5 ms·

Question I have: is it just a bunch of cells wired up, or is there a BMS (battery management system) in there doing the things you need to do to make a battery

by zevv 3y ago

Question I have: is it just a bunch of cells wired up, or is there a BMS (battery management system) in there doing the things you need to do to make a battery safe and make it last: cell balancing is essential to make sure the pack will survive more then a few charges and rides before it will kill itself. Also I would not like a battery pack that does not switch itself off when voltages or currents get too high, which is a great way to start a thermal runaway. Not a safety issue, but important to make sure the battery is not abused is to prevent deep discharge voltage or charging the battery at too low temperature.

russellbrandom 3y ago
Hi -- editor of the piece here. There is a BMS, that's the main other component aside from the cells. We had that detail initially but it got cut for space.
- deleted 3y ago
  [deleted]
- ggm 3y ago
  A shame, because seeing how you can get and apply a BMS to a build is probably where much of the readership interest lies. How 'programmable' is the BMS typically? is it arduino programming hard? Can you e.g. shape the charge profile. set the stop point, route around damaged cells? is the BMS field upgradable? I'm guessing its a commodotized un-upgradable closed solution and you set the params on purchase (alibaba) and its how it works forever.
  - sbierwagen 3y ago
    Take a look at the TI BQ79616-Q1, which has been used in some Tesla packs: https://www.ti.com/product/BQ79616-Q1 https://www.ti.com/product/BQ79616-Q1 Yes, it's programmable. Even has eight GPIO pins. It would be "field programmable" in the sense that if you scraped the conformal coating off the pogo pin pads you could reflash it... which you probably don't want to do. Despite what the article says, a BMS doesn't actually do many of the things you mention. It balances cells, monitors temps, and sets fault flags if something's wrong. A BMS chip does not charge the battery, it doesn't determine max voltage, (the charger does that) and it can't isolate a bad cell. (Because they're all welded together! Pack current doesn't actually pass through the BMS-- it only has thin balancing wires to each cell which can't handle much current.)
    - ggm 3y ago
      I take your point it doesn't do these things but the potential was there in hypothesis to control these things.
      - sbierwagen 3y ago
        Sure, but the battery+BMS can't control those things. If you wanted to set charge parameters the easiest thing to do would be to buy a third party lithium ion battery charger, like the Tenergy TB-6AB, and set a capacity limit.
    - rcxdude 3y ago
      Usually the BMS in such packs does have control over the flow in and out of the battery: it can isolate the connections if there's an overcurrent or over/undervoltage (or overtemp). That's usually the main contribution to safety. And it's also pretty typical that the BMS is what defines the charging profile: the charger basically just follows instructions from the BMS (and if it doesn't, said isolation comes into play as protection). This doesn't necessarily all happen on one chip: in the larger packs this is likely distributed between a few different components, including a chunky contactor for the isolation.
- galaxyofdoom 3y ago
  [dead]
holoduke 3y ago
Cheap active bms systems. Could be hazardous as well. But needed for charging from a 48v charger block.

by zevv 3y ago

russellbrandom 3y ago

Hi -- editor of the piece here. There is a BMS, that's the main other component aside from the cells. We had that detail initially but it got cut for space.

deleted 3y ago
[deleted]
ggm 3y ago
A shame, because seeing how you can get and apply a BMS to a build is probably where much of the readership interest lies. How 'programmable' is the BMS typically? is it arduino programming hard? Can you e.g. shape the charge profile. set the stop point, route around damaged cells? is the BMS field upgradable? I'm guessing its a commodotized un-upgradable closed solution and you set the params on purchase (alibaba) and its how it works forever.
- sbierwagen 3y ago
  Take a look at the TI BQ79616-Q1, which has been used in some Tesla packs: https://www.ti.com/product/BQ79616-Q1 https://www.ti.com/product/BQ79616-Q1 Yes, it's programmable. Even has eight GPIO pins. It would be "field programmable" in the sense that if you scraped the conformal coating off the pogo pin pads you could reflash it... which you probably don't want to do. Despite what the article says, a BMS doesn't actually do many of the things you mention. It balances cells, monitors temps, and sets fault flags if something's wrong. A BMS chip does not charge the battery, it doesn't determine max voltage, (the charger does that) and it can't isolate a bad cell. (Because they're all welded together! Pack current doesn't actually pass through the BMS-- it only has thin balancing wires to each cell which can't handle much current.)
  - ggm 3y ago
    I take your point it doesn't do these things but the potential was there in hypothesis to control these things.
    - sbierwagen 3y ago
      Sure, but the battery+BMS can't control those things. If you wanted to set charge parameters the easiest thing to do would be to buy a third party lithium ion battery charger, like the Tenergy TB-6AB, and set a capacity limit.
  - rcxdude 3y ago
    Usually the BMS in such packs does have control over the flow in and out of the battery: it can isolate the connections if there's an overcurrent or over/undervoltage (or overtemp). That's usually the main contribution to safety. And it's also pretty typical that the BMS is what defines the charging profile: the charger basically just follows instructions from the BMS (and if it doesn't, said isolation comes into play as protection). This doesn't necessarily all happen on one chip: in the larger packs this is likely distributed between a few different components, including a chunky contactor for the isolation.
galaxyofdoom 3y ago
[dead]

holoduke 3y ago

Cheap active bms systems. Could be hazardous as well. But needed for charging from a 48v charger block.