September 4th, 2012 — Projects, Uncategorized
I have been charging my electric pickup truck off of an existing standard NEMA 5-15 (120 volt 15 amp) outlet next to our garage for over a year. [And occasionally running a cable out the door from our 240 volt dryer outlet to get a fast charge.]
Finally this summer I had an electrician run a 50 amp 240 volt circuit out to the side of the garage to put in a “real” charging station. Even though the existing Zivan NG3 240 volt charger will only use 12 amps at 240 volts, the NEMA 14-50 outlet gives me lots of room for improvement (240 volts at 40 amps max continuous draw, or 9.6 kilowatts). It also allows anybody with a super big RV to plug right in!
In addition to the NEMA 14-50 outlet, I also ran a GFCI 5-20 (120 volts at 20 amps) off of the same circuit, in case we want to max out 120 volt charging. The entire circuit runs through a sub-meter that easily allows me to read off how many kWh of electricity the truck uses. So far it’s averaging out to about 7-10% of our total monthly electricity usage. (The small plug at the bottom left of the above picture is the original NEMA 5-15 outlet.)
January 22nd, 2012 — Projects, Technology
I have drawn up a schematic (click to enlarge) of the high current and sensing portions of my maximum power point tracking (MPPT) 2-phase boost converter battery charger circuit. The schematic does not include the micro-controller, MOSFET gate driver IC, and associated power supplies, as those items are on the (relatively) low-power side of things.
What do all of these things do?
- L1, Q1, and D1 – These three components make up the heart of the boost converter. When Q1 turns on, power builds up in L1 as the current rises. When Q1 turns off, all of that power exits via the only available route (out past D1) and the voltage is boosted as the inductor (L1) resists the current change. If you turn Q1 on and off very quickly (under control of the micro-controllers’ PWM output via a MOSFET gate driver) it raises the output voltage higher than the input voltage.
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November 16th, 2011 — Projects, Technology
I purchased two used GE Energy GEPVc-175 watt solar panels and mounted them to the bedcover of my truck using 10-24 machine screws and T cone washers as rubber vibration dampers. Each panel weighs 31 pounds, and is rated to deliver up to 175 watts of power in full sun (at around 36 volts each, or 73.4 volts at 4.7 Amps in series). I am still waiting on a group of Georgia Tech ECE students for the magic box that does maximum power point tracking (MPPT) and voltage boosting to charge my 120 volt battery pack, but I hope to be generating 1-3 miles of my daily commute from the sun soon. As my daily commute is 4 miles, this can be a significant percentage of my total energy usage.
I have calculated that in the summer the panels are far enough behind the cab that they will not be shadowed by it, even if I have to park facing south. In the winter and early spring / late autumn I need to park facing north to avoid shading a strip of the solar panels.
I still need to figure out a way to tilt the panels towards the sun to collect as much energy as possible. This is especially critical during winter, when the solar angle is way off of vertical. As the bed cover tilts, AND the bed of the truck can tilt (the other way) I figure I can work something out (with a few pieces of wood cut to the correct height, or linear actuators if I want to get fancy.
October 16th, 2011 — Projects, Technology
This graph shows the voltage (multiplied by 10, so 65=6.5 volts, and 50 = 5.0 volts) batteries 1-6 of my electric pickup while accelerating. My first battery (blue) is consistently 0.1 volt below the others, so I am keeping an eye on it. But this graph shows that although it is a 1/10th of a volt lower, it does not sink lower than the other batteries under load, so it appears to be holding up well so far.
The graph also shows off my new (to me) Pak Trakr system. The Pak Trakr system connects to each battery in your pack with small remotes that daisy chain together. Each remote monitors six batteries and transmits the voltage levels once a second to a display and optional serial data logger.
June 8th, 2011 — Projects
This picture shows off my new flush-mount laser cut panel with voltage meters installed. These new gauges are Datel self-powered LED voltage displays (DMS-20PC-8-DCM for the red traction pack display and DMS-20PC-0-DCM-B for the blue accessory battery display). They are considerably more expensive than my previous gauges ($50 for the red and $59 for the blue) but have two major advantages. First, they actually fit inside the dash, so I can flush mount them instead of building a box around them. Second, they are “self-powered”, which really means they have their own DC/DC converter built in and draw power from the source they are monitoring. But, because each gauge has it’s own DC/DC converter, they are completely isolated from each other (something that my previous “isolated” DC/DC converter didn’t really do well.) Having all the power circuitry integrated into the gauge also greatly simplifies the wiring.
The gauges come with metal clips to fix them to the back of a panel, but the clips were too big for my opening. I improvised with a very close fit on the cutouts and some large rubber bands. If I ever need to replace the rubber bands, I just unscrew the four 6x 5/8 inch screws to remove the panel. (The screws are not exactly balanced on the panel as I was matching up to pre-existing holes.)
I wanted two different colors for the accessory and traction pack voltage, so I paid $9 extra to buy the blue LEDs for the 12 volt accessory battery. It turns out that this was a mistake. The blue gauge is much brighter than the red one, and at night it is blinding. I wired up a toggle switch to allow the driver to turn it off when driving at night. (The red gauge is just right, easily visible in the daytime but not too bright at night.) If anybody wants to buy a blue self powered voltage gauge for $50 including shipping I’d gladly sell it and buy a red replacement.
May 15th, 2011 — Projects, Technology
I received a VWRAS2-D12-D9-SIP isolated DC/DC power adapter from Digikey and built an updated voltage gauge module with dual gauges (one for the 12 volt accessory pack, and one for the 120 volt traction pack). The gauges were slightly too large to fit inside the dash, so I built an enclosure out of craft plywood that sticks out flush with the bottom of the radio.
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March 25th, 2011 — Projects
Our “new” electric pickup came with a 240 volt twist-lock connector where the gas cap would be. This is great for plugging into a 240 volt outlet, such as used by an electric range or clothes dryer, but we are primarily charging it with a 120v convenience charger. (So called because 120v outlets are more convenient to find. It actually takes about twice as long to charge using 120v so from a time standpoint it is less convenient.)
I decided to add a second 120 volt plug behind the fuel port door so that I could plug in either voltage cable. Continue reading →
March 23rd, 2011 — Projects
The electric pickup truck uses a vacuum pump to generate vacuum for the power brakes (and move vents in the HVAC system). It has a pressure switch that turns on the pump when the vacuum drops to under 15 inHg and turns it off once the pump has raised the vacuum to 25 inHg. The current system has a small 3″ by 1.5″ PVC cylinder as the vacuum reservoir. As soon as you press the brake the pump turns back on, and cycles on and off relatively frequently. I wanted a larger vacuum reservoir so that the duty cycle on the pump would be longer (it would stay on longer, but also stay off longer) and so that even when the vacuum drops to 15 inHg I could still operate the brakes several more times while the vacuum pump was working.
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March 22nd, 2011 — Projects
We have driven our electric S-10 pickup for a month now, putting 187 miles on it and charging it 20 times (averaging around 9 miles per charge). We used around 132 Kwh of electricity to re-charge it (13% of our total household electricity usage for the month) which cost around $13.20 (or 7 cents per mile). The truck is averaging around 700-720 Wh of power per mile driven. If we were paying $3.75 per gallon of gas and getting 20mpg on an equivalent vehicle, the energy price comparable MPG rating of the truck would be 54mpg. The chart above displays the watt/hour per mile calculation for our first 20 charges. As you can see, the numbers jump around depending upon where we drive, what route we take, what speed we drive, etc. We are also in the process of breaking in a new pack of batteries).
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March 5th, 2011 — Projects
The S-10 electric pickup has an analog voltage gauge in the instrument cluster which is useful to get a general picture of how the battery voltage is changing while you drive, but hard to read with any real accuracy. The previous owner had also wired 12v and 120v wires into the center of the dash in an attempt to set up a digital volt meter on the traction batteries. But the 12v supply burnt out his volt meter, and when I purchased the truck it was dead. I bought a 200 volt LED panel display from a surplus supply house for $12 to replace it. I also added a 1A fuse on the 120v supply line in the engine compartment as a safety feature.
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