Battery *SYSTEM* for portable class D

ATAUDIO

Member
2011-05-01 10:56 am
Wien
As I have already said hijacking other posts I am doing my iteration of a portable sound machine. I have reserched on this topic here, but I found nothing really exaustive, so please excuse me if there will be some repetition
Also I feel it might not be the right forum, but seems that portable and class D come all together here.

I am oriented to use a 12V battery for my TA2020, but I am not yet sure what battery and charger (a SYSTEM alltogether) to use. I have past professional design experience with sealed acid, but I believe they are just too heavy for this application. I am looking for 2/3 hours of play capacity at full power, something like a 7Ah SLA, I would think.

I would also like to use the same Power Supply that comes with mx Class D ( a 14 V 5A switcher) as a charger, as in any coomercial portable sytem.
There are some Lithium candidates, I cite oly 2 of the many you can find as example, reagrdless of the vendor:
A monitor type battery:
NEW 12V 9800mAh Super Polymer Rechargeable Lithium-ion Battery | eBay

and a motorcycle type battery:
Shido YTX5L-BS Lithium Ion Batterie - Lithium Ionen Motorradbatterie 12V racing | eBay
The basic idea is to use diodes (power schottky) to protect the power supply from reverse flow and a limiting resistor of some 5 Ohm to limit charging current. Schematic of your choice, I can post something in case.

Is this feasible ? Is this safe? I am quite afraid of Litium chemistry possibility to start fires.
I would think that the motorcycle battery, considering its operating environment (poor chargers, outdoor use, presence or nearby fuel) would be more robust.

Last option, good old Ni-Mh AA x 10 (2600 mA/h), that you can find often in special offer (even good brand ones) at supermarkets. I could not finf nice battery holders for 10 pieces, tough, only for 4 max.

Would you share your experience or your technical toughts?
 
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You can't buy li-ion batteries from outside the EU due to new international transport regulations. Technically you probably can buy them but they can't ship them directly to a consumer by any means unless the pack is certified. You will not find cheap li-ion that can pass the certification.

Go LiFePO4 instead. Don't need a special charger either.
 

ATAUDIO

Member
2011-05-01 10:56 am
Wien
You can't buy li-ion batteries from outside the EU due to new international transport regulations. Technically you probably can buy them but they can't ship them directly to a consumer by any means unless the pack is certified. You will not find cheap li-ion that can pass the certification.
Go LiFePO4 instead. Don't need a special charger either.

Thanks for your comment.
There are vendors, in EU. I suppose they come via sea to the vendors.
But, as I said, I won´t discuss the vendors issues, here, but the technical side.

I know that Portable power tools use LiFePO4, but I did not find them in a convenient format for our use, nor I have details on how they should be properly charged and discharged.
Unless the Motorcycle (and others in SLA form factor) are of the same chemistry. At the moment I did not find any confirmation of such fact, even from reputable Motorcycle shops or electronics vendors. Technical documentation seems very poor on this relatively new kind of batteries.

I concour that the cheap Lithium -ion should be avaided, at least with the cheap chargers they come with. The good ones, used in RC models (beacuse Li-Ion have the highest power density) have sophisticated chargers, with a special monitoring connector, and so they seem complicate for our use.

As a follow up, I am thinking to implement a simple minimum voltage relay that cuts off the battery before it goes too low. That would damage the Lithium batteries, exposing also them to the risk of thermal runaway, in theory.
Again, unless the motorcycle battery (or any other type) has already protection circuits built-in in the battery. Some telephone batteries have.
 
A vast array of lifepo4s are available. Usually in standard SLA sizes with built-in BMS. You can use regular SLA chargers and get 80-85% of the capacity or buy any of the many lifepo4 chargers available. I would stay far away from motorcycle LiFePO4s as they rate batteries completely differently and cannot be trusted to give the real Ah value.

For example this 12V 7Ah SLA standard sized one. It is certified for air transport so no problems in delivery. 12V 7ah lithium iron battery /lifepo4 scooter battery-in Storage Batteries from Electrical Equipment & Supplies on Aliexpress.com
 
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ATAUDIO

Member
2011-05-01 10:56 am
Wien
A vast array of lifepo4s are available. Usually in standard SLA sizes with built-in BMS. You can use regular SLA chargers and get 80-85% of the capacity or buy any of the many lifepo4 chargers available. I would stay far away from motorcycle LiFePO4s as they rate batteries completely differently and cannot be trusted to give the real Ah value.

For example this 12V 7Ah SLA standard sized one. It is certified for air transport so no problems in delivery. 12V 7ah lithium iron battery /lifepo4 scooter battery-in Storage Batteries from Electrical Equipment & Supplies on Aliexpress.com

Very interesting. I also have noted that motorcycle battery are trycky rated (i.e. a 7Ah SLA sized is only a 3 Ah inside)
Your battery is also some kind of "scooter" stuff. I guess not an electric scooter( they are usually 36 V, I believe), but just a small morcycle stuff.
The interesting thing is that you know the chemistry and that the Battery Management System is defenetely inside, as specified.
BTW This was the best I had found from a locally reputable source (available in many sizes):
Vision Lithium-Eisen-Phosphat Akku 12 V 4,5 Ah (L x B x H) 150 x 65 x 105 mm im Conrad Online Shop | 251470
Other experiences/ideas? I believe the battery issue is very important for a (light) portable device.
 

ATAUDIO

Member
2011-05-01 10:56 am
Wien
I was building Sat's design and needed a battery setup also. It was getting pretty heavy so I decided AGAINST SLA's. I ordered 4 3.2v 15aH cells (LifePo4) for $117 shipped (Canadian dollars).

Should be here this week we will see how it goes.

Yes, that is a possibility, but if you got the bare cells, *in theory* you should use a proper Li-rated charger (possibly with the connector that monitors each single cell) This would add another $50 -150 (depending on the quality of the stuff) and possibly deprive you of the freedom to supply your Boominator with the same charger for an "indoor use".
 
Please note that the ones I linked above are not 2.75kg as it says on the factory's page (yes, it's the actual battery factory's own webshop page). They are 1049g to be very exact.

EDIT: btw, the reason motorcycle battery specification can't always be trusted is that they count the number of times it can crank an engine and compare against what size of lead battery would crank the same number of times. That's the value they write on the battery which is completely misleading. Not all lists the true capacity and even if they do, they don't list under which conditions.
 
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wy2quiet

Member
2012-08-20 9:14 pm
Yes, that is a possibility, but if you got the bare cells, *in theory* you should use a proper Li-rated charger (possibly with the connector that monitors each single cell) This would add another $50 -150 (depending on the quality of the stuff) and possibly deprive you of the freedom to supply your Boominator with the same charger for an "indoor use".

Absolutely. I know about battery technology fairly well as I was into hobby grade R/C for many years and already have a LifePo4 charger.

With the cells I bought, I purchased a JST balancing connector.
 
Hi folks!
I'm replying here, hoping there's some link between this thread and my issue...

I want to use LiFePO4 batteries to power a class-D amplifier at about 24V, power would reach about 60W. I already have 8x 3,2V-3300mAh cells.
Stacking them all in series seems pretty straightfoward, however I'm just curious if there's some more clever way to do the job, like having fewer cells in series for instance, in addition with a DC/DC converter...

can anyone please help me select the best option?

maybe with some clue regarding which balancing circuit could be used?

Thanks :)