Tuesday, 8 March 2011

You Live And Learn

Well, I thought I'd made a good and well thought out solution to the switching of my generator and shore power.  I even went the extra mile and doubled up on the relays to provide a large (so I thought) redundancy.

I sought advice from a national electrical component tech. dept. explaining what I needed to do and how much current was being handled.  Based on this advice I purchased the replays in the previous blog.

On posting the blog one of my readers pointed out that should one of the relays become stuck it would be possible for either to back feed the shore power or permit the genny and the shore power to both be supplying at the same time, which is exactly what is trying to be avoided with the relays.

I posted this on CWF and if you follow the thread you will see there were other concerns.  One member went through the relay spec. and spotted that the relays weren't even up to the un-switched load.  Combined they amounted to 6 amp, not the 60amp I had discussed with the supplier.  60amp is way over what I needed but remember I had doubled up everything.

It was decided on the forum that what was needed to do the job was a contactor not a relay.  Think of it as a industrial heavy duty relay.

So this is what it looks like now..

On the right

The black box on the left is a Galvonic Isolator.  I'm not even going to try and explain what this does, but you can see here.

It really goes to show how combined knowledge can prevent a problem later on.  I am very grateful to all contributors on this issue.