Small LiFePO4 Charging Abandoned

[ko4nrbs]

My search for a safe and reliable LiFePO4 Solar charger was unsuccessful. I found a few that advertised the ability to Solar charge LiFePO4 cells but upon further investigation, I wasn't comfortable with their Float charge voltage.

Decided to just go ahead and use Lithium Ion 18650 cells and this charger:

https://learn.adafruit.com/usb-dc-and-solar-lipoly-charger

Note from the manufacturer:
In marginal solar conditions, the board will charge intermittently. If there is not enough solar energy to charge the LiPo continuously, it allows the large capacitor to build-up a charge, then transfers that to the LiPo.

At their suggestion, I will connect my Digital camera as suggested:
Another approach is to bypass the load-sharing circuitry and connect your load to the GND and B+ pins. That will effectively put your load in parallel with the battery.


Now to find a good outdoor and waterproof 6 volt Solar Panel.

Bill

[Sunking]

Bill, me conflused. You open with:

My search for a safe and reliable LiFePO4 Solar charger was unsuccessful. I found a few that advertised the ability to Solar charge LiFePO4 cells but upon further investigation, I wasn't comfortable with their Float charge voltage.My search for a safe and reliable LiFePO4 Solar charger was unsuccessful.

Next paragraph you say"

Decided to just go ahead and use Lithium Ion 18650 cells and this charger:

So you found a solar charge you are going to buy that can charge LFP or LCO 18650 cells. You got exactly what you were looking for.

I did not look at the Adafruit controller specs, but I suspect it is a Float Charger your set for 3.6 volts if using LiFePo4, and 4.2 if LCO. It is shuts off or terminates the charge when the battery is fully charged OK. But if they Float maybe be an issue. Lithium batteries do not like being held at full charge voltage after reaching full charge. For your purpose you do want to Float but at some voltage less than 3.6 volts. Ideally you would like something variable you can control a bit like adjustable 3.4 to 3.6 volts. 3.45 seems to be a good number for several manufactures like A123 System that recommend their 18650 cells at 3.45 volts per cell.

I suspect it would be easy to Hack the Adafruit controller to customize the voltage. Hell that is what Adafruit is all about. I use to use their Uno a bit, but moved on to Teensy 3.2 and up. So you might want to look into it.

[SunEagle]

My search for a safe and reliable LiFePO4 Solar charger was unsuccessful. I found a few that advertised the ability to Solar charge LiFePO4 cells but upon further investigation, I wasn't comfortable with their Float charge voltage.

Decided to just go ahead and use Lithium Ion 18650 cells and this charger:

https://learn.adafruit.com/usb-dc-and-solar-lipoly-charger

Note from the manufacturer:
In marginal solar conditions, the board will charge intermittently. If there is not enough solar energy to charge the LiPo continuously, it allows the large capacitor to build-up a charge, then transfers that to the LiPo.

At their suggestion, I will connect my Digital camera as suggested:
Another approach is to bypass the load-sharing circuitry and connect your load to the GND and B+ pins. That will effectively put your load in parallel with the battery.


Now to find a good outdoor and waterproof 6 volt Solar Panel.

Bill

You do understand that those little Lithium batteries really do not have much of a life cycle in terms of daily usage.

I have gone through about a dozen of them (they power my 808 keychain cameras) due to no longer holding a charge after many uses. They are nice an compact but IMO have a short life.

[ko4nrbs]

Bill, me conflused. You open with:


Next paragraph you say"



So you found a solar charge you are going to buy that can charge LFP or LCO 18650 cells. You got exactly what you were looking for.

I did not look at the Adafruit controller specs, but I suspect it is a Float Charger your set for 3.6 volts if using LiFePo4, and 4.2 if LCO. It is shuts off or terminates the charge when the battery is fully charged OK. But if they Float maybe be an issue. Lithium batteries do not like being held at full charge voltage after reaching full charge. For your purpose you do want to Float but at some voltage less than 3.6 volts. Ideally you would like something variable you can control a bit like adjustable 3.4 to 3.6 volts. 3.45 seems to be a good number for several manufactures like A123 System that recommend their 18650 cells at 3.45 volts per cell.

I suspect it would be easy to Hack the Adafruit controller to customize the voltage. Hell that is what Adafruit is all about. I use to use their Uno a bit, but moved on to Teensy 3.2 and up. So you might want to look into it.

They told me it was only good for charging Lithium Ion cells and shuts off the charge at 4.2 volts. I'm ok with that and will forget about the LiFePO4 cells for now.

Now to locate a good and reliable 6 volt Solar Panel.


Bill

[Sunking]

They told me it was only good for charging Lithium Ion cells and shuts off the charge at 4.2 volts. I'm ok with that and will forget about the LiFePO4 cells for now.

Bill you still might be confused.

18650 cells are available in both LiFeP04 (LFP or lithium iron phosphate) 3.6 volts, and LiCoO2 (LCO or lithium cobalt oxide) 4.2 volts. All 18650 means is the dimension of the cell they are contained in of 18 mm diameter and 650 mm long. It does not tell you what is inside. In fact there are 5 possibilities, LFP, LCO, LTO, LMO, and NMC.

The charger you linked to has two charge voltages available of 3.6 volts for LFP cell, and 4.2 volts for LCO, LMO, and NMC. So if you want LFP order LFP 18650 cells and a 3.2 volt charger.

If 1860 are not large enough use 23650's in LFP and use a 3.6 volt chargers. LFP is the easiest most forgiving to charge, fairly safe, with fairly long cycle life. If given the choice charge at 3.45 volts as that will double cycle life and only gives up 5 to 10% capacity.

Hope that helps.

[ko4nrbs]

The charger you linked to has two charge voltages available of 3.2 volts for LFP cell, and 4.2 volts for LCO, LMO, and NMC. So if you want LFP order LFP 18650 cells and a 3.2 volt charger.

This is what I saw in the description: Am I missing something?
3.7V/4.2V Lithium Ion or Lithium Polymer battery charger

Thanks for the explanations!!

Bill

[Sunking]

I had a brain fart. LFP is charged at 3.6 volts. Nominal is 3.2 volts.

[ko4nrbs]

I had a brain fart. LFP is charged at 3.6 volts. Nominal is 3.2 volts.

Been there and done that!! I do appreciate your feedback.

The following are some small and inexpensive USB chargers some are using with Solar Panels. I found lots of info on this web browsing.
These are used because they don't have settings in the Firmware that have to be manually set before they will begin a charge.

This one is the latest version of the Miller ML102 and takes only Unprotected cells due to a size restriction!!
Miller ML-102 (Latest is Version 8) Will avoid Version 7 after reading it's review!!

http://budgetlightforum.com/node/40359

Xtar MC1
http://lygte-info.dk/review/Review%20Charg...20MC1%20UK.html
Xtar MC1 Plus
http://lygte-info.dk/review/Review%20Charg...1Plus%20UK.html
Xtar XP1
http://lygte-info.dk/review/Review%20Charg...20XP1%20UK.html


NiMh Charging (I will avoid Solar charging NiMh)
From the web:
When it comes to charging NiMH cells, I strongly recommend that you use a buffer battery, because the -dV/dt algorithm used by NiMh smart chargers is not very tolerant of interruptions in power, especially when a NiMH cell is approaching full charge.

If a cloud passes in front of the sun, you don't have a buffer battery and the NiMH charger resets, it can lose track of the recorded voltage it needs to spot the -dV/dt endpoint. This can cause your cells to be overcharged, reducing their capacity and service life.

Bill

[Sunking]

If you use a Buffer Battery, you do not need any other battery like NiMh or LFP. You just take a 30% loss of power doing that. Use a regular 12 volt battery, and then use a voltage converter to what ever voltage you need. A lot less expensive and less complicated. Hell you can even find drop in replacements 12 volt LFP batteries that can use any off the shelf solar charger. Think outside the box.

[ko4nrbs]

If you use a Buffer Battery, you do not need any other battery like NiMh or LFP. You just take a 30% loss of power doing that. Use a regular 12 volt battery, and then use a voltage converter to what ever voltage you need. A lot less expensive and less complicated. Hell you can even find drop in replacements 12 volt LFP batteries that can use any off the shelf solar charger. Think outside the box.

Good idea. Thanks.
Bill