Battery/Regulator query

[Cossaro]

It looks like you are running Lithium ion batteries cossaro. How much extra detector time did you gain after making the modifications?

the original one have 1000 mA, the new Panasonic Lithium have 2200 mA and 80 gr. lower weight, the extra time is simple to compute... 2200/1000 = 2.2 x

Yesteday i've tested on field, and found some difference on my sover:

1) better stability on max sensivity

2) non need to retune the treshold when the "vol" control is growing from min to max

3) more confortable usage, the right-signals are clear and "softly"

4) the deep search ist's the same, don't change from 12.5 to 14.5!

5) when you change from 12.5V to 14.5 the threshold level decrease about 10-15% and you must retune the level (this confirm the absence of regulator on main-power rail for the H-Bridge!)

that's all, today a new test on different context.

[J_Player]

Hi Cossaro,

It sounds like your new Li-ion batteries are a great improvement. What kind of battery did you use before you changed to Li-ion? How many grams for old battery?

[Cossaro]

Hi Brian,
1. Li-ion batteries have internal resistance a little higher than nickel base batteries. But as a Li-ion battery goes through it's discharge cycle,
this internal resistance increases noticably.

5....There is an overheating problem if the battery is shorted, connected to a load higher than the recommended safe limit

with 100-200mA discharge current this is not a real problem. If you exclude GP3000 and a few other, ther's no MD that use more than 100mA.

2. Li-ion batteries will become useless in 2-3 years whether you use them or not.

the life if NiMh it's about the same

3. Temperature helps to cause a Li-ion battery to die sooner. The worst working environment for Li-ion batteries is to be fully charged and kept warm.

the Li-Ion cell used in a notebook are tested for 50 C, this is almost good for tropical enviroment usage (added to low discharge usage).

4. Li-ion batteries need a special charger that works much different than nickel or lead batteries.

this is true, a special charger for each one. A lot of low cost chip are on the market to build your custom charger for only 5$.

The deep discharges shorten the life.

a real "point blank!" that need attention...
but a smal battery-meter to 2.8VxCell it's easy to implement and a lot of MD gone crazy when the right power is missing.

...try to fully discharge a very-very common Pb-Acid battery and leave it 5 days without refill, this cell is widely used in all UPS and power-backup system but all of us don't care about this fact, its' true?

My feeling is Li-ion batteries have not reached as mature a stage of development as the NiMH batteries have.

... i'm discordant, each tecnology need some special instructions and IMH the main reason for the usage of NiMh or NiCd in this portable device is the cost.

[J_Player]

Hi Cossaro, You are right.
While notebook Li-ion batteries may be tested for 50c, their internal resistance rises a lot sooner if they are used at that temperature, and their useful life is noticably shortened. One manufacturer of Li-ion batteries says "Do not use or subject the battery pack to intense sunlight or hot temperatures such as in a car in hot weather. Otherwise, acid leakage, overheating, smoke emission can occur, Also, its guaranteed performance will be lost and/or its service life will be shortened".

Neither Li-ion or lead acid batteries should be allowed to fully discharge because of the damage to the battery chemistry. NiMH batteries are more forgiving when fully discharged, but still not a good idea. Some Li-ion battery pack manufacturers include a protection circuit inside the pack that will disconnect the battery if any cell drops below 2.3 volts. A battery meter to show low battery is also a good idea. Another method is like the Goldscan 5 detectors with a low battery warning about 15 minutes before the NiMH battery charge is depleted.

I have found the life of NiMH batteries are not the same as Li-ion. Both NiMH and Li-ion batteries are rated for about 500 times recharging. But I have not seen any of my NiMH batteries dead in 2-3 years, only the laptop computer Li-ion battery. I have NiMH batteries more than 5 years old that work nearly as good as new, with maybe 300 recharge cycles. Only the Li-ion batteries become useless in 2-3 years whether re-charged a few times or a lot of times.

I have no doubt Li-ion batteries can work well for a metal detector for a knowledgable person who knows how to care for them. It seems to me it is a personal choice whether to choose NiMH or Li-ion for the trade off of lighter weight and low self-discharge.

For a metal detector that uses higher current than is safe for 2200 maH Li-ion cells, there is higher current rated Li-ion available.
The Sanyo CR23500SE Li-ion is rated 5000 maH and it's not much larger than the 2200 maH cells.

What kind of battery did you use before you changed to Li-ion?