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Offline SeagullOneTopic starter

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Battery rating question
« on: December 18, 2007, 11:45:24 AM »
I want to make sure I understand something correctly:

I have two Sealed Lead Acid Batteries that say 1.3Ah, 20HR. I'm pretty sure this is the same thing as 1.3 Ah (20 Hour rate). Now, does this mean the battery has a total of 1.3 Ah (which would be pathetic for a large scale robot), or does this mean that the battery has a total of 1.3 x 20 (26 Amp hours?) I want to make sure I understand my batteries.

Thanks in advance.
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Offline david_or_johnny

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Re: Battery rating question
« Reply #1 on: December 18, 2007, 02:13:54 PM »
If you'd tell us the size, please?

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Re: Battery rating question
« Reply #2 on: December 18, 2007, 03:01:39 PM »
hmmmm I've never seen that before . . . got a pic or a specsheet?

I suspect the 20HR means either 20 hours to recharge, or perhaps it will last 20 hours for its originally intended purpose.

What is the voltage?

Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #3 on: December 18, 2007, 03:13:10 PM »
The Voltage is 12V.

I can't provide a picture because my camera needs repairs, but the specs go like this:

Panasonic
Rechargeable Sealed Lead Acid Battery
LC-R1213PU (12V, 1.3Ah/20HR)

Constant Voltage Charge

Voltage Regulation
Cycle us : 14.9V ~ 14.9 (25 degrees C
(Initial current : less than 0.52A
Standby use : 13.6 ~ 13.6(25 degrees C)

Matsushita Electric Industrial Co., Ltd.

Nonspillable


The dimensions of the battery are about 3.5" x 1.5" x 2"

Thank you
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Offline sdk32285

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Re: Battery rating question
« Reply #4 on: December 18, 2007, 03:46:14 PM »
The standard method for computing/measuring ampHours is over the course of 20 hours (some batteries use a different time base to confuse you) .
 
So the battery can maintain a constant (1.3A/20) 65mA for 20 hours before reaching ~10V at which point it will need to be recharged.

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Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #5 on: December 18, 2007, 04:35:44 PM »
Okay, so to determine the total amp hours for the best performance of the battery, you divide 20hours (or whatever the time frame might be) into the listed Amp hours.

In my case, 1.3 Amp/20HR= a steady 65 amps in 20 hours, giving off a total 1.3 amps in those 20 hours. Let me do the math here:

If my battery disappates 1.3 Amps in 20 hours, than that means it disappates 26 Amps in one hour. Correct?

So if I have two motors that draw on average 5 amps each, 26/5 = 5.2 hours... then the other motor 5.2/5= 1 2/5 hours. That's pretty fair, I guess, considering that I have two of them. Wired in parallel that gives me 2 4/5 hours. Almost three hours if those batteries are only powering the motors, and that assuming the robot's motors will always be rotating and the robots never stationary. (Hopefully the motors will draw less, say 3 amps [There stall current is 10 Amps]. I have a second power supply for the robot's servos, and a third for its on-board computer.

Wow, that was fun. I think I've learned a thing or two about batteries.

Am I correct?

Modified:

Wait a minute, that's not right. 65mA in 20 Hours, 0.065 * 20 = 1.3...wait a minute, if I use those batteries to power two motors that draw 5 amps each those batteries'll zapped in a heartbeat!
« Last Edit: December 18, 2007, 04:38:31 PM by SeagullOne »
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Offline airman00

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Re: Battery rating question
« Reply #6 on: December 18, 2007, 06:30:31 PM »
1.3ah means it is able to give out a steady 1.3amps an hour when it is discharged evenly over 20 hours


you have 2 5amp motors, so I would go ahead and get a 20ah battery

IT DOES NOT HAVE 26 AMPS!    :o

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Offline david_or_johnny

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Re: Battery rating question
« Reply #7 on: December 18, 2007, 09:22:15 PM »
Energy density is pretty uniform for lead-acid batteries, and so if a 3 x 4 x 2.75 in lead acid battery is 4.5 Ah, your pack scales by volume.

Offline sdk32285

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Re: Battery rating question
« Reply #8 on: December 18, 2007, 10:51:22 PM »
Another thing with lead acids is that you don't want to run it below half of its rated voltage or you can severely shorten its life.
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Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #9 on: December 19, 2007, 08:17:25 AM »
Thanks for all the info everybody. A 20Ah battery would give me the stuff I need, but if they come around 20lbs each, those things'll really way down my machine.

I think I'll consider switching to Ni-mh or Ni-Cad, since those things put out more power for their weight in proportion to Sealed Lead Acid. I'm taking a good look at these here.
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1347

If I buy or two or four of them, I'd get the power I need for my robot's motors.

Wire the packs with dual parallel adapter(s) from Trossen, and I can recharge all packs with 7.2V-12V smart charger from the same sight as the battery packs.

Correct and safe?

Modified:

Whoa! Maybe these instead:
http://www.robotmarketplace.com/marketplace_battlepack_nimh.html
12V 60 amps continuous. And a lot cheaper too!
« Last Edit: December 19, 2007, 08:26:28 AM by SeagullOne »
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Re: Battery rating question
« Reply #10 on: December 19, 2007, 08:25:34 AM »
Quote
In my case, 1.3 Amp/20HR= a steady 65 amps in 20 hours, giving off a total 1.3 amps in those 20 hours. Let me do the math here:

If my battery disappates 1.3 Amps in 20 hours, than that means it disappates 26 Amps in one hour. Correct?

uhhhh no. At 1.3mAh, if you drain 1.3A for one hour, it will be dead after that hour.
http://www.societyofrobots.com/batteries.shtml

As sdk32285 said (I learn something every day) is that they slowly drain the battery over 20 hours when the manufacturer rates the battery in the lab. So basically 1.3A/20h = 0.065A drain for 20 hours. If they ran the test over 10 hours, that 1.3A rating might end up being 1.4Ah, or 1.2Ah, simply because the drain rates aren't perfectly linear. sdk32285 said 20h is the industry standard, that way all manufacturers rate their batteries in the same fair way.

Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #11 on: December 19, 2007, 08:28:40 AM »
Quote
In my case, 1.3 Amp/20HR= a steady 65 amps in 20 hours, giving off a total 1.3 amps in those 20 hours. Let me do the math here:

If my battery disappates 1.3 Amps in 20 hours, than that means it disappates 26 Amps in one hour. Correct?

uhhhh no. At 1.3mAh, if you drain 1.3A for one hour, it will be dead after that hour.
http://www.societyofrobots.com/batteries.shtml

As sdk32285 said (I learn something every day) is that they slowly drain the battery over 20 hours when the manufacturer rates the battery in the lab. So basically 1.3A/20h = 0.065A drain for 20 hours. If they ran the test over 10 hours, that 1.3A rating might end up being 1.4Ah, or 1.2Ah, simply because the drain rates aren't perfectly linear. sdk32285 said 20h is the industry standard, that way all manufacturers rate their batteries in the same fair way.


Yes, I began to suspect that when I second-guessed my work. Thanks.
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Offline david_or_johnny

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Re: Battery rating question
« Reply #12 on: December 19, 2007, 08:49:43 AM »
If weight is a major concern and money isn't, I'd suggest looking at LiPo such as MaxAmps.com. They are very high capacity and you can wire two in parallel for more capacity, whereas with NiMH and NiCd you can only wire them in series.

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Re: Battery rating question
« Reply #13 on: December 19, 2007, 08:54:57 AM »
Quote
They are very high capacity and you can wire two in parallel for more capacity, whereas with NiMH and NiCd you can only wire them in series.
?

You can also wire NiMH and NiCad in parallel, I do it all the time ;D

Offline david_or_johnny

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Re: Battery rating question
« Reply #14 on: December 19, 2007, 09:31:12 AM »
Really?

I hear that if you wire NiCd and NiMH in parallel, they will auto-self-discharge; that's why nobody in the RC hobby ever wires together two in parallel for increased runtime but instead goes up a cell size or switches to LiPo. Then again, I have never tried it in fear of damaging the expensive Sub-C cells like IB4200 and GP4300, so I'll take your word on this one.

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Re: Battery rating question
« Reply #15 on: December 19, 2007, 09:37:41 AM »
The self discharge happens with any battery type, when you put two batteries together in parallel that do not have equal charges. You must make sure that both batteries are the same exact type, and you should only charge and discharge them while connected in parallel.

You also should not combine an old battery with a new battery, even if they are the same type, as the discharge rates will be different.

Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #16 on: December 19, 2007, 12:16:13 PM »
Interesting stuff, guys. :)

Okay, new feedback on a new battery pack. Before I purchase this, I want to make sure it will do the trick for my robot.

http://www.robotmarketplace.com/marketplace_battlepack_nimh.html

12V, with 60Ah continuous. And it weighs less than two pounds, for only about a hundred dollars.

(I want to make sure I know what 60Ah continuous means...will it give lasting efficiency for two 5Amp motors?

Have to find the right charger too.

I'll take a closer look at those Lipo batteries though. I hear they're very unforgiving if you overcharge them...
I think the chauffeur did it.

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Offline airman00

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Re: Battery rating question
« Reply #17 on: December 19, 2007, 12:39:44 PM »
yes that will give MORE than lasting for your motors

6 hours of continuous use before you need to charge ( thats only when they power the motors only)
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Offline SeagullOneTopic starter

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Re: Battery rating question
« Reply #18 on: December 19, 2007, 01:03:18 PM »
Are you sure they have that much power? They say real bold on this sight that they're 3600 mah, but then in small type, listed under "BPK-3200N-12 BattlePacks"  that they're 60ah continuous? You did see the link, did you? I just want to make sure, because that sounds like a really good deal!

Sorry if I sound a little incredulous. I just want to know for certain how much power those batteries in the link have...
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Offline airman00

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Re: Battery rating question
« Reply #19 on: December 19, 2007, 01:07:49 PM »
It might be 3600 mah for the battery, and then since its a pack, there are a few batteries with 3600 mah in parallel, so it ends up being 60A

thats my guess
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Re: Battery rating question
« Reply #20 on: December 19, 2007, 01:22:12 PM »
yeap, that battery looks good.

at 60A, expect really bad stuff to happen if you accidentally short a wire ;)
take precautions, gloves, etc . . .

Offline david_or_johnny

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Re: Battery rating question
« Reply #21 on: December 19, 2007, 01:49:49 PM »
Heh, reminds me of the time I was soldering leads onto a very high quality IB4200 pack. The solder in wire form touched both terminals at once accidentally (they're about 6 inches apart!) The current flow was too much for the solder and it melted on the other terminal.

Offline robonoob

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Re: Battery rating question
« Reply #22 on: December 19, 2007, 01:52:12 PM »
with this topic i wanted to ask how many amps does a servo need.. i want to know what battery should i buy... :) i will need to power 3 servos and i IR sensor :D

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Re: Battery rating question
« Reply #23 on: December 19, 2007, 01:55:37 PM »
Depends on the servo. About .3A for the small ones and up to 1A for the large ones.

Offline robonoob

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Re: Battery rating question
« Reply #24 on: December 19, 2007, 01:57:44 PM »
Depends on the servo. About .3A for the small ones and up to 1A for the large ones.
well i think i'll be using like $8 standard servos... anyway do the batteries have mA or A marked on them too? or only mAh?

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Re: Battery rating question
« Reply #25 on: December 19, 2007, 02:01:08 PM »
Quote
well i think i'll be using like $8 standard servos
spec it for .5A and you should get a good estimate.

Quote
anyway do the batteries have mA or A marked on them too? or only mAh?
yeap, just look up the datasheets

 


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