Does anyone who has the rechargeable battery pack for the MXT know how many cells they have in it? It would make sense if it was 8 just like if you were using alkalines because a) it would be the same size and b) the manual says the threshold for the low-battery indicator is 8v which is well below the nominal voltage for 8 NiCads or NiMH cells which is 9.6v.
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How many cells in the rechargeable pack?
- Thread starter PSS1963
- Start date
Thanks, that's great! It will save me some money because I already have a charger that I use with my NiMH pack for my 6000 (4 C-cells in series with a blocking diode). I can charge 8 NiMH AA-cells by grouping them 4 in series in paralell with the other 4 in series. Add a blocking diode and the whole mess will have exactly the same voltage requirement as my 4 C-cell pack!
Hello Pete,
there are some instructions around the net-world on how to add a 9th cell into the batterypack.
But there will also fit 10 AAA NiMh cells. That is what I'm using.
[video]https://www.youtube.com/watch?v=k0frjkbrBhc[/video]
Another solution to get some more battery power is to use 8 AA NiZn cells. This NiZn has 1.6 Volts and will hold 1.5 Ah.
But from what I've heard they need some power drain to work best at full charge. With low power consumption they have a very short life cycle.
And the MXT is low power.
May be this is useful?
there are some instructions around the net-world on how to add a 9th cell into the batterypack.
But there will also fit 10 AAA NiMh cells. That is what I'm using.
[video]https://www.youtube.com/watch?v=k0frjkbrBhc[/video]
Another solution to get some more battery power is to use 8 AA NiZn cells. This NiZn has 1.6 Volts and will hold 1.5 Ah.
But from what I've heard they need some power drain to work best at full charge. With low power consumption they have a very short life cycle.
And the MXT is low power.
May be this is useful?
Thanks Vito! Does anybody know how long the MXT runs on 8 NiMH? When I converted my old 6000 blue box from NiCad to NiMH, I went from getting about 4 hours use out of a charge to being able to detect all day without it showing any signs of going flat - frankly at this point my old detector easily outlasts me! 
Hello Pete,
I'll try to do this.
Schützenverein - shooting club
PR (Preußen) - Prussia
Ströhen - this is the most nothern village of the district Minden-Lübbecke in the province Nordrhein-Westfalen
e.V. (eingetragener Verein) - registered association
but now back to topic - I think the MXT will run 6 to 8 hrs with a rechargeable 8-AA NiMh 2100mAh battery pack, if not longer. But I don't know for sure.
May be some one who really knows will chime in.
I'll try to do this.
Schützenverein - shooting club
PR (Preußen) - Prussia
Ströhen - this is the most nothern village of the district Minden-Lübbecke in the province Nordrhein-Westfalen
e.V. (eingetragener Verein) - registered association
but now back to topic - I think the MXT will run 6 to 8 hrs with a rechargeable 8-AA NiMh 2100mAh battery pack, if not longer. But I don't know for sure.
May be some one who really knows will chime in.
6-8 hours is actually quite adequate . . . especially since I would probably be using cells with at least 2600 mAH.
Also, thanks for the translation! I used to belong to a shooting club when I was in college. We sometimes competed against the big U.S. military academies in Annapolis and West Point. They were tough competitors but we mopped the floor with the Coast Guard team!
-pete
Also, thanks for the translation! I used to belong to a shooting club when I was in college. We sometimes competed against the big U.S. military academies in Annapolis and West Point. They were tough competitors but we mopped the floor with the Coast Guard team!
-pete
If you are building your own rechargable battery pack keep in mind that many of us agree that the MXT suffers several aggravating symptoms when voltage is 10 volts and less. These range from excess chatter and erratic behavior to loss of depth. An 8 cell NiMH pack will produce 9.6 volts at full charge while an 8 cell Alkaline pack produces 12 volts. To counter this and achieve a closer replication to Aklaline results build a 9 cell NiMH pack which will provide 10.8 volts and a longer run-time compared to 8 cells. As mentioned, a 10 cell NiMH may be possible and would provide 12 volts. I was not aware 10 cells would fit but if so that would be a better option if you are already building your own pack anyways.
Larry (IL)
Well-known member
Rechargeables for the MXT is a touchy subject because of the higher operating voltage of the MXT, as Aaron pointed out, below 10 V, the MXT family can get a bit chatty.
If you like to tinker in electronics, I would suggest making a 9 cell NiMh pack or two and for those who has a little extra cash, the R-N-B 3100 LI-ion, http://rnb-innovations.com/ is the way to go. On the other hand, $150 for a rechargeable pack will buy a lot of alkalines.
I have heard that the higher voltage NiZn with their own charger will work but you will be changing and charging them quite often.
If you like to tinker in electronics, I would suggest making a 9 cell NiMh pack or two and for those who has a little extra cash, the R-N-B 3100 LI-ion, http://rnb-innovations.com/ is the way to go. On the other hand, $150 for a rechargeable pack will buy a lot of alkalines.
I have heard that the higher voltage NiZn with their own charger will work but you will be changing and charging them quite often.
Aarong81 said:
Thanks for tipping me off about the erratic behavior . . . Whites has the low battery indicator in the machine set to trip at 8v (according to the manual at least) and if it is already acting funny at anything below 10v then one could be using it for a while before realizing anything was wrong - they really should fix that - at least send the warning when it hits 10v - that way the user could make an informed decision as to whether to live with it and keep hunting or quit for the day or pop in a fresh pack.
My intention wasn't to build a custom battery pack but to use rechargeable cells in the holder they provide for alkalines, then to move them to battery holders attached to my charger to recharge them. I'm not sure if the battery compartment in the machine is roomy enough to accommodate an extra cell or two - I haven't seen it yet. Also, I'm skeptical about substituting the smaller AAA cells for the AA cells in order to fit an extra one or two, as suggested earlier, because it would would entail an immediate loss of mAH rating and subsequently run time. Vito - how many hours can you get from a 10 AAA cell NiMH pack before getting the erratic behavior described here?
One thing I should point out about the voltage ratings of cells . . . the numbers printed on the cells and packaging are "nominal" ratings. A fully charged NiMH cell will have closer to 1.4v rather than the 1.2v nominal rating and a fresh alkaline will be closer to 1.6v rather than 1.5v. The Wiki article on NiMH says that the average operating voltage is 1.25v. Where these two types of cells really differ, though, is in the discharge characteristic. An alkaline cell will lose voltage more or less linearly as it is discharged while an NiMH will plateau at some voltage for a large part of its discharge then fall off abruptly at the end.
One important bit of info we need to really sort this out, is how many operating hours can we get from an 8 AA cell NiMH pack before the erratic behavior starts? If the answer is 6-8 I can probably live with that but if it is say 4 or less then I would consider that inadequate.
-pete
Larry (IL) said:Rechargeables for the MXT is a touchy subject because of the higher operating voltage of the MXT, as Aaron pointed out, below 10 V, the MXT family can get a bit chatty.
If you like to tinker in electronics, I would suggest making a 9 cell NiMh pack or two and for those who has a little extra cash, the R-N-B 3100 LI-ion, http://rnb-innovations.com/ is the way to go. On the other hand, $150 for a rechargeable pack will buy a lot of alkalines.
I have heard that the higher voltage NiZn with their own charger will work but you will be changing and charging them quite often.
Yeah, Larry, the answers aren't easy and like most things in engineering, involve compromises. Quite a few years back I was working with a guy, Dave, on a 16 bit A to D converter to go in MRI machines and he told me about his "water bed theory of electronic design" . . . basically, you push down over here and it pops up over there. LOL! I've come to realize that many things in life follow that same principle.
-pete
[attachment 305242 RechPack.jpg]
Fits the standard battery pack, is easy to do, is low budget (depending on the charger) and gives you 12 Volts.
Works best for me...
@Pete - Have not tested it when voltage will drop below 10 Volts for now. This is still on the to do list.
Fits the standard battery pack, is easy to do, is low budget (depending on the charger) and gives you 12 Volts.
Works best for me...
@Pete - Have not tested it when voltage will drop below 10 Volts for now. This is still on the to do list.
Here is a mod someone did with their MXT battery pack to get 9 AA rechargeable cells. Some users insist any voltage above the 'low battery' indicator provides the same voltage past the voltage regulator. I agree with the theory and I would side with that reasoning in VOLTAGE ALONE. I assume it has something to do with the total current(amps/wattage) rather than simple voltage which the voltage regulator only controls volts. Think about a car battery charger at 12 volts/10 amps vs 12 volts/50amps, the voltage is the same either way. That being the case, I would almost expect a different experience using 10 AAA cells even though it would meet the voltage requirements it may lack amperage.
I would trust better results from 9 rechargeable AA cells instead of 10 rechargeable AAA cells. As mentioned already, another downfall to 10 rechargeable AAA cells is that you could only achieve half the maH. That not only affects the lifespan but also the wattage/current(volts+amps=watts) available at a given time.
When AA rechargeables are running mid/low, do they provide the same amperage as AA Alkalines at the same mid/low range? Voltage is only HALF the equation and, in fact, you cannot calculate the watts/current without knowing BOTH volts and amps. AAA will lack the amps that AA will have. As "efficient" as the MXT is, it still requires a substantial signal(wattage) be sent/received through the coil.
SOURCE
I would trust better results from 9 rechargeable AA cells instead of 10 rechargeable AAA cells. As mentioned already, another downfall to 10 rechargeable AAA cells is that you could only achieve half the maH. That not only affects the lifespan but also the wattage/current(volts+amps=watts) available at a given time.
When AA rechargeables are running mid/low, do they provide the same amperage as AA Alkalines at the same mid/low range? Voltage is only HALF the equation and, in fact, you cannot calculate the watts/current without knowing BOTH volts and amps. AAA will lack the amps that AA will have. As "efficient" as the MXT is, it still requires a substantial signal(wattage) be sent/received through the coil.
SOURCE
Larry (IL)
Well-known member
Rob (IL), the Moderator of the V3i forum, is the root of the 9 cell battery packs you are talking about Aaron. I have one or maybe more of his modified packs. The main purpose of the mod is to increase the milliamp HOURS at a usable voltage above 10 volts for the MXT. In short, a battery pack that runs longer at a usable voltage. The current draw (amps) and power (watts) are of little concern because of the low power consumption of most general purpose metal detectors. Additional voltage above what is needed also serves no purpose because the usable working voltage is regulated by all detectors. A ten cell pack does not last longer or work better than a 9 cell pack, in fact just the opposite is true because of the lower capacity (milliamp hours) of the AAA batteries is about half of a AA battery pack. In theory, the AAA battery pack will last only half as long as the AA battery pack.
Aarong81 said:
I definitely agree that 9 AA cells is probably going to provide more run-time than 10 AAA cells for the simple reason of substantially greater mAH rating. This configuration also provides a voltage within spitting distance of 8 alkalines: 9 x 1.4 = 12.6 vs. 8 x 1.6 = 12.8 Even if we take a more conservative stand and only allow for the average operating voltage for NiMH (as stated in Wiki) of 1.25v per cell, we still get 11.25v - well above the reported threshold for wonky behavior. Plus we know that the rechargables decline in voltage differently than alkalines as they discharge and will likely remain at an acceptable voltage for a good long time before slipping below that magic 10v level. That having been said, I think Vito has shown that the AAA cells can provide adequate current to run the machine - big question remains - for how long?
I do think, however, that we are making a big assumption about a metal detector having a voltage regulator between the battery and the circuit board:
My main reason for saying this is that voltage regulators waste power - and the bigger the voltage difference between the input and output side, the more power they waste! In electronics, power is defined by the formula P = V x I where "V" is the voltage across the device (the difference between the input and output sides) and "I" is the current passing through it. For the sake of example . . . if the input side was 10v and the output side was 5v, for any current being drawn, half the battery power is being wasted - it's dissipated as heat!
A second reason for not using one is the problem of "headroom". They require a minimum amount of voltage difference between the input and output sides in order to even function and pass any current. For example, the popular 78xx series 3-terminal regulators (the third terminal is ground reference) need 2 - 2.5v of headroom to function - that means your battery needs to supply that additional 2 - 2.5 volts just to get the regulator to work!
Third reason for not having a regulator - and this is more of a suspicion on my part, rather than a conviction - is that it may be completely unnecessary. Back in the old days of TTL (transistor/transistor logic), digital circuits had to operate at 5v - but we don't use that anymore. These days digital circuits use CMOS (complementary metal oxide semiconductor) which operates over a wide range of voltage. At this point, the shrewd reader will ask "what about the analog portions of the detector?" This calls for some speculation on my part because I have neither a schematic to consult nor a recently built machine to open up and look at but I would make an educated guess that a good portion of this circuit will be made up of op-amps (operational amplifiers). These have a multitude of uses beyond simply amplifying a signal, including active filtering, signal mixing and level comparing. Whole books have been written about the many applications for op-amps and guess what? - they operate over a wide range of supply voltage too.
If I was the engineer tasked with designing a metal detector (or any device that runs on batteries) I would strive to make it's operation as immune to supply voltage as I possibly could - it's just basic. In reality, the range of supply voltage that produces acceptable operation may still be only a couple or a few volts wide but that's probably preferable to using a voltage regulator given their drawbacks.
If anybody can produce a detector schematic that shows they actually do use a regulator, please post a link - I'd love to see what their circuit architecture looks like!
Sorry for the length of this . . . anybody still awake gets a standing ovation!
-pete
Pete,
The fact that the mxt acts different at and below 10 volts supports your point. Otherwise, if it has a regulator(may very well), it shouldn't affect anything as long as the voltage stays above 8 volts. I'd love to have the schematic too and I have asked for it here before. It's guarded info from Whites and only certain employees are trusted with them as to not allow them to the public. I have, however, seen a portion of the schematic posted on here in casual modding(adding backlight, ground grab switch, ect) in the persons pictures. Both of these pictures show the schematic for the MXT. I think the user Vito may have the schematic if you want to ask him. In a different topic he provided a small picture of a portion of it showing how the TRAC switch is wired. I really doubt he stumbled across the exact portion of the schematic that he needed on the internet. SOURCE That link is to the topic he provided the picture of the switch on the schematic.
The fact that the mxt acts different at and below 10 volts supports your point. Otherwise, if it has a regulator(may very well), it shouldn't affect anything as long as the voltage stays above 8 volts. I'd love to have the schematic too and I have asked for it here before. It's guarded info from Whites and only certain employees are trusted with them as to not allow them to the public. I have, however, seen a portion of the schematic posted on here in casual modding(adding backlight, ground grab switch, ect) in the persons pictures. Both of these pictures show the schematic for the MXT. I think the user Vito may have the schematic if you want to ask him. In a different topic he provided a small picture of a portion of it showing how the TRAC switch is wired. I really doubt he stumbled across the exact portion of the schematic that he needed on the internet. SOURCE That link is to the topic he provided the picture of the switch on the schematic.
Yeah, that's a great point! If it did have a regulator, I would expect it to work more in a go or no go kind of way, rather than the performance gradually dropping off as the voltage falls. I don't have my MXT yet, but if I did and wasn't worried I'd void my warranty, the first thing I'd do is pop the "hood" and have a look.
Anybody with an off-warranty MXT that knows how to recognize a voltage regulator circuit want to volunteer?
-pete
Anybody with an off-warranty MXT that knows how to recognize a voltage regulator circuit want to volunteer?
-pete
Larry (IL)
Well-known member
Both owners manuals for the MXT and MXT pro has the following statement:
If using rechargeable batteries 8 volts
is surely the end of their performance. If you are
using quality alkaline batteries you do have a
reserve after 8 volts. The MXT utilizes a low
voltage regulator.
They do not state if a high voltage regulator is utilized but it is good electrical engineering to include some kind of overvoltage protection such as a fuse, or on low powered circuits, a high voltage regulator........
If using rechargeable batteries 8 volts
is surely the end of their performance. If you are
using quality alkaline batteries you do have a
reserve after 8 volts. The MXT utilizes a low
voltage regulator.
They do not state if a high voltage regulator is utilized but it is good electrical engineering to include some kind of overvoltage protection such as a fuse, or on low powered circuits, a high voltage regulator........