Basic Nissan Leaf 7 module Lithium setup with Generic Chinese BMS

[fstop]

I know there is hesitancy by some to use a BMS that has integral load switching (FETs, in most cases AFAIK), but I wonder if a "hybrid" approach may also function similarly but use the type of mechanical load connections that are mostly outlined in this thread (solenoids / relays)?

It seems that you could use the BMS internal load switching to only switch the coil of a mechanical switch if you felt that was preferable to letting the BMS's switching ability handle it, but I'm probably missing something.

In this scenario there is an external manual ON / OFF switch for the BMS that controls the passing of voltage through the device. The BMS itself can obviously also control this, if it detects low / high cell voltage etc... In either case, the load or charger would be disconnected.

I guess what I'm wondering is could this simple arrangement allow you to only use the BMS' switch to control the coil of a solenoid that actually switches the load, only using the BMS for monitoring and shutdown?

In the "normal" configuration of this BMS as it is designed, the cart main power connections are at "A" and "B".

I've personally had BMS units where the current is switched internally in use for a lot of miles and 1.5 years now (2 different batteries with such units over that time) and - knock on wood - have had no issues with failure. If it were to become an issue though, I'd like to understand how other options might work.

My thoughts have been that these BMS units are relatively inexpensive (and reliable in my experience), and if you had identical replacement units available (which I acquired at purchase of my current battery) you could quite easily just replace it and carry on. I figured if you could get maybe 2 years out of one it would be worth it, and the better solenoids cost the same as these units in many cases.

Not planning on implementing this approach at the moment, but really looking to see if it would work as drawn?

[WC53]

I think that was what Sergio did in his thread. In high amp cars and boat uses, bms controlling a relay seems to be the norm, with the higher amp expensive BMS units all use external relays and contactors. If you derate the cheap units by 50% for safety you don’t have much left.
Use the bms as a temp and voltage safety and possibly for charging (depending on current)(but still a relay) and a shunt for capacity?

[Volt_Ampere]

Your cart already has a high current relay (the main contactor) You can use a small relay to interrupt the main contactor control circuit if you want a Low Voltage cutoff. I just went with a very loud alarm - thought that was adequate for me.

[WC53]

This true, but folks still run current through the bms

[Pat911]

If the BMS is adequately specified, then there is no problem with that. I run charge current through the BMS but only use the BMS to interrupt the key switch during discharge. I have an accurate SOC meter based on coulomb counting so I know exactly how much life I have left. I recharge at anytime but never let the battery get below 20% SOC.

[molfpedal]

Originally Posted by fstop

I know there is hesitancy by some to use a BMS that has integral load switching (FETs, in most cases AFAIK), but I wonder if a "hybrid" approach may also function similarly but use the type of mechanical load connections that are mostly outlined in this thread (solenoids / relays)?

It seems that you could use the BMS internal load switching to only switch the coil of a mechanical switch if you felt that was preferable to letting the BMS's switching ability handle it, but I'm probably missing something.

In this scenario there is an external manual ON / OFF switch for the BMS that controls the passing of voltage through the device. The BMS itself can obviously also control this, if it detects low / high cell voltage etc... In either case, the load or charger would be disconnected.

I guess what I'm wondering is could this simple arrangement allow you to only use the BMS' switch to control the coil of a solenoid that actually switches the load, only using the BMS for monitoring and shutdown?

In the "normal" configuration of this BMS as it is designed, the cart main power connections are at "A" and "B".

I've personally had BMS units where the current is switched internally in use for a lot of miles and 1.5 years now (2 different batteries with such units over that time) and - knock on wood - have had no issues with failure. If it were to become an issue though, I'd like to understand how other options might work.

My thoughts have been that these BMS units are relatively inexpensive (and reliable in my experience), and if you had identical replacement units available (which I acquired at purchase of my current battery) you could quite easily just replace it and carry on. I figured if you could get maybe 2 years out of one it would be worth it, and the better solenoids cost the same as these units in many cases.

Not planning on implementing this approach at the moment, but really looking to see if it would work as drawn?

This thread is precisely that. Sergio only uses the BMS to control charging directly and monitor battery ( cell and pack) voltages and trigger shutdowns via external relays. His drawing is in the 1st or 2nd post in this thread as well as a very thorough explanation. I came up with a way to use it on Ezgo RXV carts so that shutdowns would not lock the cart up immediately using the accelerator circuit in the RXV in combination with the relay system. That can also be found in this thread.
For those on a budget it enables using a much lower cost BMS than a Zeva or Chargery. And less worry that the fets will fail.


Sent from my iPhone using Tapatalk

[fstop]

Sergio's drawings appeared more complex and I wasn't exactly sure why (which is why I posted this) but I think it had to do with his charger, and maybe there was no "on off" switch for the current output of the BMS he was using - other factors as well maybe. I'm sure whatever he designed was bulletproof though.

I have always had a shunt-based SOC meter as well, as mentioned above.

Also as mentioned, I have had zero issues running current through the BMS (and have a relatively high performance cart), so will continue to do so but wanted to see what others thought of the super simple approach in my drawing. Thanks for the comments and suggestions.

[fstop]

Originally Posted by Volt_Ampere

Your cart already has a high current relay (the main contactor) You can use a small relay to interrupt the main contactor control circuit if you want a Low Voltage cutoff. I just went with a very loud alarm - thought that was adequate for me.

Interesting approach! I think I'm more comfortable letting the controller continue to handle the main solenoid at the moment though.

[Volt_Ampere]

Originally Posted by fstop

Interesting approach! I think I'm more comfortable letting the controller continue to handle the main solenoid at the moment though.

You just add another contact in the relay circuit (or throttle circuit) Normally, the controller still controls the solenoid.

[Murby]

Originally Posted by molfpedal

This thread is precisely that. Sergio only uses the BMS to control charging directly and monitor battery ( cell and pack) voltages and trigger shutdowns via external relays. His drawing is in the 1st or 2nd post in this thread as well as a very thorough explanation. I came up with a way to use it on Ezgo RXV carts so that shutdowns would not lock the cart up immediately using the accelerator circuit in the RXV in combination with the relay system. That can also be found in this thread.
For those on a budget it enables using a much lower cost BMS than a Zeva or Chargery. And less worry that the fets will fail.


Sent from my iPhone using Tapatalk

The problem with the cheap BMS's is not JUST that they pass all that current through them, its that they are cheap BMS's to begin with. They use cheap and undersized components, undersized wire, and are built to the bare minimum survival specs.

I can't even count the number of times I've heard of batteries being ruined because a Chinese BMS drained a cell to zero.

I understand its not that big of a deal to lose a cell in a 50 or 100 ah pack, but I've seen people use these cheap BMS's on off-grid packs with 500ah systems.. and loosing a 500ah cell is an expensive problem.

Some folks don't have a lot of choice, and for a golf cart, I can kind of understand.. Just be careful and don't go parking a lithium ion golf cart running a cheap BMS in your garage. When these BMS's fail with phosphate batteries, its just a big smoker.. You open a window, air it out, buy some new batteries. but when they fail with lithium ion packs, things can catch on fire.

I made a chart:
Expensive LiFePO4 + Cheap BMS = Get Smoke, Lose Money
Expensive LiFePO4 + Good BMS = a good investment
Cheap Lithium Ion + Cheap BMS = Fire, Lose Money, Cart, Maybe your house.
Cheap Lithium Ion + Good BMS = a good investment with only slight risk.

I like LiFePO4.. but dang are they super expensive and bulky.. and since most of them are made in China, you never really know what you're getting. They might advertise 2000 cycles but you won't know until years later, if ever.

Lithium Ion is cheap, packs a lot more power than the phosphate cells in the same volume, and since they're used in EV's, they are generally readily available. Problem is, you need a good quality BMS to prevent the guys with long water hoses from showing up.

Good BMS's.:
REC BMS
Batrium
Orion
And I think Elithion Lithumate should be included as I'm hearing good things. They make a Vinci-LV that is field configurable (GUI Interface) , expandable, comes with CAN interface for a charger, and can operate in a master-slave config without special ordering. $350, which isn't a bad price at all if you're spending $1500 or more on a battery. Best of all, made in Colorado..