Garden Tractor Battery

[Shevek]

So I bought myself a battery from Sears for a large rover that I've been building. This battery is to run two 12/24VDC motors that I believe are power-wheels motors, and the bot itself is fairly heavy. (40lbs ish, sans battery, give or take) Anyway, I got this battery:

http://www.sears.com/shc/s/p_10153_12605_02827199000P?vName=Automotive&cName=Batteries&Chargers&sName=Lawn%20&%20Garden%20Batteries&psid=SHOPPING01&sid=IDx20070921x00003d

but after talking to a few people and reading up on it, I'm seriously afraid of shorting this thing and killing myself. Are there any reasonable alternatives, maybe a battery that will at least put out 12 volts for a decent amount of time and a similar amperage? Sorry I'm really bad at determining important things like what kind of batteries / amperage / voltage etc. I need. Any info would be appreciated.:)

[lnxfergy]

put a fuse in the line...

-Fergs

[Shevek]

I meant more that I was worried about safety in the construction of the bot. Seeing as how it is possible to make this battery explode, say by dropping a screwdriver or wire across the terminals, I would rather use an alternative, if one exists. I know on my school robotics team we used a small battery with about the same output that was smaller, (about 6"x4"x6") and i don't believe was lead acid. Although I could be wrong there.

[lnxfergy]

I meant more that I was worried about safety in the construction of the bot. Seeing as how it is possible to make this battery explode, say by dropping a screwdriver or wire across the terminals, I would rather use an alternative, if one exists. I know on my school robotics team we used a small battery with about the same output that was smaller, (about 6"x4"x6") and i don't believe was lead acid. Although I could be wrong there.

That's what I'm saying though... insulate the terminals, and have a fuse very close to the battery. Any battery could explode if you draw too much from it. The key is to properly shield and fuse the supply lines.

-Fergs

[ScuD]

There's no battery with that kind of output that withstands shorts.

It's like making an omelet without breaking eggs. Use caution just as you would with your car battery and there's no reason to be afraid.

It's either that or go with low voltage, low current. And even that can explode. Ever tried hooking up an electrolytic capacitor the wrong way around?

Point is, you need power. The only way to handle it is with safety.

[Shevek]

Got it, sorry I misunderstood Fergs. I appreciate the help guys, I guess I'll stick with this :)

[Adrenalynn]

Throw some duct-tape over the terminals and be happy

[Adrenalynn]

The only way to handle it is with safety.

I'm gonna cut you some slack 'cause you're ESL. But "the ONLY way to handle it"??? You could handle it with reckless abandon if ya wanted. :P

[ScuD]

hmm.. I haven't been called ESL before.. what's that? ( there's no RTFM so i'll AA :p)

You're right though. There's more than enough candidates for Darwin awards out there.

[Adrenalynn]

"English as a Second Language"

[ScuD]

Ah, I thought it would have something to do with E.T.

I must say I'm a bit dissapointed...

[shobley]

Hang on, isn't that a starting battery?

I'm no expert at battery identification but that does not look like a deep cycle battery. I think you might want a deep cycle battery for powering a 'bot.

Something like this:

http://www.batteriesplus.com/pc-36587-86-marine-deep-cycle-battery-werker-sliu1dc.aspx

Here's an article on battery types:

http://en.wikipedia.org/wiki/Deep_cycle_battery

[Shevek]

Yeah, you're right, I should probably switch this out for a deep-cycle battery. What do you guys think about gel batteries?

[Adrenalynn]

Maintenance-free, no nasty stuff spilling at inopportune moments, same instantaneous current delivery. The only thing not to like about Gels is that it's a *bunch* more expensive to come up with the kind of A/h you can get from a marine battery.

[Shevek]

I think that the gel battery seems like a good choice, as I don't believe I need much in terms of A/h. I am using a pair of Power Wheels Motor Gearboxes, but I don't have any specifications on them, so I don't know what kind of A/h I need.

Picture: http://lib.store.yahoo.net/lib/mendingshed/motgb.gif

[Adrenalynn]

You need infinite A/h. So do I. Dang the stupid laws of thermodynamics anyway...

A/h is Amp Hours. If you have a 1A/h battery, it would deliver (in a perfect world) 1A for 1hr, or 2A for 30mins or 4A for 15mins, and so on. In practice, you can't run a battery to dead, so that number goes down.

So the two important questions when sourcing a battery: How much does the device draw and How long does it need to run?

[Shevek]

Realistically, this thing needs to run for about 10 to 20 minutes, maybe less, it's really just an experiment. The problem though, is that I have no idea what it draws, because I have no documentation. The motors were scrap from an old robot from my robotics team, and I never received any documentation with the parts. All I know is that the company that gave them to me called them "12/24 VDC Power Wheels Motors".

[DC Robotic]

As Adrenalynn stated, Amp Hours actually available are less than Spec. For Lead-Acid and for most Gel-cell types you should figure 50% of stated capacity. Deeper discharges will significantly shorten the life. Gel-cells just rock in comparison to standard lead-acid batteries. Their charge acceptance is often twice or more the rate of lead acid. They deliver more current. Their self discharge is much lower. and probably the best part is they don't spill. Often you can even mount them upside down. You will not destroy clothes or drip acid on important things as you move, install or work on them. They do not require a special charger. I have used the Lifeline brand for several years. That said - They do cost more.

If you have no idea of the motor draw. Can you test with an ampmeter in operation? If not, you might have to guess by estimating the amount of work the motors are doing and their efficiency. Or possibly by finding a similar device or application and estimating from that.

[Adrenalynn]

http://www.modifiedpowerwheels.com

Don't forget to come back and let us know what the experts there had to say!