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[on:]

I have a large robot and am looking for a good 12 volt power source. I need to use a battery so nothing that plugs into the wall will work.
The battery can way up to 45 pounds no heavier. I need to draw anywhere between 2 amp to 10 amps constantly, and at some rare instances it could go up to 18 amps but only for a few seconds. I was looking into sealed lead acid battery's but was not sure what amp per hour rating to use or to even use a completely different kind of battery. what do you guys think I should do. The longer the battery lasts the better but I would like to know the minimum size to get and then decide if I should get a larger one based on getting a longer capacity.

 Thank you for helping.

[Reply #1 on:]

You're not talking small here. Seems like SLA might be a good choice. An 18 Amp-Hr 12V SLA weighs 13-lbs
and costs $50. You can get a rough estimate of the runtime by dividing by current, 18 A-H/2 A = 9 hrs,
18 A-H/10 A = less than 2 hours. So for selection, you need to also figure desired runtime into your calculations.
Also, the voltage will probably sink faster for higher currents, due to heating losses, etc.

[Reply #2 on:]

I need to draw anywhere between 2 amp to 10 amps constantly

For how long? You really need to know the voltage, current and capacity requirements (as well as the physical constraints) before you can make a sensible decision.

[Reply #3 on:]

You might look at deep cycle trolling motor batterys.

[Reply #4 on:]

the 2-10 amps would depend on what is running in the robot.
2 amps if headlights are on
1 amp if water pump is on
1 amp if wireless router is on
1-2 amps if servos are moving
2 amps for other lights
2 amps minimum for electronics (including raspberry pi )

[Reply #5 on:]

the 2-10 amps would depend on what is running in the robot.

How you calculated the current doesn't matter from the point of view of the battery. What's important is how long the battery needs to sustain that current, and whether there are any other constraints. Do you care how heavy it is, or how big? Is your 'bot going to turn upside down or get bashed? Do you care how easy it is to recharge or how many times you can recharge it? How important is cost?

[Reply #6 on:]

-weight should not matter as long as the battery is under 45 pounds
-the robot will not turn upside down but will go at inclines at 30 degrees
-the robot might get bashed
-I want the battery to last many recharge cycles
- cost is not too important but cheaper is better
- I also don't care how long it charges even if it charges for 2 days thats fine.

[Reply #7 on:]

You didn't answer the most important question - how long does the 'bot need to be able to run for on a single charge?

[Reply #8 on:]

at least one hour. I would like 3 hours though but might stick to 1 hour based on cost of battery

[Reply #9 on:]

at least one hour. I would like 3 hours though but might stick to 1 hour based on cost of battery

Thirty amp-hours would be no problem for an ordinary cheap small lead-acid car battery. I doubt that you are going to hit it hard enough for physical damage to be a problem, as long as you don't have something literally attacking the case of the battery trying to break it.

[Reply #10 on:]

Have you looked into the new batteries made for RC cars?  I can't help you with the math but maybe an idea:

http://www.hobbypartz.com/98p-40c-5000-2s1p-hardcase.html?gclid=CLTL39LSjrQCFSPhQgodhT4A3w

Here's a pretty nice charger (imho), I have both this & the X4 http://www3.towerhobbies.com/cgi-bin/WTI0001P?I=LXBJBY&P=8

HTH

[Reply #11 on:]

I would use sla33-12fp 12v 35 ah about 25 pounds each, a pair will push a wheel chair all day long with a 300 pound druler at the stick or motivate a battle bot that crushes the competition. Avalable at ebco battery co columbus ga. It is on there web site.