Last month we spoke about Lithium-ion (Li-ion) batteries. But Texcel doesn’t actually use these batteries in its GTMs and ETMs – we use the NiMH battery type. So it makes sense to discuss these battery types too.
What is a Nickel Metal Hydride battery?
The NiMH battery is a development on the Nickel-Cadmium (NiCad) battery. In the NiCad battery, the negative electrode is cadmium. The NiMH battery replaces the cadmium electrode with a hydrogen-absorbing alloy. The major advantage of this change is that cadmium is highly toxic. The downsides are that NiMH is more expensive and less efficient.
This type of battery was first launched in the early 1990s and by 2010 the world was producing over 1 billion cells annually.
However, it is now generally accepted that over time, Li-ion batteries will replace them in most applications.
Why are they good?
- High power – up to 1,500 W/kg.
- Packaging flexibility.
- Long life.
- Wide operating temperature (-30 to +800C)
The NiMH battery has dominated the hybrid electric vehicle (HEV) market for these reasons.
How do they compare with Li-ion batteries?
- They tend to be preferred in the HEV market because of their greater operating temperature range, lower risk of fire, they are less expensive, and they are easier to recycle.
- On the other hand, they cut power suddenly when they run out of charge rather than slowly running down. They also self-discharge over time, so that if they are left sitting around, they need recharging before use.
- For these reasons, the electric vehicle (EV) market prefers the Li-ion battery.
- In addition, the Li batteries have a higher energy density and are light weight.
Recycling:
NiMH batteries are regarded as “environmentally friendly” in that they are relatively easy to recycle. Nickel (and iron) from batteries is used as an alloy in stainless steel, so is profitable to recover.
Texcel’s use of NiMH batteries:
The properties Texcel takes advantage of are:
- The wide operating temperature – not only do some monitoring locations become very hot in summer, but they can also become very cold in winter!
- The packaging flexibility allows Texcel to shape the packaging to fit efficiently into both the GTM and the ETM.
- Freight issues – as a general statement, there are fewer issues associated with shipping NiMH batteries than there are with Li-ion batteries, an important issue for Texcel.
How does Texcel deal with the self-discharge issue inherent with NiMH batteries?
As noted above, NiMH batteries do discharge over time if they are left sitting around, so they do need to be recharged before use.
The most important thing Texcel does is to provide a “smart” charger with all monitors. This charger will start a “fast charge” when it is first connected but will then fall back to a “trickle charge” once certain conditions have been met.
