Date: Sat Jan 14, 2006 2:34 pm. By: Pop
Well, from the look of the other responses, I guess I stand corrected, but ... I still think it's an unsafe setup from both a personnel and an equipment viewpoint. I'm not saying it WILL happen, but I am saying it MAY happen, and over time it's very possible. Here's some food for thought, and also BTW, I'm NOT passing judgement on any of the opposing posts because to a degree, they are all correct also, but ... just not completely.
Food for thought: -- A batch of batteries all from the same manufacturing lot will likely be well matched. -- From different lots, that's not so likely. One weaker battery in the lot will always use the other batteries to maintain its charge, as opposed to all of them giving their power to the load. -- Battery failure curves and timing is notoroiously unpredictable. Sooner or later one or more batteries will begin to "feed from" the others. -- Battery replacement will need to be done in full group at once. If one battery gives out over only half or less of its expected life, replacing that one defective battery will result in that battery immediately having to "help" the rest of the batteries to rise to its potential storage capacity. To be sure all batteries are supplying power to the load, they all have to be changed at the same time.
Constant, daily attention and inspection of the battery lot would be necessary to insure a modicum of safety and efficiency.
Someone mentioned fuses: I assumed each battery would be fused, which looks like it may have been a serious oversight on my part. IMO, fuses would be a must.
Diode isolation is simple, cheap and pretty much guarantees, within reason, that: -- Catastrophic currents can never go INTO any battery from another; -- The batteries only supply power to the load, not to each other, resulting in a loss of efficiency.
Depending on the types of diodes used, the voltage losses will range from 0.15V max up to 0.9V or so with germaniums. 0.1V drops are nominal for the better material diodes. Both are neglible losses when considering the efficiencies likely without them, it just dpeends on your pocket book and desire to approach nominal.
Someone mentioned blowing the diodes: Not if they're specced right. Diodes have a reliability rating far in excess of batteries. Any blasted-open diode can be accurately assumed to have saved the day in more expensive components. Combined with fuses you have a pretty reliable system that should last for years. You'll get the best output, not go down should one battery die, and be able to replace just one battery at a time instead of the entire group, knowing it won't degrade efficiency.
Someone mentioned fear-mongering, and if that's what you consider this, then so be it. It sort of depends on whether you want a fix or repair daily or the best reliability and efficiency at a reasonable cost/watt. So, yes, you can just parallel them and it'll work. But it can be made to work a lot better and for less money in the long run.
If you wish to respond to this, that's fine: I'll discuss, but I won't debate or argue; no future in that.
HTH,
Pop
"Pop" wrote in message : In the interest of no responses yet, I'll offer you what I know : and let those with actual experience chime in when they see your : message. : : Batteries, I believe, MUST be ISOLATED from each other!! So far, : assuming the batteries are all in about the same condition, you : probably haven't had any damage yet, but I'm pretty sure it's : coming! : Something as simple as a diode can be used to isolate the : batteries. The "trick" is to NEVER let one battery be able to : supply power into another battery. Depending on the : circumstances, not having that isolation could result in anything : from a short battery life to an explosion that might be pretty : but also might be pretty dangerous. : : When you tie two batteries together in parallel, they will try : to instantaneously become one battery. If one battery is, say, : 12.5 volts, and the other battery is, say, 12.0V, they will : source/sink current until they are both the exact same voltage. : The amount of amperage that will generate will depend on a lot : of things, but mainly the battery's internal resistances. For a : half volt difference, you may or may not notice anything going : on. : Now, let's draw some power off them. They aren't likely to be : perfectly identical, so one will start to "drain" at a different : level than the other. One battery will supply current at a : higher rate than the other. But when the load drops, or is : removed, now the two batteries will again try to come to : equilibrium, which means they will attempt to instantaneously : move to identical charges. Now, THAT situation could be many, : many amps, in the extreme limited only the the very low battery : internal resistances and the wiring resistances. In the extreme : it could be like shorting one of the batteries and super-charging : the other way above its safe charge current. And bloomo; : something has to give. With luck, it'll be a shortened battery : life until it becomes simply a resistor. Without luck, you have : sparks, melting, possible implosion/explosions and lots of acid : flying around in addition to the heat. : : I would disconnect the batteries ASAP until you can learn more : about how to isolate them from each other and get a safet setup : in there. : And yes, I know it's possible to parallel batteries in some : battery operated equipment, but that's a different game with : entirely different possibilities in most cases. That's why most : things you see have series battery arrangements vs parallel - : much longer battery lifetimes. : : HTH, and I'm sure someone with actual experience will be along : soon. : : Pop : : : : "Tim" wrote in message : :: Apologies if my question seems very basic. :: :: I want to create a small off-grid system to provide lighting : and :: occasional power to a small stable block. To this end I have : purchased :: the following: :: 4 x 110Ahr leisure batteries :: 1 x 80W solar pannel (which came with a small 8amp charge : controller) :: 1 x 2Kw (modified sine wave) inverter :: :: I have assumed that I can connect the batteries in parallel, : and have :: done this in what may seem to be an odd way by connecting each : one :: separately to a common point, i.e. I have four leads for each : of +ve :: and -ve comming to one junction (for each pole). From that : point I have :: leads running to the inverter. :: :: I did this so that I could easily remove any one of the : batteries for :: off-site charging if required, leaving the rest to power the : system. :: :: I have also assumed that I can simply connect the appropriate : terminals :: from the charge controller to the common junctions and the : solar panel :: will charge all the batteries together. :: :: The charge controller does have a couple of terminals that are : supposed :: to go to the load (i.e. the inverter) but I don't want to use : them as I :: will be pushing far too much current through such a small : device. :: :: I have read some messages in this group that have worried me as : I am :: now concerned that connecting my four batteries together will : cause :: them to either overheat or be somehow not correctly balanced. :: :: Am I doing anything wrong in the set-up I have proposed. By the : way I :: have not yet actually connected it all together, but I have all : the :: kit. :: : :