Hi there.
Does anyone here have experience on using a small solar panel to charge a 3.7v LiPo thru the typical TP4051 charger? Either using the popular ebay board, or a wemos Battery shield.
I have some devices (Wemos Mini mostly) which are into DeepSleep for 10min and only wake up for 10 seconds to transmit the readings, so basically the discharge rate is minimal. I have them chargind with variated small solar panels, which I had bought some time ago, different models, and Im not getting a decent charge rate, I need 100% sun (not on an overcast day) and it only charges during 2 or 3 hours during the day
I was wondering, maybe these chargers, that come preconfigured with the 1Ah charge rate (jumper in the jp1) need to be modified with the according charge resistor to rduce the charge rate to something closer to the solar panel capabilities, maybe if the charger is trying to pull 1A and the solar panel is providing 300mAh, the voltage is getting so low it doesn't stand
As no-one has yet answered I will point you to my YouTube video #50 TP4056 UPS - protect from power outs and brown outs which uses a TP4056 but the principle is the same.
If your solar panel provides the correct voltage then no matter how small the current it provides it will be enough to trigger the charging process (although it may not be enough to charge the battery or replace what has been used, of course).
Yes, you do have to be careful with that pesky resistor or you can easily overcharge smaller batteries but I suspect yours are at least 1AH capacity so should be fine (if you read the comments on this video you will see this was a cause for concern for one viewer which prompted me try a couple of things out).
Sorry I said TP4051, it was TP4056 as you stated in your reply
My issues is more related to the solar panel itself and their behaviour "under the sun". I have one small (maybe 10x10cm) solar panel that lights up the red charging led in the TP board, but the battery voltage (monitored thru Analog in in my Wemos board) isn't rising while the led shows "charging".
Then I switch to an oversize (for this project) solan panel, maybe (20x20cm) and the charging light turns on again BUT I DO see the battery voltage rising up.
Sorry I don't have the specs for these panels (I bought them a long time ago and there are no markings) but I wouldn't expect to be needed a 20x20 panel for such a small battery, Im just suspecting the smaller is 5V and it needs 100% direct sun straight into the panel, and maybe the larger one is 6V and just an overcast day is enough to get something close to 5v to activate the charging function, what do you think?
I just want to replicate the device and be able to know what panel is the smallest one that fits here
I think you should measure the panels, voltage and current, there is not much point in speculations what voltage they may be.
I just want to replicate the device and be able to know what panel is the smallest one that fits here
You already said the TP4056, as standard, charges at 1A so for a 5V input thats 5W, a 20x20 panel is around 5W, but thats in full sun. So to be able to charge at 1A in average conditions, you probably need a solar panel 3 times the size you already have.
As for the smallest panel you can use, how can anyone advise unless you tell us the average daily power consumption of your 'devices' ?
I don't have a real measurement for this, but this is a Wemos board running:
10 minutes at deepsleep which is 40uA
20 seconds at 100mA
{repeat}
So on average, on this 3.7V 600mA LiPo cell, with no charging at all, it drops something like 0.2 a day. WHich means for me that a really small charger should suffice with clear view of the sky for a small (but full) charge every day
I just measured them under direct sunlight:
Small one: Open output 8V, short circuit 140mA
Large one: Open output: 7,3v, short circuit 500mA
Hidden from the direct sun but under undirect light they still provide
Small one: Open output 6,3V, short circuit 6mA
Large one: Open output: 5,8v, short circuit 20mA
Small is marked only "Sunwalk 001 110x110mm ROSH"
Large is marked "Starsolar CNC 165x165-6"
have you watched the youtube videos by julian about charging ?
Do you confirm that when there is zero input, that the charger circuit is not draining ANY power ?
what is the voltage under full sun ? under partial sun ?
if your current out is drawing down the voltage, then change the resistor value.
understanding the data sheet for the chip seems your main goal.
dave-in-nj:
have you watched the youtube videos by julian about charging ?
Yes I had already watched it but it talks about using the TP charger, which I already have in lots of other projects (mainly BLE iBeacons with a 18650 battery) but using a 5v 1A power supply to be charged, but it's not talking about it's capabilities about charging on any other voltage slightly under or over 5V, and with different currents, like I get with a Solar Panel
dave-in-nj:
Do you confirm that when there is zero input, that the charger circuit is not draining ANY power ?
what is the voltage under full sun ? under partial sun ?
if your current out is drawing down the voltage, then change the resistor value.
understanding the data sheet for the chip seems your main goal.
The voltages and amps were shown in my last comment, from what I see both panels should be fine but I may have to add the charging "PROG" resistor to lower the A so the voltage while charging on overcast sky doesn't drop that much
srnet:
Its vital that you plan based on the real measured values.
Well tbh I wasn't planning with fully detailed calculations as my gross numbers are highly covered.
Let me explain
MY Wemos pulls 100mAh during 30 sec. Then goes into deepSleep for the next 10 minutes, which pulls 43uAh
Considering this duty cycle I would be using 240mA in 24h
My solar panel provides: Small=145mAh Large=500mAh. Small would charge under the sun in 1.5h (which I get here these days), and large would charge fully in 30 mins. Both would do
Then I still think the voltage on the smaller one is dropping due to the total A pulling from the TP4056, under the required minimum voltage so it's not really charging, despite the red led is lit for 8h/day
To be more concise, this is the graph for the battery voltage for the last 24h. LINK
Currently working with the large (165x165mm) panel for the last 2 days
As you can see the battery tops at 4.04v after charging and drops down to 3.96v, which is a minimal discharge during the evening-night period, which any small solar panel should be able to recharge in minutes (it's a 650mAh battery)
Not a bad option, but I truly need some more backup, if the solar panel breaks or the weather becomes extremely dark (like really bad stormy days all in a row) I have lots of "reservoir" in a 650mAh battery, this circuit drops 0.08v from this battery on a full day with nom charging, so it would still work for several weeks if the panel is not charging and as the voltage is being measured by the device and sent over to Thingspeak, I get a warning if it gets too low, with time enough to go to the location a replace the solar panel or see what's wrong.
