Opel Ampera/Chevrolet Volt

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Zanimivo je da je napisano da je ohranjena le dobro in ne odlično?!! saj danes ob skoraj vsaki kanti napišejo da je odlično ohranjena.

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First of all, the need for cell-balancing is 100% normal. Any well designed EV energy system will include it. Generally it does not indicate a battery or cell issue exists, instead it is a means to improve performance and increase cell longevity. Cell balancing capability is necessary due to slightly different chemical concentrations within the cell electrolyte created during production, discrepancies in cell loading due to electrical connection variables, as well as cell temperature variations that can occur within the pack during charging and operation.

The Volt battery pack has a total of 288 ~3.75V cells and connected in a 3P96S arrangement with 3 cells connected in parallel and 96 of these cell groups (aka triplet) connected in series to create the 360VDC pack. The Volt’s Battery Management System (BMS) can trigger a 3-cell group/triplet balancing event anytime current is flowing through the battery (actively loaded) either during charging or discharging. It occurs when the BMS measured voltage of any group/triplet exceeds the average voltage for the 96 groups being monitored; by a preset amount, for a defined period of time.

Direct monitoring of the cell group voltages (and pack temperatures) is handled by four Battery Interface Control Modules (BICM) that are mounted on top of the different sections of the pack. These BICMs each communicate on a discrete CAN bus channel directly to the Battery Energy Control Module (BECM) and it then relays the collected pack data values to various other modules on the main GMLAN network, which includes the Hybrid Powertrain Control Module 2 (HPCM2) sometimes called the Vehicle Integration Control Module (VICM) the "manager" of the BMS.

Each of the 4 BICMs also includes an internal network of 24 transistorized switches that can individually activate and selectively place a load resistance across ANY of the particular cell group/triplet that BICM is connected to. However it is technically HPCM2 that manages the cell-balancing process and determines if/when any cell group is exhibiting a higher than desired “active” voltage (and SOC obviously) and if necessary communicates which group/s require balancing back to the Battery Energy Control Module (BECM). The BECM then communicates to the appropriate BICM requesting it turn on a particular switch and resistive load until such time it is able to “draw down” the offending triplet voltage to an acceptable voltage level.

Generally, this occurs quite infrequently on the Volt, attributed to very accurate quality controls present during cell manufacturing and the very consistent cell temperatures exhibited during operation (and charging) due the design of the Volt’s actively heated/cooled pack. In fact, in-house testing has shown that even during daily use, the Volt BMS spends very little time actually balancing any of the cell groups (triplets) and over a 6-month period of operation approximately 12-24 hours in total might be spent with any one of the 96 cell balancing channels "active".

Yes, the energy drawn by the BICM is converted to heat at the resistor, however due to the low applied group voltages (typically 2-4 volts) and high resistance of the applied dummy load, the parallel current flow thru the BICM is actually quite low. Therefore the system is able to quickly balance the offending cell behavior and any heat generated is simply dissipated by the load resistor to the surrounding airspace thru conventional heat-sinking that is surface mounted to the main board of the BICM.

Now in the case of the DTC P1EA4 it indicates that BICM 4 was requested to activate one or more of its cell-balancing resistors (by the HPCM2 and BECM) however internal active monitoring of the transistorized switch, indicates at least one of the transistorized switches did not turn ON or OFF properly. P1EA4 (as well as similar DTCs for the other 3 BICMs) is a type B DTC, which means it will only illuminate the MIL after 2 consecutive trip cycles with a detected FAIL of the diagnostic routine and during that period cell balancing capability will be disabled.

It is possible the triggering of this DTC was due to a temporary or intermittent condition within the BICM but if continues to set this DTC it will require that the pack be removed, opened up and BICM 4 replaced as a first corrective measure. Failing that, if the DTC persists the entire pack or section would probably be replaced, only due to the fact that portions of the wiring interface between the BICM and the individual cell groups is currently not something serviced separately in the field.


HTH
WopOnTour

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