Tech Tips

Silicon Controlled Rectifier and High-Frequency Battery Chargers

C-Tech supplies a wide variety of battery chargers. There are two main types of chargers, with multiple voltages: Silicon Controlled Rectifier (SCR) and High Frequency. This article will give an overview of using SCR and High-Frequency chargers, as well as their advantages and disadvantages.

Silicon Controlled Rectifier

The SCR is basically a high-speed switch that can be shut on and off as many as 1000 times per second. By varying the "on" time, the output voltage varies. This is a highly efficient means of controlling voltages and reduces the heat generated and amp draw of the traditional basic transformer type chargers. Chargers using SCR circuits are charged when the voltage drops below a certain threshold. Once fully charged, they turn off completely. This eliminates the problem of overcharging and batteries becoming boiled. SCR chargers are easily repairable with mostly readily available repair parts like fuse assemblies, relay boards, SCR assemblies, control boards, circuit breakers, ammeters, and transformers.   

SCR chargers are prone to variances in input voltages (AC) which will affect the output voltages (DC). These usually have a pre-determined “start rate,” voltage/amperage output, and a pre-determined “finish rate.” These rates taper as the battery becomes charged, but the start rate will stay the same when the charger gets plugged in. SCR chargers have a large transformer and these are usually much heavier than the High-Frequency chargers. This adds to the “landed cost” for the customer. These produce a noise level of about 80dB from the SCR oscillation. Input voltage and hertz rating are preset so correct voltages are a must when ordering.

High-Frequency Chargers

High-Frequency chargers use newer technology with transistor controller circuitry and are the most common in our industry. Through the use of integrated circuitry, these chargers will produce a high output voltage and amperage when first hooked up to “excite” the plates in the batteries. In most cases, these weigh about 60% less than the SCR version as they have multiple small transformers. Input voltages and hertz ratings are internally adjusted through the use of integrated circuitry. By using multiple transformersHigh-Frequency chargers require less energy and are more efficient than the SCR versions. This means that the overall cost of charging the batteries is less. With a noise level of about 50dB, the High-Frequency chargers are much quieter and more compact than the SCR versions.

The two main suppliers for High-Frequency chargers are Signet and Delta-Q.

  • Signet Input (AC) Voltage: 90 to 283V (AC) - automatically adjusts
  • Signet Input Hertz: 47 to 73Hz - automatically adjusts
  • Delta: Input (AC) Voltage: 93 to 265V (AC) - automatically adjusts
  • Delta Input Hertz: 48 to 70Hz - automatically adjusts
  • 24V chargers must see at least 13.8V (DC) from the batteries for the charger to turn on.
  • 48V chargers must see at least 27.9V (DC) from the batteries to turn on
  • Algorithms are preset and require no adjusting
  • Vehicle interlock option standard: prevents the use of equipment when charging cycle is in progress.
  • Self-diagnostics built in with flashing LEDs to troubleshoot problems
  • Flooded or Gel compatible
  • Failure to set algorithm can result in improper output, overcharging, failure of the charger to turn off, undercharging, batteries overheating, etc.

Important Information

Fully charged deep cycle batteries will put out 2.30 to 2.45V per cell. This means that fully charged batteries will put out the following:

24V system →


27.6 to 29.4V

36V system →


41.4 to 44.1V

48V system →


55.2 to 58.8V



SCR and High-Frequency battery chargers both offer advantages and disadvantages. Selecting the appropriate battery charger depends on the battery, the specific application need, and budget.

C-Tech offers the most expansive selection of SCR and High-Frequency battery chargers for your equipment on our secure website here. Our friendly and knowledgeable staff is available to help you select the correct battery charger for your boom or scissor lift. Questions or comments? Contact us at 1-888-755-7311, email us at, or chat with us online.