Stay connected to your scientific instrumentation

InstruMan is a project willing to improve the experience of an operator dealing with scientific instrumentation, making it faster and direct.

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Practical applications

New feature for android version! Battery Charger!

Please be aware that I’m not liable for any damage could happen to things, people, to yourself or anything else if you decide to try what is written in this post.
The purpose of the app and this post is to share my knowledge with interested people and everything you decide to do with the app and this information is your business, I’m not advising anyone to do what you’re about to read.

Since the Voltcraft PSU is a very powerful and versatile instrument, and combined with the Victor 86C which is a good and cheap measure device I had to test how this instrument works when you try to charge a LiIon battery. First of all, charging these batteries in the wrong way and without human supervision could lead to fire, venting and/or explosions. So put extreme caution in what you’re doing when you’re dealing with lithium batteries.
Charging lithium batteries is not difficult, and you don’t need expensive devices, you only need to make sure the instrument delivers an accurate amount of power into the battery without exceeding a certain limit. Lithium battery charging cycle consists of two phases: the first one is a constant current phase where you set the PSU to a certain value of current – which depends on the battery capacity and quality – for a certain amount of time until it reaches a limit voltage – typically 4.1 or 4.2 volts – and then it switches to a constant voltage cycle. In this last phase the current slowly drops until it reaches a low cutoff value – 10% of the initial current – where the PSU stops delivering current and the charging process is complete.
The most dangerous risk you run into when you decide to charge a LiIon battery is overcharging it; in other words when the battery is charged to a voltage higher than its limit, that is typically 4.20 volts. If you charge it over this limit, lithium metal starts to build up into the cell and you increase exponentially the risk of venting and flaming. Therefore batteries shall never be charged over their limit voltage.
The major downside of the Voltcraft PSU is that it doesn’t have a high accuracy since voltage is only measured with one decimal precision, hence I decided to limit the voltage to 4.1 volts, to stay in the “safe” zone thus lowering the risk of overcharging. I also added the possibility to use the Victor 86C multimeter to monitor the charging process by measuring cell voltage, also adding a safety stop to the charging app when voltage rises over 4.20 volts.
InstruMan app lets you choose a custom charging current, and I suggest you use 0.5 A or 1.0 A for most of the cells, unless you know that you can safely charge a certain cell at a higher amount of current. Please take note that generally batteries are charged at 0.5C, in other words half of their capacity, so if you’re charging low capacity cells – lower than 1000 mAh – you have to drop the charging current accordingly. For instance if you’re charging a 500 mAh cell it’s better to set the current at 200 mA.

You can also choose the limit voltage up to 4.1 volts, so if you want more safety you can choose 3.9 or 4.0 volts, but this way cells won’t be fully charged. And lastly you can choose the low cutoff current, the current where the charging process stops, which I suggest to be the 10% of the charging current (typically 100 or 200 mA).
If you decide to use this app to try charging your batteries, please make sure to set up the cables and battery so that you don’t risk any short or poor contacts with the multimeter and the PSU. Also monitor every step of the charging process and don’t leave the battery alone. Unless you have built a 100% risk less setup you always have to give a look at the battery and the instrumentation.

This post will be updated with pictures and screens of the charging process.

Building a Calorimeter

An useful idea to take the most out of this software is using it combined with the supported instrumentation to build a simple calorimeter.

The voltcraft power supply can be used as a power source to power up a device that generates heat. The Victor multimeter used as a temperature sensor can monitor heat gain and loss.

All needed mathematics and physics are embedded in the software, so let’s see step by step how to set up this experimental apparatus.

Firstly we need to engineer and build our apparatus. We need to create an insulated chamber where to place our heat source immersed in the appropriate fluid, which has to have a good heat exchange rate to take the most heat from the device, but not too high to prevent heat loss to environment. We place the device in a known mass of this fluid and wire it to the power supply, then we need to put a stirring device, such as a magnetic stirrer, to prevent temperature differences in the fluid. We put the termocouple in the fluid at an appropriate distance from the heat source and we close the chamber tight. Then we insulate this chamber by making a vacuum chamber around it our using an insulating material.

We can now link our instruments to the computer and start InstruMan software. We need to set up in the Heat Exchange tab the Heat Capacity of our fluid. We can insert an expression that will be integrated by the software, or we can use a constant value.

By default software is provided with expressions for Air and Water. Now we’re ready to start our experiment by creating a new log in the left panel and pressing the Start Everything button in the bottom toolbar (the one with a stopwatch icon).

Software will automatically record electric power consumed and heat produced, so when the experiment is finished you can export data and charts to Excel and you can further elaborate it, by calculating yield and power loss for example.