Instrumentation - FAQs

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I just installed a new battery gage. The gage indicates “full battery”, but I know that this battery has been in use for several hours, and the battery capacity is much lower than “full”. Why does the gage show Full?
A new gage installed for the first time will read “Full” (the final step of our Quality Control procedure is to reset the gage to full). As vehicle use begins, the energy from the battery is used, and the gage will move quickly through its steps to “catch up” with the true battery capacity. The process of the gage dropping from full to empty will take at least ½ hour on a loaded battery.
How does the instrument measure the discharge of the battery?
The instrument measures the Voltage under Load below a ‘reference”. As the vehicle is operated, the load on the battery causes the voltage to drop below this reference level. The gage will accumulate the time the voltage is below the reference. When the voltage is below the reference for a sufficient period of time, the gage will reset its timer, lower it’s reference, and indicate a lower state-of-charge. This process is repeated until the gage reaches “empty”. If the load is removed from the battery, the voltage will rise above the reference, the timer will stop, and the gage will continue to indicate the current state-of-charge. This technique of voltage-time integration to calculate the battery state-of-charge is far more accurate than using a simple voltmeter.
Why is it important that the wire from “Battery Plus” connects to the first positive vehicle connection (before all switches and fuses), and the “Battery Minus” wire connects to the first negative vehicle connection ?
Every wire has a resistance, which will produce an additional voltage drop when there is a load on the battery. The intent is for the instrument to measure the drop in voltage (under load) of the battery. If there is an additional resistance (extra wire, keyswitch ,etc) that causes an additional drop in voltage, the instrument will behave as if the battery voltage is dropping lower than it really is, and the gage will show “empty” before the battery is “empty” Voltage under load measured at the battery, should be within 1% of the voltage at the instrument terminals B+ and B-". Example: a load on a 24 volt battery causes a voltage reading of 22.6 volts when measured at the Battery Terminals. The same load, when measured at the B+ and B- terminals of the instrument, is 22.2 volts. (a .4 volt difference. .4 divided by 22.6 = approx. 2 %. This is not an acceptable installation.
Will Curtis BDIs work on Sealed Lead-Acid Batteries?
Yes, if the Discharge Setting is correct. Although each manufacturer’s sealed battery may have it’s own unique characteristics, we have found that the setting “R” (which has an “empty” voltage under load value of 1.86 volts per cell) is appropriate for most sealed (VRLA- valve regulated lead acid-) applications.. Curtis Model 803 has a wide range of adjustment, and is therefore recommended for sealed (VRLA –valve regulated lead acid-) batteries.
I have a Curtis 802 (or 803) installed, and it always reads “Full”? What is wrong?
Model 802 is “ Dual Voltage” gauge. Your gauge may be connected to the wrong “Battery +” terminal. The 2436 model has the ability to measure a 24 volt battery OR a 36 volt battery, depending on the wiring. There are 2 terminals on the back of model 802: Battery HI ( Pin1), and Battery + LOW (Pin5) . If the gauge is installed on a 24 volt battery, then the Battery + “Low” terminal is connected (because 24 is ‘lower’ than 36). In this case, no connection is made to Battery + “High” --- If the instrument is measuring a 36 volt battery, then the Battery + High is used, and no connection is made to Battery + Low.
I have a Model 802 BDI (or 803) installed and it goes rapidly down to Empty and stays there. What is wrong?
For a 2436 Model that is being installed on a 36 volt battery, you must connect “Battery + High ” (because 36 is ‘higher’ than 24) and leave “Battery + Low ” unconnected.
Resetting the Gage to Full: What is the difference between OCR, HVR, and CTR?
OCR (Open Circuit Reset) -- This method of resetting the gage to Full is used in applications where the battery is charged while disconnected from the gage. (typical of forklifts). When the battery is disconnected, charged, and then reconnected, Curtis models with OCR will reset to Full (‘jump’ to Full), IF the voltage is greater than the OCR reset level voltage. Example: 900R24BN. The “B” in this model means that the open circuit reset level is 2.09 Volts per cell. (12 cells x 2.09 = 25.1 volts); if the gage sees a voltage higher than (approximately) 25.1 volts per cell, it will reset to Full. HVR (High Voltage Reset) – This method of resetting the battery to Full is used in applications where the battery is charged while connected to the gage (typical of golf cars and scissors lifts). The gage will reset to full when the charging voltage exceeds the HVR reset level, and maintains it for 6 continuous minutes. Example: 900R36HG: the H reset level is 2.35 volts per cell (18 cells x 2.35 = 42.3 volts) When the charging voltage exceeds (approx.) 42.3 volts and stays above this level for 6 continuous minutes, the gage will reset to Full. (Note: 900RBN models include both HVR and OCR) CTR (Charge Tracking Reset). This method of resetting to Full is useful in applications where the battery is partially charged before being put back into service. Models with this feature will track and display state of charge incrementally when the battery is being charged. Model 803 and 3000 series enGage models have CTR.
What is the difference between a Curtis BDI and a Voltmeter?
A voltmeter will show the instantaneous voltage. When a load is put on the battery (such as lifting a pallet of 180 cases of beer), the voltage display will fall to a low reading, and then go back up when the lift has been completed. With a voltmeter, it is difficult to tell the battery state-of-charge. The Curtis BDI uses an algorithm that monitors the battery when it is under load. The battery state-of-charge is displayed in a Full to Empty display (like an automobile fuel gage).
Will Model 906 12volt work with a 12 volt Nickel-Cadmium (NiCad) battery?
Probably not. The voltage response for NiCad batteries is very “flat” which can make it difficult to track. However, if data on a specific battery model is available, we can evaluate if we have an appropriate BDI for a particular application. Please check with Curtis Applications Engineering Dept. The Curtis 933/3 (or 803) shows Empty too soon. I only get 2-3 hours of work from the battery and the Specific Gravity is 1200. I’ve double-checked the installation of the gage, and it is correct. If a battery is being discharged at a high rate, the SG that corresponds to 80% discharged will be significantly higher than if the battery is being discharged at a lower rate. For a certain battery type, a 600 amp-hour battery with a constant load of 100 amps is being discharged at the 6-hour rate. The SG at 80% discharge for this battery is 1.180. If the truck using this battery did very heavy work (an average load of 222 amps (2-hour rate), the battery is no longer a 600 amp hour battery in terms of useable capacity. In this instance, the useable capacity of the battery (at this high discharge rate) is 444 Ampere hours. The 80% Specific Gravity corresponding to 80% discharge is approximately 1.220.