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Author Topic: Current Limiting while Riding  (Read 423 times)

Kocho

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Current Limiting while Riding
« on: April 05, 2017, 11:01:51 PM »

I'm curious whether the "Batt Dischg Cur Limited" message that we see in our log files appears when we attempt to ask for more current than the bike is willing to supply? Or does it happen for other reasons, regardless of how hard I'm riding? Looking at my logs, sometimes I don't see it for many minutes after I start riding, but once it appears, it keeps appearing every one minute until I stop riding... And yes, it does appear more often at lower SoC, but there does not seem to be some "magic" threshold (e.g., I sometimes see it above 80%, sometimes I do not see it below 80%).

Also, the "limit" is not always progressively lower as the SoC gets lower - sometimes I get 97% of max current at 60% SoC (so only 3% reduction in current), sometimes I get a bigger reduction even at higher SoC... And at lower speeds the reduction is not necessarily smaller: at 2000 RPM I might see 77% while at 4000 RPM 87% (i.e., I got 23% reduction in power at low RPM vs. only 13% at high RPM); and sometimes it's the other way around more reduction at higher RPM than at lower. Seems kind of random, probably is taking into account temperatures, cell balance, etc., but I can't tell a pattern related to MinCell voltage for example (and the log does not seem to list cell balance)...

« Last Edit: April 05, 2017, 11:04:51 PM by Kocho »
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'15 Zero SR

hubert

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Re: Current Limiting while Riding
« Reply #1 on: April 06, 2017, 12:31:59 AM »

I looked at this quite a few times. It seems to appear every minute (the same rate as the riding log) when the MBB calculates that if applying the max allowed current (7C) the cell voltage would drop below the minimum limit. This depends on actual SOC but also on internal resistance, which is a function of battery temperature. This resistance may be also "recalibrated" depending on actual voltage drop caused by the battery current. Kinda extrapolation.

However, it seems strange because in my case, the 100% 7C is 690A, but the actual logged battery current never comes near to this value, even at almost 100% SOC and maximum speed on the trafficless highway. This 7C would mean instant power output of about 75kW which is way more than the rated max power.
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2014 Zero S
Velomobile "Quest"
Mitsubishi i-MiEV

rayivers

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Re: Current Limiting while Riding
« Reply #2 on: April 06, 2017, 02:06:10 AM »

Having owned two 2.8's (which are surely the current-limiting flagships of the Zero line) for several years now, I encounter noticeable limiting at every throttle twist and SOC level.  It seems to me like two separate limiting functions may be occurring simultaneously:

a) BMS limiting, determined by SOC, controller current demand, and (sometimes) pack temp; and

b) MBB / Sevcon limiting (as seen in the logs), which I believe may be used for some or all fly-by-wire throttle functions, modulating battery-current demand, and (sometimes) thermal strategy.

I think the non-thermal BMS limiting is a long-time-constant function, taking place slowly as the battery drains and preventing controller demands from taxing the battery.  The MBB/S limiting is much faster and (IMO) used for a number of functions, almost like a controller subroutine that continues to run after being initially called.

All just the usual Zero-owner guesswork, FWIW.

Ray
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'14 Zero FX 5.7 (now 2.8, MX), '14 Zero FX 2.8 (street), '08 YZ250F, '82 RM250Z, '75 MR175, '74 CR125M (175cc)

nevetsyad

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Re: Current Limiting while Riding
« Reply #3 on: April 06, 2017, 04:14:00 AM »

I need to look at my logs when my bike comes back from the shop. I've been having problems going over 60-70MPH at times on my 2015 SR. No errors or alerts, sport mode or custom, no matter what, when below 70% of so SOC, I can't get over 70 or so MPH.
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2015 Zero SR (4+ months in the shop), 2016 Zero S (Random freeway shutdown, heading to shop soon)

Kocho

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Re: Current Limiting while Riding
« Reply #4 on: April 06, 2017, 04:33:41 AM »

That's a problem. Mine does reduce top speed and torque with reduced SoC, but even at 50% I can easily hit 90mph and acceleration, while not up to the max at full SoC, is still pretty brisk. You should have plenty of speed and power at 70% SoC in Sport mode, much more than in eco mode at any SoC.

I need to look at my logs when my bike comes back from the shop. I've been having problems going over 60-70MPH at times on my 2015 SR. No errors or alerts, sport mode or custom, no matter what, when below 70% of so SOC, I can't get over 70 or so MPH.
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'15 Zero SR

JasonS

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Re: Current Limiting while Riding
« Reply #5 on: April 21, 2017, 10:51:04 PM »

I've been seeing similar issues on my 2015 SR. (Including the Current Discharge Limited log entries, or whatever the exact language is).

Question to all of you - did those of you experiencing this problem recently have your bike in and possibly get a software update?

My problems started after an onboard charger failure (literally on the way to have it repaired, so before any possible SW updates), so I'm not sure if SW updates have anything to do with it or not, but I did get an update since the failure.

Just posted this: http://electricmotorcycleforum.com/boards/index.php?action=post;topic=5386.0;last_msg=38587

Here's the bulk of the info from that post that's relevant to this thread:
Quote
Recently, my onboard charger failed (Dec '16).  It took about a month to get it to the dealer (thanks to Christmas vacation schedules and such), and during that time my bike sat at ~60% SOC (that was how high it got the night the charger failed.).

When I rode it to the dealer it had decreased to about 56%.  It was chilly that day - 40's I think, but bear in mind I ride year-round, 50miles round trip, sometimes in even colder weather (but usually hotter!)  I experienced something that has never happened to me on the bike before. The power of the bike kept dropping.  At the start of the leisurely 30-35 mile ride, I had to do about three or four miles in interstate.  My top speed was fine - maybe I was having a hard time at around 75 or 80, but I really wasn't trying to go faster. (I wanted to take it easy, because it was chilly, and was longish ride to start out a 56%).  The rest of the ride was back roads as I wiggled over to Conroe, TX, which I anticipated doing at mostly 50-60mph.  Over the course of the trip, though, my top speed got lower and lower, finally limping along with a max speed of ~35mph, with an associated loss of power/acceleration (i.e., I wasn't hitting a limit at 35, it was just running out of oomph.)  I think my SOC on arrival was around 20-25%, but I don't have that written down. 

Since the charger incident, I've been back in the dealer a few times for follow ups on this, and it still hasn't been resolved, though sometimes it's not so pronounced. 

Before this incident, I've had the bike down into the teens, (and even single digits once or twice!) while exploring the limits of the bike, and not seen this kind of behavior.  Conversely, last Friday (Apr 14) I got home from my commute with 15%SOC (dramatically lower than normal for my 50mile round trip, which used to land me home at ~35% pretty consistently), and the bike was topping out at 25mph.  That was scary.  I was having a 'Fred Flintstone' moment, where I had a strong urge to help paddle with my feet!  (The least exciting drag race ever: I pulled away from a stop sign, went full throttle, and by the time I got to my street, about 1/8 to 1/4 mile away, I was bumping along at 25mph.  Still full throttle.)

Anyway, when this type of powerloss/speed limit is imposed, it feels quite different from the 'governor' type limit.  When you crank on the throttle, it just feels like the bike's power output sags.  Almost like at a certain point (which moves as it gets progressively worse), increasing the throttle further causes a slight reduction in power, and then further movement has no effect whatsoever.

I'm still collecting logs and data as I discuss this with Zero.  They're telling me this is normal, and I'm saying "BS!"  I think I have a new battery pack in my near future, or at least a cell replacement or two, because at this rate (I'm currently at 197-- miles, just over two years old), there's no way it's gonna make it to five years/300,000 miles.  [and still be 'better than 80%']
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2002 BMW R1150RS
2015 Zero SR
Houston TX

Kocho

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Re: Current Limiting while Riding
« Reply #6 on: April 21, 2017, 11:53:26 PM »

On my '15 SR I do experience decreased performance at lower SoC, but I don't think as dramatic. I avoid riding it below 40% due to the decreased performance and also it is not great to discharge it too much if possible. But I've ridden it a few times in the teens and once or twice down to 0%. Near 0% SoC the bike indeed limps pretty slow. But at 15% my recollection is that I was going considerably faster than the 25mph you mention. In fact, I think I was doing decent highway speeds at under 10% SoC trying to reach my office and charge there - I must have been doing at least 60mph I think. On that day I did over 80 miles of mostly highway riding on a single charge, much of it around 70mph and I barely made it home limping at the end with charge in the single digits and eventually down to 0%. But it was warm weather - maybe the bike throttles down even further in cooler weather?
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'15 Zero SR
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