I'll add it to the todo list for once I have the cells to build my next two packs.
JK 4S 200A BMS
- Thread starter Nami
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I'll add it to the todo list for once I have the cells to build my next two packs.
Rednecktek
Solar Wizard
Braver man than I!
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The 5-wire "main cord" is shown as a switched grounding connection in Nami's previous diagrams.
If heating pad current will be below 3A, and total power also below the limit on an 8S "25.8V" battery pack, the heating pad "ground" can be wired directly to the bundled 'main cord' of green wires. The black and red wires ARE NOT currently used at all: They are only present on the connector for a possible future power supply, to be designed JK. The heating pad "hot" connection, and any heating pad switch, should be left enabled at all times. The JK will enable the "main cord" grounding connection whenever the detected battery pack temperature has fallen below the 'minimum charging voltage' temperature setting of the BMS.
In my upcoming test configuration, using a single 4S battery of adequate size, I will be testing two ways. First, with a single "12v" heater pad connected directly from the +12v bus to this grounding cord. That test will run at slightly over 2A.
Then I will re-wire, using this switched grounding connection as the "coil" ground of a normally off (NO) automotive-type mechanical Relay. This Relay will have a "12V" coil (matching my 4S battery pack), although automotive-type Relays with "24V" coil voltage are readily available as well. An 8S "24v" battery pack would use one of those instead. In this configuration, the Relay "Load" terminals interrupt the permanently connected "hot" wire, which is driving two parallel heating pads @ 2A each, 4A total current. (The pads are permanently connected to the main grounding bus, outside of the BMS.) Use of the Relay supports higher current to the pads, through the Relay's "load" terminals, while using hardly any current at all to activate the coil. In my production configuration, I will have 3 heater pads.
Will your heater pad consume more than 3A? And, was this "verbal diagram" sufficient for you?
Braver man than I!
If cheap 150 or 200 amp anl fusses are used It shouldnt be too bad.
hwse
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Andy at Offgrid garage did just that only he used closer to 0% (2.5v) vs 100% (3.65v) You can watch it go crazy high amps (or not) starting at 12:30
So 0% and 100% is bad mojo, what about 10 and 90? Or 20 and 80?
I didn’t like how he slowly clamped the bus bars, sure it was his method of protection, but it glossed over true inrush current at the lower delta cells of say a BMS/breaker closing in. There’s bound to be a safe margin. He’s shown it multiple times on his three bank set up it, opening and closing breakers.
I didn’t like how he slowly clamped the bus bars, sure it was his method of protection, but it glossed over true inrush current at the lower delta cells of say a BMS/breaker closing in. There’s bound to be a safe margin. He’s shown it multiple times on his three bank set up it, opening and closing breakers.
hwse
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He did is slowly so that he could monitor and make adjustments rather than an all or nothing. The point was that even at the extreme 0%/100% the current was not off the charts. Yes, it did exceed the 200A limit on his meter but not by much. This is evident by the fact that after a few seconds of messing with it, he was able to tighten everything down and it was less than 200. His point was that as long as you are not going to the extremes of differential voltage (outside of the knees) then you can connect and there will be only minor current (60A or so)
He was not advocating that this is good practice. He was testing at the extreme limit to find out what would happen so that the rest of us could learn at his expense.
They have too much delay, in shutting down the sudden excessive current. The BMS (for either the sender or receiver) could be easily become fried, if this instantaneous amount exceeds the maximum instantaneous capability of the BMS. That would either leave the battery completely unprotected, or totally unusable.
Totally unusable is the more likely case, and the failure is more likely with the receiving battery (because the physical limits of the charging circuit path are probably lower than the limits of the discharge path).
That's why UpNorthandPersonal describe fast-acting Class-T fuses as the only viable solution for this situation. Cheap ANL fuses burn out too slowly, one or both BMS units will already be dead before an ANL burnout occurs.
I agree that "slow clamping of the bus bars" provided a highly effective (and undesirable) additional protection. He should have had the bars clamped tight from the beginning, and used a 500A battery switch to engage the connection.
In the photo above, the cross-sections of his bus bars look too small (to "support" much more than 250A without creating very high resistance). So even though he "claimed" the discharging pack to be 100% SOC, it actually discharged with very high internal voltage drop - probably "behaving" like a pack at relatively low SOC.
For a pair of 280aH battery packs built like mine, built with thicker bus bars clamped tight at the beginning of the test, an AWG 4/0 "test" could possibly reach the 350A "instantaneous discharge" limit of the BMS, and I will be trying to approach that instantaneous discharge figure on the single pack under test. I will also be testing with substantial continuous current in resistive loads, both below and above the default 200A continuous limit, and verifying a programmed change in that limit to be successful.
I do not intend to "test" maximum input current near the limits the of BMS device, having no wall chargers capable of doing that. I could thertically create a test similar to the video, but its set-up would be very time-consuming. Instead, I will configure my charge sources, 65A+30A, to run with maximum CV @ 14.6V within a couple of tests. The first test will simply run charging with the default and higher charge current limit (100A continuous) and verify that charging runs uninterrupted until one of the cells reaches the individual default cell limit 3.65V, and that balancing of approximately 1A occurs afterward. (I will load a single cell with a 'moderate' resistive load to hold its voltage down, while 'balancing' attempts to bring it back up to match the other cells.)
Then, after discharging the battery to a lower SOC, I will reduce the charging limit to only 70A, and verify that use of the first "source" runs without problems, but adding the second disables the charge circuit.
I don't know whether any default values are provided for "Charging Low Temperature Protection" and "Charging Low Temperature Recovery", but I will be modifying these values to test for functionality of the heater circuit. (2A - 26 Watts without a Relay, and then using an automotive Relay with miniscule "coil current" on the BMS port to drive two pads at 2A each. The design limit of the heater circuit interface is 3A.) The ability of LFP cells to accept charge current increases over a range of temperatures, but the two provided switches are of course ON/OFF. I will be testing with a lower-powered wall charger. For testing with temp sensors in an ice bath, I am inclined to invoke "protection" at around 4C, and set "recovery" to a slightly higher value - maybe 6C. I don't know if the values may be set the same (some differential might be required). I will probably use 3C/4C in production with my higher-powered charging sources.
Thanks for clearing up the red and black wires on the heating port pigtail. Has anyone determined if the JK BMS records the current being drawn thru the heating port?
No idea - yet. I'll report if I see such a number in either the hard-wired monitor or the Android App. In any case, I'll be using a pretty accurate "coulomb counter" monitor on that interface during upcoming testing, and I can compare any JK- presented number (on the hard-wired monitor, of the Android App) to the current being shown on the "coulomb counter".
For the moment, my new-to-me 200A JK BMS with heat function is not activating successfully. Both the simple display (with a white activation button on the side) and the pushbutton switch can turn it off, and attempt to turn it on. But, when an attempt is made to activate the BMS with a 4S LFP pack at 1.32V (already in good balance), the simple display monitor shows some unexpected things:
In all cases, the BMS does a partial startup, ending with audible beeps and a blinking LED (indicating that Bluetooth is inactive). The default value for "battery size" is documented to be 400 ah, so I am unclear what the 0.0% figure is referring to. Maybe it's a display of current, rather than SOC.
In any case, I can't activate the Charge /Discharge/Balance circuits from the cellphone App, because Bluetooth won't come up. I hope that the undocumented error code "9" corresponds to a user-fixable problem. The draft manual only describes lower-numbered error codes 1 thru 5.
- An "ERR" code within a box in the upper left side of the display, showing code 9.
- A small red warning triangle on the upper right side.
- The very curious value 0.0%, in big yellow lettering, is present in the middle of the Display (presumably referring to a calculated remaining SOC).
- Below that 0.0% value, a bright bar indicates the battery to be almost completely full, and the correct voltage 13.2V is shown on the lower right.
In all cases, the BMS does a partial startup, ending with audible beeps and a blinking LED (indicating that Bluetooth is inactive). The default value for "battery size" is documented to be 400 ah, so I am unclear what the 0.0% figure is referring to. Maybe it's a display of current, rather than SOC.
In any case, I can't activate the Charge /Discharge/Balance circuits from the cellphone App, because Bluetooth won't come up. I hope that the undocumented error code "9" corresponds to a user-fixable problem. The draft manual only describes lower-numbered error codes 1 thru 5.
Andy (Off Grid Garage) ran into that same error. It is due to the default config being set to 8 cells rather than 4 in your setup. You might rewatch his review as he ran across a couple of other little gotchas on the road to getting it working
hwse
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Another of the things that Andy found was that the default chemistry was not LFP so that needed to be changed as well as the limits.
I can now connect, but cannot set parameters from the Bluetooth/Android App. It insists that I have "failed password verification" every time, both before resetting the default PW ('1234') and modifying it to be '12345'. Restarted the phone and the BMS as well, for both password values.
Unsure whether I should perhaps downgrade to the previous version of the App. I am running V4.6.5.
Or 12345678
The manual linked from within the Resources has that password in it: https://diysolarforum.com/resources/jk-bms-active-bluetooth-bms-manual.250/
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