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).

The post Increase Discharge Power with a Series Resistor appeared first on Amicell - Vencon.

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.

The post Running Under Linux appeared first on Amicell - Vencon.

For very special battery testing you might not want to use the built-in constant current load on the UBA.

The UBA is limited to discharging up to 2.5A per channel. This discharge rate is adequate for testing 99% of the batteries on the market. It is not sufficient to properly test batteries that are rapidly discharged in normal use (for example, some medical applications, UPS batteries and remote control aircraft and cars). For these batteries you should discharge them at a similar rate to the rate they get in normal use.

In other situations you might be fortunate to already have a constant current load that you would prefer to use. For instance, if you have a 10A logic controlled constant current load you could use your UBA to control it. This application note describes how to build and control an external discharger.

Schematic

Circuit Description

This circuit contains two remotely controlled loads. The top part of the schematic is a regular off-the-shelf voltage regulator configured as a constant current load with on/off control. The bottom of the schematic is a MOSFET used to control a power resistor.

Inside your UBA, there is a 10 pin accessory header. On it are two programmable digital input/output lines which for controlling a remote load are configured as outputs. Pin 3 is digital output #0, pin 6 is digital output #1, pin 1 is digital ground, and pins 8 and 10 are analog ground. The accessory header is accessible by either removing the top cover of your UBA or by using an extension connector on the back of your UBA (preferred).

Caution The digital lines on the accessory port go directly to the digital output IC on the UBA. There is no extra static protection. You must take full static protection precautions when handling the connections and when designing the circuit. Your warranty does not cover any damage caused by static or mistakes in connecting to the accessory connector.

After power up digital control line 0 is high and line 1 is low. You can select the active state of the digital signal (see Setup). These digital lines can source and sink up to 2mA. Since there are two digital lines you can build up to two loads.

The circuit shown here contains two independent circuits for discharging. We built this circuit to test external load discharging, normally you wouldn’t build both circuits together.

Controlled Constant Current Load

The constant current load operates by supplying a fixed voltage to a resistor, Rprog. The load current is thus Vo/Rprog, where Vo is the output of the regulator, 1.235V for the MIC2941A part that we used. This circuit isn’t very practical since the output current is limited by the current limits of the regulator (usually around 1A) and all the power is dissipated in the regulator. Thus if you want to be able to test an eight cell battery your maximum current is limited to about 500mA with the regulator heat sinked. Since the UBA can discharge up to 2.5A there isn’t any advantage with this circuit. In addition, this circuit can only discharge down to about 2V, thus it can’t test a single cell (NiCd or NiMH). Instead of the voltage regulator used here you would probably use a commercial high power constant current load, or build your own to really take advantage of this technique.

Switched Load

The bottom part of the schematic is a switch load. This circuit uses a power resistor for the load (Rload in the schematic). This circuit is simpler than the constant current load. Ideally you would use a precision power resistor for the load. Thus the discharge power is dissipated in a resistor, which is simpler to work with than an active device. For the high power load that we sell, we use a circuit similar to this to control the load which is a bank of light bulbs. Light bulbs have the advantage that they are inexpensive and somewhat constant current over their voltage range. Thus, as the battery voltage drops the current doesn’t drop as quickly as if using a resistive load.

This circuit requires that the resistance of the load be accurately known. This isn’t easy when the load resistors heat up and change their resistance. This is even more difficult when using lamps for the load as their resistance is non-linear (changing with voltage). For resistor loads the higher the wattage and the lower the tolerance the better. You should be using a resistor with a wattage of at least four times the power you intend to dissipate in it and with a tolerance of no more than 2%. For the high power load which we sell we provide a circuit which measures the current and feeds it to the UBA which uses this information to calculate battery capacity.

Another advantage of the resistive load is that it has no minimum voltage. The current doesn’t suddenly drop off below a certain voltage. Thus a resistive load is ideal for testing single cells.

Setup

In order to use your external loads you need to add these lines to your calibration file describing the load: For the Constant Current Load:

*ExtLoadDevice: name model aichan limit control Iin0 Vout0
ExtLoadDevice: My600mA_CC 2 -3 1 My600mA_SW 0.618 0

*ExtLoadControl: name model dochan maxamps
ExtLoadControl!: My600mA_SW 2 0x ! 1

For the Switched Resistor Load:

*ExtLoadDevice: name model resistor limit control
ExtLoadDevice: My10R 3 10 20 MySwitch

*ExtLoadControl: name model dochan maxamps
ExtLoadControl!: MySwitch 2 x1 ! 2

The lines starting with an asterisk (*) are comments.

The “ExtLoadDevice” & “ExtLoadControl” lines describe the constant current load (top half of schematic). Even though the constant current load is a single device, it is described by two lines.

The “ExtLoadDevice” line is for the constant current load. The model is ‘2’ which means that it is a constant current load. The analog input channel is ‘-1’, which means not used. The current limit is 1A. The load is controlled by the external load control “CCSwtich”. The “0.618 0” means that the load current is a constant 0.618A.

The “ExtLoadControl” line says that we are using an External Load Control. The first number, model number of 2 means that it is an on/off switch. The second item is 0x, which means that we are using the digital output 1 and it’s turned on by a low signal (digital output is specified in the form …cba where a is digital output “0” and can be “1” for high signal to turn load on, “0” for low signal, or “x” for not used and Similarly “b” is for digital output 1). The “!” means that the complement of the dochan is used to shut the load off. The last number is the maximum current that this switch can handle. In our case, 1 Amp.

The next set of “ExtLoadDevice” & “ExtLoadControl” lines describe the switched resistor load (bottom half of schematic). The external load device is the resistor and the external load control the FET.

The “ExtLoadDevice” specifies a model 3 device (resistor) with resistance 10 Ohms, maximum power 20W, and controlled by MySwitch. The “ExtLoadControl” specifies an electronic switch (model = 2) which is turned on with a high on digital output 0 and has a maximum current of 2 Amps.

Note the exclamation mark (!) after the ExtLoadControl for both the constant current load and the resistive load. This means that the external load control should be turned off after initialization. Leaving out the exclamation mark means that the digital output lines are kept at their default state: high for DO0 and low for DO1. If you were to build this load advice I’d recommend that the digital outputs be swapped so that the default states turn off the load.

Once you have the calibration file modified, run UBA Console. Open a Multitester and select the “External Load” tab. You can choose the external load device and control to use. You can then turn them on or off. Once you are confident that your setup is working you can try a battery test.

Go to “File|Battery Analysis Routine Designer” and start a new battery analysis routine. In the load action click on the “External” tab. Choose “Primary” for both the External load device and control. Save the BAR and setup a battery analysis. Before you start the battery test select the “External Load” tab and under “Primary external load device” select the load device you want to use and under “Primary external load control” select the load control. Start the battery test.

Improvements

We can make an improvement to the constant current load. The problem is that if the battery voltage drops below 1.9V the load current will drop, but UBA Console won’t know this. The solution is to specify how much current the load draws at different voltages. We measured this and found out that below 1.5V the load current is almost 0 and above 1.9V the load current is constant. We can specify this on the ExtLoadDevice line as follows:
*ExtLoadDevice: name model aichan limit control Iin0 Vout0 I1 V1 I2 V2 I3 V3
ExtLoadDevice: My600mACC 2 -3 1 My600mASW 0 0 0 1.5 0.618 1.9 0.618 2.0
The aichan value of “-3” means that UBA Console is to use the battery voltage to determine the load current based on Current/Voltage pairs.

Let’s look at each Current/Voltage pair:
0 0 0 1.5 means that at 0V the current is zero and at 1.5V the current is also 0.
0 1.5 0.618 1.9 means that at 1.5V the current is 0 and at 1.9V the current is 618mA. Values between 1.5V and 1.9V are extrapolated.
0.618 1.9 0.618 2.0 means that at 1.9V and at 2.0V the current is 618mA. UBA Console interprets this as meaning that for battery voltage equal to or greater than 1.9V the load current is 618mA.

Email us with any questions, and to let us know if you’ve built an external load.

appnote_uba4.1 Do-it-Yourself External Battery Discharger

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