Troubleshooting Lithium Ion Battery Issues

troubleshooting-lithuim-ion-battery-contactor-failure

Or: With Great Complexity Comes Great Responsibility

troubleshooting-lithium-ion-batteryModern lithium ion batteries (generally LiFePO4 based) are an interesting mix of being more complex and, simultaneously, simpler to use than conventional lead acid batteries (flooded, AGM, or gel batteries). They weigh a fraction the poundage of conventional batteries, store much more power, charge much faster, do not off-gas during charging and  there is no additional maintenance required – no water added, no other extra requirements other than managing charge and discharge.

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Lithium ion batteries also generally come with a Battery Management System (BMS)* that prevents over charging or discharging by opening an electronically controlled contactor to disconnect the battery. Since over-charging or discharging too deeply is the number one source of damage to rechargeable batteries, this is a major advantage indeed, especially given the high cost of lithium ion batteries compared to their lead acid counterparts.

It does however, make the system a bit more complex in implementation and troubleshooting – and knowing enough to recognize problems and troubleshoot them is really incumbent on the owner. Should a component of the BMS fail to protect the battery from over discharge, you can easily, and permanently, damage the battery severely shortening the life of an expensive piece of equipment. Should the BMS fail to protect the battery from overcharge however, the consequences can be much more dire.  If a cell reaches a critical threshold (the exact threshold varies depending on the specific chemistry) the battery can literally catch on fire. Leaving aside the expense, logistics, and time involved in having a professional troubleshoot your electrical system, safety alone mandates that the owner needs to be the first line of defense.

Understanding Your Electrical System is Critical

It was really driven home to me just how important really understanding how your electrical systems work when I encountered a particularly strange problem with our 1998 Foretravel U320‘s, newly renovated 12-volt electrical system. The new 12 volt system was prematurely showing a high voltage that indicated a complete charge, but was, at the same time, generating under-voltage alarms after only discharging on minor loads for a short period of time. I adjusted the solar panel charge controller voltage settings to see why they weren’t charging right and spent hours scratching my head and cycling through potential scenarios to find one that fit the symptoms. More head-scratching, research and testing ensued.

Long story short, after a LOT of testing the voltages at various points in the system with a multimeter, we finally determined the source of the strange voltage readings. It turned out that the contactor, which is the part of the BMS that opens the positive feed to or from the battery to protect it from an individual cell becoming over or under voltage, failed in a singularly unusual way. Testing showed that the contactor had developed an internal resistance that was causing roughly a 1 volt differential across it. This played hell with trying to charge the battery. The 12 volt system bus voltage would read 14.3+ when the battery was actually only at 13.3 volts. Then, when we started discharging, the battery would read 13.2 volts while the 12 volt bus voltage was only 12.2 volts at rest, and substantially lower under load.

Upon examination, it became obvious that the contactor was the source of the problem as it showed fairly significant evidence of having sustained a large surge of power. Note the blackening around the post? Luckily, when we ordered our battery I had an extra contactor installed to handle connection to the alternator, but we didn’t end up using it, so I actually had a spare contactor identical to the one that failed sitting right there on the side of the battery. Fifteen minutes of work (taping all electrical cable ends as I removed them, etc) and the failed contactor was switched out for the spare. After replacing the contactor, the voltages returned to normal values and the entire system returned to working as designed.

Why Did it Fail?

Why did the contactor fail in the first place? That’s still an unknown, though my money is on an electrical casualty we suffered when we hooked up to a power pedestal at a campground that had some internal damage and fried one leg of our 50 amp service panel on the bus (Learn from our mistake – always use a surge protector!). Replacing the damaged breakers seemed to restored all functionality, or so we thought.  Our inverter/charger later developed some issues, so our current working theory is that the inverter caused a voltage spike that damaged the contactor. It’s also possible that it was originally damaged during installation of the system, and it just took some use of the system to develop the actual failure. We’ll probably never know the exact cause, but operating with a damaged contactor was crippling the entire 12-volt system, as well as creating a potentially hazardous situation and/or a damaging fire.

What are your thoughts? Are the benefits of lithium ion batteries worth the added complexity? How important do you think it is to understand your system yourself as opposed to seeking the opinions of a trained service technician?

  • sometimes also known as an Energy Management System (EMS) or in the case of our specific Balqon unit, an Energy Storage System(ESS).

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