Taming Lester

Alternative Fuels of all sorts, Biodiesel, Electric, Human Power, Steam, etc.

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anekut
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Post by anekut »

I might build a higher power charger too, but I don's really see the point of the huge transformer.
Sharkey
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Post by Sharkey »

I wouldn't want to carry the Lester around in the car, for that the K&W will suffice, but there are advantages to using a transformer-based charger:

1) ISOLATION: The transformer makes very sure that the traction pack is never "hot" with respect to the AC line, lessening the chance of getting a shock when servicing the batteries while being charged. I've gotten bitten many times this way, and it's not pleasant. I removed the GFCI from my charger very early in the game due to nuisance tripping.

2) BETTER POWER FACTOR: A transformer-based charge can match the output voltage to the pack voltage better, so less phase control is needed, improving the PF significantly. Residential watthour meters don't charge extra for low PF's, but commercial meters do. Either way, low power factor will cause heating in cordsets, connectors and fuses/breakers, which represents inefficiency and real power lost.

3) CHARGE RATE: There are only so many amperes you can suck out of a 120 volt outlet. 240 volt chargers allow you to step up the current while stepping down the voltage.

4) PACK VOLTAGE MATCHING: We luck out on the SCT's as fully charged voltage is about 130 volts, within the 156 volt peak of a 120 volt AC line, but if you were running 120 volts or more, you'd need a step-up transformer to boost the line voltage to match the pack voltage. If you are going to have to have a transformer anyway, might as well use it to give you the benefits listed here as well.

A high frequency, switching charger might be able to deliver some of the above advantages (not PF, though), but I like heavy iron, it's much more rugged, and can be worked on when it quits. Besides, I already had the Lester, and it was either fix it up or throw it into the recycle dumpster, I'm tired of having a lot of useless equipment laying around.
Sharkey
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Post by Sharkey »

Who says I never finish projects?

Well, everybody, basically.

Just to be unpredictable, I've completed the construction/rebuilding of this charger. Last week had a couple of days of wet weather, and to stave off boredom and feel like I was acomplishing something (as well as clearing room in the garage for more projects), I sat down and built the circuit board that was needed to control the charger. A few last-minute design changes as I was doing the construction enhanced the operation, and the whole thing is now buttoned up and ready to fast charge the EV.

Here it is jamming some amps into an already fully-charged traction pack:

Image

The little trolley it's sitting on was a small welding project from last year, some leftovers from a bunch of retail display shelving that I recycled. About all that's left to do is paint the red metal frame and the charger is complete.

Oh, I guess that means that the Lester isn't really done....
AccordGuy
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Post by AccordGuy »

Nice one, it looks good. The wires look back to front though... massive fat AC lead and scrawny looking DC lead? :wink: Although I guess the AC lead has further to go and you're only stepping down from 240V to 130V.

I've got a similar project waiting for me this summer / autumn. I've got a big 30V toroidal transformer waiting to become a 24V battery charger before the winter when the solar power fades out.

I picked up a load of 6mmsq cooker cable at the car boot sale at the weekend. Dunno what I'm gonna use it for but it was just 4 Pounds for 16m of the stuff brand new in the shop tags, so I couldn't resist it.
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Post by Sharkey »

The cables might look backwards, but there's a reason for that.

Both input and output are 6 gauge (8.37mm) which is capable of 40 amperes continuous. The output side is simple twisted pair with PVC-type insulation. The input side is four #6 conductors, one for each leg of the 240 VAC, a neutral (grounded conductor which allows the charger to operate from 120 volts if required) and a ground (earthing) conductor. These are all rubber coated conductors sheathed with a rubber "SO" type cable covering which also contains fiber strands for reenforcing. This cable is rated by MSHA (Mine Safety and Health Administration) for severe service duty. It's probably a bit more than what was called for in the application, but since I had it in the scrap bag of wire, I decided to use it.

I'll have to take the car out for a jaunt and run the batteries down a bit so I can see how the charger does with a depleted pack. Trying to charge a full battery isn't telling me very much about performance.
Sharkey
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Post by Sharkey »

Two weeks ago during some nice weather, I decided that it was time to take the EV Rabbit out for a spin to loosen up the brake calipers and get some lubricant on the axle bearings. I dug the Pusher out from under it's winter wraps, put a charge on the engine starting battery and fired it up.

Took the car and Pusher down to the road where I disconnected the trailer and left it at the end of the driveway. Put seven miles on the car in electric-only mode, not much of a trip, but enough for a test, and about as much as the batteries were up to without some exercising discharge/charge cycles to wake them up.

Used the Pusher to help the car up the steep part of the driveway where traction is a problem, then hauled out Lester for some real world charging. With an actual discharge on the EV battery pack, I was easily able to hammer 40 amperes into the cells, adjusting the charge rate control for as much or as little as desired. Here's the proof, an honest 40 amperes into the battery:

Image

When I finished the rebuild of the charger, I put the metal cabinet back into place, enclosing the transformer and wiring. I noted that one of the aluminum panels had been replaced with an obviously homemade sheet steel panel. Perhaps the original aluminum panel had been damaged or lost? Whatever, I didn't care, as the replacement panel was made well enough, and had a nice painted finish on it to prevent rusting.

Well, now I have a new project, replacing the panel. An aluminum panel is needed because the steel panel reacts to the magnetic filed produced by the transformer during high current charging. It vibrates at 60 Hz with a terrifying buzz, making the charger seem as if it is about to explode! I eventually had to remove the screws and run the charger without a side panel as it was driving me nuts!

Image

This photo is interesting for a couple of reasons. for one thing, it's heavily (and rather badly) photoshopped to lessen the contrast between sun and shadow, making it possible to see into the carport. More notable is that it shows almost all of my EV gear in one shot. There is the EV and Pusher, Lester, the hood of the Electrak and it's charger (more on this later), my electric lawnmower (for trimming where the Electrak can't get), and the BIOBZL Rabbit is thrown in for good measure. I didn't stage these things for a photo, or even think about it when I took the picture, the stuff was all just out in one place at the same time.

Last week, I did some mowing with the Electrak, then put it on the charger to fuel up. The charger is a modified Todd Power Source charger that has the internal connections set for 36 volt output. I was in the garage doing something and heard a nasty crackle sound and looked out in time to see the Todd burst into a column of smoke and flames! Damn, fried it again! These chargers are prone to flame out for no particular reason. I used to take them in for repair as a side job, but after having too many of them blow up in my face during testing, I quit.

Anyhow, until I can get the Todd repaired, I used Lester to charge the tractor. I had to set the charge control fairly low because of the voltage mismatch, but it did a fine job of replenishing the electrons.

Now, about that undersized output wiring. I figured that the maximum output of the Lester would be 40 amperes, so #8 gauge wire would be large enough. Unfortunately, I didn't calculate for the fact that the charger doesn’t put out pure direct current, but pulsating DC. This wouldn't normally be a problem, but the batteries in the traction pack act like a filter capacitor, one that is at the end of a resistor in the shape of two wires. What I find is that the #8 wire gets warm, even hot enough to make the fairly stiff plastic insulation nice and pliable. The 50 ampere Anderson connectors that make the connection between the charger and the batteries get pretty warm too.

So, what I need to do now is increase the gauge of the wire to handle more current. I measured 20 amperes of AC current on the wiring while charging at 18 amperes of DC current. Adding these together gets me 38 amperes, about as much as the wire is capable of.

I'm also going to look into providing some filtering in the form of a large capacitor inside the charger to try and smooth out some of the AC component before I try to send the voltage to the batteries. It's doubtful that I can filter it very much, particularly when charging the Electrak at 36 volts, but any reduction in the AC ripple will be an improvement.
AccordGuy
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Post by AccordGuy »

Is there a risk that other things apart from the feed wires are heating up too? Like the internals of the batteries themselves?
Sharkey
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Post by Sharkey »

Batteries have a pretty large thermal mass to dissipate heat. This has been a topic of discussion on EV lists for a number of years, and the conclusion is that an AC component to charging current doesn't hurt batteries, and in fact can aid in charging during cold weather by helping to warm the cells.

The heating effects are more pronounced on wiring and connectors where a limited amount of dissipation is available. For example, I feed the charging current into the Electrcak via the "accessories" receptacle, which is a 20 ampere twist-lock connector. It gets actually hot while chraging with the Lester. I'm already working on installing an Anderson connector to charge directly to the batteries instead of using the receptacle.

Eventually I need to get the Todd charger repaired. It operates from 120 volts, and is very compact so that I can plug in wherever I use the tractor. For example, I usually charge from the electric service down by the end of the driveway when I am mowing in that area. The neighbors allow me to plug in for free. If I have to haul Lester down there to charge, I'll need a 240 volt outlet, which isn't installed there. Plus, I'm not too crazy about having to lift the big charger in and out of a trailer behind the tractor.

Heavier wire, installed capacitance, and a rebuild of the Todd. Oboy, more projects....
AccordGuy
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Post by AccordGuy »

Just as an aside, I was at the local DIY / garden store at the weekend and they are now selling these cordless electric cylinder mowers. Not sure how good / powerful they are but I might give one a go as it would save using the mains mower on our small lawn and I could charge it up from my solar power.

Anything would probably be better than the cheap hover mower I have now that breaks at least five or six of its clip-on plastic blades every time I cut long grass or hit a paving stone.

In fact, the shop seems to have gone mad on battery operated things this spring - hedge trimmers, strimmers, small chain saws, branch loppers. If nothing else it will reduce the number of accidents - eliminating the "death from electrocution by cutting the cord" type to just the "cutting random body parts off" type. :roll:
Sharkey
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Post by Sharkey »

Still an ongoing project.

Today Lester got "C".

Capacitence that is...

Image

After posting that the AC component of the charge current seemed to be a problem, TMAX sent me a box with four 740 mfd, 250 volt electrolytic capacitors to smooth out the fluctuations. Over the last couple of weeks, I've dabbled at getting them installed, and this afternoon connected them using a cut-out square plate of copper for superior current handling capability. The caps are connected to the charger output using #8 wire.

Not shown is the 30,000 ohm, 5 Watt wire wound resistor that I have to install to act as a safety bleeder to insure that the capacitors don't hold a charge when the charger is turned off and disconnected from the battery pack. 2960 mfd of caps charged up to 130+ volts would be enough to throw you to the ground if you got hold of it accidentially.

Looking at the output on the oscilloscope without the capacitors, I see a nasty 78 volt alternating current ripple riding on top of the DC charging current. With the caps in the circuit, and powering a 100 watt light bulb, there is only a .745 volt ripple. Of course, this will worsen when the charger is being required to supply more current into a battery, but I'm hopeful that the caps will help lessen the heating of the conductors when charging vehicles.

If there is still an issue with the wiring heating up, TMAX also sent me a long hank of #6 twisted pair wire that I can substitute for the #8 that is on the output of the charger now.
Sharkey
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Post by Sharkey »

Tried the charger on a partially discharged ElecTrak battery today. The capacitors have helped a lot, the cables hardly got warm at all at 20 amperes of charge current. Before they'd be all melty after a few minutes at that level.

[edit] In the afternoon I put an Anderson connector and some #8 wiring on the tractor so that I can charge the batteries at a higher rate with the Lester. After running the tractor down the hill to retrieve some firewood, I used the charger at 40 amperes to fast charge the tractor batteries. The wiring got warm, as expected, but not flaming hot. I might still put the #6 wiring on the charger's output pigtail, but things are much better with the new filtering. [/edit]
AccordGuy
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Post by AccordGuy »

Dunno about flooded batts but having just changed my solar bank to be gel types, I read that Deka and Yuasa (makers of VRLA gel and AGM packs) both recommend that there be no AC ripple to the charge current or else it will shorten the battery life.

The two old 24V chargers I have both are SCR types that put out full wave ripple but the Yuasa switch mode one I scored puts out pure DC with no AC component.

I remembered your postings here on the DC wiring and noticed that the SCR chargers have over-sized DC wiring and the 6A Yuasa charger has much thinner wiring than the SCR 7A charger. Measured 7A DC current from the old charger and another 8A AC, so they were right to beef up the wiring!

I'm scouting around for some big capacitors right now :)
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