12v 17 amp battery pack?

[SilicateWielder]

Hey guys, I have a qurstion for you all

 

How would I go abour building a battery pack capable of supplying a minimum voltage of 12v while being able to provide at least 200 watts worth of power? I'm using this to power an ultra portable PC that I have in the works

 

It has to use 18650 cells or something that will fit into to the top portion of the case, which has a depth of approximately 2.1 cm from the bottom aluminum lip

 

this is the space I am working with, it's approximately 32.54 cm by 34.6 cm

 

[Enderman]

Just buy a 3s lipo, those are 12v when fully charged.

[SilicateWielder]

Just now, Enderman said:

Just buy a 3s lipo, those are 12v when fully charged.

How do I go about charging it then? Don't i need a charging circuit to safely recharge the battery?

[Enderman]

Just now, UnbrokenMotion said:

How do I go about charging it then? Don't i need a charging circuit to safely recharge the battery?

Yes...just like 18650s do....

 

[Hackentosher]

Damn it, @Enderman, you beat me to it

 

[dany_boy]

Do you care about the weight and size all that much? For that kind of Energy, I would recommend you to use lead acid batteries with a high power buck converter. Also:

Quote

Yes...just like 18650s do....

Not all 18650s have a built in circuit, and those that do not have a charging circuit, but a protection circuit. To charge such a monstrous lithium based battery bank you NEED a constant current and constant voltage charger capable of monitoring each array of cells. Lead acid on the other hand is much more forgiving and motorcycle battery chargers are cheap and readily available. (Mechatronics engineering student here)

Cheers

[SilicateWielder]

1 hour ago, dany_boy said:

Do you care about the weight and size all that much? For that kind of Energy, I would recommend you to use lead acid batteries with a high power buck converter. Also:

Not all 18650s have a built in circuit, and those that do not have a charging circuit, but a protection circuit. To charge such a monstrous lithium based battery bank you NEED a constant current and constant voltage charger capable of monitoring each array of cells. Lead acid on the other hand is much more forgiving and motorcycle battery chargers are cheap and readily available. (Mechatronics engineering student here)

Cheers

This is what a BMS is for, However finding one capable of handling 17 amps of current is proving to be a challenging task.

 

I already looked into using Lead Acid cells and they just dont make them small enough for my needs. Anything I put into my PC must have a thickness at or under 2.1 cm; This is why I am opting for 18650 Lithium Ion cells. (Please don't tell me to use LiPo, those things are just way too dangerous)

 

Do you know if premade CC/CV charging PCBs are a thing? Integration into the PC is key here.

[dany_boy]

17 hours ago, UnbrokenMotion said:

This is what a BMS is for, However finding one capable of handling 17 amps of current is proving to be a challenging task.

 

I already looked into using Lead Acid cells and they just dont make them small enough for my needs. Anything I put into my PC must have a thickness at or under 2.1 cm; This is why I am opting for 18650 Lithium Ion cells. (Please don't tell me to use LiPo, those things are just way too dangerous)

 

Do you know if premade CC/CV charging PCBs are a thing? Integration into the PC is key here.

To be honest I have never dealt with such high capacities on lithium technologies, and I dont think you will find any pre-made solutions that are simple to use (as in like a laptop). One option would be to use chargers like the ones used for Radio Control models, but those require some user input in order to start charging. If you have knowledge in electronics you could look into something like the linear tech LTC4007. You would still need a balancing circuit though. (Linear tech has some more powerful and advanced options, but you would need to design and build them yourself)

Cheers

Edited November 18, 2016 by dany_boy
Added some aditional info

[corrado33]

19 hours ago, UnbrokenMotion said:

(Please don't tell me to use LiPo, those things are just way too dangerous)

Your conclusion that 18650s are any less dangerous is false. Incorrect usage/charging of any Li based battery will eventually cause it to catch on fire and explode. Correct usage/charging of either is equally safe. 

 

There is a REASON fireproof charging bags exist for Li based batteries.

[Factory Factory]

17 A is a lot lot lot of amps for LiPo/LiIon. If you're using 1C, 2600 mAh cells, you'll need at least 7 cells in parallel to get 17A discharge.

 

And if you need a very solid 12V, I'd do a 4S or higher pack that gives out greater than 12V and regulate it down.

 

Put these together, and your battery pack is going to be a 4S/7P = 28 cell pack.That's a lotta batteries. If you can find reliable 2C discharge cells, you can do a 4S/4P pack, or just 16 cells. 

 

You can get high-discharge LiPos, like 10C, and manage a 4S/2P = 8 cell pack. Or if 17A is an overspec, there are cells that will sustain 16 A discharge and 24 A peak. You could do a simple 4S pack of that. At 16 A of draw they'll last about six minutes, though.

 

And yes, pre-built charger and general management PCBs for all sorts of cell arrangements are available. You can usually find them and the batteries from drone enthusiast stores.