Need help understanding Amps -vs- Volts

1670 Views 2 Replies 2 Participants Last post by themadscientist, Jan 18, 2011

themadscientist

Discussion Starter · Jan 18, 2011 (Edited)

Hello everyone, new dude, likely with an old question, but I hope you can square me away on this.

I get the basic idea that many configurations of battery pack can achieve the same watts, ex.

2 6V 10A batteries in series = 12V @ 10A = 120W
2 6V 10A batteries in parallel = 6V @ 20A = 120W

Right? (if I messed that up I'm more confused than I thought)

The question that I have, well a couple actually, are:

Two theorhetical EVs using these packs would display what characteristics?

Would the high amp EV behave differently from the high watt one?

If so, how?

If I understand the concept, I would expect the high amp 120W EV to accelerate and achieve a higher top speed than the high watt EV, but have less overall range. Am I correct?

Assuming that, when configuring my pack, as long as it can deliver adequate amps for the maximum loads the EV will experience, extra amps are uneccesary?

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icec0o1

· #2 · Jan 18, 2011

You have it mostly correct. The range for both packs would be the same (as you should imagine) as you pointed out both configurations come up to 120Wh.

The higher the voltage, the faster a motor would want to spin. The motor amps represent the instantaneous torque. At 12V, 10A a motor would spin up at twice the speed if instead you were feeding it 6V, 20A but it would have half the torque. To equalize things, you could just add a 2:1 gearbox to the 12V, 10A scenario and you would have it almost identical to feeding it 6V 20A. The gearbox reduces efficiency but so do higher amps.

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themadscientist

Discussion Starter · #3 · Jan 18, 2011

Well I am looking at a potential vehicle. honestly, I think when I tally up the costs it's going to be dead in the water, but I can't even do that until I have a good grasp of what I am talking about.

It's a Japanese model Nissan 240SX and I think I can bring it in around 3000lb complete with motor, electronics and battery pack. I plan to retain the gearbox and clutch. The ultimate goal would be the following.

Very high potential power in the motor.
I would like to daily drive it at normal highway speed, but if some guy gives me a dirty look at the light I want to be able to stomp him real proper. I run across ICE cars in the 300hp range frequently so I want to talk to something like that if I choose. Of course excessive use of heavy foot would shorten the range, but that leads me to the next expectation.

Reasonably long range.
I would like the vehicle to be able to push at minimum 60-70 miles on a charge if driven on varying grades at highway speed with no juvenile alpha male sillyness along the way. If I can't drive to work and back with great confidence, the whole thing is a waste of time.

A staged build.
I cannot drop a whole lot of money at a shot, but I am hoping, though careful planning and judicious parts selection to be able to get it up and running and increase the power and range in steps as I can afford it to reach the aforementioned goals.

I am thinking, if I start with the ultimate goal and devolve the build I can identify areas where I can go cheap at the outset and then bolster as I can afford it. Ex. start with a small pack and be content with a surface road power neighborhood EV until I can increase the size of the pack. Ex. grab a Warp 9 for now and be content until I can stack another on it for more speed.

I expect that there will be things that are not negotiable. Ex. If I am going to build towards X amps, I need to make sure that I start with a controller that will be able to handle that when I get there. Revisiting it and buying a new one because I cheaped out at the start seems pennywise pound foolish.

If I'm floating along on fanciful balloons of naivite, please pop some and get me closer to earth.

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