Re: "Racing" the Duff Beer Electric Car

Have you considered a constant current bulk charge for the initial charge? You should be able to get them in reasonably good SOC before having to kick in a balancing setup.

Re: "Racing" the Duff Beer Electric Car

Sure, that's basically what a battery charger does, CA, then CV. Now I just need a bunch of CA power supplies that put out thousands of watts for really cheap. Actually, I think that Ricky is working on something like that. Unfortunately, all of the high power DC power supplies that are cheap put out a constant voltage. If you connect one of those to a battery, then it makes a big spark and melts the charge connector. It's exciting.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

Ah.. Ok. Since you are using about 140vdc you can use industrial DC motor drivers as bulk chargers. They have current limiting circuits. You set one up with the right voltage and with the current limiter dialed down, it could be the ticket for a reasonable cost.

Re: "Racing" the Duff Beer Electric Car

I've been helping Roger in the background - I hadn't even though of using DC motor drivers.  That is an excellent idea.  They are built to deal with and control high current draw spikes (zero speed startup current), which in a charging application is in-rush current at battery hookup...

Must do more research.

Apparently my name is really "Craigers".  Who knew?
We might be yellow, but at least we are slow
I'm a WINNER!

Re: "Racing" the Duff Beer Electric Car

DC motor controllers could handle the CA portion.

Charging needs to happen like this:

1. Constant current at some settable rate until voltage rises to a settable target voltage
2. After voltage target is reached, then constant voltage until current drops to<3% of rated current, but no longer than 30 minutes. You could actually ball-park this to 30 minutes at constant voltage and still be safe and effective.
     - This transition needs to be pretty seamless. If you go CV before the battery has reached the voltage threshold, then the charger will try to           instantly bring the battery to the target voltage. This will damage the charger and melt stuff.
3. No voltage or current. It has to cut off after 30 minutes.


Now for the fun part:

There are three sets of 147.6v battery packs in the car. Each battery is composed of three 49.2v packs. Each pack is composed of twelve 4.1v cells. Each cell is three 4.1v pouches, but we only manage to the cell level because the pouches are in parallel.

A cell should charge to 4.1v, but must not charge to over 4.2v, or it will damage the cell and possibly start a fire. Some cells will charge faster than others, so this should be managed.

The lowest chargeable unit is a 49.2v pack because that's the only thing that has terminals that will support significant power transfer.

The highest chargeable unit is a set of three 147.6v battery packs in parallel.

At all times, I need to be putting 9000w of output power evenly into a set of three battery packs. That can be broken down into whatever divisions of voltage and current you like, as long as it is divisible by 49.2 volts, the lowest chargeable unit.

All of this needs to be built and tested in the next two months.


I think that covers the charging logistics.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

Wow. That is about 20hp in power. Hm. Will have to think about the best way to achieve that. Without breaking the bank.

Re: "Racing" the Duff Beer Electric Car

We will dump some money in this thing if we have to.

Cost-wise, the conventional solution would be something like an Elcon PFC3000 charger for $1100. That would put 3000 watts into a 147.6v battery pack. We'd want an Orion 36-cell BMS for $890 to monitor and balance the cells. Round that to $2000 and we'd need three of those setups, so $6000.


The cheap option that I tried at Barber was EV-Peak A9 12-cell balancing chargers for $160/ea. We'd need 9 of those for $1440. Then  we'd need to power them. They require 15v-32v DC, which we did with used 12v HP server power supplies in sets of two in series that can be bought for $15/ea. We'd need 18 of those, so $270. All together that's $1710. Round up to $2000 after I buy spares.


So our tentative charging budget is north of $2K if that helps. We have generators for the AC power. Sam's Club sells a 5500/6875 220v unit for $399 that is pretty good.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

Progress, maybe.....

Based on my current theory that the charger blowuppiness is some kind of inrush-current/impedance-mismatch problem; I ordered some 500-ohm 50w resistors and built an output cap pre-charge dongle:

http://www.carolinahondas.com/members/roger-albums-stuff-picture6629-precharge.jpg


I plug in the charger output to this for a couple of seconds, and it smoothly (and with no giant scary lightning-bolt arcing like it usually does) brings the output filter caps in the charger up to within .1v of battery pack voltage. Then I remove the dongle (the output caps discharge some, but it is very slow) and plug the charger directly in to the battery (again, with no big fat arcs or other 'splodiness) and start charging.

I just did this with five brand new A9 chargers in a row and ran them all up to 1000w with no failures. I could not have done that at Barber. I will run them all through a couple of full charge cycles and see how things work.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

More batteries arrived today, and a new popup. After getting all of our stuff wet at Barber, we are finally spending some $ on good popups and letting go of our flimsy $99 Wal-Mart specials:

http://www.carolinahondas.com/members/roger-albums-stuff-picture6630-popup1.jpg

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

How about something like this??

https://www.dropbox.com/s/gf1ly0mirgt6g … G.pdf?dl=0

https://www.dropbox.com/s/qsxd3ktlbhbm8 … 6.pdf?dl=0

Re: "Racing" the Duff Beer Electric Car

Those would work, but then I have to do cell management. That charger would require something that would balance 36 cells, which is an expensive battery management system. The cheapest/dirtiest form of cell management that I can find is a balancing board ( http://www.batterysupports.com/44v-48v- … p-268.html ), but those only go to 24 cells, which would leave me electrically breaking up battery packs to charge them, so I'd have to use a 12s battery balancer and three lower voltage chargers for each battery pack.

Craig is working on building a battery balancer that would probably work well with those chargers, but I don't really want to lean on him to hurry it up since I'm not paying him anything. If he gets something built that will handle 4Kw and 36 cells and doesn't cost very much, then those chargers are probably what we'll be using.

I have a 48v 12s eBike charger and 12s balancing board on order so I can test them, but it's still way more expensive than drone chargers, and the last balancing board that we tried exploded. They aren't really designed for taking them on and off of batteries continually.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

Based on what you are seeing now do how balanced are the cells staying? You may not need to balance them on every charge cycle if they are reasonably matched. That would reduce how many balancers you need.  Also if you don't try to charge them to the top amount you may lesson the need for balancing on every charge.

Re: "Racing" the Duff Beer Electric Car

Unfortunately we don't have enough information to say. We've only turned 44 laps on the new batteries and we don't log cell voltages. I did see several that were over .1v off in a pack after one discharge, which could be bad if not managed. We never charge them all the way up or drain them all the way down. We stay between 3.2 and 4.1v. Also, they are not very well matched. I've pulled them out of four different vehicles, so they are from different lots and are in varying conditions. I also didn't keep track of which batteries came from which vehicle, so within one pack there can be cells from three different vehicles.

The only EV's that I see that don't manage cell voltages are LiFePo-powered, and that chemistry is a whole lot more tolerant of abuse. Nobody that I know of is running big LiPo batteries unmanaged; the failure modes are too catastrophic. That's not to say that we haven't considered it, but I'm not comfortable running these batteries without some type of cell management.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

Well, That is about all I can contribute. If you want the contact info for the people that quoted me the battery chargers let me know. You would order those directly from the manufacturer in China. The lead time is about a month according to the documentation.

If I get back to the east coast in time for the CMP fall race I'll bring a generator.

Re: "Racing" the Duff Beer Electric Car

Thanks, I'm guessing that we'll be using something like that whenever Craig gets his balancer sorted out. I'm really looking forward to Craig getting his stuff ready so we can race against another EV.

Everybody grab your brooms, it's shenanigans!

Re: "Racing" the Duff Beer Electric Car

rmcdaniels wrote:

In our limited practice at Barber, they tended to discharge evenly.

Not really. Within 10mV is "even"; we're getting them way out of balance discharging them so rapidly. The more we do it, the worse they'll get. We're happy to get hundreds of cycles from them, whereas Chevy needs thousands of cycles over a decade.

Ricky tried one at Barber and it blew up...

I found a reasonably understandable engrish version of the instructions. They were very clear on connecting each cell, individually, in order. Or "the smoke will be generated". :-) Cell 13 was connected out of sequence for a millisecond and it fried the balance circuit -- the resistors for sure, the chip most likely.

...inrush current problem ...

And that problem apparently extends beyond vaporizing traces and capacitors. There's research that shows cells within unbalanced packs can actually reverse polarity on those spikes. They were investigating why BMS components were failing.

Using a raw Cisco 4500 PoE feed can work, but there has to be a current limiting regulator. Craig's playing with one I dug up that's pretty basic and cheap to build -- the main CC FET is the only special part, 'tho we may want to use a single chip "current sense amp" instead of doing the calculations for op amp feedback. (and those things can handle in-rush limiting ramp up) If you attach the PS with a limit resistor (I had some 10ohm 100W with me), it'll work perfectly. But it'll take about a week to charge. ;-) If you bypass the resistor after connection ("pre-charge" style), it'll also work... by dumping everything the PS can because the cells will happily soak up over 300A and the alarm light comes on. Of course, that's with zero per cell balancing or monitoring, which will end up boiling electrolyte. (I don't think those LG cells can actually burn -- "vent with flame". I've seen EV West overcharge the hell out of similar packs.)

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