The Solectria Sunrise
The Sunrise EV2 Project Homepage
Welcome! We are a group of dedicated electric vehicle enthusiasts whose goal is to create an affordable, high performance electric kit car that anyone of modest skill can assemble. The Sunrise EV2 is a four-passenger pure electric sports sedan, designed to meet all the safety, performance, and comfort requirements of a modern state-of-the-art automobile.
The original Sunrise was designed by Solectria Corp. using the Hypercar principles of Amory Lovins. It achieved remarkable efficiency and range, through the use of lightweight construction, innovative design, and superb aerodynamics. Unfortunately, only a handful were produced.
We bought the last unfinished Sunrise from Solectria CEO James Worden. It is being redesigned as a kit car, along the lines followed by manufacturers of light plane kits for the EAA (Experimental Aircraft Association). The steps are:
Our goal is to make the Sunrise EV2 as modular and open source as possible; like a PC clone, where many different parts can be used, from many different vendors. We'll provide the basic "box". Builders can then use any motor, controller, batteries, charger, interior, and instrumentation they like. Depending on your budget and performance requirements, your Sunrise can be AC or DC, lead-acid or lithium batteries, etc.
We look forward to having a community of Sunrise EV2 builders, where members can exchange ideas, buy/sell/trade parts, and assist others in building their cars. Check this website out occasionally to see how we're doing.
November 24, 2013: The Lincoln Mark 8 parts car's rear fender wells have been cleaned, smoothed, primed, and waxed to make a plug mold for the Sunrise EV2 chassis. The wheel wells on standard cars are very rough, so smoothing them took a lot of work. But, it's necessary to make the mold easier to pull apart. Smooth wheel wells also reduce drag; a spinning tire generates a lot of wind resistance (which automakers usually ignore).
Other recent updates:
In this section, I'll be regularly posting EV tips and techniques to save you money, find parts, measure performance, and improve your EV. As new ones appear, the old ones will move to the Lee's EVs page. Purchases contribute to the Sunrise EV2 Project. If you like what you see and want me to write more of them, please click the "donate" button below. :-)
Snubbers for High Voltage Switching
You often see a spark when you open a switch. A little arcing is inevitable. But if it is not limited, it will damage the switch and shorten its life. It can even cause the switch to fail shorted, and thus leave the load still powered! Snubbers are simple little circuits that reduce the stress on switches, so they can handle more power and last longer. Think of it as a "shock absorber" for electrical circuits. Snubbers easy to add, and provide cheap insurance.
"Switch" means any device used to turn things on and off. It can be mechanical (switch, relay, contactor, fuse, circuit breaker, etc.) as well as solid state (diode, transistor, TRIAC, MOSFET, IGBT, etc.) Solid state devices are especially easy to damage -- just one instantaneous over-voltage event can destroy them!
Resistive Load: The type of load makes a big difference. With an ideal resistive load, the current simply starts when you turn it on, and stops when you turn it off. Suppose we are switching a 10 ohm resistive heater (Rload) across a 100 volt battery (see illustration). The switch voltage (red) is 0 volts when on, and 100 volts when off. The current (green) is 10 amps when on, and 0 amps when off. Simple!
Inductive Load: Inductive loads are very common. They include relay and contactor coils, motors, transformers, heaters with wirewound elements -- even just a length of wire has inductance. Inductors act like flywheels; they fight to keep the current from changing suddenly. Look at the illustration with inductance added to Rload. The current rises slowly at turn-on, as the inductance fights the change. If the load is a relay or contactor coil, this means it pulls in slower. It takes about 3 time constants (T=L/R) for the current to reach its final value. With the parts shown, T = L/R = 10mh/10ohm = 1 msec; so it takes 3 msec to reach 10 amps.
But look at that turn-off spike; it's over 350 volts! The inductor is trying to force the current to keep flowing despite the open switch. It "kicks" the voltage up and up, until the switch arcs or the transistor breaks down. In fact, an inductive load can easily produce peaks over 10 times the supply voltage. Unless your switching device has a huge voltage rating, it will fail.
Also notice the high-low-high-low ringing. Real circuits also inevitably have capacitance. This capacitance works with the inductance to form a resonant circuit that "rings" like a bell when struck by that high voltage "hammer". It causes interference, like a "pop" in your radio, or noise glitches in unrelated circuits.
The most common snubber is the "freewheel" diode (shown in yellow). A diode is connected across the load, oriented as shown to provide a path for the inductive current when the switch turns off. The diode clamps the voltage to no more than 1 volt above the supply (note the step to 101 volts). A diode snubber is cheap, easy, and effective. Use a diode with a voltage rating at least twice the supply voltage, and a current rating equal to the load current. In this example, use a 200v 10a diode.
The low clamping voltage has one drawback: It makes the load current slow to fall back to zero -- it's that 3 msec T=L/R time constant again. If you're driving a relay or contactor, a freewheel diode across its coil makes it turn off slowly, which is bad for its contact life. For a faster turn-off, you need to raise the clamping voltage. There are several ways:
Add a resistor in series with the diode. To clamp at 100v, R = 100v/10a = 10 ohms. When the switch turns off, the coil current diverts to the snubber diode and resistor, producing a 100v drop. The switch sees the sum of the supply voltage and clamp voltage (200v in this example). The total resistance has doubled to 20 ohms, so L/R is half as long; the load turns off twice as fast.
Add a zener diode with the desired clamping voltage in series with the diode (shown at right). When the switch turns off, the coil is held at the clamp voltage until it runs out of stored energy. Turn-off time is about twice as fast as a resistor-diode snubber with the same clamp voltage. The switch sees the sum of the supply voltage and zener voltage (100v + 100v = 200v in this example).
For a clamp voltage greater than the supply voltage, use a single bidirectional zener, ZNR, or MOV. Turn-off is very fast, and you only need one part. With a 150v part, the switch will see 100v + 150v = 250v peak. That's pretty high, so this approach is more practical for low-voltage circuits. For example, a 24v bidirectional zener in a 12v circuit will limit the switch to 36v peak.
Zener diode directly across the switch. This provides better protection for the switch if the power supply voltage is noisy or unknown.The switch is clamped to the zener voltage (which must be higher than the supply voltage). The load is clamped to the zener voltage MINUS the supply voltage. For example, a 150v zener clamps the load to 150v - 100v = 50v. This is a good method when the switch has a definite voltage that you must not exceed (such as a transistor or MOSFET).
Resistor-Capacitor Snubber: Note that the rise and fall times aren't quite instantaneous. Every switch (mechanical or solid state) takes time to open or close. As it changes, it briefly sees both part of the supply voltage, and part of the load current. A mechanical switch will arc during this time, when its contacts aren't quite fully opened. A transistor will dissipate power during this time, when its apparent resistance is changing between on (low) and off (high). How bad is it? Due to the inductive load in this circuit, the switch can be dissipating 100v x 10a = 1000 watts peak!
Diode snubbers clamp the voltage, but don't do anything about the rapid rate of rise in voltage. RC snubbers add capacitors to slow down the rate of rise, to give the switch time to fully turn off before it gets "hit" with the full off-state voltage.
An RC snubber is shown at the right. The snubber capacitor slows down the rise to 0.5 msec, to give the switch time to fully open before it sees the peak voltage. It also reduces the peak power in the switch, by delaying the voltage peak until the current has fallen to a low value. This puts less stress on the switch, so it runs cooler and lasts longer. The RC snubber still provides a fast decay in the load current, so relays and contactors will drop out quickly. It also lowers the LC resonant frequency, reducing noise.
The resistor in series with the capacitor has two jobs: It damps out the oscillations (like padding a bell). And it limits the peak current to charge the capacitor when the switch turns on (that's the green current spike you see at 1 msec).
Finding the "perfect" values for an RC snubber is challenging. For an analytical approach, look here. Or, you can use a circuit simulator, like LTspice. If you have an oscilloscope, or can see the contact, the Edisonian approach works; experiment with different values to minimize the peak voltage and arcing. Luckily, the values are not critical; capacitors from 0.01uF to 10uF, and resistors from 1 to 100 ohms work well for mechanical switches. In general, the higher the current, the higher the capacitance. The faster the switch, the lower the capacitance (so solid state switches use smaller capacitors). Then pick a resistance high enough to limit the peak turn-on current to something the switch can handle, but low enough to damp out the ringing.
RCD snubber: Diodes, resistors, and capacitors can be combined to make especially effective snubbers. The diode provides a predictable peak voltage limit, and removes that nasty turn-on current spike. The RC network slows the rate of rise, and gets rid of the ringing and noise. The most common RCD snubber circuit is shown at the right.
When the switch turns on, the diode is reverse-biased and so does not conduct. The resistor charges the capacitor to the supply voltage. Choose the resistor to keep this current low, so the switch turn-on current spike is negligible. After a few RC time constants, the capacitor voltage equals the load voltage and the snubber current falls to zero.
When the switch turns off, the load current shifts to the snubber. The diode gets forward biased, and conducts. The switch voltage rises slowly, as the inductive energy transfers to the capacitor. This limits the rate of rise in voltage, to give the switch time to fully turn off. When the inductor current falls to zero, the diode again blocks. The snubber resistor then slowly discharges the capacitor back to zero, so the circuit is ready for the next cycle.
The RCD snubber is a good way to maximize the power and life of a given switching device. It provides fast load turn-off, low stress on the switch, low noise, and the part values are relatively independent and easier to calculate:
Across the load, or across the switch: These examples show snubbers across the load. Snubbers can also be placed across the switch, if that's more convenient. But if the snubber fails shorted, it turns the load ON! There are special UL-recognized fuse resistors, MOVs and ZNRs (zener diode replacements), and X-type (across the line) and Y-type (line to ground) rated capacitors for this purpose that are guaranteed to fail open, and not explode or start fires if they fail.
Switching AC loads: The above assumes a DC load. If you're switching an AC load, the snubber circuit has to be bidirectional. Freewheel diodes and snubbers with unidirectional zeners won't work. You have to use RC snubbers, or snubbers with bidirectional zeners, MOVs, or ZNRs.
Parts for Snubbers: Snubbers need to handle high peak currents and voltages. Ordinary "cheap" resistors and capacitors are likely to fail. Types of parts to use:
I normally have these parts in stock for EV projects. If you
need some, email
me with a description of your load and I'll send you the parts for FREE with a donation to the Sunrise EV2 Project. Merry Christmas, and thanks for reading this far! :-)
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Interested? Want to get involved? There are several ways you can help.
Contact us: Questions or comments? Corrections or problems with this web site? Contact Lee A. Hart by phone at (320) 656-9574, by email, or by mail at 814 8th Ave N, Sartell MN 56377-2240.
Design: Producing the best possible EV requires the best possible minds. The Sunrise EV2 development team has over 100 years of combined EV experience, but we are still learning and improving as we go. If you have ideas for improvements, can help with vehicle design, construction, or testing; or have skills you think we can use, please contact us!
Labor: The Sunrise EV2 prototype is being assembled at our shop in Rice MN. At present, we are building our prototype composite body and the molds to produce it. It's very labor intensive, so if you're in the area and have some time, please contact us about a visit. See and help build the prototype, and in the process learn how to build your own Sunrise EV2.
Components: Most of the parts and materials to build the Sunrise are being donated by our development team or interested individuals. Our motor, controller, and innumerable tools and shop time have been provided, but there is alway more. Do you have any EV related parts that could be of use? Contact us and see!
Donations: Developing a car is an expensive project. The project is entirely funded by our development team and donations from interested individuals and businesses. Donations will be credited toward future purchases of Sunrise EV2 products. Contributors are also given special attention by members of the EV2 team! Send donations to the Sunrise EV2 Project c/o Lee A. Hart at the above address. To contribute using Mastercard Visa or Paypal, use the "Donate" button below. Every penny helps!
The Sunrise EV2 Project, copyright 2007-2014 by Lee A. Hart.
Website created 2/4/2008 by admin. Last update 3/2/2014 by Lee
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