Impossible lipo charger

HI,
Serious help needed, why all low (below 5v) voltage battery chargers/boards does only half the job, they just cut off power but not back on!?
Goal is: power the supply unit to charge 1 cell LIPO battery: with power cut OFF when battery charge reaches 4.1v and turns charge ON only when battery reaches 3.6v (adjustable V is disarable option) in other words i need battery costantly powered, but charge only when battery is drained to about 20% and stop charging when battery charged to about 90% capacity

I think i found solution how to go around it, but no board witch could do that so i need help building one.
My thought was put clamp voltmeter on battery leads to detect lowest 3v volts, then voltmeter send signal to relay witch powers ON entire charging circuit to recharge battery and switches relay OFF when voltmeter detects 4.2v Only problem i am just amature understand just basic paramaters
arduino probably could do the work but i have no clue what components to buy to make it happen.
Thanks for advice or links

Why not get a specialized LiPo charger chip such as the MCP73831?

...R

Agreed the MCP73831/2 will do the job, and the auto restart of charge is when the battery voltage falls to about 95% of full charge voltage.

Far better to use a device designed for the job.

Get a DIY circuit or software wrong and your battery can explode or catrch fire.

Nice chip but it will not do what the OP specifies! Recharging begins at a point which cannot be adjusted and is higher than he wants.

I agree this isn’t for amateurs, but the OP gets one thing right, he’ll keep his lipos happier cycling them as he suggests.

a7

alto777:
, but the OP gets one thing right, he’ll keep his lipos happier cycling them as he suggests.

Better than with a professionally designed charger?

Why?

...R

Chip and programing gonna be too complicated considering your advide on wrong inputs battery can blow up.

Truth is that battery inside phone i need it constanly ON CHARGE while once in while using it.
I found online an usb cable $80 but it does just half the job it diconects when battery full and thats it you have to unplug and plug back again.
if i could make it charge fully then stop, then start charging when battery is low. That would work for me.
Anyone can tell witch components to buy i posted in picture (relay, voltmeter) and how to make them talk to eatchh other ?

many thanks

Robin2:
Better than with a professionally designed charger?

Why?

...R

A LiPO cell life will be maximised if it is charged gently, not charged fully and never discharged fully.

The OP wanted cycles between not fully charged and not fully discharged. I assumed he was reading the same things as I.

I built a microprocessor-based single-cell charger / discharger by hijacking a cheap charger, surrounding it with relays and using measurements of the cell to connect and disconnect, as appropriate for the task, either the charger or a dummy load for discharging.

The little cells are cheap enough, so who cares. But batteries of larger cells can get a bit spendy, so taking care of them makes more sense.

a7

alto777:
A LiPO cell life will be maximised if it is charged gently, not charged fully and never discharged fully.

From my reading of the specs the MCP73831/2 perfectly matches that requirement.

It will also help the battery life if it is discharged gently - but that is beyond the scope of the charger.

…R

This lithium charger IC has auto-recharge, and is only 88 cents:

https://www.digikey.com/product-detail/en/microchip-technology/MCP73833T-AMI-UN/MCP73833T-AMI-UNCT-ND/5818702

I honestly can't see a reason to drag a lithium down to 20% and then only charge to 90%. They are happy in a constant state of "topped off".

If you are trying to cap your battery's output voltage, there are better ways.

Could you shed more light on why you want such a weird charge strategy?

Truth is that battery inside phone i need it constanly for months ON CHARGE while once in while using it.
I found online an usb cable for phone $80 but it does just half the job it diconects when battery full and thats it you have to unplug and plug back again.
if i could make it charge fully then stop, then start charging when battery is low. That would work for me.

Goal is: power android PHONE 1 cell LIPO battery: with power cut OFF when battery charge reaches 4.1v and turns charge ON only when battery reaches 3.6v (adjustable V is disarable option) in other words i need battery costantly powered but charge only when battery is drained to about 20% and stop charging when battery charged to about 90% capacity

there are android apps to controll bluetetooth and wifi modules, but how to put it together?
i thought i could download android app witch plays sound battery full or low at percentage i need, then sound triggers voice sensor witch turns relay on/off conected to phone power supply.

arduino android bluetooth app could do the job to switch bluetooth controled relay but how to pair it with anohter apps notifications?

and worst of all i am not IT ingineer and could not do nothing with chip gys suggested. ready baked boards i can wire/solder myself but arduino programming gonna be issue

Are you intending to use this 'charger' on the battery that is inside the phone, whilst its also inside the phone ?

Robin2:
From my reading of the specs the MCP73831/2 perfectly matches that requirement.

It will also help the battery life if it is discharged gently - but that is beyond the scope of the charger.

...R

You must be reading a different data sheet:

"If the voltage drops below the recharge threshold, another charge cycle begins and current is once again supplied to the battery or load. The recharge threshold is factory set."

And set quite high as a percentage of full charge. The OP wants to charge less than fully, and discharge quite a bit but again not fully. That chip will not do that. Not without help.

a7

Soleen:
Truth is that battery inside phone i need it constanly for months ON CHARGE while once in while using it.
I found online an usb cable for phone $80 but it does just half the job it diconects when battery full and thats it you have to unplug and plug back again.
if i could make it charge fully then stop, then start charging when battery is low. That would work for me.

Goal is: power android PHONE 1 cell LIPO battery: with power cut OFF when battery charge reaches 4.1v and turns charge ON only when battery reaches 3.6v (adjustable V is disarable option) in other words i need battery costantly powered but charge only when battery is drained to about 20% and stop charging when battery charged to about 90% capacity

there are android apps to controll bluetetooth and wifi modules, but how to put it together?
i thought i could download android app witch plays sound battery full or low at percentage i need, then sound triggers voice sensor witch turns relay on/off conected to phone power supply.

arduino android bluetooth app could do the job to switch bluetooth controled relay but how to pair it with anohter apps notifications?

and worst of all i am not IT ingineer and could not do nothing with chip gys suggested. ready baked boards i can wire/solder myself but arduino programming gonna be issue

I get all that, but WHY do you wan to leave it plugged in, but drain the battery to near depletion, then charge it to not full? What is wrong with letting a standard charger (or the build-in phone charger) keep the batt at or near full?

alto777:
And set quite high as a percentage of full charge.

I have not seen any evidence that that is a bad thing.

...R