Disclaimer
Frequently Asked Questions |
| 1. I want to
convert my (...insert your car make and model here...] to an electric. I want 70 mph top
speed, and about 50 miles range. Which drive system and battery do I need? First, please note - currently there are no batteries offered on MME web site. Currently we only provide electronic hardware. You have to realize that there is no answer to this question without knowing much more about your conversion and its purpose. It is similar to asking when buying conventional car "which engine option - gasoline or diesel do I need and what fuel tank size do you recommend?" The answer will be - it depends. There is no one to tell you you need exactly 100hp gas engine and 5 gal tank. Same for electric drive system, is's not as simple as "50kW drive and 10kWh battery will do it". It might, but this doesn't make such vehicle suitable for you. Wimpy Geo Metro can go 70 mph and
so can latest Porsche. Porsche can sure reach it far quicker with more fun factor, but
this wasn't in the question. So the answer is - it depends. - How quickly you want to be able
to reach that speed Unless you have answers to these questions, my (or everyone's) answer will be "it depends". 20kW might do it for some vehicles and 50 kW won't cut it for others. If you did not pick the vehicle yet, my only advice is - pick the one you'd love want to drive, which suits the purpose (whatever it is), electric or not. Else you end up with the vehicle you don't like in general. Once you settle on what you want the vehicle to do, pick the lightest the most aero one with strongest suspension (if you plan to use heavy battery) and in decent shape. Keep in mind, if you get a rust bucket, even for free, you'll end up with an electric rust bucket, nothing more. And, should you get tired of it and decide to sell it, for a casual buyer, as a vehicle it will still worth nothing just like original rust bucket was to you. 2. Fundamentally, why would I choose AC system over comparable power DC system? Probably to say "Because GM, Ford or Toyota know better what they are doing" (EV1, Ranger EV, RAV4-EV Shevy S10 Electricar all use AC drive systems) will not be a good enough answer... OK, few main reasons: Reason 1 - of course natural regenerative braking without extra hardware. Deceleration during regen can be the same as acceleration during drive - the system is symmetrical in this respect - you can supply into the battery as much current as you can take out of it. It should be mentioned that few DC systems with special controller and (usually) SepEx DC motor also offer regen (at extra complexity and cost). Reason 2 - favorable torque - RPM characteristics providing constant torque for wide range of RPM. This provides constant acceleration regardless of the speed (within certain limits), and often allows driving without shifting gears. To get fair comparison, a DC system can be set up to provide constant torque if the controller is programmable - it has to work at the current limit at stall and low RPM. This way constant torque can be achieved as well; however top rotor RPM speed of a typical DC motor remains about twice as low as for an AC motor requiring to shift gears in this case, thus loosing torque at the wheels. Normally vehicles using DC systems avoid need for shifting by starting on 3rd or even 4th gear so the RPM at freeway speeds remains manageable. This, however, aside requiring very large motor (to provide high starting torque at the wheels while on 3rd gear), greatly stresses transmission components normally not intended for such abuse, sometimes resulting in broken gear teeth, stripped splines, twisted shafts, damaged CV-joints etc. AC setups don't have these issues. Reason 3 - no motor brushes. Sure, unless abused, the brushes can last very long time, and yet there are all these issues with brush advancing, seating, commutator arcing and self-destroying at high RPM etc. If electric reverse is used, the requirements for brush advance for forward and reverse rotation direction are contradictory. If you want to avoid these problems all together, consider AC motor. Reason 4 - programmability. Strictly speaking, this is not the property of AC system in oppose to a DC one, a DC controller can be made programmable and be as sophisticated as any AC one. But great majority of the DC controllers are not programmable, especially with EV specific parameters. For featured on this site AC inverters a user has access to the software and able to set all the parameters to adapt not only the battery parameters but driving style. For example: Max battery voltage for regen and Min voltage for driving (for battery protection), max battery current for driving and regen separately, throttle response profile, off-throttle regen option, tachometer output, creeping current, power mode and economy mode limits, acceptable inverter and motor temperature, electric reverse, safe motor RPM range (separately for forward and reverse) and many more others. All programmable parameters can be displayed on a PC/laptop screen in real time in digital and analog graphic form as you drive, so you can optimize the settings while in the vehicle. Configurable graphs plotted and can be stored for later analysis and comparison. Try to find a DC controller offering this. Reason 5 - safety. Well known fact that if a DC controller's power stage fails, entire pack voltage is applied to the motor and you better have good circuit breakers, fuses, kill switches and good reaction time if partial failure happens to be at the intersection while you are waiting your green. In contrast, power stages of AC inverter are used to *generate* power for the motor, not *regulate* it, so in case of a failure AC generation just stops and so AC motor just looses power. Reason 6 - easier (smaller gauge, more flexible) battery wiring. This actually applies to a high voltage AC systems (typically using higher voltage and lower current than DC systems of the same power). Since resistive power losses equal I2R where I is current through a conductor and R is its resistance, the lower current, the lower losses. Note, the *battery* voltage U is not part of equation. (don't confuse voltage drop U *on the wire* which is part of equation with total system (battery pack) voltage U which is potential between supply wires). So with typically lower voltage and thus higher current systems you're forced to use heavy gauge wire - typically with crossection area ~100 mm2 (US gauge 2/0) or larger. Even fine stranded welding cable of that size is not very flexible if a short pieces needed for battery interconnects, not to mention need for heavy duty lugs, crimpers, etc. Now and then you hear the stories of melted battery posts, loose connections due to the lead creep etc. This is all due to high current draw: little resistance increase due to loosen connection will cause generating enough heat to cause the damage. And it is hard to keep connections tight because lead the battery posts usually made from, creeps ("cold flows") under pressure and no matter how well your connections tightened, they will loose over time. All the same applies to AC setup with the exception that loosen connection for low current system will not cause nearly as much trouble as for high current one because of flower voltage drop on loose connection and thus less heat generation. Yes, you do have more interconnections to make, but this is one time thing, while maintaining tight connections is ongoing maintenance. For the high voltage system (312V...336V) you can use thin ~30 mm2 wire (US gauge 4) which is far easier to handle, bend and route in tight places. The amount of connections is typically higher than for low voltage systems Of course, if a low voltage AC system is used, this advantage is lost. Reason 7: Excellent thermal reserve characteristics. Technically, it is not AC vs. DC feature, but you will be hard pressed to find a water cooled DC motor. This also means no large fan which takes extra space, consumes extra energy and produces extra noise. Reason 8: Naturally, electric reverse accomplished by adding only a small toggle switch on the dash. All it makes for an inverter is to swap sequence of 2 phases, so the rotor runs in opposite direction. A DC system requires reversing contactors, not to mention that the brush advance is far from optimal when DC motor runs in reverse. At low speeds, however, it is not that critical for a DC drive; nevertheless commutator and brush damage has been known issue while driving a DC motor in reverse while it's advanced for forward rotation. Please ask me or John Wayland how do we know. Reason 9 - ease of
installation. Despite common opinion, let's evaluate complexity of the system from the
user stand point, as a black box. Complexity of an AC inverter or a good DC controller
itself is not the concern, they are both very complex microprocessor based units. We
evaluate difficulty of installation. Basically to wire a Siemens AC system you have to
make 6 connections: 3 phases to the motor, 2 cables to the battery (through the external
contactor box if short inverter is used), and plug encoder cable. The rest is low voltage
wiring: +12V DC-DC output - to 12V wiring system in the car, enable and "start"
wires from the ignition switch. Also, 3 wires to the throttle pot, 3 - to the direction
switch, 2 - to optional start inhibit switch. All this wiring harness is pre-made
and included. Since typical DC system doesn't have other controls (temp sensors input,
power reduction indication, etc.), will stop here for the fair comparison sake. There are other good reasons as
well. For Siemens systems it is for instance motor-inverter matching parameters, i.e.
motor's stator winding parameters and magnetic characteristics are stored in inverter's
EEPROM to maximize performance and efficiency working with that particular motor. Usually
in case of DC systems the motor manufacturer has no idea what the controller running it
will be, and vice versa, so agreement and more-less precise match between the two is not
possible. It is up to the user to puck components to match. We're not discussing relevance
of mismatch (for a DC chopper it's not critical), we' re stating the fact that it does
exist. Now, there are certainly circumstances when none of above is relevant: - You build a drag racing vehicle
on a budget and 1/4 mile time is your top priority. Your torque is not limited by your
controller in a sense that you can always bypass it shorting your batteries directly to
your motor for duration of your run. 3. Well, but it all comes to the cost. I've heard AC systems are much more complex and thus expensive than simpler DC systems providing the same power. Is that true? That is true, though *much more* is relative. Currently EV AC inverter is more expensive than a DC controller for 2 main reasons: because it is more sophisticated device offering more, and because it's not mass produced in millions. AC inverter is always matched to the motor it runs, thus achieving optimal performance and highest efficiency. A software model of the motor is stored in the inverter's memory (therefore the system is only sold as "matching kit"). A DC system does not care (to a degree) what motor is connected to it - it fundamentally it only chops the battery power modulating it, without regard of the motor limits. Whether all of this is relevant to you is your decision. As with everything, you get what you paid for. 4 Since AC requires high (typically higher than DC) voltage, my battery will be twice as big, heavy and expensive now. No. First, and AC drive can be made for any arbitrary low voltage, for instance see an OEM EV with 96V Siemens system - VW CitySTROMer. Recent fork lifts and golf carts with AC drives use typical 36 or 48 V AC systems. High voltage is used to take advantage of high speed AC drive and ability to cover all drive speeds on one gear if desired. Any motor is also a generator and produces voltage as it spins (at the same time as being supplied with voltage). It's called back EMF (electro motive force) voltage. To make motor produce torque (and so power) you need to supply current in. You only can supply current in if the voltage from the battery exceeds back EMF voltage (which is being subtracted from the battery voltage). So the higher battery voltage - the more RPM AC motor can afford still making torque up there as the battery voltage stay above back EMF longer (toward higher RPM). That is the same concept for any motor, AC or DC, it's just DC motor can't handle high RPM because of mechanical limitations of commutator and brushes, so can't take advantage of higher voltages. Now, back to battery question - the vehicle range only depends on the battery capacity - amount of Wh stored on board. For the same range the amount of Wh (and the battery weight) is the same and has nothing to do with type of the drive system - AC or DC. If you use twice as many batteries to gain voltage for AC drive, each battery can be twice as small (and light and cheap), so total battery weight and cost in theory remains the same. In fact, the battery for AC driven vehicle can be a bit smaller than for typical DC one because of regen. In reality, retail cost of the battery is not exactly proportional to its capacity, if you buy 70Ah lead acid battery for $200, this doesn't mean you will be able to find the same brand 35Ah one for $100. But it should be close to that proportion, certainly twice as much voltage DOES NOT mean twice as big, heavy and expensive battery (for the same range). The only price disadvantage might be if you use some sort of battery regulators - for twice as many of the batteries you'd need twice as many of the regs as well. 5 How do I size the motor? How much power do I need? What horse power engine equates to, say, 30 kW motor? These are very valid and important
questions to answer right. First, don't get obsessed with raw power unless you plan to
drag race and enjoy breaking and fixing things. In contrast, electric motors are always rated at maximum continuous power output, say 30 kW (which is 40.2 hp). Typically good EV motor can output peak power at least 5 times of rated power (provided, inverter and battery are capable of supplying it), so a 30 kW motor can give you 150 kW (or >200hp) for acceleration or passing. So in a first approximation 30 kW motor might give you at the same *acceleration* performance as 200 hp engine in the same car. Practically, electric motor is even better than that because it develops full torque instantly right from the start (0 rpm) while ICE doesn't make any power until the shaft ramps up to at least or so 500 RPM. In essence you have far more area under torque curve for electric motor, even though high peak number for engine is higher. Practically this means it feels more powerful than number of kW would suggest. So as a rough rule of thumb, an ICE engine with X hp power will equate to the electric motor with X/4 hp electric motor rating. In our example, 200 hp engine (making 30-40 hp average) will need to be replaced with 200/4=50 hp motor. Since 1 hp is 0.746 kW, 50 hp motor is 50*0.746=37.3 kW. This is what you have to choose for substitution to keep the same performance. Granted electric motors have their limitations and in some sircumstances are not as much superior compared to gasoline engines. When it comes to long runs uphill or towing heavy loads, situation is different. Engine becomes relatively more efficient (say 20% instead of 10%) but most importantly spend most of their running time near peak power RPM. They can supply 200 hp continuously (many minutes or hours). if they have to. Granted, 37kW rated motor cannot provide that power for longer than couple of minutes, it will overheat. You'd need ~150 kW *rated* power motor (and battery and controller/inverter also capable of sustaining this demand). Such motor will likely be as large as heavy as 200hp engine. For such applications (where continuous power demand is close to peak power demand) EVs are not as good alternative to conventional vehicles. Luckily, for typical passenger cars and typical driving pattern transporting people, this is not the case. 6. One of typical emails with typical questions I get quite regularly: "First, I'm still trying to figure out the motor-tranny question. Will I still need to make my own adapter plate? Second, What kind of performance
can I expect, roughly. Is there any "quick-n-dirty" correlation that can be made
between ICE hp and DC (or AC) kW? Even if it's as simple as 1kw roughly give the
equivalent as between 1.5 and 3.6 hp, that would help a lot. The short answer: There are two kinds of components:
EV components and components useable in an EV. Except for specific applications like a fork lift or a golf cart, unfortunately there is no OEM EV DC components industry. That does not mean at all that DC motors out there are not useable for a on-road vehicles, especially conversions by hobbyists. A KTA Kit #4 is a good example - collection of the hardware best useable for an EV. All the components are generic industry components. You cannot point to any component designed specifically for OEM EV. Many are not even intended for outdoor use. They *can* be used in an EV since can handle the application, but *the best* only because there is nothing better out there among generic components. And, of course, the total cost was the top priority. <<< DISCLAIMER: this comparison is not to discredit such excellent suppliers as KTA or any others. This is purely technical comparison of the hardware>>>. The longer answer: Kit #4 Components OK, we'll try to do part of your homework and look at each component closely. This is typical amateur (e.g not OEM grade) kit with intent to put a car on the road as inexpensive and quick and simple as possible. While there is nothing wrong here, these kits address amateur market well. OK, let's ask some relevant
questions. =================== What's its continuous power? Does
it provide regen? Is it made for outdoor (not even mention automotive) environment? Are
all the terminals enclosed as any serious standard requires? Is it water proof? How do you
optimize it for your motor (one size cannot fit all)? Is it even programmable? How do you
cool it of? Can it run the motor in reverse (without extra contactors)? Can it limit motor
RPM to the safe level? Siemens inverter is made for OEM EV, some features are here: http://www.metricmind.com/features.htm.
They are there because the driver expects them to be there, there are no really
unnecessary bells and whistles. How many of those Curtis controller can even remotely
match? What happens if it fails short? Can you depend on it for 10-15 years of daily use?
What's the warranty period? - GE TQD-200 Dual Circuit Breaker - KTA Switchplate & hardware
for TQD-200 A charger is not part of the drive system and thus is not discussed here. - Prestoflex #2/0 GA welding cable Disclaimer: All discussion above is not to diminish the value of KTA kits - they allow quickly and inexpensively get your feet wet. It is only to illustrate that this is amateur approach for tinkerers who know their EVs in and out and can take care of the problems. It is not for majority of people who just wants dependable transportation they become accustom to driving ICE vehicles and doesn't want to drive a "project" car. 7. I've heard that with AC drive no gear switching is needed, making it possible to lock on one gear or going "direct drive" eliminating gear box all together. Is this a good idea? First, proper definition: it is customary to call fixed singe gear transmission "direct drive". If that would be the case, if one welds shift stick to permanently select second fear, the car would become "direct drive", but this is not the case. Technically, "direct drive" applies to wheel hub motors or if the motor shaft directly linked to the wheel shaft, no gears. More common understanding, however, is that the presence of any fixed ratio gear box between motor shaft and the wheel shaft still called direct drive as long as no gear switching is possible. For example, connecting the motor directly to the drive shaft of the RWD car would be called "direct drive", even though final differential with fixed gear is present. So, Due to much wider RPM range with useable torque than DC systems can offer, indeed entire driving speeds range can be covered with one, usually second, gear. People have done it and it works very well. Many OEM AC drives (notably made by MES-DEA) even come with AC motor already integrated with single gear reduction gear box for all driving conditions. However one should consider following: 1. The torque at the wheels is what moves your car. Obviously, by retaining the stock gearbox, you retain the option to increase this torque shifting to the lower gear. There can be situations when you need that extra torque: - Climbing hills. With depleted battery you may be unable to climb 25% grade at all if your transmission is locked on the second gear. You may be unable to climb steep spiral entry to an airport multi-level parking garage or even steep driveway. Having low gears available solves these problems. - Safer driving. There might be situations when while cruising on the third gear you are squeezed between huge SUVs and they don't even see you. Getting out of this situation as quick as possible may be critical to avoid an accident. On the second gear you can leap forward in no time leaving those SUVs in the dust - your acceleration will be as much greater than on the third gear as the ratio between these gears (provided you're in linear torque region of the drive AC motor). - Fast take offs. If you like to race on the streets and be ahead of everybody when the light turns green, the first gear is an answer. Caution: high torque at the wheels can cause loosing traction on wet surfaces easier than you might expect, be careful. 2. Energy savings. You may find out that on freeway driving on the third gear puts you in most efficient operation spot compare to any other gear. Thus this is preferred gear to spend least amount of precious Wh stored in onboard battery. Ability to select gears on freeway vs. around the town would be very beneficial. This impacts regenerative braking ability and efficiency as well. 3. Lifetime of the motor shaft bearings. The bearings are the only parts of the motor that wears out and determines its lifetime. Depending on RPM it is rated in several thousands of hours of operation which usually far exceeds the life of the vehicle. Obviously, the lower RPM, the longer the motor will last, and likely can migrate to your second conversion car. So if the torque at the wheels is enough to maintain desirable speed on the freeway using third gear, it is advisable to do that rather than stick to the second gear. Running on the second is doable, the motor will likely run at around 5000 RPM (AC motor limit is usually about 10,000 RPM), but it may not be the most efficient spot for the motor. Also on the lower gears the gearbox will get unusually hot increasing its wear and wasting battery energy. So while driving on the lower gears all the time is technically possible, it makes no practical sense and usually is more wasteful. 4. Extra conversion work. The stock gearbox is already there for "free", assembled, tested and operating reliably and efficiently. It will take extra effort to disassemble the box, remove all "unneeded" gears, lock the shift lever on one remaining gear and put it all back together. As the result, the weight saving is negligible, and you end up with the same result as someone who retained original gearbox but just don't use other gears. Besides, you no longer *have choice* to switch gears if for whatever reason you want to. For RWD cars eliminating fear box entirely trying to link the motor directly to the drive shaft doing to differential won't work because the gear ratio in differential (usually 1:3 to 1:4) is not high enough to get the motor to spin at normal RPM. It's the same as having it on the forth gear all the time (which is usually close to 1:1 or no gear box at all), but on the forth gear your take offs will be very sluggish and modest incline (6%...8% grade) will be difficult to overcome. At the highway speeds a wheel makes about 600 RPM, so it's almost 10 times slower than the optimum motor shaft speeds. Only special multi-pole AC motors (often Brussels DC ones which are technically AC motors) can handle that. So the conclusion is you want to retain your gears. 8. To clutch or not to clutch? This is also highly debatable question and really is a matter of preference. Any manual gearbox will allow shifting without disengaging the clutch as long as motor and transmission shafts RPM are nearly the same. After short practice is possible to shift with no clutch fairly quickly. Since in general shifting is not needed, you can drive on the second gear from dead stop to freeway speeds and then, when the situation on the road allows, pick the time and shift to the third gear. This may take 3-5 seconds, but no longer matters much as you already move at steady speed along with the traffic. Test your donor car before conversion - for some cars it is difficult to shift without clutch unless you stop. In other words, if you want to eliminate the clutch, no problem with the driving, just retain the gear box and ability to shift (don't remove any gears). 9. How does the AC drive systems compare to DC drive systems? There are two main components in the drive system working together: a motor and a DC power converter (or AC inverter) allowing adjusting amount of power delivered to the motor per driver's demand. Looking at each component separately most significant differences are: Most commonly used AC induction motor - in general simpler construction and lower cost than comparable power most common series DC motor. Very reliable, no commutators to fan out, comm bars to lift or brushes to wear or spark. Available in great variety of the sizes and working voltages. Usually higher power models have higher voltage and lower current than DC motors. Torque is constant regardless of RPM (up to a point determined by the voltage, which is usually limited by the inverter). Siemens motors, however will work at as low as 140V or so with high voltage inverters and at just 70V or so (same motors) with low voltage inverters, just performance and efficiency will be poor. Whether it will be good enough, only simulation can tell. Low voltage inverters (65-180V) are not offered for sale in the US and Canada. Regenerative braking is native for AC motors. Separately excited DC motors also offer regen (with somewhat more complex controller), but most widely used series DC motors are practically not suitable for regen operation mode. A few examples of the conversions done with Siemens systems at different voltages: 96V system - VW CitySTROMer DC motor - in general reliable, but the presence of commutator and carbon brushes is the most troublesome part of a DC motor. Bottom line - brush assembly and commutator ire mechanical parts, and it is known fact that reliability of mechanical parts is not as good as properly designed solid state equivalent. It is similar comparison of a hard drive with solid state RAM disk. Hard drives are very reliable these days, but once in a while you hear that an HD fails, doesn't read, doesn't boot and it's not a matter of whether, but when. AS far as DC motors: brushes spark and wear out. It sure may take long time - thousands of miles. Well, make an error advancing them wrong (or run backwards fast) - brushes will be destroyed in 50 miles. Spring tension have to be within specifications. With increased tension excessive friction and wear of the brushes and copper bars occur; if tension is insufficient, excessive sparking, bouncing and overheating as well as increased EMI level become a problem. For higher power models working voltage is lower and current is higher than that of an AC motor. Torque is highest at 0 RPM and from that point is approximately inversely proportional to RPM (provided, the current has room to increase). Talking about cost, EV specific AC motors are more expensive than industrial fixed frequency motors (due to the special magnetics design to handle variable frequency and high RPM, presence of the shaft speed encoder, and other differences), and mainly because of very low production volumes. Also, very low thermal reserve of DC motors often presents cooling problems. AC power inverter - far more complex and sophisticated than DC converter. Complexity comes from the need to generate 3 phases of the output voltage with simultaneous frequency and amplitude changes, which is constantly calculated (with high speed CPU) based on the shaft rotation sensor signal, instant output demand and other information. The sine wave shape is usually synthesized using PWM technique. Usually therefore larger and more expensive than PWM DC converters. However, as semiconductor technology advances and control functions are integrated into couple chips, the price difference diminishes rapidly. Most of the complexity and cost of an AC inverter is in its software. In case of inverter failure, AC motor will simply stop since AC voltage for it no longer will be generated. DC power converter - simpler, lighter and less expensive than comparable power AC inverter. Exclusively use proven Pulse Width Modulation technique (changing duty cycle of relatively high frequency output pulses per driver's demand) to control amount of energy delivered to the motor. Motor acts as an inductor filtering out (averaging) output current. There is significant draw back - in case of the converter failure, usually full battery power will be applied to the DC motor and vehicle can suddenly get in motion with highest possible motor torque. This potentially dangerous shortcoming is one of the major reasons why large auto makers chose AC systems for their vehicles. High end models are microprocessor controlled while more common models are not programmable and are hard wired pieces of hardware. Therefore there are very few established mass production (full size EV) manufacturers which will use a DC drive system (mostly Sep-Ex motors). Think about it: trustful large scale manufacturers in Europe like BMW, Mercedes-Benz, Volkswagen, Fiat, and Opel all have unmatched technical experience, they know what they are doing. And they all have chosen industrial strength Siemens drive systems for their production electric cars. Why? There must be a good technical, economical and safety reasons for that, not to mention that Siemens have designed and built its systems specifically for these manufacturers responding to their performance and reliability requirements. In the US Ford and GM also have chosen to use an AC drive system in their pilot production lines. In fact most of the hardware components are directly based on Siemens designs. For the lack of better analogy AC system vs. DC system comparison is similar to fuel injection vs. carburetor comparison. Both sure work, and it is not about power - a large quad barrel carburetor can result in more raw power than fuel injection system for given engine displacement. In essence carburetor is a hole with a shutter controlled by the driver's foot, a variable valve. Similarly, DC controller is a valve between battery and DC motor. Carburetor does not generate fuel flow, it controls existing flow. That is why if return spring breaks, you get full throttle flow, just like failed DC controller. On the other hand, AC system is like fuel injection system - it generates the flow. If it breaks - no flow and no runaway situation. Yes, the simplicity is an advantage, no one chooses more complex (and so potentially less reliable) solution without benefits which outweigh drawbacks of complexity. It is easy to understand carburetor and troubleshoot it in the garage, and much more difficult to understand fuel injection system unless its schematics and firmware source code is provided. Yet, fuel injection systems practically took over. Why? Because potential benefits such as extreme flexibility, getting inputs from multiple sensors and ease of changing characteristics - it's all in software. Upgrade the chip and you get totally different behavior. And, reliability of more complex fuel injection system is the same or better than that of simple carburetor. When was last time your fuel injection computer broke? Don't get wrong impression. DC systems have been successfully used for EVs for years. In fact, for so long, that many consider it de-facto standard and anything else seem unproven experimental solutions. Also there were no AC designs available for EVs for a long time, so DC solution set many minds as if this is the only good choice. But so, for a long time, were carburetors. Well, both systems have their uses, and low budget DC systems may be better to start with. Once you taste an AC solution though, you won't go back. 9. What is the best way to increase the power of the system? The mechanical power of the motor really represented by the torque of its shaft. The torque depends on the motor current (for given RPM), and the current primarily depends on the voltage applied (Ohm's law). if you want more power and about to pick the motor, for given power go with higher voltage. Practical implications - reduced heat losses on the connectors and wires which are less bulky than the ones designed to handle high currents (the power lost on the cables and terminals is proportional to square of the current, P=I2R) 10. Which motor do you recommend (or firs my application better): 18 kW 1PV5105WS12 or 30 kW 1PV5133WS18? This is similar to asking the salesman: "Should I get this Honda with V4 or V6 engine in it?" No one can answer this question of personal preference for you. I can tell you exactly what the performance (0-60 mph acceleration and top speed) will be with both choices, but I can't decide for you what do *you* want. Obviously, with more powerful 5133 performance will be better, but still the judgment call whether this difference is important to *you*, to your expectations, driving style, purpose of the vehicle and finally worth the price difference, ultimately is only yours. 11. Can I connect batteries in parallel to increase the total output current capability? While this works and used quite frequently, it is not a good idea at least for two reasons: 1. No two (or more) batteries are created equal. As soon as you connect two in parallel, the better one with higher voltage will briefly "charge" the weaker one to some voltage in the middle, maintaining it there and thus discharging itself. The better battery will work harder under load while weaker one will have to work less in the beginning of discharge cycle. The current supplied by each under load is NOT the same and depends on internal resistance and state of charge of individual batteries. 2.
Since the voltage is the same on all connected in parallel batteries, there is no
equalizing possible during the end of charge cycle, so the weak battery will be constantly
overcharged and the strong one (requiring more voltage) - undercharged. Situation will get
worse with each charge-discharge cycle causing premature degradation of stronger batteries
first. Weak batteries will start loading remaining ones and eventually whole pack exhibit
loss of capacity and premature failure. Expect to have the lifetime of the pack of yellow
top Optimas 1.5 to 2 times shorter than without connecting batteries in parallel, unless
you provide means of monitoring EACH battery condition separately and act as soon as
imbalance is detected. 3. For AC solution the current is not a problem - it is easy to find a battery capable providing 280A peak current. Therefore there is no need to parallel the batteries. If there is room, connect in series as many as will fit and suspension will handle (without severely compromising handling). If all the batteries you want for given voltage don't fit, use smaller ones but keep the voltage the same rather than fewer batteries. 12. What are the safety features built into Siemens inverters? There are several protection safety measures implemented to take care of the hardware, but most importantly - of YOU. 1. Both positive and negative main contactors have magnetic arc suppression devices providing reliable disconnect under full load, so no open flame or burnt by arcing insulation is possible; 2. Emergency Off input directly routed to the main contactors coils. As soon as input disconnects from the ground both main contactors drop off and disconnect main battery 3. Traction battery and power stages are isolated from the logic and vehicle ground 4. The voltages, currents and
temperatures in critical points are being constantly monitored. If predefined limits are
exceeded, 5. The Start Inhibit interlock can be wired so that it is not possible to drive off while charging cord is plugged into the mains, even if there is no mains voltage applied. 13. Is the regenerative braking current adjustable? Yes, in two different modes. The regen current by off throttle is proportional to the pedal position (between completely off throttle and pre-definable point (as default - last 10% of the pedal travel). Beyond that there is either predefined regen current controlled by the brake light switch, or proportional control if optional brake potentiometer is used. These modes are described in detail in downloadable Installation Manual 14. Can it regen rolling backwards? Yes, it can, same as forward. 15. What happen if I press accelerator and regen pedal simultaneously? You set in regen or acceleration pedal priority in the software. If you choose Accelerator, then if both pedals pressed simultaneously, regen input is ignored, and vice versa. For other specific questions welcome to call or e-mail to Metric Mind Engineering. |