How to use external battery with Polaroid Cube+

 

Background

At the turn of the year 2018, I bought a cheap Polaroid Cube+ action camera - new one. The price in the offer was 49 € (fortynine euros). The camera is a very functional device for its very small size. It has a digital image stabilizer, a wide-angle lens, the image resolution (one of three options) is FullHD 1080p 60 FPS and the best thing is that the camera is really small. The dimensions of the camera are only 35x35x35 mm. As far as I know, this is the smallest action camera with these features - and in this price range. There is a strong magnet at the base, which keeps the camera attached to suitable surfaces. There are also shortcomings: There is only one operating switch, which requires precision when operating the camera. Of course, there is no screen, so the image cannot be monitored.

The camera has been used e.g. in the videos of this Munkkirasti blog's Christmas calendar.

Problem

The new battery lasted about as long as the memory card was full. So in practice, at least half an hour. The camera worked about three summers in more active use, and in the end, the hours of use were not very many. Then battery life became a problem. The battery eventually died quite quickly after the problems started, and the situation was that the camera only stayed on for about two minutes when filming.

The reason for the really low price was probably told at the same time. An old lot that was leaving the market and it was known that the batteries were second quality. Of course, when I bought it, I realized that if the price is less than 20% of the price of a roughly equivalent GoPro camera, not everything is as it seems. I'm writing this in March 2023 and it looks like the Cube+ is still on the market. The price in Finland is around 180 €. In five years, the price of the camera has tripled. Pretty much. A camera called Gembird BCAM-01 caught my eye. The technical data are similar to Cube+, the case is also from the same mold with minor differences. This price is 16 (sixteen) €. So for the price of Cube+ you get eleven of these. I don't really wonder about this, because it's not the topic of this story.

So the batteries were at the end of the road.

Old shells.

Camera batteries are not replaceable. However, a video was found on Youtube where they are exchanged:

So the camera has two 300 mAh cells connected in parallel. The measurement showed that one of the cells was completely dead. And since the cells are in parallel, even an intact cell could not keep the camera running

The problem is that these 300 mAh cells, which measures are 25x19x6 mm, are not available anywhere - absolutely anywhere. My conclusion was that the cells were made just for this camera. There are two of them because they can be packed into a smaller space. I found equivalent cells a couple of millimeters larger, but the solder lugs are on the shorter side, not the longer side. In the attached video, the guy can squeeze the cells inside the case, even though he's doing it tight.

Original circuit diagram

Solution

I use the camera in a headband mount I built myself, which is modified from a headlamp headband. This build has plenty of room for a external battery, so I completely abandoned the battery inside the camera. The large external battery not a problem in terms of weight, as this camera setup is significantly lighter than the headlamp I use for night orientation.

I already have 18650 cells, which I have used when building the battery pack for the headlamp I use in night orienteering. One 18650 has the same nominal voltage as Cube+'s battery and has a capacity of approx 2000-3000 mAh. These cells are available with a significantly higher capacity, but let's start with the one that happened to be available.

I bought a case for one 18650 cell with a charging circuit. After wondering for a while (when I couldn't get the camera to start due to another reason), I reasoned that since I don't charge the external battery through the camera, I can completely remove the protection circuit of the battery inside the camera.

New circuit diagram.

The purpose of the white wire was not clear. Since the original cells are in parallel, and not in series, this cannot be an balance contact between the cells - as is the case, for example, in the protection circuit of two cells connected in series. It doesn't look like a cell temperature sensor wire, because no temperature sensor is attached to the cells. Of course, the temperature sensor can be in the protective circuit itself. I connected the extra wire to positive and it seemed to work.

Assemblying

Battery case opened and connector with wires are in place.

The plastic inside the battery case has been cut to the extent that the wires going to the camera have been soldered directly to the contacts against the battery poles. Please note that the body of the coil shown in the picture is broken. It was like that when new, luckily it still works.

The battery case has two connectors. USB output and Micro-B USB input. The Output connector is not needed, so it is covered.

The wires coming from the camera's pcb are extended inside the camera with thicker wires that come out of the hole on the side of the camera.  

See picture below: Camera case is open and battery wire has been extend (solders are covered with yellow heat shrinks. New red cable goes under the one of top pcb and comes out on opposite side of case. The most top pbc is laying at the bottom of the picture at the end of the flat cable. Extra special care must be taken to ensure that all small parts are preserved and that the connectors between circuit boards are not damaged.

 

The new power cable has a connector so that the camera can be removed from the headband during transport and placed in its own rubber protective hood. The headband and the battery case in it are better able to withstand transport as they are. The camera has its own little box for transport.

The camera originally had a seal and it was splash-proof. Now there is a hole in the case and after several openings the case has suffered a little, so it is no longer tight. It doesn't matter, because I only  shoot a orienteering videos in dry weather. I noticed that when it rains, a drop of water easily gets stuck on the lens and the image is then so distorted that the video is unusable. So this is only a dry weather camera.

Usage

The battery can be charged while in the case by connecting any charger with a USB connector to the Micro-B connector. There is no need to disconnect the camera because the charger is not connected to the camera. There is a battery protection circuit in the battery case. I usually remove the camera before charging, but that's to make it easier to transport.

Note! When connecting the camera to the computer, the connector between the battery case and the camera must be disconnected, otherwise the computer via camera will try to charge the battery directly without a protection circuit. This would be easy to fix with a single diode, but the connector is naturally opened before connecting to the computer, because the camera is removed from the headband during transport home, as I wrote in the previous paragraph. Maybe in version 2....

The cell can also be removed from the case and charged with a separate charger. I have an Orbit Microlader charger for model aircraft batteries, with can be also find out what the capacity of the battery is by charging process. The latest check said that the actual measured capacity of the cell in this camera project was  1950 mAh. That's 225% more than the rated capacity of the original battery and is definitely enough for me. And if that's not enough, the cell is changed in a couple of seconds.

Using the camera, i.e. shooting, is done in the same way as before changing the battery.

With one 18650 cell, the camera's operating time is at least 300 min. As I write this, I've shot for about 5 hours on the first charge and the battery still has charge left. The charge is therefore quite sufficient for my needs. In order to be able to use this properly, you need a memory card significantly larger than the original 8 GB, which can hold a video of about half an hour long.

The only downside to this setup is that the camera's internal clock doesn't work. It resets when the battery is removed and the date of the image file is always 31.12.2014. And of course, you can't use the time stamp that comes into the picture, if you wanted to.

Of course, I could put videos here that I shot with this camera, but it's not worth the trouble. Youtube degrades their quality and you have already seen 5K videos, which this camera is not capable of. There are orientation videos here on Munkkirasti, but they don't tell much about the camera's features. When running in the forest, the head shakes so much that the camera's image stabilizer cannot stabilize the image enough. If a some application has been used to connect the map to the image, the image is stabilized by software and the result is black bouncing frames in the image, and further deterioration of the image quality.

Here we go again towards the next problem...