Power bank

[ProLogic]

I'm looking for a power bank that can power my portable speaker that i have built, it needs to supply 12v and be fairly small

The speaker unit contains a 10Wx2 amp from Rapid E and a 30 LED VU meter that uses 600ma at 12V.

Looking for multiple different power banks so that i can pick the best size that fits.

 

Any suggestions?

[mariushm]

Most power banks will output 5v to a bunch of USB ports, where each USB port will be limited to at most 2..2.5A , which means the maximum output on a USB connector will be about 10-15 watts at most. 

Your VU meter, if it really uses 600mA at 12v, it means just by itself it would use 7 watts.  The 2x10 watts amplifier would be about 80-85% efficient, so if it really produces 20 watts of sound, it would use eat up around 25 watts from the power supply or about 2.5A.  So both together will exceed 3A at 12v. or about 35 watts, which is at least 2-3x the maximum regular power banks can normally output. 

 

The lithium batteries they use inside output a voltage between about 3.7v (when discharged) and about 4.2v when fully charged. The power banks have a DC-DC converter which boosts this lower voltage to 5v which is needed for USB. In order to keep the costs down and the amount of circuit board used by the dc-dc converter in the power bank, the dc-dc converters can't output more than around 10-15 watts at any output voltage so even if you'd modify a commercial power bank to output more than 5v, you'd just lower the output current so that in total, the converter won't output more than 10-15 watts. 

 

You would be better off to simply buy an actual lithium battery pack and a separate charger. Battery packs have multiple individual batteries in series, along with protection circuitry and the wiring required to evenly charge up each individual battery in the pack and prevent them from being overcharged.

By packing several batteries in series, the minimum output voltage of the battery will always be above a specific voltage, for example between 13v and 22v, so you can use a more efficient dc-dc converter to take this higher voltage down to 12v. At the same time, these battery packs can supply dc-dc converters with a lot more current, so producing 30-40 watts at 12v would not be a problem for these battery packs.

 

Here's an example of a good battery pack : https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-5s-25-50c-lipo-pack.html

It outputs up to about 18.5v and 5000mAh which is a lot of energy,  compared to a cheap power bank that has 5-10000 mAh but at 3.7...4.2v (and then raises it to 5v for usb)

To charge such a battery pack, you would need a battery charger that has that JST-XH balancing connector to make sure each battery in the pack is charged to the same level as the other batteries in the pack, and a charger that can output this higher voltage (18-20v).

Here's a good example, a charger that supports battery packs with up to 6 batteries in series : https://hobbyking.com/en_us/imax-b6ac-v2-professional-balance-charger-discharger.html

 

As for actually getting 12v, there are plenty of step-down ("buck") dc-dc converters on eBay which can be configured to output 12v from a higher voltage, and they're cheap (around 2-3$) .. so you can connect them to the battery output and have them produce 12v without any worries.

If you want something more professional, you can buy commercial dc-dc converters

 

Here's an example of a professional DC-DC converter, this takes in up to 36v DC and outputs up to 12.6v (you configure the output voltage with a resistor between a pin and ground pin), and can do up to 3A ( at 12v = 36 watts) : http://uk.farnell.com/texas-instruments/ptn78060waz/ic-isr-3a-adj-o-p-smd-78060/dp/1109705

 

[mariushm]

If you want a cheaper solution, you could go for 8 AA ni-mh rechargeable batteries and a couple of 4 battery holders.  When discharged, you can just put them to charge overnight.

 

Battery holder  (4 AA batteries ) : http://uk.farnell.com/keystone/2478/battery-holder-leaded-4-x-aa/dp/1650685

 

Rechargeable ni-mh batteries are cheap, and you can charge 4 at a time, it would take a few hours for each set of 4 batteries. So you can just buy 16 batteries and replace the set of 8 when needed with the freshly charged 8 pack.

 

8 batteries will give you a voltage between about 8x1.1v = 8.8v and 8x1.35v = 10.8v when full, at around 2500mAh, so you'd need a step-up (boost) dc-dc converter to produce 12v from that lower voltage.  They're cheap on eBay, a few dollars.

 

 

[ProLogic]

1 hour ago, mariushm said:

Most power banks will output 5v to a bunch of USB ports, where each USB port will be limited to at most 2..2.5A , which means the maximum output on a USB connector will be about 10-15 watts at most. 

Your VU meter, if it really uses 600mA at 12v, it means just by itself it would use 7 watts.  The 2x10 watts amplifier would be about 80-85% efficient, so if it really produces 20 watts of sound, it would use eat up around 25 watts from the power supply or about 2.5A.  So both together will exceed 3A at 12v. or about 35 watts, which is at least 2-3x the maximum regular power banks can normally output. 

 

The lithium batteries they use inside output a voltage between about 3.7v (when discharged) and about 4.2v when fully charged. The power banks have a DC-DC converter which boosts this lower voltage to 5v which is needed for USB. In order to keep the costs down and the amount of circuit board used by the dc-dc converter in the power bank, the dc-dc converters can't output more than around 10-15 watts at any output voltage so even if you'd modify a commercial power bank to output more than 5v, you'd just lower the output current so that in total, the converter won't output more than 10-15 watts. 

 

You would be better off to simply buy an actual lithium battery pack and a separate charger. Battery packs have multiple individual batteries in series, along with protection circuitry and the wiring required to evenly charge up each individual battery in the pack and prevent them from being overcharged.

By packing several batteries in series, the minimum output voltage of the battery will always be above a specific voltage, for example between 13v and 22v, so you can use a more efficient dc-dc converter to take this higher voltage down to 12v. At the same time, these battery packs can supply dc-dc converters with a lot more current, so producing 30-40 watts at 12v would not be a problem for these battery packs.

 

Here's an example of a good battery pack : https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-5s-25-50c-lipo-pack.html

It outputs up to about 18.5v and 5000mAh which is a lot of energy,  compared to a cheap power bank that has 5-10000 mAh but at 3.7...4.2v (and then raises it to 5v for usb)

To charge such a battery pack, you would need a battery charger that has that JST-XH balancing connector to make sure each battery in the pack is charged to the same level as the other batteries in the pack, and a charger that can output this higher voltage (18-20v).

Here's a good example, a charger that supports battery packs with up to 6 batteries in series : https://hobbyking.com/en_us/imax-b6ac-v2-professional-balance-charger-discharger.html

 

As for actually getting 12v, there are plenty of step-down ("buck") dc-dc converters on eBay which can be configured to output 12v from a higher voltage, and they're cheap (around 2-3$) .. so you can connect them to the battery output and have them produce 12v without any worries.

If you want something more professional, you can buy commercial dc-dc converters

 

Here's an example of a professional DC-DC converter, this takes in up to 36v DC and outputs up to 12.6v (you configure the output voltage with a resistor between a pin and ground pin), and can do up to 3A ( at 12v = 36 watts) : http://uk.farnell.com/texas-instruments/ptn78060waz/ic-isr-3a-adj-o-p-smd-78060/dp/1109705

 

I'm sure putting Lions in a wooden box is safe

I'm also not planning to run the VU meter on batteries, and i don't mind less volume.

 

I have however seen powerbanks that supply 65W at 220V so i'm sure there is something i could use.

[Hackentosher]

@iamdarkyoshi