A way to charge your dual cell, 7.4v (two 3.7v in series), Li ion batteries internally

[hardenc10]

I've been searching for a while for this because I want to make a VV mod with an internal charging circuit so I can just plug my mod in the wall or preferbaly a USB port, which I think this is capable of. I am going to try it using a 7.4vdc lipo battery pack or 2 18650's. This is what I found: MCP73213 or the Eval Board: MCP73213EV-2SOVP
You can order them here:

MCP73213 at - AVNET

MCP73213EV-2SOVP at - Digi-Key

Let me know if anyone thinks they might ues this in a mod or has experience with these products. Thanks

 

[Java_Az]

Pretty sure there is a typo on the data sheet. I believe that 4 volts input should have been a 9 volts. Unless this chip somehow boosts there is not way 5 volts from USB will charge 2 li ions to a final voltage of 8.4 volts. I have worked with some of there other chips and usually for a 2 li ions in series you have to give at least a 8.7 volt input for the chip to work. I would send their support a message and ask them about it or post on their forum. I could be wrong, but i kinda doubt it.

 

[hardenc10]

Yea I was wondering how that was possible but would be cool if you could

 

[brewsterfrank]

Pretty sure there is a typo on the data sheet. I believe that 4 volts input should have been a 9 volts. Unless this chip somehow boosts there is not way 5 volts from USB will charge 2 li ions to a final voltage of 8.4 volts. I have worked with some of there other chips and usually for a 2 li ions in series you have to give at least a 8.7 volt input for the chip to work. I would send their support a message and ask them about it or post on their forum. I could be wrong, but i kinda doubt it.

but if you could get the 8.7 input voltage this would work for an internal charger correct? just wondering as i dont mind taking the batts out of my VV to charge before i got to bed.

 

[CraigHB]

I'd use the MCP73862, that's the full featured dual cell controller.

Minimum input voltage is 8.7V for all of the Microchip dual Li-Ion charge management controllers. It says the min is 4V under Input Voltage Range , but that's only for the logic circuits, not for charging. They don't make that clear. If you read the device overview, it states input voltage must be 300mV higher than battery voltage for charge mode to engage. So, when battery voltage is 4.2V per cell, input is 8.7V minimum.

One thing I question is none of Microchip's dual cell controllers appear to have any utility to monitor each cell individually for balancing. I would have to assume these are non-balancing charger controllers which is a bit sketchy. Not sure if I would be comfortable with that.

 

[Java_Az]

One thing I question is none of Microchip's dual cell controllers appear to have any utility to monitor each cell individually for balancing. I would have to assume these are non-balancing charger controllers which is a bit sketchy. Not sure if I would be comfortable with that.

When i first started looking for a 8.4 volt charger i thought the same thing. Even if they don't balance kinda figured they would at least have a voltage sense lead for the middle of the pack. But MicroChip is not alone No one seems to offer that, TI linear,national and the list goes on. I think it is pretty safe though as long as your batteries are protected and packed together. When i test my individual battery voltage, they are always withing a couple hundredths of a volt of each other. I would worry about non packed batteries or single cells though. Could mix batteries with totally different voltages and that could be bad. If you look at where these chargers are used in the industry ,they as far as i have seen are used for li po or li ion packs and not single cells stacked.

 

[unloaded]

Have you looked at some of the connectors with switches in them? You could cut the series circuit with them and charge them in parallel. A completely different way to skin the cat but doable and easier for me to wrap my head around 8)

 

[Java_Az]

Have you looked at some of the connectors with switches in them? You could cut the series circuit with them and charge them in parallel. A completely different way to skin the cat but doable and easier for me to wrap my head around 8)

Thats actually how i planned on doing it from the start. You still run into mixing up single cells if using one charger. Really i would rather charge in series then parallel for dual batteries i think it is much safer. A dedicated charger per a battery would work fine for single cells. But then you add up the switch and 2 chargers and your using up a lot of real estate.

 

[VpnDrgn]

I have suggested a few times using a batt pack and a 1-4 cell charger. Then you only need a charging port
and no extra circuits taking up space in mod. This was shot down many times because of needing to keep
up with another charger and not "plug into any usb port". It never clicked for me that, as Java pointed out,
you have to have 8.7v to charge batts in series. The convenience of usb was never really viable anyways.

That brings me back to a batt pack and charger. Battery Junction explained to me that their batt packs
are assembled with a pcb configured for multi cells with added poly fuses and are designed to work
in conjunction with their multi-cell charger.

A lot of people ask "why bother?". I am one of the ones that think the convenience ( admittedly minor )
of not having to take the batts out is worth it. Of course, I am also a moderate vapor, so keeping a
mod charged is not that difficult. My little 14650 box mod would last me over a day, so charging every night
leaves me with mostly full power all day.

 

[CraigHB]

The only way I see to incorporate USB charging with series cells is to use two separate charger controllers, one for each cell. You could drive both controllers off a single port if you program the charging rate accordingly. However, you'd have to switch battery configuration back and forth from charging to powering to charging. You wouldn't be able to power the atomizer and charge simultaneously. It would be possible to switch battery configuration automatically with some power FETs slaved to the atomizer switch or by using a multi-pole atomizer switch.

Otherwise, I would go with a balancing charger and the required multi-pole charging port. Though you could easily use any kind of connector you want. An 1/8" stereo mini-jack might work well. You could also use a couple small barrel connectors.