To GB and all. Ref your posts above, I have made comments below. I haven't even looked at posts since I read this one from you earlier. Hope it is still relative.
Hang in there with Tom, Andy. He will teach you well. Amp hour is the correct formula. But. And with no disrespect to Tom. A racing pack is considerable different. For me it is about the amps. I understand the amps. Power comes from the amps.
Power comes from Voltage(E) & Amps(I). Power=E multiplied by I . A battery just by itself with nothing attached to it has the potential of providing a certain qty of amps for a certain length of time depending on the "load" (resistance it will feed once it is connected). For racing or for any other use, there needs to be a way to document the amount of that potential. The standard (developed back when Pope Paul was a choir boy) is to provide the qty of amps the battery can provide in 1 hour's time. That is called the Amp/Hour Capacity. (note that some batteries such as Lithium Ion, AGM because of the way they are made, can provide extreme amount of current faster than others, some companies rate their batteries on different amounts of current for different amounts of time/current flow (depending mostly on which makes their batteries appear best). The only way to compare apples to apples is to use a standard. The standard is and hopefully forever will be, Amps per Hour (total amps the battery can provide for 1 hour) (Save the difference in discharge curves till way later in discussion)
Amps also keeps your pack from dropping voltage. I build the battery pack form the controller down. If you have a 750 amp controller. That is all the amps you need from your battery pack. There are controllers on the market that will allow you to build your battery pack with enough amps to keep you from dropping voltage while only sending the desired volts to the motor. I hope that I don’t make us all just a little more dumber with my two cents. But at least I understand my self.
GB, it is apparent that you understand current and voltage, however, I disagree somewhat with the way you explain it and I think sometimes your "causes and effects are backwards". Bare with me a minute while I (again) go back to my water comparisons...
Please picture this:
We have a five gallon bucket full of water hanging 10' up from a tree limb.
There is a small diameter hose connected to the bottom of the bucket that hangs down to just above the ground.
The hose has a clamp holding it the closed just below the bucket.
We remove the clamp and water begins to flow.
It takes 1 hour for all the water to drain which means the flow is 5 gallons per hour or Gph, correct?
For a moment, think of the bucket and water as a battery, the hose as the wiring, and the water flow the current. If so, the 5 gallons per hour flow rate equates to 5 Amps in one hour or 5Ahr total capacity.
Now, let’s go back up the water system.
I add a small decorative water wheel at the bottom of the hose.
I fill the bucket back-up with 5 gallons of water and remove the clamp on the hose.
Water flows at the rate of 5 gallons per hour and the water wheel barely rotates.
It is apparent that we need to increase the water flow to get the water wheel to speed-up for the “look” we want.
The only thing restricting (“resisting”) the amount of flow is the size (cross sectional area) of the hose.
To increase the “cross sectional area” (to lower the resistance) of the hose, we have to increase the inside diameter of it.
Okay, we replace the hose with a larger one, doubling the cross sectional area.
Again, we fill the bucket, remove the clamp and the water wheel turns, but WAY TO FAST.
We have measured the time to empty the bucket with the larger hose at 30 minutes.
If we had increased the hose by 4x it would have only taken 15 minutes to empty the bucket.
Okay, too much water turning the wheel, so now we need to reduce the amount.
Instead of trying to find a hose between the two sizes we tried, let’s add a adjustable valve.
A valve will let us “CONTROL” the amount of water. Controller? Yep.
So, as with the water, we can add a electric current controller to a circuit that can vary the current.
With a controller, the foot pedal electronically controls the current flow.
Some controllers also allow controlling the maximum current and voltages through programming.
Important facts are:
The maximum current that is available from the batteries to a load is based on the voltage of the pack, its maximum Ahr capacity and the resistance it sees.
I = E/R, once you have the maximum current available from the battery, the total resistance of the motor doing the work and the adjustment of the controller limits it. That’s the real purpose of the motor controller.
GB, as you are aware (based on your past comments), you can always go to the max in voltage and Ahr capcity, then use the controller to drop back to the voltage and current you want the motor to see. I, on the other hand want to design to what I want without paying for more than I will use. Also, since you are building a cart as “unlimited” or a “exhibition class” the maximum battery capacity doesn’t matter. But in the case of a 48, 72 or 96 volt “class” (racing groups/sanctions, etc.) the class is specified by total voltage and Ahr capacity of the battery pack, rather than what is actually delivered to the motor. So using a controller as you have mentioned wouldn’t really be an option for what I want to do
Now, for the fun part of all this
550 amp controller.
130-volts to the motor.
Run time 8sec.
Using your formula. What would your pack consist of? Battery amperage? And how many. weight is big factor.
My pack will consist of 22 of the odysses 680's The will pack will be series & than parallel.
pack weight will be 330.lbs
Sounds like a fun thing to do. Might have more questions, etc., but I’ll start working on something as soon as I can. I’ll advise status with posts. Perhaps others will join in the fun. Perhaps you could change the parameters to max size of the cart, a certain top speed, ¼ mile time, etc. and design toward those parameters, or specify max voltage, cart weight? That way we could design to come-up with type motor, controller, batteries, etc.?? Whatever would be the most fun and provide the best education for all of us participating...
