The best charge IC for low voltage / solar panels ?  - Page 1
Forum section: electronics / beginners

author: kikivoinea
author_rank: Newbie
timestamp: May 21, 2018, 11:48:31 am
content: I am working on a project , that include an solar panel with an output of around 5V and 100mA.What would be the best IC for this project?Are there better options than BQ25504 or LTC3106?I want to charge an 1S LiPo batteryTnx

author: Seekonk
author_rank: Super Contributor
timestamp: May 21, 2018, 01:05:37 pm
content: I would hardly think you need more than a TP4056 and a 5.6V zener. It is unlikely you could gain much by operating at power point.

author: killcode
author_rank: Contributor
timestamp: May 22, 2018, 01:35:42 am
content: As Seekonk said - not much to be gained by using a switching charger over a linear one at that input voltage and charge current.

author: kikivoinea
author_rank: Newbie
timestamp: May 22, 2018, 12:10:04 pm
content: thank you for your responses.I was thinking that the panel is not that big/powerfull. So a great efficiency is needed.

author: DTJ
author_rank: Super Contributor
timestamp: May 22, 2018, 12:17:49 pm
content: Have you tested your panel to see what output voltage it gets in real conditions.My limited experience is that the data sheets can be quite 'generous'. The output voltage may be less than the 5V for much of the time. Just a thought.

author: kikivoinea
author_rank: Newbie
timestamp: May 25, 2018, 09:47:52 am
content: Yes. It variates.That is why I think an IC would be good , for harvesting the most out of it.

author: Seekonk
author_rank: Super Contributor
timestamp: May 25, 2018, 01:15:59 pm
content: Almost any small buck converter like a $1 2596 board can be converted to operate at power point. Just takes a FET or transistor to control the on/off pin.

author: kikivoinea
author_rank: Newbie
timestamp: June 04, 2018, 09:34:32 am
content: But I think I need a boost converter , due to the not-so-perfect solar conditionsSo , besides TP4056 , LTC3106 or BQ25570 , or simillar , wouldn't be ok?

author: Seekonk
author_rank: Super Contributor
timestamp: June 04, 2018, 06:09:05 pm
content: Can't even start till we know exactly what the panel puts out. There are no 5V panels. What is it open circuit and what does it put out at say 40ma. I won't even bother looking, can't even think of a MPPT chip. They may say they are MPPT, but they are not. They are actually MPPC. There is an efficiency cost to these chips at low power and your panel is about useless to harvest much. One thing you will learn is it doesn't really matter much. You have too much light or not enough for the controller to matter.

author: kikivoinea
author_rank: Newbie
timestamp: June 05, 2018, 10:24:35 am
content: Well , it is an custom flexible panel , and with full sun , I get 5 Volts

author: Seekonk
author_rank: Super Contributor
timestamp: June 05, 2018, 05:23:53 pm
content: Nothing is just 5V. You know nothing till you test it with a load and without. I suggest you look at typical panel power curves.

author: DavidMenting
author_rank: Contributor
timestamp: June 05, 2018, 07:25:34 pm
content: It might be worth checking whether you need a boost converter or MPPT at all. Often, the efficiency of these low voltage converters is not all that great. If the maximum power point of these solar cells is close to the voltage of your LiPo, you could hook the panel up to your LiPo directly through a FET. The maximum panel current is your maximum charge current. Once the cell reaches full voltage, you turn off the FET.You need battery cell protection though, and of course monitor the battery temperature. Also, it's smart to choose your battery cutoff voltage conservatively (for example 4.0V instead of 4.2V).