Message to Eric Foster.

[Anonymous]

Hi-Eric, I have been wanting to ask you this question for a long time now,I can never quite understand why??-in all the machines that you make,which are very-very good machines,there is no doubting that.Why-you dont make full use of all the new Hi- powered NiMH batteries available on the market today,even the AA ones are from 1500 ma,to 1650 ma capacity,No memory,top up at any time,also available in C & D cells,etc,which are only slightly more expensive than ni-cads,and try to get some weight off some of your units, the battery weight alone in the Deepstar makes it weigh a ton,and spoils the whole thing because of that,at one time you were moving in the direction of lightweight low power drain units,but to me -you seem to be moving in the wrong direction totaly,with todays modern NiMH batteries available everywhere, could you not aim towards the extra power and capacity being used to reduce some of the weight on the Deepstar,or better still,get the batteries right out of there and into a seperate plug in unit on your waist belt or something,to save people developing a crick in their necks.All your units would benefit and no doubt improve sales if you could slim your battery weights down a bit.

 

[Anonymous]

Hi Terry,
Good question. The total weight of the Deepstar control box is 5lbs (2.27kg) of which 2lbs (0.9kg) is the battery. The sealed diecast aluminium case weighs in at 2.25lbs (1.02kg) so the case is, in fact, the heaviest item. The battery pack in the Deepstar is made up by a company that specialises in battery packs and whose advice I take on suitable cells The current pack uses 12 x C cells of 2.2Ah capacity and I have used them in all the Deepstar, Goldquest and Goldscan production going back to the mid 1980

 

[Anonymous]

Hi Terry and Eric
In Denmark you can buy NiMh from a company called GP-Batteries. AA you can get for 1900 mAh and the big A ones for 9000 mAh. Thats fantastic.
Mark

 

[Anonymous]

Hello All,
Actually, NiMH batteries do have a few drawbacks. They have very high self-discharge rates (several percent of capacity per week) and relatively short cycle life, as low as perhaps 500 cycles in the cheaper brands (such as GP). They're also degraded by fast-charging at over 1C; the self-heating causes them to lose capacity and they don't ever recover it.
There's no denying NiMH's excellent A-H capacities and their environmental friendliness. I design power electronics for a living and have worked for places where I've designed NiMH into several products (telecom test equipment, computers, etc). However, sometimes the older technology wins out over the newer stuff...you'll never see NiMH batteries in spaceborne applications due to their lower reliability, shorter lifespan, intolerance to cold-charging, etc, when compared against NiCADs.
If it's high-capacity and cycle -tolerance you're after, consider Litium Ion. It's much more costly than even NiMH but other than intolerance to high temperature charging and exposure to mis-charging; they're about the best technology we have at the present time.
I should point out that you CANNOT charge NiMH in a common NiCAD charger and expect any kind of decent performance out of them. NiMH needs to be charged at higher rates than the cheap NiCAD chargers provide and they also have to be terminated using a special monitioring technique that either senses relative temperature rise or a depression in charging voltage rate. There are some good IC's out there (such as the excellent Maxim MAX712) that are purpose-designed to charge NiMH properly.
Lithium Ion requires even more care in charging so a "cheap and cheerful" approach is completely out of the question. Again, specialized LiIon charger control IC's are plentiful so using LiIon is a LOT easier than it was a few years ago.
Still, if it's the simplicity of a dropping-resistor charger you're after and don't have a problem with the cadmium content in your country, NiCAD's are a hard act to beat!
Regards,
Geoff (Austin, TX USA)

 

[Anonymous]

Hi Geoff,
Many thanks for that input. As you can well appreciate, batteries are an integral part of metal detector design and particularly so for pulse induction. PI detectors have a relatively high current requirement i.e. Deepstar at 450mA and Aquastar at 550ma so high capacity, reliability and long life are desirable requirements. I will have a look at Lithium Ion and see what is available.
Eric.

 

[Anonymous]

A very nice description of technical issues in the design of equipment for NiCad batteries appears the button below: The Video Battery Handbook. Anton Bauer makes batteries for professional videocameras. Of particular interest is the discussion on the benefits of high voltage batteries and low cutoff voltages in the equipment being powered, allowing memory effects to be handled and maximum operating time extracted from the battery.
Joe

 

[Anonymous]

[No message]

 

[Anonymous]

Eric, Watch out for Lithium Ion batteries as there are some severe drawbacks if you try to use them in a high drain application. The manufacturers will not sell the bare battery to you here in the USA. You can only buy them when they have had a protection circuit mounted to them. Without the protection circuit these batteries are very dangerous and will explode in a major way if shorted! The main problem is that the protection circuit will limit the instantaneous current that you can draw from the battery. This is not great for a PI where you want to draw Amps for short time periods. My guess is that you would have to charge a large capacitor from the battery for a Lithium Ion to be useful with a PI. The higher voltages these cells provide and their very flat discharge curve make them excellent for many applications. They are a really fine technology but I doubt that they would be much use for a PI. Nickel metal Hydrides are also a very good battery. As of today, the Nicad still has the highest discharge capability of all the regular rechargables.

 

[Anonymous]

There is a relevant article "Li-polymer batteries up ante for portables" by Vincent Biancomano, Electronic Engineering Times, 4 December 2000, page 145. See <www.eet.com> for an electronic copy, with luck. The article basically says that NiCad batteries rule for heavy-drain applications, probably including pulse-induction metal detectors.
Joe

 

[Anonymous]

I see that the URL was stripped by the WebBBS software. The correct URL is on the button below.