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Old 09-04-2018, 01:31 PM   #1
Rwalsh77
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Default Lithium Club Car Parasitic Drain

Looking for some help guys! converted a few carts now but this newer Club Car is giving me trouble. I have wired all the new parts in twice now but i am still seeing about 1 volt per week drop when not in use; which can be problematic to say the least.

48v Chevy Lithium
48v->12v reducer run through a relay on the key switch (this is functioning)
all 12v accesories run directly through reducer

any help is appreciated at this point

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Old 09-04-2018, 03:05 PM   #2
Sergio
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Default Re: Lithium Club Car Parasitic Drain

Any other electronics, BMS, on-board charger, etc connected?

Series or Sepex?

Pictures would help visualize the setup.
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Old 09-04-2018, 03:15 PM   #3
Fairtax4me
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Default Re: Lithium Club Car Parasitic Drain

Connect an ammeter on the pack negative and try unplugging some things and see if you find something that lowers the current draw.
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Old 09-05-2018, 06:42 PM   #4
siwaniuk
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Default Re: Lithium Club Car Parasitic Drain

Any luck in finding out your issues? I seem to have a draw as well. 16 volts and 1 amp. Not sure what from. Please keep us posted


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Old 09-06-2018, 08:37 PM   #5
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Default Re: Lithium Club Car Parasitic Drain

Ok....from everything I've read your BMS is constantly monitoring your batt charge for low end voltage. So, if your BMS isn't drawing power from a separate source, and is using power from your Lith batts, I would think this may be a "culprit" to look at. Maybe?
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Old 09-06-2018, 08:44 PM   #6
sunking
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Default Re: Lithium Club Car Parasitic Drain

The BMS is a drain and the number one killer of lithium batteries. Your BMS likely uses Vampire Boards aka Bleeder Shunts and Voltage Monitor. You cannot turn them off as they get powere directly from the cell it is connected across. Not only is a parasitic drain on the cells, but the number one killer. When they fail, they fail shorted when the MOSFET shorts out and pits a .5 to 1 amp load on the cell as if it were turned on during a charge cycle to Bleed Power Off. When MOSFET fail puts a Resistor right across the cell and will completely discharge a cell beyond threshold causing th ecell to go into reverse polarity. Game over, destroyed cell.

A lot of guys, myself included who build DIY EV's do not use a BMS. We Bottom Balance and that is it. We charge to 90% SOC and never ever fully charge a pack. Charge to 90% and you double cycle life. Eliminate the BMS and you eliminate over discharge.
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Old 09-07-2018, 08:10 AM   #7
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Default Re: Lithium Club Car Parasitic Drain

I've wondered about the drain of a BMS, but never considered a BMS failure destroying a cell... Good to know.

So how do you cutoff the charge cycle to get it to stop at 90%? Do you just get a power supply with a max voltage that equates to the voltage of your pack at 90% and use that to charge?
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Old 09-07-2018, 09:18 AM   #8
DaveTM
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Default Re: Lithium Club Car Parasitic Drain

Quote:
Originally Posted by sunking View Post

A lot of guys, myself included who build DIY EV's do not use a BMS. We Bottom Balance and that is it. We charge to 90% SOC and never ever fully charge a pack. Charge to 90% and you double cycle life. Eliminate the BMS and you eliminate over discharge.
What your saying makes sense. However, is it possible to power the BMS from my existing 12V marine battery that I use just for lights and winch?

BTW, I've read a few post where guys will just do a bottom balance and using a light bulb, bring any cell that is high down to the other cells. How often do you check for cell balance?
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Old 09-07-2018, 11:10 AM   #9
sunking
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Default Re: Lithium Club Car Parasitic Drain

Quote:
Originally Posted by bronsonj View Post
So how do you cutoff the charge cycle to get it to stop at 90%? Do you just get a power supply with a max voltage that equates to the voltage of your pack at 90% and use that to charge?
You got it. Before you march off and do that, voltage you use depends on what Lithium chemistry you are using. Example for LiFePO4 is 3.4 volts, while the others will vary from 4.0 to 4.2 volts.

Here is the deal. Commercial EV Manufactures like Nissan, Chevy, and even Tesla will not allow any customer to ever fully charge the battery. If they did, they would go bankrupt with warranty claims. What most folks do not know is lithium battery cycle life is short. LiFePO4 is the longest lived of all the lithium Ion Batteries. LiFePo4 if you were to buy the best LiFePO4 cell, A123 SYSTEMS, Only carry a 1 year warranty and have roughly 1000 cycles. The Panasonic cells Tesla uses are only good for 500 cycles.

So how do they get around that. Simple they never allow you the customer to ever fully discharge or charge the cells. Depending on which manufacture you are talking about like Tesla only allows the customer to go up to 80% and discharge down to 20% where as Nissan with smaller batteries go 90/10. Commercial EV manufactures do not Top Balance, they Middle Balance.
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Old 09-07-2018, 11:47 AM   #10
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Default Re: Lithium Club Car Parasitic Drain

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However, is it possible to power the BMS from my existing 12V marine battery that I use just for lights and winch?
Certainly, all BMS systems draw there power for the battery pack. But that is not the issue. The problem child is the Vampire Bleeder Boards and how they operate. Each cell has its own circuit that draws power from the cell, not the pack. As you charge the pack, the Vampire Boards are monitoring voltage, and when the voltage hits 100% SOC the Vampire wakes ups and Bleeds the cell. It turns on a MOSFET Switch that puts a resistor right across the cell and drains the charge bypassing current around so the other lower cells can catch up and charge fully. When the Last Vampire Board turns on signals the charger to turn off. Meanwhile the Vampire Boards stay on until cell voltage drops and disconnects the load resistor. That is the part that can destroy a cell. When MOSFET fail they fail shorted which means you have the Bleeder constantly discharging the cell until dead.



Quote:
Originally Posted by DaveTM View Post
BTW, I've read a few post where guys will just do a bottom balance and using a light bulb, bring any cell that is high down to the other cells. How often do you check for cell balance?
Perhaps some do that, but not most of us who Bottom Balance. Allow me to make this very clear. Do not Bottom Balance unless you have a lot of experience with batteries and how Lithium Ion batteries operate. There is no commercial way to automate Bottom Balance.

The way it is done is when you receive your cells, you put them all in parallel and walk away for a day and let the cells equalize. This is Mid Balanced. Then keep the cells in parallel, and then fully DISCHARGE them. For LiFePO4 cells down to 2.3 to 2.5 volts At this point we know exactly the capacity and voltage is of each cell. Every cells has 0 Amp Hours and 2.5 volts.

Now assemble cells in series and charge to 90% SOC. Keep track of AH as you charge. So when charging stops, you can see how many Amp Hours went in, say 100 AH. You know every cell will have exactly 100 AH. You can use Coulomb Counting with Lithium, so when you see you have used 80 AH you had better get recharged.

You eliminate the possibility of over discharge. Example say you build a 16S 48 volt pack from LiFePO4 cells. You set your Low Voltage Disconnect to 48 volts (3.0 vpc). AAt 3.0 volts per cell a LiFePO4 cell is roughly at 10 to 15% SOC. The danger voltage for LiFePO4 is actually 2.0 volts. So with a LVD set to 48 volts you never ever come close to over discharge which would be down to 32 volts and you wil never come close to that voltage with a LVD set to 48 volts. You charge to 54.0 volts, and LVD = 48 volts.

With Top Balance you only know one thing. What full charge voltage is. You do not know capacity because AH tolerance is +10 -5%. Pack capacity is determined by the weakest cell. So if you have 100 AH cells, it is possible some cells are as high as 120 AH and lowest is could be 90 AH. In that case you have a 90 AH battery. So if you Top Balance the voltage is only equal at the TOP. As the cells discharge, the voltages will not be equal. The deeper the discharge goes, the wider the voltage spread will be. That is where the weaker cells get destroyed. The weakest cell can very easily be less than 2.5 volts while all his buddies are still at 3 volts or higher and will destroy the weaker cell.

With Bottom Balance the voltage and capacity are known at the Bottom at 2.5 vpc. So when you charge all cells have the exact same AH capacity and determined by the weakest cell in the series chain. When charge the cell voltages will not be equal, only at the bottom will voltages be equal.

So what us DIY EV guys are doing is mimic what commercial EV manufactures use Mid Balance.
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