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Old 04-20-2014, 02:29 AM   #1
kyleservicetech
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Default Spektrum DX8 transmitter Battery

I've been noting rather low battery voltage on my DX8 transmitter LCD display for awhile. After pulling the battery out of the transmitter, its voltage was generally around 5.1 Volts DC.

Last Friday, after three flights of 6 minutes each, the DX8 low battery alarm went off. Again, the battery was pulled and measured 5.1 Volts DC.

Just could not figure out why Spektrum would have a battery voltage indication that was off by 0.9 Volts DC.

So, that battery was pulled from the transmitter, and checked on my Western Mountain Battery analyzer, at 300 Ma. The attached battery discharge curve shows the DX8 Battery voltage was correct, and that the battery voltage under light load is pretty much kaput.

So, its connector was cut off, and four Sanyo Eneloop "AA" Nih cells were wired up. And, the DX8 transmitter shows good voltage on the battery.

You'd think a $400 transmitter would have a battery that would last more than a year and a half. But, quality Eneloop batteries are cheap enough.


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Old 04-20-2014, 02:55 AM   #2
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Known issue with the DX8 displaying voltage lower than it actually is. Typically 0.5 v discrepancy. Supposed to be fixed in a software update.

The batteries life expectancy can depend a lot on how it is cared for... We used to EXPECT NiCd/NiMh to need replacement every year regardless of care, but now if you care for even cheap ones properly you can get up to 12 years of service.

Actual cost of the DX8 is $300... (its always on "sale")
http://www.horizonhobby.com/products...ode-2-SPMR8810
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Old 04-20-2014, 03:02 AM   #3
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Originally Posted by fhhuber View Post
Known issue with the DX8 displaying voltage lower than it actually is. Typically 0.5 v discrepancy. Supposed to be fixed in a software update.

The batteries life expectancy can depend a lot on how it is cared for... We used to EXPECT NiCd/NiMh to need replacement every year regardless of care, but now if you care for even cheap ones properly you can get up to 12 years of service.

Actual cost of the DX8 is $300... (its always on "sale")
http://www.horizonhobby.com/products...ode-2-SPMR8810
Yup, $300. But mine came with three receivers and a telemetry module that were worth well over $100 total.

H'mmm thinking about that software update. Might just leave well enough alone, as is often said, "If it works, don't fix it!"

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Old 04-20-2014, 03:50 AM   #4
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The updates are worth doing. Latest update to the DX 18 changed it from 30 model memories to 250.

Just stay away from the beta updates. Let someone else experiment.
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Old 04-20-2014, 04:39 AM   #5
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Get the lipo. It's like you never have to charge it again!
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Old 04-20-2014, 04:41 AM   #6
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Originally Posted by xmech2k View Post
Get the lipo. It's like you never have to charge it again!
Yeah
I thought about that, or for me, the LiFe's. But, that might happen when these Sanyo Eneloops give up the ghost.

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Old 04-20-2014, 09:39 AM   #7
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Originally Posted by xmech2k View Post
Get the lipo. It's like you never have to charge it again!
OK ... here's a question.

Denny is using LSD NiMH in his Tx ... he chose Enerloops, I choose Grundig ... we both get excellent storage capability and excellent output ...
I don't know what mA capacity Denny's are but mine are 2300mAh ... and they power my Tx's for over 9 hours before LVA sounds. I still have at least a good amount for landing etc.
Denny and I can charge via the Tx socket without opening the battery compartment, no need to remove battery ... we just plug in and charge.

So what is advantage of the LiPo over this ?
Capacity ? None - I have 2300 mAh ... more than the average LiPo used in Tx's.
Long term storage of charged capacity ? None - he and I use LSD NiMH .. I can leave my Tx while I'm away on assignments and return and use without charging. But in fact as I can just plug in and charge without opening Tx ... I can stick my 50mA charger on and forget it ... so no matter what - I always know I have full charge anyway.
LiPo of 2100mAh capacity in fact will need charging way before my 2300mAh NiMH ... because I can run my NiMH down further than you can run your LiPo down ... and still have perfectly good cells... (That is with the 200mAh deducted of).

I can also buy my NiMH cells over shop counter locally .. I can swap one or more instead of a whole pack ... they are cheap as well ....

So again ... Why ? So far I see no advantage - in fact I see factual reasons to NOT change.

There is of course another factor that will play on this ... to use a LiPo in many Radios today requires a voltage regulator / stepper as the LiPo's do not match radio requirement. Most radios are matched to NIXX cell counts ...

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Old 04-20-2014, 09:44 AM   #8
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Originally Posted by kyleservicetech View Post
Yeah
I thought about that, or for me, the LiFe's. But, that might happen when these Sanyo Eneloops give up the ghost.
LiFe ... yes

LiPo ... why ?

The Enerloops or any other LSD is far better actually as I explain in prev post.

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Old 04-20-2014, 10:37 AM   #9
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Why? I don't know all the technicalities. I just know with the stock batteries, it seemed I had to charge my Dx8 after every outing. With the lipo, I can't remember when I had to charge it last. Really!
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Old 04-20-2014, 10:53 AM   #10
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Originally Posted by xmech2k View Post
Why? I don't know all the technicalities. I just know with the stock batteries, it seemed I had to charge my Dx8 after every outing. With the lipo, I can't remember when I had to charge it last. Really!
It used to be that Tx's and Rx's were supplied with 500mAh NiCD's ... then NiMH .. so in effect you only had about 2hrs use if lucky.
I used to have a field charger that could hook up to my field box or car ... to boost charge Tx and Rx's. I now have that on my yacht to charge up NiMH etc. that anyone uses while on board.

Those days now gladly are gone and we have high capacity cells over shop counter. Such as my Grundig 2300mAh.

Tx's typically sit about the 250mA figure ... so you can see quite easily that todays higher capacity cells are fully capable of looking after that. The 250 in fact does not alter much as the Tx is transmitting each ch continuously in sequence so no matter what command you give - it is only a change of code in the signal .. operate ALL ch's and its still 250mA. Unlike a Rx pack which has to supply differing mA / A depending on loads on servos.
I can say and this is no invitation to the Doom and Gloom boys about Rx packs - I find my Grundigs supply all my Rx needs where non lipo .. even my larger servos fine with NEVER a trace or hint of 'brown-out' ...

My point is based on capacity and time able to use. Plus the convenience of plugging charger into Tx. LiPo of 2100 will give 80% maximum ... 1680mAh safely ... which is then 6.7 hrs. My NiMH at 2300mAh can supply much greater % .. lets say 90% for sake of discussion and if we deduct the 200 capacity difference ... we say my NiMH are 2100 same ... this is now 1890mAh .. = 7,6 hrs and the voltage has not changed as much as a LiPo does ... I'm still pushing out near full voltage.

Not trying to create an argument - I just don't see any advantage in LiPo.

My 9xr is on LiPo ... but that's because HK designed and created a LiPo specifically for it ... but it still needs Tx case opened to charge the darned thing... why they couldn't have sorted that as well - eludes me.

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Old 04-20-2014, 10:56 AM   #11
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Originally Posted by solentlife View Post
So what is advantage of the LiPo over this ?
Capacity ? None - I have 2300 mAh ... more than the average LiPo used in Tx's.
The main advantage is exactly what you mentioned, capacity. In the case of the DX8 the replacement LiPo is 4000mAh compared to the stock NiMh which is 2000mAh. This is because you can squeeze a lot more mAh into the same physical size of pack if you use LiPo technology vs NiMh.

In practice the LiPo in the DX8 lasts far more than twice as long compared to the stock DX8 battery because Lipos have virtually zero self discharge. The DX8 doesn't need the case opening to charge, you just plug the very same charger as you use for the stock NiMh battery. Spektrum did the job properly and included internal charging circuitry suitable for a LiPo. It would be wrong to condemn LiPo technology just because of the poorly executed application in the 9XR.

Low self discharge Eneloop (or similar) do close the gap somewhat but still don't offer the mAh capacity advantage of the LiPo. Personally I never had much luck with cheaper brands of low self discharge NiMh, they all died after relatively few cycles.
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Old 04-20-2014, 12:14 PM   #12
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Originally Posted by JetPlaneFlyer View Post
The main advantage is exactly what you mentioned, capacity. In the case of the DX8 the replacement LiPo is 4000mAh compared to the stock NiMh which is 2000mAh. This is because you can squeeze a lot more mAh into the same physical size of pack if you use LiPo technology vs NiMh.

In practice the LiPo in the DX8 lasts far more than twice as long compared to the stock DX8 battery because Lipos have virtually zero self discharge. The DX8 doesn't need the case opening to charge, you just plug the very same charger as you use for the stock NiMh battery. Spektrum did the job properly and included internal charging circuitry suitable for a LiPo. It would be wrong to condemn LiPo technology just because of the poorly executed application in the 9XR.

Low self discharge Eneloop (or similar) do close the gap somewhat but still don't offer the mAh capacity advantage of the LiPo. Personally I never had much luck with cheaper brands of low self discharge NiMh, they all died after relatively few cycles.
Ok - first JPF - please stop harping on the 9xr and 9x ... you have a fixation on it and it gets a bit boring after a while.

On Lipo's for radios - most posts and references I find are for the standard 3S 2100 ... then it is lucky that DX8 has gone for a greater capacity. That obviously is because they are using a lower cell count and can up the capacity ... physical size and all that.

My point about raising the discussion LiPo vs NiXX .. is for more general .. but in the case of DX8 - I accept it is not the norm and can have advantage. That is definitely not the case with other radios where a 3S 2100 is the norm.

Second -if you have had bad luck with LSD ... then you have had bad cells or bad management of them ... my Grundigs are in their 3rd year and STILL performing excellently. Only just a few months ago in support of a post about LSD NiMH - I purposely discharged my Tx LSD's by leaving the Tx on ... the LVA sounded first intermittent warning at 9.5hrs ... steady warning at 10hrs.
The Tx was still in full control of all ...
I certainly consider that a good result. I know others who achieve similar.
And just for you JPF ... my Radiolink (Futaba recase) is same on LSD's. My JR Propo on NiMH from a 3rd party Battery outfit in UK - who provide custom packs - that is same ... unfortunately the JR is now out of use but battery pack is still A1 ...


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Old 04-20-2014, 04:38 PM   #13
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Nigel,

Sorry, the point I was trying to make is that the requirement to open the case to charge your LiPo isn't an inherent fault of a LiPo battery, but is a issue with the implementation in that particular Tx. IMHO it's unfair to criticise all Tx LiPos because of that.

LiPo's will always be much lower cell count than NiHh because a single LiPo cell is around three times higher voltage compared to a single NiMh cell. The 2s LiPo in the DX8 actually has a significantly higher voltage that the NiMh it replaces, despite having less cells.

You would only need a 3s LiPo if the Tx was designed for eight NiMh cells (9.6v). Many Tx's these days are designed for lower voltage operation, so 2s LiPo is more than enough for them.


But I agree, the 'best battery' for a Tx depends to a large extent on the Tx itself. The DX8 along with most new Spektrum Tx's are designed for LiPo's and benefit from much increased energy density that a LiPo offers, plus easy hassle free charging. Other Tx's might be better off using low self discharge NiMh, which are still a perfectly good option. The NiMh also has some advantages over LiPo in that it does them no harm to leave fully charged for long periods.

In fact i think that the very best option might actually be a LiFe pack, I'm not sure why Tx manufacturers havent gone that way?

The low self discharge NiMh I got were 'off-brand' cheapos off eBay, so probably not representative of what to expect from good quality batteries.
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Old 04-20-2014, 05:12 PM   #14
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JPF ... no prob.

I think the case opening of most brand radios to charge a Lipo is a valid point. With your DX8 - that has been solved by them designing a charge circuit to handle it being a LiPo. Most do not. They provide a NiXX format circuit for charging via the Tx socket. It's likely you could charge a LiPo via the socket - but how about balancing - a fact that LiPo's need more than other formats.

If the Tx is designed to be able charge IN SITU a LiPo - then great - I would use and be happy with such... for the exact reasons you give - higher capacity per physical dimensions of the LiPo.

It is also interesting that even HK has seen the potential for conflagration with LiPo's and designed its 9xr pack with protection circuits built in. Some have mistaken these for just charge related issues ... but if looked at properly - it's about safety as well ... not to over-charge and also not to over discharge. Both conditions can lead to unsafe LiPo when recharged or handled.

The world is evolving ... moving on ... yesterdays best tech is todays dinosaur. So as LiPo and Tx tech evolves - soon we will be discussing why change FROM LiPo to a newer type !!

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Old 04-20-2014, 06:47 PM   #15
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Fair point about balancing. There is no balance ciruit built into the DX8 charger. Perheps you could say the same for NiMh, they too dont have any balancing facility unless you take the cells out and charge individually. I don't know enough about NiMh to say if they benefit from balancing or not?

The likes of laptop batteries are also LiPo and they dont have balance connections either, so perhaps on low discharge rate duties balancing isn't really and issue?
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Old 04-20-2014, 07:54 PM   #16
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I think the biggest difference in charging of LiPo and NiXX ... is that NiXX continues charging at trickle rates once it reaches Delta and cuts of main rate. That is with the higher rate auto chargers like the Pro-plus I use. It charges at up to 1A ... Delta peaks and drops to 50mA trickle.

Lesser rate chargers like Futaba / JR wall chargers are usually low rate anyway ... all mine (I have 3) are 50mA both Rx and Tx... constant.

A LiPo charger shuts off once it detects full voltage if not in balance format.

Also I am told by a Batt Tech - that it is highly unlikely that a NiXX will ever charge up past it's max design voltage - unlike LiPo which can go over ... if not monitored and subject to auto shut off.

I have and I'm sure you have seen readings on a Wattmeter / charger display .. Cell over-voltage on an occasional LiPo ? I've never seen that with NiXX.

So in essence, I suggest that a NiXX pack will balance out on its own by virtue of the cells will not go over-voltage, the charger reverts to trickle charge once it detects full state- therefore the trickle charge will bring up any cell lagging behind ... any cell that is full will basically prevent charge to itself as it's only low rate trickle. If you see what I mean !

Well lets put it this way - When I charge my Tx NiMH .. I have checked them in a Cell Checker and they all are same level. Without need for balance leads etc.

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Old 04-20-2014, 08:32 PM   #17
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The Spektrum DX6i I purchased in December 2013 is pretty easy to charge. It came with a 5.5v - 0.15A charger, plug adapter and (4) Spektrum AA Ni-MH 1500mAH, 1.2v batteries. The adapter fits into the TX.....making charging without removing batteries "less hassle"..... be it a very slow charger.

I've tested various Ni-MH AA's (Energizer, Duracell, Rayovac, Spektrum and Monster) rechargables rated btw. 1500mAH to 2450mAH.......using both the Spektrum charger and external wall mount "fast" chargers like the Duracell ion Speed 4000, 3v....775mA. (I have other wall mount chargers like the Energizer model CHVCM 2.6v...260-300mA and Monster Power 2.3v...600mA), but the Duracell, so far, has been the fastest and most reliable.

The Spektrum TX has never gaged the voltage rate of any of the batteries more than 6.0v (all of which have less than 10 hours of use, and having all been discharged at the same rate (using the same MagLite flashlite), down to 4.0v, (checked with the same voltage meters CEN-TECH digital and Extech digital).

The Spektrum never charges any of the batteries, after 10 hours, to be higher than 5.7v (that's what it reads). But, after having externally charged with the Duracell, the TX has shown a reading as high as 6.0v and the charge times (based on Mah size of the batteries) have never been more than 2 hours for any of the battery brands or mAh......the higher mAh's seem to charge faster (btw. 15min to 30min less)........All tests done with set's of (4) same brand and mAh ratings.

So, even though the Spektrum charger is more convenient, if I want more voltage stored....I use the external charger......I'm just glad I can get everything charged to at least 5.7v.......

Note:

The manual that came with the TX states they do not recommend lipo's to be used.....but it does not state "do not use lipo".....

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Old 04-20-2014, 10:34 PM   #18
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mmmm The only trouble is the 6i is in reality old hat now .. it's been around quite a while, and despite it's upgrade to the x format ... it's still an old radio.

Judging by others posts - Spekie has now accepted the use and installation of LiPo's ... whether that's good or bad - I'm out on that ... as I see it - it depends on the radio and how it's put together - NOT what we decide to put in it. Apparently the DX8 is LiPo designed.... indicating Spekie has moved on.

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Old 04-21-2014, 12:50 AM   #19
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Pizzano is right. LiPo is not recommended for the DX6i or the other older generation Spektrum Tx's such as the DX7. The voltage regulator in these Tx's wasn't designed for the higher voltage produced by a LiPo and might fail if you use one (though some do seem to get away with it).

On the newer generation Speky Tx's (DX8 and onward) there is the option in the programming to select LiPo. On the DX18 LiPo or LiIon are the only options, no option for NiMh exists.

FWIW higher voltage on the battery does not increase the transmitting power of the Tx one iota. The Tx has a voltage regulator that steps the voltage down to the level required by the internal circuitry. Within the regulator's working range it doesn't make any difference what the input voltage is, the output voltage remains constant. So the Tx's output power and range is totally unchanged between a freshly charged full voltage battery and one that's hitting low voltage alarm. Obviously if the voltage drops too far it comes to the point that the correct voltage cannot be maintained by the regulator, then bad stuff will happen, but providing you stop flying when the alarm sounds that wont occur.
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Old 04-21-2014, 01:09 AM   #20
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Increasing voltage after the regulator is more likely to fry the chips than increase output power.

Some who tried the LiPos in X9303's found out that when the regulator fried it could send full LiPo pack voltage to the TX's chips and they just melted down the whole TX.
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Old 04-21-2014, 01:52 AM   #21
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Originally Posted by solentlife View Post
OK ... here's a question.

Denny is using LSD NiMH in his Tx ... he chose Enerloops, I choose Grundig ... we both get excellent storage capability and excellent output ...
I don't know what mA capacity Denny's are but mine are 2300mAh ... and they power my Tx's for over 9 hours before LVA sounds. I still have at least a good amount for landing etc.
Denny and I can charge via the Tx socket without opening the battery compartment, no need to remove battery ... we just plug in and charge.

So what is advantage of the LiPo over this ?
Capacity ? None - I have 2300 mAh ... more than the average LiPo used in Tx's.
Long term storage of charged capacity ? None - he and I use LSD NiMH .. I can leave my Tx while I'm away on assignments and return and use without charging. But in fact as I can just plug in and charge without opening Tx ... I can stick my 50mA charger on and forget it ... so no matter what - I always know I have full charge anyway.
LiPo of 2100mAh capacity in fact will need charging way before my 2300mAh NiMH ... because I can run my NiMH down further than you can run your LiPo down ... and still have perfectly good cells... (That is with the 200mAh deducted of).

I can also buy my NiMH cells over shop counter locally .. I can swap one or more instead of a whole pack ... they are cheap as well ....

So again ... Why ? So far I see no advantage - in fact I see factual reasons to NOT change.

There is of course another factor that will play on this ... to use a LiPo in many Radios today requires a voltage regulator / stepper as the LiPo's do not match radio requirement. Most radios are matched to NIXX cell counts ...

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That says it all!

It goes back to the old KISS (Keep It Simple Stupid) argument. LiPo batteries work just fine. But I've just finished checking out four 2200 Mah 3S LiPo batteries from a club member that were questionable. Three of them dropped below 4 volts when a load of one amp was placed on them. The last one only had about 20% of rated capacity.

Compare that to a decent Nih battery pack, which when they are getting old, just slowly fade away, leaving you plenty of time to replace it before it causes a problem.

It's just me, but I'll just keep using Nih battery packs in my transmitters. On the other hand, receiver packs is a real different story however.

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Old 04-21-2014, 01:59 AM   #22
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Never assume a battery can't be overcharged... You can explode NiCd or NiMh by overcharging.

And the only type battery I have ever had burn by accident was a NiMh. (2200 mah 4 cell being charged on an OEM Hitec wall-wart that came with their 6ch FM radio system.)
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Old 04-21-2014, 02:02 AM   #23
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Originally Posted by JetPlaneFlyer View Post
Fair point about balancing. There is no balance ciruit built into the DX8 charger. Perheps you could say the same for NiMh, they too dont have any balancing facility unless you take the cells out and charge individually. I don't know enough about NiMh to say if they benefit from balancing or not?

The likes of laptop batteries are also LiPo and they dont have balance connections either, so perhaps on low discharge rate duties balancing isn't really and issue?
By the nature of these Nih (and the old Nicads for that matter) they do not need balancing. The Nih cells are self balancing. During the charge cycle, the voltage on each cell slowly creeps up to around 1.35 or 1.4 Volts DC, depending on the value of the charging current. When these batteries hit full charge, their voltage drops, very slightly, like about 1/2 percent or so. Those peak chargers watch for that slight drop in voltage, and shut down the high charge rate.

As for the Laptop computers, their batteries generally have balancing circuitry internal to the battery. That is one reason those computer batteries are so expensive. (Yeah, I've pulled apart a few of those packs.)

That goes back to the original source of those A123 cells, pulled out of the Dewalt 36 Volt battery packs. I've pulled cells out of three of those packs over the years. Built inside the pack is a potted circuit board that is permanently wired across all twelve cells in the pack. The purpose of that circuit board is balancing the battery pack while it is being charged. The circuitry also shuts off the drill during use when any cell drops below safe voltage levels.

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Old 04-21-2014, 02:17 AM   #24
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Originally Posted by fhhuber View Post
Never assume a battery can't be overcharged... You can explode NiCd or NiMh by overcharging.

And the only type battery I have ever had burn by accident was a NiMh. (2200 mah 4 cell being charged on an OEM Hitec wall-wart that came with their 6ch FM radio system.)

Years ago, it was not possible to blow up a Nicad battery. Those batteries were mfg with a thin disk inside the battery that sealed the battery. If the battery is overcharged, that thin disk bulged outward. This takes over 100 PSI. The outside positive cover had a sharp pin point that punctured that disc, ruining the battery, but prevented an explosion.

Nowdays, they are using a rubber seal that can vent if the pressure gets to high. But sometimes those rubber seals don't vent, and the thing blows. Last year, a club member tried charging a 4 cell Nih pack with the wrong setting on a cheap charger. The battery blew, put a hole through the side of the fuse, and pieces of that battery put holes in another model 10 feet away.

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Old 04-21-2014, 02:45 AM   #25
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Wrong.... People have blown up NiCd from the first that they were put on the market.

The big scare in the early 1970's was NiCds being dangerous because they exploded. The cause of them exploding was similar the the cause of the LiPo fire scare.... improper charging. Stick a Nicd AA in a charger made for "Dry Cells. The charger will try to push it to 2.0 V Leave it on there long enough and it will explode.

Then there's the powered sailplane competition that still specifies NiCd. They push the NiCds so hard that they occasionally have one explode from overheating.

And the old timer + resistor based 15 min fast chargers for NiCd could blow the batteries up if the timer got stuck.
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