Few lithium swap questions

[Sergio]

There are two issues with that kit from techdirect, one is the discharge current path going through the BMS, that one can be resolved easily.

Unfortunately that would exacerbate the second problem, instead of using solid bus bars they used a circuit board for the discharge current path between modules.

The diagram I posted on my thread provides full isolation of charge and discharge paths which allows for a future second pack to be paralleled.

If you are just using a single pack (7 or 14 modules), You could eliminate two of the relays that provide charger controller lockout and charge/discharge auto mode switching and let the BMS control the charge path.

I will try to post a simplified diagram this weekend if the three relay setup looks complicated.

In either case You would still need to remove the circuit board connecting the modules, cut the balancing wires connector off the circuit board, crimp individual ring connectors in each wire and attach them to the module terminals with the new copper bus bar.

[WalterM6]

Looking at the PCB at TechDirect it makes me wonder if the copper bus bars can be applied over the top of the PCB. Holes look large enough. I wouldn't want to buy one to try it but maybe somebody who has already bought one might want to try it.

[Sergio]

The copper bus bar needs to be in direct contact with the module terminals so they cannot be placed above the PC board.

If the bus bars are placed under the PC board it may short out the circuit board and you would have a void under the middle terminals and the pack + and - terminals as they are not connect to a bus bar.

[Volt_Ampere]

PCB is a bad idea for the high current golf cart application. I would just get the Leaf modules and build up your own pack.

[panteramatt]

Sergio, can you tell me how that 100amp BMS from aliexpress you posted would work? Would we all need like a 400amp or better for these carts?

[molfpedal]

Originally Posted by panteramatt

Sergio, can you tell me how that 100amp BMS from aliexpress you posted would work? Would we all need like a 400amp or better for these carts?

You do not run the discharge circuit through the BMS. That is the point of Sergio’s cheap bms setup. It doesn’t see the current when you are driving only charging. The relays in his setup work off of the voltage of the pack cells, the key switch and charger circuits to safely shut down the cart in the event of high or low voltage in the pack or individual cells.
Maybe Sergio will explain it a little more clearly.
I wish I had seen his setup before I bought my 300amp BMS.


Sent from my iPhone using Tapatalk

[panteramatt]

Found this, thought it could be useful:

To respond to your question, yes it can be done and has been done. The Nissan Leaf cells you have pictured are ideal, but some fab work is required to mount them since they are not designed to fit into the battery trays. This can be as simple as a piece of aluminum angle iron with holes drilled to match the thru holes on the cells and holes to bolt to the old battery tray rails.

To go this route, I recommend going 58.8v. This requires:

7 Nissan Leaf G1 or G2 cells. If you get G3, you will have to get four (they are fused together in pairs that cannot be separated. One will be unused). Each generation had higher amp-hour rating, still way less than lead acid but it is comparing apples and oranges. Lithium has a shallow discharge curve over longer usable voltage range, so range is comparable. More on that later. About $500 on eBay.
You will need a BMS (Battery Management System). This is essentially a simple circuit that ensures each cell is not under or over charged, and also monitors battery temperature to disable the pack should one start to heat up. Zeva makes one with a touchscreen that isn't cheap but is fully featured for around $300.
A controller capable of 60v. Most aftermarket controllers can handle this. Check your model online. About $300 (used) to 600, recommend 500 amps.
A charger, up to 12 amps. The higher the amperage, the faster the charge. Mine goes from dead to full charge in 3 hours with 10 amps. Prices range from $50 for 4 amps to $180 or so for 10. Look on eBay for 58.8v lithium charger.
2 gauge welding cable, lugs, and shrink wrap. If you don't already know how, learn to make your own cables to length. Comes in really handy and really dresses it up with nylon braiding. Plan to sped $100 here. I try to find the cable used.

Your controller and motor do not care what your battery chemistry is. Connects the same way your old pack did with a main positive and main negative. The BMS is really the only thing that is foreign to most people, but if wired correctly the entire setup is maintenance free. Just check your connections to make sure nothing came loose. Use blue loctite on the bus bars and never worry about it again.

Even though the cells on eBay are used, you get 3,000-5,000 cycles out of lithium over the 1,000 of lead acid. Should last 3-5 times as long, depending on how many cycles are on the cells you buy. If you get twice the log out of hem, you are ahead.
Sell your old charger for about $200, your old controller for about $200, your old battery cores for $10 each, and you have done the conversion for about the same as new lead acid.
The pack weighs about 45 lbs when all assembled with plates. Saves 300-400 lbs of weight.
No poisonous, combustible, or corrosive gases are emitted.
Charges faster than lead acid.
Discharge curve is amazing. When battery pack approaches 50v which is almost dead, it still feels like a fresh charge.
Voltage drop on acceleration is minimal. Lead acid dips way down on acceleration, but lithium maintains most of its power so acceleration is crazy. My steel framed, limo style, 23" tires, and fiberglass body and roof get to 20 in 2.5 seconds.
Range is similar to lead acid. I get 20 miles out of my pack if I drive it with performance similar to lead acid by not stomping on it on acceleration or going full speed everywhere (goes 30). If I do abuse it, I get 14-15.
If you want to double your range, wire another $500 pack in parrallel.

[keepinitreal538]

Originally Posted by Sergio

Just to clarify, the link You posted refers to the Second generation of the Leaf automobile itself.

The G1 and G2 references you find are based on the different versions of the original 24kwh leaf module (the first two pictured below):

G1 -> 2011-2012
G2 -> 2013-2015 aka Lizard battery

As mentioned the Leaf does not have a Temperature management System (TMS) and the G1 batteries suffered fast degradation in very hot areas like Arizona.

Nissan instead of re-engineering the Leaf to add a TMS, decided to adjust the battery chemistry so it would be more tolerant to severe hot climates and the G2 or Lizard battery came out in mid 2013.

The G2 battery did not completely solve the problem in the hot areas, but it did resolve the issue almost everywhere else.

Unfortunately Nissan also extended the pack discharge and charge levels allowed at the same time they released the G2 modules so while the battery chemistry was more tolerant to heat, the batteries may have had a harder life.

You can definitely build a 7 module pack for under $900 including BMS and charger, the kits from TechDirect are not engineered for golf carts, but the modules and box are fine.

I think the Leaf modules have the best layout for a DIY build and if properly designed from the beginning, you can build a 7 module now and later build another 7 module that can be paralleled with the first without having to reconfigure the entire pack.

Sergio Techdirect has kits on there website under "golf cart batteries" are you saying these would not do good in a cart? if so why? im still learning so please be nice lol

never mind i finished reading the post lol.

[a_machinist]

Originally Posted by keepinitreal538

Sergio Techdirect has kits on there website under "golf cart batteries" are you saying these would not do good in a cart? if so why? im still learning so please be nice lol



never mind i finished reading the post lol.

@Sergio any comment on this? I need to make a purchase soon.


Edit: sorry missed a page

[kmoorhead]

Originally Posted by Sergio

There are two issues with that kit from techdirect, one is the discharge current path going through the BMS, that one can be resolved easily.

Unfortunately that would exacerbate the second problem, instead of using solid bus bars they used a circuit board for the discharge current path between modules.

The diagram I posted on my thread provides full isolation of charge and discharge paths which allows for a future second pack to be paralleled.

If you are just using a single pack (7 or 14 modules), You could eliminate two of the relays that provide charger controller lockout and charge/discharge auto mode switching and let the BMS control the charge path.

I will try to post a simplified diagram this weekend if the three relay setup looks complicated.

In either case You would still need to remove the circuit board connecting the modules, cut the balancing wires connector off the circuit board, crimp individual ring connectors in each wire and attach them to the module terminals with the new copper bus bar.

Sergio, did you ever post a diagram of this without the 2 relays? Thank you in advance.