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48-Volts and beyond: Hybrid changes and DTC tips

Tuesday, January 1, 2019 - 08:00
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P0A80 – Battery performance

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While the first two DTCs may not appear on the newer 48-volt micro hybrids this battery performance DTC will most likely be applicable to just about any hybrid or EV on the road regardless of voltage levels. The P0A80 is a generic DTC and the reason a lot of battery packs get replaced. This DTC basically says the hybrid battery pack “smart” module has detected a variation exceeding 0.3 volts between pairs of battery modules. Battery modules in the case of the older (and popular) NiMH battery packs are either cylindrical (appearing like large D-cell flashlight batteries) or prismatic (flat rectangular) groups of six 1.2-volt cells in series equaling 7.2 volts. Two NiMH battery modules are then wired in series to comprise a battery block (Figure 6).

Figure 6 - Measuring between these points with a DMM for each pair of HV battery pack modules (called V-blocks by some OEMs) confirms what the smart battery unit / battery control module (A) measures and displays on your scan tool. Contactors (B) a.k.a. relays close when commanded to connect the battery pack’s output to the vehicle’s high voltage cables.  Higher voltage systems require another contactor (C) and power resistor (D) to reduce high current inrush into the inverter on power up.

The battery blocks are then wired in series within the pack to comprise the HV battery pack’s total voltage. The battery control module/smart battery unit monitors the internal resistance, temperature, voltage and current draw of the total battery and its individual blocks. If the blocks are not nearly identical in voltage under various conditions, the module with flag this DTC. However, diagnostic charts for this DTC can be a bit confusing (Figure 7). The charts instructs techs to use a scan tool to monitor the voltages between the various combinations of blocks. You’re supposed to replace either the battery pack or the battery control module depending on the outcome of the battery block voltage comparisons. The key word is “ALL” in the chart when the question is posed regarding “are all the battery block voltages greater than 0.3 volts from each other?” Toyota makes this distinction clearer than Nissan by stating that a common symptom of a faulty battery control module (battery smart unit) is ALL of the battery blocks being 0.3 volts different than each other.

(Image courtesy of Toyota) Figure 7 - P0A80 - Numerous HEVs, including Toyota, lead technicians through a process of observing battery block PID voltages. A faulty pack will typically have a few blocks (two 7.2-volt battery  modules connected in series equals one 14.4-volt battery block) with voltages varying over 0.3 volts from each other. If ALL the block voltages are greater than the 0.3 volt spec from each other, the Electronic Battery Control Module (battery smart unit) is faulty.

48 volts? Again?

Didn’t the industry already try that once? Forty-two-volt dual voltage systems were designed and ready to implement in the late 1990s. The 42-volt systems did NOT make it from the engineering labs of OEMs and into consumers’ driveways outside of the few exceptions of GM’s early BAS (Belt Alternator Starter) blue cable models and the PHT (Parallel Hybrid Truck). Neither the 42-volt BAS or PHT technology had the latest Li-Ion high output/low-weight battery packs that today’s HEVs and EVs are equipped with. Inverters and DC-DC converters used IGBT (Insulated Gate Bipolar Transistor) technology that was state of the art then. A new technology referred to as the “Viper inverter power switch” by Tier 1 OEM supplier Delphi Technologies allows for new inverters and converters to be 40 percent lighter and 30 percent smaller. This leads to a 25 percent higher power density increase. The Viper power inverter switch also does away with wire bonds and tedious connections, which can lead to quality and reliability issues.

Figure 8 - Watt’s Law displayed tells the story mathematically why 48-volts is better than 12. Same wattage (electrical work) means lower amperage (and cable size) when system voltage is higher.
(Image courtesy of Delphi Technologies) Figure 9 - Adding to the weight and cost advantages of 48-volts are the smaller power electronics (DC-DC converter on left) and common chassis grounds (center) shown in this photo with an uninsulated connection of the two brown negative cables. Sealed connections for the 48-volt positive circuits (blue cables) are maintained for safety’s sake.

Unlike more complex and higher voltage HEVs/EVs, a 48-volt system will not propel the vehicle around town without the gas engine contributing power. Then why bother? Increasing voltage for high wattage accessories and functions is fueled by a simple electrical principle called “Watt’s Law” (Figure 8). The higher the voltage, the lower the amperage required for a given electrical work requirements (watts).  While higher voltage systems are typically required for propelling the vehicle without the I.C.E., the extra voltage that 48-volt systems afford have a fair amount of other benefits. A 48-volt system is quite adept, being able to spool up an electric super-charger to launch the vehicle faster and smoother, eliminating turbo lag. Other heavy electrical (high wattage) load such as A/C compressors and electric power steering motors will run more efficiently on 48 volts as well.

48-volt system safety and simplicity

GM advised technicians back in their small niche 42-volt era (BAS/PHT) to practice similar safety precautions they were in the habit of doing on higher voltage systems during the service of the high-voltage side of the vehicle. OSHA regulations however, are laxer with voltages under the 50-60 volt region that borders the realm of injurious to lethal. This eliminates the need for heavier and more expensive circuits that lead to DTCs such as P0A0D and P0AA6. That means 48-volt and 12-volt systems can both share a chassis ground (Figure 9).

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