need equasions to figure out a motors power consumption

[mashersmasher]

hello! i have a 94v 18amp treadmill motor that i want to use for a motorized little vehicle. problem is that i want to figure the power consumption before i get batteries to suit it. what i was thinking is that i would use 4 24v tool batteries in series and add some in parallel if space was available. what i want to find out is how long 4 of these batteries would run but i don't know the equasions

**broken link removed**

 

[k7elp60]

The first thing you need to determine is the current drawn by the motor. The current drawn by the motor is directly related to the load on the motor.
If the motor draws 5 amps continously then for 1 hour of operation the batteries must be able to supply 5 amps for one hour. One of the specifications of batteries is there rating and this is in AH(amp-hours) Different chemistries of batterys have different AH, and the larger the physical size of any battery the larger the capacity in AH.

 

[AllVol]

The first thing you need to determine is the current drawn by the motor. The current drawn by the motor is directly related to the load on the motor.
If the motor draws 5 amps continously then for 1 hour of operation the batteries must be able to supply 5 amps for one hour. One of the specifications of batteries is there rating and this is in AH(amp-hours) Different chemistries of batterys have different AH, and the larger the physical size of any battery the larger the capacity in AH.

While I was reading to make sure my answer would be correct, you answered the question. Good job!

 

[mashersmasher]

well the batteries are 24v and i just saw that they have 1.7ah so if the motor is 18a would it last .09h (1.7/18) or .37h ((4*1.7)/18) if the batteries are wired in series? thanks for the info thus far!

 

[Pommie]

A better way to calculate it is in watts. Your motor is approximately (94*18) 1.7kW and your batteries are (24*1.7) 40W and so 1 battery would last (40/1700) 0.023 hours or 1.4 minutes. You do of course need 4 to get the correct voltage and 4 will last about 6 minutes. This all assumes that the batteries give out their rated current, in reality when discharged at a high rate there capacity drops quite a lot.

Mike.

 

[mashersmasher]

ike... suppose i'm going to have to go up to car batteries :S

edit: from what i've read most car batteries have around 50 ah. thing is they are 12v each so i would need 8... i think it might as well get a half decent motor if i'm going to spend that kind of cash.

 

[Hero999]

Car batteries aren't designed for deep discharge, you want to use SLA batteires, 8 12V 50Ah batteries would keep your vehicle going for about 2 hours 45 miniutes.

 

[mashersmasher]

ya i suppose this is true.

i was thinking of getting $100 and some worth of these to power it. i was thinking of putting them in 24v (really 25.9) bars with sets of 14 (7 sets of 2 in parallel). that way i could have 2 sets of 4 bars so while one was set is charging i can use the other. each pack would give a modest hours worth of run time if the 2400mah figure is right

edit: scratch that >.< misleading pic made it look like it was a pack of 5

 

[Boncuk]

A better way to calculate it is in watts. Your motor is approximately (94*18) 1.7kW and your batteries are (24*1.7) 40W and so 1 battery would last (40/1700) 0.023 hours or 1.4 minutes. You do of course need 4 to get the correct voltage and 4 will last about 6 minutes. This all assumes that the batteries give out their rated current, in reality when discharged at a high rate there capacity drops quite a lot.

Mike.

Hi Mike,

objections here. One battery of 24V/1.7Ah won't drive the motor. 4 batteries of 1.7Ah connected in series will drive the motor, but won't increase the total capacity.

Hans

 

[Ubergeek63]

A better way to calculate it is in watts. Your motor is approximately (94*18) 1.7kW and your batteries are (24*1.7) 40W and so 1 battery would last (40/1700) 0.023 hours or 1.4 minutes. You do of course need 4 to get the correct voltage and 4 will last about 6 minutes. This all assumes that the batteries give out their rated current, in reality when discharged at a high rate there capacity drops quite a lot.

Mike.

That only holds true for full load. The actual load depends on efficiency, "road" condition, tire condition, weight, grade, wind resistance and perhaps other factors I could not think of off the cuff.

While it is true that "capacity drops quite a lot" for lead acids which only supply 50% of the rated capacity at high load, modern chemistries are much more resilient with some only taking a 10% hit.

Dan