Battery Dilemma

[Hippogriff]

I have created a circuit embedded inside a top hat, for parties, that controls three sets of RGB LED strips around the outside with various effects - each having a 5cm (3 LED) piece connected to a 15cm (9 LED) then finally connected to a final 5 cm (3 LED) piece... so, either 15 LEDs (or 45) for each of the three rows / lines that I have.

During testing, using my benchtop power supply, the draw of the circuit varies between 0 and about 0.5 amps (obviously the LEDs are doing different things all the time) and I removed full white as one of the colour choices just to reduce the overall requirements.

Powering this circuit by battery is a must, obviously, and I have been experimenting with two approaches - the first and most preferred is using a very small 23A 12v battery, the second is using a larger PP3 9v battery.

The circuit contains an ADP667 outputting 5v for the PIC microcontroller so I can happily change between both types of batteries without worrying about that too much.

My experiments with both have shown that neither is perfect - with the 23A I get bright LEDs but its mAh rating is 33 (although I'm not sure at what circuit requirements) so they do not last that long. With the PP3 I get less bright LEDs, as it is only a 9v battery, but the capacity is said to be around 565mAh - again, though, I'm not sure at what kind of circuit rating. I am not a fan of the less bright LEDs as part of the time that I will use the hat will be during the day.

Is there something out there that exists that is a 12v battery but with more capabilities than the 23A type while avoiding an extreme size increase... up to PP3 size or slightly larger would be perfect?

I've been thinking that connecting two of the 23As in parallel might well help, but I'm just curious if there's another battery I'm not aware of.

When a battery's specification says that it offers 33mAh capacity or 565mAh is there a standard expectation of what the connected circuit will be drawing?

 

[Nigel Goodwin]

Use AA's or even AAA's, PP3 are VERY low capacity, and the 23A a great deal worse.

 

[Hippogriff]

Thanks.

I realise there are always trade-offs, but I already have a 3 x AA battery pack that gives around 4.5v and I would need an 8 x AA battery pack in the top of a hat to produce 12v (or two of these 3 x AA packs (which I do have) to produce 9v via 6 of them. Sure, it may last a long time, but I think the benefit would be outweighed by the inconvenience and I'd pefer to carry a few spares with me and have a simpler, lighter, hat. 6 x AAs might well last a lot longer than 1 x PP3 but the PP3 is better in this instance I reckon. The weight of 8 x AAs would make the hat fall off my head, I'm sure.

However, trying to think laterally, what do you think having 2 x 2CR5s connected in series would be like? 2CR5 is rated at 1,500mAh. I'm not sure there is an easy way to use it though, as it doesn't appear to have terminals like other batteries. Never seen one in the flesh, but maybe two of those could work inside a hat? Just trying to think of any and all options...

 

[audioguru]

You should look at the spec's for the batteries on the website of a battery manufacturer.
Energizer's A23 12V alkaline battery can supply only 0.6mA for its rated capacity of 55mAh. its capacity is rated when its voltage has dropped to 6V (half). Its capacity is about 30mAh with a load of 10mA. It might be a few minutes if it can drive your LEDs.

Their little 9V alkaline battery (PP3) has a capacity of 625mAh at 25mA or 350mAh at a load of 500mA when its voltage has dropped to 4.8V (almost half).

They have a nice lithium 9V battery (PP3 size) that has its voltage stay above 8V for a long time with any load current up to 1A. But it is costly.

 

[Hippogriff]

Thanks for this.

I have been doing some testing / observing - to check what my circuit's draw really is. So, when connected to my bench PSU, I see the following maximum draw amounts when it cycles through its randomised effects...

With the PSU set to 12v...
Max. of 0.12 amps when doing the red-only Knight Rider effect
Max. of 0.29 amps when doing the multi-colour flashing effect
Max. of 0.43 amps when doing the multi-colour solid colour change effect

With the PSU set to 9v...
Max. of 0.06 amps when doing the red-only Knight Rider effect
Max. of 0.11 amps when doing the multi-colour flashing effect
Max. of 0.15 amps when doing the multi-colour solid colour change effect

Obviously this is with the circuit as-is, doing random effects, if I wanted to test a true maximum I would code the PIC so that it set all LEDs to fully on and then compare (which I might do). However, it's starting to look like I need to accept the PP3 and sacrifice full brightness to me...

I think I can see a datasheet for Energizer's PP3 9v 522 - that shows the 625mAh at 25mA. Am I correct in thinking you're referring to the best choice as being the LA522? That looks to be about £8 on eBay.

I was also thinking - instead of having a wide range of different colours (some like 255,215,0 for gold or 173,255,47 for GreenYellow) would I help myself if I limited my colour selection to those that are either 255 or 0 - i.e. red, green, blue, magenta, cyan and yellow? That way, I'd still get some nice colours for my effects, but I'd not be lighting as many LEDs when I'm randomly selecting colours.

 

[audioguru]

You can change resistor values to make the LEDs brighter with the 9V battery. But then the battery will not last long and you might even see it dying which will make the LEDs slowly dim.

 

[Hippogriff]

Nah, it's an RGB LED strip, all resistors are built-in.

 

[alec_t]

I think most people at a party won't be able to differentiate many colours......especially after a few drinks. So if you can have fewer LEDs on at a time that will conserve power.

 

[Blueteeth]

why not a couple of rechargable AA's with a boost converter? You can buy pre-made modules pretty cheaply with efficiencies > 90%. They'll give you longer life than the PP3, roughly the same size, and work down to a lower nbattery voltage so you squeeze more power out of them.

 

[Hippogriff]

I don't think it's something I can really consider as my PCB is already created and embedded in the hat - I'm taking a LED circuit I usually power from the mains - I'm really at the point now where I'm just choosing the best battery for brightness and longevity now, although there's obviously going to be a compromise - brightness, longevity or a heavy head.

I would like to understand how a boost converter might be used in this kind of thing, to get 5v for the PIC and 12v for the LEDs, as I've never tried one before. At the moment I'm providing either 12v or 9v and stepping down to 5v for the PIC.

 

[Hippogriff]

You can buy pre-made modules pretty cheaply with efficiencies > 90%.

Do you know of any examples?

 

[Blueteeth]

You could boost 2.4-3.6V from AA's (NiMH rechargable) to 9-12V, then a small 5V linear reg for the PIC. I mean its more hassle, more money (to buy a module) but its perhaps another solution to think about Or of course, battery voltage to a stable 5V, then yet another boost to 12V - but two converters in series, lowers efficiency and is even more hassle.

Something like this, which are all over ebay:
**broken link removed**

Granted, they are cheaply made, so their rated efficiency is usually over stated. But they'll work, and you may be able to up the output voltage so it can run from 2-4V, and output 12V for your LED's, then a simple 7805 to the PIC.

Of course, the DIY approach will give you greater felexibility, but more hassle in terms of making another 'piggyback' PCB. You mentioned your peak current requirement for the 12V line was 0.43A. Thats quite a bit of power - over 5W, a PP3 9V would definately struggle with that, and whilst AA's can kick that out, getting a boost converter to handle that much power from a low voltage source is tricky. With 9V your peak current was 0.19A ? 1.7W thats a lot lower.

If the higher voltage is only for the LED strings (in series) then it *may* be more prudent to buy premade LED modules, designed to work from 5V DC, that have on board boost converters specifically for the LED strings. It'll take in 5V and some form of PWM control (from your PIC) and may be more efficient. That way you only have to provide 5V to the entire system.

Note: I do tend to grossly over engineer things sometimes. Powering things with batteries brings several restrictions to the table, power consuption, battery life, battery voltage (which drops as the battery discharges), size, weight.... cost. The reason AA's are mentioned is that for their size/weight, they have much greater power density than PP3's - which can't provide much current, and their voltage drops to ~7V rather quickly. And rechargable batteries can kick out virtually their entire capacity quite quickly, providing several amps over as little as 30 minutes, because of lower internal resistance.

How small must this battery be? In the modern age of mobile phones, mp3 players etc.. one can usually find batteries used for products as replacements all over the web, ebay, amazon etc.. whilst they wo'nt be 'standard' like AA, or PP3, they may suit your purpose if they are rechargable.

 

[Hippogriff]

So... my thoughts...

I already have a 3 x AA holder which I've tested with the voltmeter and it produces 4.5v, as you'd expect. Those 3 x AAs would easily fit into the hat. It'd be a lot heavier than the single 23A or the single PP3 - but it would fit and it would work - if I could then get 12v to my existing circuit.

Obviously, it then only provides 4.5v, so what I was thinking was... could I use the 3 x AAs to provide power to a separate, isolated, boost converter, which would output 12v that could then go into the existing circuit - 12v going to the LEDs and 5v going to the PIC via the ADP667?

So - question 1 - is there a boost converter module that will allow me to take 3 x AAs and provide 12v output?

I can't help think that I'm getting something for free with a boost converter.

Anyway, to help visuale things, here is my circuit embedded inside the top hat (with no LEDs connected to it when I took the image) and the 23A battery in place. Granted, I do have some space to play with, however, I don't have enough (I reckon) for 8 x AAs providing the 12v that I'd ideally want... nor do I have appropriate battery holders - but I'm not against buying one.

**broken link removed**

At the end of the day, a single 9v PP3 might still be the way to go - I'll just keep a couple of spares in the pockets of my combats. I don't want my hat to be so heavy it just keeps falling off my head.

 

[Hippogriff]

Hmmm, is it this that I could work with?

**broken link removed**

This looks a bit better quality...

https://www.ebay.co.uk/itm/DC-DC-Co...ultDomain_0&hash=item19caa3914b#ht_1699wt_954

Delivery times could be the killer.

 

[Blueteeth]

Yes, those sorts of boost converters will work well. However! (theres always a but) you metioned feeling like you're getting something for nothing, well, there are alway catches Firstly, that boost converter in the link has a minimum input voltage of 3.7V. Your AA's will happily provide more than that, unless compeltely drained (unless they are rechargable, which are 1.2V nominal, where-as alkelines are 1.5V nominal). That minimum voltage I suspect is when the boost converter will be at its lowest efficiency, I'm guessing here but 70% sounds like a worst case fro modern boost converters. So should you need to provide 5W of power, at 12V, with 70% efficiency, the batteries must provide 5/0.7 = 7.15W of power - wasting over 2W in the conversion.

So the price you pay for being able to run somethign at a lower voltage is efficiency :/ Loss of power results in heat, which *can* mean heatsinks (depending on power requirements) which increase size and cost etc.. everything is a trade-off with power circuits.

All that said, your peak power at 12V was less than 0.5A, which isn't too high. Also, powering from 3xAA's, isntead of two begins the minimum voltage up above 3V - below 3V and it gets more expensive using boost converters for 12V, so the requirements here aren't that strict, making it far more likely to find a relatively cheap 'off-the-shelf' converter such as the one you linked on ebay.

Now, getting 5V from 12V is trivial, using a linear regulator, but they are wasteful. If you measure the current drwa from your PIC, it'll probably be quite low <10mA. The regulator would draw this 10mA, plus a small amoutn of current for itself, at 12V. Considering the lower power, it doesn't seem very wasteful to me although some could argue it seems silly boosting from 4V to 12V, then using a wasteful linear regulator to get 5V from it. Whilst its not that efficient, its convenient, cheap, and easier than using two boost converters one for 5V and one for 12V.

Depending on how the PIC is used, and what model it is, some PIC's work down to 2.0V. Of course if whatever its interfacing with requires more than that, then you can't run it at a lower voltage, but you may be able to run the PIC directly off batteries, leaving the boost converter purely for the LED's (which won't care much about switching noise).

 

[Blueteeth]

Just checked the datasheet for the chip they use on that converter, its peak current is 5A, which leads me to believe its only '90% efficient' when the input current is >1A. At a low input voltage, and as you're running it at lower power (you're numbers implied a maximum of 5W through put) it might be over kill, and not as efficient as other methods - although it IS cheap and convenient

 

[Hippogriff]

It's a 16F1823 and I already have the 5v from the 12v via the ADP667 so that's all cool. So, I see what you're saying, if I have around 4.5v from my 3 x AAs then why would I convert up and then back down to 5v via the ADP667 (as, surely, the PIC will run with 4.5v). I understand that, but I already have the PCB done and dusted (and, as I say, it was designed to run from a 12v PSU) so I could say I'm taking the modular approach.

There are so many of these converters on eBay (but, seemingly, nowhere else that I can trust and get something quicker - like a shop or an online store that's not in China and suffers from huge delivery times) and it's a bit of a minefield. However, this one looks good as well - **broken link removed** - yes, I've noted the output current at 0.3 amps, but I figured I might even get rid of the solid colour change effect in my hat and stick with Knight Rider, colour beat and colour flasher - as they all have colours that are on and then off - possibly saving some power.

 

[Hippogriff]

Very interesting...

https://www.dimensionengineering.com/AnyVoltMicro.htm

 

[Blueteeth]

I get ya, so the board is designed to take a 12V supply and uses that to supply 5V for the PIC. And you want to power this with batteries. Yeah, I've been plugging the 'use a boost converter module!' thing because it would mean just another PCB between your battery pack, and your PCB. No mods to the PCB itself, it just effectively turns 3xAA's into a 12V battery - albeit with losses = lower battery life.

That particular module looks like its a boost converter, with a 'charge pump' added to create a negative voltage - but you can just ignore that, if not used it sohuldn't take up any extra power, and with an 'idle' current draw of 8mA, looks like quite a nice converter! The pkea output of 0.3A I suspect is when its output voltage is 24V, I'm pretty sure you'll easily get 0.5A+ out of it, at good efficiency, when boosting 3 x AA's to 12V. These chinese ebay sites provide very cheap converters, with 'ok' PCB construction (they're rarely professional and pretty) and they DO work, but they don't provide much inthe way of dynamic specs, and as you said, shipping times are crippling. But..... for the money? I've ordered several of these things, and they do the job just fine, especially for the price.

I did design a discrete boost converter (transistors, diodes, resistors and caps..) that steps up 3-5V to 12V, but its from scratch, and its efficiency isn't great. Much easier to buy a premade module I guess. I'll keep an eye out for ones available in the UK. Some places like 'coolcomponents.co.uk' sell Sparkfun modules, they might have something..

 

[Hippogriff]

So, I found this AnyVolt Micro at **broken link removed** and - although it's quite expensive - it does look very cool and does carry some protection features, just in case. I've read the PDF and there are some limitations - I did find it odd it didn't seem to have a table for 4.5v input (but 3.3v and 5v) but I guess that's just down to them putting in the most widely used or something.

I'm seriously tempted. Just going to continue my research for a little bit.