Overclocking a Bitaxe: AxeOS 2.15 guide with measured values and limits

Overclocking a Bitaxe means raising the clock of the mining chip (Frequency) and, when it becomes necessary, its core voltage (Core Voltage). More clock gives almost exactly proportionally more hashrate. More voltage does not add a single hash; it only keeps the chip stable at a higher clock and produces heat. This guide shows how to unlock overclock mode in AxeOS 2.15, which steps to take, what others have measured with real devices, and where firmware, cooling and power supply draw the line. We checked every limit in the source code of AxeOS 2.15.3 and the Nerd firmware 1.1.0.1.

What overclocking gets you, and what it does not

AxeOS calculates the expected hashrate from clock, core count and chip count and shows it in the dashboard as “Expected”. The BM1370 in the Gamma, GT, Nerdaxe Gamma and NerdQaxe++ has 2,040 cores, so every MHz adds 2.04 GH/s per chip. Since AxeOS 2.11 the firmware counts the hashes directly in the chip; the measured hashrate therefore follows the clock almost exactly as long as the voltage is sufficient.

Power, on the other hand, grows roughly with clock times voltage squared. 10 % more voltage means about 21 % more heat. At the same voltage a higher clock even becomes slightly more efficient, because fan, ESP32 and losses stay the same: in a series of measurements at a fixed 1150 mV, the energy per terahash dropped from 16.5 J/TH at 500 MHz to 14.7 J/TH at 800 MHz. As soon as you raise the voltage, the picture flips: a Gamma at 625 MHz and 1250 mV needed 19.8 J/TH in another series instead of 16.6 J/TH at factory settings. The rule is therefore: clock first, voltage only as much as needed.

With the stock cooler and stock power supply, 1.17 to 1.3 TH/s are realistic on the Gamma, 1.4 to 1.5 TH/s with better cooling. If you want a multiple of that, you need more chips: a NerdQaxe++ hashes at 4.9 TH/s out of the box, with an efficiency similar to a stock Gamma.

Unlocking overclock mode in AxeOS 2.15

Out of the box, Frequency and Core Voltage on the Settings page only offer drop-down lists. For the BM1370 (Gamma, GT, Copperzilla) these are 400, 490, 525, 550, 600, 625 and 690 MHz and 1000 to 1250 mV; for the Supra Hex 702, 400 to 575 MHz and 1100 to 1300 mV. Free values are only available in overclock mode, and there is no switch for it in the interface.

Step 1: In your browser open http://bitaxe.local/#/settings?oc; the IP address works instead of bitaxe.local too. The ?oc suffix unlocks the mode permanently; it stays active after a restart.

Step 2: Frequency and Core Voltage are now free number fields. Above them is a yellow warning: “Custom settings can cause damage & system instability. Only modify these settings if you understand the risks of running outside designed parameters.”

Step 3: Enter the new value and click Save. No restart is needed: AxeOS applies clock and voltage while running and ramps the frequency in small steps of 6.25 MHz. The set clock then appears in the dashboard as “ASIC Frequency”.

Going back: at the very bottom of the page there is now a Disable Overclock Mode button. It switches the input back to drop-down lists, but the saved values stay until you pick an entry from the list. You get the factory state back with “525 (Default)” and “1150 (Default)”.

Factory values and measured values per model

The table shows what the firmware presets for each device and, next to it, settings that others have measured with real devices. These are single devices and no guarantee for yours.

Three things matter when reading this. First, chips vary: five Gammas drew between 19 and 23 W at identical 678 MHz and 1180 mV, and in a test of three Gamma 601s only one managed 625 MHz, the other two already hit the test tool's temperature limits at 550 MHz. Second, a watt is not a watt: on the Gamma AxeOS shows the power of the voltage regulator plus a 5 W allowance, on the GT plus 10 W and on the Supra Hex plus 25 W. At the wall you measure more. Third, the values come from different setups; whoever manages 750 MHz at 1150 mV usually has a better cooler and a good chip. The series come among others from the result files of the Bitaxe Hashrate Benchmark, a series by a US retailer with a Gamma 602 and reports in the issues of the firmware projects.

Preparation: five minutes that pay off

• Current firmware: this guide describes AxeOS 2.15. Updating is easiest with flasher.bitaxe.de; with “Keep configuration” your Wi-Fi and pool are kept.
• Note the baseline: let the miner run for an hour at factory settings and write down the 1h hashrate, Error, ASIC Temperature, Voltage Regulator Temperature, Power, Input Voltage and Fan Speed. Without these numbers you will not know later whether a step brought anything.
• Check the cooling: heatsink firm, fan free, air can flow in and out. Overclocking exposes every weakness of the setup immediately.
• Know your power supply: how much power does it deliver continuously? Subtract 20 %; what is left is your budget. More on this below.
• Automatic Fan Control on: automatic fan control must be running, otherwise you lack the headroom when clocking up.

Overclocking step by step

1. Raise the clock by 25 MHz

In overclock mode raise Frequency by 25 MHz, leave Core Voltage unchanged, Save. On the Gamma that is from 525 to 550 MHz. 25 MHz is small enough that you know exactly which step was one too many if problems appear.

2. Watch for 15 to 20 minutes

The values need a few minutes to settle. Then check in the dashboard:

• Hashrate: the 10-minute average is at least 95 % of “Expected”. Below that, the voltage is not enough for this clock.
• Error: permanently below 0.1 %. Short spikes right after a change are normal. A firmware developer calls “anything less than 0.1%” good (discussion).
• Temperatures: chip up to 65 °C, voltage regulator up to 85 °C.
• Input Voltage: no “Danger: Low Voltage” warning, on the Gamma ideally above 4.9 V.
• Power: within your power supply budget.

3. Raise the voltage only when needed

If the hashrate falls below 95 % of Expected or the error rises permanently, raise Core Voltage by 10 to 20 mV and watch again. More voltage than necessary only produces heat. For the BM1370 the AxeOS list ends at 1250 mV; many retailers advise staying below 1300 mV for continuous operation. There is no public datasheet with an official upper limit for the chip.

4. Find the limit and step back once

Repeat steps 1 to 3 until you hit a limit: temperature, power supply budget or a voltage you do not want to exceed. Then go back one step. That one step of distance is your reserve for warm days.

5. 24-hour test run

A setting that holds for an hour is not stable yet. Let it run for at least 24 hours, better two to three days and through a warm afternoon. If hashrate, error and temperatures stay calm, it is your new standard.

Temperature limits: where AxeOS steps in

Automatic fan control only regulates on the chip temperature; you set the target with “Target Temperature” between 35 and 66 °C. It does not take the voltage regulator into account. That is why the regulator usually becomes the limit when overclocking: in a series at 1250 mV the chip only rose from 49 to 62 °C between 525 and 800 MHz, but the regulator from 57 to 94 °C. The front fan barely cools it, as the firmware developers confirm. So always watch both values while tuning.

If the chip exceeds 75 °C or the regulator 105 °C, AxeOS stops hashing, sets the fan to a fixed 100 %, waits at least 30 seconds and until the regulator is below 95 °C, and then carries on with 100 MHz less clock and 100 mV less voltage. It saves these lowered values permanently, and every further trigger lowers them again. The dashboard shows “Device has overheated - See settings”. This is how you clean up afterwards:

1. Fix the cause: location, fan, cooler, room temperature or too much clock.
2. On the Settings page set Frequency and Core Voltage back to your stable values.
3. Switch Automatic Fan Control back on. The overheat protection switched it off; otherwise the fan stays at 100 %.
4. If the Disable Overheat Mode button is still shown, click it only now; AxeOS itself reminds you to reset clock and voltage first.

Do not underestimate the room temperature. A setting that runs calmly in winter at 19 °C can trigger the protection in summer at 28 °C. If you tune in winter, check again in summer or leave more headroom from the start.

Power supply and plug: the underestimated limit

On the Gamma and all 5 V Bitaxes, the power supply is a chain, and the weakest link decides how far you get:

With the stock power supply and stock jack, the Gamma therefore tops out at about 24 to 27 W as shown in AxeOS. Depending on the chip that is roughly 650 to 700 MHz at 1200 to 1250 mV or 750 to 800 MHz at 1150 mV. A stronger power supply only helps up to the jack. One of the Bitaxe developers puts it in a nutshell: no matter how many watts your power supply has, if the connector has too much resistance the Bitaxe faults (issue 1188). Short cables and a firmly seated plug are a must when overclocking.

The 12 V devices have a higher limit, but it exists. The Bitaxe GT 801 starts from 11.0 V and switches off below 10.5 V; retailers recommend 12 V at 5 A for factory settings and 12 V at 10 A for overclocking. The Supra Hex 702 needs a power supply of about 100 W. On the NerdQaxe++ the stock 12 V, 10 A power supply has little reserve; by the 80 % rule you stop at about 96 W. Older revisions also have an 8 A fuse on the board that blows above roughly 100 W. Everything about choosing a power supply is in power supply for the Bitaxe.

Typical signs that the power supply is at its end: the message “Power Fault Detected. Check your Power Supply.”, the warning “Danger: Low Voltage”, a rising error without a temperature problem, and restarts under load.

Undervolting: more efficient instead of faster

Tuning also works the other way round. Lowering the voltage at the same clock saves the most: a good Gamma chip ran at 625 MHz with only 1100 mV at 14.6 J/TH, clearly more efficient than at factory settings. If you mainly want it quiet, lower clock and voltage together, for example to 490 MHz and 1100 mV; that costs about 7 % hashrate. More in making a Bitaxe quieter.

The lower limit shows up with the same check as for overclocking: if the hashrate falls below 95 % of Expected or the error rises, the voltage is too tight. A NerdQaxe++ at 740 MHz with too low 1150 mV only managed 66 % of its expected hashrate and used more energy per terahash than at factory settings.

Overclocking the Nerdaxe and NerdQaxe (NerdOS)

The Nerd firmware takes its own route. Next to the heading of the “Mining Settings” card sits a small button with a warning triangle, almost invisible by default, with the tooltip “Danger Zone”. One click switches to “Advanced”: frequency and core voltage become free fields, and fan control shows extra options. A double click switches to “Pro” with the parameters of the PID control. The browser remembers the level for 24 hours.

If a value is above the highest entry of the list, NerdOS opens a warning dialog “Saving Unsafe Settings” when you save. The firmware itself lists the risks there, including “Voids your warranty”, “May cause permanent hardware damage” and “Reduces device lifespan”, and with a wink “MAY SUMMON DRAGONS”. After “Proceed Anyway” the values are applied within two seconds, without a restart.

The Nerd firmware sets hard limits per board. On the NerdQaxe++ up to revision 6 they are 800 MHz and 1400 mV; the developer calls exactly that the absolute maximum. Revision 7 allows up to 1000 MHz. If the chip exceeds the “Shutdown Temperature”, 70 °C out of the box, NerdOS switches off the core voltage and shows “MINER OVERHEATED” or “VREG OVERHEATED”; the miner then needs a restart. Setup and fan settings are explained in the NerdQaxe++ setup guide.

Automatic tuning: benchmark tools

Neither AxeOS nor NerdOS has an autotune function. The developer of the Nerd firmware explicitly declined it because automation goes wrong on some devices, and points to external tools (issue 482). These open source programs run on your computer and control the miner through its interface on the Wi-Fi:

• Bitaxe-Hashrate-Benchmark (Python): starts at 500 MHz and 1150 mV, raises the clock in 25 MHz steps as long as the hashrate reaches at least 94 % of Expected, otherwise it adds 20 mV. Every step runs for ten minutes. Default limits: chip 66 °C, regulator 86 °C, 40 W.
• bitaxe-benchmark-webgui: the same method with a web interface and ready-made profiles for the Gamma and NerdQaxe++.
• NerdQAxe_hashrate_benchmark: for NerdOS devices, limited to 100 W by default.

Set the tool's power limit to your power supply, on a Gamma with the stock power supply to about 24 W instead of 40 W. The tools measure ten minutes per step; they do not replace the 24-hour test run of the best setting.

Cooling: what helps when overclocking

• Bigger heatsink: the ICE Tower Kit, the ICE Tower Low Profile Kit, the copper heatsink or the AXP60 Copperzilla copper cooler lower the chip temperature noticeably and create headroom for more clock.
• Better fan: the Noctua NF-A4x20 moves more air at the same noise level than many stock fans.
• Cool the regulator: a fan on the back of the board or small heatsinks on the voltage regulator components lower its temperature noticeably. Only mount them with electrically insulating thermal pads: a metal heatsink touching two contacts can destroy the regulator and the chip.
• Tuned from the factory: the Bitaxe Copperzilla is a Gamma with a large solid copper cooler that runs at 750 MHz and 1200 mV out of the box under OSM-OS.

All routes to more cooling and less noise are compared in making a Bitaxe quieter; the accessories are under Bitaxe cooling.

Symptoms after overclocking

• Hashrate clearly below Expected, error rising: too much clock for the voltage. Add 10 to 20 mV or go back one step. The error value is explained in Bitaxe hashrate error explained.
• “Power Fault Detected. Check your Power Supply.” Power supply or plug at the limit, the regulator's overcurrent shutdown or a core voltage below 1000 mV. After an overcurrent shutdown only a restart helps.
• Fan permanently at 100 %, clock lower than set: the overheat protection has triggered. Check values and Automatic Fan Control as described above.
• “Device frequency is set low - See settings”: the clock is below the lowest preset, on the Gamma below 400 MHz, usually after several overheats.
• Restarts without a temperature problem: almost always the power supply.
• More rejected shares: these usually come from the network or the pool, not from the clock. The error in the dashboard is the better measure of stability.

Is overclocking worth it?

In solo mining your chance of a block rises exactly in proportion to the hashrate. 600 MHz instead of 525 MHz at the same voltage bring 14 % more chance for about 2 W more power; that is almost always worth it. 625 MHz at 1250 mV, on the other hand, bring 19 % more hashrate for about 40 % more power and noticeably more heat and noise. The range where overclocking pays off most is therefore more clock at the same or only slightly higher voltage. What that means in euros and block chance is worked out by the mining calculator and finding a block with a Bitaxe.

Overclocking makes the most of an existing device, but it does not replace the next device class. If you want to multiply your hashrate, more chips get you further than more voltage; the miner comparison puts the devices side by side.

Frequently asked questions about overclocking a Bitaxe