TheBackShed.com

Forum Index : Microcontroller and PC projects : LiPo's for projects like the Game*Mite

Page 2 of 2

Author

Message

matherp
Guru

Joined: 11/12/2012
Location: United Kingdom
Posts: 9153

Posted: 01:58pm 23 Oct 2023

Copy link to clipboard

Print this post

The float charging issue is easily dealt with. See my circuit of the high spec gamemite.
In the RC world where we really use Lipos we now discharge batteries to about 50% for any extended period of storage. The RC lipo chargers now have this as a standard facility.
My drone batteries even have internal software to self discharge to that level after 24hours of non-usage.
My biggest batteries are 6s 5000mah with a 75C maximum continuous discharge rate (>300A) so you don't want these letting go both from a safety and expense perspective
Edited 2023-10-24 00:08 by matherp

robert.rozee
Guru

Joined: 31/12/2012
Location: New Zealand
Posts: 2350

Posted: 02:28pm 23 Oct 2023

Copy link to clipboard

Print this post

lizby said

Quote (c) if you are drawing power from your cell at the same time as you are charging it you risk effectively 'float charging' the cell indefinitely. needless to say, this may lead to an undesirable outcome.

What is the "undesirable outcome" which may occur from this [...]

from https://en.wikipedia.org/wiki/Float_voltage :

"Lithium ion cells have to be float charged with extra care because if they are float charged at just a little over optimum voltage [...] the chemical system within the cell will be damaged to some extent. Some lithium ion variants are less tolerant than others, but generally overheating, which shortens cell life is likely, and fire and explosion possible other outcomes."

cheers,
rob :-)

Mixtel90

Guru

Joined: 05/10/2019
Location: United Kingdom
Posts: 6826

Posted: 03:19pm 23 Oct 2023

Copy link to clipboard

Print this post

Of course, the only batteries certified for use with Raspberry Pi boards are liquid electrolyte Leclanché cells. A compact pack of four of these (a mere 300mm x 300mm x 280mm, including their wooden crate) provides the requisite 5.6V to act as a standby source for the 5V USB input when fed via a standard silicon diode.

;)

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

thwill

Guru

Joined: 16/09/2019
Location: United Kingdom
Posts: 4047

Posted: 03:29pm 23 Oct 2023

Copy link to clipboard

Print this post

Mixtel90 said Of course, the only batteries certified for use with Raspberry Pi boards are liquid electrolyte Leclanché cells ...

Probably a darn sight easier to get hold of than consistent, easy to understand, easy to follow advice

.

EDIT: I was all set to out of an over-abundance of caution replace the 1.2K with 4.7K for future kits until Rob's tidings of doom: "... if you reduce the maximum charging current too much then there is the risk that charging may never terminate."

Thanks folks,

Tom
Edited 2023-10-24 02:37 by thwill

Game*Mite, CMM2 Welcome Tape, Creaky old text adventures

Mixtel90

Guru

Joined: 05/10/2019
Location: United Kingdom
Posts: 6826

Posted: 04:48pm 23 Oct 2023

Copy link to clipboard

Print this post

I'd stick 2K2 in. It's roughly C/2 for a 1Ah cell, which is really as small as you want to go. It'll charge in about 2hrs, which is bearable for most people, I think. There's no point in going down to C/10 on something where there is air around the battery to allow a degree of cooling - certainly no lower. This is a game. People will want it to charge reasonably quickly so that they can play it.

I'm leaving mine at 1C. The cells didn't warm up noticeably.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

bigmik

Guru

Joined: 20/06/2011
Location: Australia
Posts: 2914

Posted: 10:18pm 23 Oct 2023

Copy link to clipboard

Print this post

Hi Rob, All,

I am 99% certain that the way we have Game*Mite configured it is not possible to draw from the battery at the same time as it is being charged.

The output of the TP4056 module reflects the voltage on the battery. Let’s say a maximum of 4.2volts, this output is passed through a diode to the VSys line.
The only way the module is charged is when a USB is plugged into the Pico. Let’s say this is 4.8volts, this is also through an onboard diode on the Pico to VSys.
As the voltage coming from the USB is higher than that coming out of the module no power would be drawn from the battery if power is connected to the Pico (which is where the module gets its charge input from)
What that means is that the USB would be charging AND supplying all of the current required to drive the Pico.

If you were really concerned there is a link near the 14pin TFT header that will shut the PICO down (all the 3v3 power will stop) when the battery is charging.

@Tom,
I think you can safely leave the module as is with your 1000mAh battery but if you were concerned change R3 to 2k2 to supply max 500mA.

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

thwill

Guru

Joined: 16/09/2019
Location: United Kingdom
Posts: 4047

Posted: 09:32am 24 Oct 2023

Copy link to clipboard

Print this post

Thanks folks, I'll order some 2k2's.

Best wishes,

Tom

Game*Mite, CMM2 Welcome Tape, Creaky old text adventures

thwill

Guru

Joined: 16/09/2019
Location: United Kingdom
Posts: 4047

Posted: 02:29pm 24 Oct 2023

Copy link to clipboard

Print this post

(final?) observation on the USB-C version of the TP4056 modules that I've got I think they are 0402's, but on the Micro USB version they are 0805's. I'm hoping/suspecting there is enough room for an 0603 on the former ... they really don't seem to want you adjusting these, WTF.

Best wishes,

Tom
Edited 2023-10-25 00:29 by thwill

Game*Mite, CMM2 Welcome Tape, Creaky old text adventures

Page 2 of 2

Print this page

To reply to this topic, you need to log in.