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Author Topic: Balance Voltage in Storage  (Read 959 times)

Kocho

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Re: Balance Voltage in Storage
« Reply #15 on: February 13, 2017, 09:14:33 PM »

That logic is sound, and I agree a conservative estimate is safer. You are saying more than 30% SoC loss per month this way. But I think, based on my observations on my bike, the pack is not losing charge that fast. I think the BMS continuous draw is closer to 0.15W rather than to 5W. If that lower figure is close to correct, it would result in about 1% loss of charge per month on an 11kW pack. While I don't know what the exact loss % per month is, on my bike it seems to be closer to 1% per month than to 30% - there is barely any change in SoC reported on the app over several months unplugged...

I've been checking my bike every few weeks and the reported SoC has not budged one bit. If anything it rises a few percent in the hours/days after the bike is shut-off after last use, and then stays constant for the next few weeks. I'll report here again the next time I check my SoC - last night it was 53%, 4-5mV imbalance.

Is anyone seeing faster decline in SoC when unplugged?

I went to go fix that section and realized I shuffled some notes into the wrong section and fixed that.

I did make a back-of-the-napkin calculation, though: if the BMS continuously drew 5W, a 2016 11.4kWh nominal battery would draw down 100% SoC to 0% in about three months.

So, 10% per week is a reasonable figure if conservative; kind of a worst case way to know when to go check on the bike just in case.
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'15 Zero SR

BrianTRice

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Re: Balance Voltage in Storage
« Reply #16 on: February 19, 2017, 11:22:44 AM »

I've updated it again with the 150mA figure and some back of the napkin maths, but suggesting monthly checkups anyway, because we can't say what rate someone is going to get, especially if there's a slow problem.

http://zeromanual.com/index.php/Usage#Storage
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2016 Zero DSR, 2013 Zero DS, 2012 Suzuki DL-650 V-Strom Adv

MajorMajor

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Re: Balance Voltage in Storage
« Reply #17 on: February 20, 2017, 01:47:33 PM »

Can the SoC calculations be trusted after the bike has been sitting for a few months? Is it possible that under load the SoC will suddenly drop from 40% to below 0%?
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Lamac

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Re: Balance Voltage in Storage
« Reply #18 on: February 20, 2017, 03:42:49 PM »

To All of you,

i dont understand this topic,

to store the bike with 100% soc is just killing the battery !

read the comment from farasis battery engineer here in this forum.

if i store the bike at 30%, after 5 month i have still 30% ?

how about this?

greeting :)

lamac
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Kocho

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Re: Balance Voltage in Storage
« Reply #19 on: February 20, 2017, 07:49:00 PM »

In my case the SoC was fairly real. After having sat at high SoC for several weeks, I rode it for 30+ miles to bring it from 80%+ to 50%+ SoC. That's about normal for the kind of riding I do.

It would be good to also monitor the voltage of the pack and the cell balance, not just the % SoC, and to do as much of that as possible while riding.

I don't even know if the BMS is actually consuming anything when the bike is off and unplugged and has been off for some time. Would be good if someone in the know chimes-in about that (i.e., if the BMS remains on or shuts off completely, I know it's on for a few minutes after shut off as I can see the indicator lights on the front of the battery, bit after a few minutes they seem to go dark). The reported losses in SoC are so little, that it might just be normal battery self discharge.

Can the SoC calculations be trusted after the bike has been sitting for a few months? Is it possible that under load the SoC will suddenly drop from 40% to below 0%?
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'15 Zero SR

BrianTRice

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Re: Balance Voltage in Storage
« Reply #20 on: February 21, 2017, 10:35:13 AM »

Let's see how this flies (making this up based on what I've heard):

The most conservative thing you can do is:
- Once a month, take the bike out and ride it down to 20%.
- Charge it back up to 100% to balance cel voltages.
- Ride it some more to get it to 60-80%.
- Put it back in storage unplugged and set a reminder for the next month.

This would seem to me to cover absolutely all the bases I've ever heard. How does that sound?
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MajorMajor

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Re: Balance Voltage in Storage
« Reply #21 on: February 21, 2017, 01:00:49 PM »

Sounds like an absolute nightmare...
Might not even be possible if you live in a cold climate.
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Shadow

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Re: Balance Voltage in Storage
« Reply #22 on: February 21, 2017, 01:39:38 PM »

Sounds like an absolute nightmare...
Might not even be possible if you live in a cold climate.
In cold climate you'd just power your 120VAC Christmas holiday lights off the battery pack. No need to ride the bike.
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MrDude_1

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Re: Balance Voltage in Storage
« Reply #23 on: February 21, 2017, 09:47:19 PM »

To All of you,

i dont understand this topic,

to store the bike with 100% soc is just killing the battery !

read the comment from farasis battery engineer here in this forum.



as great as this theory is.... 100% charged is not at the cell max they're rated at.... and even if you do this "abusive" behavior for years you wont have any degradation that you could compare and measure against the expected best case degradation. while keeping the cells at 4.2 does kill them fast, simply limiting it to 4.15 drops that down significantly... and gives you some overhead.
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BrianTRice

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Re: Balance Voltage in Storage
« Reply #24 on: February 23, 2017, 08:23:48 AM »

I proposed something conservative, not some minimum requirement. Clearly the manufacturer's recommendations are working fine for people so far.
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2016 Zero DSR, 2013 Zero DS, 2012 Suzuki DL-650 V-Strom Adv

Low On Cash

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Re: Balance Voltage in Storage
« Reply #25 on: February 23, 2017, 08:48:56 AM »

To All of you,

i dont understand this topic,

to store the bike with 100% soc is just killing the battery !

read the comment from farasis battery engineer here in this forum.

if i store the bike at 30%, after 5 month i have still 30% ?

how about this?

greeting :)

lamac

Lamac,

Most Lithium cells have a self-discharge rate of 2% to 3% per month, so if you store the bike with 50% SOC, in 6 months it would only lose an average of 15% and therefore the pack would remain at a safe 35% SOC.  While you could store here at 30% you would be getting pretty close to to the critical area. 
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Kocho

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Re: Balance Voltage in Storage
« Reply #26 on: February 23, 2017, 07:35:34 PM »

Just FYI, 10 days later, the reported SoC and cell balance has not budged one bit. Still exactly the same as seen below. Meanwhile, my Zero app has apparently auto-updated on my phone, so I had to attempt a couple of re-connects to the bike (no need to re-pair though). The new app reports exactly the same values as the old one.

Since the weather is warm this week, I'm charging now and will be riding the bike to work a few times, so sorry, I probably won't be providing any more long-term storage SoC measurements off the grid and without charging. But based on the two winters so far that I've had the bike like that, I see no reason to keep it plugged when not in use - mine kept its cell balance and charge with negligible losses.

. I'll report here again the next time I check my SoC - last night it was 53%, 4-5mV imbalance
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'15 Zero SR

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Re: Balance Voltage in Storage
« Reply #27 on: February 23, 2017, 08:12:35 PM »

Thanks for the reply - you might try running that battery as low as you can to get all the cells down and hopefully a fresh charge and balancing might bring them back to specs. Let us know!
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Kocho

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Re: Balance Voltage in Storage
« Reply #28 on: February 23, 2017, 10:05:01 PM »

Low, your reply is probably not meant for me, but I'm curious - why would you recommend to run the battery down low? I thought on a Li battery that's not a good idea and also not necessary, since the BMS in the Zero only does top-balance after full charge. What would bringing the charge low accomplish?

Thanks for the reply - you might try running that battery as low as you can to get all the cells down and hopefully a fresh charge and balancing might bring them back to specs. Let us know!
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'15 Zero SR

Fred

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Re: Balance Voltage in Storage
« Reply #29 on: February 24, 2017, 03:18:50 AM »

I'm picking up my new 2016 FXS in a few days. I assume it will have been manufactured quite a few months ago and been sitting unplugged in a crate all that time. I wonder what state of charge it started with and where it will be now. I'll check the logs from the initial charge that the dealer does.
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