Build Thread: EZGO TXT 48 to BMW Lithium 55.5V

[jhornbr225]

I did the overkill and OCD thing of working from the bottom of the pack when paralleling them up.

I used some alligator clips and a resistor to clip the two banks together as I measured, cut, crimped the ends on, and heat shrunk each cable (and let it cool) as I went along. So as I went, each cell had a number of minutes with the resistor before I installed the cable.

Yes, I'll agree, probably a little overkill, as each set of the batteries had been charged with the same BMS very recently, and measured within 10-30 millivolts. But, Oh well, can't be too safe.

I can say, so far, with the supposed 150Ah rating of my cells, and it being winter, and not using the cart much, I have not charged my cells again after the initial charge.

[Caleb_mock]

Originally Posted by Pat911

0.1v difference is fine (Battery voltage, not cell voltage). As said, they will balance themselves. The only issue is if there's a very large difference, say one pack at 50% and the other at 100% then there will be very large currents flowing as they try to balance themselves. This may or may not be a problem depending on the BMS rating and its settings.

Don't worry, I won't do that!

[Volt_Ampere]

If your packs are not close enough before paralleling, you can either charge the lower one some or discharge the higher one some. I have not done this but you could also put a lamp between the positive terminals and let them equalize relatively slowly. When I built up my Leaf pack, the modules were already very closely matched in voltage so I just put on all of the bus bars that connected them in pairs.

[Caleb_mock]

I've made some progress in the past few weeks. In the beginning of the month, I bought and installed an Alltrax XCT48500, MZJ-400 Solenoid, and Alltrax bluetooth module from ScottyB. The price was super and there were a lot of small parts included that made the install go somewhat well.

http://cartsunlimited.com mentions that the Alltrax are dummy proof. I definitely put that to the test by installing the battery terminals backwards.

With just the new controller and still old batteries, the cart was able to finally start working. I can take it around 9pmh uphill and 14 mph on flat land. I'm running the stock 6 AWG cables still, so I've started to notice heat stress on the batteries and cables. One battery DEFINITELY has a bad cell, so I'm eager to see how the lithium battery does.

[Caleb_mock]

Most of my parts are here:

2 - 120 amp 14S JBD BMSs
1 - 120 amp 4S JBD BMS (for the aux battery)
1 - 15 Amp 57.4V WATE Charger (4.1v / cell)
1 - 20 Amp 16.4V Wate Charger (4.1V / cell)
All the relays, diodes, and other little components recommended to have the solenoid control discharge.

[Caleb_mock]

Last week, I took the first battery that will be modified and cut the busbar. I was able to make a small tab out of the aluminum that I hope will handle enough current for the cart. I ordered a set of connectors from Germany rated for 250 amps. The connectors are slightly too large for my tab, but with a small crimp and a 4mm screw drilled in the center, I think there will be a strong, vibration resistant connection.

If anyone has any advice on this tab, I'd love to hear it.

[Caleb_mock]

Tonight, I finally started the install.

First thing, get the battery tray clean. I don't have an angle grinder, so I took a paint scraper, wire brush and Coke Zero to the frame.

It took a few hours, but I was able to get it clean enough to paint. After two coats of Ace's Rustoleum knock-off, it look's "factory fresh."

I couldn't help myself and went ahead and placed the battery tray down and laid the batteries and chargers where they're going to be. Quite happy with how it looks.

Next, I need to figure out exactly how to secure everything and make the final wiring arrangements. I've been prepared to use a solenoid controlled discharge (a la Sergio) but I don't exactly know how to wire relays for the charge side in parallel. Does anyone know the best way to modify this diagram to make it work? It would be much cleaner if I could wire the cells in parallel. I have connectors for the BMS leads that are capable of holding an 8 awg wire. Is an 8 AWG enough for cell balance leads if the main discharge will be coming from two larger busbars and paralleled?

I wish that I had just bought the 16S version and connected 3 of these 120 amp BMS's. I'd be able to put the batteries in parallel and be done with this darn project.

[Volt_Ampere]

Where did you source your chargers? I may need a backup for my charger that I have been using for 5 years.

[bronsonj]

Lookin good! Nice progress and I love how the BMW cells sit in the cart with so much space left over.

How did you make that battery connection? How did you get it to adhere to the aluminum tab? I've found my connection with a single 1/4 inch bolt has held up great over the years. Just need to make sure it's protected/prevented from making contact with the next cell. A simple piece of plastic can take care of that.

When you are looking for mounting options keep in mind they need to stay put if you happen to lay the cart over... Not a fun thought, but it's a lot worse if you have a 140 Ah lithium battery flopping around when your cart is sliding on it's side...

Originally Posted by Volt_Ampere

Where did you source your chargers?

He has the WATE brand charger so that'd be aliexpress I'd imagine.