08-26-2021, 09:20 PM | #1 |
Gone Wild
Join Date: Apr 2020
Location: Hurricane, Utah
Posts: 2,743
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Ah or V?
Cart has been in storage for many months (we moved and I didn't have any room for it where we were staying for months) and I had barely finished it before we decided to list the house so it did not get much use. I thought that I would throw it on the charger (first time ever) the other night to top it off (2 Chevy Volt batteries in parallel, 48V and 100 Ah). I was concerned as to when it would shut off so I killed it the first night before it stopped and powered it back on again the next night and watched it; it shut itself off at 50.26V so I was happy.
I reset the Ah gauge to 0 (that is how mine reads) and will keep an eye on it as we finally get to use the cart a bit. Question is am I better off recharging when the Ah gets to a certain level or when I drop to a certain voltage? I have a BMS on each battery and have the ability to set an alarm on my meter for HV and LV but have not done so yet. This cart is mostly for my wife so I just want to let her know what to watch for to avoid any issues. Thank you for any answers! |
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08-26-2021, 10:29 PM | #2 | |
Gone Wild
Join Date: Dec 2016
Location: Kingsland, Georgia
Posts: 1,825
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Re: Ah or V?
Quote:
I don't know what voltage readings you should have on the NMC packs but on the LFP packs 50.2 is less than 15%. I must be missing something. My 72 Ah pack at 20% is 51.2. Let's see if someone (Pat911 or Volt_Ampere) can jump in here and educate us both! |
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08-27-2021, 07:46 AM | #3 |
Gone Wild
Join Date: Apr 2020
Location: Hurricane, Utah
Posts: 2,743
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Re: Ah or V?
Thanks, Tom. When I got the batteries initially I checked them with my MM and they read a bit over 48V as I recall. I did not check the pack after charging with my MM this time (it is in storage somewhere; I will have to go find it and bring it back to our rental) but will just to confirm meter accuracy.
Things that I have read in my searching is that my max top out should be around 54V with a charger, and when I had the charger built I had a lower voltage shutoff programmed in to be safe (I can provide that info if anyone needs it). I was down to about 46V on my gauge and she ran just fine (I am not getting full pedal-will work on that-and am running around 24 MPH on the high end). I just do not want to mess this thing up by doing something stupid, so I am here begging for insight! |
08-27-2021, 08:21 AM | #4 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,123
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Re: Ah or V?
The critical thing is minimum cell voltage. Your BMS cutoff should be based on cell voltage for your particular cells. Use SOC % for a reference of when you need to charge. Volt cells will have a reasonable voltage vs SOC curve (very nonlinear but enough of a change to be able to predict SOC). Amp Hours can be used if you have history for your pack. What I would do is measure pack voltage vs Amp Hours for a discharge cycle or two and determine at what AH or voltage you need to charge. But have your BMS protect your cells by cutting off if any cell voltage gets too low.
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08-27-2021, 08:40 AM | #5 |
Grumpy Old Guy
Join Date: Jun 2014
Location: SEMO
Posts: 2,701
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Re: Ah or V?
The NMC packs sold by Big Battery show a full charge voltage of 50.4 volts. I'm no expert but have been researching alot.
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08-27-2021, 08:51 AM | #6 | |
Getting Wild
Join Date: Jul 2021
Location: GA
Posts: 79
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Re: Ah or V?
Quote:
High voltage cutoff: 50.4V Low voltage cutoff: 36V (40V for increased cycle life). But, no idea how the BB-BDGR battery differs from the Leaf battery pack. Although chemistry is same... |
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08-27-2021, 09:34 AM | #7 |
Gone Wild
Join Date: May 2012
Location: Rio Verde, Az
Posts: 7,123
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Re: Ah or V?
OP has a Volt battery pack. Not the same as most of the drop-ins. If it's 14S then the max voltage is 58.8V at 100%.
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08-27-2021, 05:19 PM | #8 |
Gone Wild
Join Date: Dec 2020
Location: Melbourne, Australia
Posts: 1,919
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Re: Ah or V?
The BigBattery NMC batteries must only be 12s with the cut off voltages given.
To the OP, I would go with aH, not volt. Probably easier for your wife to interpret anyhow. |
08-27-2021, 11:38 PM | #9 |
Gone Wild
Join Date: Apr 2020
Location: Hurricane, Utah
Posts: 2,743
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Re: Ah or V?
Thank you all. So do you think that if I went with 50 Ah as the low point that would be acceptable (it would be easy for the wife to remember as opposed to some random value)?
I am trying to keep it simple as well as safe; appreciate all of the input! |
08-30-2021, 07:55 AM | #10 | |
Gone Wild
Join Date: Apr 2020
Location: Hurricane, Utah
Posts: 2,743
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Re: Ah or V?
Quote:
Took it for a pretty good run yesterday with my wife and a niece and nephew onboard. She did great (couldn't get much over 18 mph with the cart loaded up) and we went about 6 miles or so overall I would guess. Down to 49V and thinking (based on what I am reading-please correct me if I am wrong!) that I will charge again at 40V (I will keep an eye on Ah as well and try and determine a baseline. I do have BMS on each battery. Here's the specs on the batteries: Number of cells 36 Construction 12 in-series x 3 in parallel Length 9.5" Width 9.5" Height 10.5 Weight 45 lbs Output terminal M6 nut Amp Hour 47 Total Voltage 50vdc Cell Specifications: Cell type Laminate type Cathode material LiMn2O4 with LiNiO2 Anode material Graphite Rated capacity (0.3C) 17 Ah Average voltage 3.8 VDC Maximum Voltage 4.2VDC Minimum Voltage 3.0VDC Thank you all; much appreciate the input |
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