I tried to google my question but I have been unsuccessful.
i would like to use two 3.7 Lipo batteries in series then use a 3.3vdc regulator to power my circuit. i was planning on usig one TP4056 module for each battery, for charging.
the reason i was planning on putting the batteries in series is so that the regulator would act propperly, i dont think the 3.7vdc would be enough to get anything out of the regulator?? also my sensor requires 3.3vdc for opperation and i would prefer to give it 3.3vdc instead of the 2.5 to 4.5 that the batteries in parallel would provide.
so my part list is
tp4056 x2
3.7 1200mah Lipo batts x2
AMG8833 x3
Teensy 3.2 x1
if that gives y'all an idea of what my power requirements are.
back to the original question...
how would i charge the two lipo's sepperately but use them in series?
What if you use this Regulators. It is good for .5Amp load. If you need more then this you could run 2 regulators an power different boards from each. I don't know how much you need. It seem that you could keep the battery in parallel , the batteries would last longer. https://www.mouser.com/ds/2/308/CAT6219-D-117625.pdf
You can use this Step-Up/Step-Down Voltage Regulators it work with input voltages that are higher than, equal to, or lower than the regulated output voltage, making them especially well-suited for battery-powered applications in which the battery voltage begins above the desired output voltage and drops below the target as the battery discharges.
DudeGuy:
...i would prefer to give it 3.3vdc instead of the 2.5 to 4.5 that the batteries in parallel would provide.
A LiPo @3.3volt is almost discharged, and you shouldn't go much below that.
A buck or buck/boost converter is not 100% efficient, and also needs some idle current to work.
A single battery (or batteries in parallel) are much easier to charge (with one charge controller chip).
Your Teensy board might already have a 3.3volt LDO with a very low dropout voltage.
The LP38691 I see on some boards has a typical dropout voltage of 65mV@100mA.
Others use a regulator inside the MCU (do your homework, and read the .pdf of the MCU).
Leo..
Yes, that's why I wanted to put the batteries in series and use a 3.3 regulator. If I were to use the batteries in parallel without regulation the voltage from them is too variable to have a consistently working circuit
I think I just explained that battery life could be worse with two batteries in series.
The LDO that your board might have (check it) only drops ~65mV, so you can drain the battery to 3.365volt before the MCU voltage drops below 3.3volt. And that might not even be a problem (depending on sensors).
Leo..
https://www.pjrc.com/teensy/schematic.html
I would base my decision on the volt drop of the onboard regulator.
If that is low enough, I would go for a single cell setup.
The Teensy documentation recommends 3.6volt minimum on V-in, but the regulator .pdf states a typical dropout voltage of 65mA@100mA.
You might have to measure that dropout voltage yourself.
Leo..
billhowl:
You can use this Step-Up/Step-Down Voltage Regulators it work with input voltages that are higher than, equal to, or lower than the regulated output voltage, making them especially well-suited for battery-powered applications in which the battery voltage begins above the desired output voltage and drops below the target as the battery discharges.
Buck/Boost regulators are switching regulators. For such low power you would be better with a linear LDO regulator.
Switching adds high frequency noise (around 60Khz usually) and wastes power. Without a load on it, ie. with your circuit switched off the Buck/Boost will probably draw 10-20mA idle depending on it's design.
Switching regulators and PSUs are only really for when you want to draw multiple amps where linear regulators struggle.
As to your original problem. If you want to use the 18650s in series you can't really charge them in parallel. You can charge individual cells by putting the charge voltage across just one cell with the pack (7.4/8.4V) output disconnected. You won't be able to charge both at the same time though, not without an 8.4V charger.
You can get multi-cell charge BMSs similar to the TP4056 but I can't vouch for their quality.
You can also get cheap RC Hobby LiPo chargers which will charge 2 series packs. You will need to connect a standard JST balance lead and wire it correctly though. The charger will correctly charge and balance the pack in series.
DudeGuy:
I tried to google my question but I have been unsuccessful.
i would like to use two 3.7 Lipo batteries in series then use a 3.3vdc regulator to power my circuit. i was planning on usig one TP4056 module for each battery, for charging.
the reason i was planning on putting the batteries in series is so that the regulator would act propperly, i dont think the 3.7vdc would be enough to get anything out of the regulator?? also my sensor requires 3.3vdc for opperation and i would prefer to give it 3.3vdc instead of the 2.5 to 4.5 that the batteries in parallel would provide.
so my part list is
tp4056 x2
3.7 1200mah Lipo batts x2
AMG8833 x3
Teensy 3.2 x1
if that gives y'all an idea of what my power requirements are.
back to the original question...
how would i charge the two lipo's sepperately but use them in series?
any advise would be greatly appriciated.
To charge Lipo's search for RC chargers and batteries. We use and charge multi cell packs that are all in series. You will need a LiPo balance charger to reduce the risk of damaging you, your house and the batteries. If treated badly they will go up in flames. Here is a link to a pdf on connections used