Running Pimeta v1 or v2 on single 9V cell - Page 2

I used to run my pimeta1 and 2 with a single 9v. I had no problems with sound quality and run time got me 'a few days' (at work, not 100% use while at work). I would not get a week from the battery but a partial week. fwiw. (using 8610 style op-amps and regular alkaline 9v batteries).

I might be hard on them, too, if I were aware of a better charger, and didn't know as much as I do about how NiMH batteries actually behave, as opposed to how we'd like them to behave. Batteries are weird.

Yes.

Between "lithium" and "specialty item" it's about what you should expect.

The predecessor to this, the FC-9V4LN. It'll do both NiMH and LiIon, and is what I use for both chemistries.

I don't suppose you have a second meter on hand so you could give battery voltage at the same time?

Also, you haven't yet done the test I'm after yet. Charge the battery, let it sit for at least an hour, run the amp from it for a minute, measure the voltage under that load, then turn the amp off, wait a minute, and measure voltage again. Then you may want to repeat after more hours of use or rest to see how that changes the results. Between those measurements, Ohm's Law, and known-good characteristics for your battery, you should be able to estimate its health.

Forget playing music through the amp: pretend it's a ~60 mA constant current source. Adding a headphone load only confuses matters. If you felt you absolutely had to do that, you'd want to use a sine wave source, not music.

That is indeed worrisome, but not very helpful in telling us what to look at next. You've muddied the waters too much by using a near-random test signal and not giving voltage numbers.

Do you have a scope and a signal generator? Some square wave tests would be in order right now. If you can't do that, then at least an RMAA test? Pay careful attention to the test setup at the bottom of that page. The obvious way to do this test is wrong.

Did I miss seeing high-res pics of both sides of your board?

The red H-65 PIMETA just ran continuously for 4 hours on the Maha, at which point it died within seconds, as happens when NiMHs are truly exhausted. Then I switched to the LiIon, and ran for another 5 hours before I turned the amp off, as I had other things to do.

It *can* be done.

I was a little bored earlier so I grabbed my Pimeta 2 prototype off the shelf in the closet, unplugged the TREAD and plugged in a bran new (right out of the package) CTA 325mAH 9 volt NiHM battery.
I set the Fluke view forms software to log the data for 4 hours from my Fluke 45 and the results were:

The idle current with OPA2132/OPA132 op-amps = 48.73mA.
The peak current draw with the amp playing music into my SR60s = 52.845mA but it should be noted that was at a SPL that would cause severe brain damage. :P

Although the battery completed the "test" I will have to recharge it to get a more accurate assement of the battery runtime with this op-amp combination.

The battery was still running strong @ 49.4mA but like I said, it was taken was right out of the package and any kind of runtime numbers would have been inconclusive.
Will run the test again later today and see what I can get with a fully charged battery.

I am not aware of it being a low self discharge type NiMH battery.

I'm impressed. Alkalines don't cope well with high discharge. It's why a set of AA NiMHs can last longer than a set of AA alkalines in a digital camera, despite the NiMHs having a lower mAh rating. The high surge power used in writing photos to the card and charging the camera's flash beats the alkalines up, making them perform badly.

EDIT: A Duracell 9V alkaline datasheet I have here only characterizes it up to 50 mA. It doesn't give a maximum recommended load. I've seen 0.1 C given for AAs, but the cells are larger. If we could go with that, it would be about 60 mA for your typical alkaline 9V, but I put the practical limit at 30 mA to account for the small cell size in 9V batteries.

EDIT 2: In any case, this is why you're not getting 10 hours, even though 60 mA into 600 mAh says you should.

Maybe. It could be right on the edge of oscillation, too. That's why those square wave tests would be valuable. Also, pics, so we can see if you've left something out that you oughtn't.

That can also explain it.

Anytime you put several rechargeable cells in series and let them sit for a long time, you risk cell reversal. This happens when one cell drops in voltage past 0 V while one of its neighbors still has enough voltage to push energy back through the zeroed cell. That cell then starts showing a negative voltage, and takes on damage as a result.

Best practice is to leave a battery with about 50% charge when not in use, and not leave it on the shelf too long. This is also why you see so many recommendations not to leave a battery in an idled device, since the trickle current it draws will accelerate the onset of cell reversal. At least with the battery out of the device, all you have to contend with is self-discharge.

Typical value for a 9V alkaline.

Re: your question of what current my red PIMETA is drawing, it's about 57 mA. I just repeated the Maha test, and got another 4 hour run from it.

Yea, my Tek 'scope is not working either. It's in the closet now for 5 years!

I've updated the PIMETA v2 docs to distill some of what we've covered here.

Better coverage of how NiMH batteries behave, with pretty graph

Redrawn schematic, human-friendly

The schematic shows the left and right C6L/R in parallel with R4L/R but the parts selection guide suggests they are in parallel with the R6s?

And...I assume that is the same as what's referred to as a "R4 cap" in the "square wave test"?