Background: the Battery Charger and DC Power System

In this project, the customer operated a test facility that required a stable DC power system backed by batteries. The system included an AC-input battery charger, a bank of lithium-ion batteries and a DC distribution bus feeding measurement equipment and control electronics. Under normal operation, the DC bus had to remain within tight voltage limits, even when the grid was noisy or when loads changed quickly.

A new generation of hardware increased the charger power and added more loads to the DC bus. The design team expected that the combination of higher power switching stages, new battery chemistry and more cables would change the EMC behaviour. They had to prove compliance in an industrial environment and wanted to avoid multiple, expensive rounds at a certification house.

To manage this risk, they approached TPS for emc testing for battery chargers and DC power systems as a pre-compliance project. The goal was to understand how emissions and immunity changed across different charge states and load conditions and to identify any design changes needed before booking full certification.

EMC Challenge: Changing Behaviour Over the Charge Cycle

Initial checks on site and in the lab showed that the system behaved very differently depending on the battery voltage and whether the charger was in bulk, absorption or float mode. Several EMC challenges stood out:

• Conducted emissions on the AC input of the charger and on the DC output lines, with different patterns at low and high battery voltage.
• Radiated emissions from long DC cables and the cabling between the DC bus and sensitive measurement equipment.
• Immunity sensitivity during fast transients on the mains and DC bus, where some devices on the DC distribution experienced resets or incorrect readings.

The customer realised that testing only at “nominal” voltage would hide important behaviour. Any realistic emc testing for dc power systems had to include multiple operating points across the charge cycle and a representative set of loads.

TPS EMC Test Plan for Battery Chargers and DC Power Systems

Together with the customer, TPS defined an EMC test plan built around the real use case of the DC power management system:

• Defined operating windows. We agreed on several key operating points: low battery voltage with high charge current, mid-voltage at steady-state load, and near-full voltage with the charger in a lighter operating mode.
• Representative loads. The DC bus was loaded with a combination of real equipment and programmable loads so that current levels matched expected field conditions.
• Targeted EMC tests. For each operating point we measured conducted emissions on the AC input and DC output, checked radiated emissions around the cabinet and ran fast transient and surge immunity tests on both mains and the DC bus.

The plan followed the same principles as the TPS EMC pre-compliance guide, but tailored to the specific risks of chargers, batteries and DC distribution.

Debug and Design Improvements

With the test plan in place, the TPS team and the customer ran through several focused EMC sessions. For each issue that appeared, they adjusted the design and immediately re-measured the effect.

• Input and output filtering. Filters on the AC input and DC output of the charger were tuned to reduce noise at the key frequencies where limits were exceeded. Small changes in component values and placement led to noticeable improvements in conducted emissions.
• Cable routing on the DC bus. The path from charger and battery to the DC distribution rails was reorganised to separate noisy switching loops from sensitive measurement lines, reducing radiated emissions from long cables.
• Protection and control behaviour. The team added monitoring and soft-limit functions so that the DC power management system reacted gracefully to fast transients instead of causing voltage dips that upset connected equipment.

These steps turned the EMC lab time into a hands-on design workshop rather than a pass–fail exercise, giving the team confidence in how their battery charging system behaved under stress.

Results and Takeaways

After applying the agreed changes, the customer returned to a third-party EMC lab for formal testing. The updated charger and DC power system achieved:

• Stable conducted emissions results on both AC and DC lines, across the tested charge states.
• Radiated emissions from the cabinet and cabling within limits, with clear margin in the problematic bands identified earlier.
• Robust performance during fast transient and surge immunity tests, with no unexpected resets or measurement errors on the DC loads.

Even more importantly, the customer gained a repeatable approach for emc testing for dc power systems. They now plan EMC pre-compliance sessions whenever they change charger topology, battery capacity or DC bus architecture, instead of discovering problems only at the end of a project.

How to Prepare Your Own DC Power System for EMC Testing

If you are working on a battery charger or DC power system, you can prepare for EMC testing with TPS by collecting a few key pieces of information up front:

• A diagram of the system showing AC input, charger, batteries, DC bus and major loads.
• Battery chemistry, capacity and expected voltage range, plus main operating modes of the charger.
• Typical cable lengths and routing between charger, batteries, DC bus and sensitive equipment.
• Any previous EMC or field issues, including noise on measurement channels or unstable behaviour during disturbances.

With this information, our lab team can design a focused EMC test plan for your battery charging system or DC power management system, run pre-compliance checks and help you walk into third-party EMC certification with much less uncertainty.

Talk to an EMC Engineer About Your DC Power System   

Key questions this case answers

This case study speaks to the core search questions behind EMC testing for battery chargers and DC power systems:

• How EMC behaviour changes with battery voltage and charge mode in a real DC power system.
• Which EMC tests matter most for battery charging systems and DC power management systems.
• What kinds of design changes—filters, cabling, grounding and control—most effectively improve EMC margins.
• How to prepare data and hardware so an EMC pre-compliance session with TPS gives fast, actionable results.