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7.2VDC NiMH battery packs on my microRendu sound better than that over priced $50 iFi wall wart and right up there with my lab grade LPS. $30 and change for the 5Ah battery, about $60 for the larger 10Ah unit.After verifying E-Stat's comment that the ESR for Li-Ion types is higher than NiMH I went with NiMH, and discovered some other advantages over Li-Ion.
NiMH batteries have a much flatter (nearly ideal) discharge curve. In other words, as the battery discharges and depletes, the voltage stays very constant. Li-Ion on the other hand tends to sag downward linearly over time.
But NiMH have some disadvantages. NiMH energy density by weight is almost half that of Li-Ion. In other words, NiMH weighs a lot more for a given amount of energy. NiMH also have a higher self-discharge rate of about 20-30% per month vs 5-10% for Li-Ion. None of these are an issue in my application.
Of course if you're inclined to spend the big bucks there's the UltraCap LPS-1 for $400.
$30 NiMH 5Ah Battery gets about 16 hours of run time before recharge
$60 NiMH 10Ah Battery gets about 32 hours of run time before recharge
10Ah and 5Ah 7.2VDC NiMH batteries side-by-side
The microRendu with my DAC attached draws about 250mA so do the math on run time. Rather than depleting the batteries completely I derated the run time figures above by about 20%.
[Edit Oct 1 2016]:
My micrRendu with DAC attached presents a 250mA steady load on the 10Ah 7.2v NiMH battery pack. The battery measures 8.2v fully charged, 7.6v after 18 hours, 7v after 36 hours. Remove it from the system and place it on the charger. A slow charge takes ~12-hours, a fast charge ~6-hours. I prefer the 1-Amp slow charge vs the 2-Amp fast charge as the fast charge makes the battery quite warm and I charge the battery unattended.Under my normal listening conditions of maybe 2-3 hours per day, the 10Ah battery should last about 2 weeks before a recharge.
I already own the charger from a previous battery setup for a phono preamp. The charger is about $30.
Edits: 10/01/16 10/02/16Follow Ups:
FYI.Most of us who're running battery supplies since years use
A123 LiFePO4s. No NiMHs.
ESR subject and more have been brought up more then once at AA or elsewhere. ;)To give you one more idea:
Many of the former battery lovers went ahead and switched to
Super/UltraCaps some years back (I think it started around 2010/2011).
That'll relieve you from the annoying battery charging process and can provide even lower ESR. The overall performance turned out to be at least equal or even better than LiFePO4 supplies. (If you have your grounds under control)
Meanwhile a few vendors jumped on that train and offer supplies at
ridiculous prices.
Enjoy.
Edits: 10/04/16 10/04/16
Most of us who're running battery supplies since years use A123 LiFePO4s. No NiMHs.That's fine, but NiMH was exactly what I needed for my specific requirements. I too have LiFePO4 batteries including a 12.8v unit by Battery Tender and a handful of LiFePO4 18650 and 26650 cells. LiFePO4 would not have been a good fit for my needs. At 3.2v per cell LiFePO4 batteries or battery packs would have put me too far below or above my ideal voltage range and I didn't want to use a voltage regulator.
I used what I had on hand for my specific application, and it was good fit. I already had one 7.2v NiMH battery pack and the battery charger to go with it so I just bought another larger 7.2v NiMH pack, along with a couple cables. While one pack is on the charger, I can use the other pack to play music. With NiMH it is much easier to arrive at the ideal voltage range I wanted (7 VDC for mRendu) as each NiMH cell is 1.2v.
Many of the former battery lovers went ahead and switched to Super/UltraCaps some years back (I think it started around 2010/2011). That'll relieve you from the annoying battery charging process and can provide even lower ESR
Really? UltraCaps don't need to be charged? Sign me up!
I also own some UltraCaps but the complexity of safely charging them unattended is more than I want to deal with. Do you know of any readily available off the shelf wall wart or power brick style UltraCap chargers with auto shut-off? ;-)
Edits: 10/04/16 10/04/16 10/04/16 10/04/16
"...I used what I had on hand..."
Ok. I buy that. I just wanted to mention LiFePOs, so that people don't think NiMH is the best of all choices.
All these battery packages also need cell-balancing while charging etc.
All that is not as easy as it might looks on the first glance.
I still think SuperCaps can do better.
Just saw that UPtoneAudio offers the LPS-1 400$ Ultracap device (1.1A limit). Obviously 1.1A is quite low.
Perhaps something you should have a look at!??!
"I just wanted to mention LiFePOs, so that people don't think NiMH is the best of all choices."
Sure, but IMHO "the best of all choices" is very application dependent. NiMH is in fact the best of all choices for -MY- application and not only because I already had one on hand.
The ideal voltage for the microRendu is 7v and with NiMH I can get a nominal 7.2v because each cell is 1.2v (6 cells x 1.2v). Had I gone with LiFePO4 (at 3.2v per cell) I would have been around 6.4v with two cells (kind of low) or 9.6v with 3 three cells (too high). From experience, I know that the microRendu runs quite warm at 9v so I didn't want to go there.... AND I didn't want to use a voltage regulator on the battery output to lower it. A two cell LiFePO4 6.4v battery pack is too low and approaching the drop-out limit for the microRendu's internal regulator.
Of the "Lithium family" I agree that LiFePO4 is the way to go. They don't have quite the energy density of other Lithium types but they're so much safer. They also have a nice flat discharge curve whereas other Lithiums taper off linearly as they deplete. But NiMH was my choice given the details provided in the prior paragraphs.
Yes, SuperCaps are awesome but the complexity surrounding their use is not something I wanted to deal with, and I didn't want to pay $400 for the UpTone LPS-1. Ouch! It's expensive BECAUSE OF the complexity in properly dealing with UltraCaps. A 7.2v NiMH pack was the obvious choice given the parameters I wanted to meet for MY application.
NiMH D batteries have a very flat discharge curve, so you won't get any peakiness until they're pretty much flat. Also, 1.20v is their nominal voltage, just before the elbow/drop. With 6 in series, you're probably closer to 8.4v after they've been freshly charged.
That Tensai brand is fairly adept and at 8000mAh and with only a 250mA draw, you get a lot of music before you need to recharge.
Chris
...sometimes simple is better and the NiMH solution is simple, inexpensive, and suits my application requirements more closely than other battery types.
Edits: 10/04/16
I'll have to try this Abe. Thanks for sharing.
Aren't you guys worried about fire risk? My understanding is that LiFepo4 has little or no such risk. I used LiFeSo4 batteries for 3 years or so with no problem. I am now using a Vinnie Rossi DHT with microRendu output voltage port so I am officially out of battery usage now.
Edits: 10/09/16
LiFePo4 is generally considered the safest of the three common li-ion chemistries, but if you use a quality CC/CV charging algorithm and don't run them dry, you're fine there.
Chris
Fire? You're probably thinking of Lithium-Ion (Li) or Lithium-Ion Polymer (LiPo or Li-Poly) batteries. I'm using NiMH batteries.
The material within NiMH batteries is inherently non-flammable which is not the case for any Lithium types including the Lithium Iron Phosphate family (LiFePO4, LiFeSO4). Lithium Iron Phosphate (LiFe) types are considered to be much safer than Li-ion and Li-Poly but they still have shipping restrictions for good reason.
However, "NiMH batteries are considered to be "Dry cell" batteries and are unregulated for purposes of transportation by the U.S. Department of Transportation (DOT), International Civil Aviation Administration (ICAO), International Air Transport Association (IATA) and International Maritime Dangerous Goods Regulations (IMDG)." Not so for batteries in the Lithium family.
ANY battery can be a fire hazard if improperly handled, charged or discharged.
Any fully charged battery can only dissipate overcharge energy as heat. My 10Ah NiMH battery has a thermal cutoff circuit but at the 1-Amp charge current that I use on it, the battery barely gets warm during charge. It's spec'd for up to a 3-Amp charge current. I charge at 1/3 of that rating. Additionally, the smart charger shuts off once the battery is fully charged.
At a discharge current of only 0.25-Amps for my microRendu & DAC, the 10Ah NiMH battery doesn't get warm at all. The battery is rated for up to 30-Amps of discharge current. I am 120x below the maximum current spec.
I am not worried at all.
I use the Sonore Signature Power Supply for my microRendu. But, I will probably check out Abe's solution since it doesn't cost very much.
If we stop hearing from Abe, I guess you'll have your answer :-)
Not that you need the exact same setup but here is what I have:
7.2v 10Ah battery with standard male Tayama terminal at end of cord:
http://www.batteryspace.com/customized72v10ahnimhbatterypack3x2rconfigurationtrail-techfemaleplug.aspx
Charger with female 5.5mm x 2.1mm barrel connector at end of cord:
http://www.batteryspace.com/multi-currentsmartcharger1-2aforany48v-108vnimhnicdbatterypacks-ullisted.aspx
A a couple standard Tayama female to 5.5mm x 2.1mm barrel adapter cables:
http://www.batteryspace.com/Connector/Adaptor-From-5.5mm-x-2.1mm-Barrel-Male-to-Standard-Tamiya-Female.aspx
And here's the other battery that I have. It's a smaller 5Ah model:
http://www.batteryspace.com/nimhbatterypack72v5000mah6xc36whfor6vportabledevices.aspx
I paid online via their website and PayPal.
.
Since I moved the Touch to the garage, I sold the linear I was previously using and run a 12Ah Jockery battery (cell phone charger) instead.
I recharge it using a standard iPhone charger every couple of days. It has an illuminated three element meter. When it gets down to one bar, time for the recharger!
I also have two 2.2Ah units that I got as freebies at conferences. They work fine for a short time as well.
Thanks E-Stat & Abe.
The USB phone battery jockeys are not NiMH.. Correct? And the NiMH battery packs are 4.8, 6.0, 7.2V.. Correct? Wondering if anyone has tried powering a RPi with the 4.8V NiMH pack?
Those 5v USB battery packs for charging phones and other gadgets use batteries in the Li-Ion family. They also typically use a 'boost converter' chip, essentially a DC-to-DC switching power supply to regulate the output to 5vdc. This means you are not getting "ultra-pure" DC power directly off the Li-Ion battery but through the switcher. The output is no longer as 'clean' as what the battery cells may provide but dependent on the DC-to-DC switching chip and filtering.This may or may not be important to you. An RPi doesn't necessarily require ultra clean DC power.
The nominal voltage of a NiMH cell is 1.2v so four of them in series in a battery pack will provide ~4.8v. However, the voltage is typically a little higher by a good 5% or more so the 4.8v battery will work for devices that require 5v.
For example, my 10Ah 7.2v NiMH battery pack showed about 8.2v right off the charger. That's 14% greater than 'nominal'. It measured 7.6v after powering a 0.25A (250mA) load for 18 hours. That's still 5.5% greater than the 'nominal' 7.2v.
If you apply the percentages to a 4.8v NiMH battery pack, it should be within range for powering a device that requires 5vdc.
Edits: 10/01/16 10/01/16
I see from your source that an equivalent 5V NiMH battery pack would run about $67 + charger.
If you buy a battery from them, you have to be careful to choose the right connector type for the battery and/or an adapter cable for your device as well as the charger.
I had to DIY a USB to barrel one for the Jackery to fit the Touch.
Why would an RPi not require clean power compared to other devices?
Cut-Throat
A PI as any other computer appreciates rock solid and clean supplies.The PI onboard supply is all but a high quality PS/regulator implementation.
Pair that with a mediocre external supply and you might see weird things happen. Especially if you start with things like overclocking, heavy DSP
work asf.
Beside that the PI 5V rail is offered to external devices such as HAT DACs or your HifiBerry (I've been running a HB DAC+ Pro of that 5V rail for some time).
In such as case the quality of 5V would have a direct impact on your DAC performance.
The same applies to USB BUS powered audio devices.IMO the quality of the PI supply does matter in many cases.
Edits: 10/04/16
I have been recently using RPi with MoOde Audio; quite an improvement over Volumio or piCore, IMO. I do use a choke LPS, BTW, and don't think "clean power" is the transformative thing for the Pi; improvement, yes, but still a way to go.. Through the Pi's USB out, the highs are awful i.e. fatiguing. I am playing wait-and-see with the Pi HAT boards; perhaps something will come along to make it a better listen. Certainly seems to be some interest and activity out there now.
I am using the Rpi Model 3 B...... I have a Hifi Berry Digi+ with Coax out. I don't use the USB. Also a Linear P.S. - I also run PiCoreplayer 3.02 -- I prefer LMS as I am using it throughout my network and House.Cut-Throat
Edits: 10/01/16
Did you get the transformer upgrade?
Yes, I actually have one of each! One I use with Optical (Non-Transformer) and the other with Coax (Transformer)
Cut-Throat
Give this a try it will give a further level of improvement.
Thanks Abe. Very good info.
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