Thread: 12v vs 24v

I'm trying to wrap my head around the concept that a 24v tm with 2 batts will last longer than a 12v with 2 batts. It has been explained that the 12v would need to run on a higher setting to achieve the same speed but my question is if the boat weight and the speed are the same it seems like it would require the same amount of energy regardless of what setting the motor is running on. Are the 12v motors less efficient than the 24v?

Originally Posted by BigKyd

I'm trying to wrap my head around the concept that a 24v tm with 2 batts wired in series will last longer than a 12v with 2 batts wired parallel. It has been explained that the 12v would need to run on a higher setting to achieve the same speed but my question is if the boat weight and the speed are the same it seems like it would require the same amount of energy regardless of what setting the motor is running on. Are the 12v motors less efficient than the 24v?

There you go. Pan Man posed a 12 vs 24 chart somewhere in this forum.

Energy used in an electrical circuit is expressed in watts. Watts is the result of Voltage times current. Thus a 12 Volt motor using 2 amps is using 24 watts. Now a 24 Volt motor only uses 1 amp to produce the same 24 watts. In DC circuitry remember P= I X E

Power is Watts or P in the equation 24 watts= 2 Amps X 12 Volts
Current is Amps or I in the equation
Voltage is Volts or E in the equation 24 watts= 1 Amp X 24 Volts

So in terms of current load for the same power rating 24V is more efficient than 12V.

Originally Posted by hays47

Energy used in an electrical circuit is expressed in watts. Watts is the result of Voltage times current. Thus a 12 Volt motor using 2 amps is using 24 watts. Now a 24 Volt motor only uses 1 amp to produce the same 24 watts. In DC circuitry remember P= I X E

Power is Watts or P in the equation 24 watts= 2 Amps X 12 Volts
Current is Amps or I in the equation
Voltage is Volts or E in the equation 24 watts= 1 Amp X 24 Volts

So in terms of current load for the same power rating 24V is more efficient than 12V.

A 24V system and 12V system have identical efficiency. 24W is 24W whether it's 12V@2A, 24V@1A or [email protected], and the power consumed from the battery is the same (except for some anomalies due to battery physics).

If you have two motors, one 24V and one 12V producing identical thrust, the 24V motor will draw less power due to the lower current in the motor windings. Motor windings are a big problem because the wire has a nasty feature that causes the resistance to increase when it gets hot. Resistance and higher current in the winding are especially bad because power loss in the winding is determined by the current squared times the resistance. So your 24V motor loses 1X1XR Watts while your 12V motor loses 2X2XR Watts.

In English, that translates into a 24V motor has only a fourth the winding loss of a 12V motor. Worse yet, the higher winding current in the 12V motor causes the windings to get hotter, making R bigger and causing the losses to be higher.

I guess I'll have to pony up then, was hoping I could get away with a 55# but it sounds like 24 is a must for pulling cranks.

Catfan- agree about the heat and windings but they did not repeal Ohms law, :-0

Batteries are rated in ampere hours. So the 24 pulling 1 amp and the twelve pulling 2 amps is probably offset by the 24V system needing 2 batteries. However the 12 pulling on the one battery will discharge it quicker than the 24V system would on the 2 batteries agreed ?

Originally Posted by hays47

Catfan- agree about the heat and windings but they did not repeal Ohms law, :-0

Batteries are rated in ampere hours. So the 24 pulling 1 amp and the twelve pulling 2 amps is probably offset by the 24V system needing 2 batteries. However the 12 pulling on the one battery will discharge it quicker than the 24V system would on the 2 batteries agreed ?

Indeed it will, but the OP is about a 12V two battery system, so it's on equal footing capacity-wise with the 24V system.