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In Reply to: RE: NiMH battery packs on my microRendu streamer - pics posted by soundchekk on October 04, 2016 at 04:07:19
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 10/04/16Follow Ups:
"...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
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