My first DIY battery bank + solar cell

[ddarlington36]

Ok i'm a first timer at building my very own battrybank/solar. My charging circuit is the mp1405 w/ the protection circuit built in. I'm going to be using this to charge multiple 18650's 3.7v x6 in a parallel setup combined with a dual usb boost to 5v for the usb devices. I've choosen a 1.6w 5.5v 266ma for the solar panel and i will attempt to wire it to the input on the mp1405 chip.

Ok i have a few questions first if anyone has experience with this kind of chip i think it uses the tp4056 ic/mp1405 can it charge multiple 18650's aslong as it's a parallel setup?

My next question is about the blocking diode i'm NOT exactly sure which one to use how do you go about figuring out which one? I choose a zener 1n4734 5.6v. I'm really thinking this isn't the correct one to use. Plz help .

[solar pete]

Ok i'm a first timer at building my very own battrybank/solar. My charging circuit is the mp1405 w/ the protection circuit built in. I'm going to be using this to charge multiple 18650's 3.7v x6 in a parallel setup combined with a dual usb boost to 5v for the usb devices. I've choosen a 1.6w 5.5v 266ma for the solar panel and i will attempt to wire it to the input on the mp1405 chip.

Ok i have a few questions first if anyone has experience with this kind of chip i think it uses the tp4056 ic/mp1405 can it charge multiple 18650's aslong as it's a parallel setup?

My next question is about the blocking diode i'm NOT exactly sure which one to use how do you go about figuring out which one? I choose a zener 1n4734 5.6v. I'm really thinking this isn't the correct one to use. Plz help .

Hello ddarlington36 and welcome to the neighborhood. I got no idea, but there are a few people around the place who might pop in and try to help. Remember electricity is dangerous (it can kill you if you dont know what your doing) so there are some who dont like to comment on diy stuff. Read up and keep asking questions, someone should be along at some stage, cheers

[PNjunction]

Ok i'm a first timer at building my very own battrybank/solar. My charging circuit is the mp1405 w/ the protection circuit built in. I'm going to be using this to charge multiple 18650's 3.7v x6 in a parallel setup combined with a dual usb boost to 5v for the usb devices. I've choosen a 1.6w 5.5v 266ma for the solar panel and i will attempt to wire it to the input on the mp1405 chip.

First of all, how are you going to balance them, especially if it is just one honking parallel setup? Also, what are the exact make / model / and quality of the cells? Are they new or used? Are you sure they are not counterfeit or have overstated capacities that are just not possible?

Frankly, you'd be better off asking this question over at Candlepowerforums in their "Flashlight Electronics - Batteries Included" subforum where many might have experience with this charging board, and can ask further questions that I don't see as a danger outright.

Not trying to shoo you away, but want you to get the best answer possible and return safely of course!

[ddarlington36]

First of all, how are you going to balance them, especially if it is just one honking parallel setup? Also, what are the exact make / model / and quality of the cells? Are they new or used? Are you sure they are not counterfeit or have overstated capacities that are just not possible?

Frankly, you'd be better off asking this question over at Candlepowerforums in their "Flashlight Electronics - Batteries Included" subforum where many might have experience with this charging board, and can ask further questions that I don't see as a danger outright.

Not trying to shoo you away, but want you to get the best answer possible and return safely of course!

Well i wasn't quite sure the best place to start asking questions like these so i figured a solar enthusiasm users might have some experience but i will take a look on candlepowerforums.

Balance charging wasn't really a avenue i wanted to venture into besides this is basically just a batterybank with a solar panel nothing quite that drastic.

But as far as i knew i thought aslong as its a parallel setup that balance charging isn't needed that only applies to "series" configurations right?

The batteries in question were not purchased from ebay i picked a reputable company band new cells :
LG INR18650HG2
3000 mAh High Discharge Flat

Specifications:
Nominal Capacity: 3000 mAh
Nominal Voltage: 3.6V
Discharge End Voltage: 2.5V
Standard Charging Current: 1A
Max Charging Current: 4A
Charging Voltage: 4.20+-0.05V
Max. Continuous Discharging Current: 20A
Internal Resistance: <20 milliohms


Thanx for the input,

[PNjunction]

Oops - too tired when I replied - yes parallel should be ok, BUT it could get very exciting if there is an extreme difference in charge when you first parallel them.

Op "HKJ" has done extensive charger and battery reviews over at Candlepower and may have covered yours already just in case you are interested.

For the blocking diode, try to use a "schottky" diode rather than a common germanium to get the lowest voltage drop. Forget the zener. Pick one about double the amount of current or more, since edge-of-cloud effects can cause current spikes.

I don't know what your level of expertise is, and even though your cells sound legit, I'd still be tempted to put them through a run or two through either a hobby-charger, or perhaps one of the more consumer friendly Xtar, Fenix, Nitecore, etc chargers to see if they can detect any problems first.

Obviously you are doing this for fun and education - but you know that you can just go with a commodity item like a 14 watt Anker panel and one of their pre-built battery banks already right?

[Sunking]

But as far as i knew i thought aslong as its a parallel setup that balance charging isn't needed that only applies to "series" configurations right?

Yes and No.

How do you charge a Lithium Cell to 100% SOC? There are a couple of ways to do it. In a manufactured charger made for Lithium cells you would float charge a cell at 100% SOC until charge current tapers to 5% of C and then terminate right? I assume you are talking about LiCo cells right? If so 4.2 vpc until current tapers to 5%. That is for a single cell. For multiple cells in series you now have to use some sort of Bleeder Board to clamp 4.2 volts and bypass current right? Well the cells are in series, but the regulation is in parallel of each cell.

But there is another way. If we want to maximize cell life, we do not charge to 100%, we limit charge to 80 to 90%. That makes life simple. We just use a regular Float Charger set to something less than 100% SOC voltage like 3.55 volts. We can leave the battery on Float until needed or the sun goes down and have roughly 90% capacity with extended cycle life.

Lots of ways to get the job done. Your application wil decide what the best route is.

[ddarlington36]

Oops - too tired when I replied - yes parallel should be ok, BUT it could get very exciting if there is an extreme difference in charge when you first parallel them.

Op "HKJ" has done extensive charger and battery reviews over at Candlepower and may have covered yours already just in case you are interested.

For the blocking diode, try to use a "schottky" diode rather than a common germanium to get the lowest voltage drop. Forget the zener. Pick one about double the amount of current or more, since edge-of-cloud effects can cause current spikes.

I don't know what your level of expertise is, and even though your cells sound legit, I'd still be tempted to put them through a run or two through either a hobby-charger, or perhaps one of the more consumer friendly Xtar, Fenix, Nitecore, etc chargers to see if they can detect any problems first.

Obviously you are doing this for fun and education - but you know that you can just go with a commodity item like a 14 watt Anker panel and one of their pre-built battery banks already right?

Thanx for the feedback on the diode that helps me a ton i kinda figured i had the wrong diode. I do have a consumer based 18650 charger xtar vc4 so far it charges anything i throw in there.

Yeah i did know that i could just buy a retail batterybank that has solar panel incorporated to the back i did want this project to be a learning experience if i decide to take things further in the future I'll have some experience with the basics.

[ddarlington36]

Yes and No.

How do you charge a Lithium Cell to 100% SOC? There are a couple of ways to do it. In a manufactured charger made for Lithium cells you would float charge a cell at 100% SOC until charge current tapers to 5% of C and then terminate right? I assume you are talking about LiCo cells right? If so 4.2 vpc until current tapers to 5%. That is for a single cell. For multiple cells in series you now have to use some sort of Bleeder Board to clamp 4.2 volts and bypass current right? Well the cells are in series, but the regulation is in parallel of each cell.

But there is another way. If we want to maximize cell life, we do not charge to 100%, we limit charge to 80 to 90%. That makes life simple. We just use a regular Float Charger set to something less than 100% SOC voltage like 3.55 volts. We can leave the battery on Float until needed or the sun goes down and have roughly 90% capacity with extended cycle life.

Lots of ways to get the job done. Your application wil decide what the best route is.

Well by liCo do you mean lithium-ion cells these terminate @ 3.7/4.2v. I was under the belief that since it was parallel i wouldn't have to worry about the charging process but after reading you're post now I'm doing my homework reading up on float curve/voltage on parallel setups thanks for the info.

I have came across lithium solar charge controller that incorporates the float voltage and then it starts curving down the applied Ma the closer it gets to the float voltage and then trickle charges from there. But i'm in the dark from the point if i can charge them individually or just like they are (parallel). [URL ] http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=221799418649&cat egory=58288&pm=1&ds=0&t=1437935466159[/URL ]

[PNjunction]

Thanx for the feedback on the diode that helps me a ton i kinda figured i had the wrong diode. I do have a consumer based 18650 charger xtar vc4 so far it charges anything i throw in there.

Great - use the VC4 to charge them all to full before you configure them into parallel with each other to avoid any excitement. You may be interested in a great technician-review of it here with details you'll find nowhere else like thermal imagery etc. He does this to all the stuff he reviews: I use something else.

http://lygte-info.dk/review/Review%20Charger%20Xtar%20VC4%20UK.html

BUT, that charger appears to always want to charge to full. In a solar application where one wants to get the most cycle life out of them, you don't want to charge them to full as Sunking pointed out. Thus, if your charge board that you intend to use with solar has a user-selectable upper voltage limit, try not to go higher than 3.9v. Perhaps 4.0v max.

NOTE TO LURKERS: These are NOT lifepo4 chemistry lithium cells in this project, and any voltage references are not valid if you are using lifepo4. The ones here are not lifepo4.

Thus the reference to 3.55v in the earlier message pertains to lifepo4, but not to these cells. It is easy to forget sometimes when you work with both lifepo4, and say lico02, Linmc, or anything else. It happens, so be sure to keep the chemistry of your cells in mind. Ie, just "lifepo4 is different from everything else and has a different voltage range" will keep one on track.

[SunEagle]

Great - use the VC4 to charge them all to full before you configure them into parallel with each other to avoid any excitement. You may be interested in a great technician-review of it here with details you'll find nowhere else like thermal imagery etc. He does this to all the stuff he reviews: I use something else.

http://lygte-info.dk/review/Review%20Charger%20Xtar%20VC4%20UK.html

BUT, that charger appears to always want to charge to full. In a solar application where one wants to get the most cycle life out of them, you don't want to charge them to full as Sunking pointed out. Thus, if your charge board that you intend to use with solar has a user-selectable upper voltage limit, try not to go higher than 3.9v. Perhaps 4.0v max.

NOTE TO LURKERS: These are NOT lifepo4 chemistry lithium cells in this project, and any voltage references are not valid if you are using lifepo4. The ones here are not lifepo4.

Thus the reference to 3.55v in the earlier message pertains to lifepo4, but not to these cells. It is easy to forget sometimes when you work with both lifepo4, and say lico02, Linmc, or anything else. It happens, so be sure to keep the chemistry of your cells in mind. Ie, just "lifepo4 is different from everything else and has a different voltage range" will keep one on track.

Good clarification on the battery chemistry and associated cell voltage.