what if I use household 9v batteries?

[Weird Al/ Tony]

Ok so you have your big 12volt wheel-chair/motorbike batteries for most of these robots. so what would happen if i used some 9v like smoke detector type batteries. i know they wouldnt last long but could I power some 12 volt motor, if i got like 2 together. or does size matter?

[Jeffy]

Size matters for the capacity of the battery. Batteries are rated on an amp/hour basis. A 9v smoke detector batter is much below 200 miliamp/hours.

Also batteries have a peak amperage that they can give off in an instant. This peak amperage depends greatly on the capacity of the battery. A 9v probably couldn't even give enough amperage burst to power an unloaded cim motor.

So, unless you wire about 100-9 volts in parallel, then I wouldn't use them for anything more than they are designed for.

[sanddrag]

Originally Posted by Jeffy

OUr kit batteries can give 18 amps for one hour.

The above is not correct. The capacity of the battery is not constant for different loads. Due to the chemistry of the battery, it is not a 1 to 1 relationship between current draw and run time. The capacity of sealed lead acid batteries is typically rated based on a 20 hour discharge. According to the spec sheet, the MK ES17-12 has a capacity of 8.1 Amp-ours under an 18 Amp draw, meaning it would last about 25 minutes before it will be depleted.

[Ether]

Originally Posted by sanddrag

the MK ES17-12 has a capacity of 8.1 Amp-ours under an 18 Amp draw, meaning it would last about 25 minutes before it will be depleted.

... and for purposes of the above specification, "depleted" is defined as a battery voltage of 9.6V under an 18amp load. So, depending on your application, you may consider the battery to be "depleted" well before 25 minutes. There's not enough info in the spec to determine how low the voltage of a "depleted" battery will go (compared to a fresh battery) when under more severe load, like on an FRC robot with 4 CIM motors trying to push another bot.


~

[Jeffy]

Originally Posted by sanddrag

The above is not correct. The capacity of the battery is not constant for different loads. Due to the chemistry of the battery, it is not a 1 to 1 relationship between current draw and run time. The capacity of sealed lead acid batteries is typically rated based on a 20 hour discharge. According to the spec sheet, the MK ES17-12 has a capacity of 8.1 Amp-ours under an 18 Amp draw, meaning it would last about 25 minutes before it will be depleted.

Im sorry, robot withdrawl? Its been 7 days since I had to change a battery :/.

[EricH]

They would... and they wouldn't.

They'll have an extremely short life in competition, and they'll power the motor at about 3/4 voltage.

Just use a 12V battery. If you can't do that, a pair of 6V batteries in series would probably work.

[Weird Al/ Tony]

yeah thats what i figured. and hey i got a little mini bot to work. in other words, tiny wire, from battery to switch, to vibrate motor from old xbox controller, towire back to battery. very simple aye?. but still fun, and it spins in a circle lol i'm so bored lately