Higher capacity Li-Po Batteries for handheld? (SOLVED)

[Bender]

I have 2 Li-Ion Li-Po batteries for a portable system I want to wire together for a longer run time
I undertand that this should be done in parallel, but there are 3 contacts, do I simply wire the corresponding contacts together like this?


I know this is a pretty basic question but I've heard of Li-Ion battery exploding or catching on fire if not wired correctly so I'm a little paranoid
Thanks!

[MonMotha]

DO NOT WIRE LITHIUM ION BATTERIES IN PARALLEL.  THEY CAN EXPLODE IF YOU DO.

Simply wiring them up like that also nicely defeats the thermal protection (which is what the 3rd wire is used for).

You have to switch between them instead.  Essentially, you drain one, and when it's "close to dead", you quickly switch over to the other one using some electronics.  I would not classify this as a DIY project.

it is technically possible to put Li-Ions in parallel, but you have to be very careful about how you do it.  Again, I would not classify it as a DIY project.

[Turnarcades]

I wouldn't advise it. It may be wise instead to do use a larger-capacity alternative power source. I was recently viewing some battery hack videos on youtube for a similar reason, and as long as you can regulate the voltage and resistance, a higher-capacity power source could be used.

Upgrading the Benderama?

[Necro]

Don't LiIon's have little microprocessors in them to control charging as well so they never go fully dead or overcharge?  (either of which kills the battery immediately)

[Bender]

Thanks everyone I guess I'll abandon that idea

Actually I just found out that they are Li-Po and not Li-Ion, Does that make any difference?
 
so anyone know a good source to get a 3.7v LiPo I could use?

Upgrading the Benderama?

no, this is for another _little project I'm working on

[MonMotha]

Don't LiIon's have little microprocessors in them to control charging as well so they never go fully dead or overcharge?  (either of which kills the battery immediately)

So-called "smart batteries" do.  These batteries will generally have 5 or more terminals (BATT+, COMMON, SCL, SDA, RTH) rather than 3.  Typical Li-Ion batteries rely on an external charger to properly charge them.  Most do usually have some sort of "permanent fail" trip (usually a fuse sensitive to both electrical current and temperature) to prevent "venting with flame" and similar malfunction.

I greatly prefer the smart batteries as a designer.  They're way easier to work with.  However, the "dumb" batteries are quite a bit cheaper in some cases, especially small packs.

[Bender]

the batteries I have are 3.7v 2000mha and I'd like to at least double that
I've been able to find 4000mha, and 5000mha C40, for RC cars but don't know how to wire them to the 3 terminals on the handheld or what the "C" rating means
anybody have any ideas?

[grasspuddle]

'C' rating is the max charge/discharge current they can give without failing/catching fire.

Search for RC planes and the like. Thats where I got my Li-Polys. And people do put them in Parallel. Just be careful with charging and the current draw.

[Bender]

do you know if they come with 2 or 3 contacts?
If 2 how would you wire them to 3 contacts

[grasspuddle]

Only Li-Poly i've bought have been to prototype some electronics. They were bare packs with soldered on metal tabs as the +/- connections. You can try looking at the options here:

http://www.sparkfun.com/products/8484

What voltage do you need to power your device? What is the current draw?

[MonMotha]

I usually see it expressed as "40C" rather than "C40", but, yeah, I assume that's the "C rating".  Essentially, "C" is the charge capacity of the device with the time divided out (so a 3700mAh battery would have C=3700mA).  A "40C" battery means you can safely draw "40C" (or 40*3700mA or a whopping 148A).  40C is quite high - these packs are normally used in things like power tools, but RC cars/planes would also benefit from the high power availability.  One can typically charge at 1/10th the discharge rating or 1C, whichever is higher.  A typical discharge rating is more like 4-5C.

Chances are you can safely substitute a higher capacity Li-Po (not necessarily conventional Li-Ion) in discharge only.  It may not drain it quite as far down as you'd like it to (early cutoff), but this isn't a huge deal and will in fact tend to lengthen the lifespan of the battery.

However, the charger may get confused.  If the charger is external, this isn't a problem: just use a different charger suited to the new battery (available from the source of the battery, likely).  If the charger is internal, you may have some problems with it not fully charging the battery and/or reducing lifespan of the battery, but it's not likely to be a safety hazard.

Be cautions substituting a convention Li-Ion for a Li-Po.  The electrical behavior is subtly different and will probably confuse the charger.  Again, if the charger is external, just get a suitable charger.  It's not likely to be a safety hazard on discharge but could be.  Discharge shouldn't be a big deal though again you may have early cut-off problems, and Li-Po is often discharged deeper than cell Li-Ion, so you may actually discharge too deeply and wreck the battery quickly.  Do note that there are several subtly different cell-based Li-Ion chemistries, too, and depending on which one you sub in, you might get different behavior.

As for terminal mapping, you'll need to figure out what each one does.  There's no real standard.  Sometimes they are marked "+", "-", and "T".  + is the pack + terminal, - is the pack - terminal (common), and T is the safety thermistor.  If the battery only has two terminals, then it does not have a safety thermistor.  Not all batteries have one, and it's not always used, especially on devices that don't have an integral charger.

There's also no real standard on the safety thermistor.  Some use 1ks, some use 10ks, some use 100ks, and they'll all use various types (some are PTC, some NTC, all of them have different curves).  This may confuse the charger and dischage device into either going into shutdown prematurely (possibly immediately) or may defeat the thermal safety entirely.  Again, be careful.

Let me put safety this way: I'm a EE (Computer, but same idea) by trade.  I pay special caution when working with 3 main things: CRT monitors (high voltage), line voltage AC (high instantaneous power capability), and lithium batteries (high instantaneous power and explosion risk).  This should tell you something.  These things have crazy energy density and can discharge fast enough to cause thin wires to VAPORIZE if the safeties are defeated.  Be careful.

[Bender]

MonMotha,

Thanks so much for the info!
I don't think I'll do it unless I can find a Li-Po back with 3 terminals
cause I'd be using the internal charger from the device

[Paul Olson]

Does the device use Li-POs originally? If not, you probably wouldn't want to charge them in the device. On Li-POs, you have a common ground and one wire for each cell so you can balance the charge. So if the device is LI-PO powered now, it would have a 2 cell, 7.4V battery.

I am pretty sure that is accurate, but I have only been dealing with LI-PO for a couple of weeks now, so I could be off a bit.

[MonMotha]

Some Li-Po batteries bring out each cell in a series string to a terminal, while some don't.  Some are internally in parallel and need more complicated cell balancing.  Some do cell balancing internally, but these are usually the smart batteries.  They have internal MOSFETs to bypass parts of the string and ask the charger for various charge voltages and currents to keep things balanced.

He's talking about 3.7V which would be a 1SnP configuration.  These will usually only have 2 or 3 terminals.

[Bender]

just an update on this thread

I took apart the Gp2x Wiz battery (caution as everyone says! I did this with a utility knife and a huge spark shot out as I severed the cell casing inside the plastic housing and ruined that battery, I'd use a some dull plastic tool next time)
There is a little PCB inside and 1 cell that is 3.7v 1900mha with a plus and minus connector, I did a little research and found the capacity runs at under 1 amp, so it was just a matter of finding a larger capacity cell. I found one (link below) it was not too expensive either, I got a 5100mha one
Just soldered it to the original PCB and bingo! went from 6-7 hours of playtime to 16-18 Hrs Woo Hoo!!!! charges and discharges perfectly, and nothing heats up at all! even after running straight for 18hrs
Just a heads up this battery is way to big to fit inside an unmodded Wiz I'm using this in a bigger housing

[Turnarcades]

You think this might work in a Dingoo A330? Looking to boost the play time in mine and the battery is a similar long battery too.

[Bender]

I think so, it's just a matter of getting one that fits in the case
the battery I used is WAY too big to fit in the case