Voltage Ratings

[Don]

Please excuse what may be a simple question. What does the voltage rating mean? I read of people using 18 cells on a motor rated for 12v. Doesn't this cause a lot of problems or can you get away with it with cooling and short runs? What are the consequences of running a motor below or above its rating?
Thanks
Don

[AndyKunz]

Shorter motor life is a given, but this is racing and you are expected to shorten the life a bit. The Graupner voltage ratings mean nothing - don't worry about that part. Other companies really mean something.

Brushes wear quicker, bearings wear out quicker, and you risk overheating if you put too much prop on.

Andy

[Andrewg]

the variable that is important is the rpm/v

[H20Cat]

Somewhat the same topic....

So let's say that I have a 700BB 8.4v motor and a 700BB 12v motor and let's say a 35" hull....

Which motor should I use? The 8.4 on 12-16 cells or the 12v on 18-20 cells and why?

What are the benefits of having higher cell counts?

[AndyKunz]

Originally posted by H20Cat
So let's say that I have a 700BB 8.4v motor and a 700BB 12v motor and let's say a 35" hull....

Which motor should I use? The 8.4 on 12-16 cells or the 12v on 18-20 cells and why?

What are the benefits of having higher cell counts?

I would use the 12V motor on 18-20 cells. It would have the appropriate torque for a bigger boat like that. If you are talking about an outrigger, though, the 8.4 on 16 would probably be better.

A higher cell count gives you higher possible power output. It also gives you more RPM. The downside is that it will eat your brushes faster.

Since both motors are dirt cheap, why not get one of each?

Andy

[Andrewg]

This is a fun question.

the 12v will have a less output (285w) than the 8.4v (351w) on 16 cells - which will take each motor to the safe rpm limit. However on a well setup boat this may mean a speed difference of 1-2 mph.

The 12v also pulls only 14 amps vs 24 for the 8.4 (this is runnign a setup at maximum efficiency). This means if use 1700AUP's which are light the boat will weigh 2oz more than a 12 cell setup using 3300's but give the same runtime ie around 7.5 minutes.

The 12 v motor has a good torque output and withthe lighter cells has torque/kg about 12 or 16 cell 8.4 setups so acceleration should be good.

However using mroe cells is not cost effective. A 700 on 12 x GP3300's s will perform as well, as will a 16 cell setup. Both will do so at less cost.

Within the same cost envelope the 12v motor may be restricted to fast scale style work like smaller ChrisCraft. Otherwise it may be cheaper to sell or swap it for a 8.4v version of the motor.