Guys,
I'm on the horns of a rather large dilemma here.
Please bear in mind that this is going to be a rather long post as I explain what exactly I'm on about.
OK, we had a CD (Civil Defence) exercise here last weekend and so I'm told now (Thursday) the batteries in the Fire Station next door that run the radio equipment, didn't cut the mustard (so to speak), in fact they wimped out after half an hour of discharge. [Linked Image]
The Fire Chief tells me he would like the whole system ripped out and replaced, as it's been there since the mid 1960's and it's only been used once a year since then.
The batteries are all sulphated to bits and it's a wonder that they haven't caused a Hazardous Chemicals incident.
It's a whole bunch of 1.2V lead-acid cells hooked up in Series-Parallel to give 14V at the transcievers end.
They were purchased second-hand from the old Telecom exchange at the time.
Now I would like to start from scratch here and install a new system altogether, here are some ideas I had:
  • The whole system as I see it would be 12VDC, I need the Control circuit to still be operational under Mains failure, so that isolation can still take place.
  • Radio gear will be supplied at 13.8VDC as is normal.
  • Battery system will be made to automatically switch over upon Mains Failure, to ensure radio gear keeps working.
  • I am also loking to interface some sort of a solar recharge feature into this system, so that there is no need to manually recharge the battery banks up, this is the reason IMO why we are at the stage where we are now.
  • We need at least 4-500Ah (maybe even more) of capacity in the cell banks, when the original system was installed we only had a single transciever (the Main Station radio),now we have Inter-service (Ambulance, SAR, etc) and a link to the local Amateur Band Repeater.


I'm pretty much up with AC switching systems, but DC is not something that is first hand to me.
What sort of batteries should we be buying for this application?, that will not be too worried by sitting for a while un-used, but still fully charged.
I was thinking of using two 3pole AC Contactors (one for -ve and the other for the +ve of the Batteries), with a 12Volt DC coil in each contactor, would this be enough contact area for switching DC?.
I've already worked through interfacing a couple of PV panels into the system.
Now the question of protection, what sort of fusing is best on a system like this one, considering that it is DC?.
Any help I can get with this, wiil be gratefully recieved, I've just hit a stumbling block in my head over this one. [Linked Image]