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  • Reccomended Standby Battery

    Currently i use a sealed lead acid battery from a UPS.

    I am killing these batteries because i believe they are undercharged and overworked.

    I am looking for the best most rugged type of Deep Cycle battery that i can get that will withstand being deeply discharged and recover well.

    Currently with my driving habits i only get long periods (about an hour) of charging twice a week so it should be able to withstand a 250 ma standby draw inbetween these times and be able to recover fairly fast.

    Am i asking too much of a battery?

    I am hoping one of the heavyweights have something brilliant to add to my battery problem
    -Jesus- King of Kings Lord of Lords

  • #2
    Just a quick reply, I could be wrong but IMHO (as you suggested) you’re asking a lot because of the small charge time.

    I described the problems I had with this and the battery I’m using in post 66, 67 of my worklog. I’m drawing around 320ma but even a constant 250ma over a few days with a short recharge time is going to be a problem for any battery.

    Have you accurately measured the charging voltage across the AUX battery in relation to the Main Battery. IE how much voltage drop do you have between the two and importantly, can the Vehicle charge system supply enough voltage to correctly charge a Deep cycle battery, which can be as high as 14.6v to 14.8v.

    Hopefully OldSpark will correct the voltages I quoted if I’m wrong!
    Last edited by Mickz; 11-15-2011, 06:14 PM.
    Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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    • #3
      The charging voltage is around 13.7 back where the aux batter is. Not sure exactly what the alternator is putting out. Maybe the problem is the 8g wire and the distance that i have in between the main battery and the aux battery. I have the Aux battery and isolator in the trunk.

      Maybe i should hook up a solar charger or something to supplement the charge from the alternator.

      Originally posted by Mickz View Post
      Just a quick reply, I could be wrong but IMHO (as you suggested) you’re asking a lot because of the small charge time.

      I described the problems I had with this and the battery I’m using in post 66, 67 of my worklog. I’m drawing around 320ma but even a constant 250ma over a few days with a short recharge time is going to be a problem for any battery.

      Have you accurately measured the charging voltage across the AUX battery in relation to the Main Battery. IE how much voltage drop do you have between the two and importantly, can the Vehicle charge system supply enough voltage to correctly charge a Deep cycle battery, which can be as high as 14.6v to 14.8v.

      Hopefully OldSpark will correct the voltages I quoted if I’m wrong!
      -Jesus- King of Kings Lord of Lords

      Comment


      • #4
        Yes, 13.7v is not really enough; I also have mine in the trunk and 4G cable would be the way to go especially as the battery gets larger and capable of drawing a higher charge current. Quite a few things to consider with charging current, charging time and heat etc if you let them discharge too far.

        OldSpark posted a really great link on batteries and charging which would be worth reading.

        I was thinking of suggesting a sola charger if you can get a decent large unit without breaking the bank.
        Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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        • #5
          SLAs? You mean AGM?
          (Yes, AGMs are SLAs, but so to are Gels, and many refer to semi-sealed wets as SLAs...)
          And is you battery a stand-by, or cyclic?



          Rule of thumb - no more than 50% DOD (depth of discharge) for deep cycle batteries.

          UPS batteries are designed to be discharged VERY deep - eg, down to nearly 10V BUT at a fast rate (HIGH current) - BUT should be recharged ASAP and they may only last 6 cycles (ie, 6 days if once a day).

          UPS are not cyclic batteries - they are not for daily use. (Says I that has been using an undersized 11 year old 38AH UPS AGM battery for my main and only car battery for maybe 2 years - but that is recharged immediately after cranking (at up to 45A!). Besides, it's a Yuasa.)



          Get a bigger battery, but you must be recharge it fully at "reasonable" intervals.

          Whilst a smaller battery might be ok for the discharge, it might require a longer charging time.
          A bigger battery can accept higher current & hence recharge in a shorter time. Plus since it only discharges maybe 40% rather than 60%, it will last longer.



          What you describe is what cracks me up on car audio sites. Yes, the battery does this or that, but for how long? (As in lifetime, not discharge time.)
          Luckily audio forum people are prepared to spend big on batteries, & often.


          Batteries are a compromise.
          What ages them is the combination of higher discharge current, higher recharge current, over-voltage, higher depth of discharge, higher temperature, more frequent use and the number of recharge/charge cycles.
          Now and again they require maintenance - eg, a high voltage or high-current recharge to blow away sulfation etc.

          UPS batteries are designed for high discharge rate & high DOD, but NOT for many cycles.
          Solar batteries are designed for long discharge periods with relatively low recharge rates and high DOD.
          Deep cycles are low current but high DOD.
          Crankers are for cyclic use, high current, low DOD. (So why to audiophiles want deep-cycle for voltage dips??)
          Alarm batteries are "stationary" aka non-cyclic and can be similar to UPS batteries bit with a lower discharge rate (current).

          And on it goes.
          There are only two main types of battery construction - namely crankers (high current) or deep-cycle. But there are many flavors... And then whether AGM, gel, or flooded/wet (for lead-acid batteries).



          As to voltages, it depends on the battery.
          The norm is not to exceed 14.4V long-term, but that assumes typical 12V vehicle batteries.
          Some require higher - eg, Optima, and Mickz' example.
          [ To combat sulfation (which occurs when a battery is not fully charged), voltages >14.4V are used. Hence probably why deep-cycles are higher - it's a compromise voltage - it might be better to use a higher voltage for desulfation (reconditioning) and then drop to normal 14.4V to limit gassing. ]


          What is the best battery depends on the combination of discharge and charge availability, and desired lifetime.

          Keep in mind that if a Deep Cycle says it's good for 80% DOD, it will last probably 3x longer if only taken to 50% DOD.
          And any "hot" battery will last twice as long if 10°C cooler, or 4x as long if 20°C cooler etc.


          BTW - yet again, download the Car and Deep Cycle Battery Frequently Asked Questions (FAQ) 2011 zip (updated October 9, 2011) from s19. It's probably the best info you will find for "battery basics".
          Last edited by OldSpark; 11-15-2011, 08:15 PM. Reason: spellinks...

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          • #6
            I am not sure what type of battery it is (AGM) etc. And it seems though it is a standby battery it is more cyclical and regular use battery

            I do know that I have to have something that can be inside the car. It looks like of the types you listed that a solar battery may be best but I am not sure they are a "sealed" type battery

            Thanks for the advice on the larger battery. That makes sense. I would be happy if I got 1 year out a battery (longer would be great)... currently I am only getting 3 months.
            -Jesus- King of Kings Lord of Lords

            Comment


            • #7
              Can you indicate what sort of drain (250mA?) for how long, and then what charging for how long - eg. 1 hour car drive or 2 hours with 800mA charger).

              I might be able to size a suitable battery, though that's largely a "theoretical" sizing based on whatever specs I can get.
              There can be a large variation between "theory" (though that's usually conservative - you might get away with smaller/cheaper) and the practice is tricky - ie, alternator may have 30A spare capacity, but the battery only accepts 5A and "dropping" lower ), and then my out of practice "practical" battery skills.

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              • #8
                Just remembered something about my system that OldSpark made me remember.

                The charging voltage in my vehicle is primarily governed by the state of the main battery. This is a computer controlled charging system that knows when the AC, lights etc are on and adjusts the output accordingly. What I found was in day time driving the charge voltage can drop back very quickly and appears to be mainly determined by the current consumption of the Main battery.

                So even thought the AUX battery may be low in charge, because the current drawn by the smaller AUX battery is minimal compared to the total System, the available charging voltage can drop to around 13.8 very quickly. I feel the vehicle cranking battery charges a lot faster than the smaller and most likely more depleted AUX.

                With a battery in the trunk or cabin and even with a relay bypassed isolator (minimal voltage drop) and heavy wiring you may still not have sufficient time to charge that AUX battery correctly before the charging system cuts back.

                This is the reason I went to the trouble of having a single button Hibernate at the end of the day’s driving, instant on (auto sleep) during the day and resume from Hibernate 1st start of the day. Since doing that and limiting the discharge time I have not had a problem charging the AUX with low driving times.
                Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                • #9
                  Mickz - your second para is interesting....
                  "...charging voltage ... primarily governed by the state of the main battery..." & "a computer controlled charging system that knows when the AC, lights etc are on and adjusts the output accordingly".

                  That's what regulated systems have been using for decades - even the old external electro-mag regulators since alternators began appearing in the 1960s (before that they were dc generators, though they are still regulated).


                  I often ask people if their system includes current sensing (especially for those {cough cough} "priority charging systems".
                  If it is not monitoring current, how can the system possibly know how much current is being drawn, or if the battery is full?
                  Lets ignore "intelligent" chargers for the moment. And that may include your computer controlled charging system - maybe it is truly "testing" the battery state, but few in-vehicle charging systems and battery isolators do despite their claims to the contrary. (CAVEAT - but times are changing, and I'm an Old Fart that may need some updating! But I am referring to established products that have since dropped their misleading claims.)


                  The "load sensing" claims are understood with TWO bits of info.
                  (1) A battery charging system is a "constant voltage" system.
                  (2) As loads increase, the voltage decreases so the alternator increases its (current) output to restore to the voltage set-point (and vice versa) - that is (Voltage) Regulation.

                  Hence why traditional alternators (voltage regulators) have no current sensing - they merely sense the voltage (and vary the rotor current to compensate).

                  And there the story ends.

                  ...except for some things....
                  "Computerised" regulators may simply be digital equivalents to traditional analog regulators, but it is possible that they use pulse-techniques to determine battery condition - or maybe even data sampling and comparisons. (Could the former be hazardous or noisy for modern electronic accessories??)

                  The voltage set-point was traditionally 13.8V - the "theoretical" charging voltage for a 6-cell = 12V lead acid battery. (Hence the traditional 13.8V spec-rating for 12V loads.)
                  But (in the 1980s?) that voltage was increased to a max of 14.4V, or typically 14.2V, as they found the batteries would last longer. (Despite slight gassing and higher charge current, the "reconditioning" of the battery meant longer life than that lost through the added "damage". IE - the slight sulfation of car batteries was largely removed with the increases charging voltage.)


                  Elsewhere I have written how batteries have a "rated" maximum charge current. Yet this is probably exceeded by most vehicles - ie, all the spare alternator capacity can be used to charge the battery. I have seen my 38AH AGM battery charge at 45A, and that is slightly more (LOL!) than the usual 4A or 8A maximum allowed based on normal battery specs. (Hence aren't we breaking the battery specs and voiding their warranty?)
                  What limits all the spare alternator capacity being used is the internal resistance of the battery. (My alternator probably has 75A spare capacity.)

                  But that apparent over-current isn't all to bad. After all, the batteries last for years. (I get 6-8 years from my normal wet batteries, though they'd probably only accept ~20A due to their higher internal resistance (typically twice that of AGMs) - but that still exceeds their typical C20/10 or C20/5 = 40AH/10 or 40AH/5 = 4A or 8A max charge current.)

                  Why isn't that over-current so bad?
                  That high current helps blow away sulfation. (My battery supplier reckons at least 20A is needed after a typical car battery is flattened.)
                  That high current (40A) only lasts for tens of seconds. It is well under 10A within one minute.
                  In such a short time, the battery hasn't enough time to heat up (or gas) which is the big killer. (Maybe if the plates warped from the high current, but is that a heat issue too? Surely it's not an electro-magnetic attraction - lead is non-magnetic?)

                  Plus specs are typically condensed. They are simplified for typical consumption, hence have typical use and long term specs - ie, charge currents & voltages for batteries, though specs are similar in "abridged simplicity" for almost any device. (Alas I recall LED discussions!) Specs are generally not "rigged" for extra sales. (Well not here - they'd be fined or sued, else go broke under warranty claims.)



                  Alas I sort of digressed. Again.
                  I guess I'm trying to impart that old "Batteries are more of an art than a science" philosophy. (Though that art IMO becomes "science" when you can start quantify expected behavior given enough conditions - and the plethora of info that colors the basic science.)

                  And again I try to impart an understanding of batteries. If some basics are understood, they aren't too complicated.
                  Mind you, that's a big ask. There was a (big?) time difference between my "knowing" of things and the later "understanding" of them - ie, where it became intuition and pictorial rather than a set of V=IR formulae!


                  I think it was you (Mickz) that thanked me or was rapt at my previous linking to Bill Darden's Car and Deep Cycle Battery Frequently Asked Questions (FAQ).
                  I still reckon read Bill rather than me for battery theory. I just try to tailor his gamut of info into plain English for a given situation. (Though his English is IMO far better than mine!)
                  Bill probably answers & confirms some of my assumptions or suggestions from above & elsewhere. [But again, if we differ, please let me know. PM me if needed.]


                  Poo, where were we?
                  Charging with an aux battery...
                  Assuming a relay-connected battery, then excluding (fuses & relay & ground and) cable voltage drops, both batteries see the same charge voltage.
                  They then accept current based on their own internal resistance (which decreases as the battery charges).
                  And as they charge, their charge-current drops until they reach their "float" current (ie, when fully charged) which may be up to 2A but can be as low as 10mA or 100mA etc.
                  At 10mA to 2A, voltage drops along the distribution path should be negligible (ie, ground, relay, fuses, cables). ERGO - all batteries can be fully charged. (That's a point missed by many that get sucked in by expensive dc-dc converters or aren't clever enough to reduce cable etc resistance to aux batteries.)

                  If the above batteries also have loads hanging off them, the load current must be factored in to the distribution voltage drops, but that's where fatter cable comes in.
                  Plus for the main battery, loads are effectively taken from the alternator or or fuse box, not from the battery terminals themselves. And since alternators usually sense the voltage at the battery +12V terminal, the main battery gets its proper set-point voltage (ie, alternators with S or Sense inputs - NOT single-wire D+ alternators, and ignoring ground voltage drops between the alternator and battery).
                  [ For those that read a recent thread involving diode isolators, that is one reason they are no longer used. The diode voltage drop depends on the current to each battery, and some loads must be connected to a battery - not the alternator - otherwise the engine won't start and will stall if the alternator fails. Incidentally, at great risk to myself, I established that our Police use relays to interconnect their dual batteries, and that relay is controlled by their Delco Memcal (ECU). I have yet to confirm ambulances etc, but some looked at me funny when I mentioned diode isolators - ie, like "how old is this old fart!?". ]

                  So given a low voltage loss relay or direct connected multi-battery system, and copious alternator capacity, the time to recharge any battery is determined by the charge voltage, the depth of discharge, and its internal resistance.

                  Should I have put that last line first? (LOL)
                  Last edited by OldSpark; 11-16-2011, 03:49 AM. Reason: Improved reading.

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                  • #10
                    Yes I agree with what you are saying, however my definition of sensing when the lights are on/off etc is having the CPU know what parts of system are responsible for the current being drawn. This is easy to tell without having to measure each circuit as that information is already available to the CPU.

                    In older systems (in least in my old cars) the regulator only knew that current was being drawn and “attempted” to maintain a set voltage. This new system can reasonably calculate which parts of the system is drawing current.

                    Would this not allow a designer to more intelligently control the charging system to help control long term overcharging and allow short term high charging to be kept within limits based on a rough estimation of what parts of the system are actually drawing power? Or is it simply not worth trying with the batteries we currently use in motor vehicles?

                    The system in this vehicle has a 110A alternator @ 13.5v and an ELD device to measures current, I assume most new vehicles would do this?

                    Your point about cable loss and taking into account the equipment current (PC) if mounted near and on the AUX battery feed is so true and as you say, often overlooked. Something I have bought up before with say 7A charge and 5A for the PC, the resulting 13A is enough to drop an easy 500mv to 1v or more across undersized relay contacts, fuse holders, connectors and cables and I would think would prolong the AUX battery’s ability to charge correctly by some considerable margin.
                    Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

                    Comment


                    • #11
                      Oh man, I love your recognition of the .5V - 1V drop due to your 7A & 5A aux current. If only others did.
                      The drop should drop as the aux battery charges, and maybe increasing cable size will drop the drop. Can add more cables - nothing wrong with a 100A cable protected by a 20A fuse etc. And grounds are the easiest and best to duplicate - I like redundancy (lose one ground and electrics still don't burn out).
                      And relays should be a negligible drop - if 5mΩ, that's 65mV in your system.
                      Fuses can add a bit - especially when near rated capacity. (Not that I keep telling BIG current users to use magnetic breakers or loop sensors so they do not add the fuse resistance.)

                      FYI - I use self resetting circuit breakers for my aux battery. Nothing worse than thinking you are still charging... (I haven't yet set up monitoring or alarms. Maybe next century...)


                      But 13.5V is too low for an alternator. Even old school was 13.8V. Bosch and others now typically use 14.2V. My Jap alternators seem set to 14.4V.
                      At 13.5V, I'd expect you would not get long life from your main battery. Whilst 13.5V certainly won't part-recondition your battery, it may be adequate to "reasonably" charge batteries provided it was available long enough.
                      [ I didn't mention float voltage. In theory, after charging at 13.8 - 14.4V, when the battery is full, the charge voltage should drop to float level which is typically 13.2V - 13.4V. The battery can sit at float voltage ad infinitum - sulfation does not have a chance to occur. (But if a cell fails, then 13.2V is overcharging...) But no vehicle system does this - has anyone noticed their battery voltage (and hence system) drop to ~13.2V from 13.8V - 14.4V after the battery is fully charged? ]



                      As to current monitoring, certainly no systems ever did that - yours must have been specially installed.

                      And as far as I know, no modern systems monitor current anyhow. What use does it serve? As long as voltage is maintained, the system is optimal. Even the old traditional ammeter has been dropped - largely because it offers useless information (whereas a voltmeter tells all). [ It was in that emergency vehicles and diode isolator thread where the "relays are dangerous, and are NOT isolators" poster kept insisting his alternator monitored current. He was so wrong!! ]

                      Like I said, battery charging is a VOLTAGE issue, not current. (In early AGM days, constant-current charging was the go. Even they are now constant-voltage charging.)
                      And if better battery charging is desire, then only the battery charge current need be monitored - not the loads. (The starter has to be exempted - even loop sensors have troubles handling starter currents and still having the sensitivity etc to accurately determine a float current. The same can apply to other loads - 50A of draw and trying to resolve a 100mA - 1A float current.)
                      Then there is the complication of knowing what the float current is. As the battery ages or if the float current increase, what to you do - limit the float current? Then the (internal) battery voltage drops, and (but) if that could be measured... well, there it is again - it is voltage that measures the battery state.

                      The only people I have known to install current sensors are experimenters. None have had any practical use for such current readings wrt tweaking vehicular charging systems.
                      And even if such data were to be applied, the cost and reliability far outweigh the gains.

                      The closest I have come to that is to avoid the need for those suck-in dc-dc converters to boost charging voltages.
                      I would simply insert one or a few 5c diodes (Sense circuit) to boost the alternator output voltage, and use a PWM chopper to cut back the voltage to the main battery (and maybe accessories if they were effected) in order to maintain the aux battery voltage. (In fact then the alternator's Sense line would be extended to the aux battery, and the chopper would chop to maintain say 14.4V at the main battery.) That's assuming some good reason that the remote battery is experiencing such a bad voltage drop.
                      That solution is far cheaper than a dc-dc converter. After all, the converter effectively chops the output to 14.4V. Ok, it regulates the choke's/transformer's input, but the point being that the PWM must handle the current being regulated. And a PWM can easily handle 100A etc (viz cheap 120A MOSFETs), but a choke capable of carrying 100A is a different matter. What would a 100A PWM cost? (Components - say $10? Plus connectors & housing.) Compare that to the 40A dc-dc converters sold here for up to $500!



                      Coming at this another way, HOW would anyone improve the charging system if they knew the current demands? What would they do? Pre-boost the voltage? (Think about the possible damage - especially if the load drops instead.)
                      And you'd think that if high current charging were such an issue, vehicles would at least have current limiting for the battery which is MUCH simpler than monitoring other currents. Yet no one has bothered.
                      Electric vehicles are another issue, but their entire power plant depends on an expensive big battery (an array of monoblocks). And there it is worthwhile going to expense.
                      But for most vehicles that cost $20-$30 per year in batteries (Australian prices, $120 for a good battery, or $180 if not knowing better, hence $40-$50 per year) - I spend $10-$15 per year - it isn't worth it. Especially when a battery can still fail at any time, and one of the best ways to avoid that is preventative maintenance - ie, replace the battery. Hence 10-year UPS batteries are replaced after 5 years even if never used.)


                      Fun topic isn't it?

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                      • #12
                        Oldspark...

                        While i enjoy reading your posts i was hoping it would boil down to a recomendation or at least some follow up questions on your behalf that would get us to some sort of conclusion.

                        I guess you are operating on the "teach a man to fish" principle where i was hoping you would "Give a man a fish"
                        -Jesus- King of Kings Lord of Lords

                        Comment


                        • #13
                          i would install a smart battery isolator to charge a 2nd battery. that way when it charges, its a fast charge.

                          Comment


                          • #14
                            A smart isolator does NOT fast charge a second battery any faster than the relay that we are using, nor a direct connection for that matter.
                            But the use of an isolator IMO is essential, but I've blasted enough crap out of those "smart isolators" in other threads. [So much so that the charge-light controlled relay isolator has been dubbed the UIBI - the Ultimate Intelligence Battery Isolator (which is an attack on the "intelligence" of intelligent battery isolators in systems with a charge lamp (or other charging indication).]


                            But addressing antimatter's last reply (which I was just about to submit):

                            I misread my previous email notification - I thought it was Mickz that replied. I was going to answer that at least I have taught how to fish (IMO with a cheaper yet more effective rod or net), but alas there are no fish (in Mickz's pond...).


                            And sorry for diverting somewhat to address Mickz's comments, but it contains the answer you seek.
                            I can't be more specific other than generalisations like a bigger battery unless I have more info. Hence why I asked "Can you indicate what sort of drain (250mA?) for how long, and then what charging for how long - eg. 1 hour car drive or 2 hours with 800mA charger)?".
                            If you want a short sample answer, skip to the last paragraph below. Otherwise suffer thru the next...


                            As stated, UPS batteries may not cycle many times if they are reasonably discharged. Although a life span of only 6 cycles is an extreme example based on certain batteries, it is by no means rare.
                            On the other hand, two of us have been using 11-year old Yuasa UXH38-12s (a 12V 38AH AGM UPS battery with 10-year rated life) for up to 3 years as cranking batteries for which, IMO, they should not be suited. Though I have a low current reduction starter (140A), the other is in a Mitsubishi L300 van which I suspect has a "typical" ~240A starter. I intended them merely as an emergency start battery (left in the vehicle for up to 12 months between charges), else a solar or camping battery with a lower loading (say 1A - 5A on average).
                            [ As written elsewhere, the UXH38-12s retail here for ~$670 yet its bigger ~100AH UXH100-12 (else UXH110-12) version sells for a mere ~$500 which makes it cheaper than the retail price of ~$550 for an Optima yellow-top of only ~70AH. Based on what I have experienced so far with the 38AH, I have little doubt that the 100AH would last at least 10 years, and maybe much longer. ]


                            Smaller 7AH Yuasa AGMs retail for $35, though they are the NP version (generally used for standby applications - eg, alarms etc, though also suited for cyclic applications). I got one to replace a smaller 23 year old NP 4AH that lasted at least 21 years in a domestic alarm system.

                            FYI - the NP series spec is ~160 cycles to 100% DOD, ~430 cycles to 50% DOD, and ~1200 cycles to 30% DOD where 100% DOD is taken as 1.7V/cell (10.2V) at a discharge rate of 0.17C.

                            EG - if an NP7-12 (7AH) whose full voltage is 2.1V/cell = 12.6V is discharged at 0.17C = 0.17 x 7AH = 1.2A to 30% DOD = 12.6V - 0.30(2.1V-1.7V)x6 = 12.6 - 0.72V = 11.9V, it should last 1,200 cycles at 25°C if recharged at 2.275V/cell = 13.65V (presumably immediately after discharge).
                            So 4 years if discharging an AUD$35 NP7-12 at 1.2A for about 2 hours (if I did the calcs correctly!)

                            For the above data and calcs, see NP-Valve Regulated Lead Acid Battery Manual (yuasanp.pdf), and maybe NP Series - NP7-12 (YUASA_NP7-12.pdf).

                            And as per Yuasa NP Application Guide.pdf:
                            • "C" is a value of the rated battery capacity expressed in Ah. For example in the case of NP1.2-6, the discharge rate 0.05CA means a discharge at 0.05 X 1.2= 0.06A, or discharge rate 1CA a discharge at 1.2A.
                            [ YES! - I had to check that so as to NOT divide the 7AH by 20 since 7AH is its rated C20 capacity which means "7AH capacity if discharged over 20 hours" - in other words 7AH/20H = a 0.35A discharge for 20 hours. The same battery has a different AH depending on the rated discharge time aka C-rating. Many batteries are C20 = 20-hour rates (cars etc), solar batteries can be C100 (100 hours), UPS batteries can be C1 (1 hour) and even C0.2 (12 minutes - or us that C12mins?). C10 is another common rate (10 hours).
                            And yes, I get real flustered with these calcs. I suspect once upon a time I did this more regularly and was not so confused.... ]



                            Maybe the latter "7AH = 350ma for 20 hours" is a partial answer for you...
                            Instead of 350mA for 20 hours, assume 250mA for 24 hours. That will be less than 100% discharge, so it should last at least 160 cycles - maybe over 250 cycles as a guestimate. So maybe a year (365 cycles) given the conservativeness of battery specs (eg, maybe at least 97% or batteries should exceed the spec) assuming daily charges else a battery protector (low-voltage disconnect).
                            If that's insufficient, maybe a second parallel NP7-12 - not that paralleling if without its issues , but two 7AH batteries tend to be FAR cheaper that a single 15AH or 18AH battery.

                            Comment


                            • #15
                              Originally posted by antimatter View Post
                              I am killing these batteries because i believe they are undercharged and overworked.
                              Currently with my driving habits i only get long periods (about an hour) of charging twice a week so it should be able to withstand a 250 ma standby draw inbetween these times and be able to recover fairly fast.
                              Am i asking too much of a battery?
                              Ok - trying to keep the answer simple:

                              With 5 to 7 days standby and two 1 hour periods to charge you have a real problem with your charge and discharge times (or are you also doing shorter trips throught the day).

                              With the times you quoted you are facing an uphill battle even with ideal charge installation conditions, especially if you want the battery to last for any period of time.

                              Is the AUX battery going to be handling the full load of a PC system resuming from sleep or is the system switched (and held) to the vehicle battery during engine cranking?

                              A: Reduce the discharge time. (Hibernate when left for extended periods)
                              B: Fit a solar charger. (Problems with bad days)
                              C: Connect a charger. (Practical?)
                              D: Have two batteries, one in circuit and one charging somewhere and use a parallel connection when swapping.



                              Hi OldSpark, just to clarify where I’m coming from, this vehicle is factory fitted with “Electronic Load Detection” ELD and it is part of the main under hood fuse box and also in the factory workshop manual. The ELD module is a current detection module with a FET driven output going to a control module that interfaces to the voltage regulator. This regulator interface module has a CAN-BUS control interface from the GCM-CPU and Vehicle master CPU. Unfortunately information on the control and operation is almost nonexistent.

                              That 13.5v rating of 110A @ 13.5v is a nominal power rating. The voltage across the Battery varies from 13.8v to 14.8v but not in response to any vehicle electrical load (not including the battery here).
                              The voltage appears to change in response to the amount of current drawn by the battery. Now we can talk about how useless this is, how inappropriate and incorrect it is, but it is what it is and it is what this system appears to do.

                              If the battery “APPEARS” to be fully charged (whatever correct or incorrect definition or incorrect assumptions the vehicle is using in a futile attempt to detect that condition) then the charging voltage sits around 13.8v, however it occasionally cycles up to 14.8v for short periods.

                              It will go to 14.1v after cranking the car, shortly drop to 13.8v then after a period of time slowly rise up to 14.8v where it will run for about 5 minutes before coming slowly back to 13.8v where it will mostly stay all day (observed over 2 x 5 hours nonstop driving periods), except for brief cycle periods mentioned above or until the next time I start the car. It also varies in time and voltages if I have left the lights on and lowered the DOD over what just starting causes.

                              At “any” voltage level you can turn “all” electrical devices on - Parking lights, HI-beam, Fog, Blinkers, Air-con clutch, Radiator fans etc and the voltage will not change. Except if the detect-point is right on the verge of deciding to drop back then the current from the AC-Clutch (no lights on) can sometimes make it go up a voltage step, but not for long and only at a certain point.

                              It’s a strange one I guess. I replaced the original 6 year old battery about a year or so ago. It just suddenly went HI–R in a small outback town on the 4th day into a trip in heatwave conditions. BTW the starter in this V6 is rated at 1.6kw @ 12v.
                              Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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