Rymel's Handheld PS2

[Snow_Cat]

Maybe, it would depend on the maximum power draw the batteries can sustain without failing and if the charger can support the larger batteries.
If you do put some cells in parallel, make certain that they are of the same batch and capacity...

[jdmlight]

Here's a really simple low-battery style power gauge:
http://www.reconnsworld.com/power_12vbattmon.html
The LED turns on when the battery is getting low.

[Rymel]

Maybe, it would depend on the maximum power draw the batteries can sustain without failing and if the charger can support the larger batteries.
If you do put some cells in parallel, make certain that they are of the same batch and capacity...

i don't see how the size of the battery affects the charging capability, or how power draw affects the effectiveness of the charging circuit. i also stated which batteries i'll be using so i'm not sure what you're trying to warn me about on that last part.

[Snow_Cat]

Spoiler:

The charger outputs a current (at a voltage) until it either shuts off, or the potential inside the battery is sufficient that it does not accept a current (at a voltage).

When charging at a given current a cell will charge up its voltage as it gets full. If a cell becomes over charged then it fails.
If two cells are in series then they will both have the same current, however their voltages can vary* and one cell will fill up first. As long as the charger is not pushing them to meet 100% then this is okay, but if it is then the following can happen:

1. Cell 1 reaches 100%, cell 2 is at 80%. Charger pushes onwards, Cell 1 to over charged to 110% and loses capacity, cell 2 is at 90%.
2. Next cycle because cell 1 now has a lower capacity it reaches 100% when cell 2 is at 86%.
3. An unknown number of cyles later cell 1 reaches 100% when Cell 2 is at 50%. The Charger pushes on wards.
4. Cell 1 rage quits in a puff of fire. Cell 2 doesn't like this and also catches fire. This causes a current surge and the charger overloads and catches fire.

Charging in parallel parallel things are slightly better, both cells charge until they reach 100%, but to do so they require more time or more current. Some (cheap) chargers may not be able to cope with the demand for more current and will fail, either by flaking out over a number of cycles, or catching fire.
Also, each battery has an internal reistance, that in parallel offers a discharge path for the other cell, this leads to a shorter shelf life and wears on the battery.


Discharging in series is okay since the load draws the same current from all cells, however it may discharge one cell before the other, and over drawing from any one cell may damage it, reducing its capacity.

When discharging in parallel, if one cell discharges faster than the other it well then have a lower voltage, and this will act as a short to the other one discharging it until it is at the same potential. This will effectively reduce the other cells capacity until it matches.


If the cells are matched perfectly then none of the above problems occur. However no two batteries are perfectly identical, the closest you can manage is two cells from the same batch. Fortunately most manufacturers recieve all of their batteries from one batch- (unless they are being environmentally responsible and using reclaimed parts but then the labels will be different.)


Similarly attempting to charge/discharge a battery too fast (too many Amps) will cause it to lose capacity and fail.

The reason that these cells lose capacty is that they rely on a chemical process to hold energy that is imperfect. There is always some amount of waste in the form of lost gas that is not reabsorbed, or crystal formations. In the video linked (an extreme example) the batteries are intentionally over loaded (or charged) at such a rate that the chemicals are unable to recombine and the batteries burst.


You are considering using the existing charger circuit for your batteries. And that this is probabally what I would do because I am lazy.
But I would suggest that you put (the old batteries in parallel) in series with (the new ones in parallel) to increase the maximum current, while keeping the pairs of cells as closely matched as possible.

This also avoids putting two cells at different potentials in parallel with damaging results, though after the initial charge you could re arrange the pairs however you like without this worry. (Cells are normally stored at 60-70% potental to extend shelf life, unlike batteries in use that are kept between 80 and 100%).


*This is why balanced chargers are awesome, they monitor and charge each cell** individually avoiding pushing any one cell beyond its limits.
**or pair of cells if you do the parallel thing

Blarg, I meant to click "preview".

IT is 1:13 am and I could be making all sorts of mistakes (aside from clicking the wrong buttons) so take all of this with a grain of salt.

Edit: TLDR;
Make certain that the cells/batteries can supply enough amps to run both things.

Putting cells of different capacities in parallel can be problematic for their longegivity and effective capacity. If necessary put the old cells in parallel, then on different terminals put the new cells in parallel.

.

[Rymel]

OH. i was wondering where the confusion was stemming from. i'm not reusing the batteries that came with the tv, i kind of just assumed it was a bad idea to mix different sized batteries. i'm simply using two of the batteries i linked earlier, which is gonna give me 7.4v@25.2Ah total, way more than enough juice to run two devices that are 7.4v@2A and 2.5A. i'm assuming the total draw is the greater of the two, but i could be wrong. i figured the amp-hours i'd need for a 2.5a draw using a googled amp calculator and it said 12Ah would net me 3 hours of use at @2.5a. so since i don't feel like buying bigger ones again if i did math wrong (and i like bringing shotguns to knife fights), i just looked at 12a batteries and looked for ones that would fit once paired up. also if my math was grossly wrong and i was supposed to assume 4 amps...i'd have covered my ass.

that being said, thanks a lot for typing all that out, i learned quite a bit reading that the other day. work's been eating me alive so i haven't worked on anything, but i'm hoping to start work again in a few days once parts come in the mail. it's funny you brought all that up though, cuz i was going to use one of this site's premade smart chargers, and apparently batteryspace has you covered:

http://www.batteryspace.com/pcmwithequi ... 0-265.aspx" onclick="window.open(this.href);return false;

was originally gonna use one of these, but balance is important for no-explodey:

http://www.batteryspace.com/pcbfor72v74vpack.aspx" onclick="window.open(this.href);return false;

all that being said, and all that being read just before, i...THINK i can use the onboard charge port from the tv, but since you've brought to light the importance of cell balancing, i think the first charge circuit i linked circumvents any problems i might run into.

now, it's 7:38am and i'm rushing this post out before running late to work, so apologies if i'm way off on anything

[Snow_Cat]

Sounds reasonible;

I misread your earlier postings. Your choice of battery is appropriate, and I believe that either the PCB or the original chager should work.

The original MLP555584 batteries were rated to charge at a rate of 2800 mA (max) at 4.4V(max) (1.0C, 12.32VA), and your new PL8570170 batteries are rated to charge at a similar rate of 3.0 A (nom) at 4.2V (nom) (1.0C, 12.6VA), but can charge at a rate of 12.2A!.
The only issue may be that using the original charger could take a long time to charge up if it is running at a 'safe' 70% of max rate.

notes:
database.ul.com

• BBFS2.MH46117 - Batteries, Household and Commercial - Component (MLP555584-2S1P)
• BBCV2.MH29654 - Lithium Batteries - Component (MLP555584)

I was unable to access the report from UL for the original batteries, and the new ones do not come up in the database search.
The nominal charging voltage for the MLP555584, like all lithium ion cells, is 4.2V. According to the specc sheet the second battery was tested with a charger set to at 0.1C (1250mA), well below the stated nominal current.

[Rymel]

i guess i'll test the original charger at first, wired for balanced charging and see how that goes. i can't see any other reason for that third wire to be there otherwise. i just have to find that connector somewhere as i'd rather not ruin a perfectly good 7.4v pack just for the stinking connector. any idea what it might be?

http://i177.photobucket.com/albums/w227 ... G_1259.jpg" onclick="window.open(this.href);return false;

they're used on pc boards sometimes too...

i'll be honest, a chunk of that kind of went over my head as you're very much more knowledgeable on this subject than i am, but how is it the new batteries can charge at such a higher rate? regarding a longer charge time, no biggie, i'll deal unless it's REALLY slow. worst case i just order that balanced charge circuit and open it all back up.

[Snow_Cat]

I think that looks to be a receptacle, though I am uncertain as to the pitch/size. If you could post a picture of it next to a ruler I could figure it out.

Given the amount of fire I've seen, I would not say that my 'knowledge' has been all that effective.
The new batteries may be rated at a higher charge rate because of (any of)

1. improved construction methods allowing for a greater area between terminal to accept a charge
2. improved chemistry allowing for a faster recombination/charge acceptance
3. greater optimisim by the manufacturer

[Rymel]

i swear i'm not dead. work has just been really busy lately, so i had to put this on hold. i also realized there was a smarter way to mount screw posts, and i just haven't gotten around to doing it yet. i'll return to it soon...