Archive for the ‘Batteries’ Category



I think that it is worth saying something about batteries.
In some situations it is well worth using rechargeable nickel-cadmium cells, these can be recharged many times and although you do have to buy a battery charger, and the cells themselves are not cheap but they will save you a lot of money in the long run.
You can buy solar battery chargers which are a really neat idea, indeed some of these solar battery chargers will even power small electrical items.
There are many new types of battery on the market some of which last for a very long time.
When the hospital buys or is given a new piece of equipment that uses batteries, do check that you can get replacement ones when you need them, if you can’t you could be in trouble.
Also, remember that batteries are expensive to buy and don’t store well so a mains or low voltage operated instrument may be a better option.
When an item using batteries is not in use do encourage the staff to take them out of the instrument, this can save you a lot of work should they corrode inside.
It is worth telling you about car type batteries, should you have to mix up a new mixture of acid and water, that you must ALWAYS add the ACID to the WATER. NEVER the other way around.
Remember ACID to WATER.

If you have a car battery to take out of a vehicle please do as follows. In cars, the negative electrode is connected to the body of the car. Always disconnect the negative connector of the battery first. If your spanner comes into contact to any metal part of the car while unscrewing nothing will happen. If you would start with the positive terminal and the spanner comes in to contact with the body you would cause a short circuit that could be dangerous, an extremely high current will flow and a spark could ignite fumes from the battery, I have seen it happen. After disconnecting the negative terminal you can now safely disconnect the positive terminal, now any contact with the car metalwork will have no consequences.
Installing the battery is the other way round.
On the matter of recharging batteries, you should remember that you cannot recharge ordinary torch type batteries only those that clearly say rechargeable on the outside.
You cannot use the same battery charger on lead acid batteries as on nickel-cadmium batteries.
Lead acid batteries need a constant voltage source for correct charging, nickel-cadmium (NiCad as they are some times called) batteries need a constant current source. The internal circuitry and control in each type of charger are different and the use of the incorrect type will almost certainly mean permanent damage to your batteries and could even cause them to explode.

Sealed lead acid batteries of the type used in wheelchairs also need their own type of charger.
Here are a few different sorts of batteries that you may come across in hospitals and some facts about them.
First some terms you may come across and used to describe what batteries do and how they do it.

Cycle life: indicates the typical number of charge/discharge cycles before the capacity reduces from the nominal 100% to 80% (65% for re-usable alkaline)

Fast charge time: is the time required to fully charge up a completely discharged battery.

Self-discharge: shows the discharge rate of a battery when it is not in use. Moderate means 1-2% capacity loss per day.

Cell voltage: multiplied by the number of cells tells you the battery terminal voltage.

Load current: is the maximum recommended current the battery can provide.

Exercise requirement: shows how frequently the battery needs exercising, charging and discharging, to achieve maximum service life.

Nickel-cadmium (NiCd).
Used for many portable medical appliances. They have good load characteristics are cheap and simple to use. They do not like being on charge all the time and only being used occasionally. They do like to be completely discharged now and again say once a month, if you don’t you will get what is called memory because of crystalline build up inside and the performance goes down.

Sealed lead acid. (SLA, sometimes called Gel batteries)
Used for medical equipment, wheelchairs, uninterruptible power supplies where the energy-to-weight ratio is not critical and low battery costs are desirable.
These can be left on float charge for long periods, they retain their charge for 4 times longer than a Nickel-cadmium battery. They do not like being fully discharged because they sulphate up.
Charge times are longer than a NiCd, 8 to 16 hours. They should always be left stored in a charged state.

Reusable Alkaline.
Used for light duty applications. Because of its low self-discharge, it is good for applications that are only used occasionally.
They do not like being completely discharged this shortens their life considerably.

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