USB Power Banks/Chargers

[Bobby Simons]

Does anyone have experience with these? Specifically, Id like to use it to power the Numa Compact 2X, away from an AC source. Some of them are quite powerful, Im wondering how much play time I could get with one.

Any advice would be appreciated. By the way, Ive only played it for an hour or so, but Im pleased with my purchase.

[Nathanael_I]

Its just easy math. Your keyboard pulls some number of Watts to function. Batteries are rated in Watts per hour (you just can't tell at first glance - more in a moment). So if your keyboard pulls 25W and the battery is 50W/hours, then you get 2 hours on the battery.

 

The only trick is batteries on Amazon are rated as "20,000 mA/hr, not Watt/hours. So how do you get there. mAH to Watt-hour conversion . USB 1 & 2 run at 5V.

 

So, that 20,000mAH battery @ 5V will give 100W/hr of power. Look at the specs on your keyboard, and do the simple division, and you are there!

[Reezekeys]

Its just easy math. Your keyboard pulls some number of Watts to function. Batteries are rated in Watts per hour (you just can't tell at first glance - more in a moment). So if your keyboard pulls 25W and the battery is 50W/hours, then you get 2 hours on the battery.

 

The only trick is batteries on Amazon are rated as "20,000 mA/hr, not Watt/hours. So how do you get there. mAH to Watt-hour conversion . USB 1 & 2 run at 5V.

 

So, that 20,000mAH battery @ 5V will give 100W/hr of power. Look at the specs on your keyboard, and do the simple division, and you are there!

I'm gonna go out on a limb and try do do some math: according to the manual, the Numa Compact 2X can be run from USB power but the speakers are disabled. A USB2 jack is supposed to be able to supply up to 500ma of current. Assuming the Numa uses all 500ma, a 20,000ma/hr battery should theoretically last for 40 hours. However, I believe these power banks may have current limiting circuitry that limits what the maximum current draw can be. That "100W/hr" rated 5v power bank is not really going to supply 100 watts (20 amps) for an hour, or 10 amps for two hours?

 

Bobby, I think I asked a very similar question a while back about powering my Roland A800 Pro from a power bank. It draws 300ma and the consensus was that it was doable, although I haven't gotten around to trying it yet.

[J. Dan]

Note that most times an electronic device will not actually draw what is printed the electrical specifications. Sometimes it's just the power supply size supplied, so,etimes it's a fuse rating, often it has more to do with compliance with a 3rd party approval like UL, CSA, CE, etc.

[EVC]

About doing a simple math to find time vs battery capacity, it is not that simple. Battery capacity is stated for a discharge rate of 5%, i.e, 10Ah if discharged at 0.5A for 20h. At higher discharge currents, the effective capacity is lower. So, if your load is, say, 5A, it will operate for approximately one hour and the capacity will be equivalent to 5Ah. Also the battery degrades with age and number of discharge cycles so that figure is valid for a brand new battery.

 

 

 

[Bobby Simons]

You people are awesome. I guess Ill just get one - its an easy purchase to justify as I can always get other use out of it beyond just the times I cant plug in. I have this one in my cart, let me read up a little more...

Griffin power bank

[stillearning]

I have purchased several of these battery powerbanks from monoprice. Using the 20,000 mAh size, I have no problem keeping iPad pros running for several hours when their internal battery is discharged. Ive not done the math, nor had occasion to measure exactly how many hours until Im out of power, just that its longer than I expected, if that helps.

[Delaware Dave]

Check out this option as an alternative. This Mojo user purchased a rechargeable Lithium battery to run his Mojo.

 

clonk

 

He also wrote: " .. It's a 12 volt DC lithium-ion battery pack sold for use in CCTV cameras and rated at 9800mAH (not sure I believe the rating is accurate - bearing in mind it only cost £20.) I altered the supplied lead to make it fit the MOJO, by cutting off one plug and soldering on a replacement from Maplin Electronics store - I think it's 2.5mm inner / 5.5mm outer. I've not used it to power the MOJO for more than about 15 minutes but have used it with a Roland piano for over 2 hours - the piano was driving internal speakers full volume. I am confident it would power the MOJO through a gig but if in doubt, cheap enough to have a spare.."

 

Guido then wrote: "..I wonder how long will it last. Mojo accepts 9V ~ 15V and draws less than 1A @ 9V, even though it comes with a 12V PSU rated at >2A. If your battery has a capacity of 9800 mAH at full load, it should last up to 10 hours, theoretically.."