February 2018

World Premiere Review!
Stromtank S2500 Battery Power Supply
The joys of a pure sine wave with battery power.
Review By Tom Lyle

  I've been stricken with something I like to call an "audiophile illusion of grandeur" for quite some time. It started long ago, when I first discovered that the AC power supplied to my stereo system was less than adequate. This wasn't too difficult to figure out, because in the daytime my system sounded lousy, at least compared to how it sounded at night. This continues to this day. This is because my home shares the power my electric company provides with many customers, including commercial establishments, homes, and more. As a result, the sound of my system suffers.

At about 6:00 PM the system begins to sound better. After 9:00 PM my system sounds even better, and can transport me to sonic nirvana, as if I can aurally detect the source of the recording, as if I've traveled in some sort of sonic time machine. Listening to my system late at night, I am a fly on the wall of the studio that John Coltrane is laying down tracks. I am in the 10th row of an empty Kingsway hall in 1957 as the London Symphony Orchestra belts out Shostakovich's First Symphony conducted by Jean Martinon. You get the idea. Don't get me wrong, as I might be exaggerating a bit, as my system sounds pretty darn good during the daytime hours. I've worked hard to make that happen. It's just that at night it is the only time that it sounds as if it is reaching its fullest potential. And that is maddening.

For the last 25 years or so I've tried countless "power conditioners" in an attempt to alleviate the difference in sound quality between daytime and nighttime. These power conditioners have all improved the sound of my system in one way or another, all using slightly different methods to "condition" the power. The best power conditioner I've heard so far calls itself a "power regenerator", since it converts the AC to DC, and the DC back to AC as a perfect sine wave with the frequency of my choice. Other conditioners that I've had some luck with have had cabinets filled with transformers, condensers, and other electronic parts in an attempt to at last silence the noise that comes through the power lines.

I've also used conditioners that I've had no way of knowing how they might work other than the hyperbole on the manufacturer's website, and with those components I often there was no way I couldn't open the cabinet, I suspect for fear that the manufacturer fears that I will share their proprietary methods. No matter how well or not these conditioners worked, the limiting factor has always been that they required me to plug the component into my AC wall socket. And so, the difference in sound quality between daytime and nighttime remained. My audiophile illusions of grandeur had me imagining that I can somehow do away with the power line that runs to my house that terminates at the circuit board in my basement. I've dreamt of striking a bargain with my local power company to have them install a power transformer in my front yard, and having them run a cable from one end of the transformer to my home, and the other end of the transformer connected by a cable that runs directly to one of the power company's sub-stations.

Another audiophile fantasy included filling my basement with scores of rechargeable car batteries, or perhaps lithium ion batteries, or maybe nickel-cadmium aircraft emergency batteries, or even uninterrupted power supply battery towers used by hospitals. I would then have an industrial power inverter convert these batteries' DC power to a usable 110 Volts AC for my system. I've used components that have been battery powered, including preamplifiers, DACs, and the like. But to have my entire system powered either by being the power company's only customer, or my entire system be powered by batteries remained a dream.

Stromtank At Shows... And My System
And then one day in Enjoy The Music's Munich High End Show Report 2016 was an article titled "Stromtank S5000 Massive Battery Power Sine Wave Unit". The feature spoke of a $30,000, 265-pound, two-foot square battery powered behemoth from Germany that connects to a system, removing it 100% from the electrical grid that power's one's home. I immediately started my research. It turns out that the Stromtank is distributed in the USA by Dan D'Agostino Master Audio Systems. This is the same company that sent me samples for review of their amazing $50,000 Momentum Lifestyle Integrated Amplifier and a few months later their incredible $28,000 Momentum Phono Stage Preamplifier. I was in luck. However, having Stromtank ship me a 300 pound plus crate that included their model S5000 across the country was not to be. Instead they agreed to send me their Stromtank S2500 that would be able to perform the same task as their much larger S5000. Yes, the "smaller" S2500 still had a shipping weight that was about 150 pounds, but it was certainly more practical. The smaller Stromtank would serve the same purpose: to remove my system from the power grid, and to supply my system with a pure 110 Volt, 60 cycle AC sine wave of pure lithium battery power from a component that had only one purpose -- to power my system.

Genius
The genius behind the creation of the Stromtank is none other Wolfgang Meletzky, the founder, and former chief designer at MBL back in the day. Anyone even slightly familiar with this German luxury high-end audio manufacturer will recognize it as a company that doesn't cut any corners when designing and building their gear. And so, it goes without saying (but I'll say it anyway) that the Stromtank is a component built with what seems like obsessive exactitude, and I'm apt to say that if they tell me it will improve the sound of any high-end system by removing it from the power grid, I'd believe them.

The Stromtank S2500, like its big brother the Stromtank S5000 is able to remove one's system from the power grid, delivering a pure sine wave of 110 Volts (and of course can be ordered for 220V systems). Stromtank's S2500 has a storage capacity of 2500-Watt hours (as opposed to the S5000, which has a storage capacity of 5,000Wh and the specification obviously the basis for the models' monikers). Both contain lithium-iron-phosphate-cells. These LiFe-PO4 cells are safe, environmentally friendly, very cycle-resistant and relatively lightweight. The main difference between the two models is how long each will be able to go without a charge, and the amount of power that they can deliver to a system. With the S2500 one is able to listen to music for up to 4 hours without a charge.

If the batteries charge is depleted during operation the Stromtank will automatically go into charging mode, yet the listener can still enjoy music during the charging process. This is the beauty of the Stromtank – even when connected to the AC power for recharging, the current that comes forth from the Stromtank is not taken from the grid, as this power is absorbed by the batteries. Plus, in "AC-connected mode" the Stromtank creates a stable AC-supply and has much less interaction between the grid and one's setup.

Even though the Stromtank S2500 is the smaller of the two models offered, it is still quite large and heavy. I was lucky when it was delivered to my home because the freight delivery driver was quite nice, and when he discovered what was in the large create he became even nicer, helping me lift the crate up to the front porch of my house and beyond the front door. I can't guarantee your driver will be as friendly, however, if you order the Stromtank from a local dealer I can bet they will help you install it into your system. Good thing, too, as the un-crated Stromtank S2500 weighs 134 pounds, and is 19 inches deep, 17 inches wide and a foot tall. Moving the Stromtank into my system wasn't that difficult since D'Agostino's director of sales Bill McKiegan helped me carry it upstairs into my listening room, and we both slid it across my listening room's industrial carpet into position.

After connecting it to the wall current with a standard power cable (the quality of this power cable doesn't affect the Stromtank's performance since it is only used to charge the batteries), I was shown how to use the Stromtank S2500. Operation is super simple. It's large circular front panel display glows blue when in charging mode, and green when in "off the grid" mode. There is a switch on the front panel to toggle between the two, so I simply switched the S2500 to blue charging mode when I wasn't listening. I never ran out of power when listening, as I didn't have any listening sessions that lasted that long. Plus, the battery life depends on how much power is drawn from the unit. If it sitting idle it uses much less power is drained than when the volume of one's preamp is on 11. Even if I did complete drain the power, I could have charged the Stromtank when taking breaks, then turning it back on when I continued a listening session.

Results
There are a few words when describing the sonic results of using the Stromtank to power my system: astounding, awe-inspiring, awesome, amazing, astonishing, excellent, fantastic, glorious, magnificent, sensational, spectacular, splendid, terrific, and wonderful. As I said earlier, before the Stromtank arrived, only at nighttime could my system reach its potential. But with the Stromtank my system reached its full potential regardless of the time of day. Even though Stromtank's literature promised it would make this improvement, it took me by surprise. Having my system sound the same both during the day and at night took some getting used to. In a good way.

The only "problem" I ran into was that I couldn't connect my 350 Watt per channel Pass Laboratories X350.5 power amplifier to the Stromtank S2500 and play it at excessive volumes. If I did, the Stromtank would shut down because it would become over-heated. This only happened once during my time during the Stromtank's audition period. After it shut down I had to wait a while so the Stromtank could cool down. After that the Stromtank operated perfectly, and I could listen to music again, being fully aware that if I was to connect my power amp to the Stromtank, I should be very careful about how high I turn the volume of my system, and for how long I listen to a louder than absolutely necessary. Otherwise, the Stromtank performed as advertised, and without any problems whatsoever.

It operated better than advertised, actually, because I've never experienced sound like this from my system, other than during those occasional midnight listening sessions. Admittedly, what I consider "excessive volume" might be a bit too loud for many listeners. That being said, I think that only a few listeners might have problems using the S2500 for their high wattage power amplifiers. Those with large systems and especially those with large home theater setups would most likely be better off using the Stromtank S5000. If I had a choice, I would, too, so I didn't have to worry about the unit shutting down. This is a first world problem if I've ever heard one.

Admission
There is only one other problem with the Stromtank, and that has to do with the price of admission. After using the Stromtank for a while my thoughts turned to looking forward to the day when other manufactures design and build their own battery power supplies, hopefully at a much lower price, which will enable more audiophiles to experience a sonic epiphany such as the one that I had when using the Stromtank S2500. In the meantime, anyone with enough cash on hand to purchase either a Stromtank S2500 or especially the S5000, should make a healthy donation to the charity of their choice, and then order a Stromtank.

Unless one lives in an area that shares a power line that comes from the power company with no one else, I can't imagine one being disappointed with the performance of the Stromtank. And I'd bet even those audiophiles will hear an improvement in their systems because of the pure sine wave of battery power that the Stromtank delivers. The Stromtank cannot be compared to other power conditioners on the market because it isn't a power condition. It is power. Period. And that's the beauty of the Stromtank. Recommended? Are you kidding?

Specifications
Type: Battery power AC electrical supply with sine wave generation
Input AC parameters on grid 
Input voltage range: 50 to 140 VAC / 150 to 265 VAC 
Input frequency: 45 to 65 Hz (auto sensing) 
Input current max.: 16 Aac (transfer relay) 
Input current adjusted: 14 Aac (115Vac), 10 Aac (230Vac) – factory setting 
Transfer time: < 15 ms, on grid to off grid 

Output AC parameter off grid 
Output voltage: 100-130Vac / 200-245VAC (pure sine wave +/- 2%) 
Output frequency: 50 Hz / 60 Hz +/- 0.05% (crystal controlled) 
Harmonic distortion: < 2% 
Continues power @ 25°C: 600 VA 
Power 30min. @ 25°C: 1.000 VA 
Maximum load: up to short circuit 
Maximum asymmetric load: up to P cont. 
Load detection: (Stand by) 10 W Cos φ 0.1 – 1 
Maximum efficiency: 93% (dc/ac conversion mode) 
Consumption stand-by/on: 1.5 W / 8 W 
Overload + short-circuit protection: automatic disconnecting with 3 restart attempts 
Overheat protection: warning before shut-down with automatic restart 
Operating temperature: +10 to 45°C 
Relative Humidity: 0 to 85% non- condensing 
Acoustic level: < 40 dB 

Battery power unit 
Battery type LFP - Lithium Iron Phosphate (LiFePO4) 
Nominal battery voltage: 26 Vdc 
Nominal capacity: 100 Ah 
Volume Energy Density 177 Wh/l 
Gravimetric Power Density:107 Wh/kg status 01-2017 

Typical charge current: 8 Adc - factory setting 
Working temperature: 0 to 45°C, 32 to 113°F 
Emergency charge current 3 Adc (special STROMTANK charger necessitated)
Battery Management System: Flex-BMS, single cell control, active balancing 5A 

Terminal area 
AC output receptacles: 3x Hubbell duplex, Hospital spec. grade 
3x Furutech High performance Schuko sockets 
AC output fuse: thermal – magnetic circuit breaker 
AC input connection: ICE 320 - C14 (fuse 16/10AT) 
Interface: CAN (RJ45-8 type "Com bus") * USB* 
Charge connector: use STROMTANK charger only 
Power switch: on/off ("on" = green LED) Safety key switch key switch "Release/Lock" all functions

Additional Features 
Color meteorit-gray (other colors on request) 
Weight: 134 lbs 
Dimension: 19" x 17" x 12" (WxHxD)
Price: $19,500

Company Information
WinBat Technology GmbH
Rathenower Str. 45
10559 Berlin, Germany

Voice:: +49 (30) 52688330
Fax: +49 (30) 80922343
E-mail: info@stromtank.com 
Website: www.Stromtank.com 

Unites States Of American Distributor
D'Agostino Master Audio Systems
P.O. Box 89
Cave Creek, AZ 25327

Voice: (480) 575-3069
E-mail: petra@dandagostino.com
Website: www.DanDagostino.com