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  1. dmwahl

    3-192S Arduino BMS (using BQ76PL536A)

    Here's my generic advice, I'm not too familiar with the part you mentioned although TI does seem to follow similar paths with their hardware. I'd suggest checking with TI for code examples, then hooking up a scope or logic analyzer to make sure your basic functions (read/write) are working. Once...
  2. dmwahl

    NEW FLEXVOLT 20-60V dewalt battery

    They did it to use more powerful motors, more efficient controllers, and lower resistive losses for a given power output. At the motor itself, sure, torque is just a function of current, but everywhere else higher voltage improves efficiency and reduces heat. Otherwise they could just run all...
  3. dmwahl

    Yet another BMS

    Did you have to duplicate the read process? I haven't had any issues reading from the ROM with only a single write. I have a 1ms wait between sending the address byte to read and doing the actual read since the datasheet says it takes ~200us to read from ROM, but I didn't need to do the read...
  4. dmwahl

    Yet another BMS

    No, there's a process to write to ROM detailed in one of the app notes. I forget the details but as I recall it's basically the following steps with a wait between them to allow it to actually do the write. 1) Enable EEPROM access 2) Write the byte to EEPROM twice 3) Disable EEPROM access 4)...
  5. dmwahl

    Issue with Headway 40152 battery pack

    There's likely some damage to the 0V cells, but not necessarily enough to be a problem. LFP is more tolerant of abuse than some of the other Li-ion varieties. The longer you wait to recharge them the worse the problem will be. I've done the same accidentally on my lawnmower pack (8S2P, headway...
  6. dmwahl

    BMS 12 AWG enough?

    The shunt is just a precise, low value resistor. The controller measures the voltage across the shunt to calculate current. If you reduce the resistance of the shunt by adding solder, extra wire, or whatever, then the amount of current it takes to get a certain voltage goes up (V=I*R). The...
  7. dmwahl

    BMS 12 AWG enough?

    There's no real limit to how much current the wire can carry, as long as it's not enough to damage the wire. You could send 1000A through 32awg wire as long as it's a short enough pulse and you have enough voltage to overcome the wire resistance. The limitation is thermal, not some physical...
  8. dmwahl

    BMS 12 AWG enough?

    As far as peak current, it doesn't depend on wire length, it's just a matter of power per unit length, and how well the wire can shed heat without getting too hot. The problem comes when you start either overheating something or wasting a significant portion of your total power in anything other...
  9. dmwahl

    BMS 12 AWG enough?

    10awg is ~1mOhm/foot, 12awg is ~1.6mOhm/foot. Since P=R*I^2, 45A will dissipate ~2W/foot for 10awg and ~3.2W/foot for 12awg. Compared to 3kW total, it's not likely to matter much to performance. Personally I have an 18S pack using 12awg, and no issues up to 80A peak.
  10. dmwahl

    Outdated

    I've received batteries via UPS freight, up to 8 100Ah LFP cells in a pack. Nothing special, just talk to them about what you want to do. Otherwise something like uship.com might be an option, I don't know if they have specific rules on hazardous freight, but you can ship a car with a full gas tank.
  11. dmwahl

    13.6v AC charger?

    I'll second the meanwell recommendation. They're sometimes used in commercial LFP pack designs as battery chargers, set around 3.45V/cell for float use. There are also lots of meanwell clones on ebay, amazon, etc. I've got a 25W 12V clone I got on Amazon for ~$10, bought it for a 200Ah GBS pack...
  12. dmwahl

    DIY BMS Help

    As I recall there are all sorts of rules for the FSAE. I was part of it in college, as well as the hybrid vehicle team, and for some parts the rules are such that they basically force you into a specific voltage if you want a fighting chance. Like max power, max battery voltage, max fused...
  13. dmwahl

    DIY BMS Help

    Old laptop cells aren't intended for high current even when they're new. You'll need a huge pack to get any decent power and then the weight and size may be a problem. I'd suggest checking out okashira's sale thread for Tesla cells. He can build the pack for a very reasonable price and they're...
  14. dmwahl

    DIY BMS Help

    If you're budget limited, building your own BMS will not help. Although it is a fun exercise (speaking from both personal and professional experience). Don't bother with capacitive or switched inductors, way too complicated and unless you use old laptop cells or hobby lipo (bad idea) your pack...
  15. dmwahl

    Recommended Trike for Ebike Conversion

    I'd suggest finding a local shop that sells them and go test some out. I have a KMX trike with a leaf hub motor, and works very well and is quite comfortable once adjusted. I'm ~6' and 170lb with no mobility issues. I will say that getting on and off is a bit awkward, although not bad. My...
  16. dmwahl

    LifeP04 voltage drop after fully charged...

    It's totally normal, although I don't fully understand the chemistry behind it. You can set the charger voltage lower, but you're unlikely to notice much difference other than slower charging when it nears full and maybe marginally improved life. The amount of energy actually absorbed once the...
  17. dmwahl

    active balancing BMS

    I can see how it would be of use to you bobc, but still can't think why the OP wants such extreme balancing currents. Maybe it will help the OP by putting some numbers to the problem... Say you have an initially balanced 100Ah pack, that over a single discharge goes out of balance by 5%...
  18. dmwahl

    IS Disc Mount Torque Arm, Clamping Optional

    Drilled and tapped one this weekend to make it a clamping version, photos here: https://endless-sphere.com/forums/viewtopic.php?f=31&t=69073&p=1220325#p1220325
  19. dmwahl

    18650 battery pack build Kepler style

    I like it, I've been debating how best to mount my similarly shaped LFP pack (40152 cells) and I think this is a winner. Really looks like it belongs there.
  20. dmwahl

    active balancing BMS

    Why do you want 10A balance current? The only reason I can see would be using massively unbalanced, poor quality cells, and then you should probably just replace them. For an initially balanced pack, any more than a few hundred mA is overkill with a digital system. Efficiency gains are also...
  21. dmwahl

    Experimenting with 32v DC fuses at 48v and 68v

    There's no conversion from AC ratings to DC. If there's not a DC rating on the fuse, don't use it for DC. The reason is that AC changes polarity at 50 or 60Hz. During that change the current drops to zero, which makes extinguishing the arc easier to do.
  22. dmwahl

    RC lipo to replace 24V sla in ups?

    I've used some old LiFePO4 with the crappy single cell "balancers" with a UPS and it works great. The voltage comes up to about 13.6V (3.4V/cell) and the current drops to zero. The charging circuit doesn't force a trickle current into the battery once it's at the maximum voltage, it just holds...
  23. dmwahl

    BMS ??

    As mentioned, any of the *fire batteries are basically junk. You'll find they perform a lot like worn out laptop cells, and only get worse under high drain conditions. I'd be surprised if you can get 55A out of one even in a dead short. Cells in the 18650 format are not typically rated for...
  24. dmwahl

    BMS ??

    More details on your project would help with recommendations. Keep in mind that cheap and reliable are often competing requirements.
  25. dmwahl

    3-192S Arduino BMS (using BQ76PL536A)

    Schematics are linked on the first page. PM me if you are looking for professional assistance with your project.
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