I rent a small stable yard which has no mains supply. We manage quite well using 12 volt batteries to provide the limited amount of lighting required, (and also to run electric fencers some of the time). I normally use ageing car batteries, but have also had a couple of Alpha "leisure" batteries that seem to be a compromise between deep discharge and "starters". However, I had poor life from these (well under 100 cycles) even though I do check voltages and try not to run them right down, or leave them discharged.
I wonder if I would be better with "proper" deep discharge, ideally not the 100 AH plus monsters. I'm going over from 12 volt CFLs to more efficient LEDs so would probably be OK now with "scooter" sized.
Hmmmm ... 'try not to run them right down ...'? ;-(
Now that might mean you *are* managing the discharge process accurately (in which case, that's fine but doesn't explain the low cycle count) or you are doing exactly what you say and possibly / potentially over-discharging the batteries and hence the poor cycle life? ;-(
Given that they don't recommend discharging even 'deep discharge' batteries to below 50% of their nominal capacity (and that depends on many things including age and temperature).
I think I'd like to hear how you are actually protecting the batteries first (and you may well be etc) before recommending you spend any money anywhere? ;-)
Fair comments. Low battery voltage becomes obvious when some of the CFLs don't strike properly (the fencers have a "low voltage" warning light). I don't have a rigorous process of checking voltage, it's not completely straightforward anyway because I find the system runs fine using car batteries with a single shorted cell. So I *might* be over-discharging them somewhat, which is why I wonder whether going to "proper" deep discharge batteries might be better.
Typically, I might repurpose a car battery if it seems to be getting sluggish at the start of winter (after maybe five years in the vehicle) and these batteries are usually lasting better than new "Leisure" ones, so I don't think my battery management can be too bad. I've tried using a "multi-led" battery condition indicator as something a bit simpler than a proper DVM, but it didn't last long.
I'm about to change one of the stable units over entirely to LEDs which seem to give adequate light from much lower current, so I might try running that one on ten rechargable AAs.
I've had excellent service from Tayna batteries for several different types of lead-acid batteries. A lot of the solar experimenters use second hand forklift, milkfloat even submarine batteries. Lurking on the Navitron forum might throw up sources for these.
And partly from bitter / expensive experience. ;-(
And possibly already sitting on an 'over discharged battery.
Interesting to know what voltage they consider 'low' Colin?
Hmm ... so 'stuff still works' with a ~10V battery. This suggests it could be very easy to over discharged a ~12V battery before you know it's getting low?
No. No LA battery is going to survive what could be considered as 'abuse'. All you will be doing is spending more money on lower capacity.
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If these batteries are our of sight / earshot what I would like to see is some form of Low Voltage Disconnect that take the responsibility of protecting these batteries away from you (one). ;-)
You can get them cheap enough for the sorts of currents you are talking about and can come with an audible alarm if you are within earshot.
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The thing is, if you have a fairly light load you might find that even getting down to 11V is actually too low?
'Management ...' ;-)
Unless you leave either on 24/7 (making the problem worse) and monitor it regularly I'm not sure it would help.
At least if you weren't using LA then you might not damage the cells so much but most would still enjoy proper protection if you wanted to enjoy the best life out of them.
Unless you have some form of automatic charging system that could equal or better the worst case load, IMHO, you really need some sort of LVD.
If you use solar charging there are many small charge controllers that disconnect the load if the battery voltage drops too low.
Your discharge protection system is nonfunctional and useless. You need a v oltmeter at the minimum, preferably an auto disconnecting whatsit that you can set to a suitable voltage. If you're discharging them until the CFL won 't strike you're discharging them way too far. No lead acid will surive tha t, and going to a smaller battery will worsen things considerably.
Then you need to look at the charging setup, to see whether that's ok. Thos e are the 2 main things that make the difference to battery life.
I don't know whether you could add some sort of smart control to the lights , if quick acting PIRs meant each light was only on half the time that woul d halve your energy use. PIRs work fine with LEDs, not so well with CFL.
At one time I was supplying some equipment for broadcast mobile use. Size and weight wasn't a problem, as it stayed in the van. But reliability and overall costs were - since the costs came out of my hire fee. And FWIW, I found decent quality car batteries of an adequate size - never discharged to more than about half - were far better value than specialist deep discharge types. Perhaps because of economy of production numbers.
Could be the fact that the load was pretty constant and couldn't exceed what I'd measured and therefore easy to calculate how big batteries needed made it different from yours, though. And that it was re-charged overnight after use.
No battery likes to be deeply discharged. To avoid this you should use a battery that is oversized for the job. That means that each discharge cycle will not discharge it as deeply as it would a smaller battery.
The damage occurs when a discharged battery just stands for days in the discharged state, so avoid this.
It would help if you had solar panels, just to give the batteries a bit of a charge every day.
Alternatively: Since you go to the stable yard in a vehicle, how about having an auxiliary battery in the vehicle, charged automatically from the vehicle by a volt sensing relay? That battery could be connected to your stable battery while you're there via an 12V to mains inverter and main-input charger. If you mount the inverter in the vehicle (really useful anyway) and the charger near the stable battery you could run a long mains extension to connect them (to avoid the voltage drop of running a long
12V lead). This arrangement would put the load (the lights etc) on the vehicle aux battery and also charge the stable battery. If all this seems a bit complicated it isn't really and I can help you choose an inverter etc. This idea won't work unless the vehicle has decent length journeys quite often.
Tried this in the distant past, only with a small-ish panel which was nothing like adequate in the winter. Present yard is a bit shaded but I appreciate that larger modern panels are both more efficient and more affordable. I've also wondered about using a sailing boat windmill (but wind is very variable in this location).
Nice thought, but stable is within easy walking distance. And I have batteries in two (sometimes 3) different locations with no easy wiring connection.
Thanks, I had been wondering if this might be the case too.
In fact I am starting to wonder whether, rather than have to have two cut-off devices, I might be better just to go to Lithiums (with built in protection, typically £25 for 8 AH)
If going over to low current devices, surely it pays to keep the old system and then the batteries will last even longer.
I know when caravans were converted to cfl types working from 12v it was amazing how long a battery would last. Of course back in them old days we had gas lights and the accompanying condensation!
Yes temperature is one thing many forget about, particularly in recent weather. it may well be you do heat part of the place, maybe with bottled gas, but if not and there is heating life of batteries is much better when they are in an even temperature.
Nickel Iron batteries would be good here. You're not concerned about power density, they're hard to damage and very long lasting. I don't know where you'd get them, somebody might.
Ebay is probably the only source, typically shipped from US. Edison brand. Easier/cheaper to just make some. However they disappeared from widespread use because so many were found to be non-working in railway service.
Also while NiCd & NiMH cells have no complaint with 100% discharge, the batteries do because cell capacity differences cause reverse current, which is destructive. I don't know if NiFe are similary effected, without any more info I expect it's likely.
You can buy voltage sensing relays ready made and adjustable, as used by those who tow a caravan to switch the power to a 12S socket. The actual switching voltage may need some adjustment down, the normally switch on at around 13v-ish.
Sort out your charging arrangement and loads such that you don't discharge the batteries as much and then you won't need deep discharge batteries. Housing the batteries such that they don't experience extremes of temperature will help a lot too.
Around 100 quid on ebay gets you 100W of solar panel and a charge controller.
25Ah of genuine rated capacity, with a properly engineered cyclic 12v AGM battery costs about the same. At less than 20% depth of discharge that will give you around 2000 cycles to the point of the cell retaining 80% capacity.
Approaching a decade of use from a battery under such a charge discharge regime is relatively easy.
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