Sudden drop in State of Charge.

[FreepZ]

Funny thing happened to me on the way to work today...
The State of Charge went from 20% right down to 0% in one go!


The bike lost power, but I had enough speed to get off from the fast lane onto the shoulder. Whew. After restarting the bike, the SoC was still 0%, but the bike was able to move. I got off the next exit, whipped out my phone, looked up the nearest charging station, which, as luck would have it, happened to be a BMW dealership that was a 1/4 mile away.

I got there, plugged in, and was immediately surrounded by a bunch of BMW mechanics who had never seen an electric bike before. I had a chat while waiting for the bike to get some juice.

While the bike was charging, the console was displaying a B55 error, which means:

B55 | SERVICE REQ'D B55 | SYSTEM FAULT B55 | Battery Fault: SOC Mismatch > 30%

I wonder if one of my batteries just conked out. Or if they got unbalanced because of the cold weather and me not charging them for the past few days.

In the end, I was able to get to work after waiting for the charge to get back up to 10%, and now the bike is charging happily in the office garage.

This is the first time I've experienced a sudden drop in SoC. Has anybody else had an experience like that?

Apparently, yes:

At some moment the battery level showed 39% and on accelarating on to the highway the bike suddenly dropped dead. I saw 'Service required B40'. I powered off and started again. Had to do this 3 times on the way home.

Battery level at 39%. Service required B40 BMS Back in Idle Mode. Reset by power off/on. . Rode back, battery level went on 0%. Back home system fault B55 appeared and remains in the display.
Battery level was 0% and required charging.

[Shinysideup]

Yes, this has happened to me about 3 times, but when the SOC is down around 10%, although IIRC, one of the instances was around 20%.

I associate it with colder weather and my demanding full power (WOT).

Generally, pulling over and recycling the bike allows me to make it home or to a charge station, even though the SOC shows 0%. Disconcerting, especially at night in the rain.

My "fix" for this is to be very gentle with the throttle when nearing 20% SOC.

[JeffK]

Yes, I had it a few times.
As it is very bad to run the batteries flat, the system shuts down if too much power is drawn.
This can happen on the track even with 30% SoC
There will be some warning signs before that, but you might not notice.

If my SoC gets below 20% I let go of the throttle and don't draw more than 8-9 kwh, as I hate walking.

[cybergodzilla]

I've taken mine to San Diego, Lake Arrowhead, Hollywood, Long Beach, Huntington Beach, Newport Beach, Laguna Beach, Temecula, San Bernardino, Ontario. So many places to list. My similar experience started in Corona continue to Huntington Beach arriving with a 30% charge. Hours later starting it to go charge it showed 15% and I don't trust it under 10%. That means I had 5% juice to get to the nearest charger 5 mi away.  =O Riding under 25mph on the bicycle lane, got to a station with 9%. Then as it charged, it jumped from 85% to 100% to finish charging? On my trip back to Corona at 29% and forgetting to charge overnight, I woke up to see drop again to 14%. My guess is it is a false reading caused by the cold. =/

[frodus]

I've had it twice.

As explained by Brian, if you're at low SOC, and you pull amps enough that the voltage on the pack drops too much, the BMS snaps to 0% and shuts you down. I just pulled over, turned off and removed the key, waited 5 minutes for the voltage to come back up and the BMS to sort of reset, turned power on and off I went.

So when you're under I'd say 20% and you start to get warning lights, go easy on the throttle.

Its just a safety mechanism so you don't fry your batteries by overdischarging.

[kingcharles]

I have become very good at "throttle control" at low SoC, so I can ride down to low SoC without it cutting me out. I does drop to 0% sometimes but then the bike will not shut off the drive and I just continue to ride. I use 1% per kilometre to keep track of how far I can go.
But I had already 5 years practice on my Vectrix which had the same behaviour  .

[Shinysideup]

I use 1% per kilometre to keep track of how far I can go.

Interesting: I use the figure 1% per mile, if I'm hypermiling at low speeds (under 30 mph). But it's sometimes a little less than that, so your more conservative figure is probably safer.

[GSX750ES]

I use 1% per kilometre to keep track of how far I can go.

Me to

[Shinysideup]

I have a question that arose last night when my SOC was around 60% and dropped suddenly to zero. The pack was cold; shortly after starting up and traveling about 10 blocks at city speeds, I cranked it to WOT a couple of times in getting on the freeway, (OK, while trying to keep up with another bike. I felt the slight glitch (like an ICE missing) before the green lights flashing and the RECHARGE NOW warning came up. The bike didn't shut off.

I was about 10 miles from home, late at night, on a dark freeway and tried to keep my speed as low as was safe with following traffic. I made it all the way home with the recharge warning lights flashing the whole way.

When I plugged in the charger, it showed 7+ hours of time remaining on the charge, consistent with the reported zero SOC and a 120V charger.

My question: If I had 60% SOC when the dash dropped to zero, and if I was able to travel 10 miles at zero charge, then the SOC wasn't ACTUALLY zero. But then why would the charger report that the full charge time was needed?

At what point during the charge cycle would this discrepancy get reconciled and what, electrically, is going on to create the discrepancy and to correct it? This question is academic only, since it has no practical significance.

Although it WOULD be handy if something could be done to cause the dash to report the ACTUAL SOC, after it shows "zero" so I'd know if I could get home!

My suspicion, from reading the previous posts, that this is a protective function when one portion of the pack gets too low. I just wish there was a way to override the erroneous "zero SOC" to get a true reading.

[kingcharles]

My guess is that your pack already has quite some cycles. The internal resistance will be a bit higher now. Combine this with the cold temperature of the pack and you will see significant voltage drop during WOT.
The BMS kicks in when a certain threshold is crossed and you are just reaching it earlier now.

I expect that the actual remaining SOC after such an event will still be around what was shown just before the drop. So my advice is to to memorise your average mileage per % of charge and use that to calculate roughly how far you can still travel.

The only thing I am not sure about is how Brammo programmed the battery degradation into the software; will a full charge stay 100% but with less mileage per charge or will your bottom charge %'s will become useless...