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Guide on sizing transformers for crypto mining

Overheating transformers or the presence of triplen harmonics can set back your crypto mining operation. Learn more on sizing transformers for crypto mining.

Written by:

January 18, 2022

Crypto mining rigs powered by transformers

The two main reasons why transformers fail for crypto miners and the easiest way to avoid it.

If you are a crypto miner you may have encountered problems like:

Nuisance tripping

When you blow your breaker because of current or voltage surges.

Compromised insulation

When cables or terminals distort or melt because of excess heat.

Higher-than-normal failure rates

When the transformer fails before its expected lifespan. This often happens because a transformer is being used outside of the design parameters.


These issues come back to one central problem: many miners are overloading their equipment. Crypto mining uses a ton of power (more than Google, if you can believe it) and this means that the power systems for these operations are often being pushed to the max. Further, the world of crypto-mining is still new enough that the established best-practices and derating factors (which have been time-tested in other industries) are sometimes overlooked in the designing of a new mining project. For more on that read this article.

The two main reasons why transformers get overloaded in crypto operations are:

Too much heat

Transformers are built to run at 100% load with a MAX average air temp of 30°C (86°F). If it’s running hotter than that, it’s essentially running at limited capacity. It's like a computer CPU. If those fans sound like the prop on an airplane getting ready to take off and the transformer just can't cool off, performance suffers, and eventually, the lifespan of the transformer goes down.

Triplen harmonics

Crypto mines produce triplen harmonics that circulate in the primary windings and put off heat. This is basically a distortion of the normal electrical current waveform, generally transmitted by nonlinear loads. Switch-mode power supplies (SMPS), variable speed motors, drives, and electronic devices (like servers, battery chargers, and UPSs) are examples of nonlinear loads. Harmonics create more heat, further de-rating the kVA.

Note: Harmonics only circulate in the primary windings where the primary connection type is Delta. If the primary connection is Wye, the harmonics will feed back into the utility. Utilities never want distortion on their systems, which is why most crypto transformers are Delta on the high-voltage side, and autotransformers are rarely used.

How do you avoid these common problems?

Or, if you are already running in an overload situation and you want to fix or avoid these problems, what should you do?

We can visit with your team to make specific recommendations, but the basic rule-of-thumb is to size your transformers to operate at 80% of their expected load capacity (also known as kVA). In other words, the general rule-of-thumb is to choose a transformer kVA around 120% of your expected load. This provides a 20% margin to account for overheating and harmonics. The purchase cost of a slightly-larger transformer is relatively low, and the increased lifespan makes this an easy decision.

Another factor to consider when sizing is energy consumption. This is a separate topic, but the peak efficiency of any given transformer is almost always at a place on the efficiency curve significantly below 100%. The efficiency curves of a transformer are not entirely dissimilar from the relationship of speed and miles-per-gallon to fuel consumption in your automobile. Can you drive 100 miles per hour all the time? You certainly can, but the extra wear and tear on your equipment (heat contributing to reduced life span) and increased fuel costs (lost power consumption) generally make it inadvisable to drive 100 mph on a regular basis, just as it’s inadvisable to run your transformers at or above 100% load.

If you are a crypto miner (or anyone in need of the right transformer) and need help customizing a solution or finding the right fit, we are here to help. Here is a quick story on how SCATE Ventures uses Maddox transformers to power their crypto mining operations.

And just as a friendly reminder, supply chain disruption means that you should start your planning and purchasing process early. Check out our CEO’s advice here.

Find out how Maddox can power on your next project below.

Maddox padmount transformer loaded on truck

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