Because I was very concerned about the high temperatures of the batteries in the charging process, I’ve decided to do an experiment called "Refrigerated Charging". The problem is even greater in longer charges which includes 4 hours of equalization. In the last charge, done by the traditional way, when I arrived to the bike she marked 41ºC.
As you know, the NiMH batteries have their ability affected when they reach high temperatures. From the 35ºC begins to be worrying and the higher the temperature the greater the danger of damage.
So, I’ve started an experiment with the following ingredients:
- A large plastic (7€);
- A portable air conditioning (AC) (300€);
- A Vectrix (8650€).
The idea is to provide cold air when charging the Vectrix. Since the air admission is made by the front, I’ve covered both the AC and the front of the Vectrix with the plastic, to reduce the space and increase the cooling efficiency. The hot air flow out of the AC tube was placed near a window.
The initial conditions:
- Ambient temperature of the garage: 29°C;
- Air temperature out of AC: 20ºC;
- Temperature of the battery (Vectrix indication): 35°C (after the deep discharge).
After the period of 30 minutes of ventilation (pre charging phase);
- Temperature of the battery (Vectrix reading): 30°C;
- Temperature measured at the outlet of the ventilation of Vectrix (rear end): 25°C.
After the full charge process (all phases) took about 10 hours. With 30 minutes of ventilation included, about 2.5 hours of charging, ventilation +1 hours, 4 hours of equalization, plus a few more procedures that that I could not trace because I was sleeping, produced:
- Ambient temperature in the garage: 26°C;
- Temperature of the battery (Vectrix reading): 25°C;
- Final stabilized voltage: 147V (Maximum noticed 149V, usually a normal charge produces 144V stable).
So I am happy to notify the success of my intents! Certainly it is not a convenient way to apply every day but for longer loads in enclosed and warm places, maybe can be a nice option to consider. This procedure can maintain the quality and expected life of batteries that worth much more than the cooling energy spent. Without the cooling system, I estimate that the batteries (in that conditions) would reached 45ºC (ie above 20ºC than what it was), this value make sense to me but I do not want to try it because it is known to be quite harmful to the batteries. The estimated value it is based on previous conditions (on the day before) that with a little more favorable and less loading time had reached to 41ºC.
This procedure is recommended for those who want to take care well their batteries in hot places. It is especially important when it is done a deep discharge as generally it does also the long equalization and a few more steps that I do not know what they are. This happens only in the latest version of the software (Oct 2008) and can last up to 10 hours.
In the next deep discharge (sometime in July), I will record on video all the phases and submit them here for us try to understand it. Until then, spare batteries for your Vectrix, I know I will.
(sorry my English)