least dangerous batteries for kids

Thread Starter

JunkieNL

Joined Mar 19, 2020
29
When kids are learning to make electronic circuits, short circuits are bound to happen. Especially if you have a class full of them. It's a statistical fact. I would like to connect batteries to a breadboard which, when a short circuit happens, don't blow up in their faces. Which batteries would be best suited for such a purpose? I need between 4,5 to 9 volts, so a pack of batteries in series could be considered as well.

I have seen 4,5V LR12 batteries being used for teaching purposes, but I have also heard stories about the (plastic) enclosure starting to melt when shorted. I also don’t like these because the crocodile clips that are often used to connect to the batteries can easily bridge the gap between the terminals.

I tried to decide on a battery by looking at datasheets alone, but that didn’t get me anywhere. A high internal resistance would be favourable, but the battery should also have a relatively high tolerance of heat (to a certain degree). They just don’t state information like that in the datasheet. I was hoping some of you might have some practical experience to help me out.

Batteries_comparison.jpeg
 

MrSoftware

Joined Oct 29, 2013
1,914
I don't have any statistical data to back this up, but plain old alkaline batteries seem to be relatively safe. I don't know of any stores of those catching fire or exploding. You can easily test by buying a handful, shorting them and watch what happens as they drain while shorted. I would avoid lithium, those are well known to burn and occasionally explode. You can also add safety by inserting a resistor or other current limiter close to the battery.
 

Thread Starter

JunkieNL

Joined Mar 19, 2020
29
I don't have any statistical data to back this up, but plain old alkaline batteries seem to be relatively safe. I don't know of any stores of those catching fire or exploding. You can easily test by buying a handful, shorting them and watch what happens as they drain while shorted. I would avoid lithium, those are well known to burn and occasionally explode. You can also add safety by inserting a resistor or other current limiter close to the battery.
Try and see what happens is actually a good idea. I will try tomorrow. A good experiment has never hurt anyone. Has it? :)

I would welcome a current limiter, but it would have to be practically invisible so that it doesn't confuse the students. A resistor in series is out of the question, because the voltage would drop too much under load. I might get away with soldering a glass fuse holder in series.
 

jpanhalt

Joined Jan 18, 2008
10,261
I would also suggest the classic 9V alkaline battery. Hard to install backwards. With the others, you may need 2 to 4 in series.
 

nsaspook

Joined Aug 27, 2009
7,595
I wonder if they are safer than Alkaline 9V batteries. If it is about the same, I would rather have longer lasting Alkaline.
Carbon-zinc 9 volt Safer from the stand-point of energy (higher internal resistance) delivered from a short and the electrolyte chemistry. Manganese along with an alkaline electrolyte of potassium hydroxide is pretty corrosive.
 

Ian0

Joined Aug 7, 2020
507
Avoid Lithium, NiCd, NiMH and Lead-acid due to the very high current capabilities, and the possibility of fire.
Can't beat a gold old Zinc-Carbon PP3. Seriously limited output current and a convenient voltage for most experiments.
 

Irving

Joined Jan 30, 2016
1,019
I think you need to say something about the experiments you plan to do... but I think you're worrying too much and overthinking the problem.

I teach a 10 week, 3 hours/week, basic electronics & coding tutorial to 11 - 16y olds which covers everything from a simple LED & switch through to Arduino programming a robot car. For the most part we use PP3 alkaline batteries, though for a couple of things we use a 12v, 2A PSU. The PP3 batteries are held in a battery case with an on-off switch and DC plug for the breadboard... its more reliable than simply connecting/disconnecting the 'plug-top' PP3 connector which caused hours of wasted time with broken connections and loose connectors.

I've never had a problem, not lost a pupil yet or even seen a melted wire though they try hard to bugger things up! Accidentally digging holes in each other with a screwdriver was more of an issue.

Forget zinc-carbon, they have such a high internal resistance that anything involving a sensible motor simply doesn't work and they run out of juice long before they've finished experimenting and you'll spend a fortune on batteries.

Have you actually tried shorting an alkaline PP3? Nothing much happens... its output current is limited to around 800mA - its only got the equivalent of 6 x AAAA cells inside. And with a capacity of around 4Wh, it'll just about move the robot car we build for maybe an hour or so before its dead.
 

Bernard

Joined Aug 7, 2008
5,656
If I were that concerned about batteries for experimental use, I would put 1- 4 cell, & 1-3 cell AA battery boxes, fused, & placed within a locked box. All connections brought out with binding posts. Use NiMH AA batteries. About 5V, 4V, & in series - 9 V.
 

dl324

Joined Mar 30, 2015
11,564
I wonder if they are safer than Alkaline 9V batteries. If it is about the same, I would rather have longer lasting Alkaline.
This battery will be the safest. It's a high tech 9V battery that has a boost regulator in it and it will turn the battery off if it's shorted. You have to connect it to a USB charger to reset.

https://www.ebay.com/itm/USB-Rechargeable-9V-800mAh-Lipo-Battery-For-RC-Helicopter-Microphone-New/183604216958?hash=item2abfaa047e:g:PTsAAOSwLSZcIpRZ:rk:6:pf:0

Short protection described at around 7:20
 

Ian0

Joined Aug 7, 2020
507
It interesting to see how things have changed. My school physics lab had a set of NiFe cells, enough for everyone in the class to have four or five to make a 6V supply. They must have been about 10Ah judging by the size, and they spilled potassium hydroxide solution of tipped over, and could supply enough current to melt the insulation on a test lead.
A good NiFe cell is capable of being recharged thousands of times and might last 50 years. Interesting also to note the attitude to investing money up front to get a solution that would cost less in the long term.
 

MrSoftware

Joined Oct 29, 2013
1,914
Try and see what happens is actually a good idea. I will try tomorrow. A good experiment has never hurt anyone. Has it? :)

I would welcome a current limiter, but it would have to be practically invisible so that it doesn't confuse the students. A resistor in series is out of the question, because the voltage would drop too much under load. I might get away with soldering a glass fuse holder in series.
Note that any fuse small enough to blow while connected to a 9v or D, AA, AAA battery will have a relatively high resistance itself. The idea above for PTC is not bad, it's basically a self-resetting circuit breaker. Also series resistors are used frequently, if you need a lot of current just use a smaller value resistor, though my guess is the internal resistance of the battery is already going to be high enough to prevent any catastrophic failure.
 

Thread Starter

JunkieNL

Joined Mar 19, 2020
29
I think you need to say something about the experiments you plan to do... but I think you're worrying too much and overthinking the problem.

I teach a 10 week, 3 hours/week, basic electronics & coding tutorial to 11 - 16y olds which covers everything from a simple LED & switch through to Arduino programming a robot car. For the most part we use PP3 alkaline batteries, though for a couple of things we use a 12v, 2A PSU. The PP3 batteries are held in a battery case with an on-off switch and DC plug for the breadboard... its more reliable than simply connecting/disconnecting the 'plug-top' PP3 connector which caused hours of wasted time with broken connections and loose connectors.

I've never had a problem, not lost a pupil yet or even seen a melted wire though they try hard to bugger things up! Accidentally digging holes in each other with a screwdriver was more of an issue.

Forget zinc-carbon, they have such a high internal resistance that anything involving a sensible motor simply doesn't work and they run out of juice long before they've finished experimenting and you'll spend a fortune on batteries.

Have you actually tried shorting an alkaline PP3? Nothing much happens... its output current is limited to around 800mA - its only got the equivalent of 6 x AAAA cells inside. And with a capacity of around 4Wh, it'll just about move the robot car we build for maybe an hour or so before its dead.
I have no plans yet for "high current" devices like motors. I will start with E10 incandescent bulbs and introduce LEDs later. I found 3V, 50mA bulbs, which keeps the current fairly low. Students can calculate series resistors needed for these bulbs and put the bulbs itself in series or parallel. Also they can explore the nonlinearity of the voltage and current for these bulbs. The slightly older student can use the same material to determine Planck's constant.

Your battery case look nice. How do you connect the 5.5x2.5mm plug to the breadboard? I do not like to use these:

breadboard_power.png

but a 5.5x2.5mm connector is much less likely to cause a short than two breadboard pins.
 

Thread Starter

JunkieNL

Joined Mar 19, 2020
29
Note that any fuse small enough to blow while connected to a 9v or D, AA, AAA battery will have a relatively high resistance itself. The idea above for PTC is not bad, it's basically a self-resetting circuit breaker. Also series resistors are used frequently, if you need a lot of current just use a smaller value resistor, though my guess is the internal resistance of the battery is already going to be high enough to prevent any catastrophic failure.
The problem with a polyfuse is that the students cannot see the state of the polyfuse (except maybe by feeling if it is hot). Students might falsely dismiss a correct circuit because they had a short circuit a minute ago. An advantage of a glass fuse is that I know which students need help when they ask me for a new fuse. :)

I just measured the resistance of a 0.2A glass fuse and it is about 1.1 ohm, which is about 2,5% of the total resistance at 9V/0.2A. That's not bad considering that in most situations it will be less than that.
 

Irving

Joined Jan 30, 2016
1,019
I use a matching socket wired to a 2-pin header and heatshrinked. The spacing matches the red/black rail spacing on the BB. I was going to use a breakout board, but the supplier didn't have enough stock and I couldn't wait so just made up 20 of these leads.

You can get breadboard friendly jacks. how reliable a connection they make I don't know.

Seriously, I'd worry more about the incandescent bulbs - burns, broken glass, etc. When I did the obligatory risk assessment for the school, using glass bulbs spawned a debate, but I'd already decided on LEDs. The problem with incandescents is cold resistance is not equal to hot resistance... I just use normal resistors for series/parallel experiments.
 
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Thread Starter

JunkieNL

Joined Mar 19, 2020
29
This battery will be the safest. It's a high tech 9V battery that has a boost regulator in it and it will turn the battery off if it's shorted. You have to connect it to a USB charger to reset.

https://www.ebay.com/itm/USB-Rechargeable-9V-800mAh-Lipo-Battery-For-RC-Helicopter-Microphone-New/183604216958?hash=item2abfaa047e:g:PTsAAOSwLSZcIpRZ:rk:6:pf:0

Short protection described at around 7:20
That is pretty interesting. I wouldn't have given this item a second glance. I would have discarded it as soon as I saw LiPo.
 

andrewmm

Joined Feb 25, 2011
574
The ability of "students" to blow stuff up never ceases to amaze me,
If its any use, what we use are AA and PP9 batteries in holders,
to be honest, I dont think I have used a PP9 for a few years,
just off the shelf AA's
 
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