

Joined Oct 2005
6 Posts

what is mAh? can i use a higher mAh?
hey
another total newb question from me I have a 7.2V 1700mAh battery for my electric r/c car. If i were to buy a battery, would it have to be a 7.2V 1700mAh battery, or can I go for a 7.2V 3000mAh battery!? tahnks again guys 



Joined Oct 2005
6 Posts

thanks guys really do appreciate it



Joined Oct 2005
6 Posts

so if a car comes with 7.2V 1200mAh, it wont do any damage to the car or motor because a newer battery is 7.2V 3000mAh?



Omaha, Nebraska, United States
Joined Aug 2002
656 Posts

The mah rating on the battery is like the size of the gas tank on a car like Lexi mentioned.
Here is one way to look at it. Someone please correct me if I'm wrong. A battery's capacity is rated in mah or milliamp hours. A 1700 mah battery is rated to deliver 1700 mah (or 1.7 amps) per minute for one hour. So this battery will deliver 102,000 mah (or 102amps) in one hour. 1700 mah x 60 minutes = 102,000 mah. Now take the amp draw of your car motor. Let's just say it pulls 20 amps or 20,000 mah. Take the capacity of the battery which is 102,000 mah or 102 amps. Divide by 20,000 mah or 20 amps, which the motor is pulling and you get a total motor runtime of 5.1 min. i.e. (102,000 / 20,000) So a basic formula could be; total motor runtime = (battery mah capacity x 60) / motor amp draw for your 1700 mah battery; total motor runtime = (1700 mah x 60) / 20,000 total motor runtime = 102,000 / 20,000 total motor runtime = 5.10 min. for a 3000 mah battery; total motor runtime = (3000 mah x 60) / 20,000 total motor runtime = 180,000 / 20,000 total motor runtime = 9 min. So bigger battery = more gas in the tank to run your motor. There are other ways to calculate this as well. I hope this makes sense and helps a bit. Where you can get into trouble is if you have a motor that pulls a higher amp draw than the battery is designed to deliver. Pull 30 amps on a GP2200 battery and it will be no problem. This cell is designed for high amp draw applications. But pull 30 amps on a 2300 mah AA cell that is designed for digital cameras etc. and that cell will be toast. 


New York City, USA
Joined Oct 2003
1,172 Posts

Another way to do it...
Assume 20A motor load. 1700mAH cell = 1.7AH cell (1.7 amperehours) / (20 amperes) = .085 hours (0.085 hours) * 60 = 5.1 minutes 3000mAH cell = 3.0AH cell (3.0 amperehours) / (20 amperes) = 0.15 hours (0.15) hours * 60 = 9 minutes Notice that when you divide amperehours by hours that you're left with hours, i.e., your run time. Just convert the run time to whatever units you need (hours, minutes, seconds, etc.). 


Letchworth, Great Britain (UK)
Joined Jul 2004
13,514 Posts

Quote:
Once you get the units right, it all begins to make sense: 1700mAh (or 1.7Ah) divided by 20A leaves you with time (Ah/A = hours). 



Omaha, Nebraska, United States
Joined Aug 2002
656 Posts

Quote:




Omaha, Nebraska, United States
Joined Aug 2002
656 Posts

Quote:
thanks again. 



Omaha, Nebraska, United States
Joined Aug 2002
656 Posts

I know this may seem backwards but it is easier for me to calculate the motor amp draw per minute then divide battery capacity by the per minute draw.
20 amp draw / 60 min. = 333 mah per min. 1700 mah battery / 333 = 5.1 min. just another way to look at it i guess. 
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