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Unread 08-08-2019, 12:53 PM   #391
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Default Re: Bit the bullet Leaf Lithium build

I have my home designed system based on Arduino. It monitors cell voltages, cart speed and distance, ambient, motor temp, date and time. It also does balancing much better than most available BMS's.
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Unread 08-08-2019, 01:11 PM   #392
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Default Re: Bit the bullet Leaf Lithium build

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Originally Posted by bronsonj View Post
I am one of the cheaper builds on here. I used Chevy Volt cells, but Nissan Leaf are easier.

generally... Lithium is safe as long as you don't over heat, over discharge, over charge.

I had a 47ah pack that i later doubled to 94ah. 47ah may do ok for you depending on how you use your cart and what mods it has. I use a 360 watt (5 amp) charger and it is mounted in my cart. It takes a while to charge, but works and I always have it with me.

I don't have a BMS that can handle the amperage the cart pulls, so I don't have a BMS controlled low voltage cutoff. To account for that I set the low voltage cutoff in the controller to be far higher than is necessary. My cart will cut off at 45.5V which is 3.25vpc if all my cells are equally balanced. I am using a 14 cell pack (2P14S). If you use a 13S or 12S your LV cutoff needs to be different. Please note, just using 45.5V as the LV cutoff is not the safest option... As a lith cell is drained it will lose V much more quickly. There is a 'knee' and after which the V will plummet. So if my other cells are all at 3.35V then I could have one cell at 1.95V... That would be a pack I would not want to use again as the risk of fire during a charge is much higher on cells that have been stressed. I also check my cells for balance all the time... I'm rather paranoid about it. When I first was putting my pack together I had 4 cells that were more charged than the rest and it took a while to manually balance them. But the interesting part is that while they were quite far apart when in the middle 3Vs, when I got to 4.05vpc they were all balanced... The differences between the cells were magnified at lower voltages and that's where a lot of danger can be found.

Fuses are your friend, but a fuse won't protect you from fire and overcharged cells can burn. Think Samsung Phone burn, but MUCH bigger.

Not trying to dissuade you. Just want you safe. I love my lith pack. The pack never self discharges, if I leave it at 53.4v then it will still be 53.4v two weeks later. No more acid. Much less weight. Lots of benefits and so long as you give it respect, you will be happy.
Question, i see a lot of people saying to run a BMS on charge and discharge, then I hear people not running BMS at all, I was going the route of using the BMS while charging and drawing main power right off the pack by passing the BMS, all the schematic I have seen it seems they show the wiring of the BMS to the packs but dont show the load power drain being pulled through the BMS so i'm scratching my head on what to do!, I want the BMS to control the balance of the cells on the charge side but not sure how to set it up on the dray side, any suggestions? or know where I can find the schematic showing a full setup?
Thanks~
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Unread 08-08-2019, 01:55 PM   #393
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Default Re: Bit the bullet Leaf Lithium build

IMO the most critical functions of the BMS are balancing and protecting from any cell being overcharged during charging. Overdischarge protection is important but can be handled with an alarm - at least that is how I do it.
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Unread 08-08-2019, 02:35 PM   #394
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Default Re: Bit the bullet Leaf Lithium build

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Originally Posted by Volt_Ampere View Post
IMO the most critical functions of the BMS are balancing and protecting from any cell being overcharged during charging. Overdischarge protection is important but can be handled with an alarm - at least that is how I do it.
Got it!, I can set the voltage cut off on my Alltrax controller and set the max voltage output on the charger "chargery C10235", so with the different types of BMS "active and passive" i would be lead to believe I should be using an Active BMS on the charge side? or should i add an additional BMS cable for the balance system on the charger? sorry for all the questions~ I have a ton to learn and am more of a visual learner.

this is the BMS I have. https://www.techdirectclub.com/for-n...t-battery-new/

& https://www.techdirectclub.com/for-n...nd-g2-bms-lcd/
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Unread 08-10-2019, 06:01 AM   #395
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Default Re: Bit the bullet Leaf Lithium build

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Originally Posted by Keith93611 View Post
Got it!, I can set the voltage cut off on my Alltrax controller and set the max voltage output on the charger "chargery C10235", so with the different types of BMS "active and passive" i would be lead to believe I should be using an Active BMS on the charge side? or should i add an additional BMS cable for the balance system on the charger? sorry for all the questions~ I have a ton to learn and am more of a visual learner.

this is the BMS I have. https://www.techdirectclub.com/for-n...t-battery-new/

& https://www.techdirectclub.com/for-n...nd-g2-bms-lcd/
I can't comment on the Chargery unit, but the ZEVA will balance the cells after charging takes place. It's like Robin Hood....takes energy from cells that have a higher charge (more juice) and gives to cells that have a lower charge.

Remember that when you set your controller to cut off for LV, the controller will do that when the pack voltage drops to your setting. However, the controller does not monitor each individual cell's voltage. That's where a BMS does it's job. When you set the BMS to cutoff if any individual cell drops below your cell setting, that will prevent any given cell from getting undercharged to a critical level. The BMS also monitors each cell when being charged so that no one cell get's higher than the max setting. Again....overcharging is just as bad.

Remember that once a individual cell drops a given point, the cell is now bad and cannot be recovered. And if that cell is getting charged again it's likely a matter of time before it goes to thermal runaway....or "bad things happen."

I hope this helps
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Unread 08-10-2019, 11:02 AM   #396
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Default Re: Bit the bullet Leaf Lithium build

That "80 amp" tech direct BMS has been discussed on BGW before and the current specifications of 60 amps sustained and max of 120 peak are concerning. I live in a community in Florida with flat paved roads and on my carts I normally see 45-60 amps sustained while cruising and routinely see 250-320 amps on acceleration or hills... Thats regularly drawing more than double the rated peak current of the TechDirect BMS. If you choose go with that BMS I would watch your currents and the BMS closely and please give us some feedback on how it holds up. It says " Same port of the charge and discharge" which indicates that all the discharge current passes through the anderson type connector and those small cables (maybe 8ga..?) and fuse... Your possibly creating a bottleneck with your BMS and cables so watch for increased heat in the BMS and its wires when running. The BMS's that I currently use have a 500-600 amp externally mounted (doesn't pass through the BMS) shunt or Hall Effect current sensor that doesn't limit the current you can draw from the pack. This means that the current to the motor is carried via 4ga factory cables or upgraded 2ga without restrictions.

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Unread 08-10-2019, 12:03 PM   #397
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Default Re: Bit the bullet Leaf Lithium build

Quote:
Originally Posted by Keith93611 View Post
Got it!, I can set the voltage cut off on my Alltrax controller and set the max voltage output on the charger "chargery C10235", so with the different types of BMS "active and passive" i would be lead to believe I should be using an Active BMS on the charge side? or should i add an additional BMS cable for the balance system on the charger? sorry for all the questions~ I have a ton to learn and am more of a visual learner.



this is the BMS I have. https://www.techdirectclub.com/for-n...t-battery-new/



& https://www.techdirectclub.com/for-n...nd-g2-bms-lcd/
If you're going to use the Alltrax for your Low voltage cut off leave plenty of room. As it was stated before the Alltrax looks only at total pack voltage not individual cell voltage. Check out the attached Nissan Leaf discharge curve, be careful the voltage drops off faster than you think after the "knee or cliff". This is not 100% to scale but is pretty close to how I have parameters set for my pack. The % listed is useable portion of the battery and corresponds to voltage which is listed on the dash by the volt meter to tell my wife how much "gas" is left in the tank. It seems to work better and more accurate than the SOC meter. I'm planning to drop my charge voltage 4.17v to 4.1v per cell to conserve the life of my pack.LEAF DISCHARGE GRAPH.pdf

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Unread 08-10-2019, 12:09 PM   #398
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Default Re: Bit the bullet Leaf Lithium build

Trying to attach again.

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Unread Yesterday, 10:54 AM   #399
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Default Re: Bit the bullet Leaf Lithium build

anyone know the torque specifications on a G2 pack?
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Unread Yesterday, 04:13 PM   #400
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Default Re: Bit the bullet Leaf Lithium build

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Originally Posted by Keith93611 View Post
anyone know the torque specifications on a G2 pack?


Iíd imagine 10ft/lb is plenty. I used my 12v makita impact and let the hammer hit like 5 times on each one. Donít think it needs to be that precise



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