# Increasing voltage for battery system

#### oopsies

Joined Aug 27, 2021
10
Yes. You'll find them in forklift trucks.
https://www.tayna.co.uk/forklift-batteries/lucas-2v-bs/
You buy them in individual 2V cells, so that if one cell fails it can be replaced.
So I'm looking at the first one as an example. What does the C5, C10, C20 (under capacities) stand for?

And I think I'm not understanding the relationship between voltage, current, and power (aside from the equation). I'm trying wrap my head around how to tell if I need to put in more current or more voltage into a motor. So if I put in more voltage, what happens to the motor? What happens if the motor gets less current but gets high voltage? I don't understand that relationship between those things.

#### Ian0

Joined Aug 7, 2020
3,770
C5 is the capacity if the battery is discharged over a period of 5 hours
C10 is the capacity if the battery is discharged over a period of 10 hours
C20 is the capacity if the battery is discharged over a period of 20 hours.
The difference between the three figures is due to something called the Peukert effect.

For a DC motor, more voltage will make it go faster. Speed is proportional to Voltage. Torque is proportional to Current.
Power= Voltage x Current.
Power = Torque x Speed.

#### oopsies

Joined Aug 27, 2021
10
I just read up on torque and speed... how do I decide which to focus more on? Since I can't have both, for any given motor, should I try to give it max current for torque or should I focus on giving it max voltage for speed? How does a person decide?

#### Ian0

Joined Aug 7, 2020
3,770
I just read up on torque and speed... how do I decide which to focus more on? Since I can't have both, for any given motor, should I try to give it max current for torque or should I focus on giving it max voltage for speed? How does a person decide?
The torque is proportional to the drag.
See https://en.wikipedia.org/wiki/Drag_(physics)
I presume the physics for a boat in water are similar to a vehicle in air, in which case the torque you need will be proportional to the square of the speed.

#### BobTPH

Joined Jun 5, 2013
4,051
The motor has to be matched to the propeller. A higher speed, lower torque motor would match to a smaller and / or lower pitch propeller while delivering the same power.

Bob

#### cqexbesd

Joined Dec 16, 2017
4
Slightly adjacent to your question but if you are just learning about electric motors on boats then you might be interested in https://sailinguma.com/electric-motor/ and their accompanying YouTube channel. They have several videos where they go through their system based on a fork lift motor.

Of course it’s not their main propulsion system so I don’t think they are after the speed and endurance you are looking for.

#### pvanb

Joined Apr 4, 2014
6
Am I correct in assuming a gallon of diesel fuel would provide more ( overall effective ) work energy than a half ton of batteries?

#### Ian0

Joined Aug 7, 2020
3,770
A UK gallon (4.54 litres) gives 47kWh. A diesel engine will turn that into about 15kWh of work, and 32kWh of heat.
Half a ton of lead acid batteries gives 18kWh.
Half a ton of LiPO4 batteries gives 44kWh.
Assuming lead-acid batteries and a slightly better than average energy efficiency, and you are correct!