Running a Phil Jones Double Four BG75 from USB power

[lemmywinks]

Just got one of these, fantastic little thing which is now my go to practice amp. It's the older version with the laptop DC power supply at 20v/3.25A/65w.

 

I have a 20,000mah power bank which is fine for this power/current draw and have ordered a USB cable with the correct barrel tip, will this work ok or will everything explode and leave me in tears? If it is a terible idea then what would be a suitable alternative for mains free use?

 

 

Thanks in advance!

[Bill Fitzmaurice]

20,000 mAh sounds impressive except mAh stands for milliampere-hour. That means a more sensible/honest rating is 2 Ah. That well may be compatible, but you want to be sure of it, and that the USB cable is rated for at least that. 

[lemmywinks]

The cable I bought is rated for 20v 5a.   

 

Not particularly bothered if it doesn't last for hours as I won't be gigging with it or doing any serious rehearsing, it's just something I already own so it would be nice to get a battery powered amp for the price of a cable.

[itu]

20 000 mAh = 20 Ah, which is quite a lot. 

20 Ah / 3.25 A = 5 - 7 h 

(practical amount, and the amp does not consume 65 W all the time it's ON)

 

I think the biggest issue is can you get all the current you need through the bank and the cable. There may be internal limitations in the bank how big a current is possible. If the manufacturer does not give you reasonable specs, you just have to try and find the limits by yourself.

 

USB is not that flexible system that it looks. I would consider a battery pack of the right voltage, and a suitable charger.

Edited yesterday at 09:05 by itu

[nekomatic]

I believe standard (i.e. deceptive) practice for the specs of power banks is that they tell you the mAh rating of the internal Li-ion cell, not the output. So it may actually be 20 Ah from the 3.7 volt cell, which would be about 75 watt-hours, which after boosting up to 20 volts gives you three and a half amp hours or thereabouts. 
 

If everything else performs as specified then I guess it should work, but not for as long as you might have wanted. 

[lemmywinks]

Thanks, the claimed output of my power bank on one of the USB Type-C ports is up to 20V-3.25A(Max 65W), it does give different values for the other Type-C port which is rated up to 12V/1.5A (Max 18W) so hopefully the stated spec is accurate. Guess I'll have to wait and see! 

 

Was just worried about potentially damaging my beautiful magic shoebox!

[nekomatic]

It’s possible the power bank output voltage will drop if it can’t maintain its specified power output, and I guess no-one without good knowledge of the amp design can 100% guarantee that it can’t be harmed by low input voltage, but it seems unlikely to me.