<$150 from China.
You can borrow the bms24 in my picture until you get one of these.
Ps.
Not charging. Displays 1a when shunt is disconnected.
Genrix . Nice project . A little advise , Dont make your project unnessarily complex if possible . Those NMC cells will stay tightly balanced , They should only be charged to 4.0v max and can go down too 3.0v with no damage . So that gives you a pack range of 80v to 60v . Your gem will stop running at 60v and wont turn on under 68v . In reality if your gem will be a dog when it gets that low and under sag will trip off your controller so your pack should be pretty safe . The specs show inverter shut off @ 63v so your ok there too .
Your numbers for the inverter look accurate , iām going to do the same thing as soon as i settle on final pack voltage .
I cant see any reason to run shut off relays on your Gem . Tell us how you run your Gem , High speed ? up / down hills ? lots of weight ?
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Finishing up some details:
Filed sharp edges
Added orange neutral bar
Orange split loom over balance leads
@Inwo Wow, I just found the 24S 300A BMS on Aliexpress and wow. Just over $100 is amazing. I might get one just to mess with it and learn how āstandardā BMSās are supposed to work.
I only wish they made a 400a 24s. If you drive normal, no problem. I worry crossing traffic, it will trip when needing power the most.
I could turn power down in controller I guess. 250a is plenty.
ps. first one I got 3 years ago was $350. They are most all knock-offs now.
We are in Florida and use our golf carts for power during storms all the time. HOWEVER We use common 12VDC/110VAC inverters - cheap and effective. Just movefrom one battery to the next as they become depleted. Usually run a fridge and small tv for quite awhile. Your overthinking a simple CHEAP solution to. a common application. a 1000 watt inverter is cheap, pure sine wave is NOT required for anything you have in your home.
I have a 99 buck 900 watt generator from Harbor Freight that ran 7 days during the outage in Tavares Florida a couple of years ago.
In a message dated 4/22/2019 2:47:13 AM Eastern Standard Time, electricforum@discoursemail.com writes:
Okay, seems like in practice there is low risk of permanently damaging the battery pack and may actually cause other issues by over-complicating.
I will definitely try the setup as is first and test it out. With 80v + I am interested to see what difference that makes. Then I will swap the stock ventilated 7hp motor with the 7.5 hp Ride-4-fun motor to see what that does for me. I do want to end up with some speed increase (around 35 mph would be nice on roads posted @ 35 mph). Please explain the voltage spoof and what ālvcā means. Is that low voltage cutoff?
Dave, are you saying you also know how to reprogram the controller to allow higher speed, or do I still need to get magic magnets then correct speedometer.
@inwo Please send me a link for the 20s BMS. I will probably never add cells. If you have used a similar one and like it, I am interested. I am surprised that the motor pulls more than 300a on occasion. What needs a reset if this happens? BMS?
Yes, low voltage cutout.
Controller can be programmed somewhat for more speed. I donāt do it.
Spoof raises voltage limits. Running high voltage is the most effective performance upgrade.
So, finish the pack with bms-24t?
I have not used the 20s 400a bms.
The bt bms24 has a boot button that resets controller.
You may not see 300a displayed, but a short pulse trip bms. The trip delay can be cranked up, but may not be safe to electronics.
Iāll have to search for a link.
@LithiumGods I love the name and the movie reference by the way. You jest that you are a ātrollā on a forum.
I drive the GEM around on country roads around our house and to grandmothers house we go. Mostly up to 15 mile round trips. Some 10% grades are involved. I have a trailer hitch on the truck and use that for a lawn cart type trailer and a bigger aluminum trailer for hay rides with a bunch of kids. I have trails in the woods too which are more like small roads really. Fairly demandingā¦ that is why I wanted the eL XD version of the truck with 1,400 lb payload and slightly bigger 5 bolt wheels & tires. I think it is a different gear ratio too for more torque. The lighter batteries should increase available payload. Thoughts?
The pack is looking great David. Is that orange neutral bar harvested from the Bolt?
Yes, it is.
About as far as I can go until I know which bms for sure.
Connecting a new bms-24t is the point of no return. 
If youāre not sure, you can use my loaner. Shown connected.
Did you watch crazy Grantās video?
@Old_Houseboater I did switch from battery to battery as you described once during an outage when my 18kw standby generator would not start (bad fuel solenoid). I wonāt be doing any more of that with the new lithium pack. The problem with the 72VDC inverter is (was?) Lack of options at a reasonable price. The smaller needed boost from 72VDC to 110VAC means higher efficiency and in theory less heat less voltage sag. I plan to use it for tools such as brushless electric pressure washer, PA speakers (thinking parade use), emergency backup power source for me or neighbors, camping, etc.
72v to 120vac are not commonly stocked. This one Iām looking at.
The mild mannered GEM is now the adrenaline GEM that Grant configured. 1.21 Gigawatts, great Scott! More than my truck needs, I think. Where do you get the magic magnet? Ride-4-Fun? Is it just on one of the wires like a clamp on ferrite? I talked with the Ride-4-fun guy and even he was almost talking me out of a controller upgrade.
Just split the differenceā¦ go ahead and slap on two more cells atop the pack (half kidding). 88-90v with a spoof? Is there even a suitable Delta-Q charge profile?
This is addictive and so much to consider. When I am explaining who you guys are and why I am going to Minnesota to my wife, Dad, friendsā¦ I have been saying that you are like the āgearheadsā of NEVās / GEM and part of a very specialized and small group.
It can be done. I make the MM myself. Iāll show you my huge production facility when you visit.
22s is the perfect number imho. There is no reason not to run with 20s though. Grant, myself, and a few others used 20s lithium with great results.
Cost of more cells is 1/20 cost of a 20s module each cell.
Money is better spent on high voltage than on a motor or controller. Remember that Grantās gem is stock but for battery and MM.
Dq can charge up to 99v.
Doesnāt sound like you are doing anything that is very demanding on your gem . 20s should be perfect for you . Your controller can pull 350a if it needs to . But if you watch your bms screen 99.9% of the time it wont even get close to it . Upgraded controller wont do anything for you .
20s , magic magnet and you are good to go .
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Dave, I have decided to stick with the Chargery BMS 24t. At the point where you are with the pack assembly I am totally fine with sticking with 20s. I will leave it up to you though. If you feel strongly enough that 22s is perfect and have the parts and time, I will pay the extra 2/20 (10%)
If I wildly over simplify, the ratio of speed to voltage with Grantās hot rod e4 is 42/96 = 0.4375
- 80v from a 20s would yield 35 mph (0.4375 x 80 = 35).
- 88v would be 38.5 mph.
- 72v would have a top speed of 31.5 with just a magic magnet and nothing else.
So many variables though:
- Gear ratio
- Weight
- Wind resistance
- Tire circumference
- Stock vs. the blue motor I already have
What kind of speed do you get out of your tuck and at what voltage, Dave?
Anyone else care to comment on real world experience?
Other technical questionsā¦
Is the magic magic magnet interchangeable between stock and R4F motor? I will definitely want to buy one of those from you Dave. I read somewhere on here that you can switch to kph to get an accurate speedometer reading.
Does the pack voltage affect the GEMās on board 12v converter power supply? Increase voltage?
If we go for 22s what needs to be done for voltage spoof. Do I need to remove and bring any parts?