> > >Not knowing where to begin, I'll just jump into the middle, and then either >paddle forward or backwards. > >First Question: It would appear that many EV conversions have 96 volt >systems, with 8"/9"/10" electric motors that produce somewhere around ten >horsepower, and have a 40 - 60 mile range. > These days 96V is generally considered low voltage with most conversion EVs using 120 to 144V. Also the motors you are refering to 'might' be rated at only 10 hp continuous, but can generally produce far more than that for shorter periods of time. FWIW the average gas powered car (called ICEs on this list for "Internal Combustion Engine") requires 10 hp to go 50 mph on flat ground with no wind. If you want an EV that can go 60 mph in average conditions you will generally need 15 to 20 hp.
Again a 10hp continuous rated motor can possibly produce 15 hp for 1 hour or so. > >Let's start with the batteries. What does 96 volts mean, in terms of the >amount of power that can be supplied, and the length of time it can be >supplied? I suspect the answer has something to do with amp hours. > Voltage, by itself, tells you nothing about power or how long it can last. Power(called "Watts" in electricity) equals Volts (V) times Amps (A). You are probably familiar with the term "Killowatts"(KW) 1 KW is 1,000 Watts and equals 1,000V x 1A, or 100V x 10A, or 50V x 20A, etc. 1 HP = approx 746 Watts Power over time equals energy, so you are right Amp hours with Volts does tell you how long a certain power can be produced. Let's say we need 10 hp to drive down the road at a given speed. Now that means that means that our motor has to produce 7,460 watts (10 hp x 746). But this does NOT mean that our batteries have to produce 7,460 watts, in fact they must produce far more. This is because of losses, we loose some power in the cables and some in the controller and quite a bit in the motor. These losses generally show up as heat as the component converts part of our electricity into heat. Why this happens is another lesson but for now take my word for it. So, for simplicity, most folks assume these losses add up to about 25%. That means for every kw we draw from the batteries we get 750 watts output to the wheels (about 1 hp). Makes things kinda simple eh? 1kw from the batteries equals 1 hp to the wheels. So if we need 10 hp to drive then we need 10 kw from our batteries. If we have a 96V pack that means it must produce a bit over 104 amps. A typical 6V golf cart battery can produce 104 amps for about 75 minutes before it's dead, however draining a lead-acid battery untill it's dead is hard on them and shortens theri life so most folks only drain them down about 80% or 60 minutes in this case. > >Another way to ponder the question is that, a typical 96 volt system, >consisting of either 6 volt or 12 volt batteries, produces "A" amount of >watts and "B" amount of amps, and can provide "X" amount of power at "Y" >amount of load for "Z" amount of time. > >So, what are A, B, X, Y, and Z, what are their values, and how does juggling >the mix of batteries and serial/parallel connections change those values? > Sorry no simple answer to that. Lead-Acid batteries have a pecular property, the amount of amp hours you can get out of one changes depending on how much current you are drawing. This is called the Peukert effect (named after the gentleman that discovered it). For example our 6V golf cart(GC) battery might have an amp hour rating of 225 AH, but this is at the 20 hour rate (11.25 amps for 20 hours) kinda useles for EVs since they typically draw far more than 11 amps. The rule of thumb is that GC batteries produce about 60% of their 20h rating for 1 hour, or about 125 amps for 1 hr (until it's dead, 80% is about 100 amps). So a given 6V GC battery can produce 67.5 watts (6V x 11.25A) for 20 hours or 1.35 KWH or it can produce 0.75KWH for 1 hour. A 96V string would therefor produce 21.6KWH over 20 hours or 12.96KWH for 1 hour (again these numbers are until the battery is dead). So it all depends on the battery and how fast you drain it. FWIW if you want the math, Peukert has two parts. The Peukert Exponent (usually called Peukert's Number or PN) and the Peukert's Capacity (PC). PC equals how many hours a battery can produce 1 amp, many people just use the 20 hr rating but that's usually going to be wrong(way wrong for GC batteries). The formula is A^PN*T=PC A=Amps and T=time in hours. The ^ means "raised to the power of" I've been using a T-105 battery in my examples, a 6V GC battery made by trojan with a 20hr capacity of 225AH, a PN of 1.24 and a PC of 400Ah. So with this battery determine how many amps you are going to draw, raise this to the power of 1.24 and then devide 400 by the answere and you will get how many hours it can produce that much current. Let's say 150 amps. 150^1.24 = 499 400 / 499 = 0.8 hour or about 48 minutes. About 38 minutes if we want to keep our discharge below 80%. If it takes you 150 amps to go 60 mph then you have a range of about 38 miles (at 80%).
