Rescued mine from the garage, not a lot inside. Connected across the PV panel is a blue LED and 5k1 resistor. The ouput has a 1N400? diode in series, that's the sum total of bits inside. Don't know what the ? is as that's against the tiny bit of PCB.
The 1N400? range is supposed to have between 5 uA and 50 uA at max reverse voltage and 25 to 125 C junction temp. Testing gave an open circuit output voltage of about 19 V. Apply a load and it could produce about 24 mA @ 12 V ish. Not measured the drak leakage, might do that later.
They ought to be OK provided the float is within the spec of the battery, taking into account the battery temperature. The SLA's in the alarm panels lasted far longer than those in the UPS. APC UPS's don't keep within spec of the batteries...
The diode is most likely a 1N4001, the lowest PIV rating of that series, one or two hundred volts afair. It's worth keeping in mind that this represents a volt drop equivilent to slightly more than that of a single cell but it's a necessary sacrifice not just to prevent backflow in darkness but also to stop the the LED drawing current from the load (usually a battery) and giving a false indication. Very likely the panel will be made up of 30 photocells in series so this will represent about a 3.3% sacrifice of power output.
The 5K1 resistor rings a bell. I can't remember whether I opened up the original unit or not but I certainly did for the second one on account the indicator LED wasn't working (was seeing the same 20ish open cct volts and able to draw about 80mA charging the battery).
I replaced the self flashing blue LED with an ordinary blue LED but replaced the 5K1 resistor with, most likely, a 15K one to compensate for the 100% on duty cycle and also because those blue leds can be fiendishly bright on anything more than a couple of milliamps, they use far less current than the older red and green LEDs to achieve the same brightness.
Well, the float voltage is so tightly specced that there are three different voltages quoted for the classic 6 cell battery between the AGM, Gel and flooded cell types. The optimum voltage being a compromise to avoid excess corrosion and sulphation for each of the three cell types although I've never seen anything other than 13.8v being specified for any of the 12v SLA types (55.2v for a string of 4, hence my choosing to set the float voltage at 55.3 open circuit but I think, in the light of the wiki article I should revise this down to
54.1v).
According to wikipedia, the three voltages are 2.23, 2.25 and 2.32 volts per cell. For the 24 cell battery pack I need to select between a low of 53.52 and a high of 55.68 volts depending on battery type chosen and, afair, I think VR4 trimpot covers the whole range. The last time I checked the charging voltage I think it was set to 54.3v open circuit which may well explain the relatively short lif of the SLAs (although not for the even shorter life of the car batteries).
Luckily, as well as having a cheapish Aldi DMM to hand, I've also got a Fluke DMM that _was_ calibrated just before it was gifted to me when I quit BT just over two decades ago.
When I bought the Aldi DMM, the first thing I did was to compare its calibration against the Fluke and was assured to see they were within a couple of millivolts measuring a 12v SLA (as was an even older Tandy DMM). With three DMMs to hand, I think I can be reasonably confident of their accuracy being sufficient enough to set the float charge voltage correctly.
That is indeed another complication but I have the UPS and batteries located to the basement which keeps to a fairly narrow temperature range throughout the year. In any case, I think the charging circuit includes a couple of thermistors implying that temperature compensation of some sort is applied.
The wiki article made reference to a tolerance of +/- 0.05v but it's not clear whether this is a per cell tolerance or a per 12v battery one. If it's the former, it all rather makes a mockery of the 2.23,
I set my APC "smart" UPS based on the figures from the battery makers datasheet, not wonkypedia. B-) It was set to 27.7 V, the maths and
40 C battery temp for a float charge say 26.58 V. Bring the temp down to 20 C and the maths still says says 27.3 V. So cooking even without the temp rise due to the excessive charging.
27.7 V sort of fits with the cyclic figures and battery temps around
40 C but what is the definition of "cyclic"? Daily discharges to
1N4001 is 50 V. B-) Well I just looked at th spec to get the leakage.
Mine has an ordinary LED, without a load it stays on. Once there is a bit of load it starts to flash. I guess this is some interaction between the panel load and LED. LED off volts rise, LED lights increase load, volts drop, LED goes out less load, volts rise...
Car batteries really don't like any deep discharge and aren't that keen on constant charging either. So I'm not surprised they died PDQ, I'm also on the look out for 4 12 V deep discharge batteries for the
2 kVA UPS I have kicking about. Ideally things greater than 100 AHr but then they'll probably be flooded and vented so not ideal for being in the equipment cupboard. Back of the garage and run a "maintained" mains feed in is probably the best option but I've heard stories that UPS's might object to long output cables.
An 1N5817 would be a better choice - much lower Vf at low currents.
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They are usually a fair bit better than the datasheet max ratings would suggest in terms of reverse leakage.
Old government surplus NiFe are incredibly robust if you can still find them. They scrapped a fortunes worth of the things in the early 1990's and then proceeded to destroy a complete batch of new replacement NiCd by using the same top up 30% recharging regime for a couple of years.
After that they got wise and modified the SOP instructions...
I think the big clue lies with the name of the company from which the acronymic APC was derived "American Power Conversion Corporation".
It was a company concerned with the outage rates common in many parts of the US of A so they may well have erred on the side of 'cyclic' charging voltage requirements rather than for voltages optimised to continuous float charging very rarely troubled by actual outages.
I think you may well have hit the nail on the head regarding the float charging voltage settings. Here in the UK, you can go several years between outages in urban areas where the majority of the population reside.
The only discharge events the battery is likely to experience will be due to testing, either scheduled once a fortnight or manually. The lower continuous float charge voltage setting would seem to be the better choice for the vast majority of UK users.
According to my min max thermometer, the basement temperature has been hovering around the 16 deg mark +/- 2 deg this past month or two. Istr seeing lows of 10 deg last winter so I'm going to reduce the current 55.3 volt setting down to 54 volts dead when I eventually get my next set of batteries. I can't see this doing any harm, especially in view of my experience with that 12AH SLA that's only now being recharged from the solar panels after a year of 'neglect'.
If they're the same panel as mine, the leds are self flashing and shouldn't be effected that way (the working original LED only ever flashed regardless of the output voltage on no load). Perhaps the self flashing LED happens to be substandard in regard of its maximum voltage/drive current it receives when driven by full open circuit voltage from the panel causing it to misoperate in this way.
That's pretty close to my own setup (a 2KVA / 1500W SmartUPS2000 in the basement feeding a 'protected' main supply to several parts of this 3 floor Victorian semi detached house). I think the longest run of 2.5mm flat twin and earth exceeds 20 metres (daisychained feed to my first floor 'office' and then on to the top floor bedroom) and there doesn't appear to be any problem with those feeds.
I too used to harbour thoughts of using a 100AH battery but in view of the cost and fairly constant life expectancy regardless of the chosen battery capacity, I'm looking to a more modest 12 to 25 AH battery pack for my future investment. That's not to say I wouldn't be tempted to fit a larger AH pack if the price was right. :-)
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