9V Guitar Battery

[merlyn]

More than anyone ever wanted to know about batteries ...

A 9V battery is a battery. An AA 'battery' is correctly called a cell, and a cell is basically a chemical reaction in a tin. It's the chemistry of the reaction that determines the voltage.

Different chemistries have different nominal voltages. The nominal voltage is somewhere in the middle of the discharge cycle, and is different from the fully charged voltage.

NiMH -- full charge ~1.5V, nominal 1.2V
Li-ion -- full charge 4.2V, nominal 3.7V (slight overestimate, I imagine for marketing purposes)

Inside the square tin of a 9V battery there are several cells wired in series. For Li-ion this is two cells, giving a full charge of 8.4V, and a nominal of 7.4V. For NiMH it could either be seven or eight, giving a nominal of 8.4V, or 9.6V. But at full charge eight NiMH cells give a full charge voltage of nearer 12V, which may blow some equipment to bits, so seven cells is the most common.

The nominal voltage of two Li-ion cells in series is actually 7.4V. This doesn't bother me for a guitar, as alkaline batteries go below that before they're fully discharged. I imagine a 12V Li-ion battery is three cells in series, giving a nominal of 11.1V.

[Albatross]

Please keep sharing, I find it fascinating.

[BillB]

One could have hoped too that the batteries didn't induce noise into the DC supply but they are cheap and not marketed for use in audio devices so are perfectly fit for purpose.
Yes, no argument there but they are cheap and marketed for use in smoke alarms and such like so it doesn't come as a surprise either.

I would kind of like to agree with you, but look at the marketing:



Three audio devices right there!

[Drew Stephenson]

Well, two and a half...
I mean, is an electric guitar really an 'audio' device or a mechanism of torture?

[Folderol]

Well, two and a half...
I mean, is an electric guitar really an 'audio' device or a mechanism of torture?

Ooo! Nasty

[Sam Spoons]

TBF the 'wireless microphone is clearly not, the walkie talkie pictured almost certainly doesn't use PP3s and the electric guitar may do but probably doesn't.

FWIW the ToneDexter is happy (and silent) running off the cheapo 12VDC power bank, but again it is not a cheap bit of kit and, like the LBJ, may well have a tolerance to varying voltages and good filtering of noisy DC supplies.

[BillB]

TBF the 'wireless microphone is clearly not, the walkie talkie pictured almost certainly doesn't use PP3s and the electric guitar may do but probably doesn't.

The fact that they don’t know what to stick a 9v battery into doesn’t change their willingness to market the product as being suitable for audio devices - all two-and-a-half of them.

[lead ears]

A 9V battery is a battery.

Clearly you haven't figured out that this in NOT A BATTERY.
It's a single cell delivering about 4V that goes to a DC/DC switching converter which regulates the voltage to about 9V.
It's the same structure as the modern "car boosters" that use a high-capacity low voltage battery (so it could be charge from a standard 5V USB charger) and steps up teh voltage to produce the 14V needed to boost the discharged car bbattery.

[merlyn]

I had figured that out mate.

[Sam Spoons]

The first two search results for "Li-Ion PP3 construction" I've found both have two cells, in one of them the cells are wired in parallel, in the other they are in series.

I'm guessing my old 8.4V PP3's also have two cells but with a less sophisticated BMS on board with no DC-DC boost convertor.

https://www.youtube.com/watch?v=dR_RusM99no

https://www.dr-lex.be/hardware/conrad9v.html

[Sam Spoons]

TBF the 'wireless microphone is clearly not, the walkie talkie pictured almost certainly doesn't use PP3s and the electric guitar may do but probably doesn't.

The fact that they don’t know what to stick a 9v battery into doesn’t change their willingness to market the product as being suitable for audio devices - all two-and-a-half of them.

True enough. I once bought a guitar pedal PSU from a well known guitar shop which whistled and buzzed like a B'Stard. It was a long time ago and fortunately for them I can't remember which shop it was as they were slightly reluctant to refund on it and, IIRC, refused to cover the return postage

[merlyn]

Wiring two cells in series gives a higher voltage. Wiring two cells in parallel gives more capacity.

With series wiring, the capacity of the battery is the capacity of one cell, as all cells are being drained at the same time. This is why NiMH 9V batteries have a low capacity, as the individual cells have to be tiny to fit seven into the available space.

It's better to have a bigger cell than two wired in parallel, which is why we get chunky D cells, rather than using loads of AAs in parallel.

[Sam Spoons]

Since the capacity of these (and most batteries) is measured in mAh the actual energy it represents is related to the output voltage, mWh (which is voltage agnostic) is a much more useful unit. Two 1 Ah 12V batteries can supply 2 Ah at 12V or 1 Ah at 24V depending on whether you wire them in series or parallel but they store 24 Wh of energy. The same applies to these 9V PP3 batteries, once the DC-DC conversion* has taken place it doesn't matter how the cells are wired.

* Assuming the cells are identical.

[merlyn]

You use Watt hours then Sam. It's a bigger number, so that's good. The voltage drops as a (non-regulated) battery discharges, so there are obviously simplifying assumptions made to calculate one figure.

[Sam Spoons]

There's a reason you don't pay for your domestic electricity by the amp-hours you consume . It's useful unit for comparing batteries of similar voltage but becomes pretty useless (or deliberately misleading) when used to describe something like these PP3 batteries (is it the capacity of the individual cells at 3.7V or the battery at 9V?). The ones I have claim 1200mAh which seems a pretty optimistic for such a small 9V battery but if that is the combined capacity of the two cells at 3.7V then it equates to around 500mAh at 9V which seems a bit more believable.

[merlyn]

If the voltage of the mains supply is fixed, then effectively you are paying for Amp hours. It's just that kWh is a consumer friendly unit.

We may have run into (and I'm not wanting to offend anyone) Chinese maths. The Ah could be on the 3.7V side. Oops again.

But if you find specs that give Watt hours and Amp hours for lithium batteries I think you'll find that the Watt hours are simply the Amp hours multiplied by 3.7, the nominal voltage. 3.6 is more realistic, but 3.7 makes the Watt hours look better.

[Sam Spoons]

Yes, that's what I thought, I don't know if my leccy meter measures amps or watts if it's amps and the voltage is on the low side I'll be paying for more kWh than I'm getting unless they correct for it back at base...

I first came across 'Chinese Creative Maths' (at least as related to Li-Ion batteries) when I was buying USB battery packs and realised the Ah they were claiming seemed improbable, and particularly useless as the pack could output 12VDC, mains 230VAC and 5VDC out of the USB port.

[merlyn]

On the marketing front Thomann are selling USB rechargeable batteries :

https://www.thomann.de/gb/ansmann_9v_akku_usb_c.htm

No warning that they may not be compatible with all audio equipment.

What I would like to know, if anyone has any ideas, is why one of my guitars whines and one doesn't.

[Wonks]

If the voltage of the mains supply is fixed, then effectively you are paying for Amp hours. It's just that kWh is a consumer friendly unit.

It’s also a far more accurate unit. The electric meter also measures the voltage to calculate kWh. Given that the supplied mains voltage can be 230v -6/+10%, just measuring current would give very inaccurate kWh readings.

[merlyn]

Let's put it this way -- if the current draw into your house is zero, that's costing you zero. kWh measures energy, the scientific unit for which is Joules. Not that that would mean a lot to most folks. It could be done in calories, which folks might have more of a handle on.

[tea for two]

What I would like to know, if anyone has any ideas, is why one of my guitars whines and one doesn't.

That's because one of your Guitar's gently weeps.

I shall get my coat

[awjoe]

I turn my back on this thread for a couple of days and my decision to go rechargeable has been changed for me. It pays to move slowly, obviously. (Procrastination. )

[Sam Spoons]

In my case it was actually buying a couple of those USB rechargeable PP3s and trying them in some if my gear that resulted in my discovering that my B-Band pickup equipped Emerald X7 does not like them but they are fine in my Boss RC3 Looper. Will continue to experiment ('cos it's fun innit... ).

[merlyn]

I started using USB rechargeable batteries with my multiac jazz in October 2022. I've gigged with them every week since, so I may have broken even compared to buying alkaline batteries. What's been positive about it is that rechargeable batteries have advantages and I wouldn't now go back to alkaline batteries.

What can't happen is a battery running out in the middle of a gig. How do I prevent that? Well, I could change the battery before every gig. Incredibly wasteful. The RMC preamps in my Godins do give a long battery life (i.e. they are low current) and a hundred three hour gigs is more like it.

Folderol suggested above that a performer checks their gear before a gig. It's a good idea, but even if they do, that doesn't guarantee what's going to happen to the battery an hour into the gig. Charging batteries regularly means that they are not going to run out in the middle of a gig. For forgetful types, there is less concern about leaving the guitar plugged in.

So I've gone with unregulated Li-ion batteries. One reason that I tried USB rechargeable 9V batteries was that I didn't want another feckin' charger. I've got enough of them. I bought this set of four batteries:

https://www.ebay.co.uk/itm/194907425727

It comes with its own charger, but that's better than a sawtooth wave on the battery voltage. At full charge they're reading 8.64V and they pass the oscilloscope test:



The idea was floated earlier that a higher battery voltage gives more headroom. That's like saying there's more headroom in the UK than in the US because the UK uses 240V and the US uses 110V. It's the supply rails of the audio equipment that determine the headroom e.g. +/- 17V in a mixing desk. Playing the multiac jazz with a Li-ion battery into my oscillloscope I got this:



The peak-to-peak voltage is 1.02V. OK, so I could have played harder, let's say 1.5V peak-to-peak. OK, let's round it up to 2V, which allows for using a half-brick as a plectrum. Considering that this battery will be dead at 6V, the battery voltage is not a factor.

[Sam Spoons]

Thanks for doing that test merlin, that's good to know.