DIY Battery Pack?

[Anonymous No.195026]

Dear /diy/: The Raspberry Pi is a small computer that accepts 5v input. I want to make a giant battery pack for it which I can charge via micro-usb. I want to use these batteries:

http://dx.com/trustfire-protected-18650-lithium-battery-2500mah-2-pack-blue-5790

What do I need to build such a battery pack? A voltage regulator? What can I use to interface a microusb charger to the battery pack? How do I arrange the batteries in a series if I have, say, 50 batteries? Does that depend on voltage? Thanks /diy/

[Anonymous No.195032]

>>195026
bump

[Anonymous No.195035]

even without bumps, your post will last a week.

you better change one of your requirements. it's complicated to have a battery pack that both puts out 5.0 volts, and is chargeable by 5.0 volts. so, for example, if you make a series circuit of 5 cells, you get 6.0 volts, which you then regulate with a low-voltage drop-out regulator down to 5.

but to charge a 6V circuit, you need at least 7V, so your USB charger wont work unless you add complexity, such as a boost converter.

[Anonymous No.195037]

>>195035
Sorry, I'm not used to how slow DIY is. Is there any reason that I can't have batteries power the device at 5v but charge at different voltages?

[Mad Scientist !!Q11PG81nz2n No.195038]

Just buy a cheap external battery pack. You can get them up to 21,000mah on chinavision. Cells are low grade and die fast, but easy to replace, they are just typical commodity cells. Contains all the electronics needed to do what you want.

[Anonymous No.195040]

> Is there any reason that I can't have batteries power the device at 5v but charge at different voltages?

no reason at all. it's the simplest way.

[Anonymous No.195041]

>>195040
How come you (or whoever >>195035 is) mentioned removing one requirement then?

[Anonymous No.195042]

USB has a 5v rail and a 12v rail.
Yes, even micro-usb.

[Anonymous No.195043]

>>195042
What kind of circuitry do I need to actually charge the pack as opposed to charging something with it? How does that work?

[Anonymous No.195047]

> USB has a 5v rail and a 12v rail.

nonsense. USB is 5V only.

> How come you (or whoever >>195035 is) mentioned removing one requirement then?

changing the charging voltage from USB's 5.0V to something higher is a change from your initial requirement.

[Anonymous No.195048]

>>195043
All you need is a diode really.

[Anonymous No.195054]

> What kind of circuitry do I need to actually charge the pack

depends how fancy you wanna get. you could buy a $40 device like this http://www.batterystuff.com/battery-chargers/6-volt/SON604CC.html

or you could build something as simple as this: http://circuitdiagram.net/6v-gel-cell-battery-charger.html

or you could even go simpler: 1 transformer, 1 fuse, 1 diode, and 1 power resistor whose value depends on the transformer voltage

> as opposed to charging something with it?

I dont follow you. you said the pack is supposed to power a load, not charge anything else.

[Anonymous No.195056]

>>195026
You need a charge/discharge controller designed to manage a lithium ion battery pack. If you don't use the right kind, Li+ batteries tend to get rather upset and do things like explode and catch on fire. No, I'm not kidding you.

[Anonymous No.195063]

> lithium ion

oh, if these are lithium ion then forget all I said before. you do need a special circuit for them, including a method of monitoring their temperature. Li-ions are bad news for experimenters. I never touch them myself unless they include their own chargers.

[Anonymous No.195075]

>>195063
Are nicd batteries much worse for a project like this? (That is, powering a Rasp Pi.)

[Anonymous No.195079]

> nicd batteries much worse for a project like this

nope, you'll just need 4 times the weight, and the area, to get the same amount of power. with Ni-MH, you'll only need to have 2x the weight and the area. Neither Ni-Cd nor NI-MH will blow up in a ball of flame, tho, which is a definite plus.

[Anonymous No.195110]

>>195079

lithium batteries aren't that much more dangerous. you just cant discharge them past a certain point (3-3.2v per cell in the case of lipos)

http://www.sparkfun.com/search/results?term=lipo&what=products

derp

[Anonymous No.195267]

>>195110
Yes, that's true, but that's why you need the proper charge/discharge controller to manage them. When I was working as an engineering tech at a small defense contractor I did some research on replacing two car-battery sized deep cycle batteries with equivalent capacity in Li+ cells. Many manufacturers won't even sell you the bare cells unless you demonstrate to them that you have a workable controller design to use them with.

[BSO No.195272]

cheaper solution is 6v lantern batteries but youll have to make a voltage regulator

[Anonymous No.195287]

>>195110
>Lithium batteries aren't that much more dangerous

[Anonymous No.195289]

>>195110
The real danger is in OVERCHARGING, bro.

Overdischarging is only "dangerous" as in you're risking turning your cells into paperweights.

[Anonymous No.195297]

>Lithium battery
>Implying 3volts isn't more than enough to rip the fabric of space time to pieces
>Wanting to make a pack of them

[Anonymous No.195308]

Proud to be this guy.

[Anonymous No.195311]

>>195297
Tell it again.