Looking through my sparkfun order yet again, i’ve realized I really need two things: firstly a rechargable battery 7.2V +, I have no idea how amps work, but i doubt i’ll be needing more than 2 (would a 2 amp battery work with 1 amp electronics or fry them?). The main battery would be used to drive auxiliary functions such as motors, servos, and sensors (two GM2’s, 1 servo, and 3 IR, 1 ping) The second battery will need to run a RF reciever, LCD screen, and my main board. I can’t deal with spending $15 on 4 rechargable AA’s when they’re such a pain the ass to recharge, and keep at the same level. I was looking through the li-ion batteries on sparkfun, however i have no idea which one to choose (if any). Secondly, if anyone knows of a nice solid chassis that they could link me, that’d be great.
What do you mean by 1A
What do you mean by 1A electronics? Your voltage regulator?
Any way you go you need a recharger. Its no fun having to replace and throw out batteries all the time. I got free samples from maxim of the max713 NiCad/NiMH charging IC and it works great, plus you cant beat free stuff. If youre really strapped for a charger and need something soon theres no reason you cant MAKE one with simple components.
Anyway, Id suggest the NiMH AA on sparkfun for ease of use, LiPo has a higher power density but requires special charging. But again, Im sure simple charger schematics are floating around the web if you want to go the LiPo way.
Ah, yeah, i’m going to be
Ah, yeah, i’m going to be using a 3.3 and 5v regulator. Thanks for the advice, ill search the web for a charger before i go ahead and order more AA’s.
I’ve found sparkfuns shop
I’ve found sparkfuns shop lacking good batteries, yes they have the 3,7v li-poly one, and its probably possible to serial connect it for double volt, but one bad connection when working with batteries can/will result in fire so you better know what you’re doing before you try anything stupid 
You’ll have to pay attention to the current when for example driving a motor - it will require a certain amount of current to drive. More current will let you drive a bigger motor, more volt will increase the preasure and lets you spin it faster. Not sure if it makes any sense to you.
Anyway, I would check out RC-supplies when shopping batteries instead of sparkfun. For example, hobbycity.com, have around 288 different li-poly products
Eventually, batteries are though, its hard to find something that suits you’re setup perfectly.
Edit: also, Its probably a good idea to use different power sources for your motor and the fine electronics like sensors.
I dunno 'bout LiPo’s
Man, I have heard some horror stories about those LiPo batts… Houses burning down kinda stuff. They MUST be charged in a very certain way so if you go this direction, be sure to get matched charger and batts. For my money, I would get a simple 7.2V “long-pack” --the kind that go in RC cars. You should get well over 2 amps/hrs, they are cheap as are the chargers, etc. etc. etc.
LiPo’s scare me.
I have no experience with
I have no experience with the lipo bats except for the one i have in my pocket right now - and you probably too. Cell phones have used them since the late ~90. They wont explode or burn you’re house down as long as you go down to the hobby-store and ask them for how to use them. They are very popluar and common for RC planes and choppers. But as CtC say, its easier to just get a 6 pack with nicad batteries, works like a charm.
I use LiPo batteries on one
I use LiPo batteries on one of my robots, but care must be taken. Most other robots use the 4 AA NiMh packs with no problems. The LiPo batteries do require a special charger and this has been a good one for several different chemistries. If running 7.2 volts, the NiMh RC packs are good, 2000 mAh or better rating.
**just go to radio shack **
just go to radio shack
at least the online
at least the online radioshack shop didnt have anything special when it comes to batteries, nor did their prices amaze me.
Sorry for the late reply but
Sorry for the late reply but I was in Yosemite and had no internet. I wanted to try and avoid having individual AA batteries lying everywhere and instead have a single pack (such as the 7.2V rc packs). The only reason I mentioned Li-ion, and Li-po batteries is because those were the only other batteries sparkfun had. I think i’m going to look for battery packs now, and avoid li-anything for now.
I’ve been having some
I’ve been having some battery issues as well, i think i’m going to go with 2 of these in series…
3.6v 2300mAh NiMH
http://www.all-battery.com/6v2300mahnimhsidebysiderxreceiverbatterypackswhitecconnectorforrcaircraftswalkingrobot-1-2.aspx
I say 2 because i do not really have room for 6 AA’s in a row, but i have 2 spots that i can fit 3 AA’s. My motors (2 x GM9 from solorbotics) run at 5v and right under 600mA each. So motors are 1.2a, and the rest of the electronics (Parallax propeller micro, 4 LEDs, 2 IR LEDs, 2 IR detectors) all run at under 100ma. Total current needs to be about 1.3-1.4ah. I use a seperate 5v reg for the motors, which is rated for 1.5A, and a .5a 3.3v/5v for the rest. Being that the total current is about 50% of capacity of these batteries they should work ok right, without running 2 seperate batteries sources for electronics and motors?
Also, I have ordered a while ago, but have not recieved yet, the MAX713 chip to create a battery charger. Does anyone know where i can find a circuit to create my own? Or a discription on how to actually make it work safely?
usb
I’ve charged (small) lithium batteries, you know the flat kind you get out of MP3 players and cell phones using a stripped USB cable. Worked wonders! I simply stripped the cable, taped the black wire to the - and the red to the + of the battery and plugged it into the PictBridge USB jack in my printer. However I don’t really recommend this, especially if you are already getting a charger…
PS: HEY ICON!!! I haven’t seen you on this site for months, missed you!
You can get a lipo 2-3S
You can get a lipo 2-3S charger for 5.95$ and a 7.2V 2S 20C battery pack for $12.70. In addition a 2-6 simple battery monitor for $2.99 would be good to have. Thats a total of $21.73 for parts + shipping $12.12 international airmail makes it a final total of $33.85 USD. Not bad if you ask me.
Last night i got curious and
Last night i got curious and decided to find the wall adapter from these salvaged 2way radio sets i used to have. I read right off the front of the adapter “9v 300mA”. I have been wondering about a very simple charger for my NiCad pack (7.2v 1000mA). I’m thinking as long as you know the voltage and current being produced by your wall adapter, and the voltage and capacity of your battery pack you should be able to use this very simple schematic correct? Mind you, when i first hooked up the adapter, I was ACTUALLY getting right under 12v, thats why the added diodes (the only type i had, 914 w/ about a .7 volt drop), which bring it to right about 9.5v. I tested hooking up my battery pack to this wiring, and measured the current very quickly and it was producing from what i can tell 70ma. (I’ve recently picked up a small multi-meter, cause my other one broke beyond my skill in repair, and i had to put it on the 10A setting, 0.070… 70mA right) Everywhere i’ve ready on recommendations for care of your battery packs say you should charge for like 12 hours at low current, and your voltage should be roughly at least 2v higher than what your trying to charge. If you figure 1000mA / 70mA = right over 14 hours, perfect right?
Of course you would really need to watch this thing because there are no safetys on it. My batteries were pretty dead, they had already diminished their voltage down to about 5.5volts. Its my understanding that until their capacity is almost nothing they hold their true voltage correct? so a reading on voltage at 5.5v would mean that they have almost nothing left in them. I took a voltage reading while it charged up and beyond 7.2v, but that is where i got kind of worried.... It kept going up even after 7.5v... Is this normal when charging a battery?
I forgot to add in the
I forgot to add in the schematic that I have a 330uf cap between pos and nev on the adapter side right after the diodes.
**Im not sure about NiCads,**<br><p>Im not sure about NiCads, but with NiMH they can be charged up to 1.6 or even 1.65v per cell. After the charge current is removed they then drop down to about 1.4v.
An easy way to check if it`s done is feel how hot it is. Turn it off before it gets over 40C.
Thats the thing. They are
Thats the thing. They are surpassing the 7.5v mark and i wasn’t sure if that was ok so i took it off. But they never warmed up at all actually. Still were almost cold to the touch. I know that they are accepting a charge, because i can run a motor for awhile until it finally goes dead again. So i should be good until i get my new battery packs and new charger with this simple circut. I might have a few temp sensors laying around that i could use to automatically have it shut off at a certain temp, for safety.