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Yes I’m sorry ban-all-sheds but I did not understand what you wear talking about before when you mentioned single DPs and latching contactors
And the KISS thingy sounds a bit off if you know what I mean
KISS = Keep It Simple Somehow ( Or Keep It Simple Stupid if appropriate ).
But sometimes keeping it too simple means fault conditions are not considered and then failure of a 50p diode causes £50 worth of damage and costs £500 ( or more ) in loss of productive time.
Relying on a diode in this circuit is not good practise.
As you say " if correctly specified ". All too often the only specifications considered are the maximum reverse voltage that the diode will have to block and the current the diode can carry. Works for most things but not all.
In this application it looks like 12 volts is the highest voltage but in fact there will be the back EMF's from coils and the pump applied to the diode.
Yep, hence the reason for adding a diode reversed across the coil, if the motor needs it then add one across that however it isn't the norm as would cause problems reversing it.
It seems odd to me that if it is such a bad design that the manufacturer would supply a schematic diagram incuding the same concept.
It didn't appear to bad to me, came across as a good concept. A diode is cheaper than a second relay, a single relay and diode is cheaper than a double poled relay yep, but why not?
It seems to have been wired with auto-electrical parts. And the little square relays used come with loads of configurations and I have been caught out with them in the past. Some come with back EMF protection built in. And some if required it needs to be added.
If we were using relays normally used in panel wiring then the diode is normally a add on which fits in the relay base.
It does seem to be rather cheap in design but when I looked for purpose built relays only 24 volt versions were available.
But to use a relay with at least two sets of contacts would have been the norm and to move away from the normal method is asking for problems when it comes to maintenance.
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