hi every one, I have a few questions about powering and charging my project, I'm using a 3.3v proMini, a 3.7 lithium battery.
I was planning on using a TB4056 for charging protection, it has a mini USB plug and also two pins I can connect other 5vdc supplies to. I was planning on using two 5v 30mA solar panels in parallel to equal 5vdc @ 60mA.
A) is that sufficient to charge the battery? (batt # 503759)
B) I've read that with a 3.7vdc power supply that you don't really need to use a voltage regulator on a 3.3vdc system and the battery can be connected directly to the VCC pin on the proMini
Is this a true statement?? it sounded a bit iffy to me.
A) Yes, but very slowly. You also need a charger module designed for LiPo batteries to prevent overcharging, and a protection circuit to prevent overdischarging. Otherwise you will destroy the battery very quickly.
NiMH cells are much easier to use and tolerant of abuse. They can be trickle charged by a solar cell indefinitely.
B) the ATMega processor on the Pro Mini will run at any voltage between about 2V and 5.5V. No regulator is needed, but other circuitry might. There is a regulator on the 3.3V Pro Mini and it might be damaged if you connect the battery to the Vcc pin, in an attempt to bypass the regulator.
jremington:
You also need a charger module designed for LiPo batteries to prevent overcharging, and a protection circuit to prevent overdischarging. Otherwise you will destroy the battery very quickly.
NiMH cells are much easier to use and tolerant of abuse. They can be trickle charged by a solar cell indefinitely.
He is using a TP4056 charging module, it has built in over charging protection. It's over-discharge protection is set way too low. Using a protected li-ion cell is highly recommended.
LiFePO4 cells are now easily available in the market and in my opinion a better alternative to NiMH cells. They also provide nominal 3.2V for a single cell. He can use a TP5000 module to charge these cells.
If using NiMH cells then it's best to avoid them LSD variants because they don't like trickle charge.
jremington:
I also have no idea what an "LSD" variant is, but NiCd or NiMh cells will work fine in your project.
Low Self Discharge just like 'MorganS' said, Eneloops for example, Sanyo popularized these in the market but now almost every NiMH manufacturer has their own LSD variants with different names.
BruceM:
I looked up a LiFoPO4. I don’t think that style of battery will work for my project. It looks a little bulky
They are available in a lot of different sizes. 14500 size for example is exactly the same size as a AA battery, 10440 size is exactly same as a AAA battery.
BruceM:
hi every one, I have a few questions about powering and charging my project, I'm using a 3.3v proMini, a 3.7 lithium battery.
I was planning on using a TB4056 for charging protection, it has a mini USB plug and also two pins I can connect other 5vdc supplies to. I was planning on using two 5v 30mA solar panels in parallel to equal 5vdc @ 60mA.
A) is that sufficient to charge the battery? (batt # 503759)
B) I've read that with a 3.7vdc power supply that you don't really need to use a voltage regulator on a 3.3vdc system and the battery can be connected directly to the VCC pin on the proMini
Is this a true statement?? it sounded a bit iffy to me.
BruceM:
I was planning on using two 5v 30mA solar panels in parallel to equal 5vdc @ 60mA.
A) is that sufficient to charge the battery? (batt # 503759)
Probably not, although you should have provided details of the battery rather than expecting people to use Google to find out its characteristics. The solar panels might well give you 5V @ 60mA in ideal full sun conditions, but for a practical output assume its going to be between 25% and 33% of the best case value. So you tell us, is 20mA enough to charge the battery in a reasonable amount of time? It really depends on how much the discharge rate is, and you dont say.
B) I've read that with a 3.7vdc power supply that you don't really need to use a voltage regulator on a 3.3vdc system and the battery can be connected directly to the VCC pin on the proMini
A fully charged LiPo is 4.2V, not 3.7V. So whether you can connect the 4.2V direct to the VCC of the Pro Mini (after removing the regulator) rather depends on what other stuff you are connecting to the Pro Mini and you did mention that either.[/quote]
Using a LiPo in a wearable product should only really be done if you have a good amount of experience and a full appreciation of what you need to do to make sure the LiPo is safe and stays safe over extended use. You have not mentioned what you are going to do to ensure the wearable device turns itself off if the LiPo voltage falls to around 3.3v.
Remember LiPos can and do explode if you dont use them properly, so I would recommend you use a safer alternative.
BruceM:
It’s a wearable project. For a hat. I was planning on mounting the battery under the bill of the hat. That’s why I wanted a flat Battery
You should have told us this in the first place. So I presume your LiPo battery is also going to be of small size so small capacity. While it is ok to charge small capacity LiPo cells at 60mA provided by the solar panels, just make sure you do not plug those TP4056 modules into a USB socket before you change the charge current resistor on the board because by default the resistor placed in the TP4056 board lets the board to charge the cells at 1A rate, this will cause problems for a small capacity cell.
Also make sure your LiPo battery you choose can tolerate the heat it gets from the sunlight falling on the hat.
Responding to comment 10... I'm using three 3.3volt sensors that need a steady 3.3v.(from what I remember the data sheet says) And from other answers regarding the solar I think I'll just charge by minight USB.
Thanks to MarkT for the diode suggestion.
I've also thought about using two batteries to make 7.4vdc and then using a voltage regulator. I know it will drain the battery a little faster. But in reality I only need it to run for 4 hours tops before recharging
I'm just looking for suggestions before I actually start doing anything on this project.
As far as protection goes I'll be using over charge protectors and the batteries I have looked at do have discharge protection built in.
BruceM:
the batteries I have looked at do have discharge protection built in.
Make sure that the low voltage cut off is 3.0V or more, you will need to check the datasheet for the battery.
A lot of these 'discharge protection built in' things cut off as low as 2.4V.
From Wikipedia;
Voltage cut-off in portable electronics
Some portable equipment does not fully use the low-end voltage spectrum of a battery. The power to the equipment cuts off before a relatively large portion of the battery life has been used.
A high cut-off voltage is more widespread than perhaps assumed. For example, a certain brand of mobile phone that is powered with a single-cell Lithium-ion battery cuts off at 3.3V. The Li‑ion can be discharged to 3V and lower; however, with a discharge to 3.3V (at room temperature), about 92–98% of the capacity is used.[2] Importantly, particularly in the case of lithium ion batteries which are used in the vast majority of portable electronics today, a voltage cut-off below 3.2V can lead to chemical instability in the cell, with the result being a reduced battery lifetime. For this reason, electronics manufacturers tend to use higher cut-off voltages, removing the need for consumers to buy battery replacements before other failure mechanisms in a device take effect.