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Old 17-02-2018, 10:59 AM   #11
Teedoubleudee
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I think that board might be using opto couplers.
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Old 17-02-2018, 11:00 AM   #12
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Those ready made relay boards have reverse diodes pre fitted across the relays coils, plus they usually have opto isolated relay coils too i.e. an opto isolator is between the input terminals and the relay coil.

Generally a DC operated relay should have a inverse diode across its coils to absorb the Bemf generated as the relays coil voltage collapses when the power is turned off. The Bemf can do damage to electronic circuits or switch contacts.

Dont forget any relay MUST operate and then drop away disconnecting the feed again within a maximum of 1 second when feeding a Solenoid point motor.
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Old 17-02-2018, 11:14 AM   #13
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That's cool, so I won't need them here then?
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Old 17-02-2018, 11:18 AM   #14
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Quote:
Originally Posted by JonMiles View Post
That's cool, so I won't need them here then?
No they may well be pre fitted and as the input is isolated too you don't have to worry
The 16 small square items on the right end in groups of 4 are the Opto isolators
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Old 17-02-2018, 11:28 AM   #15
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Excellent, thank you
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Old 17-02-2018, 11:48 AM   #16
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The two large ICs next to the relays are highly likely Darlington arrays and it is they that need protecting from the back e.m.f. not the switched outputs hence it is a certainty that the components identified earlier are the reverse diodes.

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Old 17-02-2018, 12:27 PM   #17
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Quote:
Originally Posted by JonMiles View Post
The relays are throwing the point motors using the power from the CDU

I like that board - tad more compact than mine which uses Maplin car 12V 10A headlight flasher relays and measures up around 3 ft by 9 inches mounted on a wooden plank with 32 relays and 4 acc decoders (2 x relays per acc decoder port and 4 ports per Hornby acc decoder i.e. 2x4x4=32).

Must get round to modernising it.
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Old 17-02-2018, 12:30 PM   #18
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lol, mine was a workaround to have modular boards and low current connectors, plus the Arduino can be used for much more.
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Old 17-02-2018, 07:46 PM   #19
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Excellent, thank you
Thats OK .
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Old 18-02-2018, 12:22 PM   #20
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You will be best fitting reverse protection diodes across your solenoids.

Because you will be switching the motors off after 10mS the CDU will not be fully discharged, so the relays will be switching off under current (probably around 6A) and the collapsing field will generate an arc across the relay contacts. Most relays will probably last a long time, but you will maximise the life of the relays by adding the diodes to shunt the back EMF. 1N4148 can be used, and they cost less than a penny each from the right suppliers.

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