Products for USB Sensing and Control

Products for USB Sensing and Control


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DC Solid State Relay - 120V 25A

ID: 3957_0

This SSR switches up to 120VDC / 25A and connects to any device with a digital output.


Quantity Available: 104

Qty Price
5 $21.12
10 $20.24

If you need to switch DC power, this solid state relay is the perfect mix of quality and affordability. Using the digital outputs from a Phidgets device, you can control the relay to silently switch a DC circuit at 120V/25A or less. There's an indicator LED on the control side of the circuit so you can tell the state of the relay at a glance.

If your SSR is overheating, you should consider getting a heat sink for safety. See the "Compatible Products" tab for a list of compatible heatsinks. This SSR comes with a heat transfer pad that can be placed between the metal base of the SSR and the surface it's mounted to in order to help encourage heat flow. It also comes with a diode that can be used to protect your SSR against back EMF.

Comes Packaged with


This relay comes packaged with a heat transfer pad and a 10A02-T diode. Use the heat transfer pad whenever mounting the SSR on a heat sink or metal surface. Use the diode in parallel with your load in order to protect your SSR. For more information, see the Solid State Relay Primer.


This relay can be controlled using a Phidgets relay output board. See the "Compatible Products" tab for details.


  1. If you're running the SSR close to it's maximum current rating, you'll probably need to mount it to a heat sink or a surface that can function as a heat sink.
  2. Use the heat transfer pad between the SSR and the heat sink. Failure to do so can cause overheating and could damage the relay.
  3. Make sure that the SSR terminal screws are tight. If the screws are not tight, the SSR will get damaged by heat generated when the power is ON.
  4. When an SSR fails, it most often fails permanently closed - leaving your load powered, and possibly creating a fire or safety hazard. Be sure to have failsafes in these situations.
  5. You can use a fuse to protect your circuit from wiring mistakes and accidental short-circuits.
  6. Make sure that you use the relay within the product specifications.
  7. Ensure that the relay terminals are covered or protected when switching high voltage loads.

Product Specifications

Electrical Properties
Isolation Method Photoelectric
Dielectric Strength 2.5 kV AC
Control Voltage Min 3 V DC
Control Voltage Max 32 V DC
Load Voltage Min (DC) 5 V DC
Load Voltage Max (DC) 120 V DC
Load Current Max (DC) 25 A
Load Surge Current 100 A
Turn-on Time Max 2 ms
Turn-off Time Max 2 ms
Physical Properties
Length 57 mm
Width 43 mm
Height 25 mm
Operating Temperature Min -20 °C
Operating Temperature Max 80 °C
Other Properties
Manufacturer Part Number KG1025D

Relay Output Boards


This SSR can be controlled using our relay output boards; ordinary digital output boards usually don't have sufficient power to activate the relay. Just connect the positive control terminal of the SSR to the +5V terminal on the relay board, and connect the negative terminal to an output on the relay board.

Product Relay Properties Electrical Properties
Image Part Number Price Number of Relays Load Current Max (DC) Load Voltage Max (DC)
1012_2 $100.00 16
REL1100_0 $25.00 4 8 A 30 V DC
REL1101_0 $50.00 16 8 A 30 V DC


If you're switching high current devices or circuits, we recommend that you use a heatsink. In some applications, you may be able to mount the relay to a metal surface which can act as a heatsink by itself. This relay comes with a heat transfer pad that you can sandwich between the relay and the heatsink or mounting surface. When screwed on tight, it will eliminate any air gaps and ensure that the heat conducts from the relay to the heatsink. In cases where the heatsink cannot dissipate heat fast enough, you should add a fan to one end of the heatsink so that air is constantly moving through the fins.

Product Heatsink
Image Part Number Price Thermal Resistance
3955_0 $5.50 2.4 K/W
3961_0 $18.00

Here's a list of our DC solid state relays:

Product Electrical Properties
Image Part Number Price Control Voltage Min Control Voltage Max Load Voltage Min (DC) Load Voltage Max (DC)
3957_0 $22.00 3 V DC 32 V DC 5 V DC 120 V DC
3958_0 $45.00 3 V DC 32 V DC 5 V DC 120 V DC