Chargers
There are two types of chargers: manual and automatic. Manual chargers require constant supervision. If not shut off after the battery is charged, damage may occur to the battery. Therefore, an automatic charger is recommended since the charger automatically monitors the charge. An automatic charger will decrease the rate of charge when it senses the battery becoming close to a full charge; it effectively shuts off when a full charge is reached. However, some charging does still continue so a charger should not be left attached to a battery for over 24 hours.
If a battery is overcharged, permanent damage to the battery may occur. 24V automatic chargers (Figure B) allow both batteries to be charged simultaneously; consequently they cannot be used with a single 12 V battery. Chargers are designed for either wet-cell lead-acid batteries or gel-cell lead-acid batteries. Therefore, the appropriate charger must be purchased to match the battery. If an incorrect charger is used, permanent damage to the battery may occur.
Multipurpose automatic chargers exist which allow charging of either a wet-cell lead-acid battery or a gel-cell lead-acid battery (Figure B). However, care must be taken to select the appropriate settings on the charger.
A final consideration in the selection of a charger is the country in which the device will be used. This is important because of the different power transmission standards in different countries. For example, in the United States, the standard for power transmission is 110 V at 60 Hz, whereas in Europe the standard for power transmission is typically 220V at 50 Hz.
Recently, manufacturers have begun to integrate the charger into the design of the power wheelchair (Figure C). This is advantageous, since the power wheelchair can be recharged anywhere there is an outlet. Since these chargers are single purpose chargers, they typically can be used on only one type of battery (gel-cell or wet-cell) and in only one country, which may be a drawback.
Safety
Safety issues should always be considered.
- Sensors should be built into the charger and wheelchair to detect if the connections between the battery and wheelchair and between the battery and charger are correct. If incorrect connections are detected then the wheelchair and charger should automatically shut down in order to prevent damaging the wheelchair, charger or batteries.
- The wheelchair, charger, and batteries can also be protected by using specially configured connectors that only allow proper connections, similar to a three-prong wall outlet, and by color coding the connectors.
- If a single purpose charger is purchased, the charger should match the charging characteristics required of the battery;
- The charger must meet the power requirements of the local country’s power supply; and
- The power wheelchair should become inoperable when the batteries are being charged.
