The vast field of HDD comprises a number of completely different reviews on the operation of lithium batteries. Such manufacturer as EPS (US) is known to produce the so called “long-lasting” SuperCell batteries, apart from other batteries reviews on which can be right the opposite from completely negative to absolutely positive.
In addition, to power its latest sondes DCI (US) company recommends the use of tandem switching on the lithium cells SAFT LSH 14 (which is "contraindicated" for other types of sondes due to the doubled supply voltage, i.e. 7.2 volts). It was therefore decided to test the lithium cells of available brands recommended for HDD use, and compare them with alkaline cells and lithium batteries.
Knowledge of datasheets (technical descriptions) of lithium cells of different producers revealed their little "trick" - all declarations on capacity of elements in ampere-hours (Ah) are related to consumed 1- 3 mA currents, which corresponds to the use in the fire-security systems, but not in the sondes.
When you increase the current consumption the capacity of cells decreases, in some of them - less, and in others – more. Interestingly, this same phenomenon occurs in alkaline cells.
The following brands took part in testing:
Eight lithium batteries of the first phase of the test: SUPER CELL, TWIN, FANSO ER251020 ULTIMATE, POWER CELL, EXTENDED LIFE, VELOCITY, BLUE (from left to right)
The second phase of the test included:
The second phase: three TWIN assembly, SAFT LSH 14, FANSO ER251020, Energizer (x 2), TF25500 battery (from left to right)
Unfortunately, there were no more items at hand! For the experimental accuracy, the load of each item was the voltage converter, the same used in sondes for HDD. The peculiarity of such elements is the constancy of power "withdrawn" from them by the external load.
Eight voltage converters with loads identical to HDD sondes
At the first stage of testing the power withdrawn from the power cell due to load was 0.36 W. This roughly corresponds to the power consumed by a sonde of FX (DCI) type in free space (outside of drilling head) or sonde DX (DCI) type in the drilling head.
At the second phase the power withdrawn from the power cell due to load was already 0.43 W. This corresponded to the power consumed by the sonde of FX (DCI) type in the drilling head.
The criterion for complete exhaustion of each of the batteries in sondes was the reduction of the voltage under the load to the operating minimum, i.e. to two volts.
The load was connected to the battery on a full-time basis and was disconnected for the night. The power of each item was measured before connecting to the load (in the idle mode), one minute after having connected to the load and at the end of the day prior to the load disconnecting. To calculate the real capacities of each cell we used the average cell voltage during the entire testing period until the complete exhaustion of the battery. Based on the measured characteristics of the voltage converters (loads) we estimated the average current consumption of each cell (battery) and the real capacity of the cell (battery) was calculated by simply multiplying the operating time till exhaustion by the average current.
The additional challenge set was the question of whether it was possible to determine the quality of the used lithium battery after having done simple measurement? The question remained unanswered due of the lack of statistics, although certain conclusions can be drawn.
An interesting feature of lithium cells is measurement of the output voltage at the moment of connecting to the load. Figure 1 shows the characteristics of the voltage changes on the lithium cell when connected to the load (related to all types of used items). Point "1" approximately indicates the cell voltage without the load, point "2" - the voltage when you connect the voltage converter (load) and point "3" – the cell voltage under the load, but after 30-40 seconds from the moment of being connected to the load. It is interesting that the smallest change between the voltages at points "2" and "3" at the time of initial switching on was with SUPER CELL battery and the biggest (without the load - 3.62 W, when connected to the converter - 1.15 W, and in a minute - 3.12 W) was with BLUE (it "died" the first).
Figure. 1. Voltage change of the lithium cell connected to load
Another feature of lithium cells, though a minor one, is the increase of the voltage under the load by the end of the working day at the first half of the testing cycle, and the same slight decrease of the voltage during the second phase of testing cycle. In the field conditions this phenomenon is difficult to register so it is believed that the lithium battery "keeps" the voltage up to the complete exhaustion.
All the data received by the parameters and conditions of testing of all the used items (batteries) are summarized in the table. The values of total operating time till complete exhaustion in hours, the average current consumption and the average voltage of each element (battery), and the calculated value of capacity in ampere-hours for current operating values are given.
|Brand of the cell (battery)||Hours before exhaustion in hours||Average current for a test cycle, mA||Average voltage for a test cycle, W||The estimated capacity of the element (battery), Ah|
The first stage of testing
The second stage of testing
|FANSO ER251020 (2)||61||171||3,374||10,45|
|TWIN LiION * (TF25500 x2)||40||163||3,675||6,53|
* - Electronics of the lithium batteries forcibly dismounts the load at the voltage reduction up to 2.5 W. Batteries allow up to 500 charge-discharge cycles.
Capacity values of cells (batteries) listed in the table are estimated values. For the accurate results we lack statistical data because there is a variation of parameters in different tests, for example, with FANSO ER251020 and TWIN. However, it can be expected that for the sondes current consumption of which is close to 100 mA in a drilling head (for example, for upgraded FX12 or FX19) lithium cells of the standard size ER251020 (CC) will be the real "100-hour" batteries.
Reviews saying that the batteries really work just for 4-5 hours can be based on the impact of other factors. In particular, no one has researched vibration resistance of the lithium cells (there is no reference to it in datasheets).
For example, three years ago vibration resistance of alkaline batteries DURACELL (standard size C, general use) has been put in question. They lost capacity in 15-20 minutes of sonde working on the rock, concrete or pebbles. Then, after some time of resting, they restored their capacity but to work with them in this mode was impossible.
So may some lithium batteries have the same issues?