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- What is the difference between Current (Amps),
and Power (Watts)?
- Power (Watts) is derived by multiplying the
application Voltage x Current required. Conversely
the amount of Current can be calculated by dividing
Power/Voltage where Voltage is the battery pack
voltage.
- Can different cells of same size and capacity
handle separate applications differently?
- Yes. NiMH cells can be designed to handle different
types of loads. For example, a cell that has high
capacity may not handle a high discharge rate.
Also a cell that has a high discharge rate may
not have high capacity. It is important to fit
the cell to the application, and not just look
for a capacity value.
- What is the self-discharge rate of NiMH?
- It is generally accepted that the self-discharge
rate of NiMH is 1/64 of the cell capacity per
day, however this can change slightly from cell
to cell. Environmental temperature can also accelerate
or decelerate this process.
- What is the best way to store NiMH?
- The best way to store NiMH batteries is in a
fully discharged state at 25°C with a relative
humidity of 65%.
- What are the methods for determining NiMH battery
pack available capacity at any time during its usage?
- There are several methods of determining capacity
of a NiMH battery pack, however some are not as
accurate as others. Probably the most inaccurate
method is to use the packs terminal voltage as
an indicator. This is due to the relatively flat
voltage profile of NiMH during discharge. The
most accurate method is coulombmetric counting.
In this method the current passing in and out
of the pack is measured and added or subtracted
from the capacity on record.
- Is a Polyswitch and a Klixon the same?
- A Polyswitch and a Klixon are not the same.
A Polyswitch uses a crystalline polymeric substrate
that becomes amorphic during an over current to
open the circuit. It can also be tripped by over-temperature
but is much slower in reaction. It should be used
primarily for over current protection. It should
only be used as a temperature device in the rarest
of applications.
- A Klixon uses bi-metal contacts that open when
heated to a specified temperature. The Klixon
also incorporates a conductor that acts as a heater
during over current which forces the Bi-metal
contact open. It should be used primarily for
temperature, but is also a good current protection
device.
- Should NiMH batteries be "Float" Charged like
Lead Acid batteries?
- No. The voltage profile of NiMH is unlike that
of Lead Acid. However modifications may be made
in rare instances, but only under the guidance
of engineering.
- What is a "C" rate?
- A "C" rate is a value of current (Amps) equal
to the rated capacity of the cell. So a 1000mAh
cell would have a "C" rate of 1000mA. "C" can
also be expressed as a proportion. An example
would be "C/2". For a 1000mAh cell "C/2" would
equal 500mA.
- What is the self-discharge rate of Li-Ion?
- The self-discharge rate of Li-Ion is very low.
We can expect to see between 1%-3% per month with
the Li-Ion technology. This compared to the NiMH
chemistries 40%-50% per month.
- What is the best way to store Li-Ion?
- The best way to store Li-Ion is at 40% at 25°C.
Storing Li-Ion in this manner will provide for
98% of initial capacity after 1 year. If the cells
were stored at 100% charge there will only be
96% or less. Fully discharged storage is not recommended
because Li-Ion does not accept overdischarge well.
- What is a PCM?
- A PCM (Protection Control Module) is a PCB used
to enhance the safety of a Li-Ion battery. It
accomplishes this task by monitoring voltage and
current. It will open the circuit between the
battery and charger/appliance when the voltage
goes over or under the pre-defined levels. It
will also open the circuit if the current reaches
a level that is not safe. This type of board is
needed on all Li-Ion packs.
- Is Li-Ion charged differently than NiMH?
- Yes! NiMH is generally charged using a "Constant
Current", where Li-Ion uses a "Constant Current/Constant
Voltage" charge method.
- What is the range in voltage of unloaded NiMH
& Li-Ion cells from 100%-0% state of charge?
- Most could tell you that the nominal voltage
of Li-Ion and NiMH is 3.6(7)V and 1.2V respectfully,
but that is only part of the difference. NiMH
cells have an unloaded full charge voltage of
about 1.35-1.40V and an end of discharge voltage
around 1.00V. During 70% of the discharge, @ rates
less than 1C the voltage will be stable above
1.2V. Li-Ion on the other hand has a full charge
voltage of 4.20V and a discharge termination voltage
of 3.00V. The Li-Ion voltage will have a linear
decreasing voltage from 4.2-3.0V.
- What is a SMB or SBS compliant gas Gauge?
- SMB (System Management Bus) or SBS (Smart Battery
System) are industry standards that allow for
battery pack/application communication. The standard
communication protocol is SBS 1.1. This protocol
is integrated into a PCB that is attached to the
battery pack. Cardio Dynamics uses this technology.
- Do we have Gas Gauges in stock?
- No. We do not have Gas Gauges in stock. This
item must be customized for each application individually.
There are lead times involved when producing a
new application gas gauge
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