Auto Top-Off Schematic?

[BeanAnimal]

It depends on a lot of factors. But the short answer is yes in theory.. You will find a LOT of folks who will tell you otherwise... but the diode is best and common practice, just as a coupling cap is used on alomst all DIP style integrated circuits but rarely specified or part of the schematic.

The diode will cost you a few cents, so it's not worth skipping. However if you MUST skip it, then you will likely be ok.

[fio1022]

Thanks for all the great info.It is most appreciated.
Another question.I should know this but I can't remember.
If the diode is hooked up as shown,is there a way to check it?Or if it is hooked up wrong,will there be any indication that its not correct?

[FuzzyLogic]

Good question! What is the proper way to test a diode?

[Chrsnwk]

This is the updated version of mine i'm planning to implement.

[BeanAnimal]

In general a diode only lets current flow in one direction. The "stripe" on the diode shows the "closed" end of the diode.

If you hook the diode up backwards in the above diagram, it will cause a direct short to ground whever the relay is energized.

Looking at the diode, you will see the STRIPE side is hooked the the postive side of the relay, with the arrow part of the symbol pointing to the stripe. This shows the direction in which current is allows to flow (from the ground side to the positive side). When the relay field colapses and postive voltage appears at the negative terminal, it is wrapped back around to the postive side through the diode. Under NORMAL operation the diode blocks the postive current from going through it to ground.

Testing a diode is as simple as hooking to to an ohmeter. It should read an extremely high resistance in one direction and a low resistance in the other.

[BeanAnimal]

BTW I listed diode part numbers as 2nxxx ... I should have said use any of the 1n4xxx type diodes.. as the 2N part numbers are usually transistors or other TTL logic.

Bean

[fio1022]

One last question on this schematic.
I want to add a third float as a safety.Would it be better to place it before fs2 or after the junction point past fs2 when looking at the line diagram?Either way it looks like it would work.
Thanks!

[BeanAnimal]

You need to add it before FS2 for it to always work as expected. If you place it after FS2, a stuck FS1 or stuck relay could cause the top-off to remain enegerized.

[GuySmilie]

Originally posted by Chrsnwk
This is the updated version of mine i'm planning to implement.

Chris, I'm just now seeing this circuit of yours and never saw where anyone (or yourself) made comment on it. Can you explain its function a bit; type switches, etc? Was this going to be a manually operated controller. Just curious more than anything. Nice board work by the way. Was this with Pad2Pad?
Thanks.