Question about Relays

[transmitterdan]

His fuse blows before there is enough current to fuse the diode open. Diodes almost always fail short then it takes a lot of current to fuse them open. Not the safest thing to do but I would also try it if no alternative while at sea.

[Tymadman]

Originally Posted by transmitterdan

His fuse blows before there is enough current to fuse the diode open. Diodes almost always fail short then it takes a lot of current to fuse them open. Not the safest thing to do but I would also try it if no alternative while at sea.

+1

Usually fail as a short circuit.

[Andina Marie]

Oh, that could be, we used a 12 volt starting battery to fuse out the diodes so there was plenty of current to fuse it to open circuit.

[FlyingCloud1937]

Originally Posted by Andina Marie

Oh, that could be, we used a 12 volt starting battery to fuse out the diodes so there was plenty of current to fuse it to open circuit.

Because the diode is in the control side circuit, there is precious little current passed/needed to operate the control switch.

You Could run it in series with a high current devise to fuse it open. To much current may/will damage the current coil. In the end you still have a failed diode suppressed relay not doing what it's design use is.

So the simple answer is to purchase a new relay, and make sure it is installed correct polarity.

Then you need not worry about future failure from a KLUDGE.

Lloyd

[Andina Marie]

Originally Posted by FlyingCloud1937

Because the diode is in the control side circuit, there is precious little current passed/needed to operate the control switch.

You Could run it in series with a high current devise to fuse it open. To much current may/will damage the current coil. In the end you still have a failed diode suppressed relay not doing what it's design use is.

So the simple answer is to purchase a new relay, and make sure it is installed correct polarity.

Then you need not worry about future failure from a KLUDGE.

Lloyd

LOL,thanks Lloyd but you misunderstand.

The diode in the relay is in PARALLEL with the coil. It is a 12 volt coil so applying a 12 volt high current source with no fuse is going to vaporize the fuse without damaging the relay.

Purchasing a new one was not an option. Our order for 1,000 relays WITHOUT diodes that took 6 weeks to arrive was delivered with diodes and it was not practical to return them. The simplest solution was to fuse the diodes out.

[FlyingCloud1937]

Originally Posted by Andina Marie

LOL,thanks Lloyd but you misunderstand.

The diode in the relay is in PARALLEL with the coil. It is a 12 volt coil so applying a 12 volt high current source with no fuse is going to vaporize the fuse without damaging the relay.

Purchasing a new one was not an option. Our order for 1,000 relays WITHOUT diodes that took 6 weeks to arrive was delivered with diodes and it was not practical to return them. The simplest solution was to fuse the diodes out.

Well you might be right, as I thought we were talking about the OP.

Lloyd

[Tymadman]

Originally Posted by Andina Marie

LOL,thanks Lloyd but you misunderstand. The diode in the relay is in PARALLEL with the coil. It is a 12 volt coil so applying a 12 volt high current source with no fuse is going to vaporize the fuse without damaging the relay. Purchasing a new one was not an option. Our order for 1,000 relays WITHOUT diodes that took 6 weeks to arrive was delivered with diodes and it was not practical to return them. The simplest solution was to fuse the diodes out.

Apart from not wanting to worry about polarity when connecting the coil, why would you bother destroying the diodes? Just curious.

[Andina Marie]

Originally Posted by Tymadman

Apart from not wanting to worry about polarity when connecting the coil, why would you bother destroying the diodes? Just curious.

Good question

They mounted on printed circuit boards that have been in use for years. As I indicated the purchasing specifications were for relays without a suppression diode. As luck would have it, the relays that incorrectly came WITH a diode had the polarity the wrong way round and fusing out the diode was easier than reworking or re-designing the circuit board.

[Tymadman]

Originally Posted by Andina Marie

Good question They mounted on printed circuit boards that have been in use for years. As I indicated the purchasing specifications were for relays without a suppression diode. As luck would have it, the relays that incorrectly came WITH a diode had the polarity the wrong way round and fusing out the diode was easier than reworking or re-designing the circuit board.

That's Sod's Law at work :-)

Another common one is ordering 24VAC coils and being supplied 24VDC (or vice versa) or in our part of the world ordering 24VAC and being supplied 240VAC (or vice versa). You definitely learn to check everything thoroughly!

[Andina Marie]

But there is a trick you can use that can be very handy. Things like 24VAC solenoid valves that are made for the HVAC market will work very well at 12 volt DC.

[Tymadman]

Originally Posted by Andina Marie

But there is a trick you can use that can be very handy. Things like 24VAC solenoid valves that are made for the HVAC market will work very well at 12 volt DC.

...yes , and won't burn out when disconnected from the valve and accidentally energised, unlike their AC counterparts. But sssshhhh! You're giving away trade secrets ;-)

[Dockhead]

Originally Posted by Andina Marie

The reverse connection may or may not have fried the diode but the relay should still work. When the diode is fried by over-current in the forward direction it acts like a fuse and OPENS, it is extremely unlikely it would short.

In the past we have deliberately removed the internal diode in relays by blowing them out with forward current. It worked 100% of the time.

When connected the "correct" way round do you still hear it "click". I suspect you have something else wrong with the wiring and replacing the relay will not cure it.

The relay seems failed short to me. No ohms of resistance across the control circuit. The control wire has voltage when it is supposed to. I don't know what would blow the fuse besides a shorted relay.