Bosch Style Relay
The Bosch Style Relay is also known as a 5-pin, 5-prong, SPDT, or changeover relay and is a variant of the ISO Mini Relay.
As compared to a standard 4-pin SPST ISO Mini Relay (with terminals 85, 86, 30, and 87), the 5-pin Bosch relay has an extra terminal 87a, which is powered only when the relay is not energized. That is, when the control circuit connecting to terminals 85 and 86 is open, high-power current is allowed to flow to terminal 87a.
Bosch is an automotive supplier that produced the commonplace 5-pin relay for the automotive industry over many years. Although the relay division at Bosch was acquired by Tyco Electronics (now TE Connectivity) in 2006, the 5-pin relay is still referred to as a Bosch style relay.
According to DIN 72552 the coil should be fed with +12V to terminal 86 and grounded via terminal 85, however in practice it makes no difference which way it is wired, unless using a relay with an integrated diode.
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