If used correctly a reed relay is a superbly reliable device. The switch contacts are hermetically sealed and do not suffer from oxidization in the same way as an open electro-mechanical relay.
Frequently Asked Questions About Reed Relays Answered
Our experts here at Pickering have put together some information about the seven most frequently asked questions we receive in order to help you get the most out of our high performance reed relays.
If you follow the tips below, it will help you to achieve a reliable design with a long life from our products.
If you still require any technical help after reading this page you can contact us. Our technical experts will be able to assist you in any queries you may have regarding our relays.
1. What is a Pickering Reed Relay?
Watch this 3 minute video to learn what a Reed Relay is and how Pickering Electronics manufacture them.
2. Switching Methods
One simple method to greatly reduce the damaging effects of hot switching, and greatly increase the expected number of operations, is to cold switch the signal. Cold switching can increase a reed relays life expectancy to more than ten billion operations.
To understand what hot and cold switching is when using reed relays and the effects different switching methods can have on relay life expectancy watch this short video explanation by clicking below:
3. Life Expectancy
The life of a reed relay depends upon the switch load and end of life criteria. For example, for an ‘end of life’ contact resistance specification of 1 Ω, switching low loads (10 V at 10 mA resistive) or when ‘cold’ switching, typical life will be more than 1 x 109 ops. At the maximum load (resistive), typical life is 1 x 107 ops. In the event of abusive conditions, e.g. high currents due to capacitive inrushes, this figure reduces considerably.
In typical applications, for example, switching 10 volts at 10 mA, the life of dry reed relays will be in excess of 100 million operations.
Pickering have carried out a wide range of life testing to understand performance at different loads and will be pleased to perform life testing with any particular load condition, to help you choose the best relay for your application. Please contact us to request life testing.
Calculate how many operations you require from the relay. If it is operated once a second, 24 hours a day, it is worth noting that there are about 31.5 million seconds in a year. The most common reliability problems are caused by abusive loads. – Read On!
4. Capacitive Loads
When capacitive loads are switched, there is a danger that the initial surge current will exceed the rating of the switch, thereby shortening the life of the relay.
To prevent this, a surge limiting device, the most simple being a resistor, should be used. Long cable runs should also be considered, they can sometimes have surprisingly high capacitance.
5. Inductive Loads
Arcing can occur when a reed switch is used to break a current to an inductive load. The back EMF can cause contact damage and should be eliminated by the use of an RC snubber, varistor or in the case of a DC load, a diode. Contact our technical department for further details.
6. How Does Temperature Affect Reed Relay Coils?
The standard must operate and must release voltages of Pickering reed relays are 75 percent and 10 percent respectively of the nominal coil voltage at 25°C, that is 3.75 volts and 0.5 volts for a 5 volt relay. It is important to consider external affects that can change these parameters, for example temperature or magnetic interaction, and any impact they may have on the operation of the part.
The copper coil wire has a positive temperature coefficient of approximately 0.4 percent per °C, so if the temperature increases by 50°C, the voltage required to operate the relay will increase by around 20 percent. It is important to remain within the maximum operating temperature specified for the device to ensure correct operation.
The operate voltage is also affected by the extraneous magnetic fields from adjacent relays, this can result in up to 40% increase in operating voltage for an unscreened relay. The majority of Pickering reed relays feature either an internal or external mu-metal magnetic screen to eliminate this problem ensuring they can be stacked side by side with no issues.
7. Operate Times
The typical operate time of a dry reed relay is between 250 microseconds and 1 millisecond, depending on switch type.
The Form A (energize to make) types in the small Single-in-Line relays are the fastest, typically 250 microseconds.
The release time is typically one half of the operate time.
8. Where are Pickering Reed Relays Manufactured?
All Pickering reed relays are manufactured in the United Kingdom and the Czech Republic.