Lithium Polymer batteries

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zebedeesknees
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Lithium Polymer batteries

Postby zebedeesknees » Fri Nov 12, 2021 4:34 pm

In my book, there are three types of Li-Po battery; safe, risky, and downright dangerous. There has been much scare-mongering, generally due to insufficient education on the subject. The question to be asked is "what purpose was that battery designed for?" Chances are strong that "it ain't for your model railway mate!"

We here have been scouring the interthingy for years, and buying what seemed at the time like a Good Idea when it appeared. Consequently, I have some of each of the above, all single cells so a nominal voltage of 3.7vDC.

Those designed for vaping machines are quite large, cylindrical, and have a capacity of 3,000mAh, or 3 Amps for an hour. BUT, that's not what they are designed to push out, 3 Amps would struggle to heat the vaping wire. They also have a 'C' rating, which will be shown as the letter C followed by a number. The C stands for Capacity - 3 Amps for an hour, but the number is a multiplier! In the case of a vaping battery, that might be 30 or more. So as well as being capable of supplying 300mA for some 10 hours, it can also, if the circuit is short enough to allow it, knock out an extremely dangerous 90 Amps for 2 minutes. That is over 300 Watts! Put your hand on to a 100W light bulb...

The just risky ones, of which I have several, are designed for toy drones and the like. They are nominally around 500mAh and have a very handy type of connector. These power the drone for approximately 8 minutes, so have a C rating of 4-ish. Around 2 amps, or 7 Watts for 8 minutes is going to get quite warm.

The same applies to those pictured below with a C of 200mAh or more. Those with a clear orange top where the wires exit have a small visible pcb which, according to my measurements, provides a constant maximum short-circuit current of 1.6A @ 3.7v irrespective of the C, even the smallest ones.
It is therefore a question of time taken to cause damage; even just as the circuit closes the output down, after some 8 minutes if the battery was fully charged, there will still be nearly 5 Watts heating whatever the current is flowing through.

The button cells are also risky, as they come 'bare cell' with no control pcb. Though possibly too small to provide enough current to cause damage, if they are discharged to below around 2.5 volts, they will not hold future charge, and if they do manage to leak, the fumes are very unpleasant and almost certainly unhealthy.

Rc Batteries.jpg


Pictured above are some of the batteries I have used, most still in service.
Top row, from left:-
New RS button cell, bare - 12x6mm 45mAh.
Same cell, fitted with a control pcb from another cell, wires clamped to the sides with heat-shrink.
LR2450 button, bare cell 24x5mm, 120mAh.

Next row:-
26X9x3.5mm, 90mAh
12x10x5mm, 55mAh
25x20x5mm, 200mAh
35x25x5mm, 450mAh
35x25x8mm, 800mAh
40x25x8mm, 850mAh.
In practice, the longest dimension is usually exceeded by 1mm or so, tight fits get tighter!
The cylindrical Magnate battery is 45x14mm, 750mAh, KR14430 and does have an internal protection circuit. Others are available...

By the way, Chinese prices for Li-Po batteries appears to be rising recently, world demand for Lithium I imagine. UK supplier prices have for now stabilised, fallen in some cases. Even Amazon have them now. Look for 'low drain applications' in the description for the safest ones.

Ted.

Terry Bendall
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Re: Lithium Polymer batteries

Postby Terry Bendall » Sat Nov 13, 2021 12:24 pm

All interesting stuff Ted for those who want to go that way as are the other posts on radio control.

quote="zebedeesknees"]In my book, there are three types of Li-Po battery; safe, risky, and downright dangerous.[/quote]

Are the hazards only from fumes as you mention or is there a risk of overheating and under the right circumstances unpleasant outcomes such as fires or melting of plastic bodies of locos? :(

Terry Bendall

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LesGros
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Re: Lithium Polymer batteries

Postby LesGros » Sat Nov 13, 2021 12:56 pm

Terry,
One of the problems with LiPo is that battery fires are incandescent. Applying water makes things worse because the fire is hot enough to separate the H2O, thus feeding the conflagration.

The BMFA have reported instances of people being quite badly burned. Advice given in the Model Aircraft community is that a LiPo battery fire should be allowed to burn out, extinguishers can then be used to save what is left of the Model, (House?) and prevent a damaging spread to the surroundings.

This is why it is also recommended that LiPo batteries be transported in fire proof containers.

Bottom line: Always use the correct charger, and read the makers warnings carefully before use.

Cheery,
LesG

The man who never made a mistake
never made anything useful

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zebedeesknees
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Re: Lithium Polymer batteries

Postby zebedeesknees » Sat Nov 13, 2021 1:57 pm

Terry Bendall wrote:All interesting stuff Ted for those who want to go that way as are the other posts on radio control.

quote="zebedeesknees"]In my book, there are three types of Li-Po battery; safe, risky, and downright dangerous.


Are the hazards only from fumes as you mention or is there a risk of overheating and under the right circumstances unpleasant outcomes such as fires or melting of plastic bodies of locos? :(

Terry Bendall

Hi Terry, let's try to avoid the unsubstatiated reports that amount to scaremongering!
The only time I have ever seen overheating and fumes is while playing with a bare cell that had only a thin film case and Bahoma magnetic connectors. I accidentally allowed a clipped-off resistor wire near it, not realising that such wires are nickel coated ferrous these days, copper being the price it is, and it jumped to the connectors and shorted the cell. It swelled rather quickly and split, allowing a white powdery fume to escape. Short removed, fumes stopped, battery ruined, no other harm done.

Any high current source should be respected. Back in my OO days, an half century ago, I was cleaning my track with wire wool after the loco kept hesitating, like yer do, and much to my surprise, the wire wool caught fire! Of course the power to the track from my Tri-ang controller had been left on, supplying what? 12vDC @ 2A? As for DCC, 16vAC @ 5A - what damage could that cause if not respected?

My message was that high output vaping batteries are to be avoided, and those with internal pcbs for use with low drain appliances are safer than your mains controller - by far!

Ted.

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Guy Rixon
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Re: Lithium Polymer batteries

Postby Guy Rixon » Sat Nov 13, 2021 3:21 pm

Apart from the risk of heating on short circuit, I've alway understood that these cells are dangerous if overcharged. IIUC, they ignite if the cell itself is overcharged and the charging circuit has to protect against this. Is that protection always in the battery itself, or is it in the separate charger?

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zebedeesknees
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Re: Lithium Polymer batteries

Postby zebedeesknees » Sat Nov 13, 2021 3:59 pm

Guy Rixon wrote:Apart from the risk of heating on short circuit, I've alway understood that these cells are dangerous if overcharged. IIUC, they ignite if the cell itself is overcharged and the charging circuit has to protect against this. Is that protection always in the battery itself, or is it in the separate charger?

Hi Guy, thank you for asking, all those in my picture apart from the bare cells, have an integral control circuit. They charge up to between 4.2 and 4.3 volts, and then the current drops to zero. If left connected to the charger, the circuit 'has a look' about every 10 seconds or so, and tops up if required. These batteries with the clear top panel and an obvious pcb in there are designed to save the application needing a dedicated control circuit.

As they are for mobile devices that could be left on the charger indefinitely by yer average consumer, they HAVE to be safe in that situation. There are several separate dedicated styles of charger pcb available - I bought several of each on this journey, but now leave those with the panel on a USB supply as continuously as my mobile 'phone and tablet. Certainly overnight!

It is easy enough to check - put your multimeter on the 10A setting, and - briefly at first - short the battery through the meter. If it doesn't go 'out of range' immediately, leave the probes on the battery wires and observe the reading. This will show the maximum current that the integral pcb will permit. In the case of those in my pic, they all read between 1.5 and 2 Amps.

Ted.

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zebedeesknees
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Joined: Mon Jul 12, 2010 5:15 pm

Re: Lithium Polymer batteries

Postby zebedeesknees » Sun Nov 21, 2021 3:58 pm

Further, one of the essences of the 5 volt railway is that I only use 1S battery cells. The 'S' stands for cell, as mentioned before. On searching Li-Po, there are 2S, 3S and up available. These are cells in series, so 2S gives a nominal 7.4v, 3S 11.1v, and so on. Seems great for running 12 volt motors, BUT - they need a dedicated charger for recharging them in series. Fine for electric flight, drones, and large scale car models where a battery swop is simple, and probably the source of many of the warning messages that simply do not apply to the low drain cells that are in the first picture.
Single cells can be arranged in series in a loco, but they either have to be wired to a charger circuit or taken out to be charged independently.

Initially, this seemed like a Good Idea, the 'concentrator' pcbs were/are readily available on eBay, and three 240mAh batteries could fit under the roofs of the bogie diesels. With this arrangement:-

Li-PoConcentrator.jpg

- there is enough space in a diesel for the batteries and the pcb mounted on stripboard, plus the loco does not have to be dismantled to charge the batteries. It is DC though, so a rectifier is needed if retaining non-polarised supply to charge, but worse, the supply voltage needs to be at least 14-16 volts to charge the batteries in a reasonable time.

On the other hand, single cells can be successfully wired and charged in parallel, increasing the effective capacity, but retaining the original 3.7vDC nominal. Though I haven't taken it apart, I imagine that the 'power bank' is so composed:-

Rc PowerBank.jpg

This one is 70x70x25mm, has a capacity of 10Ah, and cost around £20. The outputs are limited to 2A, so no less safe than your Hornby power transformer. I regard it as the water tank above the shed for steam outline, or oil tank at the refuelling point for diesel. It fits comfortably inside the Dapol water tank. It can supply all the running and charging needs of a 5 volt railway for hours, independent of any mains supply.
That 'button' on the front panel is an extra I fitted from a magnetic charger connector for USB charged devices; search 'magnetic charger' to see the huge range available. We have several, I consider them a boon, as they save damage to the devices from constant insertions and possible snagging of wires.

For accessories (or trains) that require different voltages, USB boosters with dial-up outputs are available too:-

Rc Bank&Booster.jpg

This picture shows the other side of the power bank, with it's current capacity percentage indicator.

I couldn't resist making my own version, since I had those 3800mAh vaping batteries, so to prove a point, I joined three of them in parallel to make one 11.4Ah bank, then fitted a protection circuit to the common connection for charging and use from one of the older cells, and that too has a max output of under 2A. The ends are well insulated of course!

Rc BatteryBank.jpg


Ted.


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