Battery choice advise for College project needed

Question

I’m making a project for college and am having trouble incorporating the huge size of the battery compartment, are there any alternatives I could use to 3x AA power (4.5 volts)? I’ve looked at button cell equivalents but I’m not well versed in substituting voltages and milliamps. Thanks in advance

dougw · Answer

You can get 3.9 - 4.2 V from a small rectangular Lithium polymer battery. There are also Lithium "button" cells available, but usually only 3V. What are you running from these batteries? - very few devices need precisely 4.5 V.

dougw · Answer

When they say don't use NiCad or NiMH it usually means their voltage is too low, so your device probably works better above 4 V. I would expect 5 V is okay as well given the tolerance on alkaline batteries.

beacon_dave · Answer

Sounds about right. I have found that the mAh rating is usually based upon the battery inside (e.g. 3.7v) and not on the USB 5v output. I was looking for one closer to 3,500mAh in this case to match the alkaline AA capacity but they tend to jump up in size dramatically.

However as you've mentioned previously, they do tend to hold their output voltage better than the drop off of a battery which may help in certain applications.

beacon_dave · Answer

Perhaps you could give some more information on the requirements ? 3x AAA 3x AAAA 3x N are all smaller but they will trade size for capacity. The N type is about half the size of the AA but about one third the capacity. 608306 ENERGIZER, Battery, Single Cell, 1.5 V, N, Alkaline, 900 mAh, Raised Positive and Flat Negative, 12 mm | Farnell …

beacon_dave · Answer

A simple test with an ammeter will give you an indication of what current it draws when powered up. The NiCd rechargeable batteries typically only have a voltage rating of 1.2v per cell so would drop your 4.5v down to 3.6v. What sort of reduction in size are you looking for ? Also what sort of capacity do you require ? Do the AA batteries (at around 2700mAh) currently just provide enough duration ? could you make do with less duration in favour of compactness ?

beacon_dave · Answer

1.2v at 2000mAh is significantly less capacity compared to a typical alkaline rated at 1.5v at 2700mAh so not surprising that they appear to drain quite quickly. However you need to look at the data sheets as the performance varies depending upon load, which means you need to check your current draw in normal use. Not sure if anyone is doing a lithium in N type package, however Energizer do a AAA sized one: http://data.energizer.com/pdfs/l92.pdf which is slightly smaller than AA but significantly less performance than their AA version: http://data.energizer.com/pdfs/l91.pdf Farnell is a UK based company, and they have some N type battery holders listed. Not sure if your college has an account with Farnell. If not then their sister company CPC will sell to individuals. http://cpc.farnell.com/pro-power/25vb11d/battery-holder-1xn-solder-tag/dp/BT03697 You could try Maplin, or Mouser or Amazon.co.uk etc... You could also make your own holder using these PCB style terminals: http://cpc.farnell.com/keystone/590/battery-holder-aa-n-1-way/dp/BT04910 which may be advantageous as you could fit the batteries in the spaces you have available around other parts rather than having to make room for a bulky holder. Presumably your college will have access to 3D printing facilities by now allowing you to be very creative with component mounting. With 120mm of height then you could consider stacking 3x N-type vertically in series in one corner of the case and then in parallel with the same again in the opposite corner to increase capacity.

dougw · Answer

The USB power packs jw0752 mentions are available anywhere, even Dollar Stores and are available in a wide variety of sizes.

mcb1 · Answer

I've also seen the "don't use rechargable batteries" because it has no ability to recharge, and the current available from rechargables can cause issues if there is a component failure.

Generally the normal batteries simply discharge.

I was talking with a teacher about Edison Robots ( https://meetedison.com/ ) and he showed me that the battery connections were the weak point.

However he was using rechargable batteries, and when I explained the issues with current and that pupils could stall them, etc, it made sense why they were overloading the connections, and having so many issues.

Mark

jw0752 · Answer

Fresh AA Alkaline batteries will start at about 1.6V which is 4.8 Volts for three. The nice thing about the cell phone rechargers are that they have a small boost DC to DC converter incorporated that keeps the output at 5 volts down to the shut down discharge level of the lithium batteries. Another advantage to lithium is the thin profile of many of the cells. I am not trying to sell this as a solution but it is worth a consideration. John

beacon_dave · Answer

...are there any websites that already have 3d printing designs for battery terminals available to the public... Perhaps try a search for 'battery holder' on Thingiverse https://www.thingiverse.com/

jw0752 · Answer

The empirical tests I have run on similar units indicate that if they claim 2200mAh one can realistically expect about 1500 mAh actual performance. John

jw0752 · Answer

Hi, I have found using a small cell phone recharger module useful for situations like this. You can recharge it with a standard mini USB 5 volt charger and it has an output of a regulated 5 volts. I has more capacity than 3 AA batteries and has a similar volume. John

beacon_dave · Answer

The ammeter goes in series with the load. Sounds like you've placed it directly across the battery and shorted it out.

BBC - KS3 Bitesize Science - Electric current and voltage : Revision, Page 5

PS I spotted some compact USB power banks in Asda at the weekend - might be worth you taking a look at a store near you to see if there is anything that would work.

beacon_dave · Answer

How about this USB power bank for size/price: https://www.maplin.co.uk/p/maplin-2200mah-portable-powerbank-black-n39eq (Note that their stated dimensions appear to be out by a factor of 10, either that or they have very large credit cards...)

bionicle_159 · Answer

I’m running a mini handheld arcade

bionicle_159 · Answer

I’ve got a case size with a height of 12cm and width of 10cm and a base of around 4-5cm, I need to fit a screen in at around 55 degree angle, perhaps I could try and fit the batteries in the lower half (4cm) but that is assuming that the circuit board for the controls do not occupy the area. I’d like to also fit the beeper at the same time so that might need to be placed elsewhere if it conflicts. Since it’s a portable product I’d like to still have a sufficient enough duration of power but would definitely want the physical size benefits, like the N battery provide for example, in a compact product that mine is. I just checked the rechargeable battery i used again and the Ni-Cad battery was actually a Nickel Metal Hydride rated at 2000mAH, as mentioned previously they drained quite quickly but I might need to do another test to be fully sure that it was the electronics that caused the short time of power. Is it easy to acquire the compartments for the batteries you mentioned, I live in the UK but might be able to find such things at a general hardware store if the items are widely available.

bionicle_159 · Answer

Hi, I’m not sure if the device will accept it as it says in the manual not to use rechargable batteries in general, I tried using standard rechargable Ni-Cads to see if there was any reason and they drained pretty quickly within about 2-3 hours. I’m concerned if the battery outputting 5v will cause long-term harm to the device as I’ve had past experience of CD players using the weird 4.5v rating that have overheated after extended use with 5v PSUs

beacon_dave · Answer

The Adafruit Powerboost might be another option:

https://www.adafruit.com/product/1944

https://www.adafruit.com/product/2465

It would allow you to size the battery based on space / capacity requirements, like this 2500mAh one:

https://www.adafruit.com/product/328

Perhaps not the cheapest option however.

luislabmo · Answer

Some manufacturers recommend not to use rechargeable batteries not because is a technical restriction (most of the times), it will be to stop giving false impression to the user that the device in question doesn't work according to the specs (like duration of batteries). You can see this in some flashlights where you can use rechargeable batteries but their brightness/duration won't be the same as when using Alkaline. -my 2 cents-. How about using a USB charger as suggested by others and use an adjustable switching regulator?

Luis

Battery choice advise for College project needed

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