Amperage Calculator?
 

I know I have seen one I just cant remember where. Can somebody lead me to a link. I am trying to figure out how many amps I need for a battery for this high speed event I plan on attending. It a one shot high speed run so I dont think I need that much capacity unless I need more availiable amps. I was thinking of running at least 2 3s 5000mah 30c in series for 6s that would be 150 amps continues and 200 amp burst. Should I run 2 6s 5000mah 30c in parallel for 300 amps continues or 400 amp burst. Or is that overkill? I know it is heavy @ over 2 pounds just for batteries. I was also looking at 2 6s 3300 30c in parrallel for 198 amps continues and 264 amps burst also. Which would you guys run.

The only calc I have in my site (link in sig) uses runtime and battery capacity to estimate average and burst amperage figures. Or, use an Eagletree device to get real figures. Other than that, there really is no way to accurately determine amp draw based just on the motor and setup, there are just too many variables to consider.

For speed runs, you're gonna have a pretty big initial burst and then a higher than average continuous current because you are constantly accelerating. Most setups are used for racing or bashing where you have a lot of bursts with lower overall average since there is a lot of stop and go.

the speed calculator has an amperage box IIRC.

Your motor is good for 2500w burst. I'd go for the 2x3s 30c 5000mah setup.

At 22.2volts 150amps is 3330watts. Already more than you need. And the burst is 22.2v x 200a = 4440 watts. So the two 3s are plenty.

I was thinking if I do a higher than 150 amp continues amp draw batt it would be better. I am not sure if a 10 sec 40 c burst will be enough to get to my top speed. I have seen a calculator that takes all the variables like weight, tire size, gearing, motor size. I think it fugures how many amps you need. If I find it I will post it up so you can critique it.

Click here if it doesn't show up below.

<iframe height='1200px' width='100%' name='zoho-Power_Required_Calculator' frameborder='0' scrolling='auto' src='http://creator.zoho.com/nick.maslowski/power-required-calculator/form-embed/Power_Required_Calculator/'></iframe>

I think thats it! cool Edit it keeps giving me weird numbers I dont think it works with my setup. Unless I am doing somthing wrong.

What are you putting in?

Its the most recent 30 pinion 40 spur for my g-maxx speed build. You can see the details I believe in the table.

They look about right.

681 kv motor and 14022 rpm dont look right to me. Maybe I am not understanding how this works.

Whats the motor youre using? gearing is 30p/40s? what is the transmission ratio?

Ive done the calculation with all the same input as you did but I used 8 seconds to get to top speed. I got 139 amps on 6s. That seems about right.

I am using a 1515 neu 1.5 d 2700 kv on 6s. Trans ratio is 1.72 : 1. I dont understand why it says I need a 631 kv motor and on spin it ~14800 rpm . It doesnt make sense to me Obviously I am not going to run that motor and that rpm.

The problem with this calculator is that its hard to estimate what KV the motor will get under those kinds of loads. have you run the car with this setup yet?

If you use that setup on a monster truck with that gearing it seems like it will be way overkill. If you use brians speed calculator using the setup you mentioned, you get 500mph. Youre gonna have to use a much taller gear ratio.

What kind of car is this?

http://lh4.ggpht.com/_3N0hwXEVK9I/Sr...eedmonster.jpg

You forgot to enter the differential ratio in briangs calc . Maybe it wants total finay gear ratio instead of just the tranny ratio?

Even with that its 200 mph. If you want 100, go with a 15-18 tooth pinion.

http://lh4.ggpht.com/_3N0hwXEVK9I/Sr...edmonster2.jpg

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.7222222222222223
Other Ratio: 1
Spur Tooth Count: 40
Pinion Tooth Count: 30
Total Voltage: 19.2
Motor KV: 2700
Tire Diameter (inches): 5,5
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.004
Spur/Pinion Ratio: 1.33 : 1
Total Ratio: 7.59544 : 1
Tire Circumference (inches): 15.71 inches (398.98 mm)
Rollout: 2.07:1
Total Motor Speed: 51840 RPM
Vehicle Speed: 101.52 mph (163.08 km/h)
Effective KV Value: 2700
KT constant: 0.5 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

Ok, i see what the problem is with the results in the amperage calculator. You werent putting in the diff ratio and the transmission ratio. I'm gonna have to add an input for the diff ratio somewhere. If you take the trans ratio times the diff ratio and put that into the transmission ratio on the amp calc, it should work.

1.72*3.308=5.69

http://lh4.ggpht.com/_3N0hwXEVK9I/Sr...edmonster3.jpg

I was told by Nic case when using the calc too use 3.00 v per cell not 3.7 v . I am using 3.2 and 3.30 :1 1/8 scale diffs. I come up with ~100mph. I have done this multiple times so I know my gearing is pretty close. I am just trying to figure out the amperage calc.

It looks like it will be around 200 amps. It will really depend on how fast you get up to speed. The faster you get up to speed, the more power you need. I assumed 8 seconds to get up to speed and you will cover about 700'. You can accelerate slower (9-10 seconds to get to top speed) and you can decrease your amp draw, but you will need a much longer runup distance.

http://lh3.ggpht.com/_3N0hwXEVK9I/Sr...edmonster4.jpg

Ok so it should be total gear ratio not just trans ratio. I thought that might be what the problem might of been. BTW this setup has been done with 25 pinion and 36 tooth spur with a lower gear 3905 tranny instead of a higher gear 3906 tranny and heavier revo and the best results were 91.2 mph on gps and radar.

Tire diameter is too tall I am running custom made foam tires that should have no tire growth. That look more like the results I am looking for though. Thanks

Dont include the pinion/spur. Just put in the diff ratio multiplied by the transmission ratio and put it in the transmission ratio entry.

Ah ok. that will be much easier to control too. No pizza cutters!

So it should look like this:

Battery should output at least 200 amps.

http://lh4.ggpht.com/_3N0hwXEVK9I/Sr...edmonster5.jpg

I included the pinion and spur and just mutiplied the diff gear ratio x the tranny ratio and came up with the same numbers. Looks good now.

I think the 2 6s 5000mah 30c would be too much and too heavy.

I would go with the 2 6s 3300 30 c in parallel for 198 cont and 264 burst.

Question now should I get batts with 200 amp continues or 200amp surge?

I like that choice, I was thinking the same thing about the weight.

If I step up the spur to a 42 the motor kv are right on the money. Is it true 4000 watts are needed and over 5 hp . Is the motor even capable of that? I believe the peak is 2700 watts.
Target speed (mph) 100
Pinion size 30
Spur size 42
Drag coefficient 0.65
Tire Diameter (in) 5.50
Number of Cells 6
Voltage per cell 3.00
FDR 7.938
Vehicle_speed_m_s 44.7040894081788
Frontal_area_m_2 0.04967732
Drag_N 39.545993896358
Tire_RPM 6114.64968152866
Motor_RPM 48538.0891719745
Motor_KV_needed 2696.56050955414
Electrical Efficiency 0.85
Transmission Efficiency 0.75
Input_Amps_needed 225.147173346343
Input_Watts_needed 4052.64912023417
Horsepower_needed 5.43469198856744
Distance_Covered_ft 880.001761341123
Distance_Covered_m 223.520447040894
Transmission ratio 5.67
Vehicle Width (in) 11.00
Vehicle height (in) 7.00
Configuration 4wd
Vehicle Weight (lb) 9.00
Time to get to top speed (s) 10.00
Acceleration_G_s 0.455699178472771
Added Time 24-Sep-2009 10:58:32