Using a Cryostat with a Battery Backup or Power
Conditioner: Why It’s a Bad Idea

It is common for labs to look for ways to protect critical equipment during power disturbances. Battery backups and UPS systems are often installed to protect computers, analyzers, and sensitive electronics. However, connecting a cryostat to a battery backup or UPS system is a serious mistake and can lead to premature failure of the refrigeration system.

This applies even when using a pure sine wave power conditioner with battery backup.

Cryostats use compressor-based refrigeration systems, which behave very differently from electronic loads. Understanding why is critical for protecting your instrument.

Cryostats Are Inductive Loads, Not Electronic Loads

A cryostat compressor is a high-inrush inductive load. When the compressor starts, it draws a large surge of current that is many times higher than its normal running current.

Inductive loads like compressors have several characteristics that make them incompatible with battery backups:

• Very high startup inrush current
• Rapid load changes during cycling
• Reactive power demands
• Mechanical inertia that resists sudden changes

Most UPS and battery backup systems are designed for resistive or electronic loads, not inductive motor loads.

Why Battery Backups Struggle with Compressor Loads

Even high-quality UPS systems are not designed to handle compressor startup behavior.

1. Inrush Current Overloads the UPS

When a cryostat compressor starts, the inrush current can exceed what the UPS inverter can supply. It is not uncommon to see an initial current draw 50+ amps when the compressor starts, then it will normalize to around 8 amps. If a UPS is used it will cause:

• Voltage sag at startup
• Inverter stress
• Repeated fault cycling
• Unexpected shutdowns

Over time, this damages both the UPS and the cryostat.

This inrush current issue is not limited to power outages. A cryostat compressor draws high startup current every time it cycles on. Even when normal utility power is present, most UPS and battery backup systems remain in the power path or actively regulate voltage. As a result, the UPS still limits or interferes with compressor startup, which can cause long-term damage over time.

2. Battery Systems Cannot Respond Fast Enough

Compressors require instantaneous current delivery. Batteries and inverters cannot react quickly enough to sudden inductive demands, even if the UPS is oversized.

This can result in:

• Partial compressor starts
• Stalled compressor starts
• Overheating windings
• Increased wear on start components (start capacitor and relay)

3. Frequent Switching Between Line and Battery Power

During unstable power conditions, a UPS may rapidly switch between utility power and battery power. This repeated switching is extremely harmful to compressors.

Each transition can cause:

• Brownout conditions
• Repeated restart attempts
• Excessive mechanical stress
• Thermal cycling of motor windings

Cryostats are designed for stable, continuous line power, not fluctuating sources.

Why Pure Sine Wave UPS Units Still Cause Problems

Many labs assume that a pure sine wave UPS eliminates risk. While pure sine output is essential for sensitive electronics, it does not solve inductive load problems.

Even with a pure sine wave:

• Inverter current limits still apply
• Battery discharge rates still restrict surge capacity
• Transfer timing still causes micro interruptions
• Compressor start torque is still insufficient

A pure sine wave UPS defines the waveform quality, not inductive load compatibility.

What Damage Can Occur to a Cryostat

Running a cryostat on a battery backup can lead to:

• Compressor overheating
• Premature compressor failure
• Start relay or start capacitor failure
• Control board stress from voltage instability
• Refrigeration faults and temperature instability

These failures are expensive and often not covered under warranty if improper power sources are used.

What You Should Use Instead

If power quality is a concern, safer alternatives include:

• Dedicated circuits with proper grounding
• Surge protection devices rated for motor loads
• Power conditioners without batteries
• Facility-level backup generators with proper load capacity

These solutions protect the cryostat without introducing inverter-related risks.

If protecting your cryostat matters, avoid battery-backed power systems and use solutions designed for motor-driven equipment.