Myths About Using Nimh/Nicad Rechargeables Such As Less Run Time Or Performance, & Other Info On Modern Battery Types, Plus Charging Info

[Critterhunter]

This is a re-post from me elsewhere but I thought I'd post it here to try to explode a few myths about using rechargeables, as well as other info that should be useful to the detecting crowd...

I've found in various devices for me that running 2500ma or larger capacity nimh AAs in them actually gives me much more run time than an off the shelf non-rechargeable store bought battery. The capacity of nimhs these days is pretty amazing. In various tests on the web, some claim in general a good high capacity nimh can provide up to 4 times more run time than store bought non-rechargeables. While much longer run times is well known in high current applications, there is some debate about a nimh's run time compared to non-rechargeables in low current applications.

For me I still seem to see longer run times with them even in low current applications. Shoot for the highest capacity (2500 or north of that) and you'll probably find either virtually no difference in run time that you can tell, or maybe even much longer run times. For instance, in my digital pocket camcorder my 2500ma Energizers give me more run time than good quality Energizer non-rechargeable batteries. I've never actually timed the run time but it's obvious they are giving me more run time when doing video recordings and such.

But, there is one string attached to that. Nimhs or nicads self drain in storage. For that reason run time may be effected if you don't frequently use your detector. If you are considering nimhs, there are now brands that claim low discharge for long storage when sitting on the shelf. Make sure you surf the web and see which passed various tests on this, because some have not lived up to their long term storage claims.

Modern detectors use voltage regulators to provide the circuit board with a steady, constant, non-changing voltage in order to keep things in proper specs. That means it doesn't matter if the voltage is say 10 volts or 12 volts for example, as the circuit board is still only going to see say 8V. The only time it *might* be possible to see a performance flaw is when a battery is so weak that it's voltage is sagging up and down under high power drain moments for split seconds at a time, but in fact high capacity nimhs or nicads have a much more better ability to handle higher amp draws than non-rechargeable batteries.

If you are going through the trouble of building an external battery box and using a custom battery source, I would look into lipo battery technology. All the rage in the RC crowd. MUCH lighter and smaller than the equivalent capacity in a nimh pack. I run a $7 three cell series Rhino lipo in my GT which is 12.6V at full charge (charged by a $20 computer charger that will charge many types of batteries) that is about 1/4th the size of 8 AAs, much lighter (beyond belief), and has further advantages such as 1 hour charge times that aren't pushing the battery (which can be the case with nimhs), and has almost zero self discharge when sitting on the shelf so that it's ready months or even years later if you ever went that long between charges. These lipos also hold their voltage very high until the very end of discharge, so in fact I find a 750ma pack gives me at least as long of run times as a 1000ma pack, because the faster dropping voltage of the nimh during discharge ends up tripping the low battery alarm faster for me.

However, there are special care instructions for lipos that a user should be aware of. Never puncture, never short, (which is pretty much true for nimhs or nicads too anyway), and a lipo will probably be ruined if drained below 3V per cell (9V total in a 3 cell series pack). While over discharing a lipo isn't dangerous (that's what you do to dispose of them), you should insure the device it is used in will sound a low battery alarm before it drains past 3V per cell. My GT sounds off at about 10.2 to 10.5V or so, so I have no worries about draining past 9V in total.

Incidentally, while nimhs might start out with a lower voltage than store bought non-rechargeables, over the span of discharge there will be a time when the store battery doesn't hold it's voltage as high as the nimh. High capacity nimhs have a much more "flat" discharge line in terms of voltage drop, so that further muddies the waters for people who just refuse to believe that lower voltage will get them the same performance than a higher one.

If you are interested in learning more about chargers, batteries, the charging process, and various other things you probably never wanted to know about rechargeable batteries visit the battery sticky thread in the Sovereign forum. We've linked extensive information to it found in various Findmall threads that goes well beyond specific charging information for the GT or Excal and can be applied to any detector's batteries. Much of this knowledge I've developed over years of building and flying RC electric planes. In the electric plane world if you don't know your batteries well and how to take proper care of them, it could very well cost you a plane. That's why many in RC make it their job to know this stuff, and also why battery technology in RC seems to be a good 10 to 15 years ahead of the curve in detecting circles. It's just not as vital to educate yourself on this stuff in detecting because it's not a life or death situation for the most part.

 

[Critterhunter]

I should add...

Warning: There is still much debate among many on the proper care and feeding of rechargeables, so it's up to you to take proper precautions when charging and using batteries, and you should educate yourself on the net as to just who and what you believe. Regardless of what type of rechargeable you use, always educate yourself as much as possible and charge and store your batteries in a fire proof location. I prefer to store mine in a metal box (lined inside to lesson any chance of a short) as well as to charge them in the middle of a cement floor where I can keep an eye on them. Never assume handling and use of any battery is completely safe.

For instance, many say to drain a lipo completely dead before disposal. Others, however, have reported fires when that happened. I think more than likely they were dead shorting the lipo or draining it at such a fast rate that the battery couldn't handle that fast of a discharge. Still, seek out answers on your own on the web and decide for yourself. I just know the sites I've read recommend draining it completely dead before disposal. Actually, some suggest cutting both battery leads off (ONE at a time! Cutting two wires at once can cause a short!) and throwing it into a bucket of salt water for about a week to insure it's been completely drained of all power.

And, wanted to add that my response in terms of building a custom battery box was to somebody who was already doing that for various reasons. My lipo I run in my regular 8AA alkaline holder on my GT. It easily fits inside, and I just had to solder a tiny plug to the holder inside to plug the lipo in. Should I one day for some odd reason decide to run 8AAs (why would I ever want to do that again just based on the weight savings alone of a lipo?) in the regular holder again, I can easily just move the tiny plug to the side so I can put 8AAs in.

 

[Critterhunter]

Lots of fine info there CH and I am grateful for it!!

Now all I need is a line on a good water-proof enclosure about the size of a cigarette pack with a good water-proof cover that is very secure, but easily removable when the need arrises.

Regards to you all,

CJ

Two reasons why a lipo might be your perfect solution. One, very small and compact so it would require a much smaller waterproof container than a nimh pack would.

Second (and this is for those who have waterproof machines and thus don't like to open them anymore than they have to...Which could be an arguement against using nimhs because they self discharge in storage over time and would require removing to re-charge (peak))...Lipos have an almost zero self discharge rate sitting on the shelf. For that reason you wouldn't have to re-peak a lipo after it's sat for a while like you would a nimh or nicad. However, there are nimhs these days that claim low discharge in storage, so those considering them for a detector (and in particular a waterproof detector where they don't want to open the detector any more than they have to to avoid use and abuse of the waterproof seals). Some low discharge nimhs do not hold up to the claims made, so surf the net and find sites where they have been tested to judge just how good they are at that.

Lipos are a variation of lithium ion batteries. Lipos are pretty much as light as it gets due to their internal makeup and lack of a hard outter shell. While lipos have a reputation of being more "risky", in fact lithium ion can be just as dangerous due to shorts or other matters of abuse.

Much of the bad rap lipos initially got was due to not having balance plugs and no balance able chargers being available for them in the early days. What would happen is that one cell would get over charged because the charger couldn't monitor each cell individualy, and as a result there were numerous fires caused.

These days all lipos and lipo chargers I'm aware of feature balancing while charging. But, despite that, lipos (like pretty much any other battery) have some very real potential for fires or explosions due to abuse. Puncturing them, denting them (although I've dented the heck out of some of my plane lipos during crashes and they never went nuclear and still worked fine), shorting them (if you are changing plugs on a lipo NEVER cut both wires at once or that will cause a short, and only expose the second wire after the first has been soldered and isolated to the new plug), and so on.

Also, while some lipos these days can be charged faster than 1C (a one hour charge time. For instance...A 2000ma lipo can be charged at up to 2 amps, a 1500 lipo at 1.5 amps, a 750ma lipo at .7 (that's point 7) amps), I never charge mine faster than 1C. Not just due to fire risk potential, but also because 1C is perfectly fine for a lipo but faster is pushing it IMO and may shorten battery life.

The old rule is never to charge faster than 1C, so I live by that despite higher C charging abilities of some packs these days, just so I don't charge one that can't handle anything above 1C faster by accident. Charging faster than 1C was one of the other fire risks of lipos early on and so I stick by that easy to remember math. A quick look at the capacity on the pack and I can easily figure out maximum 1C charging rate.

Also of note, there may very well be some low amp delivering lipos out there that can't even be charged as fast as a 1C rate. ALWAYS follow the instructions that are on the pack and make sure you understand them.