Building a 12V Lipo battery from three cells.

[beanflying]

Part of the issue is market segment and use of the different technologies not to mention the different electrical needs etc.

Since the early 8-10C LiPo's started appearing we R/C fliers dumped our Nickel batteries as fast as we could. Low weight and energy density is king. Balanced 12V input based chargers and simple low voltage cutouts are all we needed. Currents and discharge currents available have seen Methanol and Petrol engines losing market share too.

Low power LiPo use in phones, tablet etc is also well established but dedicated built in device specific solutions are normal.

For a lot of terrestrial applications Lead or Nickel chemistry and the low fuss fairly abuse tolerant nature of them has kept them the defacto standard until the last few years. Weight doesn't matter for a lot of applications but service life and reliability do.

So I would suggest there has not been a lot of development in systems to replace the old technologies until recently.

As for the other Lithium chemistry and LiPo's lots of work to be done.

I would agree as above Evilbay block solutions are not always the best but for a simple solution and in particular for beginners in the hobby buy them play with them and learn

[paulca]

Another  (ex) RC Flyer here.

I don't understand in this use case why something like an Accucell-6 wouldn't do.  It will be cheaper, better and safer than trying to Frankenstein something up.

https://hobbyking.com/en_us/turnigy-accucell-6-50w-6a-balancer-charger-lihv-capable.html?___store=en_us

or even one of these: https://hobbyking.com/en_us/turnigy-12v-2-3s-basic-balance-charger.html

For what it's worth, you can passively balance cells between each other:
https://hobbyking.com/en_us/turnigy-dlux-lipo-battery-cell-display-and-balancer-2s-6s.html

If you must Frankenstein something up, I recommends some of these:
https://hobbyking.com/en_us/lithium-polymer-charge-pack-25x33cm-jumbo-sack.html

Or an old metal army ammo case to put the batteries in while you torture them.

[soubitos]

Another  (ex) RC Flyer here.

I don't understand in this use case why something like an Accucell-6 wouldn't do.  It will be cheaper, better and safer than trying to Frankenstein something up.

https://hobbyking.com/en_us/turnigy-accucell-6-50w-6a-balancer-charger-lihv-capable.html?___store=en_us

or even one of these: https://hobbyking.com/en_us/turnigy-12v-2-3s-basic-balance-charger.html

For what it's worth, you can passively balance cells between each other:
https://hobbyking.com/en_us/turnigy-dlux-lipo-battery-cell-display-and-balancer-2s-6s.html

If you must Frankenstein something up, I recommends some of these:
https://hobbyking.com/en_us/lithium-polymer-charge-pack-25x33cm-jumbo-sack.html

Or an old metal army ammo case to put the batteries in while you torture them.

If we are talking about a plug-in battery pack sure it will do (yet its more expensive than other solutions)... if we are talking about a solution for a built-in battery-pack + charger/protection circuit i am not so sure.... not about its functionality or results but about its practicality...

[paulca]

If we are talking about a plug-in battery pack sure it will do (yet its more expensive than other solutions)... if we are talking about a solution for a built-in battery-pack + charger/protection circuit i am not so sure.... not about its functionality or results but about its practicality...

The OP wants to build a 3S LiPo.  He appears to want to build a charger for it using 3x single cell chargers.

He could charge the cells individually.  They would need to be wired correctly/unorthodox-ly  However you cannot use the balance charge input (if one was wired) to charge the cells individually.  They are wired in part-series.

Cell 1: 4.2V (Cell 1 only)
Cell 2: 8.4V (Cells 1 and 2)
Cell 3: 12.6V (Cells 1, 2 and 3)

A balance charger is able to derive the individual cell voltages by basic subtraction and modify each charge voltage/current accordingly.  But you can see you can't use a 4.2V charger circuit to charge individual cells (except cell 1) using a normally wired balance charge lead.

The question would be.. if the balance lead was connected directly to each cell, so for 3S you would have 6 wires.  How would the cells being wired in series for the output effect the results.

If the aim is to be able to create a 3S Lipo  capable of being charged from a USB plug, as part of a product, then that's different.

As to lead acid versus LiPo charging the only difference that I am aware of if that LiPos use a peak voltage, min current cut out, where as Lead Acid chargers usually carry on with a trickle charge mode.

[paulca]

to charging this https://www.lithiumion-batteries.com/uploads/shopping_cart/4881/large_12v-100ah-lithium-ion-battery.jpg with God knows what with LOL...

That's not that big a battery.

You'll want something like this:
https://www.lindinger.at/en/drones-und-fpv/chargers-und-power-supplies/chargers-12v/hyperion-eos-0840i-1000w-max.-40a-charger-11-30v-input-for-1-8s-lipos

[soubitos]

to charging this https://www.lithiumion-batteries.com/uploads/shopping_cart/4881/large_12v-100ah-lithium-ion-battery.jpg with God knows what with LOL...

That's not that big a battery.

You'll want something like this:
https://www.lindinger.at/en/drones-und-fpv/chargers-und-power-supplies/chargers-12v/hyperion-eos-0840i-1000w-max.-40a-charger-11-30v-input-for-1-8s-lipos

how about we talk about a few 18650's which are most probably what the original post is talking about and leave the elephants for another day? LOL
Fun aside, i am not familiar at all with Li-Ion batteries other than 18650's and a few more rare but small cells... I am building bigger packs for some applications but to put a size indicator I'd say i stay under 5A charging current and under 100W total power

Also, besides a DC UPS for a mini-ITX based PC +router and monitor, i prefer to use boost converters after say 1S4P pack to power a 9V or 12V device.... for low or lower power applications i find them easier to handle and much easier to charge and properly maintain.... well, each one chooses his own poison!

[paulca]

Speaking of Elephants:
http://www.globalsources.com/gsol/I/Electronic-speed/p/sm/1154660446.htm#1154660446

Though, above about 800A they stop being for RC motors and for electric planes.... real planes.  There is a 22S 1200A paraglider electric motor from China.  I paraglide and I am NOT strapping the kind of LiPo that needs to my back!  No sir.

Some serious kit.  I've seen 60kW rated ESCs for RC boats! Running on 28S LiPos.  Obviously the higher the series, the higher the voltage and you stop needing railway tracks to run the current.

[Mjolinor]

Here is a charger that is exactly what you are outlining. I use this to charge 2 cell batteries.

The small USB chargers only regulate the +ve side, the -ve side is connected directly to the cable as shown with the green line.

In order to connect the four wires of the charger to the three wires of a two series battery you have to connect as shown with the red line.

If you try to connect these to the same USB device or five volt source then you effectively add the blue line.

You can now see that you are shorting out the battery connected to the lower USB device.

The way round this is to use two isolated wall warts, one for each.