Using powerbank with ModDuoX

I would like to share my attempt to achieve independence from the power plug.

My device is Mod Duo X, It’s stock power supply is 12V/2A , and because of that it is a bit more tricky to feed it outdoors, comparing to the regular guitar pedals.

TL;DR:

1) Get power bank with PD.
2) Get USB PD cable with a PD decoy/trigger, that will get  12v from the powerbank.
3) Verify that output is valid by multimeter measurements.
....
4) Profits.

Details

Disclaimer

I do not recommend this for playing on stage, or any other case where you seriously need some reliability and your paycheck depends on it. I did not test it enough, and consider this as a way to do some unserious busking, playing with friends outdoors, or a way to eliminate ground loop at home when recording.

Power bank

For that task I am using power bank, Xiaomi PLM07ZM (20,000mah). This power bank has PD (power delivery) capability, and therefore is able to provide not only 5v voltage, but also 9v and 12v and even 20v for different devices for charging quickly. There are three ports - two of them are USB-A (for some unknown reason I was not able to use it for MDX, but they are rated for 1.5A for 12V anyway, less than required). Third port is USB-C port, and it rated for 12V/3A output, one ampere more than is required. That sounds good enough. Most probably, you can use other power bank with PD capability as well, but pay attention to it’s output possibilities.

Getting 12v

Next step is to get these 12v from the power bank. PD standard requires charging device to ask actively for this increased voltage from the charger, and therefore you need a special thing, PD trigger / decoy. This device requests charger to provide some specific voltage. (The same way how tablet or modern phone does)

It is possible to buy pd trigger / decoy as a naked electronic board, provide it with a diy case, and use some soldering skills create your own cable that will force power bank to provide 12v to MDX. Mentioning this in case if you have these in shops around you.

image

However, luckily, there are some cables that already contain this PD trigger inside. I’ve got a couple from China. Be sure that it has the required voltage, as there are different cables that provide different voltages. I would also seriously advise to use multimeter to verify polarity and voltage, after getting one, to be sure that seller had not mixed things up, and powerbank behaves as expected. Also, repeating this safety procedure for a new powerbank and cable would not hurt.

Anyway, I’ve got a cable like below(It is Jorindo JD0513), but of course it is not the only thing like that on the market:

There is an issue that makes this solution theoretically less reliable - connector barrel is 5.5/2.5mm, while stock MDX connector is mentioned somewhere in the forum threads to be 5.5/2.1mm. Visually, it is hard to tell any difference, to be honest. I could not find any cable with 2.1, unfortunately. Outside diameter is the same, and it fits hole perfectly, but inside - in theory difference makes connection more loose (2.5 and 2.1 is an inner diameter of the plug). I did not notice this to cause any trouble for me (probably because it is spring-loaded, and that allows to maintain contact regardless), but it would be more comfortable to know that connector is actually the same.

Anyway, I found this cable to provide required voltage with required polarity, declared amperage of my power bank has even additional 1A of headroom compared to stock, so it seems suitable.

Test

At about two hours of running MDX with about 47% of CPU load, my three years old 20k mah power bank switched to show 50% capacity with it’s 2 of 4 leds. Therefore, I think I am guaranteed to have at least 3 hours of autonomous playing, and most probably can hope for four.

UPD: Power bank finally gave up after 6 hours and 10 minutes.

Hope my experience could be helpful for somebody.

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That’s awesome! Great to see what you can do with this.

Now I’m tempted to also make my DuoX portable :slight_smile:

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THX!
Also so take over contributions to the wiki would be good.

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using a RipCord might be the better solution

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As far as I understand, RipCord does power voltage step-up conversion on it’s own. Good side is that you are not required to have Power Delivery on your source of power.

FAQ QUOTE: 
That's where Ripcord comes in - it takes the 5V from a USB port and turns it into the 9V that your gear needs.

However, downside is that you will be pulling 5V from your source of power, with amperage loss during conversion to the higher voltage. For example, if you double the voltage during the conversion, you will have half as many current amperes in the output, in proportion. (As you will have the almost the same amount of Watts, which are Volts*Amperes)

In case of my powerbank, 5V output is 3A, that’s quite a lot for a 5V charger. After conversion to 12V it should provide no more than 1.25A, and that’s quite less (by 0.75A) than stock MDX power supply provides. That’s why I dropped my initial idea of converting 5v to 12v externally (like I did for my less greedy 9v pedals before) , that I was considering before taking Power Delivery route.

Ripcord itself has limitation of 12 Watts of power:

FAQ QUOTE: 
Note that Ripcord has been engineered to operate in the 0-12W range, extended periods above 12W may damage Ripcord's circuitry and will void your warranty.
...

Ripcord can comfortably provide an output power of 12 Watts, while also catering for a peak power requirement of up to 14 Watts. Unsure of your device's power requirement? Have a look at your device manual, look up the spec on the manufacturer's product page, or ask the manufacturer. Or ask us :)

Should you wish to use Ripcord with a non-standard compliant USB port which outputs more than 2.4 Amps (some high-end powerbanks on the market can output 3-4 Amps), please ensure that the average power requirement in normal operation is under 12W. Note that Ripcord has been engineered to operate in the 0-12W range, extended periods above 12W may damage Ripcord's circuitry and will void your warranty.

12V/2A of stock MDX supply are equal to 24W, double of that limitation.(My Xiaomi power bank should be able to go up to 45W according to the specs, for comparison)

Unfortunately, it looks to me that MDX is just too greedy for this approach. Dwarf comes with the same power supply specs, according to wiki:

The MOD Dwarf comes with its own power supply which outputs 12V, 2A over a center-positive barrel-type plug.

P.S.
I do not know what is a real consumption though, I could not actually measure that, and it should depend on the CPU consumption caused by pedalboard complexity, therefore I am using label on the power adapter as a reference to be on the safe side. It might be that stock power supply is twice more powerful than device actually requires, but this assumption needs to be proved.

If you will be able somehow to measure your amperage for the actual MDX/MDW power usage, and will find it to be below than 1 Ampere (that’s 12W on 12V) with some headroom for the random spikes - then, I guess, you can use Ripcord, considering that you will measure it again after your pedalboard changes will lead to more power consumption due to CPU usage growth.

P.P.S.

I think I’ve managed to find out a way to determine an approximate estimation for the MDX consumption.

My power bank had been drained by MDX with 47% CPU usage in about 6 hours during the experiment.

Battery advertised capacity is declared by Xiaomi as 74Wh, and “rated capacity” as 63Wh (watt/hours).

It gives 74/6= 12.3 or 63/6 = 10.5 watts of power usage respectively throughout these 6 hours to spend it all, being somewhere around that 1 Ampere (12v) / 12 Watts limit I mentioned above. Considering powerbank’s age I would assume that second number is closer to reality (10.5)

I hope I had not miscalculated anything, but looks like you still might get away with using RipCord and 5V supply with no less than 3A output, but it will be quite on the borderline, it does not have any headroom for any kind of consumption spikes, and pedalboard should not binge on the CPU.

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Okay, it took me two days of scratching my head thinking of how to measure that power consumption, but finally I’ve recalled that I have another PD device capable of showing how much gas flows towards MDX.

I’ve created an ultimate cpu burn pedalboard (mostly made of chained pitch-shifters) that knocks into 100% CPU usage (95-100%) and generates tons of xruns.
image

My USB gas station shows that usage is 12V/0.9A all the way in this particular test, except for the peaks for 1A sometimes, mostly when opening a new pedalboard.

Interesting part is that contrary to my expectations, there is no visible difference between empty pedalboard with 5% CPU visual usage and my synthetic CPU burner pedalboard.

Meanwhile, pedalboard actually makes a difference. For example, opening GSynth:Deluxe pedalboard pushed usage by 0.2A to 1.2A in peak and 1.1 in general, even with CPU meter being at 40-43%. Whatever is affecting the power usage, it does not map to the visual CPU indication meter

All tests I’ve made also included a Wifi dongle and usb hub connected to MDX, and when removed - it sometimes drops consumption indication by 0.1, so I guess it consumes something measurable as well. USB peripherials also want to eat. Anyway, I’ve got 1.1A sometimes even with the peripherials disconnected.

That’s is quite in line with my previous calculations based on the power bank discharge rate.
I am not sure if the china-produced multiport usb charger should be trusted as a measurement tool, but that’s all I got for now, and now I have at least two sources of data that tell that RipCord’s capabilities quite are on a borderline of MDX requirements.

To conclude, in my experiments, MDX power usage sometimes meets 12W of maximum allowed on the RipCord with almost no headroom, but depending on the pedalboard and peripherials - sometimes exceeds them

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I expect power draw to remain constant most of the time, we intentionally make it that way in order to reduce noise.
There is a background process (with the lowest priority) consuming 100% of cpu 100% of the time.
CPU frequency is also fixed, to make things more stable in terms of available CPU load.

So if you want is reduce the power draw of the unit, some tinkering with internally running services is needed. You can also turn off the screens backlight

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Thank you for your detailed write-up @ignis32. A few years ago I bought a couple of these for my Duo and they worked great. I still use them for my busking pedal board to power a few 9v pedals and one 12v vocal harmonizer. :slight_smile: Conveniently for the Duo, they are center positive, so the included DC cable is all you need. I use a polarity converter when powering other pedals.

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Wow, that’s a very interesting insight, and explains my somewhat confusing observations.

I’ve looked into top via ssh, and looks like 100% load is on the cores 0-3, cores 4,5 are not that busy. I guess they are reserved for UI and stuff, and their load still can probably change power draw under certain conditions.

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not really, it should be all cores but due to the duox LE having 4 cores compared to 6 of production units, the tool only makes the first 4 cores busy.

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Does that mean that you can run a duox with 100% CPU utilization without hesitation, since there are still 2 other cores that are not fully utilized? :star_struck:

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I’ve got multiple xruns when bumping into 100%, so my guess is “no”)

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there is a difference between CPU load and DSP load.
the value shown on the web gui is the average DSP load, but presented as CPU% as otherwise most people would not understand it.

in 99% of cases, for what the user is concerned, the web gui cpu% is what they should keep an eye on.

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Thanks for the technical background! With the duox you can already load a lot of (audio/MIDI/CV) plugins. :+1:
If you had on the pedalboards page a #tags function that you could search for example for #duox … . :smiley:

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