A little battery advice??
Ravenkallen
Posts: 1,057
Well, hello everybody... As some of you know, i have been working on a robot for a while now. It has come along really well so far and the initial tests have been positive. The only problem i face is what to do for a power source. I have been using 6 volt lantern batteries and at 7-8 dollars each, it gets a little pricey...SO i took the liberty of buying this 12volt, 7Ah sealed lead acid battery from radioshack...
http://www.radioshack.com/product/index.jsp?productId=3932590
For someone who has very little in the way of discretionary money, it was a large investment.. I brought it home and then the questions fell over me... Would this battery be able to provide enough current to the system? How the heck should i charge it? IS it really dangerous?
I saw this charger online and i thought it might work?
http://www.batterymart.com/p-12v-500ma-sealed-lead-acid-battery-charger-2.html
This is my first foray into batteries like these and i DON'T want to damage the battery or blow myself up. Does anybody have any experience with batteries like these? Or should i return the battery and try something else?
Thanks in advance:)
http://www.radioshack.com/product/index.jsp?productId=3932590
For someone who has very little in the way of discretionary money, it was a large investment.. I brought it home and then the questions fell over me... Would this battery be able to provide enough current to the system? How the heck should i charge it? IS it really dangerous?
I saw this charger online and i thought it might work?
http://www.batterymart.com/p-12v-500ma-sealed-lead-acid-battery-charger-2.html
This is my first foray into batteries like these and i DON'T want to damage the battery or blow myself up. Does anybody have any experience with batteries like these? Or should i return the battery and try something else?
Thanks in advance:)
Comments
the Lead acid batteries are extremely heavy but they are a very good option. They are not as nervous as other types. My 7Ah are usually cheaper....
The charger looks ok, but it will take 16-20 hours to fully charge your battery. On the other hand with 7Ah it will last for a long time.
Only caution is the voltage drop across the regulator. If your former battery nominal voltage was 6V you'll have a lot of heat to dissipate. For instance a 5V linear regulator requires big heatsinks. A switching regulator will be better, and being more efficient will ensure a longer battery life between the charges, with little power dissipated.
Massimo
That charger looks OK. It fast charges at up to 15V, which seems a little high, though. Current is limited to 500 mA, so it will take a long time.
http://www.batterymart.com/p-12v-1a-sealed-lead-acid-battery-charger.html
SLA's are a proven technology and work well with nothing to worry about when treated within specs.
With that said I've used a 2amp automatic charger on my sla's when I needed faster charge.
The only problem I've noticed with my cheep 12vsla's is they don't recover very well when taken down to 6v, even when using the 2a charger.
-dan
That 1A charger looks good. It's a very safe system and time-proven. Keep your batteries topped up at every opportunity, NEVER take them below 10-11 volts or you'll shorten their life. Don't expect more than half of their rated AH capacity.
They are heavy, so your bot chassis better be strong & rigid. No servo drives here, you need metal-case gearmotors with bushings or bearings.
http://www.radioshack.com/product/index.jsp?productId=2062121
Much lighter, and closer to your initial 6V as far as voltage goes.
C.W.
http://www.batterymart.com/p-6v-4_5ah-sealed-lead-acid-battery.html
And you can find a matching 6V charger as well.
Also when charging sla batteries the charge current should be limited to 10% of the amp hour rating of battery. Charge rates higher can cause battery case damage due to heat and internal pressure.
Hope this is helpful.
Ben
I think LiMH batteries would be a better choice. Probably AA would be a good size.
I've read Duracell make better rechargeable LiMH batteries than Energizer. The Energizer batteries self discharge too fast.
The other good thing is that you will get 5 - 6 hours easy at 1 amp out of the 12V battery. You can use the 12V battery to power other things on your robot. Just remember that the higher volts, lower the amps.
Look at the bright side, it wasn't a bad buy.
I just noticed that the battery that I suggested was a NiCd, while those would be OK, a NiMH battery would probably last a lot longer.
http://www.radioshack.com/product/index.jsp?productId=11051772
You can probably find a better price somewhere other than "the shack".
NiMH batteries tend to hold up better through charge/discharge cycles as they are not as prone to the "memory effect" as are NiCd.
C.W.
For now, i can still use the lantern batteries. I have a couple left...
as far as charging . for a Uncontrolled charger A C30 is not bad .I would not go any higher .
but with as Real Charger C5+ is OK . look at a Good Universial RC car charger . most are NiMh and NiCd and Lixx compatabe and some Wil do the full 12 V charge . there not cheap $80 or so but are Very VERY usefull for any tinkerer .
with NiMh the charge profile is a tad more "picky " then NiCd or PBa . but Not as bad as Li stuff
delta T id needed .. I think the MAHA charger might work ..
PS . I make Most of My own packs .Cause you can't allwas get what you want from COTS
I should do a Vid on how to make packs some time
Peter
The SLA batteries are a good choice for many robots and I use that 12v 7ah battery for many of my robots. The latest robot uses a single 12v 7ah battery:
http://forums.parallax.com/showthread.php?118861-Homebuilt-Robotic-Platform-AKA-Retrobot/page6
Scroll down a bit and you'll see the robot. It uses a pair of the $10 surplus gear motors and has no problem with the weight. Actually having a heavy battery really low in the base makes the robot stable and less likely to topple over.
Robert
They are very forgiving and easy to work with. That is a standard size battery and if you're going to use and SLA battery then that is the one to get.
If the battery is for the robot you recently posted a video of then I think the SLA isn't a good choice.
I'd strongly suggest Nickel Metal Hydride (NiMH) batteries over Nickel Cadmium (NiCd). From what I've read (I've read a lot about batteries) NiMH hold a better charge and aren't as toxic. The only reason to use NiCds is if you get them for free.
Lithium Polymer (LiPo) and Lithium Ion hold more energy per ounce than NiMH batteries. I pretty much only use LiPo batteries for my robots. I have a lot of NiMH batteries for devices that take AA or AAA sized batteries. People will say LiPos are dangerous, which they can be, but if you use them correctly you shouldn't have a problem. I have dozens. I ruined a few but none have ever blown up or burst into flames.
I learned here on the forums about HobbyKing.com. They have pretty good prices on LiPo batteries. You do need a special charger (and balancer) to charge LiPos so that's an additional cost.
Duane
Ken informed me yesterday that my next project shall be an SLA charger (that ostensibly is primarily for robotic/mobile type applications).
I'm currently in the final testing stages of our 7.4v 2200 mAhr Li-ion Power-Pack Charger, so I'll be starting later next week on the SLA thing -
So, that being said, any and all ideas are welcome here. Talk! - we're listening (well, reading really)...
-Matt
If so, then a SLA seems a bit too big for it.
I don't have anything against SLA batteries. But they don't have the best power to weight ratio which is often important in a mobile robot. I think they might have a good power to cost ratio though.
@Matt, I'd like a good way to charge SLA batteries. I have a bunch from uninterrupted power supplies that appear dead. I'm still looking for a good source locally (I haven't looked very hard). I've wondered if the SLA batteries would last longer if I did something to condition them periodically.
I remember seeing your Li-ion charger. Do you know how the prices of Li-ion compare with LiPo? I'd think your charger would work with LiPo batteries too? It would be nice to be able to leave Lithium batteries in circuit while charging.
Duane
They seem pretty forgiving when charged. I've used drill chargers, bench supplies and a $100 Triton. The battery doesn't care....13.5V +/- and 150mA - 1A. Just don't cook it and you'll be fine. The battery last so long I wouldn't waste my money on a fancy high current charger. IMO
- What is the physical size of the robot? (small robots don't usually use SLA types)
- What is the motion (wheeled, legs, etc)?
- If wheeled, what style? Differential drive (two drive motors), separate steering/drive, or something else?
- What is the voltage of your motors and electronics? Sometimes people use two separate batteries (logic and drive power)
- How are you going to charge the battery?
There are lots of variables to think about.
No matter what battery you go with there are a couple suggestions from someone who has built many robots:
- Use a black or silver Sharpie (depending upon color of battery) and write the date of installation. At some point in the future you'll be glad you did.
- When you start using larger batteries consider adding a fuse inline with the battery. If something goes wrong you'll have some protection in place!
- Read up on the different battery types and how to deal with them. Charging and use is a bit different with each style.
Robert
One point about batteries is whether they like to be charged or discharged. Lead acids like to be charged. Leave them on float charge all the time. These modern chargers are great - when the battery is flat they charge continuously with the led on all the time, then when they are charged they change the duty cycle so the led only briefly flashes.
If you are worried about the short circuit current (yes, don't put a screwdriver across the terminals!), just install a 10A fuse. Simple and cheap.
As an aside, there has been some discussion on the picaxe forum about these batteries and cost. They are the standard battery used in house alarm systems, and alarm installers remove them and put in new ones every few years. Usually the ones that are removed are just fine, and so if you can find someone who installs alarms you may be able to pick up these batteries for free.
@Matt: I've had excellent results using this SLA charger: http://www.rpelectronics.com/fc-612c-lead-acid-gel-charger-6-12v.html I get 'em locally for ~$13. They charge 6V or 12V batteries at 3 selectable rates: 200, 400 or 800 mA, then they automatically switch a trickle charge.