Can you overcharge nimh batteries

Overcharging older NiMH batteries can also cause hydrogen to build up inside the cells. When that happens, increased pressure can cause the battery cells to rupture, rendering the battery unusable. In some cases, the buildup of hydrogen can also pose the risk of explosion. Newer NiMH batteries are designed with vents in the cells and will emit small amounts of hydrogen to prevent this from happening. Also if the cell is being slow-charged, then the temperature rise will be less.

Negative delta voltage detection: The favoured method for detecting end of charge of a NiCd cell is to use the NDV - negative delta voltage method. This method detects a drop in voltage that appears as the cell becomes full charged. However when charging an NiMH cell it is found that only a small drop in voltage is seen.

An NiMH charger must be able to detect a voltage drop of around 5mV per cell. Therefore to reliably detect such a small voltage drop, sufficient noise filtering must be introduced into the NiMH charger to ensure that spurious pickup and other noise does not trigger the end of charge.

Using charge rates of between 0. With voltage changes of only about 5mV at full charge rates, the smaller changes arising for a slow charge are virtually impossible to detect. Additionally the temperature ises indicating end of charge are also much lower and not easily detected. Accordingly slow charging NiMH batteries and cells is not to be recommended. NiMH trickle charging As NiMH batteries are intolerant to overcharge, trickle charging tem has to be undertaken with care.

How to charge NiMH batteries: guidelines In view of the fact that NiMH battery charging must be undertaken in the correct manner, a few guidelines are often helpful. Never charge an NiMH cell with incorrect charger: It is never acceptable to charge a battery of any form with a charger that may be unsuitable.

NiMH cells cannot be charged with a NiCd charger as end of charge detection will not work. Charge at room temperature: NiMH cells do not like being charged at low or high temperatures. Check cell temperature : If an NiMH cell becomes hot then the charging should be terminated. Consumer chargers do not always terminate the charge correctly. Remove the batteries when warm to the touch. Manually check on charge status: With many lower end NiMH battery chargers there is a real possibility of overcharge and there may be no back up timed end of charge.

It is therefore wise to manually check whether the battery is likely to be charged and charging should be terminated. Check on fast charge capability: Although many NiMH cells can be fast charged it is not appropriate for all.

Check on the datasheet before applying a fast charge. It is easier to detect the end of charge point when charged in this way. It is therefore acceptable to fast charge with most NiMH cells. This way your battery will be automatically protected against overcharging. For newer versions of NiMH battery, trickle charging is not the way but still using the modern fast charger is not feasible. The common smart chargers that do not heat up the battery are safe up to any limit.

Stop If the Battery Heats Up — NiMH batteries cannot be allowed to heat up while charging or it will render the battery chemicals useless and seriously diminish the battery capacity. Try to charge the battery at room temperature. Also, it would be prudent to check in from time to time while the battery is charging.

Check it by touching the battery to see if it is warm. If the battery feels normal to touch or at room temperature, let it charge otherwise unplug and let it cool. Then start recharging after a short while. Avoid Overcharging — The battery cannot be left plugged in after it is fully charged. It negatively impacts the battery in every imaginable way.

But it is also not feasible to keep checking it every five minutes so; the easiest way to protect your NiMH battery against overcharging is to use a smart charger. These chargers stop the current supply after the battery is fully charged and you do not have to fuss over anything. Memory Charging — NiMH batteries have memory charging which means they remember the last charging cycle and use it as a base for the next charging.

So, they had to be fully discharged and fully recharged for this feature to remind the battery of the level it needs to charge at. If any battery is not charged properly as specified it charging capacity diminished with every cycle which eventually will lead them to perform so poorly that is simply not worth using anymore.

The current at which your battery can be safely charged is mAh. This battery type does well with trickle charging and the ideal current for that is 0. If you charge your battery using a charger of these specifications then your battery will run smoothly for a really long time. However, some diligence is required while selecting the battery charger.

This particular type of battery performs well and lasts much longer if it is charged using low current chargers that are easily available in the market.