I'd just buy something from Hobbyking. Haven't exhaustively gone through their site but there's all kinds of choices there for circuit boards that do balancing, low cell detection, etc...
HobbyKing™ Battery Medic System (2S~6S)
HobbyKing™ Lipoly Low Voltage Alarm (2s~6s)
Fast Tech "authentic 18650" its good!
the "authentic" labels are the real deal! https://www.fasttech.com/products/0...entic-sanyo-ur18650zy-2600mah-rechargeable-li
I was surprised they air ship these by DHL > USPS ~ 7days
the "authentic" labels are the real deal! https://www.fasttech.com/products/0...entic-sanyo-ur18650zy-2600mah-rechargeable-li
I was surprised they air ship these by DHL > USPS ~ 7days
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@5th,
nice to see your amp up and running.
If you're thinking of using 8 cells max, you could use a BC8 charger, which charge/balance up to 8 cells at once.
Got an email from Intersil today about a highly integrated bms ic for up to 8 cells, it's the ISL94203.
Or you get your bms from this shop:
FunTwoo - Small Orders Online Store, Hot Selling battery atv,battery crane,battery guitar and more on Aliexpress.com | Alibaba Group
I'd go for a fresh pack made of Panasonic NCR18650B. Sure, bit more expensive but long lasting and excellent quality. We use those in 1s4p configuration with pcb from an assembler here in Germany in quantities. (They also do packs from prismatic Panasonics)
To play around with, used cells are okay if you match them again from measured performance. Doing so frequently with several step up-converters in portable soundsystems.
Thanks for the info.
These few measurements I've done of the amp are very encouraging to say the least! It's certainly high performance.
Im not sold on those 3400 cells yet > you need to drain them into the ground to get that capacity, Compared to reasonable shut off voltages ~3.0V the capacities are about the same as 2600 cells. we all know battery cycles are inverse to depth of discharge. so in the end you pay about double to get the same storage unless you discharge them more deeply. nope not there yet
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Well, our systems average power consumption is at 100uA.
About the inversion -> if you drain only 2600 from the 3400mAh, you'll get more cycles from the 3400s that the 2600s.
At our systems, cell aging is more of a concern than cycle use.
recharge them every 5 years OK sounds like a good plan
projected life time is 500 cycles down to 70% capacity hmmm 2500 years
in whos life time are you worried about. haha
http://www.quallion.com/sub-ms-space.asp
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Man, this chip is awesome. 
Bolted down a medium sized heat sink and give it some DNB to deal with. Really kicks the drums out with ease. Haven't reached 20V PVCC yet. ^^ Listening at moderate 110dB actually.
5th, may you check if your design is sensitive to GSM/WiFi noise? Maybe I need a small GSM/WiFi-Snubber. Had some noise with 10-25cm from the heat sink when using an iPhone5 connected.
Bolted down a medium sized heat sink and give it some DNB to deal with. Really kicks the drums out with ease. Haven't reached 20V PVCC yet. ^^ Listening at moderate 110dB actually.5th, may you check if your design is sensitive to GSM/WiFi noise? Maybe I need a small GSM/WiFi-Snubber. Had some noise with 10-25cm from the heat sink when using an iPhone5 connected.
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Don't know how hot these chips get - probably not very, but I have bought these heatsinks from Aliexpress for $5 ea for LM3886. They could be easily cut into 4 or 5 smaller ones for the TPA3251 for $1ea heat sinks.
(Special offer) High quality 150x60x25mm radiator Aluminum heatsink Extruded profile heat sink for Electronic heat dissipation-in Fans & Cooling from Computer & Office on Aliexpress.com | Alibaba Group
Gmarsh and DrMord: you guys are doing an incredible job on this thread - a pleasure to follow along. Finally had time to read from post 1 to here and it's a great story. Looking forward to hearing one of these.
Thanks for all your efforts and for sharing.
(Special offer) High quality 150x60x25mm radiator Aluminum heatsink Extruded profile heat sink for Electronic heat dissipation-in Fans & Cooling from Computer & Office on Aliexpress.com | Alibaba Group
Gmarsh and DrMord: you guys are doing an incredible job on this thread - a pleasure to follow along. Finally had time to read from post 1 to here and it's a great story. Looking forward to hearing one of these.
Thanks for all your efforts and for sharing.
You missed 5th element.
For the heatsink, I'm to old to jigsaw those for a final product. I don't mind if they cost $4 as they are a critical part of the system. For the prototype jigsawed stuff is okay. Actually having a 40*40*20 high fin heatsink with thermal pad attached. Board to heatsink difference is actually ~6K. Heatsink temp is at 36 degree Celsius (26C ambient), running low volume at 4 ohms, one side connected, PVCC=18V. Still waiting for the other inductors.
Edit: This heatsink shown behind the link is made with a low thermal mass baseplate. Performance is best when vented. (To my knowledge) To handle peak performance (High current bursts), a thick baseplate is better. Measurements will show. But I think this will chip will run pretty hot at high volume. (Like calculated before)
For the heatsink, I'm to old to jigsaw those for a final product. I don't mind if they cost $4 as they are a critical part of the system. For the prototype jigsawed stuff is okay. Actually having a 40*40*20 high fin heatsink with thermal pad attached. Board to heatsink difference is actually ~6K. Heatsink temp is at 36 degree Celsius (26C ambient), running low volume at 4 ohms, one side connected, PVCC=18V. Still waiting for the other inductors.
Edit: This heatsink shown behind the link is made with a low thermal mass baseplate. Performance is best when vented. (To my knowledge) To handle peak performance (High current bursts), a thick baseplate is better. Measurements will show. But I think this will chip will run pretty hot at high volume. (Like calculated before)
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I may do. Right now I'm testing and measuring different PSUs as they have quite a profound effect on the measured performance.
Well right now I am having some trouble with rising 2nd harmonic distortion towards lower frequencies. I don't know what's causing this nor how to eliminate it.
The problem is worse when the amplifier is powered by batteries than a 19v laptop brick. And improves with some large bulk capacitance applied to the rails.
It's present on both channels even with only one channel driving a load, which is odd. I have posted about this on the E2E forums.
This is not a problem at lower output powers and the absolute level of 2nd order distortion is pretty low.
I gave up trouble shooting for the moment as I wanted to listen to something.
Currently I've got them powering the tweeters in my active 4 way and they sound very nice. Nice and smooth.
Here is a preliminary 2.8VRMS into my 9.4 ohm load, albeit with the 2nd order rise.
This is with a 20kHz measurement bandwidth and is most certainly heads and shoulders above any class D amp that TI have ever produced.
It's a shame I can't get a second chip from where because then I could power the B&W FST midrange too!
The problem is worse when the amplifier is powered by batteries than a 19v laptop brick. And improves with some large bulk capacitance applied to the rails.
It's present on both channels even with only one channel driving a load, which is odd. I have posted about this on the E2E forums.
This is not a problem at lower output powers and the absolute level of 2nd order distortion is pretty low.
I gave up trouble shooting for the moment as I wanted to listen to something.
Currently I've got them powering the tweeters in my active 4 way and they sound very nice. Nice and smooth.
Here is a preliminary 2.8VRMS into my 9.4 ohm load, albeit with the 2nd order rise.
This is with a 20kHz measurement bandwidth and is most certainly heads and shoulders above any class D amp that TI have ever produced.
It's a shame I can't get a second chip from where because then I could power the B&W FST midrange too!
Attachments
It's difficult to say because my only reference systems are completely active so require more than two channels for a decent assessment. This is why the board is built for 4 channel.
My original idea was to build the 4 channels and seee how they perform. If I liked what they did I'd replace one system with the 4 channel board and then possibly replace the 6 channels in my main system with them.
So far I'm using them on the tweeters in my main system and did some critical listening and really liked what I heard. Nothing to complain about at all and I'm really keen to get more channels up and running they sound that nice. Very pleasant top end.
I have hypex ucd400 but those run the subs and my tpa3118 builds are incorporated into other systems.
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