go_away

Author Topic: 6v Battery Problems  (Read 1693 times)

0 Members and 1 Guest are viewing this topic.

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
6v Battery Problems
« on: January 28, 2012, 06:48:56 PM »
hey, im trying to figure out whether i have a defective/broken battery or a bad charger. It is a 3300 Mah 6v tenenergy battery but after leaving it on its charger for 24+ hour checking it periodically it did not get charged past 5.3 volts.

 Now before all this i had charged it overnight then used it for quite awhile messing around with the axon 2 communicating to hyperterminal. Then the battery ran out and dropped below the operating voltage at around 4.8v so i then plugged it in to be charged and like i said it did not go past 5.3v also when i plugged it back into the axon the green indicator light blinked for 1 second then went off and only the red power indicator was on. I unplugged the battery and checked the battery's voltage and it was around 4.3v and was slowly climbing its way back up. Also while plugged into the axon its voltage was at 4.3.

So im ready to buy a new battery and charger (i was looking at a smart charger) and was wondering if anyone knows of a  good 6v battery and charger to go with it and where to buy one, Thanks.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #1 on: January 28, 2012, 08:25:34 PM »
Hi,

You didn't tell which chemistry or number of cells, but it sounds like a 5 cell NiMH battery that has been discharged to the point of one cell reversing polarity to some extent.

You gotta confirm number of cells and chemistry before a substitution can be found.

Getting a smart charger (not just a semi-smart one) and making an End-of-Discharge detector that cuts the power before cell reversal occurs would be the best way of keeping the cells balanced.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
Re: 6v Battery Problems
« Reply #2 on: January 28, 2012, 09:07:13 PM »
Ah sorry i forgot and you are right it is a 5 cell niMh also the robot i am going for uses 8 servos, a blackfin camera, and  a sharp ir. Any recommendations to a good 6v battery and for the charger i was considering this http://www.trossenrobotics.com/store/p/5914-Smart-Universal-Charger-for-2-4-7-2v-NiMH.aspx

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #3 on: January 30, 2012, 08:44:09 AM »
Hi,

[...] the robot i am going for uses 8 servos, a blackfin camera, and  a sharp ir. Any recommendations to a good 6v battery

I don't know what current the Blackfin needs, but with 8 servos, I'd go a little higher than 3300mAh.
This is a 4200mAh battery, but it doesn't come cheap, so you should shop around a bit.

Another option would be to use loose cells in a battery holder. That way it's easier to keep each cell in shape, by charging them separate from each other.


and for the charger i was considering this http://www.trossenrobotics.com/store/p/5914-Smart-Universal-Charger-for-2-4-7-2v-NiMH.aspx

I have no personal experience with it, but a few points to note:
It has got fairly long leads from charger to battery and that bugs me, especially when it's supposed to use dV termination.
It terminates on -dV, which is OK for NiCd's. For NiMH, it should terminate on 0dV.
Their sales pitch: "Use pulse and negative pulse technology to avoid battery overheating during fast charging, optimized for battery pack's cycle life." is pure bullshit (if you prdon my French). A negative pulse will heat just as much as a positive pulse and there's no indication that negative pulses does anything good fo charging.

It's cheap allright, but that makes me wonder too.

Here is what I'd consider a cheap charger that will keep your batteries in shape and it works with all battery types up to ~12V, currents up to 5A and have build in balancer port for Lithium based batteries.
It might sound expensive, but it'll probably last you a life time and keep your cells happy for as long as possible.

Or, you can make a simple slow charger, from a wall wart and a handful of components, that will charge your cells in 15 hours.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline joe61

  • Supreme Robot
  • *****
  • Posts: 417
  • Helpful? 16
Re: 6v Battery Problems
« Reply #4 on: January 30, 2012, 09:31:08 AM »
Here is what I'd consider a cheap charger that will keep your batteries in shape and it works with all battery types up to ~12V, currents up to 5A and have build in balancer port for Lithium based batteries.


I've been looking into moving to Li-po or Li-ion for 3V stuff (around 3000maH, but I know just enough about that chemistry to be afraid of it, so I'm interested in this. Do you think it would be better to buy a charger specifically for lithium based batteries, or is this good (safe)? It would be nice to have one charger for both NiMH and lithium.

Joe

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #5 on: January 30, 2012, 10:01:43 AM »
Don't confuse battery capacity, such as 3300mAh, with current rating, such as 10A. They are almost entirely unrelated. A 100mAh battery could supply 20A, for example.

The Blackfin eats a good bit of current. Check the datasheet, but from memory it runs on I think 3.3V using about 0.3A, so wastes a lot through the voltage regulator.

Normally I bash Chinese products, but here is a good place to buy chargers:
http://www.hobbyking.com/hobbyking/store/__216__408__Battery_Chargers_Acc_-Battery_Chargers.html

Shipping takes like a month, but you can't beat those prices. They have a user comment/rating system so you can verify if the product is quality or crap.

I've put heavy use into this guy without a problem: http://www.hobbyking.com/hobbyking/store/__7028__Turnigy_Accucel_6_50W_6A_Balancer_Charger_w_accessories.html
The fan on it broke, though, but that's already mentioned by others in the comments. Still works otherwise after 2-3 years.

The issue with LiPos is that they have no voltages between 3.6V and 7.2V. Servos don't work at 3.6V, and they fry at 7.2V. You can get a LiFe battery, which is safer than LiPos and is about 6.5V, but you'd need a LiFe charger. LiFes don't hold as good a charge as a LiPo, however, and most servos will still fry at 6.5V. If you use either, you'd need to get a high powered switching regulator to bring the voltage down to max of 6V, losing about 10% of battery power in inefficiency.

This is why I just recommend using NiMHs for the Axon . . . much cheaper and less of a hassle. If you need more current, put two in parallel and call it a day :P

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #6 on: January 30, 2012, 11:37:33 AM »
Hi,

Don't confuse battery capacity, such as 3300mAh, with current rating, such as 10A. They are almost entirely unrelated. A 100mAh battery could supply 20A, for example.
That's a very bold (but very  incorrect too) claim!
A 100mAh NiMH battery with a 20A discharge is simply impossible!

20A equates to 200C here and you won't get over 10C max from the very best NiMH cells.
Capacity is very much related to max. discharge currents.


Also, don't confuse a good charger with one that lasts a long time. Charger lifetime is totally unrelated to quality, which is a matter of how well the charger takes care of the batteries.

Any good charger will last a lifetime if not mistreated or physically abused, but only a few of them are really nice to the battery cells.

A difference in discharge termination of only a few percent means a lot to the lifetime of the cells and when charging batteries (rather than loose cells) the charge algorithm in itself is a main factor in getting the nominal life time as well (like how well it equalizes the charge) - some may shorten life time to less than 50%.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #7 on: January 30, 2012, 12:12:38 PM »
Hi,

I've been looking into moving to Li-po or Li-ion for 3V stuff (around 3000maH, but I know just enough about that chemistry to be afraid of it, so I'm interested in this. Do you think it would be better to buy a charger specifically for lithium based batteries, or is this good (safe)? It would be nice to have one charger for both NiMH and lithium.

While I don't know this charger up close and personal, it appears to be well built, with sensible short leads and a balancer port (+ cable) and appearance and quality of the innards usually goes hand in hand. The only thing I dislike about it is the fan, as I prefer passive cooling, but that would make it quite a bit larger, so for a small portable unit, I wouldn't mind having it on my table and I might buy it some day, although I don't have  real need - toys are fun ;D

You shouldn't be afraid of lithium, just respectful towards their needs. LiFe is the safer (but somewhat weaker) alternative if you want them.

If you respect and uphold the upper and lower voltage limits of lithium and don't pierce their casings, they're quite safe (or they wouldn't be in each and every cellphone and portable music player etc.). Just make absolutely sure not to over charge or under discharge - I sometimes charge lithiums by hand with a lab supply, setting the voltage (using an external DMM) and max current by eye.

I'd assume a guy like you could easily put together a charger - plenty of complete charger chips and chip sets exists, just look at Maxims selection.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
Re: 6v Battery Problems
« Reply #8 on: January 30, 2012, 11:01:56 PM »
Thanks for the replies!

Quote
I don't know what current the Blackfin needs, but with 8 servos, I'd go a little higher than 3300mAh.
This is a 4200mAh battery, but it doesn't come cheap, so you should shop around a bit.

ill consider that but the charger you recommended is a little bit out of my price range but then again not completely neccesary if i just get a non smart charger and monitor the battery's time on it (correct me if im wrong)

also to admin if you don't mind me asking what was the battery you used for the erp as my robot and it are of similar builds?

and if i wanted to use single cells could i use just 4 rechargable aa or 8 in 2 sets of 4 layered in a parallel? (to increase amps)

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #9 on: January 31, 2012, 12:09:40 AM »
This reply is more meant for Robot_Longbordr than Soeren . . .

Don't confuse battery capacity, such as 3300mAh, with current rating, such as 10A. They are almost entirely unrelated. A 100mAh battery could supply 20A, for example.
That's a very bold (but very  incorrect too) claim!
A 100mAh NiMH battery with a 20A discharge is simply impossible!
I didn't say NiMH :P
(I meant hypothetically . . . I probably should have been more clear on that)

People often confuse a 3000mAh battery as being capable of only supplying 3A, and I'm pointing out that this is wrong. In the datasheet there is another separate current rating that must be referenced. The more modern 6V NiMHs I've seen are usually rated for ~10A. That's enough for about ~6 servos.

Quote
Capacity is very much related to max. discharge currents.
I would argue it's only a lose relation. Design, manufacturing quality, temperature, age, specific chemistry, and parallel vs serial pack designs all play a part.


Quote
Also, don't confuse a good charger with one that lasts a long time. Charger lifetime is totally unrelated to quality, which is a matter of how well the charger takes care of the batteries.
The problem with quality, and that goes with anything really, is it's hard to know until after it fails on you . . . to be sure, buy the well known brand name with the warranty . . . that will cost much more. But hey, it might save you money in destroyed batteries and replacement chargers . . .

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #10 on: January 31, 2012, 12:24:48 AM »
also to admin if you don't mind me asking what was the battery you used for the erp as my robot and it are of similar builds?
Your typical cheap hobby servo uses an average 0.5A, and peaks around 1A. It really depends on how much torque they are experiencing. So lets assume worse case scenario, and you have all servos activated at the same time . . . if you have 8 servos that's about 8A current draw.

If your battery is 3300mAh, and you run your robot non-stop, your battery will be dead in about 25 minutes. The voltage will probably drop below the Axon minimum voltage, causing resets, in about 20 minutes. But you don't run it non-stop when experimenting and programming it, so you'll more likely have an hour of play time with that battery.

This is, of course, assuming you're using small servos and your battery is capable of 10A.  Bigger servos can do more like 3A+ each, so you should measure them with a multimeter to avoid the guessing game. Some cheaper batteries claim 10A, but what they really mean is up to 10A under perfect laboratory conditions . . . giving you more like 5A in reality land.

For my ERP, I use two batteries. One big one for servos, and another small one for electronics (I put the Axon in dual power mode). That way I don't care if the servos cause my battery to drop below 5V occasionally during high torque situations. I also have extra batteries so that one is charging while I'm using the other.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #11 on: January 31, 2012, 11:16:13 AM »
Hi,

This reply is more meant for Robot_Longbordr than Soeren . . .

I didn't say NiMH :P
(I meant hypothetically . . . I probably should have been more clear on that)
The thread only discussed NiMHs, but even so, which chemistry would you credit with 200C?


People often confuse a 3000mAh battery as being capable of only supplying 3A, and I'm pointing out that this is wrong. In the datasheet there is another separate current rating that must be referenced. The more modern 6V NiMHs I've seen are usually rated for ~10A. That's enough for about ~6 servos.

This is, of course, assuming you're using small servos and your battery is capable of 10A.  Bigger servos can do more like 3A+ each, so you should measure them with a multimeter to avoid the guessing game. Some cheaper batteries claim 10A, but what they really mean is up to 10A under perfect laboratory conditions . . . giving you more like 5A in reality land.
What happened to 200C? ;)


Quote
Capacity is very much related to max. discharge currents.
I would argue it's only a lose relation. Design, manufacturing quality, temperature, age, specific chemistry, and parallel vs serial pack designs all play a part.
If it weren't closely related, max. discharge rates wouldn't be given in nC ratings.
No matter design and quality, a larger capacity within a given manufacturers range will always have a larger max discharge, as they will have the same nC rating.

Temperature will affect capacity and hence the max. discharge, but the higher nominal capacity cells will still be the one with the higher capacity and max. discharge at elevated temperatures.

I don't see where series and/or parallel packs enter the equation?
A larger nominal capacity will have the larger discharge rate, no matter how many are coupled together in serial or parallel.


The problem with quality, and that goes with anything really, is it's hard to know until after it fails on you . . .
You mean that you don't know if your tools are good or bad until they break either? ;D
I'd assume a mechanical engineer would know how to get the right stuff by eye (and perhaps by "pinging" the steel and judge by ear)?

Choosing stuff (Electronics or not) that is boxed up in a nice and sensible way, rather than poor boxes with flash from the production and perhaps wobbly or skewed where they ought to be straight goes along way - it's rare to see crappy circuits in well crafted and thoughtful laid out boxes. The same goes for components, where the poor ones usually is quite spot-able, although it is much easier to judge when you can hold the subject and examine it up close.

Even buying blue jeans, I find it quite easy to get the good stuff. We have a chain of stores that focus on blue jeans, where they're sorted by size only and good and bad qualities are mixed in stacks. Just running the hand up the side of such a stack quickly sorts the good ones form the lousy ones loaded with starch to make them appear good.

Buying poor quality is usually too expensive in the end.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #12 on: January 31, 2012, 11:51:59 AM »
The thread only discussed NiMHs, but even so, which chemistry would you credit with 200C?
A hypothetical chemistry containing anti-matter ;)


Quote
Quote
Capacity is very much related to max. discharge currents.
I would argue it's only a lose relation. Design, manufacturing quality, temperature, age, specific chemistry, and parallel vs serial pack designs all play a part.
If it weren't closely related, max. discharge rates wouldn't be given in nC ratings.
Brand-name manufacturer A makes a 6V battery and it has 5C, while crappy manufacturer B makes a 6V battery and it has 2.5C. Sure, it's related, but the difference is 2 fold. Hence loosely related :P


Quote
I don't see where series and/or parallel packs enter the equation?
For safety reasons, LiPos in consumer electronics are becoming in-series only batteries (no need to balance cells when they are in series, as current is the same for all). The output voltage stays the same but the capacity and current output are affected.


Quote
The problem with quality, and that goes with anything really, is it's hard to know until after it fails on you . . .
You mean that you don't know if your tools are good or bad until they break either? ;D
I'd assume a mechanical engineer would know how to get the right stuff by eye (and perhaps by "pinging" the steel and judge by ear)?
Unfortunately it's not that easy. I'd have to open up the casing to study the electronics inside, and then study the wiring, look up the parts, and check the soldering job. I can only guess on the software. Sure, for me with electronics manufacturing experience I can identify quality. But only after buying it and opening it up. Other people without experience have to rely on reviews.

As for mechanical tools, you don't know the quality of metal it's made from until it rusts up, bends, or dulls. And for precision tools like crimpers, it's hard to tell if it will crimp my pins right with only that 1"x1" jpeg-artifact picture on the website to judge by. :-\

But . . . what we all see is the price.

I've learned the hard way that the only sure measurement of quality is brand-name + warranty. But seeing a price tag 3x cheaper always overrules my better judgement . . .

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #13 on: February 01, 2012, 02:47:56 PM »
Hi,

Brand-name manufacturer A makes a 6V battery and it has 5C, while crappy manufacturer B makes a 6V battery and it has 2.5C. Sure, it's related, but the difference is 2 fold. Hence loosely related :P
That's comparing apples to oranges, something like arguing that a 600 CCA lead-acid is different from a 1.7Ah SLA. Apples to apples, the relation holds.


For safety reasons, LiPos in consumer electronics are becoming in-series only batteries (no need to balance cells when they are in series, as current is the same for all). The output voltage stays the same but the capacity and current output are affected.
There's a thing you didn't grasp about balancing it seems - it's not a question of series or parallel cells (eg. two cells in parallel will not need balancing). Series connected cells need balancing to keep each cell at the same voltage as they age (and then charge) differently (even NiMH and other chemistries would benefit from balancing when charged in series, but since they aren't that much of an explosion risk, nobody throws money after that).
When consumer batteries don't use balancing it's for a different reason - the sooner your battery dies, the sooner they make another buck and they die sooner as the protection circuits see the problem and either disables the entire battery or reduce the (dis-/)charge to what the weakest cell can handle.


Unfortunately it's not that easy. I'd have to open up the casing to study the electronics inside, and then study the wiring, look up the parts, and check the soldering job. I can only guess on the software. Sure, for me with electronics manufacturing experience I can identify quality. But only after buying it and opening it up. Other people without experience have to rely on reviews.
So, in essence, you say that you cannot judge quality by the immediate appearance (when actually holding the device in question)?


As for mechanical tools, you don't know the quality of metal it's made from until it rusts up, bends, or dulls.
I have to disagree strongly. They don't make lousy tools and pay a lot of attention to eg. the handle of a screwdriver - it's simply bad economy. And just clank two tools together and listen... Tells a lot about the quality to the trained ear.


And for precision tools like crimpers, it's hard to tell if it will crimp my pins right with only that 1"x1" jpeg-artifact picture on the website to judge by. :-\
Yes, you need to hold it to judge it.


But . . . what we all see is the price.
Pair the price with common sense and you might avoid a few mistakes here and there :)


I've learned the hard way that the only sure measurement of quality is brand-name + warranty. But seeing a price tag 3x cheaper always overrules my better judgement . . .
I have seen a lot of crap from brand names over the years, but in DK, there's a guarantee (by law) on all private end user stuff (including the most crappy tools).
I have returned eg. a couple of top range  (9 digits) professional Philips bench DMM's with PC interface and what not (back in the eighties this was a huge thing) and the "cheapest" of them was a little over $7000, the other around $8500 (in the mid-eighties), ordered by phone from a reputable distributor that we did business with on a regular basis, but they were so crappy made, with the buttons so loose that they rattled if you pushed the instrument, that I'd never be able to trust their precision. It has to feel right :D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #14 on: February 02, 2012, 12:36:17 AM »
I think we've hijacked this thread . . .

Quote
There's a thing you didn't grasp about balancing it seems - it's not a question of series or parallel cells (eg. two cells in parallel will not need balancing). Series connected cells need balancing to keep each cell at the same voltage as they age (and then charge) differently (even NiMH and other chemistries would benefit from balancing when charged in series, but since they aren't that much of an explosion risk, nobody throws money after that).
If a cell dies when the batteries are in series, even if one cell shorts, the good cells are not shorted - ie a safe dead battery. If a cell dies when the batteries in parallel, and that cell shorts, you could have a fire. There was an article in IEEE Spectrum, of which I can't find on a quick search, that described this much better . . . whether this reduces battery life I can't say, but their claim was that it did maximize battery safety. As you said, companies benefit from selling more batteries, but not from lawsuits . . .


Quote
So, in essence, you say that you cannot judge quality by the immediate appearance (when actually holding the device in question)?
Try judging the quality of a battery charger without being allowed to try it out - only looking at the outside casing. That's the point I'm trying to make. We often aren't able to judge the quality until after the purchase, because the item is bought online or it's covered in packaging at a physical store. Or we just aren't an expert in that particular tool (ie first charger you've owned, etc).


Quote
I've learned the hard way that the only sure measurement of quality is brand-name + warranty. But seeing a price tag 3x cheaper always overrules my better judgement . . .
I have seen a lot of crap from brand names over the years
Oh I have too. But brand name stuff has online reviews, and the warranty lets me return the crap . . .

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #15 on: February 03, 2012, 03:31:28 AM »
Hi,

I think we've hijacked this thread . . .

Considering it was on NiMH cells yes. I hope the OP got the answers he was looking for :)


If a cell dies when the batteries are in series, even if one cell shorts, the good cells are not shorted - ie a safe dead battery. If a cell dies when the batteries in parallel, and that cell shorts, you could have a fire. There was an article in IEEE Spectrum, of which I can't find on a quick search, that described this much better . . . whether this reduces battery life I can't say, but their claim was that it did maximize battery safety.

Cells don't short out, they dwindle down. This can be as bad as a short, if no safety is in place, as it will then start to charge in reverse and catch fire.
If one cell is shorted (physically), it will likely catch fire (if it has got no safety circuit).
One cell bursting into flames will likely make the remaining cells catch fire as well.

But you have to consider that the paralleling is on cell level, so a weak cell in parallel with a good cell will just make the combo seems lik a semi-weak cell - the voltage of the weak cell cannot go any lower than the good cell.
Here's how a 3S2P battery is made up.



As you said, companies benefit from selling more batteries, but not from lawsuits . . .

Exactly, that's why you don't get unprotected lithiums in consumer goods.
Remember the Apple lawsuits on their weak batteries that died prematurely on numerous consumers iPods?

It's too bad that there is such a viral spread of horror stories about lithiums. Handled correctly, they're no more dangerous than NiCd's, which probably won't scare off that many. Most of the bad rep is due to people running with half stories and portraying themselves as "experts", when they actually don't know enough to even make themselves safe - using a lithium battery for any number of charge cycles don't make anyone an expert.
Bad things happens to people being idiotic about lithiums, but more people get hurt by using sharp knives in the kitchen or by cars in traffic (even when not behaving idiotic), but I don't see as many warnings on kitchen knives or cars. Some things just have a potential for being dangerous, if you don't behave accordingly - slipping, when going down a flight of stairs, can kill you.

I read a summation of lithium related fires (on RC-universe or a similar site). All of the fires was caused by people with the head under their arm, like charging eg. a 2S on the 3S charger setting which equates to a 50% overvoltage - no surprise that they caught fire.
If people don't trust themselves that they are able to set a charger switch correctly, they should just go with one that detects and sets this automatically, rather than scaring lots of people off using lithiums.


Try judging the quality of a battery charger without being allowed to try it out - only looking at the outside casing. That's the point I'm trying to make.

It may P them off at the stores, but I always unpack the goods to avoid dud buys. Wouldn't buy anything without knowing what's in the box - if a shop won't let you open the box... There's plenty of shops.


We often aren't able to judge the quality until after the purchase, because the item is bought online or it's covered in packaging at a physical store. Or we just aren't an expert in that particular tool (ie first charger you've owned, etc).

Online shopping is an entirely different thing, of course, but packaging can be removed and judging quality should not take particular knowledge about a given product - it's a look & feel thing. I cannot explain it in words, but I never doubt my senses and so far I have only gotten crappy stuff when I knew I was buying crappy stuff - like eg. a delta grinder I got for next to nothing - I knew it had crappy nylon bearings and such, but since it's a tool I use maybe once each 3 years or so, buying an expensive pro tool would be insane. Getting stuff cheap is a quality in itself ;D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #16 on: February 03, 2012, 04:24:54 AM »
As for LiPos catching on fire . . . yes, they are designed to fail gracefully and should never catch on fire.

However, you are assuming that the factory has perfect quality during the manufacturing phase (a serious problem with batteries so I've read). Then you add in all the stupid things users do with their LiPos, as you mentioned. Accidents beyond design can then happen.

The serial configuration has the inherent ability to dramatically reduce the risks of fire. In series, if one cell shorts, the others won't. In parallel, if one cell shorts, they all do. At least so claimed by the author of this IEEE article (I found it, finally):
http://spectrum.ieee.org/energy/renewables/the-lady-and-the-liion/0

selected quote:
Quote
In the parallel laptop battery, current is supposed to flow through the parallel paths at exactly the same rate. But slight temperature differences or tiny chemical imbalances between the two paths force more current into one of them. Over time, the current imbalance between the cells can go to an extreme that forces bits of lithium metal to adhere to the anode. When this happens, the battery is able to store less energy than it is designed to store, meaning a shorter computer run time per charge. And because lithium metal is highly reactive, those scattered bits of metal can fuel a fire if a short crops up and suddenly raises the temperature of the system.

Wiring three cells in a series essentially eliminates that problem [see diagram, ” A Not-So-Simple Remodel”]. With only one path for the current to travel, it’s easier to control the flow of current, reducing the chance that lithium metal will be deposited, which would compromise the storage capability.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: 6v Battery Problems
« Reply #17 on: February 03, 2012, 05:45:52 AM »
Hi,

[...]
The serial configuration has the inherent ability to dramatically reduce the risks of fire. In series, if one cell shorts, the others won't. In parallel, if one cell shorts, they all do. At least so claimed by the author of this IEEE article (I found it, finally):
http://spectrum.ieee.org/energy/renewables/the-lady-and-the-liion/0

Looking forward to read it - too bad it doesn't come as a PDF, much easier.
But...Cells don't accidentally short by being used and if they did, the whole battery is very likely to be set off. Further a weak cell in a series string will leave the entire battery at the remaining capacity of the weakest cells, so it's use will be very degraded and it will possibly not work reliably (unless it had enough voltage to work with one cell less from the beginning and didn't pull more current than the weak cell could sustain) and if it works, the weak cell will soon discharge totally and reverse charge which is the more risky thing about it, as it's a surefire fire - actually, I think it will set off way before getting to reversing the polarity. Only way to avoid bad things is the safety circuits that shuts down the entire battery when cells become too unbalanced.
Sounds like they have their battery knowledge in less than mint condition, but I'll have to read the entire article before I can judge it.


selected quote:
Quote
In the parallel laptop battery, current is supposed to flow through the parallel paths at exactly the same rate. But slight temperature differences or tiny chemical imbalances between the two paths force more current into one of them. Over time, the current imbalance between the cells can go to an extreme that forces bits of lithium metal to adhere to the anode. When this happens, the battery is able to store less energy than it is designed to store, meaning a shorter computer run time per charge. And because lithium metal is highly reactive, those scattered bits of metal can fuel a fire if a short crops up and suddenly raises the temperature of the system.

Wiring three cells in a series essentially eliminates that problem [see diagram, ” A Not-So-Simple Remodel”]. With only one path for the current to travel, it’s easier to control the flow of current, reducing the chance that lithium metal will be deposited, which would compromise the storage capability.


From this, I'm not sure if the author really understands the concept, but I'll have to read the article, commenting on an out-of-context quote may be unfair.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
Re: 6v Battery Problems
« Reply #18 on: February 03, 2012, 02:24:06 PM »
Haha even you may have hijacked the thread it has been very educational and for the most part i have gotten what i have needed and have kinda come to a conclusion

in a previous post in a diff. thread you said
Quote
If money is an issue, why not get this instead?
http://www.onlybatterypacks.com/showitem.asp?ItemID=11502.12

I plan to buy the 6V version of this in a week or so . . .


so i followed the link and found the 6v version and now i think i should get it with this battery also on the website

http://www.onlybatterypacks.com/showitem.asp?ItemID=10414.7

or

this one http://www.onlybatterypacks.com/showitem.asp?ItemID=11373
but i have concern about this ones weight

your thoughts on this?

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #19 on: February 04, 2012, 01:21:51 AM »
Weight is only a problem if your robot can't handle the weight :P

(I know nothing about your robot)

If it's similar to my ERP, the 11373 item won't be a problem.

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
Re: 6v Battery Problems
« Reply #20 on: February 04, 2012, 01:14:38 PM »
oh Ok it uses 2 HSR-1425 servos as its 2 drive motors and is carrying 6 other servos, the blackfin, the axon, and some other hardware and the battery will be mounted in the back with the 2 drive motors.

and admin (or anyone) did you actually get this charger and was it worth the money?http://www.onlybatterypacks.com/showitem.asp?ItemID=10085.12

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #21 on: February 04, 2012, 09:06:51 PM »
They don't sell the charger that I bought from them anymore, or at least the link is now dead. (perhaps they just changed the link?)

The one I did buy was falsely advertised, not working anywhere nearly as well as they claimed. Not much later it fried itself.

Also, as for this battery:
http://www.onlybatterypacks.com/showitem.asp?ItemID=10417.7

They are lying, it's not 4500. The company label on the pack says 4500, but if you look at the individual cells on the inside it is actually 4200. I had told them that, and they admitted the mistake, but they never updated their website.

I had spoken with a rep of the onlybatterypacks company about these issues, and the guy was a complete jerk telling me I needed to go back to school (lol). So much so that I removed onlybatterypacks from the SoR parts list . . .

Now, I still use that 4200 battery and it's been good to me. You just aren't getting 4500 as they falsely claim. :P

(and I never bought from them again ;D)


edit: added picture of falsely advertised battery
« Last Edit: February 04, 2012, 09:09:38 PM by Admin »

Offline Robot_LongbordrTopic starter

  • Jr. Member
  • **
  • Posts: 34
  • Helpful? 0
Re: 6v Battery Problems
« Reply #22 on: February 05, 2012, 12:30:59 PM »
Hmm perhaps i will not go with that website and i think i should see if may battery is broken or is it my charger.

 Now my charger, when tested with my radioshack multi-meter doesn't register anything, but when i did that with a old airsoft battery charger it said it gave 12v.

 The charger i think is broken says that its output is 12v which on the website i bought it on said it could charge 6v batteries, could that have fried the battery? Also could i just take the old charger i have and use that to charge my 6v battery?Or would its 12v output fry it? and if it could work it says its output is 300ma so would that mean 11 hours of charging for a 3300mah battery?

if not would a charger like this work http://www.servocity.com/html/3_6-7_2v_nicad___nimh_peak_cha.html
or is the peak detection advertised for it a hoax?

Offline Admin

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: 6v Battery Problems
« Reply #23 on: February 07, 2012, 03:09:09 AM »
Those 'chargers' are not much different than a basic wall-wart plugged directly into a battery. I wouldn't pay more than $5 for something like that . . . actually, old wall-warts are easy to find for free. Just find one rated for ~6V and under 500mA. Also, cheap chargers increase voltage as current draw decreases, ie you can only measure the true voltage while it's charging your battery.

Trickle charging treats your battery well, but waiting ~11 hours isn't fun either. I'd recommend buying multiple batteries if you use this option.

 


Get Your Ad Here

data_list