After a year on the road with his converted 1993 Volvo 850, Udo thought it was time to sit back and ask himself: What would he have done differently, if he had known then what he knows now?
Well, Udo wishes he had paid more attention to moisture/humidity in electric systems.
Although he carefully protected connections, cables and the battery boxes against water from the outside, it turned out that the issue is more complex. For example, the battery boxes contain air that can condense.
Twice so far, the BMS has delivered weird voltage values when Udo was driving in cold and rainy weather: the lowest voltage was around one volt, the highest was five volts. The suspected but likely cause of these mis-readings: too much humidity in the battery boxes.
If the voltage values are outside the defined range of 2.5 to 4.2 volts, it is the job of the BMS to stop the provision of electric power. This means that stepping on the gas pedal has no effect. The vehicle can no longer be accelerated. Fortunately, this “weird voltage”-phenomenon only occurred briefly. Udo was able to continue his trip after a few seconds of alarm.
A way to keep humidity in electric systems under control is silica gel (dessicant) as it has the ability to absorb moisture. That is why we often find small silica gel bags in the packaging of electronic products.
The lesson learned for Udo is that he should have built all three battery boxes in such a way that he could easily open them at any time – to check on moisture and to insert/replace silica gel packets if necessary.
In Udo’s conversion, only battery box 1 in the back of the car can easily be opened and checked. Box 2 is mounted on the underbody and box 3 in the engine compartment. Both are sealed in a way that makes opening and closing difficult.
As moisture/humidity is also an issue in electric vehicles in general, OEMs and their suppliers have to cope with it, too.
For example, the German supplier Mann+Hummel introduced an “active battery venting sorber”. It features a fan that promotes air flow in regeneration mode, a desiccant cartridge to absorb moisture, and a heater to regenerate the desiccant. The unit also includes a protective membrane to keep out dust and water. Watch the video and get a better understanding of humidity issues (starts at 3.25 min.) and how to solve them.
So, it is highly recommended to take moisture seriously in your conversion project and think of ways how to control it during operation.
Therefore, it might be a good idea to educate yourself. Learn, for example, more about moisture problems in EV battery packs here.
Also, you can find more information on silica gel here.
