[skree]

I'm a dedicated modifier. I cannot leave it alone if i see a way to make it better. I have this problem almost to the point of mental illness. 
 
I may have lost my mind, or i may have come up with a really good mod. And i can't decide. If anyone in the world feels the way i do, here they be.. or at least there's people here that understand what i am on about... so i want to run it by you guys if that's ok? I won't be offended if you tell me i have indeed lost my mind. Everyone else i've shared this with except a girl i like has.. lol
 
Was reading some time ago a thread about a Cowon DAP and someone mentioned that what they wanted was a Cowon DAP that eschewed the built-in Li-Ion battery, in favour of swappable NiMH AA cells. This is especially poignant with the advent of low self discharge NiMH chemistry.
 
I noted that the BMS on most Li-Ion cells allows usage within the range of 3.0 to 4.2 volts (ish) which by my numbers is pretty close to the range one needs to keep a 3 cell NiMH pack happy.. discharge to 1.0v per cell, charge to 1.4. ish. Charge is irrelevant for me, although a 500ma charge rate terminating at 4.2v should be ok for AAs.. i wouldn't charge them in the device anyway...
 
I use a mobile phone as my source, and am wanting to add a FIIO E6. These both run off 1 cell li-ion batteries. I'm fairly new to DIY audio gear, so i may be barking up the wrong tree but i'd also like to experiment with a crossfeed - to see if i prefer the sound.
 
so i need some kind of container/bag/etc for the above - my meier crossfeed is pretty small.. the idea i've had is like having a rucksack on the back of the phone down at the bottom over the battery tray..
 
Then it hit me.. why not put a 3x AA (2000-2200ma) cell holder with cells into the bag as well! I've got a BMS PCB i cut off an old battery that worked in my phone so as far as i can see its just a case of soldering the pcb to a battery snap and feeding the cable out of the phone. 
 
This would give:
Inherently safe cell technology - As good/safe as Li-Ion batteries are, they are still a fireball in a can in the right conditions.. or a plastic wrapper. Not so NiMH.
 
The ability to change the batteries when flat, and safely transport spares.. I can and have carried AA NiMH bare in my pocket.. would never do that to a li-ion all it would take would be to forget and drop my keys in there on top of it or sit on it. Also, when the cells are dead, easy and cheap to replace.
 
Huge battery life: 2000-2200ma with ready to use LSD cells. My phone currently has 800ma. Carry a bunch of AAs with me and i could be away from a power point for a month...
 
One power source for two devices: if it works for the phone, it should work for a FIIO E5/6?
 
i can't see any electronic reason why it wouldn't work.. if there is one, please enlighten me?  Even if it does work.. have i finally gone fruitloop? it's been coming for a while tbh lol

 

[wakibaki]

If I wanted reserve power for my phone or headamp, I'd use duplicates of the batteries that are already in there.
 
The energy density of Lithium batteries is the best available. It's inaccurate to characterize them as 'a fireball in a can'. Manufacturers put them in phones, of which there are many millions in use across the world. They couldn't do this if there was a significant danger.
 
It's true that 3 NiMh are approximate to 1 Lion, but approximate is the word. The charging regimes may not be interchangeable. I'd hesitate to say they're completely incompatible, but I'd also hesitate to say 'go ahead, it'll be OK'. Some testing would really be advisable, and it could turn out to be unfavourable, in which case you'd have to revert to using Lithiums anyway.
 
Carrying NiMh cells loose in a pocket is no more advisable than carrying any other cell. You'll have 6 terminals instead of 2.
 
I doubt that there is a significant cost advantage.
 
The one advantage is that you can use primary (throwaway) cells in the battery pack, but you will be exposing the phone to overvoltage which it may not like.
 
It's not entirely crazy, but it really is giving way to your passion in favour of reason. My recommendation is, save yourself a lot of uncertainty or testing and buy duplicates or clones of the cells you already have. Look on ebay or dealextreme.
 
w

 

[skree]

it's not about reserve power, it's about a full conversion but i get you. Yeah, Li-Ions are safe given normal circumstances.. i bet the incidence of mobile phone batteries going up in flames are 1 in a billion or less.. but that isn't really the reason i'd be doing it, it's just an infintesimally small advantage in terms of my peace of mind. Energy density.. Yeah.. can't argue with that.. but AAs are higher mah than any battery which fits in my phone, by roughly 100% - Japod BL-5C rated at 1100mah, Turnigy 2200ma LSD AA - tested by me on an Accucel 6 charger at 2260-2370mah (at low charge/discharge rates).. the phone and two bl-5cs would be smaller, but the AAs are one battery pack no need to change cells to get that extra capacity.
 
I'm going to test it with respect to running the phone on an old spare phone. I'm not actually bothered about charging using the phone's charger - with changeable cells there would be no need to have a car charger or a pocket emergency charger or anything like that, i can charge them at home on my proper peak-detecting (maha) charger and carry spares - better for the cells. Another advantage would be that it would use the same batteries as my digital camera...
 
No significant cost advantage at all. The NiMHs are cheaper per watt/hour but a pack of 3 costs about the same as a dealextreme supplied Pisen branded 1200ma cell. However, one has the advantage of knowing for sure one is getting genuine, safe cells that are easy to return to the store if they don't work. I've got a Pisen BL-6C 1200ma cell on the way from dealextreme but being a 3rd party cell i'm not sure i'll be able to trust it even if it does get its full rated capacity/longevity... if it fits! it'll be tight if it does.
 
The terminals on AAs are a lot further apart than on a phone battery.. a single car key could short a nokia cell. I thought about using primary cells but yeah potentially a massive overvolt (possibly up to 30%) and primary cells are some expensive electricity. Thinking about it, the phone could run for a certain time on two primary cells so there would be some use there - i've had energizers that read 2.0v on the multimeter fresh out of the pack.. 
 
as for right away, the cost is low. I already have like 30 AA LSD cells, so all i'd need would be some kind of housing - poundland for me in the uk, dollar store for our US friends, a battery holder (65 pence) and a battery snap (12 pence) so about $2.50 or 1.75 UK sterling. (i dont have a pound sign on this stupid but comfortable keyboard)
 
I think it's more giving way to my passion at the expense of reason I like things the way i like them if you see what i mean, and i can think of a number of ways i prefer NiMHs.. but it feels a bit crazy to add bulk and ruin the aesthetics of the device. i like the simplistic engineering beauty of using the one pack to power the phone and the amp - both devices last the same time on a charge, etc. One thing i'm not sure about is the internal resistance of NiMH vs Li-Ion - would this affect an amplifier like the fiio E6? like, make it sound bad or something?

 

[nikongod]

Would now be the wrong time to recommend investing in a real power supply? You know, one that has a consistent output impedance from DC to a weak 200Khz BEFORE the bypass caps are considered.
 
I'd lean towards that. Save the batteries for portable compromises. 

 

[skree]

erm.. it's for portable use mate.. for my mobile phone/mp3 player and a micro amp i want so portable 24/7. I have a proper mains powered setup at home hehe

 

[skree]

it worked.. the first time.. kept flashing low battery but the meter read full.. mp3s worked, tried to make a call and it went off. the voltage was 4.05v unloaded, phone on 4.03v. tried to restart it and it got to the welcome screen and cut off again.
 
weird that it should behave like that with a BMS and sufficient voltage. the third pin on the BMS outputs the same 3.76v my fully charged original battery does. doubt it can be worked around.. the phone is no smartphone its current demands in call cant possibly be greater than 150ma

 

[qusp]

output Z is far higher with nimh, noise is higher, charge is slower and i would hardly use chinese turnigy as an example of high quality cells, if thats what you measure against the cheap lipo cells you used must be pretty crap. the phone will probably use something other than just voltage to tell the condition of the battery, internal impedance perhaps, which will be much higher on nimh so will always read low
 
fallen angel, compared to a proper lifepo4 pack, good luck finding a better regulator and besides HF power transient demands are not handled by the psu, they are handled by the local decoupling caps and the impedance of the battery is pretty meaningless

 

[skree]

The Turnigy cells perform very well against other 'LSD' NiMH cells in discharge tests where capacity is being measured, and output current handling is being measured. Yeah i figured it would be the internal resistance of the pack or the nimh inability to suddenly supply 1c pulses. I've been thinking about trying a 'resistances in parallel' mod 

 say some silly amount of megohms (50-200) in parallel with the pack to see if that alters the way the phone measures the battery, probably not and i've kind of given up on this mod but if it can be done, i'd love to know how it's still the most ideal method for me - the only other option is to charge things with their original battery from AAs in one of those step-up converters (2s AA > 5v 500ma) and i'd like to eliminate that step if possible, in my experience those things really are noisy, but i can continue using one no biggie, in fact I just ordered a 3x AA 'emergency' charger - Identical in design to the ones sold on dealextreme i've used before, but 3xAA instead of 2 - This means the device itself should last longer - less amperage on the input = less heat = more reliable, and be better for the cells - less amperage drawn (about 600-650ma vs 1a whilst charging my device) plus i'd expect a good full charge on a 1200ma phone battery from three of my AA nimhs. cost 3 pounds UK. God, i love the internet