While discussing ways to dock and charge a robot in a thread @Doombot created, it got me thinking about different types of battery that can be used with the EZ-B with multiple servos and sensors ect connected. To me, having a battery that can be recharged while still connected to an EZ-B which is still powered on is quite an important issue when it comes to docking.
I'm no expert by any means when it comes to different battery types (and there are many), so I wanted to get some ideas on what would be a good battery to use with an autonomous docking robot. From the other discussion, I found out that SLA (lead acid) batteries are a good option for this set up as they don't discharge then recharge during a charging cycle, but they are a bit big and bulky depending on the robot size/design, where as using a lithium polymer (LiPo) battery would be "a very bad idea" as the charging cycle actually discharges the battery before recharging the cells and could cause a nasty bang.
So I'm wondering what the deal is with nickelmetal hydride (NiMH) batteries and another type of battery I discovered, a Lithium iron phosphate (LiFe) battery, in being able to recharge safely while a device, such as an EZ-B, is still powered on. Can this be done with these kinds of batteries? I'm aware that some of this may be down to the charger itself with the amount of current it delivers while recharging a battery, but in this instance a robot would go in to a "Low power mode" releasing servos, turning off lights ect, so the only power used would be to keep the EZ-B ticking over and maybe a monitoring sensor or two.
One last thing, going back to the LiFe batteries. Has anybody used these before, specifically with an EZ-B? From what I have read they seem to be somewhat better than LiPo's in that they last longer, they are safer to recharge, about the same size, longer overall battery life (more charging cycles), they still pack a punch (current delivery), and they are apparently greener (and I'm not talking about the casing in the picture, lol). From what I have seen, they come in 3.2, 6.4, 9.6, 12.8, 16, and 25.6 volt with varying mAh choices. Would a 6.4v LiFe be a suitable or better replacement for a 7.4 LiPo battery in regards to powering servos on a revolution robot or similar?
I'll leave it there and hope you guys can give some feed back to this subject. I've posted a couple of links below about LiFe batteries incase anyone isn't familiar with them.
Thanks.
Steve. :)
I don't know anything about LiFe batteries.
NiMH can handle the inrush current like a LiPo or SLA, and can be recharged while plugged in as they are very stable. They can't be recharged as many times as a LiPo, and tend to die after about a year whether charging or not. On the other hand, it is safe to leave them on a trickle charge to keep them topped off, and they don't weigh as much as SLA.
Although every other week I read something about new battery technology , and it rarely comes to market, I did read something a few weeks ago about a new discovery in manufacturing of NiMH by BASF that increases doubles the capacity making them similar in weight per volt/amp to LiPo with much higher safety and lower cost components, and the possibility of a 10x improvement. The article said the procedure would be fairly simple to fit into existing manufacturing processes so it is more likely than some of the more esoteric improvements (like graphene sheets) to hit the market soon. The article mentioned next year, so probably 2 or 3 realistically.
http://www.technologyreview.com/news/535251/old-battery-type-gets-an-energy-boost/
Alan
(note: I have edited this post several times, so if you read it when I first posted, you may want to re-read. New link to a better article for instance)
Cool, thanks for your input Alan. Yeah these LiFe batteries are new to me too (only discovered them tonight infact), but there are quite a few online stores selling them. The confirmation of being able to recharge a NiMH while still powering something is great, but like you say, a downside of a shorter overall life span. Apparently these LiFe batteries have double the life expectancy of an NiMH so the sound pretty decent and about the average same price as a LiPo.
Just read your edit Alan, thanks. The link was an interesting read. If they make a go of that, LiPo's might be going the way of the dinosaurs one day.
I still haven't found the original article I read. It talked about what the discovery was. Something about microscopic holes in either the cathode or the anode, but I don't recall the specifics.
No worries. Interesting never the less.
I've converted all my cleaning robots, Roomba, Scooba, and Neato over to LiNMC, which is typically used for power tools requiring a high current (amperage) and electric cars and now going to also be used to power my EZB4s. There is a 14.4 vdc 6.6 amp version of the LiNMC used in the Scooba floor washing robot that should provide the power needed for multiple servo operation. The nice thing about these packs is that the stock Roomba - Scooba and Neato power supplies can be used. Each pack has power management and cell balancing built in.
@Doc.
See, that's another one I hadn't heard of. I just did a quick google search for the LiNMC and was about to say "Gee's, really?" as the first one I came across was $800. But then noticed it was a high performance 52v unit, lol. I searched on and found more LiPo priced ones around, and there's a huge range to choose from as well. That's another one I can add to the list then. Thanks for sharing Doc.
@DJ & Jeremie.
I wonder if you could tell me, would using the LiFe battery packs at 6.4v be enough or 9.6v be too much voltage to power the all of the servos or 5v regulators you guys sell in the shop? I'd like to get one of these batteries and charger to try them out, but want to be sure first before I part with any cash or risking damage any of the servos I have.
Thanks.
@Steve... I use 6V nimh batteries for most of my robot projects and they work great with servos... I also use a 6V SLA in my inMoov, again no issues... I wouldn't use 9.6v if you're using servos... The 6.4v will be fine providing it can provide the current you need...
@Richard.
Cool, thanks bud. I believe the LiFe batteries do pack a punch so delivery of amps shouldn't be an issue. I susspected 9.6 would be too much. :)
@Steve G yeah I would stick with the 6.6V LiFe since when it's fully charged will be around 7.4V anyway. 9.9V would be too much for the servos.
@Jeremie.
Thanks for confirming. I'm still in the fence at the moment, but if I purchase a LiFe battery to try in an EZ-B project I'll post a quick review.
One thing you'll want to pay attention to is the "C" discharge rating for NiMH, NiCd or LiFe batteries. Our batteries are rated for 25C. You'll likely need a battery that can do 10C or greater to meet the instant demands of the servos for a full robot. I haven't played around with too many other battery technologies with our full robot kits but I know that NiMH 'AA' 2000mAh batteries have a hard time with more than 4 or 5 HD servos. I don't know their 'C' rating but I bet it's pretty small.
That's interesting. I'll keep that in mind. Thanks again Jemerie.
I'm Hoping someone can give me a little advice. A friend of mine gave me a almost new 7.2v 4600 mAh Ni-Mh battery and charger this evening which I want to use with a v4, and I have a couple of questions.
Can a Ni-Mh battery be under volted to a point where it could be damaged (like a LiPo) or shorten its overall life span, and if so, what is the lowest voltage point it should stop being used to be recharged?
Do Ni-Mh batteries discharge the same way as a LiPo in regards to where the low voltage warning on the EZ-B can be used?
Any ideas on where I can find "C" discharges rates as Jeremie mentioned for Ni-Mh's? If had a look on the net but can't find much info in regards to this. For example, what would be the "C" discharge rate for this battery as it's identical to what I have.
The reason I'm asking is I'm looking to set up a basic docking station and want to write a script so when the battery gets too low, the robot docks and charges while the EZ-B is still on in a low power state. Obviously I know about the LiPo side of things, but I'm a little unsure about Ni-Mh's but want to use this so I can keep the EZ-B on in a low power mode while recharging.
NiMH's do not have the undervolt issue. You can probably set the low voltage level lower, though you will need to experiment with how low you can go and still move the bot and not brownout the EZ-B.
Don't know about the C rating. That was new to me as well.
Alan
@Alan.
Thanks for confirming. I had it in the back of my mind that was the case but wanted to make sure. So you didn't know about "C" ratings in these things either. Glad I'm not the only one. I've seen C ratings on LiPo's but don't recall seeing it mentioned with Ni-Mh's.
EDIT:
After a lot of searching, I found a Turnigy Ni-Mh battery with a similar spec to mine with a 10C rating, so I asume mine will be the same.