Volt Blocher

Well, it's been a long time between posts but here we is again.
Updates: There's been battery failures, the battery balancing system actually got recalled by the manufacturer...the vehicle still tries to dart into the oncoming lane, attracts valdalous whackos, won't steer straight, and bounces up and down enough so you can hear the seats creak. Despite all that we've put on over a thousand miles in the last six weeks. What can I say, we're kinda stupid that way.
As mentioned earlier I've been working with a guy in California to 'morph' his existing battery charge management system into something that will work with the AGM Lead Acid batteries in this type of car. His name is Brian Blocher, so since the board progressively bypasses current to 'block' the voltage from getting too high the product is called Volt Blocher. Clever, huh?

Here's the first functioning prototype I've built.

The big white things are resistors the dissipate the excess heat (current) to keep the peak voltage under control during the charging cycle. Even a couple tenths of a volt too high can shorten the battery life considerably. The switch is so you can set an appropriate voltage for a given temperature range: Under 50F, 45-80F and above 75F respectively. There is one board for each battery so I've built seven of them. Three worked correctly right from the beginning, one is real close and three others are off by a bit more. Troubleshooting is ongoing.

I'm very glad I got three done since we had two batteries that really needed them and one that wouldn't mind a little help. Both got 'swapped in' from the other car when we had two of the originals fail (both still awaiting warranty replacement) and since they have a little less capacity (mainly from being older) they would charge up sooner than the others and begin to vent off gas as the voltage gets too high. The electrolyte lost that way cannot be replaced. So, the battery would loose capacity, charge up even quicker, vent more, lose capacity...you get the idea. The road to ruin (kinda like the US economy...)

More to come on this topic as the rest of the boards get put in place.
In the mean time, it's driving to work and school and everywhere local.

MiscUlanEous Factazoids

Big testing excitement today:

1.) Under any sort of real world load it's become obvious that one of the batteries is failing. Only good for 6-8 miles now and that's without any really high current loading (no 300A blastoffs or hills.) We captured one of the failure events with the datalogger and sent the file off to Sean. He agrees it's bad and apparently it will be warranted. May swap in a battery from the other car to get this one back on the road.

2.) Load test: we went out with four people on the car. Not a long drive or any hills to speak of, but the people weren't exactly lightweight either. It wouldn't hit 45 with four of us in there. Scotty to Bridge: She's givin'it all she's got captn'!

3.) The specs for the new battery management board are pretty much set and Brian may have first prototypes available by mid month. Way to go! Update: Prototype boards arrived and are reported to work exactly as expected. Should have final parts in two weeks. Cool.

Always: Flies in my pudding

There's always SOMETHING...

The battery monitoring system has been acting whacky. It reports the last three batteries are continually in 'overcharge' state. The first battery (the added non-standard one) is reported as being 13.2V (which it is) while the others are at 13.4V (which they are) and that the second battery is at about 13.8V (which it isn't, more like 13.6V). Sounds like small differences I know but 0.1V is a big difference in terms of State Of Charge (SOC).

Add to which it almost always shows SOC at 100%, even when the batteries are half discharged. The current indicator shows random stuff and the temperature indication has been variable. We spent part of the afternoon re-routing wires to try and improve matters (assuming it's some kind of electromagnetic interferance problem) and putting in some quick-disconnects to make resetting the system easier. Attaching the sensor modules to the top of the batteries should help with the temp reading. We'll see how it goes.

Now add the fact the Battery Equalization system (BattEQ which is separate) has just been recalled by the manufacturer. Bummer. However this will be less of a loss than you might imagine since the large voltage difference between the first and second batteries causes it to freak out and say: "that difference is too big for me, I'm turning off" so it hasn't been all that much use anyway.

Brian Blocher has a new version of his VoltBlocher product out that is intended for Lead Acid 12V batteries. I'm going to see about getting a set of these and getting some modifications done to them to replace the BattEQ unit. More on this later, it's a pretty significant price/performance breakthrough on the battery management front.

A week of "real"

Yes there really is a back seat and we really have had real people in there. Ya stuff several of the admiring crowd in there and...it still moves, really! There's just some rubbing sounds as we have the springs set fairly 'soft' and it kinda waddles under full load.

The big news is that after we came back from a week of vacation we ended up driving it to work and many trips elsewhere for basically the entire week. A slight increase in the slack in the emergency brake cable system greatly reduced the rear brake heating. There's still a little of that so a bit more tweak may be required. Still 20 trips of over 6mi. each and four over 13mi... ya gotta say overall it's working pretty well. Good enough for the real world.

When the battery temperature is around 40deg.F the top speed is around 42. when it's more like 60deg.F it'll crawl all the way up to 44mph! Of course if there's a hill or even an incline we're talking more like 38-40. Fortunately I drop off the car-pooler during the early section of the trip to work when the max posted speed is only 30, that way I don't have to face the (mild) hills and 45mph posted sections with more than one in the car. Overall it seems to work well enough for the commute, especially (oddly enough) if the traffic is fairly heavy and thus a bit slower.
Nobody has honked or had a hissy-fit...yet.

We still have the pogo-ing front end. Sean thinks it's probably the tire. I gather the quality control in terms of roundness is, um, lacking. I put a video camera on a stick so I could hang it outside the car while moving. The video came out fine, but you can't really see anything conclusive. Guess I'll try swapping out the tire.
The batteries, charger and battery equalizer systems seem to be working OK, though there is no way you would know this from looking at the battery monitoring system. It continually complains that at least three of the batteries are in constant 'overcharge' condition and that another is 0.5V higher than the rest. The SOC meter (State of Charge - battery level) almost always shows 100%, though sometimes it will drop to 95% when we have gone 12 miles (about half the useful range) and the current sensor will still show 29Amps one minute after you have pulled to a stop. The technical term for this is "Boogered."
Gonna have to put some work into that. Having $400 worth of monitoring equipment that gives you no useful information will eventually serve as an irritant. Since we'll have the battery compartment all apart to go after this problem we should get a few useful pictures. Later.

Straighten UP and fly Left

One of the recent posts on the Yahoo group is on how well the vehicle coasts when you let off the accelerator pedal.
Hmmm, I am definitely NOT having this experience. It will coast a block on the flat (starting at 25MPH) but certainly not two.
I have been trying to diagnose what is going on:

The whole vehicle heads down the street slightly 'crabwise.'
Noticeable but not high pressure on the wheel toward the right is required to get it to go straight. (ie: it wants to wander toward the left all the time.)
The Steering wheel is not straight. Completely straightening the wheel produces a mild left turn. The opposite from what you would expect from the above.
A fairly steeply crowned road (right slope) can get it to go straight.
The front wheel/tire is not very round. Since the beginning the
whole vehicle does a hobby-horse up and down thing that is
especially noticeable around 12-14 mph. It is not the rear
tires as they have been replaced and the wheels balanced. We
have looked at the rear wheels while going to see if they
run true. I thought it might be flatspotting when parked but
the problem is still there after a 10 mile drive on a warm day.

We have checked the steering wheel vs. wheel direction. Using 6ft. long straightedge the wheel, steering wheel and vehicle center-line appear to match up.
Sean in one of his lighter moments suggested a front end alignment. Pretty funny actually.
Brake drag: There is quite a bit of brake drag (I assume) on the right rear wheel. To the point of having the wheel hub quite warm after an 8 mile drive. Being on the right the drag would cause the vehicle to caster to the right. Instead it tends to go left. If anything the drag problem is helping keep it running straight. Yes we have multiple problems.
The vehicle seems pretty stable at speed and tracks well in high speed corners (40MPH).

The investigation is ongoing.

Getting up to speed

A 'basic' 72Volt Xebra SD (Sedan) is good for about 35MPH on the flat. Maybe a little more but not much and it drops to 30 on a mild grade. The GPEV (Sean) 84Volt version is good for a solid 40MPH on the flat and will hold 35 on the same grade. We wanted more of course. There are 45MPH roads on the way to work.

First thing to check was the speedometer. They're notoriously innacurate on Xebra's. We went out and checked it against a car with a known speedometer. Surprize! It's accurate within one MPH!

Second, there's some drag and tracking problems. There will be another post on that.

Third was to change the gearing (in effect) by putting on slightly 'taller' tires.
See the last part of the post below for how that works.
We took off the 145/70R12 tires and mounted 155/80R12. The new ones have about 8% greater circumference.
Results: One mile to get up to speed and then one mile with the pedal all the way down. Same course and full charge in both cases.
Before: 41-Maybe-42MPH
After: 43-Maybe-44MPH
Pretty much what you'd expect. We also ran it up our 'test hill' and couldn't see any speed difference (controller is in current limit mode). I'd say this counts as a success.

We have noticed that after it cools down from being charged the pack shows about 92-93 volts. The controller allows a maximum of 100Volts. Looks to me like there's room for another 6V battery. 90V Xebra anyone?

Fun times: The Initial Drives

We like our parking TIGHT

So, so. how does it go?
Pretty darn good. Everything about this car seems to be a generation ahead of the other (red) one. Interior, fit and finish, doors, accessories, instruments. You name it. The powertrain in the other car is arguably more advanced, but this one seems to work better in the 'real world'. Well, excepting the loud klunk that happens no matter how you finesse the accelerator pedal. That's not what I'd call an improvement.

There are power door locks and one key works for everything. There is some motor whine but is's not real objectionable. Something is buzzing against the motor or gearbox, you can hear it rattling at certain speeds, but I'm sure we'll figure it out.
We went out for several drives with charging in-between. Getting the batteries broken in without damaging any of them. The pack doesn't look really balanced as yet. Hard to tell if it's real or just flaky results from the PakTrakr battery monitor (we've had problems before...)

With the Sean's high-zoot 84V system installed the car cruises at remarkably low current readings around town. You can get pretty decent accelation while still staying below 100 amps. This should lead to pretty decent range and battery life. Cool.

It's still voltage limited at higher speeds (above 35 mph) You can see the current drop off as the speed builds even with the pedal to the floor. Electric motors also act as generators. At a given speed there is a certan voltage the motor would generate. It's the difference between that voltage and what's available from the batteries that allows current to flow, and therefore torque generated to accelerate the car. As the 'generated voltage' (back EMF) gets higher as you go faster, the voltage difference drops until you can't accelerate any more, so you reach a steady state speed.
People tend to think that since the motor isn't all that powerful you should put smaller wheels/tires on the car to improve hill climbing ability. Kinda like with a gas car where if there isn't enough power available in second gear, you drop down to first and floor-it. DC Electric cars work exactly the opposite: The maximum torque is generated at the lowest RPM. To get the electric car to pull harder you shift up to third and floor-it, You get more power right up until you reach the maximum current limit on the controller. We're going to do approximately the same thing (gearing-wise) by putting taller tires on it. More on this later.