AGM Batteries

When you say " on" what load are you applying to them, a fridge, lights or something else ?

Is the polarity of the posts on the new batteries the same as the old batteries - just a thought

cheers

Are the two batteries connected together all the time. ie is the switch on the combined battery output?
At least that proves you connected the batteries together correctly.

Do you possess a multimeter?
Disconnect the lead to the switch and turn it on. How big is the spark when you touch the wire to the switch. Big spark or big fuse popping implies you likely have a short in the cabling. You've either wired it incorrectly or something is touching something it shouldn't.
Check the cables for any abrasion. Maybe a cable has been rubbing on something and worn through, your disturbing things may have repositioned the damaged area so it can now touch metal.

Worst case, disconnect everything after the switch and reconnect one at a time until you find the problem wire.

check for series or parallel wiring - maybe it's 24v!

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Hi Cougar,

Your expressions: "it blows the fuse on the Centurion" and "as soon as I switch it from off to either battery it blows the fuse." suggest two possibilities:
1) That you may have the batteries connected in reverse polarity. I have seen references that the Centurion has 'reverse polarity protection' in a form which will blow the fuse. Double check your battery connections and don't go only by cable colour as someone previous may have screwed it up. If you have a multimeter you can also check that the battery polarity appearing at the Centurion terminals is correct. Do this with either the Centurion fuse blown or removed and the battery switch turned on. There would be markings on the Centurion terminals as to positive and negative.
2) The Centurion may have developed a fault which causes the fuse to blow when presented with the battery. Coincidental perhaps, but possible. It would need to be inspected by a competent technician.

The Centurion 3000 was never a good unit, just a simple single stage battery charger. It attracted many criticisms. If you need to replace it there are now several good alternatives with multi-stage charging which will better care for your batteries.

Hi, if all you have done is replace the batteries it must be a short in the wiring somewhere. Possibly not to do with this action. If the fuse blows after you switch the battery on the short must be beyond the switch where presumably you have not changed anything. All I can suggest is the act of changing the batteries has somehow caused a short but it is hard to see how this could happen !! Unless the switch is close to the batteries and somehow the load side wires have come together.

Ken

Thanks all, after much climbing in, over, under and out, we have worked out by coincidence to Centurion unit is cactus.
Batteries, lights, pumps and wiring all good.
Looking at buying the Setec ST III Power supply.
Thanks for everyone's input it was very helpful
Cheers