Help with distance and speed...

[jumper]

I read about someone who made his own chassis (aluminum) and did a fiberglass body. I think he did 4 12v lead acid batteries and gets 25mph with a range of 12 miles. Here's my question... if I doubled the batteries, how would that effect range and mph?

I would like to get 35/40mph with a range of about 20+ miles.

thanks

[Cobb]

Physics doesnt work like that. When you double you speed you face 4 times the wind resistance alone, not to count rotating friction and the extra weight causes to the whole equation. I think double the batteries gives you 20% more assuming its the same old lead acid. Go lifepo4 or something and you may be able to get somewhere.

[jumper]

Thanks for the reply. I really didn't expect it to be a 1:1 ratio (double batteries = double speed and distance). I guess I'm just looking for how to get 35/40mph with about 20 miles distance. I've seen posts about the batteries you suggested, but my pockets are not that deep (I read that they were expensive).

Originally Posted by Cobb

Physics doesnt work like that. When you double you speed you face 4 times the wind resistance alone, not to count rotating friction and the extra weight causes to the whole equation. I think double the batteries gives you 20% more assuming its the same old lead acid. Go lifepo4 or something and you may be able to get somewhere.

[jumper]

Following your 20% statement. I think the mph would go up to 30 and the distance would go up to 14.4... My math is bad, but is that right?

Also, I just looked up some Lipo4 batteries and they are not as expensive as what I thought. Can you or anyone give me a link to the right kind of Lipo4?

[ecomodded]

Originally Posted by jumper

if I doubled the batteries, how would that effect range and mph?

I would like to get 35/40mph with a range of about 20+ miles.

thanks

Double the batteries but keep the same voltage will double the distance range.
Double the batteries but double the voltage and you will get "more" speed.

But (as mentioned) there are losses in efficiency due to the electric motor/ wind resistance & various frictions that increase with speed. You don't want to go to fast or have a heavy vehicle so it will be more easily powered, just keep the weight down.

You need to size the motor to the vehicle weight and size the batteries to the vehicle weight & motor + distance and your speed desired.

Do I know the math for that ? No but its out there

[Joggernot]

I have a street legal electric golf cart with windshield that can go 10+ miles at 20 mph. It has 6 12v batteries and absolutely no areomods. With new batteries it can go a little farther.

[UltArc]

Also keep in mind, you are doubling one factor and expecting two factors to double from it.

"4 12v lead acid batteries and gets 25mph with a range of 12 miles"
I could see 8 being around 35-40 mph, or 20-24 miles at 25 mph, but you can't double both factors by only doubling the batteries.

Just hypothetical here, and not considering ANY losses, to double your speed and double your distance, one would need 16 batteries. Then we get into all of the great points everyone else is making, and other factors like temperature, and road conditions that can also affect your performance.

Not trying to burst your bubble, but just noting without any loss at all and just using math, you would need 16 to do that. Real life, with other factors, I would hazard a guess of at least 20 batteries at that rate, but under 32.

[jumper]

Thanks for the reply. You said that doubling the batteries but keeping the same voltage will double the distance (all things considered) I'm a "bit" dumb about this but does that mean running in series instead of parallel (or the other way around?

At this point I would rather increase the distance more than mph.

Originally Posted by ecomodded

Double the batteries but keep the same voltage will double the distance range.
Double the batteries but double the voltage and you will get "more" speed.

But (as mentioned) there are losses in efficiency due to the electric motor/ wind resistance & various frictions that increase with speed. You don't want to go to fast or have a heavy vehicle so it will be more easily powered, just keep the weight down.

You need to size the motor to the vehicle weight and size the batteries to the vehicle weight & motor + distance and your speed desired.

Do I know the math for that ? No but its out there

[jumper]

That's cool about the golf cart. I think I've seen one or two that were geared for street use. That would be a fun way to get around

Originally Posted by Joggernot

I have a street legal electric golf cart with windshield that can go 10+ miles at 20 mph. It has 6 12v batteries and absolutely no areomods. With new batteries it can go a little farther.

[jumper]

Thank you. I do understand now that you can't increase mph and distance just by doubling the batteries. It's one or the other. As I said, I would rather increase the distance. If I kept the mph to 30 and under, I could register it as a moped...

I think I would have to redesign the frame to accommodate 16 batteries. I need to do that anyway for trips to the grocery store. Basic question (that I'm sure has been asked 1000 times), Would it be easier for me to take like an old VW and convert it rather than starting from scratch? I'm thinking it might, being that this is my first build.

Another question: can a LiFePo4 battery work along side of regular batteries or do they all have to be LiFepo4?

I also want to thank everyone for helping me understand things. You have to start somewhere and the only thing I know to do is ask dumb/basic questions

Originally Posted by UltArc

Also keep in mind, you are doubling one factor and expecting two factors to double from it.

"4 12v lead acid batteries and gets 25mph with a range of 12 miles"
I could see 8 being around 35-40 mph, or 20-24 miles at 25 mph, but you can't double both factors by only doubling the batteries.

Just hypothetical here, and not considering ANY losses, to double your speed and double your distance, one would need 16 batteries. Then we get into all of the great points everyone else is making, and other factors like temperature, and road conditions that can also affect your performance.

Not trying to burst your bubble, but just noting without any loss at all and just using math, you would need 16 to do that. Real life, with other factors, I would hazard a guess of at least 20 batteries at that rate, but under 32.