Choosing a BMS for 48V Golf Cart Battery Project

Doc3G

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FloydR suggested I begin a thread for help selecting a BMS for my current project.

Goal: Build a safe, reliable lithium battery pack that can power my 48V Yamaha golf cart for short durations (<40 minutes on mostly flat terrain). The current lead-acid group puts out just over 1kWh before hitting the 50% mark.
- I'm pretty sold on the idea of cell-level fusing, so that leaves me with 18650's in order to use the battery hookup cell-level fusing strips, as other methods of cell-level fusing that I've looked at don't seem like a good fit for a mobile application.

- Ideally, I'd like to build it from never-cycled cells. I've currently been pulling apart the 4-cell arris modem packs from battery hookup, and I've ordered both a Littokala and an Opus charger/tester that will be here Tuesday.

- I assumed the pack should be 13s but someone on the Kweld NA Facebook page said that 14s is the typical configuration for 48-volt applications, so the BMS would need to be 14s or configurable for 14s.

- I currently have a Victron shunt w/ Bluetooth to my phone and I've never observed it pull more than 170 amps. I've looked up the controller to see what the draw is rated at but haven't had any luck locating the specs, but I guess 250-300A is probably in the ballpark to be safe.

- Lastly, I know there are some awesome BMS systems out there from companies like Batrium, but given the cost of those units, it doesn't make financial sense given that I can buy a complete battery w/ a BMS that is plug and play for just about the cost of the Batrium alone, so, I'm looking for an appropriately priced solution. It doesn't have to be dirt cheap, but it needs to do the job without doubling the cost per kWh of the project.

Thanks in advance for your input.
 

Roland W

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- I currently have a Victron shunt w/ Bluetooth to my phone and I've never observed it pull more than 170 amps. I've looked up the controller to see what the draw is rated at but haven't had any luck locating the specs, but I guess 250-300A is probably in the ballpark to be safe.

- Lastly, I know there are some awesome BMS systems out there from companies like Batrium, but given the cost of those units, it doesn't make financial sense given that I can buy a complete battery w/ a BMS that is plug and play for just about the cost of the Batrium alone, so, I'm looking for an appropriately priced solution. It doesn't have to be dirt cheap, but it needs to do the job without doubling the cost per kWh of the project.
What I have seen, read and heard, the common BMS (even if you oversize it by a lot) are not good to be used as is for electric vehicles. The power electronics seems to fail easily in those dynamic load scenarios.
You can use actually a dirt cheap BMS, capable of only switching 30A, but you only use it to monitor the cells, and the power circuit is switching a high power contactor to isolate the battery in case of reaching a limit.
Think Jehu Garcia and Will Prowse have videos showing how to do this...
 

floydR

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needs a 12volt coil relay , heard they tend to run hot. Need to get the 16t or 24t versions

https://www.ebay.com/itm/Energus-Ti...55-0&campid=5337590775&customid=&toolid=10001 needs several parts not included with the BMS plus a relay. Low balancing current.

Later floyd
 

emoney

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I use a 100amp BMS from batteryhookup for my 36v cart and a Daly 120 amp for my 48v cart. Neither has given me any issues. Both my carts are stock Club Cars. Well, technically one of them is a Carryall 6, but still.

14S is normal for 3.7v Lithium cells, while 16S is normal for the 3.2v LifePo4 cells. If you buy new, right now it seems LifePo4 is what folks are using. I used the Panasonic 3.7v NCM chemistry Lithium for the 36v and the LGChem cells for the 48v, also 3.7 Li-Ion.
 

Doc3G

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I use a 100amp BMS from batteryhookup for my 36v cart and a Daly 120 amp for my 48v cart. Neither has given me any issues. Both my carts are stock Club Cars. Well, technically one of them is a Carryall 6, but still.

14S is normal for 3.7v Lithium cells, while 16S is normal for the 3.2v LifePo4 cells. If you buy new, right now it seems LifePo4 is what folks are using. I used the Panasonic 3.7v NCM chemistry Lithium for the 36v and the LGChem cells for the 48v, also 3.7 Li-Ion.

Is the Daly for the 48v a smart BMS with Bluetooth and was the install straight forward? I have seen some videos on the relays as mentioned above as well, I just don't want to need a degree in electrical engineering to hook up the bms.
 

Doc3G

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What I have seen, read and heard, the common BMS (even if you oversize it by a lot) are not good to be used as is for electric vehicles. The power electronics seems to fail easily in those dynamic load scenarios.
You can use actually a dirt cheap BMS, capable of only switching 30A, but you only use it to monitor the cells, and the power circuit is switching a high power contactor to isolate the battery in case of reaching a limit.
Think Jehu Garcia and Will Prowse have videos showing how to do this...

when you say only using it to monitor the cells, does that mean it won't shut down during over/under voltage scenarios or that it can't be used to charge the pack or both?
 

Doc3G

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needs a 12volt coil relay , heard they tend to run hot. Need to get the 16t or 24t versions

https://www.ebay.com/itm/Energus-Ti...55-0&campid=5337590775&customid=&toolid=10001 needs several parts not included with the BMS plus a relay. Low balancing current.

Later floyd

I've seen the tiny BMS before, never heard of the other company. You also mentioned this unit in my introduction thread and it seems well priced and capable of doing the job. Any advice on which of the 3 is best?

 

Doc3G

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Also, here is another total noob question, but let's say I wanted to draw 200 amps from my controller but I found a great working 100 amp BMS. Could I build two smaller packs, each with their own BMS, and then draw 100 amps from each?
 

OffGridInTheCity

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Also, here is another total noob question, but let's say I wanted to draw 200 amps from my controller but I found a great working 100 amp BMS. Could I build two smaller packs, each with their own BMS, and then draw 100 amps from each?
If the batteries are hooked in parallel, you can do this. However, if 1 BMS fails it will likely cause the other to overload and fail. Typically you need some extra head-room such as 120a-150a BMS if you want to pull 100a continuous.
 

Doc3G

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If the batteries are hooked in parallel, you can do this. However, if 1 BMS fails it will likely cause the other to overload and fail. Typically you need some extra head-room such as 120a-150a BMS if you want to pull 100a continuous.

Great, thanks for the response. I am realizing that I need some headroom and that the BMS ratings, at least on some of the stuff from China, should be discounted by up to half of the rating. That said, lets say I made my two (or 3 or 4) packs and wanted to hook them up in parallel. I'm unsure how that works since my current batteries are all in series. Do I take the positive leads from each battery and bolt them together to the positive lead from the motor controller (or a bussbar?) I'm trying to understand the flow of current in this case. So, if I have, for example, 2 packs, and I want to draw equally from those two packs and they are both connected to the controller, what prevents the controller from trying to pull more than 100 amps from a single pack? I know I could put use an in-line fuse or breaker to prevent that, but I guess I'm wondering if this is where the BMS comes in? Is it the BMS that stops the controller from drawing all the amps from one pack or the other?
 

OffGridInTheCity

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When batteries - e.g. 2 separate 48v batteries - are hooked in parallel (- to - and + to +), the current pulled out or the charge put in is equally distributed to each battery because the parallel connection ensures that the voltage on each battery remains exactly the same. The current distribution is automatic :)
Here's a quick overview of series vs parallel - https://cleversolarpower.com/batteries-series-vs-parallel/
 

Doc3G

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When batteries - e.g. 2 separate 48v batteries - are hooked in parallel (- to - and + to +), the current pulled out or the charge put in is equally distributed to each battery because the parallel connection ensures that the voltage on each battery remains exactly the same. The current distribution is automatic :)
Here's a quick overview of series vs parallel - https://cleversolarpower.com/batteries-series-vs-parallel/

Great, thanks. It's been a while since my college physics class so I wasn't sure if the natural laws of physics would evenly distribute the charge or if we had to "intervene" to ensure that it happened, lol.
 

emoney

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Is the Daly for the 48v a smart BMS with Bluetooth and was the install straight forward? I have seen some videos on the relays as mentioned above as well, I just don't want to need a degree in electrical engineering to hook up the bms.
It’s a smart BMS but I’ve also built with the non-Bluetooth. All BMS’ technically attach the same way, you just need to be accurate on where the leads go. It’s as simple as adding crimp rings and attaching them to each cell.
 

floydR

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I've seen the tiny BMS before, never heard of the other company. You also mentioned this unit in my introduction thread and it seems well priced and capable of doing the job. Any advice on which of the 3 is best?

No information on the bms but the relay/contactor used is used on many EV's
It is pretty much a toss up tiny BMS is more expensive especialy when you when you add all the extras on. Chargery bms has its good points and bad. Will Prowse did a review on one of the chargery models. his was running hot and he had a couple more complaints, the last one is pretty much an unknown.

Later floyd
 

Roland W

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when you say only using it to monitor the cells, does that mean it won't shut down during over/under voltage scenarios or that it can't be used to charge the pack or both?
It just means, it will not use its on-board Mosfets (Load switching Transistors) to switch your motor, instead it will only switch the coil of the Relay/Contactor which is switching your motor. All monitoring, safety features, balancing of the BMS are unchanged. You just need to connect common Ground of all devices.
Electrical motors are inductive loads, which can surge by more then 3 times the nominal current in certain situations. You have to keep that in mind, when you choose the BMS. If your controller can handle 300A, then the BMS must be able to handle that as well. 300A BMS's are pricey. You don't want to shoot one of those every 6 months ;)
If in your used case scenario, a lot of acceleration, stop-start, uphill-downhill, etc is included, then you might need a quite high Amp rating of the BMS if you are going for the "Load switched by BMS Mosfets" path.
 

floydR

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So p- goes to a relay control post, other control post is connected to the positive of battery (if needed corrected for relay coil voltage) relay inline either the positive lead from battery or Negative lead from battery has the relay on it?

later floyd
 

Roland W

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So p- goes to a relay control post, other control post is connected to the positive of battery (if needed corrected for relay coil voltage) relay inline either the positive lead from battery or Negative lead from battery has the relay on it?

later floyd
If your relay is a 12v, relay secondary coil plus goes to a plus of a 12v power source. Relay secondary minus goes to BMS P-. BMS B- goes to battery minus. Battery minus and 12v power source minus need a cross connection for common ground.

Battery 48v plus to motor controller plus. Motor controller minus to relay switch in. Relay switch out to battery minus (or put the switch on the high side if you want).
 
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Doc3G

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So, all of this is fascinating and sounds like a lot of fun, but it seems like my intention to make a golf cart pack as a learning process b/c I figured it would be simpler and easier vs a powerwall is going out the window due to the high current draw. Maybe I should just start with a powerwall project. My main issue is that I'm currently studying for my medical boards 12+ hrs per day so I don't have a lot of spare time to undertake a more complex project to begin with. I really enjoy building things and my ultimate goal was to harvest some of this free sunshine that the is up for grabs in the great state of Texas :D

That said, would a small powerwall be a more straightforward build? One of my specific goals would be to power my central dehumidifier predominantly via solar. This is the unit: https://www.sylvane.com/ultra-aire-...osU7vN0sIQIEWQLKwfQgJn_Kk2u6d5NgaAiGmEALw_wcB

I live on the gulf coast so it's super humid hear and the dehumidifier runs quite a bit. The specs show a max of 8A and 920 watts, so it doesn't seem like it would take a massive powerwall to drive it.

Thoughts on powerwall vs golf cart for first build? (actually, I plan to build a small cooler size portable power generator first, but after that, I mean my first full scale project).
 
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