Stromtank for mortals: power station comparison

So after I visited High End this year I thought to myself that running those systems from the mains there was stupid. The voltage would fluctuate all the time. I wouldn't even want to know what that looks like on an oscilloscope.

This really started about a year ago when I got an oscilloscope and realized that the 50Hz 230V sine wave from the outlet really doesn't look very much like a sine. Rather it looks clipped from all the SMPSs without PFC drawing current at the tops of the wave.

After trying a portable power station that I originally bought for its intended purpose I realized... holy cow. These things nowadays have a sine output that looks significantly better than what the power outlets offer! So I hooked it up to my audio system and I was greeted with two things. Loud fan noise and an actually improved sound!

So I made it my task to find one that would work like a Stromtank without breaking the bank. The one I ended up with is the Bluetti EB3A. It's now a part of my system, at least until something better comes around:


My system draws around 100W at idle, so I can get around 2 hours of listening out of a small one like this. It can be found for like 250€ and likely less if you can find a used one for a good deal.

Here's a comparison between its output under load versus mains power at the top. Even under load the top definitely looks less clipped. However don't expect to be able to plug in a cheap 100W USB C laptop charger and have it stay like that. Low power SMPSs are fine, but even a laptop charger outputting 45W made it look worse. With effects on the resulting sound.
Plug your audio system into it and plug in the crap elsewhere.



Voltage and frequency are extraordinarily stable. 230.0V, 50.0Hz. Even under heavy load. Very nice.

Finally, here's another look at it. With no load the two dominant harmonics, third and fourth order, are both roughly at -55dB. So in total the distortion should be about 0.3%.


Under load this of course gets worse, but with my chain plugged in I could never get close to the 2% figure the Stromtank S1000 is specified at.


But most importantly? How does it sound and how does it compare to the other ones I tried?
Why this one, what makes it actually practical to use?
More on that later...

 

Overall there were two standouts for me, so I'm actually keeping two. However to make this practical there's one thing it has to have and most of the cheaper ones lack:
A UPS function. This way you can use a smart plug to cut the power going into the thing and force it to use its batteries. This is what I do and it works well.

So which ones did I try and what are my thoughts on them?

• Bluetti EB3A

Ever so slightly more grit than the JNG200, but also no fan spin and better macro dynamics. Overall I find it the best sounding and also the only actually practical one.

Clarity is the best, staging the most precise, etc. It doesn't really show on a graph, but it's really quite good. Bass digs deep, seemingly improved microdynamics, simply improvements across the board. And even when running Hathor at 100dBC which draws like 250 to 300W from the plug I didn't get any fanspin. This is it.

Even so it'll ramp up the fans while charging in silent mode. Technically that could be improved by a software update. I guess I'll have to live with some fan noise when I'm not actively listening to music,

• JustNow JNG200

Fantastic sounding, fan is the quietest of the ones that have a fan spinning at these loads, just a little soft sounding.
This is what I'm going to keep for portable measurements, camping, etc. It fits in a backpack, is constructed incredibly well and is quite compact. Obviously not the highest capacity or power rating.


The others I tested I didn't find satisfactory:

• Ecoflow River 2

Sadly some transformer hum, soft sounding and even some grain.
I had high hopes for this one. The app is the best, it looks the best. A german YouTube channel said it had the best inverter. But it looks like it doesn't.
It's also more efficient both at charging and discharging than the EB3A.

• Allpowers S300

Loud fans, but bearable
Actually sounds decent, but kinda gritty, not the most well defined.
Still, this one is super cheap, but it ofc has no UPS function. Charging takes forever.

• Allpowers R600

Eliminated, both makes the transformer hum in a nasty way and has unnecessary fan spin, output had a visible blip at the zero crossing.
Didn't sound very good, either.

• Litheli B300-2

Eliminated due to annoying high frequency noise, output looked quite good though.
Sounded somewhat limp.

• EGRETECH Plume 300

Eliminated due to loud fan noise.

• For reference: Mains

More transformer hum than the good power stations.
Gritty, grainy. Claustrophobic. Good macro dynamics, but nothing the EB3A can't reach. Grey background.


I already mentioned another advantage these things have over powering stuff from the mains:
(more or less) "balanced power"
This is what the EB3A looks like with Phase and Neutral referenced to GND. This is under load and you can get it to look even more symmetrical than that.


Generally I've found that the ones that sounded the best looked the best referenced to GND. There's a bit of a zero-crossing blip visible here, but some were wildly off. The JNG200 looked quite good, aswell.
The R600 has a bit of a zero-crossing blip on its resulting Phase to Neutral waveform, which I think is what causes the transformer growl, IIRC. Even so, they generally all do a fine job of producing a good sine wave between phase and neutral.

Frankly I did not expect to see such performance for the prices offered here. This has to be a recent development.

At those prices I'd expect a proper UPS to be better. Batteries are expensive, so the less you can get away with, the cheaper it gets. My only question would be if they manage to power 200W without fans spinning...

EDIT: It looks like the ones for 1000 bucks don't have the battery capacity of the power stations here. And there are way larger power stations which could power my system for 4-8 hours of listening for comparable prices. Maybe those sound even more effortless from the more powerful inverters.

Or who knows. Maybe the more powerful ones end up making sacrifices in quality? But I doubt that.

 

Well done look at alternative power sources for gear. I've been using an older Bluetti AC50S for the last year or so with my headphone amps, but not for DAC's. Too lazy to bother, as I leave the DAC's on 24/7, but powering the SW51+ has definitely been an improvement in blackground and clarity.

I also have the much larger AC200 for home emergencies and have had to use it several times during power outages. It has been flawless. Never tried it with audio gear due to it's large size, but may have to one of these days.

 

Yeah, this is why the UPS function was a requirement for me. I can switch between battery and mains without powering down my gear. And I can do so at the press of a virtual button on my phone.

The transformer does growl a bit from doing so, but overall it shouldn't be that hard on the gear, me thinks.

 

Nice. My power conditioner has PFC, is there any reason it would interact badly with one of these do you think? (It does weird stuff like appear to be drawing a constant 6A at idle, I guess this is the phase angle change)

 

Honestly, I don't know. I don't think so. If anything I think it might help with the additional distortion under load:



Not as bad as the mains still, but we're nearing 1% distortion from my audio system. With a 60W USB C charger we're at 1% or slightly above. I wouldn't worry too much about it considering that the 13000€ Stromtank unit is rated at <2% distortion and the fact that the harmonics have a reasonably, uhm, harmonic shape to them. Also this is just one measurement, no need to worry about stuff like that 700Hz tone.

And even with highly dynamic recordings (very variable power, 105W system power now and 250W a tenth of a second later) the voltage never drops, so the output impedance must be very low. It's kind of uncanny to watch. Rock solid 230.0 Volts no matter the volume level. Of course this is a 600W, 1200W peak inverter meant to power devices that draw more current than my Ragnarok does.

I tried using the built-in USB C out instead and it doesn't seem to affect the 230V output, so there's that. This is how I'm going to use the JNG200 for measurements in remote locations.

My two major annoyances right now:

• It isn't the most efficient at charging and it also wastes power just sitting there. The fans will periodically spin up when the charge drops from 100% to 99% and it starts recharging when used in UPS mode.It also gets quite warm. Also the fan is definitely not super quiet during charging even in "silent" mode. This is why I put mine in the far corner of the room. Maybe an Arctic or Noctua replacement is possible

• I would've appreciated some kind of warning sign when the charge drops below a certain level. Maybe a beep or a notification on my phone. Maybe there's a setting somewhere. I got quite lucky yesterday when during listening I realized "Oh shit, it must be time to recharge the thing". I opened the app and saw that I was at 1%! I had narrowly averted a disaster!
  For reference, it lasted exactly 2 hours and 30 minutes and the average power draw must've been just above 100W, so at least the discharging efficiency seems to be very high. Remember this is only a 268Wh battery.

At some point I'll buy a solar panel to recharge it in addition to charging it from the wall, so my system is at least partly powered by solar.

 

Quick update:

For those who don't know, there are two electrical circuits in my room, the extra circuit dedicated to audio. They are on a different phase, aswell. However the GND is connected between the two via the Pi's HDMI through the TV, for example. And in the basement, of course. Or so I had thought.

It turns out that the outlet that I had my non-audio stuff power strips plugged into did in fact not have a GND connection!
Well, I fixed that and for some reason that got rid of most of the small step I saw at the zero crossing between Phase and GND and Neutral and GND. I'll have to redo the distortion under load tests some day, but I imagine they got a bit better.

Note that the percentage figures I gave above were incorrect by 5dB or so. I misread the scale when calculating, I think.



I did a quick blind test between the Bluetti and the passthrough AC and got it right most of the time, but we didn't do it formally and write down the results. Next time, I guess.

 

Cool, other people talking about this! I made a YouTube video about these but it's rather dry. Anyways, I also have experience with a few different models.

I have heard:

EcoFlow River Pro
Bluetti EB120
DIY battery generator utilizing a Giandel 1500W pure sine wave inverter

I agree, the EcoFlow had transformer hum. Completely ruined quiet passages in songs. Had to return. Then I tried the Bluetti. Much much better. Super analytical, detailed, with high attack. I decided to return this unit and build my own after reading impressions online. Fast forward to this monstrosity:



Giandel customer support says: "THD are all ≤3%." I have no way to verify. However there are benefits to building your own. Here is what I said in a previous review:

So there wasn't a clear cut winner for me. Overall I'd say the Giandel sounded more buttoned up and ironed out. Id say the battery upgrade had as big of an impact on the sound as some of my larger interconnect upgrades.

 

I know the "sine" that comes from our mains looks scary but it's really the DC after your precious PSUs that matters. You'll be surprised how resistant they are to AC line shenanigans, if properly designed and constructed.

 

@khbaur330162 Awesome! Do you have issues with the inverter fans running?

I'm in the process of making mine much quieter. I realized that after being left on for a longer time it heats up to a temperature where it would periodically trigger the fans to cool down a bit and then after a while the fans would spin again. Very annoying.

So in the meanwhile I added a capacitor in parallel to the fan to prevent the awful startup noise and then also replaced the stock fan with a Noctua.
Next up is a proper PWM fan control with a proper fan curve, etc. I think it's likely that running quiet fans at a low speed will be almost silent and would make a massive difference to the temperatures compared to not running the fans and then periodically ramping them up.

This is how my PC is configured for idle: 140mm fans at 200RPM are inaudible to me if you're not holding your ear right against them.

 

I used a Tripp Lite Pure Sine Wave UPS for a long while on my desk system. It had constant fan hum which I solved by placing it 12 feet away inside a baffled box made from rock wool panels.

I'm using the PS Audio PowerPlant 15 these days which while expensive still looks like a bargain compared to the Stromtank.

I have two trains of thought on power regens:

I wonder about the cost \ performance difference between your DIY approach compared to the 'low end' of commercial audiophile solutions like the PowerPlant series. @Serious , I bet you could achieve the same technical specs for 1/10th to 1/5th of the price.

and

I wonder if anyone could perceive the difference between a system being powered by a regen or mains power. Excepting of course a TT on power or fluctuating power. If I didnt see sever lags in my mains power I never would have started down this rabbit hole.

 

Neither with the Bluetti nor the Giandel. Only when charging, the chargers are loud and they are on while I sleep. Sometimes I wake up in the middle of the night when the charger kicks off. Other than that, complete non-issue. Honestly the fan never even kicks on with the Giandel, it's rated for 1500W so it's barely breaking a sweat.

 

My Power Queen 12V LiFePo battery charger kinda scared me the other day.



Not only was some plastic melting, but it was BURNING when I got home from work. No open flame, but visible carbon on the positive clip.

Here is everything after the mods:


Battery lugs for positive and negative wire, plus a 12V automotive/marine switch that looks and feels like it was stolen from a Star Wars spacecraft. Nothing gets warm anymore, and now there's no way to fail hooking it up to charge, just flip it on or off.