Monday, April 16, 2012

Throttle Bodies and Bottom Balancing

This week we do some final testing on our dual Soliton1's and dual 11 inch motors before breaking down the test bench to install the motors into the Cadillac Escalade EXT.

One of the issues with this vehicle is where to get the signal to serve as the "throttle" input to the Soliton1's.

Of course, we have two such signals routed from the accelerator itself to the Engine Control Unit or ECU.  We could simply steal one and use that.

But the Cadillac is complicated by a lot of systems.  The ECU is the heart of the beast and it takes a lot of factors into consideration before finally sending a drive signal to the throttle body. The engine of course has fuel injection for the gasoline, but the actual engine speed and power is regulated by controlling the flow of oxygen containing air into the intake manifold.  This is done with a throttle body - a round hole with a round plate we used to call the butterfly valve in the carburetor days of the 1960's.

As it runs out, the throttle body has two potentiometers each provided with 5v from the ECU.  They move with the throttle plate.  They actually operate in different directions and at different scales.  And so one varies from about 3.8v down to something less than a volt, while the other ranges from 1.2 to up over 4volts.  The ECU uses these two signals with a function in software to determine throttle position, so if either one is "off" by any appreciable amount, the mathematical relationship between the two signals fails and the ECU will shut down the system.

So we have to be careful not to "load" one signal down by feeding it into the Soliton. I'll probably build a little opamp buffer for the signal.  Something else to fail.  But it will avoid throwing the ECU into a data storm.

We've had some interest in our little cobble up to bottom balance cells.  Understand that this was cobbled together in an hour out of stuff laying in the pile on my bench.  And it was mostly a test case for the little voltmeters we found.  It actually works pretty well.  Sufficiently so that we had some viewer interest in purchasing them or at least a parts list so they could make their own and indeed two have made their own.

The problem with this is that in many ways, your mission and mine are forever different.  The bottom balancer I built has large components that are easy to identify, and it makes it easy for me to describe on camera what they do and why we want to do that.

To ACTUALLY do that, there are some better choices.  They don't show particularly well on camera, and they don't illustrate the principles quite as well.  But they are less expensive, do more and are easier to operate once you get past the small learning curve.

I've reviewed four or five of these, and I think the winner hands down is the Revolectric 1344 watt device.  It both charges and discharges and will even do "cycles" of charge and discharge. You can interface it to a Windoze PC and at that point, the sky is the limit on cell testing, bottom balancing, cycle life testing, cell matching, and more.

Economically, by the time you buy a power supply, a meter, a $55 bleed resistor, and a contactor, you're talking the same money with far more capability in the Revo device.

This week we also add to our online store with David Kerzel's J1772 kit for DIY conversions.
David sells these things on eBay.  He has a web site that isn't very well done frankly, so he sells on eBay quite successfully.  But the plastic inlet ports from China are now down to about $51.  He can mark those up and sell them on eBay all day long and MOST EV builders prefer this.

I don't.  He started out making his own J1772 ports with a work of art in 6061 billet aluminum.  The problem is, the aluminum billet costs more than the finished Chinese port BEFORE he machines it.  So he had dropped the product from his eBay store.

The problem is, I have fallen in love with it.  Yes, thrift is always a virtue.  But we build nice electric cars and do so for the PURPOSE of attracting attention so we can demonstrate the cars and hopefully convert a few more PEOPLE than we do cars.  And I've noticed they are ALWAYS curious about the charge port.

We used to use a Marinco NEMA 5-15 recessed male plug.  This allowed us to use any ordinary extension cord and plug into any ordinary 120v outlet.  In practice, we almost never charge on 120v.  We always charge on 240v at home.  But the problem was that the NEMA 5-15's are just not meant for daily use.  The act of plugging in and unplugging wears them out over the course of a few months or a year.

I've fallen in love with the J1772 standard not for the safety features, but for the heavy pistol like plug and sturdy inlet connector that it is.  This is designed for 50,000 insertions.  It is just a much more physically substantial system.

On the eCobra, we actually put David's billet aluminum device inside a billet aluminum flip over gas cap.  David liked it so well he's working on a version of this on his own.  But we also used it on the Swallow and we had one mounted behind the normal fuel door on the Escalade.  The door and interior are of course glossy black and the shiny aluminum billet just looks like a piece of jewelry there.  As one of the first things anyone is going to want to see is the charge port, we've got a nice one to view.

So I asked David to make me up 10 so I would have them.  We added them to the store, and the first three were sold out within four hours of the release of this weeks video.  Should have seven more next week.  As he makes these by hand, I'm not sure we can keep up.  Even though they are QUITE a bit more expensive than the plastic ones.

He's also updated his little circuit board that actually properly does the copilot signal AND the proximity switch.  This is what actually lets you use J1772 in your car and triggers the available J1772 EVSE, such as the GE Wattstation, to put out power.

It is a very small device and quite inexpensive.  His update includes packaging it in a plastic case that can be easily mounted.  The terminal strip is still readily exposed and clearly marked.

So with these two components, it is very EASY to add J1772 functionality to your build.  You can STILL have a NEMA 5-15 in parallel for opportunity charging at the Walmart parking lot light pole if necessary.  But with this kit, you can also make use of the many public charge stations going up, and install a proper J1772 EVSE in your garage.

In any event, we've gone from one thing to another in the EVTV store. First it was braided straps, then the JLD 404 meter.  This J1772 inlet is a welcome addition.  I don't know where all this leads.  I hadn't really pictured EVTV as a component retailer.  But we have received eight Soliton 1's and two Soliton Jr's in stock as well and I'll be adding those to the store this week.  We kind of intend to pursue it to see where this all leads.

This takes me back to the early days of the BBS.  We originally thought BBS would advertise in our little newsletter.  Instead they became readers and we wound up running an eight line BBS ourselves. Our advertisers turned out to be Cisco and Sun, and US Robotics and the companies making tools for online communications.

Similarly, I thought all these little dealers of EV components would be a market for advertising on EVTV.  They are all VIEWERS of EVTV, but not a single online retailer showed up to advertise. Just like the BBS/Internet thing, we'll wind up with the component manufacturers, but the guys just running online shops are simply not sufficiently sophisticated in the art of selling and running a buiness to be a market for advertising.

I would predict these SAME guys will grouse that we have an unfair advantage with the EVTV show.  And they will never put two and two together there or pick up on the irony of it all.

Nature of the beast is that we aren't much of a threat.  The average EV builder is if nothing else, thrifty.  And our focus is entirely going to be on the very best components we can find.  My belief is that if you build a rocket entirely of components provided by the lowest bidder, always include the cost of hiring a test pilot to fly it.  You don't want to actually be IN the rocket yourself at any given time.

If I'm building a car, I want to make careful choices, but generally go for the better device.  These choices are cumulative, and will result in a car that is either the sum of the cheapest things I could find, or the sum of some  inspired, but sometimes pricey choices.

Our entire mission is to build ATTRACTIVE and DESIRABLE cars people will WANT.  And of course I like fine rolling stock myself.  So it's all part of God's plan.

If you just want some crate to creak you along the four miles to work and back without buying gasoline, let me strongly note that that's an ENTIRELY VALID MISSION.  I  don't share it.  But it is entirely valid.

And our A123 work is a nod in that direction.  I think you'll STILL find a small lithium pack more durable and more practical than Pb chemistry battery cells. And SOMEONE is going to figure out a way to package them in a small 60Ah or 80Ah pack that will do 30-40 miles at a competitive price without 200 hours of labor.

But let me reiterate, in building a car for ME, these cells would never make the cut.  The CALB prismatics are just better in all respects and make a better, more trouble free car to last a lifetime.  I like having 100 mile range even if I'm never going to use it.

The ongoing soap opera with the company A123 is just beyond belief.  I am at this point actually embarrassed for them and about the entire topic.  I cannot conceive of a product this good manhandled so badly and on such a grand global scale involving hundreds of millions of dollars and at least three continents.  Along with taxpayer investment in an effort to make us a world "leader" in battery development.  It has reached the point of public obscenity and defies the willing suspension of disbelief necessary to follow the story.

But did I mention the 3p28S module we have in shipment from China as we speak?

Jack Rickard


  1. Jack,

    As always an interesting show!

    The PowerLab 8 appears to be slightly better than the iCharger 3010B in all respects but one. It looks like the resistive discharge is limited to 10 amps on the PowerLab 8. The resistive discharge on the 3010B is limited to 80 watts. This means that initially a 3.4 volt cell will discharge at 23 amps but this will climb as the voltage drops and at 2.66 volts will be up to the 30 amp max. So to resistively discharge a battery will take over twice as long with the PL8. The iCharger also has a way to add an external resistive load which can increase the discharge power to 1200 watts (30 amp max) but I have not used this feature yet as it wasn't necessary.

    So I think for bottom balancing individual cells the 3010B might actually be a little better because for most people they are going to run out of lead acid batteries to regenerative discharge into and will run it off of a 12v or 24v power supply.


  2. Doug,
    That problem is easy. Just connect a headlamp bulb to the car battery :). I had a little time to play with the A123 cells today. These things scare me more than anything we're gonna find in outer space! They pump out amps like its going out of fashion. A prototype 4s1p pack blew my constant current load at 300amps in spectacular fashion. Gonna need a bigger igbt!

    I have an interesting little module build in progress. Not sure if it's gonna pan out but if i knew in advance ....

    Jack have you seen this module from victpower:

    and do you have any intention of stock the powerlab in your store?

    Damien Maguire

    1. Haven't seen the module. No I don't think we'll stock it as it is once click away at and there is nothing really to add to the package...

  3. I really liked the show this week! That answered a lot of lingering questions about the battery pack and what bottom balancing really does.

    It was one of those "ah-ha" moments where I now understand why it is a good idea to bottom balance and why you should under charge the pack a little bit. I know get why the voltage variations will be exaggerated on the high end of the charge curve after bottom balancing.

    P.S. I am still plodding along with the PLC/HMI experiments. I am about to start working out how to make it do charging duty and well as instrumentation...

  4. Hello

    the A123 3p28s module looks nice , hope it performs as specs , it is very interesting indeed.


  5. Hey Jack,
    That module coming from China, who did you buy it from?

  6. I was actually pondering something more similar to the cobbled balancer, but using a programmable board (Arduino perhaps) and a series of relays. The result would be a multicell bottom balancer you can set and walk away. Useful for bottom balancing whole packs at a time, especially if you build multiple vehicles.

    - Doc

  7. This comment has been removed by the author.

    1. This comment has been removed by the author.

    2. I thought about a 2.7V zener diode DC amplified and feeding into a load.

      Bung 'em all in parallel, come back next week then pack 'em up to charger voltage and charge.

    3. Hmm, that might actually work. I'd probably prefer a shorter time span, but I think it's time to do a little shopping around on Newark or Mouser...

      - Doc

    4. Hi Doc,
      Might be a bit late for you to read this but I'd use the zener simply to set the voltage level. Relays to a big ugly current dump is certainly not off the cards.

      However, dumping 3.2v into a 2.4KW (240v) kettle is a 10amp load so its about an hour per virgin cell. I have 6 x 29 cell packs.
      Giz a week or two ;)

  8. I'm looking to build a race car light-weight, starter battery for a low compression, 8:1, 2.8 liter turbo engine. Do you think A123 cells would work and what configuration would you recommend?; 1p4s, 2p4s, etc.

    Do you think I can use the alternator with a DC inverter/charger combo, or isolate the battery from the alternator and charge it with an external charger since once started the car will run on the alternator.

    I like the 23C rating of the A123 and see it as a good replacement for a Pb battery in certain environments.

    1. I think a 4P4S configuration would work very well. And it would probably work with the existing alternator/charge system. It would be perpetually a bit undercharged, but that's ok.


    2. Jack:
      Do you think you need 4P for this application? Seems like 1P or 2P could work. You need lots of current for a short time and not too many AH. The goal is to be light weight. If the cells can handle the charge current I would think it would be OK.

    3. Thanks For the info.

      "G' damn it Gump, you must be the smartest man in the Army"

    4. If weight is such a premium how about a 4S1P battery inside the car. Have battery terminals external for your present cold starter battery.

      That will knock off plenty of mass.

  9. I see you mentioned that you have one of those A123 battery assemblies configured 3p28S on order. I was just curious, how big can they go? Can they do something like 6P12S?

  10. This comment has been removed by the author.

  11. jack,

    As you said, you use a measurement and a resitor cabel on your DIY discharger. This "workstation" chargers use the same cable and this causes a problem. Have you checked the real voltage and amps with your Fluke? Also my expirience is, that the clamps are not working at more than 20A. I had it my last video.
    For the A's it will work perhaps, but I think the CALB 180 is to big for this device.
    I think the DIY JLD bottom balencer is the best solution.


    P.S. Today I did my first test drive with my 2CV conversion. Henceforth her name shall be "Elektra".
    She is driving so beautiful..!)
    Thanks for everything, Jack.

    1. I think what I said I thought in the video Ohne. IT was pretty clear. You get a LOT more bang for your buck with the PowerLab although as one viewer pointed out, the 8 offers no advantage over the 6 for our purposes.

      Why would it not be as good for CALB's as for A123? The 0.1 ohm resistor with the cables and such winds up being about 22-25 amps maximum on a single cell. You can do that with this device.

      The problem you allude to is indeed a problem, but rather easily solved. If you shut down the current flow for 25 ms, you can take a reading and resume without really any detection of it. I'm sure this device does something like that as I found the voltage readings it displayed and a Fluke voltmeter VERY close.

      In any event, using the supplied "balance" connector works around the problem nicely anyway.

      Jack RIckard

  12. It seems to me that when driving two motors mechanically connected to one another with two controllers, you'd want the current to both motors to be the same so as to distribute the load, heat and wear evenly. I'm curious to see if this is the case when driving both motors with the same throttle signal. It's pie in the sky but it would be cool if one could slave one controller to the other, perhaps by their ethernet ports, so that they send identical currents to both motors from one control input.

    But that's pie in the sky. It'll be interesting to see what your build does.

    1. Jack could adopt a heavily choked Lee Hart batt bridge across his motors with an 0-V-0 meter. Or read the loads?

      Or just do what I'd do; nothing. Because with all things being (should be) equal, any fix apart from controller replacement with odd peak powers, might be a hiding to nowhere.

      I'm almost dead sure you cannot parallel the controller outputs. They rely on a feedback mechanism too.

    2. A lot of thinking going on here.

      First paralleling the motors is kind of like paralleling the batteries they do NOT actually fight each other. They're on the same shaft and it's really pretty much like one long motor. The current and voltage could vary in theory but the sharing of the load itself causes it to pretty much even out.

      Of COURSE you can run two motors from one controller wired in parallel. This will get you maximum voltage to each motor and so maximum rpm. But it halves the current, and so the torque.

      You can also wire them from one controller in SERIES and this will give you maximum torque to each motor, but half the voltage.

      The Zilla controller can actually operate some external contractors to in effect give you a two speed system, switching between series connected for maximum torque, to parallel configuration to allow higher rpms.

      And we use TWO controllers WHY???? We can have the best of both worlds all the time. 1000 amps at full voltage to each motor for 2000 amps at full voltage total. We think this will result in about 300 kw after voltage sag or 402 electric horsepower. The L92 engine we pulled and sold on eBay was rated at 401 hp.

      Jack Rickard

    3. And at 2000 amps, our batteries will be rated at a very conservative 5C. Hopefully sagging to 150v.

      Jack Rickard

    4. Hey Jack, Question.
      Isn't there some some of motor feedback system within the controllers to prevent over revving, watching the max load and such? That was my fear where two motors would give off spurious signals. Any Soliton/Rebirth Auto guys here to say in case someone wants to try it?

      Whatever the answer, I'm completely with you, keep them apart and separate. If something smokes, you can still get home.

  13. Jack,

    Another One bites the dust.

    Rep. Dent challenger calls for earmark ban after federally funded plant closes
    By Adam Clark
    Of The Morning Call
    4:07 PM EDT, March 16, 2012

    Democratic congressional candidate Rick Daugherty called for a ban on federal earmarks Thursday and asked incumbent Republican Rep. Charlie Dent to investigate a 2009 grant to a company that is now closing its doors.Standing in the shadow of International Battery, which told employees last week it will close, Daugherty challenged Dent to find out what happened to the $2.1 million he secured for the Upper Macungie manufacturing plant. The money was intended to fund development of a new Silent Watch system with high energy storage capabilities for use in U.S. combat tactical vehicles, according to a 2009 news release. In addition to the grant, Dent helped secure a $730,441 contract for International Battery to research advanced Lithium technology batteries for the Department of Defense. If the company didn’t fulfill its obligations, Daugherty wants Dent to get the money back. Dent’s campaign deferred comment to his congressional office. Communications director Collin Long said Dent’s office is still investigating the matter but believes the company completed the work. Dent supported an effort three years ago to impose a moratorium on earmarks. While the moratorium is still in affect, Daugherty wants to go a step further. One of two Democrats vying to unseat Dent in the 15th District, Daugherty said International Battery is a prime example of why congressional earmarks should be banned. “Earmarks for business often only profit the few at the expense of us taxpayers,” Daugherty said. International Battery owes Pennsylvania more than $2 million, and state lawyers are initiating efforts to recover some of the debt. State officials are also in discussions with the company regarding a project for which International Battery received an $800,000 grant in 2010. That project has not been completed.

  14. Doug, seems to me a good place to dump at least some of that regen is brush break-in. These two tasks kinda go together at least on the initial build. Not sure there's much point on a brush replacement down the road being complimented by an arbitrary balance, but why not?

    1. Nabil,

      That is a great idea. I should have thought of it myself. I am awaiting my H60 brushes and when they come in I will implement your most timely idea.


      What are your thoughts on storing LiFePo4 cells at 2.7 volts for a few weeks to month during the bottom balance? I mean is the low voltage going to cause a loss of capacity if stored this way or do you feel it should be fine. I guess I can answer my own question. I have four cells that have been sitting at 2.7 volts for over a month now and I have good cycle records of capacity before. I can cycle each and see if there has been any change.


    2. Doug:

      Ideally, these cells should be stored as they come shipped, at about 50-60% SOC.

      Once you have your pack bottom balanced, I always charge it almost immediately together as a pack. If it's going to sit around, I kind of let it bleed off using a DC-DC converter or whatever, heater, until it is about 2/3 full. If I'm doing other things, I'll disconnect it to let sit for a month or two while I'm doing something else.

      Jack Rickard

  15. Jack, I would like to see more information about your "thrown together" bottom balancer. I already have the 5740 meter and resistor and I can use a contactor from my EV during the initial balance. Building the thing isn't too hard, but attempting to decipher the instructions for the 5740 gave me a headache.

    1. It's very easy, but very confusing.

      1. Enter 0001 to get the relay menu.

      2. Set AH1, the HIGH voltage, to your LOWER voltage (2.60v).

      3. Set AL1, the LOW voltage, to your HIGHER voltage (2.77v).

      4. Wire your contractor to the normal OPEN contacts of the number 1 relay.

      5. Jumper 12v supply to the COMMON terminal of relay 1.

      uses separate wires to connect your voltage input across the cell. Set the voltage range to 10volts and I think the decimal point to 3.

      Use cables that can carry at least 30 amps to the contractor and resistor to bleed the cell.

      If the voltage is HIGHER than 2.77v, the contractor will energize bleeding the cell.

      When the voltage bleeds down to 2.60v, the contractor will OPEN removing the load.

      If it rises above 2.77v, it will close again. After two or three cycles, it should settle just below the 2.77v.


    2. At the risk of sounding like Dan you can buy cheeper components for a bottom balancer. A continous duty 80A starter solenoid can be had for about $17.00 (no need for high voltage contacts)and a .1 Ohm 200W resister with bolt terminals from digikey is about $27.00

  16. Jack,

    Great recap on your philosophy of battery management. Several times you mentioned that the cells have different capacities. Can you put a number on the variance of the cells? Is it 1% or 10% or somewhere in between?


    Brad Lindberg

    1. Depends on the size of the cell of course. I would say currently on CALB 180 cells we see anything from 196 to 204 Ah. So on the order of 4% variation. It is not as great as the BMS people portray it.

      Jack RIckard

  17. Jack: when bottom balancing, is it in your view necessary or useful to do several cycles of "bleed down - let it recover - bleed down- let it recover..." or would you just bleed down once to (say) 2.75 volts at 0.1 C and then let it recover to whatever it feels like...?

    1. A quick take works pretty well John. But in practice, I've actually been overnighting them and redoing them. This is because we are working currently with very SMALL capacity cells and so it becomes more critical.

      On 180 Ah cells, we basically bleed the whole pack down to 2.90-3.00v as a set using whatever is available, heater, lights, dc-dc converter, whatever. Then we individually bleed down to about 2.68 volts and let them bounce back. Your goal is really += 0.1 volts on the larger cells, the hundredths really are overkill.

      On 20Ah A 123, I'm getting +- 0.05 but doing two iterations.

      Yes, they definitely "bounce". If you are adding energy to get to 2.75 with a power supply, I do about 2.85 volts and they will "fall" to 2.75 or thereabouts. When discharging at 30 amps, 2.68v will "bounce" back up to 2.75 or 2.78.

    2. John,

      You ask about bleed down and recover. My idea is to discharge the cells individually down to 2.0V at some reasonable current and call it good. I have an automated discharger that can do up to 30 amps which is a reasonable comphromise between speed and accuracy. The reason I think this will work is that the primary reason for bottom balancing is to protect the pack from an over discharge driving event. This would normally occur at a 100+ amp discharge so a bottom balance really doesn't need to be all that precise. It does occur to me that the other reason to bottom balance is to protect the pack from discharge due to parasitic loads. And my approach will not do this as well as the careful balance that Jack is doing. I will be testing this by bottom balancing a two cell pack consisting of my worst cell and my best cell and seeing how well they dump together. I am running a couple of tests and the first one was to see how much damage occurs from leaving a cell in a discharged state for an extended period. The initial result appears to be that leaving a cell at a resting state of 2.7v does lose some capacity. I only have a single data point at this time but that one looks like it is a little less than 0.5% per month of lost capacity. This first test was for a cell left with a resting charge of 2.7 volts for 70 days. The result was worse than I would like but better than I expected. I have 5 other cells in this same situation so I will know more soon.


  18. I don't know if anyone seems to realise this but the Soliton is NOT the only controller that can idle a motor. The Curtis 1238 actually has this capability, although I can't actually testify as to how to set it up. No doubt with far greater difficulty than the Soliton.
    The guys at HPEVS have implemented this on a VW Jetta with a DSG automatic transmission, which can been seen in the "On road conversions" section of their website. I have had the pleasure of driving this car and I can testify that it is OUTSTANDING.

    I personally view the idle function in a manual or auto transmission vehicle as a possible cheap and easy way to keep the stock aircon, power steer and even the alternator setup in the vehicle, which simplifies the conversion and makes it cheaper - albeit at an efficiency loss. Having said that though, the financial saving of not requiring a DC/DC converter, Sierra a/c system (+ plumbing, wiring etc) and cobbling up some aftermarket or co-opted power steering system from another car (toyota MR2?) is quite large.

    I recognise that there is an efficiency price to be paid, and the concept will not suit all commuting styles, but a couple of extra cells is a LOT cheaper than the electrical equivalents of the aircon and power steering - and I can more easily afford 50c a day of extra electricity than 2-3 grand in EV parts in one hit.

    1. I said it was the only SERIES DC controller that offered IDLE. The HPEVS is actually quite easy to do this. It has a CREEP value you can set so that when you come to a stop, it will "creep" forward with no throttle input when you release the brake. This works with the manual transmission.

      With an auto transmission, which I haven't actually tried, it should idle the tranny.

      Jack Rickard

  19. Hello Jack,

    I thought this news might be of interest to you and your reader:

    I know you talked about it in a previous EVTV weekly show, but it is about IBM's Lithium-Air battery. It is always nice to have an update on theses news.

    Hopefully, they will take the road from unubtainium to something we can buy... eventually.

    1. Yes, we are following it. The diagram is more telling than the video. They are getting closer on the electrolytes which are the heart of the problem. The Lithium metal cannot come in contact with any form of water. It really has to be entirely sealed.

      Using carbon to "wick" the oxygen is quite mechanically cunning.

      I would think the separators become part of the problem at this point.

      Jack Rickard

  20. Jack,
    I have not posted to this blog yet but at the risk of sounding stupid in front of everyone I am here now to bare my soul. Thank you for the review on bottom balancing great show. I was curious if it is possible to connect the entire LiFePo4 prism pack in parallel and bottom balance the entire pack then re-connect in series and charge to 80 percent, or does each cell have to be bottom balanced individually?
    Mark Bush

    1. Mark.

      Yes, and no, and it's not stupid at all.

      You cannot really balance these cells by just connecting them in parallel, which I've seen some of the BMS guys actually do. It is kind of a useless exercise. On the flat part of the curve, there is insufficient difference in potential to accomplish this task.

      HOWEVER. If you connect them in parallel, and bleed them down to 2.75v - on the vertical face of the discharge curve, they will indeed balance very nicely.

      Here's the problem. It would take FOREVER on a large pack. Bleeding 30 amps on a 180Ah cell things move along pretty quickly as long as you are starting at 3.00v. Ten cells in parallel would be 10 times as long as your cell then in 1800Ah.

      So there is really no gain. Doing 10 cells serially takes the same amount of time at a given current level as 10 cells in parallel.

      As a practical matter, if we are assembling a pack, we simply discharge each cell to 2.75v before installing it. Once they are all installed, we charge the whole pack as a string normally.

      On an EXISTING pack in the vehicle, we drive the car until we are down around 3.00v per cell and then find the LOWEST cell. We monitor that and use something like the heater or DC-DC converter to gradually bleed down the pack until that lowest cell is 2.5v.

      Then we bring put the low ones with a charger and down the high ones with a bleed resistor until they are all lined up.

      So there just isn't really a need or an occasion where massively paralleling the cells offers any advantage.

      Jack Rickard

    2. Mark,
      No question is stupid. Only the answers. J. miserably failed in that regard ;)

      Point taken. Each A123 20AH comes half charged. I, for instance have to lose 10A per cell before the voltage slope. Discharging a lot of cells at a low voltage is slower than a high voltage using the same load.

      So, 240v (75 cells) fed into an electric kettle at 2.4KW is better than one 3.2V cell in the same one hour of discharge.

  21. Jack,
    Your explanation on bottom balancing couldn't be better I don't think and answers lots of questions. Thank you!
    If you want to take a look at an early electric vehicle, there's a 1909 Walker Electric Delivery Van on ebay for lots of money,but what little specs there are, are interesting for such an old EV. Here's the link:


  22. I'm so sorry to hear of your Mother. Hope you are all dealing with it ok.
    Mine is fiercely independent and is doing far more than her fair share with my Dad who's very weak with Parkinson's and Alzheimers.

    Love is a great driver for life. x

  23. Jack, please accept my heartfelt condolences on the passing of you mother. I met her briefly at EVCCON and she struck me as a vibrant and energetic person, and especially seemed to enjoy the runs down the tack with Matt.

    Persuant to her final wishes, I shall bring a little something with me to EVCCON 2012 and we shall toast her memory.

    Best wishes to you and your familiy at this sad time.

  24. Jack,

    My condolences to you and your family on the loss of your mother.

  25. I got an EVTV grin with the throttle control "success" moment. The sounds, lights, and industrial 'feel' of the equipment reminded me of a funky '50s sci-fi flick.

    1. Sorry, I forgot to share Brian's quote: "It seems to be responding to the command precisely". My mind's ear added ", Captain/Prof. Rickard" to the end of it!