Nickel Metal Hydride Batteries (Nimh) - ROBBE PROFI Notice D'utilisation

13.2

NICKEL METAL HYDRIDE BATTERIES (NIMH).

In the last few years, modern nickel metal hydride batteries
(NiMH) have developed as a real alternative to NC batteries.
They are now capable of bearing high currents and can there-
fore be used as batteries for remote control systems as well as
drive batteries. As a rule, they offer 1.5 times the capacity than
NC batteries with the same weight and are also environmen-
tally friendly.
Charge rate
The term "charge rate" (C) has established itself for the size of
the charge and discharge currents. It creates the connection
between the charge current and the battery capacity.
If, for example, a battery with a capacity of 600 mAh is to be
charged with a rate of '1 C', then there must be a current of
600 mA flowing.
Forming
A new battery, or one that has not been used for a long period
of time, must be formed before use. A battery which was
exhaustively discharged, which can lead to some of the cells
having their polarity reversed, must also be formed again first.
The battery is formed over 24-26 hours with a charge rate of
0.1C. The Profi Homecharger has the regeneration mode (D/C)
available for this purpose.
Charging
A charge rate of up to 0.1 - 0.2 C is called normal charging.
Since you can always charge the battery more than you can
discharge, the charge time for normal charging with 0.1 C is
not 10 hours but 16 hours. That means that the overcharge
factor is 60% for normal charging. Longer charging of this type
damages the battery and should therefore be avoided as the
electrical energy introduced is not longer saved, but chemical
processes are released which reduce the service life of the
battery.
There is an accelerated charging if a charge current flows at a
level of 0.3 - 0.5 C.
Quick charging is when you charge the NiMH batteries with
rates of more than 0.5 C.
With larger charge rates than 0.1 C, the charge current must
be interrupted as soon as the battery is fully charged. The digi-
tal delta peak process, for example, is suitable as disconnect
criterion. This evaluates the undervoltage which occurs when
the battery is completely charged up.
Depending on the level of the charge rate, a battery builds up
different crystal structures. For this reason, with high current
discharging of drive batteries there must be a quick charge.
The higher the charge current selected, the lower the voltage
collapse during discharging.
We recommend the following charge rates for NiMH batte-
ries:
High energy batteries, 0.5...1 C, please also observe the bat-
tery manufacturer information.
High current batteries, usually 1C, some battery types can be
charged with 1.5...2C. Observe the maximum charge current
details of the battery manufacturer.
Profi-Home-Charger
25
Self-discharging
NiMH batteries lose about 1.5% (at 20°C) of their charge per
day. After approx. 75 days the full battery is completely
discharged. Batteries must therefore be recharged before use.
Storage
If a NiMH battery is not to be used for a foreseeable amount of
time, store it in a cool and dry place (10 to 30°C); the battery
should have a capacity of at least 30...100% before storing.
Then, after one forming, the battery will gain nearly its full
capacity.
Service life
Depending on the application and use of the charge proce-
dure, NC batteries have a service live of approx. 500 to a maxi-
mum of 1000 cycles. After this the battery is used up and must
be disposed of in an appropriate manner.
Temperature
The NiMH battery heats up very markedly during high current
discharge. The cells must therefore be cooled down before
charging. A warm or even a hot cell absorbs less charge and
can accordingly release less energy.
Discharge end voltage, exhaustive discharge
Measured under load, the permissible discharge end voltage is
approx. 1 volt per cell (this is automatically set by the Profi
Homecharger).
Exhaustive discharge will occur during further discharging.
This can lead to pole reversal of one or several cells. Pole
reversed cells change their polarity.
There is minus potential at the plus pole and plus potential at
the minus pole (if there is low loading check with the voltme-
ter). If at all, cell defects can be prevented only by immediate
14 - 16 hour normal charge.
Avoid exhaustive discharges with NiMH batteries; exhaustive
discharges can lead to irreparable cell defects.
When handling NiMH cells, some safety precautions must
be observed to prevent bodily injury or material damage.
You assume responsibility when using these batteries.
- Never allow NiMH cells to come into contact with open fla-
mes as there is a risk of explosion.
- Never open NiMH cells with force as there is a risk of acid
burn.
- Never short-circuit NiMH cells as there is a risk of burning
and explosion.
- Never allow secreted electrolyte to come into contact with
skin or eyes. If this should happen by accident, rinse gene-
rously with water and find a doctor. Never put batteries in
your mouth as there is a risk of poisoning.
- Never solder with the solder iron on the cell casing.
- The minus side of the cell is particularly sensitive.
- A charged NiMH battery is not a toy. Batteries should be
kept out of the reach of children.
- Observe the information from the corresponding battery
manufacturer when charging and discharging.
Order No.
8194