CASP Service Information Letter, February 2013 – CRITICAL CALIBRATION INFORMATION
- When would you Slow (Alt) Charge NiCd’s?
- Can you charge single cells, as well as 6, 12, 24 volt and other packs with a CASP?
- Do you need to discharge a battery before charging?
- Why is it that when I try charging my fully discharged NiCd battery at the C rate, the CASP charges OK for a few minutes, then terminates, indicating that the battery is charged?
- Why does an external voltmeter, when connected across my battery, always read a different voltage than the value displayed on the CASP?
- How long are the Standard CASP Battery Cables?
- Can I order and use longer cables than the ones I received with my CASP?
- What is the tolerance and wattage rating of the Battery Cable ID resistors?
- What is the SMOOTHING FACTOR and how is it used?
- What is the SAMPLE RATE and how is it used?
- Will changing the SMOOTHING FACTOR, and thus the SAMPLE RATE, allow me to get more precise measurements of my battery’s voltage?
- Why do some Battery Parameter Table printouts have the SMOOTHING FACTOR shown in table 099 (or 098) and others do not?
- Why use such a complicated equation for SAMPLE RATE?
- What is the effect of adjusting the SMOOTHING and, therefore, the SAMPLE RATE?
- What is the time limit on CASP graphic plots?
- What is the maximum value for the CASP elapse timer?
- What can cause a FAILED HIGH IMPEDANCE error message?
- After charging a battery, why does the charge amp hours reported significantly exceed the battery amp hour rating?
- Does CASP “handshake” with their serial Epson compatible printers?
- With a CASP/2500 set for AUTO PROCESS, why does a failed battery print detailed results, while a good battery does not?
- Can I reprogram my old CASP/1100 or CASP/1200 with my new CASP/2500?
- Will a 220 VAC 50 Hz. line effect the ability to communicate with CASP using a Personal Computer and Christie communications software?
- What is the data acquisition rate for a CASP?
- Can CASP discharge current capacity be increased by connecting two (or more) channels in a parallel or serial configuration?
Q: When would you Slow (Alt) Charge NiCd’s?
A: When it is (1) a new pack, (2) a pack that’s been in storage for many months, (3) a pack with severely unbalanced cells or (4) a consumer-grade pack or one with high impedance.
Q: Can you charge single cells, as well as 6, 12, 24 volt and other packs with a CASP?
A: Yes, as long as it doesn’t require more than 78 volts or 14 amps.
Q: Do you need to discharge a battery before charging?
A: No, the CASP’s CPU knows when a battery is partially charged, and will bring it to a fully charged condition, without risk of overcharging.
Q: Why is it that when I try charging my fully discharged NiCd battery at the C rate, the CASP charges OK for a few minutes, then terminates, indicating that the battery is charged?
A: Several things could be happening. The battery could be defective, the battery parameter tables may have an erroneous entry, the wrong cable may be connected to the CASP, or some other “Cockpit” error may be occurring. All of these items should be checked and determined to be correct. If no “Cockpit” errors are found, then try charging the battery at a C/2 rate. If you are able to charge the battery for a longer time period before termination occurs, you have probably been trying to charge the battery too rapidly. For optimal charging you need to determine the value of “n” in the C/n equation. For the CASP/1500, /2000 and /2500 you can do this empirically by trial and error, by plotting the charge curves, by reviewing the battery specifications, and/or by contacting the battery manufacturer. For CASP/1000, /1100 and /1200, you will be unable to modify the pre-programmed battery tables without the TD-639 or TD-700 software unless you have a CASP/1500 or CASP/2000 from which to download. The unit may have to be returned to Christie if custom programming is required for your batteries.
Q: Why does an external voltmeter, when connected across my battery, always read a different voltage than the value displayed on the CASP?
A: When charging (or discharging) a battery, the CASP turns off the current to (or from) the battery for 10 milliseconds each second, to measure the battery voltage. During this 10msec period when no current is flowing, the CASP is able to read the true open circuit battery voltage. Synchronizing the voltage measurement with this “quiet” period eliminates any possibility of IR drop errors in the interconnecting cables, which a regular voltmeter is incapable of doing.
Q: How long are the Standard CASP Battery Cables?
A. Thirty (30) inches without battery clips or connectors. Clips or connectors may effect the length slightly. Cable lengths (within reason) are not critical and may be customized to fit specific applications.
Q: Can I order and use longer cables than the ones I received with my CASP?
A: Yes. For constant current charging, CASP controls the current to the battery to compensate for any line losses in the cable. Additionally, as described above, the CASP turns off the current to the battery every second to measure the voltage. In this mode, CASP behaves as a high impedance voltmeter, therefore the line losses are negligible. In constant current operation, CASP acts like a remote voltage sensing power supply thus compensating for line losses in cables of reasonable length.
Q: What is the tolerance and wattage rating of the Battery Cable ID resistors?
A. All resistors are 1.0%, 1/8 watt, resistors except for cables numbered 109, 115, 120, 123 and 124. These five cables are 0.5%, 1/8 watt resistors.
Q: What is the SMOOTHING FACTOR and how is it used?
A: The SMOOTHING FACTOR is a modifiable (firmware 6.x and higher) number in the CASP tables. It directly effects the time between charge and discharge voltage value samples which, in turn, effects the quality of the voltage slope data used for slope sensing termination, graphic plots and various other calculations. Its most observable effect is on the resolution and appearance of the graphic plots of voltage and slope produced by the CASP/1500, /2000, /2100, /2200, /2300, and /2500. Also, even though the CASP/1100 and /1200 do not plot graphs, the SMOOTHING FACTOR is still important and is used for both curve calculations. The CASP/1100, /1200, /1500 and /2000, with software version 6.x, store the SMOOTHING FACTOR value in table 099. CASP/2100, /2200, /2300 and /2500, with software 7.x store the SOOTHING FACTOR value in table 098. The following equation shows how the SMOOTHING FACTOR is employed: SAMPLE RATE = 1 + ((Nominal Amp Hour / Charge or Discharge Amps) x SMOOTHING Value)
Q: What is the SAMPLE RATE and how is it used?
A: The SAMPLE RATE is the result of multiplying the SMOOTHING value by the ratio of the “Nominal Amp Hour” to the “Charge or Discharge Amps”, then adding 1.0 to the product. CASP takes the “Nominal Amp Hour” and the “Charge or Discharge Amps” values from the battery parameter table being used. In firmware versions 6.x, CASP gets the SMOOTHING value from table 099. In firmware versions 7.x, CASP obtains the SMOOTHING value from table 098. The following equation shows how the SAMPLE RATE is calculated using these three values: SAMPLE RATE = 1 + ((Nominal Amp Hour / Charge or Discharge Amps) x SMOOTHING Value). The SAMPLE RATE determines how often the collected voltage data (measured once per second) is sampled. These samples are used in various calculations, one of which is to calculate the charge and discharge battery voltage curve (both graphed and ungraphed). The change, in the sampled battery voltage, is used to find the battery voltage curve’s slope (dv/dt). Finally, the slope values are used in slope sensing charge cut off, curve plotting, and other CASP calculations.
Q: Will changing the SMOOTHING FACTOR, and thus the SAMPLE RATE, allow me to get more precise measurements of my battery’s voltage?
A: Only to a point. The SMOOTHING FACTOR and SAMPLE RATE do not effect how frequently CASP measures and collects the battery voltage. That occurs once per second to allow excess power and excess voltage safety checks. If the SAMPLE RATE equation is inspected, it is obvious that for a SMOOTHING FACTOR value of zero (0.00), the maximum SAMPLE RATE is once per second. This corresponds to the maximum rate that CASP can collect the battery voltages. So, the SMOOTHING FACTOR may be adjusted to reduce the SAMPLE RATE to less than one sample per second, but never more than one per second.
Q: Why do some Battery Parameter Table printouts have the SMOOTHING FACTOR shown in table 099 (or 098) and others do not?
A: Some older versions of CASP firmware did not permit adjustment of SMOOTHING by the user. Its value was optimized at Christie and set at the factory. Currently 7.x and 6.x firmware versions permit the adjustment. However, Christie does not recommend modifying the default factory selected value except to users with extensive experience in CASP parameter settings. Keep in mind that entering an incorrect value for SMOOTHING could detrimentally effect CASP’s ability to detect “A” and/or “B” charge termination.
Q: Why use such a complicated equation for SAMPLE RATE?
A: The SAMPLE RATE equation: SAMPLE RATE = 1 + ((Nominal Amp Hour / Charge or Discharge Amps) x SMOOTHING) allows the voltage change, between samples, to be roughly the same and independent of charge or discharge rate. It causes the slope curve data to appear similar (for termination or plotting purposes) even though a lower or higher charge/discharge current is used.
Q: What is the effect of adjusting the SMOOTHING and, therefore, the SAMPLE RATE?
A: Increasing the SAMPLE RATE and, thus, the time between samples allows more time for the voltage to change. Larger voltage changes allows a more accurate calculation of the voltage curve’s slope and improved resolution and over all curve shape. However, too much time between samples, causes a loss in resolution and the curves (both graphed and ungraphed) start to get “chunky” and discontinuous even though the overall shape is good. On the other hand, too little time between samples produces “noisy”, erratic curves lacking evenness. Thus, correct optimization of SMOOTHING is critical for good plots and accurate charge termination.
Q: What is the time limit on CASP graphic plots?
A: For firmware 6.x and 7.x, it is unlimited. On some earlier versions of firmware there was a limit of somewhere around 40 hours, depending on the value of the “NumPass” variable in memory. The 6.x and later firmware use a dynamic interleaved memory storage scheme so the plot buffers never fill up.
Q: What is the maximum value for the CASP elapse timer?
A: The elapse timer can indicate a value of “59:59:59” before starting over at “00:00:00”.
Q: What can cause a FAILED HIGH IMPEDANCE error message?
A: This indicates that, while charging, CASP measured battery voltage above 95% of the pre-programmed “Rail Voltage”. Several things may have caused this:
- A defective battery, with one or more cells with high impedance.
- A “Rail Volts/Cell” value in the Cell table set too low.
- “Charge Amps”, “Number of Cells” or some other entry in the Battery Parameter table is set incorrectly.
- The cable is pointing to the wrong Battery Parameter table.
- The cable is pointing to an “empty” Battery Parameter table set to all zeros.
Q. After charging a battery, why does the charge amp hours reported significantly exceed the battery amp hour rating?
A: Several things might cause this:
- Most batteries require more charge to be put into the battery than can be drawn from it.
- Most new high quality batteries are rated conservatively and thus can accept and deliver more charge than the nominal amp hour rating.
- The battery parameter table used may have an entry error.
- There may be a parallel current path with the battery which, in constant current mode will extend the charge termination time, or, in constant potential mode will increase both the current drawn and extend the charge termination time (ie: a defective CASP discharge circuit or a battery still attached to an operating device).
Q: Does CASP “handshake” with their serial Epson compatible printers?
A: Handshaking is user selectable and is determined by the Printer Code in Table 099, 7th item, first bit. If the first bit is “0”, no handshaking occurs. If the first bit is “1” then full RS-232 handshaking is enabled. The latter is the recommended condition, particularly if the user is printing all of the battery parameter tables or doing large data dumps, otherwise some data loss may occur. Handshaking is required when the printer buffer becomes filled while a data stream continues to be transmitted.
Q: With a CASP/2500 set for AUTO PROCESS, why does a failed battery print detailed results, while a good battery does not?
A: The CASP/2500 has been designed to automate and simplify battery processing. If good batteries process uneventfully, no details need to be reported. However, should a battery fail and require special attention, the CASP was designed to offer comprehensive information so as to assist the operator in determining the best course of remedial action.
Q: Can I reprogram my old CASP/1100 or CASP/1200 with my new CASP/2500?
A: No because the CASP/2500 was configured to operate in an “automatic” mode. In order for it to do so, extensive software changes were required resulting in a sacrifice of this feature. Fortunately the TD-639, Christie’s PC/CASP interface software, is being replaced by the TD-700 which is a greatly improved PC-to-CASP communications package. The TD-700 runs under Windows 95, 98 and NT, and will allow complete and easy re-programming of Christie’s full line of prior CASP models. It will include, among many other features, uploading, downloading, editing and remote operation from a PC. TD-700 will be available by the end of 1999.
Q: Will a 220 VAC 50 Hz. line effect the ability to communicate with CASP using a Personal Computer and Christie communications software?
A: No. CASP should work fine at 50 Hz. There aren’t any line frequency dependencies in serial communications with CASP. If problems are experienced with PC to CASP communications or remote operation, it is most likely due to the connecting cable, a mismatch in baud rate (9600) between the PC and CASP, incorrect timing of CASP power ON or a defective or an incorrectly set Serial Communication Port on the PC. Also, TD-639 requires COM Port number 1. It will not work on higher numbered ports.
Q: What is the data acquisition rate for a CASP?
A: “Data acquisition rate” is not a very applicable term for CASP. However, the open circuit terminal voltage of the battery being processed is measured once per second throughout the processing cycle. In constant current mode, the current control point is set by the microprocessor and maintained at that value by an analog feedback loop. Thus, the current control has no digital “data acquisition rate” associated with it.
Q: Can CASP discharge current capacity be increased by connecting two (or more) channels in a parallel or serial configuration?
A: No. The same discharge power dissipation circuit is used by all channels. Two or more channels cannot access this circuit at the same time, and no benefit would be realized if they could. Also any attempt to do this could result in damage to the CASP that would not be covered by Christie’s warranty. However 2, 4, and 6 amps of additional CASP controlled discharge capacity can be obtained by using Christie’s CDC-65 Discharge Booster.