[JohnLL]

I am interested in getting a Virtue 1.2 and using it with batteries. I have considered paring it with a Pass B1 buffer with also takes 24V. The B1 current draw is tiny.
It would be great if I could use the same batteries. Is this doable? Would I have created a ground loop with the battery ground and the IC ground or are there other issues? Thanks John

[panomaniac]

Hi John,
 You can use the same 24V batteries for the amp and Pass buffer.  I don't think you'll have trouble with ground loop.

You may find that separate supplies for the amp and buffer sounds better, but it won't hurt to try running it all off on battery pack.

[JohnLL]

nt

[cynan]

What about running 5 6V SLA batteries in series to get a 30V power source? I noticed that the 6V SLA betteries seem to have a higher maximum current  than the 12V. The 12V don't get much higher than 15A for any sustained period, while the 6V double this - is this extra current with the 6V batteries a problem when powering on the unit (will the soft-start circuit be able to handle the 6V batteries?)?

[Vinnie R.]

What about running 5 6V SLA batteries in series to get a 30V power source? I noticed that the 6V SLA betteries seem to have a higher maximum current  than the 12V. The 12V don't get much higher than 15A for any sustained period, while the 6V double this - is this extra current with the 6V batteries a problem when powering on the unit (will the soft-start circuit be able to handle the 6V batteries?)?

Hi cynan,

A fully charged 6V SLA when removed from the charger is more like 6.9V.  6.9V x 5 = 34.5V (at turn-ON), so besides in-rush, check with Virtue that the initial turn on voltage of 34.5V is ok.   I'm pretty sure it does not want to see more than 30V.

Also, charging five 6V SLA batteries in series is not an easy task.  I suppose you can do it in parallel, but it will be much easier with two 12V batteries.

The higher current rating of the 6V battery is because there is half the cells (a 6V SLA has three cells, while a 12V SLA has 6 cells).  So the output impedance is half for the battery, but once you string them in series, the impedance all adds back up.

Finally, there is no way you are going to come close to needing anywhere near 15A for a sustained period of time.  That's a LOT of power, which the amp will never draw (unless it accidentally gets shorted out  )

Hope this helps,

Vinnie

[virtue]

Vinnie,
Is there such a thing as NOT fully charging an SLA battery?
Hypothetically, if we can handle 39v on the next TWO.2, would it be possible to provide a charging solution that made sure the battery never output any more?
Vis a vis the ONE.2, 34v could be harmful (it's only got 2 oz copper, tiny power traces), but more importantly it's not useful because of the gain settings on the TC2000.  It's optimized for 30v and if you want to more gain, run a higher voltage input signal (through a pre-amp) and hope that you don't torch the amp
Seth

[imassarano]

Hi Seth,

This is my first post on this circle, and the first for many moons on this site, as I have been unemployed during this time I have not wanted to actively participate. But now that things are improving, I cannot resist any longer. So hello to all .

None the less, I have followed what's going on on many of the threads, and the use of battery-powered amplifiers greatly interests me.

The batteries that get mentioned are SLA type, however, I would like to know if LiFePO4 Li-Ion rechargeable batteries would do the trick. Obviously, I would welcome anyone with any experience of using this later technology to give their views.

Isaac

[Vinnie R.]

Is there such a thing as NOT fully charging an SLA battery?

Hi Seth,

If you had three 12V SLA batteries connected in series, when they are fully charged (right off the charger), they will each have a voltage (for a brief amount of time) in the range of 13.5 and 13.8V per battery (This is the "float charge" voltage).  So the max voltage upon turn-on can be 41.4V.

Once in use, a fully-charged SLA battery drops fairly rapidly to around 12.9V.  It is the "surface charge" of 13.5V to 13.8V per battery that you need to be aware about, because your amp WILL briefly see this when switched ON (maybe for under 60 seconds - but it depends on the loading).

So you would need to put some voltage clamping that prevents any voltage higher than 39V.  This would also be a good idea for those using external linear or SMPS, as their output might change a bit as well.  At time = 0 when you turn on such a supply, its voltage might briefly be higher than it is rated for, until the load is presented to the supply and the supply's feedback stabilizes the voltage (this should happen quickly, but you still need to be aware of it).  I've seen this even with "regulated" power supplies.  Also, upon plugging them into the AC outlet, some of them (I've found this more with SMPS type supplies) have an initial "overshoot" (even if it is very brief in time that you can trigger on your osilloscope) - so  protection at the input of your amp will prevent these brief "spikes" from hurting your components if they cannot go beyond 39V.

You cannot limit the charge of the SLA to 13V because the cells in the battery will never reach a full charge and the battery life will reduced.  Like all batteries, SLA batteries need to follow a proper charging procedure to obtain the rated cycle life of the battery.  A big enemy of batteries is undercharging as well as overcharging.

I would like to know if LiFePO4 Li-Ion rechargeable batteries would do the trick. Obviously, I would welcome anyone with any experience of using this later technology to give their views.

Hi imassarano,

These can be used via a custom make pack, but the LiFePO4 pack should have a PCM (protection circuit module) installed - which will prevent over-voltage and thermal runaway conditions while charging this type of battery , which can explode if not properly implemented and charged. 

LiFePO4 also has different discharge characteristics (discharge curves are not as flat as SLA), but they do have great cycle life, and are also high-current output, and can be deep-cycled without harm (SLA's hate deep cycling).  But expect the LiFePO4 pack + required PCM + charger to be very expensive - and note that they also have "peak" voltages (fresh off the charger), working voltages, and cut-off voltages.

If you make a LiFePO4 pack with 12 cells, the nominal voltage should be 38.4V (nominal voltage = 3.2V per cell x 12 = 38.4V) - but the peak voltage after charging will be around 3.8V per cell x 12 = 45.6V.  The cell's cut-off voltage is approx. 2V.  So 2V x 12 = 24V cutoff.   So that is quite the voltage drop from 38.4 to 24V, and the Tripath amp like Virtue is optimized (via "modulator feedback resistors") to sound and function its best at a much smaller power rail voltage range. 

The SLA battery discharge curve much flatter, so the voltage remains more contact over the discharge cycle...


I hope this info is helpful,

Vinnie

[imassarano]

Vinnie,

Thanks, very interesting .

So basically, from what I can gather from your extensive answer is  a LiFePO4 pack with a PCM is a no go because of a too variable voltage range, however, would employing a full-time smart charger improve the outcome?

Isaac

Corrected text.  I.M.

[Vinnie R.]

Vinnie,

Thanks, very interesting .

So basically, from what I can gather from your extensive answer is  a LiFePO4 pack with a PCM is a no go because of a too variable voltage range, however, would employing a full smart charger improve the outcome?

Isaac

hi Isaac,

I'm not sure if the PCM can be adjusted to allow the pack to turn OFF at higher voltage than 24V.
It would be idea if you can do this via the LiFePO4 PCM, but you might be cutting the overall "play time" of the battery because it was designed to run over a wider discharge curve.  It is best if you look up the datasheets of these batteries and look at their discharge curves.  They usually plot the voltage on the Y-axis, the Time in the X-axis, and give you different curves based on the load (in Amps). 

With our RWA SMART board, we switch OFF power when the voltage of the SLA battery reaches approx. 11.5V (but we can easily adjust this via firmware).  So a three 12V SLA battery supply will shut-off at approx. 34.5V.  That is a lot sooner than 24V 

Best regards,

Vinnie

[imassarano]

Vinnie,  Sounds like you are doing a sales job on me (Actually, I've got your Black Lightening page bookmarked already ).  I've spotted a mistake in my previous post, should read: "full-time smart charger", , i.e. having the pack under constant low current till cut-off. Anyway, this is what I have found, with the TWO.2 in mind (may be a pair of employing 2 packs).  http://www.batteryspace.com/lifepo426650battery384v68ah26112wh30aratewithpcm.aspx

[cynan]

The sources I can find indicate that the peak voltages (at full charge) for LiFePO4 cells are 4.1V to 4.2V, while the nominal voltage is 3.5 to 3.9V. Therefore, with 7 cells in series, you would be seeing peek voltages of about 29V and nomial voltages in the 25V to 27V range. This would be ideal for the current virtue power supplies.

While LiFePO4 cells have a shutt-off voltage of under 3V, isn't this battery chemistry more resiliant (and even more responsive) to limitting discharge to way before this occurs. Looking at discharge curves, it seems that these shutt-off voltages are achieved suddenly and that most of the discharge life of these cells occur above 3.4V to 3.5V.

So, besides the high cost of these cells, LiFePO4 may actually work well.

Edit: Most importantly, what makes LiFePO4 most desirable is that they seem to have the flattest discharge curve of any common battery chemistry. I would like to try a 7 or 8 cell LiFePO4 supply. The 8 cells are rated at 29.6V - and if you pick the right cell, should maintain a voltage of 29 to 30V for about 70% or 80% of its discharge life - though they have peek full-charge voltages of about 33V. If only there was someway to easily regulate this initial peek voltage...

[Vinnie R.]

Vinnie,  Sounds like you are doing a sales job on me (Actually, I've got your Black Lightening page bookmarked already ).  I've spotted a mistake in my previous post, should read: "full-time smart charger", , i.e. having the pack under constant low current till cut-off. Anyway, this is what I have found, with the TWO.2 in mind (may be a pair of employing 2 packs).  http://www.batteryspace.com/lifepo426650battery384v68ah26112wh30aratewithpcm.aspx

Hi imassarano,

ok - I saw your link.  Here is what that pack is spec'd for:

Voltage: 38.4 V (working) , 43.8 V (peak) , 24.0 V ( cut-off)

Check with Virtue, but the peak voltage (fully charged) looks too high, and the cut-off is quite low at 24V.

You'll also need a charger (looks like the one you need is $60), enclosure for the batteries, switch, etc. 

The warranty on that battery pack is 30-days.  For a $375 battery, I wish they can give at least a year warranty.  With SLA, good quality batteries are typically under $25 per 12V, 5Ah battery - and with proper voltage monitor (ala SMART baord), they cannot be damaged due to deep-cycling.

Also, it says: # Must wait min of 30 minutes after battery is fully charged to allow the pcm to perform balance function on all the cells within the pack.   

While LiFePO4 cells have a shutt-off voltage of under 3V, isn't this battery chemistry more resiliant (and even more responsive) to limitting discharge to way before this occurs. Looking at discharge curves, it seems that these shutt-off voltages are achieved suddenly and that most of the discharge life of these cells occur above 3.4V to 3.5V.

So, besides the high cost of these cells, LiFePO4 may actually work well.

I'll check out the datasheets and discharge curves when I get a chance.  Yes, they are more resilient to being deep cycled (but they seem to shut off at too low of a voltage of 2V per cell).  They also need a PCM board for balancing of the cells and charge management - and I wonder if that board can be tweaked to shut-off before one reaches the 2V per cell.

Interesting stuff - whenever the heck I get some free time, I'll try to reach it more... 

Vinnie

[imassarano]

Vinnie.
  

[cynan]

imassarano,

I think something like this would be better suited. It comes with the PCM which limits output current to 10A and balances cells after charging. It also comes with a fire/water proof enclosure!

http://www.batteryspace.com/li-ionboxbattery296v52ah154whinwaterandfireproofenclsourebl-lch4p2s8wcwp-2p.aspx

Or you could make your own battery with 2X the capacity with 7 or 8 of these:

http://www.batteryspace.com/polymerli-ioncell37v10000mah9059156-1c37wh10arate-ulunapproved.aspx

And the PCM

http://www.batteryspace.com/pcmwithequilibriumfunctionfor296vbatterypackat10alimit.aspx

About $290 for an 8 Cell Unit. Then you need the enclosure, wirring and charger

Charger for $50: http://www.batteryspace.com/smartcharger10afor296vli-ionpolymerrechargeablebatterypack.aspx

Still the issues of 33.6 V peak voltage and the potentially low cut-off as menstioned by Vinnie.

[JohnLL]

It's nice to have real battery experts here. I have tried to teach myself, but I still fall in the "little knowledge" category and have some basic questions.  I had intended to series 2 Powersonic 12v, 9ah,  (#1290). I picked these because they are smaller than 4 5ah batteries and they still have a decent internal resistance (13 m/ohms).
If I am reading it right, the graph indicates they will provide 45 m/amps for 11 hours and still not fall under 12 volts. At 24 votls in series that is ~ 1.1 watts.

In my home office environment I am using less than a watt. My speakers are only 87 db efficient but I am only playing them 60-65 db’s and often less when I am really really working. I borrowed a meter and it is a lot lower than I would have guessed. In the evening I might play them 70-75db on average (peaks aside) but that is about it if I want to maintain domestic tranquility.

So the question is how long will this battery last? The difference between 87 and 65 db is 22. I understand power has to double for every 3-db increase in volume and assume the same thing works in reverse. Am I using .2-.3 watts for a typical hour? I just want to know if I am anywhere near to the ballpark. If I missed it a mile please be nice.

The second question is that I have read that charging batteries in series will result in an uneven voltage charge between batteries. Is this a sonic problem?

Finally I would like to ask the Virtue staff what the power connection is on the back of the Virtue 1.2.  Thanks! John

[cynan]

JohnLL,

Your reasoning makes sense to me - though I also fall under the "little knowledge" category. I would think you would have to allow for additional power usage due to the amplifier not being 100% efficient (though I think the Virtue amps would be fairly efficient as far as amplifiers go). Also, if I'm not mistaken, the 87 db at 1 watt/meter is per speaker. I don't know if you can figure this out measuring both speakers at once (well, I suppose you could estimate that the db level should be about 3 db higher with both speakers rather than one alone, running at the same wattage per channel. If so, you could pretend that you are producing 62 db/speaker at 65 db?).


Also, a note regarding Lithium cells. Some Lithium cell chemistries (ie,  LiCoO2, LiMnNio4) seem to have a nominal voltage of 3.6V while (newer?) LiFePO4 cells seem to have a nominal voltage of 3.2V - which is what Vinnie was obviously referring to. Sorry for the confusion

[Vinnie R.]

Hi JohnLL,

You need to factor in the "quiescent current" of the amp.  This the current draw of the amp even when there is no signal being fed to the amp.  You can check with Virtue, but I'm sure it is over 100mA.  Then you have avg. current draw - which is based on your speaker impedance (which varies with frequency, and the volume level you play at).  And yes, the speaker efficiency comes into play because you need to output a larger signal with lower sensitivity speaker to obtain the same SPL output of a higher sensitivity speaker.  Then there is instantaneous current draw (for the dynamic peaks in the music).  Even the type of music comes into play when it comes to power consumption. 

The second question is that I have read that charging batteries in series will result in an uneven voltage charge between batteries. Is this a sonic problem?

It eventually can be a problem when one battery becomes quite out-of-balance with the other.  So if one battery is outputting 12.5V and the other is down to 11V (and dropping because it is the weaker battery because it was being over or under charged for quite a few cycles), then the voltage to the amp will drop - and if you have no circuitry that is monitoring this and provide a 'cut-off' feature when the voltage drops to a threshold, then you could be playing at a much lower voltage than what is in the amp's comfort range - resulting in reduced output power and distortion. 

Also, a battery that is "beat" will no longer accept adequate charge from the charge, so it will "trick" the auto charger into thinking that both batteries are fully charged (switch to float charge mode prematurely, which doesn't help charge the other battery adequately). 

If you charge in series with a 24V charger, it is really important that both batteries are as closely matched as possible. 

With our new SMART 1224 board, we charge all batteries in parallel with a 12V charger.  This way, all batteries see the same voltage, and if each battery is a little different, it will be able to draw it own required current and all the batteries equalize at the same voltage. 

The ultimate solution is one charger per battery, but this gets complicated 

Finally I would like to ask the Virtue staff what the power connection is on the back of the Virtue 1.2.

Seth told me that it is a 5.5mm / 2.1mm DC barrel jack (center pin +).  I also needed to know this because we make Black Lightning SLA battery power supply units for this amp (as well as his other models coming out).

Also, a note regarding Lithium cells. Some Lithium cell chemistries (ie,  LiCoO2, LiMnNio4) seem to have a nominal voltage of 3.6V while (newer?) LiFePO4 cells seem to have a nominal voltage of 3.2V - which is what Vinnie was obviously referring to. Sorry for the confusion

Cynan is correct!

Still the issues of 33.6 V peak voltage and the potentially low cut-off as menstioned by Vinnie.

Yes - I would definitely contact Virtue about this, as this voltage is above his 30V max input spec found here:
http://store.virtueaudio.com/category-s/27.htm

And yes, even the extra 3.6V is enough to push the output driver chip over the edge 

Best regards,

Vinnie

[JohnLL]

Thanks Vinnie,
I assume my reasoning was in the ballpark but I oversimplified things-maybe alot. No surprise as I do not begin to have electronic chops and I appreciate you even responding to my questions.  The best, John

[virtue]

Sounds like y'all ought to buy Vinnie's pack at the special price he's offering and send the balance of money you would spend on the Li-On solution to a charity of your choice and the time lost not building it to your favorite companion   We tested some Chinese lion gel packs around 2 years ago for Sensation and were just too frightened by the explosive potential.  Roger refused to work with them in fact and I think they're buried in his back yard.  I hear the new ones are safer   Also, Vinnie explained why SLA would give equal or better performance.  As I keep relearning in this business, sometimes perfect IS the enemy of the good.

The ONE.2 should be stable at 34v however you won't get any power advantage because of the way we've throttled the Tripath controller.  Notably, running over 30v is not advisable because the bulk cap is rated only 35v in order to get more capacitance for the size.  The buffer is already modest.  Also, the ONE.2 uses 2 oz copper and the traces on the power chips are quite fine.  I think it will survive 34v but we don't test at that voltage.  In short, you're on your own!

The 28v+ you'll get out of a 24v pack fully charged, is just about right!