Ronaldo47

It depends. Some years ago I salvaged a 12V Sonnenschein SLA from some old equipment. It read 0V on my meter, and connecting it to my ancient (1960's) non-smart trickle charger, resulted in no detectable current flowing. A colleague who had formerly been a chemist involved in battery research at GEC, said that, if it had become flat due to non-use rather than from discharge into a load, connecting it to a charger via a high resistance might revive it, although it might take weeks. It only had a nominal capacity of 7.5Ah, so I tried connecting a 12V 2.2W bulb in series to limit current. It did work, the bulb starting to glow dimly after a week, and it eventually restored about 5Ah, but it did indeed take many weeks. Not really an economic proposition unless money is tight (as it was for me at the time!). Reviving a completely flat battery, probably wouldn't work with modern smart chargers because they will only provide an output if they detect that they are connected a partially-charged battery, but charging one that is not completely dead at a very low current, might show an improvement. However, if you can afford it, probably best to just get a new set: scrap merchants should give you a good price for the old ones.

I use small (12Ah) SLAs in our electric bikes. According to manufacturers' data sheets (downloadable from the Web sites of electrical distributors like CPC Farnell and RS components, and giving data applicable to all capacities in their respective ranges) , a typical life for a standard SLA seems to be around 5 years, but life is dependant on the depth of discharge and the number of charge/discharge cycles. I have found that around 7 years of useful life for my application is typical, by which time capacity has halved. The last set of higher quality ones I got that were designed for traction applications, was said to be around 9 years, but they cost more than twice as much as the ordinary type and seem to be available no longer: no doubt ousted by lithium types. Cheaper SLAs are normally intended for uses such as standby power supplies and emergency lighting rather than traction and multiple deep charge/discharge cycles

My first house was in the London Borough of Barking. I had a Romford post code, and was on the Ilford telephone exchange.

McDonalds is usually good for free WiFi!

I found I was getting significant gravity flow in the central heating I installed in my house in the mid-1970's when operating it with the pump turned off. On discussing it with a heating engineer he mentioned that a lot of the older tabulated data I had been using to design my system, would have been based on flow though iron pipes with relatively rough internal walls, and that the smooth bored copper pipes I was using had a lower flow resistance than my tabulated data indicated. My recollection is that, for laminar flow, resistance was inversely proportional to the fourth power of diameter, and that slow bends were highly advisable, as the sharp 90° bends that seem to be the only thing that most stockists have nowadays, do introduce significant resistance. There is a type of system called the one-pipe system, where you only have one pipe which runs around in a loop from boiler flow to boiler return, and to which one pipe the radiators are connected by tees. The radiator closest to the boiler gets the hottest water, while the others get hot water diluted by the cooler water that gets returned to the pipe from the 'return' ports of all the upstream radiators. My school, built in the 1920's, had such a system, where the 'one pipe' was of large diameter (from memory, 4 or 5 inches diameter) and the radiators were connected to that one pipe by 1/2" or 3/4" branches with manual and lockshield valves for balancing. All iron pipes of course.