amazon for just over $30. It measures about 18.5" x 14", and puts out 1.16A at 17V.

I am still thinking about how to plug this into the power bank. I'm thinking a barrel connector would probably be nice and work well. Suggestions are welcome.

Newpowa 20w Watts 12v Poly Solar Panel

Daox · 08-11-19, 09:00 AM

I got the second largest piece of this build 3d printed up. It took 10 hours to print, but its on the more dense side. For reference, it is around 7.5 x 3.5 x 1.75 inches.

Daox · 08-12-19, 09:12 AM

The largest print is now done. This one took 23.5 hours to complete. I'm pretty sure that is the longest single piece I've printed.

So, here we have the two halves of the battery enclosure box.

08-04-19, 05:36 PM	#11
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I went ahead and ordered two of the ebay dc-dc converters listed above. These are also from China. I searched for a lot of alternatives, but I was unable to find one here in the US that had the power I wanted plus the undervoltage protection that this board has. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-04-19, 06:20 PM	#12
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I am looking for one final piece before I continue with the mechanical part of this project. I would like some sort of state of charge meter. I'd like to keep it simple to eliminate phantom load on the power bank. I think something that activates with a push button would be good so it completely disconnects when not in use. It doesn't need to be an active system. However, the only other type of system I'm aware of is a voltmeter. This really isn't the greatest way of measuring state of charge, especially with LiFePo4 batteries. You guys got any suggestions for this? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-04-19, 07:43 PM	#13
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	Just build a dual comparator circuit with one output to trigger around 3.15V and another around 3.45V. That will give an easy indication of low and high charge. If you want more accuracy, you'll have to use a BMS with that feature which is hard to find for one cell LiFePO4. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

08-05-19, 08:07 AM	#14
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Thats pretty much what I was thinking. Thanks for confirming Mike! You've been quite helpful on this project and I appreciate it. I was able to find a nice LM3914 board which drives an LED bar graph with a push button right on it. It seems pretty perfect for the job. They have two pots, one to adjust the 'full' voltage, and one to adjust the 'empty' voltage. That is also ordered and now on its way from China. https://www.ebay.com/itm/LM3914-3-7-...02d0%7Ciid%3A1 Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-06-19, 01:19 PM	#15
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Here is a rough electrical diagram of the power bank. It's pretty simple and we have talked about lost of the parts thus far. The one we haven't yet is the switch. I'm not confident that the dc-dc converters will not suck power while not in use, so I added the switch to power them off when not in use. I imagine the charge controller is made to not drawn down the battery it is made to charge. I think it would be nice to probably put a led on the dc-dc output as well just to make sure it is actually charging. I'll probably add that. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-07-19, 04:38 PM	#16
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	With the electrical stuff mostly figured out for now, I am going to switch over to making the enclosure for the power bank. Thankfully, my 3d printer is big enough to handle this task. Here is my initial design. It still needs some work, but I think it looks pretty nice. Here is an exterior shot. The USB plugs are on the right with the LED meter on the left. Still going to have to stick a switch in there somewhere. Here is an inside shot. The larger grey boxy thing is the charge controller, and the two other smaller ones are the dc-dc converters. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-09-19, 06:49 AM	#17
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	To keep things moving, and be able to print items before I get the electronics I had to change the design a little. I added a bunch of mounting holes to the main housing for flexibility. Once I get the electronics, I'll make up some small brackets to hold them to the housing. This will allow me to get the housing printed up. Its going to take approximately 17 hours, so I'd like to get it done sooner than later. This also allows future changes and upgrades or parts replacement with something other than the original parts without having to reprint the large housing. Here is a picture. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-09-19, 07:29 PM	#18
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I also ordered my solar panel for this project the other day. I went with a 20W 12V panel from Newpowa. I got it on Amazon for just over $30. It measures about 18.5" x 14", and puts out 1.16A at 17V. I am still thinking about how to plug this into the power bank. I'm thinking a barrel connector would probably be nice and work well. Suggestions are welcome. Newpowa 20w Watts 12v Poly Solar Panel Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-11-19, 09:00 AM	#19
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I got the second largest piece of this build 3d printed up. It took 10 hours to print, but its on the more dense side. For reference, it is around 7.5 x 3.5 x 1.75 inches. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. Last edited by Daox; 08-11-19 at 05:29 PM..

08-12-19, 09:12 AM	#20
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	The largest print is now done. This one took 23.5 hours to complete. I'm pretty sure that is the longest single piece I've printed. So, here we have the two halves of the battery enclosure box. Attached Thumbnails __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.