Taming Lester

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Sharkey
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Taming Lester

Post by Sharkey »

Now that I've gotten the EV Rabbit back on the road, I have some charging issues to address. The on-board charger on the car is a K&W BC-20, which is small, light, and powered by a normal 15 ampere 120 volt wall receptacle. While this is convenient for opportunity charging, and works fine when I am at home and have a lot of time to charge, the current output of the K&W leaves something to be desired when filling up the batteries fast is required. The K&W is rated at 20 amperes, but it will only do this from a solid 20 or 30 ampere circuit, then then only for a few minutes until it heats up and cuts back power to keep from cooking itself. Most of the time, I see 17 amps of line current, meaning about 14-15 amps into the batteries. I usually have to cut back on the power when charging from 15 and 20 ampere outlets to keep from overheating the cord and plug ends. Even the higher power outlet that I tacked into the radio station's sub panel restricted the charging current to about 10 amperes into the battery, meaning that I had to wait around for three hours to fill the batteries before heading home.

What I really need is a way to hammer ampere-hours back into the batteries at a high rate, preferably from a 240 volt source to keep the line losses and voltage drop to a minimum.

From the factory, the car came equipped with a Lester "Lestronic" charger, an old-tech, transformer-based monster that weighed in over a hundred pounds, and sometimes even worked. Here's the manual on mine, in case you want details. This charger operates from 240 volts, and the voltage-regulated output is 32 amperes of charge current. The biggest problems with these chargers are that they are big, heavy, and in my case, broken. I did receive the original charger when I bought the car, even though it already had the K&W installed. The Lester was mostly complete, but was missing some circuit boards, and the power relay.

Last week, I dug the charger out of the storage locker to have a look at it to see if there were any salvageable parts. My intention was to maybe get it running and leave it at the radio station for fast-charging the car on trips to town. As it was, it was not useable, but the transformer is still good, and the SCR rectifiers operable. Time for a new project.

I stripped it down to a bare chassis, just the transformer, the SCR's and the fuse block. After that, used the high pressure washer to blast the chassis and transformer clean of accumlated dirt. A few minutes of compressed air hose-down followed by hours sitting in the full sun dried the components. Then I used my Variac to apply voltage to the input side of the transformer to see if it was OK. To preclude fireworks, I did all my testing at 24 volts of input, 1/10 normal. I looked for 1/10 normal output from the transformer, and also checked several additional secondaries on the transformer for voltage levels.

Next, I tried firing the SCR rectifiers, using a diode between the gate and anode terminals. The result was DC output at approximately 12 volts (1/10 normal output).

Here's a shot of my test setup. The 'scope shows a perfect rectified full wave signal, and there’s a 25 watt, 12 volt lamp under the funnel to the left of the frame as a load (the funnel is used as a shade, I was tired of seeing spots):

Image

In the background on the left is a tangle of wiring and connectors that I removed from the chassis. I'm starting with a bare bones chassis and working my way up from there.

When the Lester was designed and built, the control circuitry was designed around discrete components, because that was about all that was available at the time. These days, there are integrated circuits that can replace all of the circuits in the original controls, and will provide more features and better control of the voltage and current.

For instance, to control the SCR rectifiers, I'm looking at using the TCA785 phase control IC. This is a one-chip solution to a whole PC board full of discrete components in the Lester, and will give much tighter timing of the thyristors than the original.

That's the start. Next I'll try raising the input voltage (slowly and carefully) to 120, and then 240 volts, using a high-wattage light bulb as a load. If that doesn't produce smoke, I'll try connecting to the EV's batteries and see if I can produce some brute-force charging. Once the phase control chips come in, I can try some voltage and current regulation, and start assembling some protection circuitry.
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Dennis The Bus Dweller
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Electronics thoughts form a carpenter

Post by Dennis The Bus Dweller »

Hey Sharkey

I don’t know a lot about this stuff. I just buy a lot of solar stuff for both grid-tie and my own off-grid systems so let me throw this out to you. I have a hand full of the xantrex “freedomâ€
Peace along the way
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Sharkey
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Post by Sharkey »

Dennis, thanks for the tip, however, the EV has a 108 volt battery system, 18 golf cart batteries in series. It takes a finish voltage of 130 volts DC to top the cells up, I don't think Xantrex/Trace has an inverter with that kind of input voltage.

The transformer in the old Lester is custom matched to charge this battery pack, I just need to put together some electronics to control the charge rate and finish voltage. For the short term, just controlling the charge rate will be enough, I can keep an eye on the voltage and manually shut down the charger when it nears full charge. At that point, I can let the K&W take over, it has the smarts to protect the batteries from over charging.

Using the Lester means that I can be back on the road in an hour rather than three. It will also mean that I can drive into town, stop by the station to check in and charge, then go run errands or eat lunch on the beach before coming back to finish up work and charging before heading home. The way it is now, once I get to town, I have to stay at the station and charge before I can go anywhere, and even going down Highway 101 for a cup of espresso means going back on the charger for as much as another hour. I'd much rather cut that time to something manageable.
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Dennis The Bus Dweller
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Post by Dennis The Bus Dweller »

I see, That little rabbet must be pretty havy then. What about the pusher? Hows that going these days?
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Post by Sharkey »

The EV weighs in at 3,100 pounds, which is one reason that I built the suspension up to race-prep specifications.

Here's what the batteries look like in the rear of the car

Image

And here they are with the cover and carpeted deck installed:

Image

The Pusher is getting use each time the car goes out of the yard. The steep part of the driveway is too rutted and covered with loose, fist-sized round rock for the EV to get up without assistance. It has plenty of power to make the grade, but not enough traction, so I use the Pusher to turn it into a four-wheel-drive so I can get back to the house without a lot of wheel spinning.

Today's Lester adventure is that I got brave and powered the charger up at full line voltage while connected to the car's battery pack. Not all at once, of course, I eased into it while watching the gate voltage and current while powering a 300 watt, 130 volt lamp. Now I am really seeing spots. When it looked like there wouldn't be any flying pieces, I installed a 100 ampere DC rated circuit breaker and 12 gauge pigtail that mated with the EV's Anderson connector. The K&W has a mating Anderson connector, so making the switch between chargers was simple. I used to use this connector when I charged the car direct from photovoltaic power (130 VDC @ 8 amps)

I put the whole mess on an old typing table frame, and powered it up at 120 volts first (the Lester has a 120 volt tap on the transformer primary). I was able to push 18 amps into the already fully-charged battery pack for a brief period. I didn't want to fry anything, especially since the Variac I'm using is rated at 10 amps, and it was passing 20.

Next I tried 240 volts, but I had to keep a lid on the current, as the name plate on the charger indicates that it draws 29 amps at this voltage. I did increase the current until I saw 20 amps of battery charge current.

Image

That's about the end of the line until I have the phase control IC's so I can vary the charge current continuously from 0 - 100%, whatever that turns out to be. The Variac won't stand too much abuse, and it makes a lot of ominous humming sounds under heavy load, I don't think it was designed for this much current at such an awful power factor.
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Post by AccordGuy »

I guess the problems of EV charging should be less in Europe where we have 220V (240V in the UK) in every house. Most houses have a 100A grid feed and at least a 30A cooker spur. As residential feeds are 120V in the US, where are you getting the 240V for the transformer from?
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Post by Sharkey »

Although the standard appliance voltage in North America is 120 volts, that is derived from center tapping the utility mains transformer. Every service entrance consists of two 120 volt legs, out of phase with each other by 180 degrees. When the common center tap of the utility transformer (called the "neutral" here) is ignored, there exists 240 volts between the two 120 "hot" legs.

Nearly all higher power appliances and tools here are 240 volt, water heaters, cook stoves and ovens, large HVAC compressors, well pumps, etc. It's just the small appliances that get the 120 volt, for the most part.

Then there's 208/240 three phase, which is more industrial. Nearly all of the higher power radio transmitters that I work on use three phase.
lemmiwinks

Post by lemmiwinks »

I think our 3 phase power (in Australia) is 415V though I'll be the first to admit I know very little about AC power.
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Post by Sharkey »

Lester got some attention today. Since we are having some hot weather, I decided to stay in the garage and out of the sun. This allowed me to complete the 240 volt AC wiring to the input of the charger. A three pole contactor with the associated on/off circuitry, wiring to the fuse holder, wiring to the primary of the transformer, and the feed for the cooling blower were all completed, with all of the crimp lugs soldered and heat shrink-wrapped for current handling and safety.

Image

Good thing I work cheap, the same amount of hours on a clients project would have netted me about $200. Now I have to make something useful out of this project, I've gotten invested into it. Other than the $15 or so in parts I've ordered, this has been a junk-box parts construction.

Today was also the first time I've powered the charger up on 240 volts without a soft-start circuit (the Variac). I had to do it sooner or later, and now there are at least some proper fuses in the circuit. The SCR rectifiers weren't set up for DC output, but I did run a light bulb on the AC secondary of the transformer, and test the blower, using the center tap of the primary of the transformer to supply 120 VAC from the 240 volt supply.

Next I'll have to build the new front panel, properly mount the start/stop pushbuttons, and then begin the DC output side of the circuitry. When the IC's I've ordered come in, I'll be all ready to either put the charger into service, or clean blackened soot off my glasses...
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Post by AccordGuy »

You sound like my friend at uni... His final year project was a 3-phase invertor running from a car battery in the lab. It was all going swimmingly and worked, right up until the demo to the lecturer whereupon it promptly caught fire on the bench :D

Mind you... this wasn't an isolated incident. He also nearly electrocuted himself while prodding around in a CRT. He was smart enough to not touch HV stuff with his fingers but got a shock through the pencil he was using... Graphite core... DOH!
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Post by Sharkey »

More Lesterisms.

Yesterday, while I was in town, I did some shopping around for a set of cheapo jumper cables to hack up for heavy cable to use as the output wiring of the charger. Looks like I can get some auto-store cables in 8 gauge (good for 40 amps continuous) for around $14. On a whim, I went into the St. Vincent DePaul thrift store, thinking I might find some used cables. No such luck, but what I did find was a bin with second-hand appliance cords, and specifically, a 50 amp, 240 volt dryer cable, complete with crow's-foot male plug -and- an attached female flush-mount receptacle for $2.99. Wotta deal. At the checkout counter, I learned that red-tag items were 10% off on Tuesdays, and that I got an age 55-and-better 10% discount as well, bringing the total to $2.41. The receptacle alone would have cost me $12 at the hardware store, and the cable probably another $19. Gotta love the throw-away society.

Anyhow, I now have an AC input cable and plug good for the full rated output of the charger, and have modified my long 240 volt extension cord with the receptacle so that it can feed the charger. I am building the charger's systems to carry the full rated output, meaning that the input side of the charger has to carry 30+ amperes, the input cable, fuses, contactor, etc, are all rated for at least that current. Circumstance may dictate that I cut back the current while charging the car due to available current from the source, or while using the long extension cord, but I will have the ability to charge at full output when conditions warrant.

Still thinking about jumper cables for the output, but the cheap appliance cords are tempting, two 6 gauge wires and one 8 gauge, and for pennies on the dollar...

It was a dark and stormy day today, perfect for staying inside and mucking about with electronics, so after lunch, I got busy and breadboarded up the phase control circuit prototype that I'll eventually build to control the charger.

After a few false starts, a capacitor in the wrong place, and an error in the datasheet that gave the value of the ramp capacitor 1,000 time too low, I got the circuit to function on a battery and audio generator. Once that was accomplished, I built a "Lester simulator", which was to use a 12 volt transformer and a couple of low-current SCR devices configured exactly like the big charger for a test. No sense blowing up my entire test bench with 120+ volts at 30 amperes if things go wrong for an instant.

Amazingly, it worked the first time! I used a small pilot lamp as the load, and was able to vary it's brightness with an adjustment of the control pot.

Here's a pic of the setup. I used every clip lead I could find to interconnect the battery, two AC transformers (one for sync reference, and another to operate the SCR's and lamp), the 'scope, multimeter, etc. A cobbled-together mess, but it proved the circuit.

Image

The lamp is glowing at about half brilliance under a red lens, while two traces show on the 'scope. The left half of the screen shows the AC sync sine wave (slightly distorted by clipping at the IC), and the right side shows the output of the SCR's, a bit less than half-power one each half-cycle of the output of the transformer. rectified to DC.

Now that I have proven that it's possible to run the circuit without smoke at low voltage, it'll be time to rig Lester up for a high voltage, high current test. Stay tuned for details (from a safe distance).
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Post by Sharkey »

It's tempting to take another photo of today's work, but to the untrained eye it would just look like more wiring spaghetti. Suffice it to say, I integrated the phase control breadboard with the skeleton of the Lester, and managed to run the charger with the new controller chip. Starting with 12 volts and working my way up to 120, the circuit performed as designed and expected. I spent some time fine tuning component values so that I can begin construction of the permanent circuit board. I don't think I'll try the charger at 240 volts until I get rid of the cliplead hell that the setup is now. Too many chances to a tiny short circuit to turn into a big ball of plasma.

Amazingly, I haven't fried a single component. Usually, I cook a few things while breadboarding, which is why I usually purchase more than one of any IC's that I'm experimenting with.

Looks like I may have nailed down a source for some heavy cable for the charger output, more on that when it arrives.
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Post by Sharkey »

This project moves forward, however slowly. Actually, given that I have numerous other things that are much more important, that it is getting an attention at all is surprising. With Fall approaching, I should be spending all my time getting roofs repaired, the walls put up on my storage building, and some firewood cut, split and stacked.

The charger does have some priority, as the full-time project for the radio station that I've been anticipating for the last six months may actually be getting under way within a week or two, and I'll need to drive into town nearly every day until it's completed, Using the EV to rack up those miles will be a real fuel budget saver. Being able to charge up the EV at a fast rate will be important if I expect to be able to use it as daily transport.

Yesterday, I finished the wiring on the chassis, installing the AC input wiring and DC output cable. The AC wiring is a good length of 8/4 SO cable, #8 gauge, four conductors (two hots, a neutral and ground) sheathed in tough rubber. The cord cap is a 250 volt, 50 ampere, two-pole with a ground.

The DC cable is about ten feet of #8 twisted pair, a gift from TMAX from his stash of old Telco wiring salvaged from the dumpster behind LA7. I installed the 50 ampere Anderson connector that mates with the EV's battery pack on the far end. These cables will do the job for now, If this charger gets a lot of use, I might replace the twisted pair cable with some more supple auto jumper cable wire, which is probably a bit better protected in an exposed application.

Finishing the chassis wiring required me to complete the make-over of the front panel of the charger, as several switches, circuit breakers, and pilot ights, etc. needed to be installed for the wiring to be soldered in place internally. Here's a pic of the old front. There were multiple cartridge fuses for apparatus that no longer existed, large gaping holes for cables that were lost long ago, and a socket for a "watthour counter" that incremented a mechanical counter on the dash of the EV. All of that's gone now.

Image

To correct the panels appearance and function, I needed to replace the panel entirely, or at least cover it so I could lay out my components in an orderly manner according to my own design. Scratching around in the woods where I store leftovers from the bus building yielded some aluminum sheet, whcih I grafted to the front.

Image

The only things I retained were the ammeter and the "overtemp" light, which will be a simple power indicator now. The original "push to start" and "reset" push buttons were of questionable quality, so I dug through the junk box of switches and found some better replacements, using them as "Start" and "Stop", controlling the AC contactor in the charger. The DC Disconnect is a pair of 100 ampere circuit breakers. I used two, one each in the positive and negative DC legs because the breakers are rated at 95 volts DC, and the EV battery pack tops out at 130 volts DC. I wanted to be sure I could shut off the feed to the batteries without any sustained arcing. The DC Disconnect breakers have an internal microswitch for alarm control. In this application, I used this switch in series with the contactor control circuit. The DC breakers must be in the "on" position to turn on the charger's AC power, and if there is any fault in the DC side of the charger that causes the breakers to trip, the AC side of the charger is de-energized as well. Fail safe!

The "Current Adjust" control will be connected to the phase control circuit that I've prototyped, but now need to permanently build on a perf board. It may seem to be crowding the pilot light, but in the next stage of construction, I'll add a voltage control to the front panel, and it will be mounted to the right of the current control.
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Post by anekut »

is this working now? I just got finished replacing a blown triac in my Russco.
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Post by Sharkey »

So close, but not ready yet. I need to fabricate the phase control circuit on a perf board and install it, then the charger will be done. I'll need to do this soon, because I want to begin using the car to go into town to work on the transmitter facility that I'm building. I've already told the electrician I need an exterior outlet to connect the charger to, so when the building is built, it will have the proper hookup for the new-and-improved Lester.
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