GT battery life and charge cycles

[sierraimage]

I looked around for this on the forum and figured it would be on there but, I couldn't find it. Simple question I guess and many can give their experience or info.

On the GT (blue box) how many hours of detecting can you get out of one charge? How many times can the batter be recharged before it's done? How long does it take to charge the battery (i was reading 14 hrs +).

Also, I hear a slight buzzing sound inside the battery when charging, do any of your make the same sound.

thanks for your feedback.

 

[deepdiger60]

Right on top of this forum is all the infromation you need to know about batteries Jim
http://www.findmall.com/read.php?21,1731560

 

[Critterhunter]

The stock GT pack is 1000ma, and I think from memory the GT draws about 50 to 60 millamps of power, so the math says about 20 hours per charge of run time.

The buzzing of the pack while charging is normal. Others have reported it.

How many cycles of life you get out of the pack is a hard thing to pin down. It depends on how well the battery has been taken care of. If you use an aftermarket charger and say are pushing fast charge times of say 1 hour or less (1C or more in charging terminology) that could shorten it's life. A good way to tell is if the pack gets hot it's being pushed while charging. Also, I exercise my nimhs or nicads one or two times a year by hooking to a car tail light bulb and draining them dead. After the bulb goes out let it sit hooked up to it another half hour or so to insure all the cells are at equal discharge. Then re-charge. Do this charge/discharge about 3 times and it should greatly increase the capacity of the pack, as I've recovered bad packs this way that wouldn't even hold an hour's run time on some devices.

If you have access to an aftermarket charger, charging at 1C (1 amp for a 1000ma pack) during these 3 cycles can break down crystals that form that can only be broken down by an aggressive charge rate. Some will blast a pack at say 2 or 3C (WARNING: VERY RISKY!). If I do such a high charge rate (say 2 or 3 amps on a 1000ma pack), I don't like to do that for more than say 5 minutes as you could very well blow up the pack or something, but I will get that aggressive when it's a last resort.

Usually a 1C charge rate until charged done 3 times during the drain/charge exercise cycle will break down the crystals and recover the pack. Some nimh and nicad cells are designed to handle aggressive charging of say 2 to 5C or even more, but those are usually cells designed for things like RC cars or planes. I wouldn't trust pushing the cells for a metal detector at that rate. Maybe 2 or 3C but only for maybe 5 minutes max, and even then you are asking for a fire or worse IMO. If you decide to use an aftermarket charger for such a thing, you must charge through the two main battery leads, and that's also where you'd hook up the car tail light bulb to drain the pack.

If you to drain a pack on a car tail light bulb, do not let it set for days dead like that. It should be charged right after draining, because cells that sit completely dead like that can reverse polarity. Even if done right away, there is debate on the web as to if it's ever a good idea to drain packs completely dead for exercise. I always have and have never had a pack go south on me, and always get increased run time (capacity) from a pack when it's exercised like that. For that reason, even if the capacity of the pack seems fine I still like to exercise them like this (3 charge/drain cycles) about once or maybe twice a year to keep them at top capacity.

As for charging, look on the wall transformer. I believe for the GT it says 100ma? If so, 100ma divided into a 1000ma pack = 10 hours charge time, but in reality it often takes longer due to two things- The charging process is inefficient and so energy is wasted. And, packs will often hold a good bit more capacity than what it says on the label. A 1000ma cell, for instance, can easily hold say 1300 to maybe around 1600ma if the cell is in good/exercised shape. I use an aftermarket charger that displays the capacity put back into the pack, and often cells hold much higher capacity than the label says. A real indicator that a pack is going down hill is if it holds less than the listed capacity. If exercising it (sometimes I'll exercise a pack 5 or 6 times to get the capacity back, but 3 usually does the trick) doesn't increase capacity then it's for sure going down hill.

Some people think only nicads had to be excercised to erase a memory problem they could develop. The truth is it's still a good idea for nimhs to "build their muscles" in terms of growing their capacity here and there, and also modern nicads don't seem to suffer the memory problems they used to years ago. That said, nimhs tend to have higher capacity than nicads, and nimhs also tend to be lighter. No sense using nicads when you have a choice IMO, but to this day they are popular among some in RC because they *tend* to be able to put up with the abuse of being charged at super high rates better than nimhs. That line is blurring now though.

 

[sierraimage]

Thanks Critterhunter. I did read that post in the battery section of the forum. Just interested in some real life usage times. By the math above it looks like around 10 hours of hunt time.

What do you make of the buzzing sound inside the battery when it's charging?

Thanks

 

[Critterhunter]

It should be about 10 hours of charge time, 20 hours of run time. I think the wall transformer is 100ma output divided into 1000ma pack, and the Sovereign draws about 50 to 60ma (depending on target/no target under the coil) so about 20 hours run time roughly.

Don't know why the pack buzzes but it has to be the "charge" circuit. I need to open mine and see what is going on in there component wise. Curious if it is cutting off the charge when peaked or if it never does and just dims or turns off the light when the pack starts drawing lower current due to a full charge. Still waiting for one of you guys to tell us solid if the light just dims or goes out when charged, but from memory I think it only dims. Seems pretty primative, but that's chargers/batteries for metal detectors. They are about 10 years or more behind the RC crowd in battery technology. If anything the stinking light should go out to tell you the pack is charged, and not just get dimmer so it's a subjective thing that people might miss.

Don't be fooled, the Sovereign may look primative but there is a wonder of technology behind those simple looking analog controls that other detector makers are still trying to catch up with 20 years after this thing was introduced. It will hold it's own or better anything on the market IMO. To use such primative sub-A cells in the GT/Elite, and with a low capacity of like 20 years ago in terms of what nimhs will hold these days, it seems like building the space shuttle and then strapping a coal burning boiler to it to power the thing. That's why I run a 3 cell lipo in my GT's alkaline holder. About 1/4th the weight, smaller, and with much longer run times if you use a higher capacity pack. I'm using a 750ma 3 cell Rhino in mine (about 1/3rd the size of a pack of smokes) and I still get I think longer run times than the 1000ma nimh pack. That's due to the lipo holding it's voltage very high until the end of discharge, where as nimhs or nicads (like store bought non-rechargeables) drop their voltage much more faster during the draining.

By the way, I think some of the older models before the Elite use Sub-C cells. Ouch! Talk about a weight issue, and I thought the Sub-As in my GT pack were heavy. Lipos are dirt cheap if you know where to look. I paid $7 for mine and bought two, and use a $20 computer screen charger to charge them. Don't mess with lipos though unless you read up on them and know how to feed and care for them, but man if I was using an older Sovereign with Sub-C cells I'd sure look into it for the weight reason alone, if not the cost factor of saving big money. At least people should look into putting some regular AA nimhs in the thing, which will save weight and probably triple or more the run time if you buy big enough capacity of cells. Those are cheap too if you look in the right places, and if you don't know how to build your own pack there are many battery sites that will custom build them dirt cheap for you.

 

[sierraimage]

I want to understand more about using "lipo's", I don't know what they are and don't want to screw up my GT.

How is the standard 8X AA charger pack for the GT? What is the hunt time using the AA alkaline? Also, can I use rechargeable AA in the regular pack...or will it be too much running 8X 1500ma rechargeable in the regular AA alkaline pack?

Im trying to plan my back-up power when this nimhs crashes...which by the buzz I think that a sign of things to come. Cant stand spending $106 on a new nimhs pack for it.

 

[Critterhunter]

The "buzz" is normal. Many reported it. Don't mess with lipos unless you read and learn (links in the battery sticky). Also a link near or at the bottom of the battery sticky about running 8AA nimhs in the regular holder working fine for some like Kered. Only thing is to peak the pack that day or a day or so before as nimhs will self discharge over time on the shelf and only running 8 (versus 10 in the stock rechargeable) won't hold the voltage as high, so that's why it's important to peak right before use and not store on the shelf for weaks. But there are now low-self discharge nimhs that will still hold near full sitting for weeks or months on the shelf you might look into on the net. Some didn't hold up to the claims so research that. And also run 2500ma or higher cells. Running higher capacity cells won't hurt a thing. That just means more run time. And thus the voltage will drop slower than smaller capacity cells too so you won't trip the low battery alarm as fast. It's voltage you have to worry about ruining a device. Too high and it could blow things, but not an issue with 8AA nimhs or nicads, and not an issue with a 3 cell series lipo either.

If you want to run regular non-rechargeables in the 8AA holder I'd look into lithium ions like the Energizer non-rechargeable disposable ones at Walmart and such. Yea, they cost more, but they will run probably 2 to 3 times longer or so, so they are worth the bit more you pay over regular batteries, and they weigh next to nothing compared to regular batteries.

 

[Rick(ND)]

Actual run time is around 10 hours and charge time is more like 12-14 hours. On the older Sovereigns the battery packs that Minelab made used 10 of the AAA batteries in them, Sun Rays used the AA batteries and why the run time was longer using the Sun Ray packs.

 

[Critterhunter]

From the GT's manual...

A green light will appear on the battery pack during charging. A completely flat battery will take approximately 12-14 hours to fully charge. The green light on the battery pack will fade/dim once it is charged fully. A fully charged NiMH pack will give between 15 and 20 hours detecting time, depending on the number of targets found and the level of threshold used.

That jives with the amp draw of the Sovereign from memory to be around 50 to 60 millamps depending on a target being under the coil. The GT's pack is 1000ma in capacity. Older Sovereigns I'm sure had lower capacity nicad packs of perhaps 600 to 800ma maybe (guessing)? In that case lower run times would be had.

As for charging, as I said before, charge time on a completely fully dead pack will take longer than the math says due to the inefficieny of the charging process, and the fact that good cells will usually hold more capacity than the label says.

I'm glad to see the manual states the light dims. That should clear that part up.

Here's a pic of Kered's XS-2a Pro stock pack from Minelab. My eyes might be playing tricks on me but those sure look like Sub-C cells, bigger than the Sub-As used in the GT and Elite. Anybody think they look only Sub-A in size? Either way, even if they are at least Sub-As, much beefer than a typical AA nimh. These kinds of cells are generaly meant for high amp draw applications. Much more robust than what is needed for the low current draw of a metal detector.

 

[Critterhunter]

Since this thread is linked to from the battery sticky under the topic of using rechargeable AAs and also about using Energizer non-rechargeable lithium AAs from walmart and such, I figured I'd post this link to another thread that has more info on that, and more importantly info on using rechargeables AAs kept real simple by just buying 8AA 2500ma or higher batteries from walmart or something and using the simple charger they sell with them up there. Can't be any easier. Just put the batteries in the charger and let the Energizer charger do it's work. Then throw them in your regular 8AA alkaline holder and off you go.

http://www.findmall.com/read.php?21,1753039,1753042#msg-1753042

 

[Critterhunter]

Since the sticky link (to this current thread you're reading right now) mentions this thread to also contain info on rebuilding stock packs, I wanted to make sure people knew that the link in the message above this one also has further more detailed info on stock pack re-building such as what size cells the packs of various models might have, and how you might replace the cells or build a new pack with smaller/lighter cells with even greater run time these days.