The standard UBA5 can charge at 2A maximum per channel or 4A if you parallel both channels (or even more if you parallel channels from multiple UBA5s). You can charge at higher currents by having your UBA5 control an external power supply using its digital outputs. This application note explains how.

Circuits

The digital outputs on Acessory1 can be used to control the charge current either directly if your power supply supports that feature, or by using either of the circuits below.

The circuit below uses a P-Channel MOSFET (or you can use a PNP bipolar transistor with appropriate resistors).

Notes:
Choose R1 and R2 such that V_GS is 10 to 15V when Q1 is on.
To handle a wider variety of power supply voltages you can parallel a 15V zener diode with R2.

The circuit below uses an electronic relay:

Notes:
This circuit drives the electronic relay directly off of the UBA’s digital output.
If the UBA’s digital output is insufficient to control the relay, then add a drive transistor.
A mechanical relay can be used in place of the electronic relay, but a drive transistor will be required, and you will not be able to use PWM charging (explained below).

In either circuit, a “high” on the UBA digital output will connect the external power supply to the battery. Note, you must either use a power supply with a current limit or add a resistor in series to limit the charging current to a safe value for your battery. The power supply can be setup in either of two ways:
1) The output voltage can be set so that it’s the appropriate charge voltage for the battery, for example, the power supply’s voltage is set to 12.6V for a three cell lithium cell battery (3 x 4.2V).
2) The output voltage is set higher then the charge voltage of the battery. The UBA will then control the charge current by altering the duty cycle of the charging pulses (PWM). This method is better in that the UBA knows the charge current during the constant voltage phase and hence knows when the battery is fully charged.

Calibration File Modifications

To control the digital outputs, we need to add some lines to the UBA’s calibration file. Specifically an External Charge Device that specifies the charge current and an External Charge Control that specifies how the charge relay (or transistor) is controlled.

External Charge Device

The lines below describe an External Charge Device with name My3ACharger and a power supply with a 3A constant current.

*ExtChargeDevice: name model aichan do Ro limit control Iin0 Vout0 Vout0ExtChargeDevice: My3ACharger 5 -1 x 0 100 ERelay1 3 0

External Charge Control

The lines below describe an electronic relay with name ERelay1 that is controlled by digital output ‘0’ and is active high (the ‘i’ in ‘xi’).

*ExtLoadControl name model dochan maxamps
ExtChargeControl: ERelay1 2 xi ! 0

More information on using external devices for control can be found in our External Devices Manual (available on the Support page of our website).

UBA S/W:

The latest version of UBA S/W (version 2.00B4 Released December, 2019) supports constant voltage charging using an external power supply and an electronic relay controlled by a digital PWM signal from the UBA.

In the charging action you would select the Digital Ou
tput option (Digital OP) as shown here:

Leave the parameter field (“A0.5,1.0,2.0”) default. More information on the parameter field can be found in the help file (click “Help” to access it).

And select the External charge control and device as shown:

Then when starting the battery analysis you would select the appropriate external charge control and device as shown below:

That’s it, now start the analysis.

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Although small in size, the UBA5 still packs a punch with 90W of discharge power using both channels. But for some batteries, that’s not enough.

You can increase the discharge capability of the UBA5 by having it control external loads. The UBA5 has two digital outputs on its accessory port (and more on a second accessory port) that are under BAR program control and can be used to turn on or off an external electronic load or control an external relay, either electronic or mechanical. More information about using the UBA digital outputs can be found on our External Devices Manual available on the Support page of our website. We also have an application note: External Battery Discharger. But there’s another way to increase the discharge power of the UBA5, and it offers the advantage of being very simple and allowing control of the discharge current. The solution is to insert a power resistor in series with your battery as shown below:

The series resistor “drops” the voltage that the UBA sees, and thus the UBA’s internal power dissipation is reduced and you can discharge your battery at a higher rate (with the maximum set by the UBA’s maximum current, not the UBA’s maximum power). The beauty of this solution is that if you tell the UBA the value of the series power resistor, it will calculate the voltage drop on the resistor and use the actual battery voltage for its report and graph. The result is that you can triple the UBA’s power handling capability for minimal cost.

This is best illustrated by a couple of examples:

Example 1:
Test a 11.1V 3S Li-Ion Battery (or a 12V SLA) at 12A or 24A

You will need our UBA5-24A battery analyzer that can discharge at up to 12A per channel with the standard UBA5 45W limit per channel for this analysis. This battery analyzer model is designed for testing single lithium cells. At a 12A load, a li-ion cell will generally supply anywhere from 3.6V to 4.1V a few seconds after the load is applied. For this example, we’ll assume that the battery supplies 3.9V at a12A load after one minute, So the UBA5 will be dissipating 46.8W which exceeds its 45W limit. The UBA5 can allow this for the two minutes while the battery voltage is dropping.

Below is the test result of testing a single cell at 12A connected directly to the UBA5-24A (series resistor not used). Notice the full 12A discharge current.

Now let’s test a 11.1V lithium ion battery at 12A. We will use a 0.7 Ohm 100W resistor in series with the battery. Now when the UBA5 sets its load to 12A, 8.4V will drop across the 0.7 Ohm resistor, and the UBA5 will see just 3.6V (using the high value of 4V per cell with the application of the 12A load). 3.6V times 12A is 43.2W, which is within the UBA5’s 45W limit. The result is that we are discharging a 11.1 3S lithium ion battery (or 12V SLA) at 12A. If we used two 0.7 ohm 100W resistors (one for each channel) we could discharge the battery at 24A with our UBA5-24A.

Procedure

Start up the battery analysis as you normally would but on
the Options tab enter the resistor value in the Fixture resistance field. In my example, I’m using a 0.7 ohm resistor and I’ve added 0.025 ohms for the wire resistance. This UBA5-24A has the Vencon optional temperature probes installed so I’ll use them to monitor the battery temperature. Below is a screen shot of the running analysis. Notice the 12A measured load current and the 134W dissipation.

Here is the analysis result:

Notice how the battery is being discharged at the full 12A up until the 10 minute mark where the load current starts to decrease as the battery passes through 10V. The reason for this is that the voltage that the UBA5 sees is dropping below the minimum guaranteed battery voltage for full load. At a battery voltage of 10.2V (3.4V/cell), the UBA5 is only seeing 1.5V (10.2V – 12A x 0.725ohm). If a series resistor with slightly lower resistance or lower load current was used then you could avoid this current drop off. But if you use a series resistor that has a resistance too low, then the UBA5 will see a voltage that is too high at the beginning of the analysis and drop the load current to stay within it’s 45W limits. So there’s a balance between a series resistor that has a resistance too high or too low. But once you find the optimum resistance, you can triple the load power of your UBA5 setup for minimal cost.

Example 2:
Test a 44.4V 12S Li-Ion Battery at 2.5A

Although we make UBA5’s with extended voltage ranges, they do still retain the 45W per channel load limit which can be an issue for batteries with a capacity greater then 1Ah. The easiest solution is to simply parallel both channels, which gives you double the load current. Or we can add a power resistor in series with the battery.

For this example, I have a 2.5Ah 12S battery that I want to test at 1C (2.5A) using my UBA5-60V. This is about 125W (4.1V/cell x 12S x 2.5A) – too much for a single channel, or even for two paralleled channels.

Let’s do the math:

Maximum voltage that the UBA5 can handle at 2.5A: 45W / 2.5A = 18V.

Assume a 4.1V per cell voltage on the battery (it will start at 4.2V and quickly drop down, but not as much as the previous example as we’re just drawing 1C from the battery). So the initial battery voltage will be about 49V. Thus we need our resistor to drop 31V (49V – 18V). Calculate the resistor required using Ohms law and you get 12.4 ohms (31V / 2.5A), and 78W (31V x 2.5A).

I have a 12.5 ohm resistor, so let’s check the minimum voltage:

Assume a 2.9V/cell cutoff, so the minimum voltage will be 34.8V (12S x 2.9V/cell).

At the cutoff voltage, the UBA5 will “see” 3.5V (34.8V – 2.5A x 12.5V), which is fine.

I ran the analysis on my 12S battery.

Remember to enter the series resistor’s resistance on the Option tab when starting the analysis (the 25milliohms of wiring resistance in this example isn’t significant):

Here’s the analysis results:

It works, our 12S 2.5Ah battery is being discharge at 1C and gives us 2.1Ah (it’s an old battery).

Notice the knee in the discharge curve at 40 minutes. This because for this test I used two 6S batteries in series and one had a slightly higher capacity then the other, so the lower capacity battery was discharged first . Also the actual load current was closer to 2.6A (I was using an uncalibrated UBA5-60V) so the final voltage that the UBA5 saw was right at its minimum which caused the slight rounding of the discharge current at cutoff.

So for a minor cost of a power resistor, you can triple the power handling capability of the UBA5-60V (same for the UBA5-44V).

Combining Channels

You can use a second series power resistor on the second channel to double the load current. In the examples above, if you used another 0.7 ohm (example 1) or 12.5 ohm (example 2) 100W on channel two, you can discharge your 12V battery at 24A (example 1) or your 12S battery at 5A (example 2). If you’re combining both channels, then enter the parallel resistance of the batter, i.e. 0.35 ohms for example 1 or 6.25 ohms for example 2.

Note: The second negative battery lead (connected to channel 2) is optional for testing at 12S (as only 5A flows through a single negative lead), but highly recommended when discharging at 24A.

Charging with a Series Resistor

The UBA software only compensates for the fixture resistance during load, not while charging. For constant current charging (NiCd/NiMH or initial phase of Li-ion/SLA charging), this has little if any effect, but it will slow down the charging a bit during the constant voltage phase. In our example above, a 2A charging current through the 0.7 ohm resistor result in a voltage drop of 1.4V, or 0.5V per cell. The UBA5 will still be able to charge your battery, it just will take longer. If you are using the UBA5 in this setup to charge your battery then you can minimize the voltage drop during charging by adding a Schottky diode in parallel with the series resistor. This will the voltage drop will only be about 100mV per cell (example 1) or 30mV per cell (example 2).

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The above setup is designed by your engineering department, so that the operator only has to click one button to set the battery to a specific SOC. Here we’ve made two buttons for the operator, click the first button to measure battery capacity, or click the second button to put the battery into a 25% SOC. The flexibility and power of the UBA5 software is such that you can add as many buttons as you want, name them, and have them run any analysis that you’ve written. All these capabilities are in the software that’s included with your UBA5!

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You can now download UBA5Demo the “no install” version of the UBA S/W that includes a simulated UBA5!

After downloading, unzip the file (right click and choose Extract All …) then run UBA5.exe.

This is the latest version of the UBA5 S/W and it works without a UBA5 by simulating its operation connected to a battery (more accurately a “super capacitor”).

The UBA5 help file, UBA.chm, is included.  If you get “navigation to the webpage was canceled” or a blank page  when viewing it, then right click on the file in explorer, select Properties, and “unblock” it.

UBA5.exe doesn’t install any files on your PC, and when you exit it, it erases any data it stored in the Windows Registry.

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The first specification to check is battery capacity, which is straight forward when using the UBA5.

Where the UBA5 really shines, is in it’s ability to run custom life cycle tests. You can specify the depth of discharge, the discharge current, the charge current and the charge algorithm. Then let the UBA5 do its work. Life time testing can take a few days for short tests, or months for testing hundreds of cycles.

In addition, the UBA5 can control external devices during these tests, such as temperature chambers or external loads or chargers.

The following graph shows a life time test of a 1Ah lithium battery. A UBA5 ran over 2000 cycles on this battery over a period of 6 months. At 400 cycles the battery was down to 80% which is generally considered the end of life of that battery. But we kept on running the test. At 2000 cycles the battery was down to 60% of its rated capacity. So from these test results we can see a rapid drop in capacity vs cycle time, but then the decrease in capacity slows down.

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For example, in this setup the operator can choose from one of three selections that you’ve programmed for this battery, i.e. Form, Quick Test, and Full Test, or open a multitester to just check the battery voltage.

The operator can click on any of the running channels to monitor the analysis.

When the analysis concludes, the operator is presented with a Pass / Fail display:

All these customizations can be programmed and then the software can be locked down on the production floor so the operator cannot change any of the settings.

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Contact us to get your copy.

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What is cadmium migration and how do I prevent it?

Red Scholefield replies:

It has been accepted as dogma that today’s Ni-Cd batteries are not harmed by continuous overcharge as long as the temperature in overcharge is maintained at or near room temperature. Those knowledgeable about batteries however, are beginning to espouse a somewhat different story. To maximize battery life it has been recommended that the overcharge period or float charge of the battery take on an entirely different character than continuous constant current overcharge that has been the “acceptable” method. This “alternate” technique pulse charges the battery on a relatively long duty cycle. A battery is maintained at a full state of charge once it is completely charged and in overcharge (as is evidenced by a finite temperature rise or after an input of 160% of rated capacity), by a pulse of charge current in the C/10to C rate range and sufficient to replace energy lost by self discharge. This pulse of charge current is only applied to the cell for 1 hour out of 24 in the case of C/10 rate or in the 5 to 6 minute range each 24 hours for a C rate pulse. The theory and countless “casual” laboratory observations support this pulse technique over the “less expensive” constant current overcharge presently popular in the consumer product charging regimes. There is overwhelming evidence that constant current, even at very low “sustaining” rates, contributes to “cadmium migration” that forms a conductive bridge through the separator medium from the negative to the positive plate.

There is overwhelming evidence that constant current, even at very low “sustaining” rates, contributes to “cadmium migration” that forms a conductive bridge through the separator medium from the negative to the positive plate.

The rapidity of the reaction forming this cadmium bridge is a function of the current density and time. There is evidence to suggest that the conditions existing at a C/10 to C/20 overcharge rate contribute to the speed of the cadmium migration more than higher overcharge rates. The higher temperatures produced in higher overcharge rates cannot be ignored as playing a role in seemingly slowing the cadmium migration while at the same reducing battery life by increasing separator degradation. Where the optimum balance point of these opposing actions falls is left as yet one more challenge to our testing programs. It appears however, reasonable to assume at this point in time, that pulse charges at the C rate that will result in a “net” charge input equivalent to a continuous C/10 are much less conducive to cadmium migration than a continuous C/10 overcharge rate. While the beneficial impact of this pulse overcharge has not been quantified to any degree, the observations of battery testing personnel and more sophisticated battery users cannot be ignored. The creation of an economical means for pulse overcharge will be the challenge faced by the engineer wishing to design a product for optimum service life.

Questions and answers from Red Scholefield, Battery Engineer. Reprinted with Mr. Scholefield’s permission.

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UBA S/W running on Linux can be seen in this screen shot.

The Procedure
When we first wrote this application note back in 2003 there was a whole procedure that needed to be followed to get the UBA S/W to run.
Now thanks to the effort of the Wine developers, the S/W installs and runs without any problems. We used the latest version of Ubuntu (version 10) which loads Wine version 1.20.
So here’s the procedure: run the UBA S/W installer under Wine from a USB key, CD or download.
Follow the install instructions and you’re done.

Comments, questions, accolades? Let us know.

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