[Tesseract]

Originally Posted by dladd

I got an email back from Dimitri confirming what I suspected, the EVDisplay will NOT track such a low current draw, and as such the traction pack could be slowly drained over days without knowing it.

Don't be too hard on him - being able to resolve 0.1A out of 1000A requires circuitry with 0.01% precision, resolution and accuracy (and 14 bits of dynamic range if digitized) which is pretty much impossible to come by in the high noise environment of an EV. Hall effect sensors are an inexpensive way to make isolated current measurements, but they are typically only good for about 9 bits of resolution (that would be 2^9 or 512 steps). That is to say, at best you can hope for +/-2A out of 1000A.

It is possible to make higher resolution/accuracy current measurements in the face of so much noise but it requires a precision shunt feeding an isolated instrumentation amplifier. This will set you back a solid $200 in parts - I know, because I built one for our dyno...

[dladd]

Originally Posted by Tesseract

Don't be too hard on him - being able to resolve 0.1A out of 1000A requires circuitry with 0.01% precision, resolution and accuracy (and 14 bits of dynamic range if digitized) which is pretty much impossible to come by in the high noise environment of an EV. Hall effect sensors are an inexpensive way to make isolated current measurements, but they are typically only good for about 9 bits of resolution (that would be 2^9 or 512 steps). That is to say, at best you can hope for +/-2A out of 1000A.

It is possible to make higher resolution/accuracy current measurements in the face of so much noise but it requires a precision shunt feeding an isolated instrumentation amplifier. This will set you back a solid $200 in parts - I know, because I built one for our dyno...

certainly not meaning to be critical of the EVDisplay! It's doing exactly what it was bought to do, track my battery usage in daily driving use. I'm just pointing out that in my case, I have no mechanism to prevent a slow draw from draining my very expensive cells to zero as the car sits right now. And no way to even know if it's happening!

I fixed the shifter temporarily with zip ties, and ordered a new shift cable bushing from ebay for a more permanant fix... Seems it's a very common Saturn problem, so common that there's a guy on ebay with the username saturnbushingman selling the part to fix it.

[Dave Koller]

The AUX battery you are using can't me much in amp-hours (not cranking amps but amp-hours) every time you apply brakes may bring it down quick - but the iota should be covering that when running. When you were talking about a volt meter for the battery - you might consider an amp meter (on the 12 volt side) to monitor some of the discharge - it can show a short or just sitting there can show the draw and you can disconnect things one by one to find the really big draws.... More of a clue as to what is pulling down the battery.

[dladd]

Originally Posted by Dave Koller

The AUX battery you are using can't me much in amp-hours (not cranking amps but amp-hours) every time you apply brakes may bring it down quick - but the iota should be covering that when running. When you were talking about a volt meter for the battery - you might consider an amp meter (on the 12 volt side) to monitor some of the discharge - it can show a short or just sitting there can show the draw and you can disconnect things one by one to find the really big draws.... More of a clue as to what is pulling down the battery.

that's a good idea, I would like to put an ammeter on the 12v side. One of these days... In the mean time, I've still got the DC/DC hooked up full time. I figure it's fine for now since I'm driving it every day, there's little chance of it bringing down my traction pack.

Got the shifter fixed today, my zip ties worked OK, but did pop off a few times in the last week. Always when shifting into reverse, so no big deal (since that pretty much means I'm backing out of a parking spot). I used the Delrin bushing made by saturnbushingman on ebay, easiest fix ever! According to those in the know, the next failure will be the plastic cable end, but there's a pretty easy fix for that too when it happens.

New question... going back once again to my problem of excess driveline backlash. How much is too much? Right now if I put it in second gear (my normal starting out gear) I can turn the motor shaft back and forth by hand about 45 degrees before being stopped by the wheels. The movement is in the transmission, as I can visually see that the CV shafts are not moving. Is this normal, or is this my problem? I'm trying to decide if I need to replace the transmission, or look elsewhere for my problem.

[dladd]

No input on the trans huh? I suspect it's fine, everything else about it seems ok. Good shifting, fairly quiet, and it's smooth as long as I gently preload it before taking off. Downhill starts are the toughest to avoid the dreaded oscillation. I think I need to add a motor mount to the bottom of the motor on the passenger side (instead of on the midline of the motor where it is right now), and I'd like to replace all the suspension bushings to eliminate any slop in there. It's a crazy suspension setup (to me, anyway) where the sway bar doubles as a lower control arm. I've never personally seen a car like this before, maybe it's common but it's new to me. Seems like it is really dependent on the rubber bushings, which of course are almost 20 years old now.

anyway, now that school's out and I'm not shuttling kids to and from school, my daily mileage has dropped to the point where I'm only charging every other day or so. Car's running quite well, still more finicky than I'd prefer, my wife doesn't like to drive it at all... I find it quite fun, and it sure performs well in the heat! I have not missed the air conditioning at all, the fact that it's only really used locally makes it workable. I'm never in the car for more than 30 minutes at a time. Who cares if it's a bit hot?

My "plan" was to do a pretty major teardown this summer to replace/upgrade the clutch and rebuild the front suspension, but I've decided not to do it for now cause the car is so good in the summer. I'd rather wait till coooold weather comes back instead (which really drops the battery's performance), so I'll wait till this winter... unless something else breaks and forces the issue before that. In the meantime I've settled on a happy medium of 500a battery and 650a motor side. It's plenty of performance to keep up, and only slips the clutch if I do something stupid (like a full throttle launch in 3rd gear).

nothing else to report, just been driving every day!

[dladd]

arg. my charger died last night. It won't power up, nothing looks to have gone wrong on the car side, the MiniBMS powered relay is still on so no cells overvoltaged or anything, but the charger was off and had only put about 10ah into the cells overnight before going off (about an hour of charging).

I do have a second charger (charges at 5.8a) but this is the third time in the past 6 months that I've had something unexpected kill my charging overnight. Once was a brownout that shut off the charger, one was a dead 12v battery that caused the MiniBMS to cut power to the charger, and now this. Not a major deal in that I do still have a gas powered car, but the reliability of charging is a significant issue for a car as a daily driver.

It's a cheapo charger, looks a lot like this one, and as far as I can see there is no fuse. There must be one in there somewhere though, right? I'll pull it apart and look inside when I get the chance.

Anyway, it's time to evaluate my charging options! I've been wanting to go higher power (I'd like to get around 30a into the batteries) and get J1772 compliant so I can take advantage of the ever increasing number of public charging stations around here, time to get serious about it.

[JRoque]

Originally Posted by dladd

Anyway, it's time to evaluate my charging options! I've been wanting to go higher power (I'd like to get around 30a into the batteries) and get J1772 compliant so I can take advantage of the ever increasing number of public charging stations around here, time to get serious about it.

Hey. The Evnetics guys are working (or planing) on a charger. I bet it will be solid, like everything else they put out. Alternatively, you can search this forum for an "open source" charger and build your own.

If I had to buy one, I'd look for one that's isolated, first and foremost. Then add safeties like auto turn off based on voltage, current and time settings.. everyone forgets the time variable, don't they? Externally controlled is nice too but only so it terminates charging cycle before that "time" setting or current/voltage. None of that BMS controlling when charging starts, how long it goes for or setting of voltage/current levels.

JR

[dladd]

Originally Posted by JRoque

Hey. The Evnetics guys are working (or planing) on a charger. I bet it will be solid, like everything else they put out. Alternatively, you can search this forum for an "open source" charger and build your own.

If I had to buy one, I'd look for one that's isolated, first and foremost. Then add safeties like auto turn off based on voltage, current and time settings.. everyone forgets the time variable, don't they? Externally controlled is nice too but only so it terminates charging cycle before that "time" setting or current/voltage. None of that BMS controlling when charging starts, how long it goes for or setting of voltage/current levels.

JR

I am not going to build my own, but I am somewhat looking into the EMW charger. It's a little bit overkill at 10kw, but looks good. Not isolated though, I believe. I'd love to see what the Evnetics guys put out, but that's probably too far away for me. There's also rumors that Synkromotive will package and sell a kit to work with their controller to handle charging, but details are impossible to get. Not sure of the timeline on that one either...

in the meantime I'll just keep on plugging in every chance I get at 5.8a. I'm on a flat metered rate, so it doesn't matter what time of day I charge (on a high mileage day, I cannot fully recharge overnight at 5.8a, I need to do some supplemental charging during the day).

[dladd]

i feel like I want to post a monthly update, but quite frankly there is nothing to say...

I've been driving it, charging it, and driving it. Then charging it. I have not yet gotten around to a whole bunch of little things, I'm starting to think I never will.

Still getting by with just the 5.8a charger too, pretty much just always keeping it on the charger if I'm not driving. I want a bigger faster charger, just can't quite pull the trigger when I'm getting by OK as it is.

[dladd]

I had a failure today! A wire broke off right at the terminal inside of the small Anderson connector that goes between the charger and the batteries. My fault, they are really not designed for daily usage, and I don't have any strain relief on the wires. With the charger currently out of the car, I have to connect/disconnect the Anderson every time I plug in.

Fortunately my other (dead) charger has the same connector on it, so I snipped it off and wired it onto my working charger. Back charging again!

The kids are back in school, so my mileage is back up to 30-40 miles per day which is challenging to keep up with when my charger only charges at 5.8a. For a 40 mile day I'll use around 85ah, so at 5.8a it takes over 14 hours to charge. Basically it means if I'm not driving, I'm charging.

I've really got to make a decision on a higher powered charger...