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2 ways to use the OKS BMS Mobile App on Amazon Fire tablets

Tested on:

  • Fire HD 10 (11th Generation)
  • Fire 7

Amazon Fire tablets are cheap, yet they look and feel like a far more expensive tablet. In fact they are the best cheap tablet we have tried using by a wide margin. The screen is high resolution and its responsive, and the battery life is excellent.

So what’s the catch? The tablet is basically an Amazon ad delivery platform. It has a special version of the Android operating system and it has a lot of built in junk that you can’t delete. It also has it’s own version of an app store called the Amazon App Store. It does not come with the google play store, so you can’t load most of the apps that you are used to having. Unless, of course you hack it!

(We have not tested our app on older generations of Fire tablet hardware. If you encounter an incompatible device please let us know.)

Method 1: Sideload the Google Play Store APKs

We followed this guide on Howtogeek.com and successfully loaded the Google play store on our Fire HD 10 tablet. (Here’s a PDF of the instructions, in case the link breaks in the future) It’s a bit of a PITA because you have to identify 4 different APKs that match your hardware version and sideload them on the tablet. It’s worth the effort though, because then you can install any Play Store app normally, including the Overkill Solar BMS Mobile app. When tested on the Fire HD 10, the app performed flawlessly. You still need a google account to use the play store

Method 2: Sideload the Overkill Solar APK

The Overkill Solar BMS Mobile App can be sideloaded from the .APK file on Fire tablets just like any other Android device. Grab the latest release from our Github, enable permissions for installing 3rd party apps on your device, and install. HowtoGeek.com also has a helpful guide for sideloading apps. (click here for PDF copy)

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16 Cell Layout with a Pathfinder BMS

While I’ve been working on the new user manual, the programmer is making great progress on the firmware.

I’m pretty happy with how the new illustrations are looking. Here’s a preview: The cell connections for a 48v 16 cell LiFePO4 battery:

Figure? Shows the general layout of a 16 cell battery. Note that the most positive terminal (BC16) on the group of cells is connected only to BC16 and the “+Cell” terminal of the BMS. The “B+” terminal connects to the positive side of your electrical system.

The most negative terminal (BC0) on the group of cells is connected to the negative (or ground) side of your electrical system. It is OK to connect this wire to a chassis ground, if applicable.

It is difficult to draw all 16 cells on a single page. See figure? For a zoomed-in view of the balance wire connections. All 17 balance wires (AKA voltage sensing wires) must be connected as shown. See note 1.

Note 1: Which stud to use? Where is BCx?

We usually specify that each balance wire should be attached to the positive terminal of the corresponding cell. 

For example, connect wire BC2 to the positive terminal of Cell 2. 

This is only for consistency in the instructions, because anywhere on the node between 2 cells is the same as far as electricity is concerned. 

For example, wire BC2 can be connected to the positive terminal of cell 2, or to the negative terminal of cell 3, or it can be bolted or soldered to the center of the bus bar connecting these cell terminals. In fact, attaching the wire to the center of the bus bar may be technically superior, but we don’t think it’s worth the extra effort in practice.

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Pathfinder BMS Prototypes!

Good news, I finally have a complete Pathfinder BMS on my desk!

Status

I will be putting these up for pre-sale ASAP, but there is still work to do.

At a minimum, the datasheet needs to be finished before pre-sale can start.

After that, the firmware needs to be finished.

These BMSs are capable of OTA online or offline (UF2- drag-n-drop) firmware updates, but we will not ship them until the firmware is fully functional.

Pathfinder BMS feature list:

• 170 amps continuous duty rating.

• M10x1.5 solid brass studs with stainless hardware.

• Screw terminals accept up to 14ga wire for the balance wires. (18ga wire is recommended)

• Works with LTO, NMC, and LiFePO4.

• 3-16 cells LiFePO4 or LTO, 3-12 cells NMC.

• Cell count is field configurable, with various pre-set configurations available. (4s and 16s pictured above).

• Battery voltage up to 64v, and as low as 7v.

• Advanced State-of-Charge monitoring algorithms via a Texas Instruments BQ34Z100 Fuel Gauge chip.

• Positive-side switching (More intuitive, allows a chassis ground to the cell negative)

• Base plate with mounting ears and optional DIN rail mounts.

• 1 amp high current passive balancer built into the base plate.

• Modular open frame design, integrated air cooled copper heat sink.

• 2 external cell temperature probes + 2 internal temperature sensors.

• Wired discharge shutoff switch.

• OLED display and button pad.

• USB-C For wired monitoring and updates.

• Bluetooth and Wifi remote monitoring via optional internet connection.

• Password protection and encrypted wireless data.

• NO user accounts, NO spyware, always free monitoring applications.

Stay tuned, updates will be coming frequently now!

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New BMS current ratings

TLDR: 175 Amps

We are in the process of testing prototypes of the new Nomad and Pathfinder BMS to find the thermal limits and current ratings. (The current rating is determined by temperature limits)

In this test we have a constant current flowing thru the BMS main board. The target temperature for the advertised current rating is 50c, while sitting flat on the test bench at an ambient room temperature of 23c.

The BMS has a temperature sensor in the center of the MOSFET array (in addition to 2 external probes to measure cell temperature), and it will have a default cutoff temperature of 85c to protect the BMS. The BMS hardware can operate safely up to this temperature limit, so there is considerable headroom over the base current rating to account for higher ambient temperatures or temporary surge currents.

In this thermal camera photo, the temperature has stabilized at 50c with a constant current of 175 amps.

Tentatively, based on this testing, the base model Pathfinder BMS will be advertised with a 175 amp constant current rating. The Nomad BMS will be offered with fan cooling, which can as much as double the free-air current rating!

As this testing program continues we are gathering data for derating (and up-rating) curves based on ambient temperature and duty cycle.