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Author Topic: E.A.A. PSP-2 and nimh batteries  (Read 3582 times)

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Offline Since85

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E.A.A. PSP-2 and nimh batteries
« on: July 26, 2013, 12:24:48 PM »
Does anyone power their PSP-2 with rechargeable AA batteries? I am just wondering about current draw on these batteries vs. alkalines. I know that many recorders have a "nimh" setting due to the slightly lower nominal voltage. I am wondering if the flashing light will come on the preamp earlier due to this difference.  ???

Should I go with the 2,700 mah batteries, or use Eneloops? Also, how many hours are you getting before the flashing light comes on (w/ phantom on)?
 Any specific experience with this would be appreciated, thanks!

« Last Edit: July 26, 2013, 01:14:46 PM by Since85 »

stevetoney

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #1 on: July 26, 2013, 01:39:13 PM »
The PSP2 runs fine on ni-mhs.  Yes, since the voltage on the ni-mh batteries is a little lower than alkalines, you can expect that the flashing light will come on a little sooner. 

I don't run my preamp with phantom, so I can't tell you what to expect as far as run times with phantom on...depends of course on the mic draw, but I'm pretty sure you should have no problem getting a full show with a set of normal ni-mh's. 

Without phantom, my PSP2 pulls around 350ma.  Here's a quick and dirty calculation to help you out...

Energizer ni-mh's have a capacity of I think 2250mah (it could be 2400 but for the sake of conservatism, I'll go with the smaller number).  2250mah / 350ma = 6.4 hr

Lets assume with phantom, you pull 500 ma.  With the run-of-the-mill ni-mh batteries you get from Wal-Mart for $12 per 4 pack, you should be able to get around 2250mah / 500ma = 4 1/2 hr. 

I have several battery sleds that work in my PSP2 (modded them myself from cheap $2 sleds I bought from an electronics supplier) so quick change-outs is nice.  Saves time from fumbling around to change batteries out while the music is going on and you're missing it.
« Last Edit: July 26, 2013, 01:50:18 PM by tonedeaf »

Offline hi and lo

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #2 on: July 26, 2013, 02:06:39 PM »
Yes, the PSP-2 does run fine on NiMH batteries. However, I don't believe the low power light will come on sooner. NiMH chemistry has a flatter discharge curve than Alkaline, so if anything it should come on later than Alkalines. In fact, it might not even give you much advanced warning at all since NiMH batteries maintain a stable voltage until they are almost entirely discharged, at which point the voltage rapidly falls.

Here is much a better explanation of this than I can provide:

Quote
Low internal resistance allows NiMH cells to deliver a near-constant voltage until they are almost completely discharged. This will cause a battery level indicator to overstate the remaining charge if it was designed to read only the voltage curve of alkaline cells. The voltage of alkaline cells decreases steadily during most of the discharge cycle.

Regarding current draw, although I have not explicitly measured this on the PSP-2, I cannot possibly imagine it's pulling 350mA without phantom on. I've been able to run the PSP-2 literally all day on 6xAAs (easily 10 hours) with the phantom on and there's no way it would last this long if pulling 350mA, let alone 500mA?

I'll test current draw when I get home, but I believe it's going to be much closer to 200mA w/ phantom on. Bottom line, I know it will last far longer than 4-6 hours and even running it all day at Mountain Jam this year, the low battery indicator never came on at all.

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #3 on: July 26, 2013, 06:51:20 PM »
Running on Alkaline's it's rated at 10 hours w/ 48v on
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stevetoney

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #4 on: July 26, 2013, 08:21:11 PM »
For the OP, the bottom line is you're OK using Ni-MH batteries, but for purposes of fun discussion and battery banter...I'm gonna nit pik your response a little bit.  In the end, it really doesn't matter though. 

I agree with your comment about how the flat part of the discharge curve is flatter on NiMh batteries than Alkaline, but when you check the details you'll notice that NiMH batteries start at a lower voltage than Alkaline.  You'll also notice that, as you mentioned, when the battery gets to the end of it's usable range, it discharges to zero very quickly and the curve become almost vertical.  The alkaline curve certainly discharges at a quicker rate than when it's on the flatter part, but it's doesn't go to a near vertical slope like the Ni-MH battery does. 

When you have a six pack of AA's, a tenth of a volt on a single AA cell, means the starting voltage on a pack is going to be six tenths higher on the alkalines that the Ni-MH.  The flat part of the curves are also going to be higher by six times the difference.  If the pack is 2 or 4 cells, there is less voltage difference on the flat part of the curves between Ni-MH and Alkaline packs.  If you superimpose the curves, it might be a number of hours before the voltage on the alkaline pack decreases and crosses below the voltage on the flatter Ni-MH curve.  So, at that point yes the Ni-MH voltage might be higher than the Alkaline, but then at the end, the vertical cliff of the Ni-MH will again take it below the voltage of the Alkaline.

Taboot, if your ni-MH batteries are not new, they will have a higher internal resistance which will cause the flat part of the curve level out even lower...and again when you multiply that by six times, the difference between the flat parts of the curves widens even more so that the crossing point of the two curves goes even farther out to the right.

To be honest, it's really not a cut and dry winner on either side becuase the run time on each battery is all dependent upon what is the voltage cut out setpoint on the preamp.  If that setpoint occurs at a point where the Ni-Mh may happen to be at a higher voltage than the Alkaline, then the Ni-Mh would be the winner.  If the setpoint is at a point on the curves that's farther left or right from that point, then the Alkalines might be the winner.

Anecdotally, the phenomenon I've described above was shown by people when we were testing out the Tascam DR100MKii when it first came out a couple of years ago.  People were discovering that they could run their units without problems as long as phantom power wasn't on.  However, if they swtiched on Phantom, there was a high current draw and, with alkalines they could get maybe an hour and a half of run time before the low battery cut out was reached.  Using Ni-mh, especially older used ones, the run time was 15 to 30 minutes. 

(Don't be misled by the above, the run time SHOULD be much longer...the reason for the really short run times is that the cutout setpoint on the tascam is set too high.  Tascam still hasn't fixed this through a firmware update.)

What it showed is that the lower voltage setpoint was reached much quicker using the Ni-MH than the Alkalines...which I think was a result of the fact that the flat part of the curve on the Ni-Mh occurrs at a lower voltage...particularly when you have 2, 4 or 8 batteries providing 3, 6, and 12v nominal voltage. 

Yes, the PSP-2 does run fine on NiMH batteries. However, I don't believe the low power light will come on sooner. NiMH chemistry has a flatter discharge curve than Alkaline, so if anything it should come on later than Alkalines. In fact, it might not even give you much advanced warning at all since NiMH batteries maintain a stable voltage until they are almost entirely discharged, at which point the voltage rapidly falls.

Here is much a better explanation of this than I can provide:

Quote
Low internal resistance allows NiMH cells to deliver a near-constant voltage until they are almost completely discharged. This will cause a battery level indicator to overstate the remaining charge if it was designed to read only the voltage curve of alkaline cells. The voltage of alkaline cells decreases steadily during most of the discharge cycle.

Regarding current draw, although I have not explicitly measured this on the PSP-2, I cannot possibly imagine it's pulling 350mA without phantom on. I've been able to run the PSP-2 literally all day on 6xAAs (easily 10 hours) with the phantom on and there's no way it would last this long if pulling 350mA, let alone 500mA?

I'll test current draw when I get home, but I believe it's going to be much closer to 200mA w/ phantom on. Bottom line, I know it will last far longer than 4-6 hours and even running it all day at Mountain Jam this year, the low battery indicator never came on at all.

This makes sense.  For clarity, when I stated 350mah I was basing this on the sample run-times I was getting using several batteries that I have of known capacities.  I have a smart battery charger, so what I did was discharged the battery with the PSP2 connected and then recharged the battery with my smart charger, noting how many mah it took to recharge.  I did this three or four times and got around 300 to 310 mah, so 350mah I was using was conservatively high for purposes for calculating runtimes.  Obviously, whenyou recharge batteries, there are some inefficiencies from what goes in versus what you can get back out.  I always knew this, but could never measure what the inefficiency was...so for purposes of making sure I had enough battery power for festival weekends, I always knew that the 350mah number was conservatively high.
« Last Edit: August 01, 2013, 05:39:48 PM by tonedeaf »

Offline hi and lo

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #5 on: July 29, 2013, 03:14:25 PM »
No problem, Tonedeaf. My response is below and I'd welcome any input from others that probably know more about this than both of us combined!

I agree with your comment about how the flat part of the discharge curve is flatter on NiMh batteries than Alkaline, but when you check the details you'll notice that NiMH batteries start at a lower voltage than Alkaline. 

I think it would really help to visualize the discharge curves. First, the starting voltage of both chemstries is irrelevant to this particular discussion. As evidenced by the discharge curve, although the alkaline battery has a significantly higher starting voltage, it quickly falls below the normal operating voltage of NiMH batteries after only being ~1/3 discharged and spends ~2/3 of its life at a voltage below NiMH.



You'll also notice that, as you mentioned, when the battery gets to the end of it's usable range, it discharges to zero very quickly and the curve become almost vertical.  The alkaline curve certainly discharges at a quicker rate than when it's on the flatter part, but it's doesn't go to a near vertical slope like the Ni-MH battery does. 

Here is where a visualization really helps. First, notice that the Alkaline curve has a dramatically reduced 'flat part' the discharge curve. The voltage drop is far more linear over time

Second, both chemistries will achieve a 'near vertical' slope when discharged beyond their capacity. This is not a phenomenon specific to the NiMH chemistry.

When you have a six pack of AA's, a tenth of a volt on a single AA cell, means the starting voltage on a pack is going to be six tenths higher on the alkalines that the Ni-MH.  The flat part of the curves are also going to be higher by six times the difference.  If the pack is 2 or 4 cells, there is less voltage difference on the flat part of the curves between Ni-MH and Alkaline packs.  If you superimpose the curves, it might be a number of hours before the voltage on the alkaline pack decreases and crosses below the voltage on the flatter Ni-MH curve.  So, at that point yes the Ni-MH voltage might be higher than the Alkaline, but then at the end, the vertical cliff of the Ni-MH will again take it below the voltage of the Alkaline.

Taboot, if your ni-MH batteries are not new, they will have a higher internal resistance which will cause the flat part of the curve level out even lower...and again when you multiply that by six times, the difference between the flat parts of the curves widens even more so that the crossing point of the two curves goes even farther out to the right.

Again, voltage drop at the end of a battery's life is irrelevant because it happens with both chemistries. The NiMH curve does not 'overtake' the Alkaline curve prior to the cell being fully discharged and the point at which we declare a cell discharge (1v, in this case) has to remain constant between chemistries because our electronic devices will not care about battery chemistry; all they care about is being above the minimum operating voltage.

Regarding multiple cells and aside from some tangentials (re: resistance), it's not really relevant to this article. You're either above or below the minimum operating voltage and with NiMH chemistry, you simply add another cell to make up the difference (aka 9.6v rechargables).

To be honest, it's really not a cut and dry winner on either side becuase the run time on each battery is all dependent upon what is the voltage cut out setpoint on the preamp.  If that setpoint occurs at a point where the Ni-Mh may happen to be at a higher voltage than the Alkaline, then the Ni-Mh would be the winner.  If the setpoint is at a point on the curves that's farther left or right from that point, then the Alkalines might be the winner.

Using the graph to visualize the low-votlage setpoint should help to illustrate how this isn't actually the case. This would only matter if the low-cutoff voltage was set to ~1.2v (assuming a 1.5v standard). If set anywhere below this voltage (i.e. just slightly above 1v), the indicator will always come on first with Alkaline chemistry and second with NiMH chemistry. This is why a low-battery indicator designed for use w/ Alkaline batteries will overstate the charge when using NiMH batteries and might not alert you to a low-battery condition before it's practically too late.

I can't really speculate on why you observed the behavior you did with the DR-100 and there are too many variables in play to draw any conclusions and/or apply them to this discussion.

stevetoney

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #6 on: July 29, 2013, 04:30:56 PM »
Good response.  The only comment I have is that your visualization doesn't account for the fact that alkalines are always new where ni-mh rechargeables are only new at the start of their life, and the graph shown is representative of a new set of rechargeables.  As ni-mH batteries age the graph degrades both in terms of the voltage the battery will provide on the flat part of the curve and the total capacity supplied until the battery drops off on the vertical cliff at the right.  That said i don't think you see much voltage drop until the battery is under a decent load (used rechargeables develop increased internal resistance under load, which reduces voltage and increases heat).

I can't really speculate on why you observed the behavior you did with the DR-100 and there are too many variables in play to draw any conclusions and/or apply them to this discussion.

The intermediate term solution for the problem was that people went to higher voltage battery chemistries, such as Zinc rechargeables.  When they did, they got acceptable run times on the DR100MKii because the low voltage cut out wasn't reached as quickly with the Zinc chemistry, which has a higher voltage on the flat part of the discharge curve than either alkalines or older Ni-MH. 

But it was also clear from the experiences and lessons-learned from the ts.com members from the DR100MKii situation, that simply measuring the battery voltage of an older set of nimh rechargeables wouldn't have given as high a nominal voltage (at least not under heavy load) as a new set of alkalines, or else the ni-mh batteries would have provided longer run-times than the alkalines before the low voltage cut out was reached.

« Last Edit: July 30, 2013, 07:37:14 AM by tonedeaf »

Offline Since85

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #7 on: August 01, 2013, 01:49:40 PM »
Thank you for the constructive comments here.
What I am essentially wondering is if there is any change in the "quality" of the PSP-2 output signal (strength, dynamic range, etc...) as battery voltage drops.
If the light is flashing as voltage drops, is the signal any different than a full strength battery?

Since you start with a lower voltage initially with a nimh battery, this is what my reservation has been with using them in this particular preamp.

Offline hi and lo

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #8 on: August 01, 2013, 01:56:47 PM »
Thank you for the constructive comments here.
What I am essentially wondering is if there is any change in the "quality" of the PSP-2 output signal (strength, dynamic range, etc...) as battery voltage drops.
If the light is flashing as voltage drops, is the signal any different than a full strength battery?

Since you start with a lower voltage initially with a nimh battery, this is what my reservation has been with using them in this particular preamp.


No, there should not be any sonic differences. The PSP-2 is designed to work with an input voltage as low as 5v. And, per the discussion above, NiMH batteries only start out at a lower voltage. Once an Alkaline battery is partially discharged, it will likely be outputting a voltage that is lower than NiMH.

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #9 on: August 01, 2013, 02:56:45 PM »
Does anyone want to sell me one of theirs :P ;D
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stevetoney

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #10 on: August 01, 2013, 03:04:43 PM »
I agree with Hi and Lo's response above.  In many many hours of PSP2 operation (and I know I've had situations where my voltage has dipped low and the light is flashing), I've never heard any sonic drop-offs.   

I do have a question though for you ...I don't recall, but I don't think I've ever run the PSP2 batteries down completely.  I usually use external batteries to power mine with AAs inside as backup so typically don't see a flashing light when I record. 

However, the question is, if you run the unit down, does it actually reach a cut voltage or does the light simply start flashing, or maybe both (one voltage to warn of low battery voltage and another voltage where it cuts)?

The reason I ask is one of my preamps (Oade m118, which is basically an m148 but lower 18V phantom voltage instead of 48V) just keeps operating once the batteries start to go dead.  What happens is the signal strength starts to drop off, but the sound quality of the recording is still fine even though the levels start to die off.  Over the course of the next oh ten or more minutes the levels just gradually fade to zero.  At some point, there's just not enough power to drive the components and you start to hear distortion, but even after the levels start to die off, I can 'fix' some of that ten minute or so section of the music by adjusting levels in post and the recording still sounds OK. 

Curiouis if the same thing happens on the PSP-2 or if it just cuts out at a low voltage setpoint?  TIA!
« Last Edit: August 01, 2013, 05:37:15 PM by tonedeaf »

Offline hi and lo

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Re: E.A.A. PSP-2 and nimh batteries
« Reply #11 on: August 01, 2013, 05:10:31 PM »
Good question... I'll go out on a limb here at the risk of being wrong.

The m118 doesn't use a dc/dc converter circuit (at least, I don't think it does), so as the output voltage of the internal batteries fall, so do the power supply rails (to the circuit; not talking phantom power here, although that would fall too). The amplification circuit can operate on a wide range of supply voltages (although you're losing headroom as the voltage drops) and the unit still passes a signal.

When a dc/dc converter is used (99.9% certain this is the case with the psp-2, although I haven't taken it apart to confirm), the minimum voltage requirements become pretty strict (5v). Anything below the minimum and the circuit ceases to function normally, more or less cutting off at a certain point.

 

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