Hi all, first post but by what I've read so far I think I found the right place to ask my question(s)

We're building a total loss electric go kart which needs to run off of one 12V battery. At max output, our motor pulls 50-60amps so we need to "de-tune" or limit current in order to have the battery last the entire one hour race. Basically, we go full out the first few laps then step things back a few notches for the rest of the race. We've been thinking of running a 12V to 24V converter in hopes that this would increase motor speed and allow us to gear for more top speed, but I'm wondering what impact this would have on battery life. However, not sure if this would have the effect we're hoping for. Any thoughts?

Thanks in advance!

 

12V @ 60 Amps is 720 Watts which is a pretty substantial load. Since I can't see the nameplate data on your motor I can't begin to make suggestions. What is the rated motor voltage? Assuming your motor is designed for 12 V operation running the motor at 24 V may be damaging the motor. The only merit to running the motor at for example 24 V would be that it would half the current. The 60 Amps becomes 30 Amps but you have doubled the 12 V supply voltage. Your best solution is a bigger battery for example a 12 V 100 AH (Amp Hour) battery would, in theory, deliver 100 Amps at 12 V for 1.0 hour. How are you throttling your motor speed?

Ron

 

Racing IS the place to have power control, AND Racing is not the place for economy. What you need to have is an efficient power control, which will be a Pulse Width Control for the motor power. That will allow setting the power to what is required, and not any more than that.
In addition, you need to understand that battery power is limited.
So the other function your control scheme needs is possibly a scheme to boost the voltage to the motor as the charge is depleted. That is not simple.

 

If you double the voltage on a 12V motor to 24V, you will also DOUBLE the current it may try to pull under acceleration etc.
Although the cart wiring resistance to the motor will most likely become the limiting factor in not actually achieving double the current.
Does it have a motor speed controller, such as PWM presently?
That will almost certainly get damaged, unless it is rated for 24V and 100+ amps.

You battery will run out even quicker......
You just need a bigger battery.

 

Driving a 12 volt motor with 24 volts may indeed draw twice the amps, as well, giving you four times the power. For some short time, until the motor burns out. It could work in a "funny car electric dragster for a FIVE SECOND run, though. No way could it last for an hour race.
ALSO, WHAT is " a total loss electric go kart "???? I have not seen that phrase, except to describe collision damage to a race car.

 

, our motor pulls 50-60amps

You might be losing volts in the wiring. Check that first.

 

Doubling the voltage (12v to 24v) will make the motor spin twice as fast as the nameplate. The current will depend on the friction and wind loads and acceleration (not the motor voltage) but exceeding the motor nameplate amps will certainly lead to motor failure.
The battery duration (not life) will depend on the battery watt hours and the energy drawn from the battery. Assuming a higher top speed, and the same battery, the duration will be less.
Consider that a converter from 12V to 24V at 60A is a fair bit of power electronics, which is itself will have losses.
My recommendation would be: install the largest battery that the rules allow; install the largest motor that the rules allow (motor voltage matched to the battery); test what the average power consumption is (you may need to make gearing changes) and drive it to that limit.
This is a typical engineering problem, with multi variables. We can give you some guidelines, but only your testing and calculations will derive the optimal solution.

 

First; Welcome to AAC.

12V @ 60 Amps is 720 Watts

If you use a boost circuit to jump to 24V then the math is - assuming you have 100% power conversion (no power loss from your boost circuit) 24V @ 30A, which still equals 720W. But in the real world you won't get 30A and you won't get 720W.

As others are telling you, you need a bigger battery, not a higher voltage. Perhaps a different kind of battery than the one you're using. Usually when people talk about 12V batteries they're most often talking about Lead Acid batteries, whether they are Wet Cell, Sealed Lead Acid (SLA) or AGM batteries. (AGM = Absorbed Gas Mat or something like that). A 12 volt lithium ion battery pack can deliver higher current and has a better discharge rate than Lead Acid batteries. And you can take your pack to around 15V with the addition of another series Li-Ion batteries. BUT with Li-Ion you have to manage the charge rate properly or you will have a lot of excitement, smoke and flames. Then you'll truly have a

total loss electric go kart

Not only do you have to be concerned with charging you also need to limit how much voltage drop the batteries experience. Go too low and the batteries can overheat and again with the excitement. If you escape the fire you still can damage the batteries to the point where they won't perform the way they were intended to.

Let me ask the question nobody else has thought to ask so far: What kind of 12V battery are you using at present?

A few other questions maybe: Is this a regulated sport where you have oversight by a safety committee? If so, what are the rules? If this is something you and your friends are building just for the fun of it - you really need to stop and get some very clear insight and knowledge about what you're attempting to do. ESPECIALLY if you involve Li-Ion batteries. None of us here at AAC want to see you get hurt because of something we said - or neglected to say.

 

To get the most possible out of whatever battery you have you will need a 100%efficient pulse width modulator power delivery control. Power spent spinning the wheels is wasted. Just short of wheel spin is the most effective. Watch some "Funny Cars" race to understand that. If they lose traction and spin the tires they do not go as fast.

 

keep in mind that unless you are turning energy to heat - EVERY energy conversion COSTS you...

the motor is 12V*60A=720W load
using voltage conversion you are introducing circuit that account but ts for further energy loses say you have converter that is 85% efficient. that means your load becomes 720W/0.85 = 847W while your motor is still using 720W. you just added another 127W that turns to heat. this too comes from battery.

so if battery life is of concern, do not convert energy, match motor to battery.

 

LIKE I STATED: Use an efficient PWM power controller. I am sure that a circuit is available from somebody here. THAT will be the way to apply only the power needed at that moment.
AND, I am still wondering what is "a total loss go kart."?????