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Thread: Issue with Alternator Noise through Car PC

  1. #31
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    Quote Originally Posted by OldSpark View Post
    Why would you want to separate 2 charging batteries? (Other than the few exceptions I described.) LOL you crack me up!

    If you don't understand why you want to separate batteries when they are not charging, fine, risk thernal runaway (since you have AGMs) and double their failure rate, etc.


    An alternator is a constant voltage charging system, How many times do I have to repeat? It puts out its "target" voltage continuously - it never ceases - unless it is EMS controlled or the engine stops etc etc. You claim to have some magical switch that somehow isolates the "full" battery from the regulator, though it seems your battery never gets fully charged - or does your alternator voltage drop when a battery is full?

    My info is wrong? Where?

    Relays are dangerous for separating> QUICK - call the authorities and have then banned at once, or at least excluded from battery switching (interruption currents above several Amps DC excluded - as with breakers and fuses).

    Ghetto rig? What - all those approved voltage and other sensing battery isolators, and mechanical switches?

    I'm saying a relay is better than an isolator(sic) - you are merely furnishing support for it - ie, relays have higher capacity, they waste less energy, they run cooler, they are not as old as diodes, etc.
    I merely asked why spend over ten times as much for an oldskool diode isolator that has problems such as uneven battery voltages (as is your problem) and that does not allow current sharing as is desirable and many applications else is of no concern in others (and would prolong battery life in both cases). They are also not as configurable, expandable, or augmentable.

    Sorry - but I do not see diode isolators used in newer cars with dual batteries. Which ones do?
    And out of interest only, which cars or vehicles come standard with two batteries hardwired in parallel?

    And pray tell, how would a diode isolator not drag down the alternator during big amp sucks? (Your audio battery taking the full surge. If it were the lighting or main battery, then the flicker or dip would be worse!) Albeit that the main aim of audio systems is to reduce the audio dips, other dips being secondary, and another issue or topic.)


    Your problem with your relay was that you had your 2 batteries connected together whilst cranking. That has NOTHING to do with the relay. (I recall your line "What's wrong with paralleling 2 batteries anyway?")
    But that problem does not occur with the UIBI or other isolators I have described. And that is why I generally advise against IGN and manually connected isolation.

    I have no doubt you are speaking from word experience. But words from where?
    I have real world experience with a plethora of power systems, whether UPS, uninterruptibles, HVDC, battery, etc, as well as various safety and advisory forums (as in organisational - not php!), and familiarity and involvement with several Standards and - more so - the changes adopted for various safety reasons (especially for emergency crews like fire; also former hazardous earthing/grounding practices; vehicular safety (competition, domestic) - just to mention related industries).
    That is why I have reservations about the dual-battery system(s) described in that ambulance spec, but I do understand why they might desire that. But that is not the norm, and tends to be different from other emergency vehicles - eg, police, fire and recovery vehicles - they will generally not have parallel batteries for cranking etc, they tend to use fully separated battery systems with a typical relay auto-isolator,often with manual overrides or other contactors to bridge batteries in emergencies.

    If you don't have a problem with your aux battery, then why did you write that stuff about why you have your switch, and what is the problem you described in that other thread?
    As I said, your isolator has a 0.3V voltage drop (minimum). I'm sure you can measure that. That can be problematic for vehicles that have higher than normal battery voltages - the alternator outputting 0.3V higher than that (at low loads; more at high loads) becomes an issue for other equipment, lighting etc.


    Please stop misleading people, whether that is deliberate or otherwise.
    Or start addressing or explaining your issues so this can progress.

    Provide links or post info that describes your switching arrangement, or links that describe alternators that stop charging when a battery is full (as opposed to batteries not accepting charge current - other than float current - when they are full. Ergo, the common way of ascertaining a full battery whilst being charged).
    Or provide some base diagram. If it's the drawing you posted on the other forum, then I ask if we use a charging-connected relay, why add a diode isolator?

    If that is too big an ask, then forget your zero-load running vehicle etc.
    Go back to your original point and address that current surge which, as I have repeatedly written, does not occur in UIBIs and voltage-sensing isolators.
    You still have not addressed that and answered my question about it (or questions, I asked at least twice!)
    No problem.. I did long ago when I first installed it, and found it later to be the alternator. I never have voltage problems now. The problem was the relay setup i was using fried the plates in the battery.. I thought autozone was crazy when then tested it, till numerious ppl told me so... I was trying to put the starter by itself then and wire everything else to the aux battery when I got the isolator and new batteries, but found out i didnt have to.. Why would you want to isolate 2 banks while charging? like I told you in the example.. Place an device that requires the voltage to be steady (like an inverter) and connect your relay.. start car and watch it blip off for a second as the car draws current from your aux. I dont want to share my aux power with the car.. I want my pc, inverter, screen, ps2 ect... to have a separate battery all the time.. even when charging.. My gadgets dont interfer with the main battery, and my main battery doesnt interfer with my aux battery.. Hence when I start it there isnt that surge of juice being sucked from my aux.. You talk about isolators how bad they are, have you ever felt your relay? they get very hot. I would too a plunger driven on a metal plate to make a connection ntm the resistance it takes electrically to make the relay work.. No way.. I wouldnt want moving parts in my setup ever again, unless of course I Was aiming to parallel my main with aux... but why do that when my banks are completly separate and I have become accustom to this.. if I wanted paralle then I'd do that without the relay, or add them to either bank I choose.....Love it, WOnt change it and am very happy with it.. Trow and amp meter between your relay and watch the amps when you connect your weak aux battery.. Thats Because of the rush of current from your main battery trying to equilize the aux battery.. If it works for you cool.. but all your really doing is paralleling batteries with the exception of removing it while the car is off.. but then throwing it back dead for the other battery to rush current to it and try and bring it back to top... the added strain on the alternator is just not worth it in my eyes


    btw zero load doesnt exist.. in theory tho engine doesnt pull power. The computer does as does fuel pump, but if your alternator is oversized like mine dont you think its possible to bring the battery to charge quicker? if there isnt a large draw the alternator has to compensate for that and allow to gear up or kick back depending on the demand.. also yes I did test it and its so minute it doesnt matter. I did have this addressed when i got my alternator having the regulator adjustable so i can make up for this difference because my isolator can do up to 24v
    Last edited by Simbalage22; 08-20-2011 at 11:18 AM.

  2. #32
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    Old Spark is right ppl.. drop your isolator and use a relay.. Come on here! is that what you want to hear.. I may not word things right because I have mental issue's, but I do know what i have seen with a continous duty relay.. and even if I had the relay on the key (later moved to a switch) shows that even with restart off and on.. the starter draggs down the aux for the few seconds you crank vehicle.. thats why ambulances dont use relays because that 1 sec can be someones life..

  3. #33
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    I wasnt complaining on this form about it.. you must be referring to the post I linked which is indeed years old.. Why are u so against isolators?
    Jeeps and other trucks have 2 batteries.. parallel. No isolator, no relay.. from factory with 2 under the hood. Installed car audio years ago at car toons.. seen it all. relays are marketed as isolators and this is not correct. hell every kid in science knows what happens when you thow a dead battery at a full bank.. the full batteries rushes to bring the dead battery to its charge while actually killing the charge the good battery had
    Last edited by Simbalage22; 08-20-2011 at 11:44 AM.

  4. #34
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    Quote Originally Posted by highamperage View Post
    Hello! I'm having an issue with my Truck PC system and am looking for some pointers.

    My system is as follows:
    - 2nd Battery connected to main battery/alternator via one cable & negative mounted to screw in chassis/bed
    - Pure Sine inverter connected to 2nd battery
    - Car PC connected to inverter
    - USB 7.1 Sound Card, connected to two amps. (One for speakers, one for sub)
    - Computer Connected to Double Din VGA touch screen
    - Running Windows 7 & Centrafuse 3

    When the vehicle is operating I get a VERY annoying whine which corresponds to RPM. I've tried a number of things to remedy the issue:
    - Plug in PC to normal wall outlet (Solved Problem)
    - Try new inverter (Did not solve problem)
    - Try DC-DC PSU (Did not solve problem, made problem dramatically worse.)
    - Try 3 different computers & power supplies (Did not solve problem)
    - Tried using a laptop (Solved Problem)
    - Disconnected power to 2nd battery (Solved Problem)
    - Tried new sound card (Did not solve problem)

    The problem is obviously with the computer/inverter, not the amps or sound system itself. The laptops power supply must be able to filter this out. But I am at a loss on an acceptable solution, short of replacing my system with a laptop. Conventional wisdom says its a grounding problem.... but since the inverter is connected to that 2nd battery, wouldn't that help filter it? Would using too small wire to the inverter itself cause this? Any suggestions?

    Thanks!
    Btw sorry there, did u ever figure out your problem. I have had several types of ground loops and always track to down to ground, cheaply made amps ect.. try a filter on the inverter to see if thats the cause. then go down the chain to see where it is comming from.. if you changed nothing but tried a laptop the whine is comming from the pc.. for testing try a ground lifter on the pc to "See" if its picking it up from the inverter. Do you have the pc going throught the headunit.. turn the vol down on pc and try connecting it streight to the amps.. what Hu are u using?
    Last edited by Simbalage22; 08-20-2011 at 11:37 AM.

  5. #35

  6. #36
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    I'm glad you finally realised there is never "no load", whether it be a fully-charged battery's float current (typically up to 1-2A) or the power required by an engine and vehicle gauges etc.

    And I presume since you replaced your original faulty alternator, you would know what model it is and how it was modified to "stop charging" a full battery. Else you should know whatever was added to do that - some sort of switch (because the Vanner does not do it).


    I was going to reply with a summary of your arguments in favor of a relay, but maybe later.

    Most know how I almost always recommend an isolator - probably even OptimaJim (Optima's eCare Manager who posted on mp3car that there are "no problems paralleling Optima batteries").
    I have also described the merits of diode isolators - no moving parts, and simple to wire.
    But you have outlined their disadvantages - wasted power (heat), limited size, old technology, etc. (And describe situations that do not occur with the (auto) isolators I describe - eg, current surges. In setups like yours, one battery cannot discharge into another if using relays and the alternator is charging.)

    To quote one Diode Isolator link "(Diode Isolators are)... not used much these days but can be found on older vehicles".
    That is correct, the industry has moved to OTHER isolators - generally relay, but some newer FET switching types. And they have their reasons.


    But I'll have to defer until later (other-life issues - I hate them!), though a quick look at your http://pysystems.ca/blog/tag/fire-hazard/ support my views entirely - but maybe I'll get your point later.

    And I found another that also reckons relays are not (battery) isolators, but that has some quite funny-cum-ridiculous other statements. And guess what - he sells diode isolators!


    Hopefully I'll be back tomorrow to post my summary. And maybe look properly at your replies above.

  7. #37
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    Quote Originally Posted by OldSpark View Post
    I'm glad you finally realised there is never "no load", whether it be a fully-charged battery's float current (typically up to 1-2A) or the power required by an engine and vehicle gauges etc.

    And I presume since you replaced your original faulty alternator, you would know what model it is and how it was modified to "stop charging" a full battery. Else you should know whatever was added to do that - some sort of switch (because the Vanner does not do it).


    I was going to reply with a summary of your arguments in favor of a relay, but maybe later.

    Most know how I almost always recommend an isolator - probably even OptimaJim (Optima's eCare Manager who posted on mp3car that there are "no problems paralleling Optima batteries").
    I have also described the merits of diode isolators - no moving parts, and simple to wire.
    But you have outlined their disadvantages - wasted power (heat), limited size, old technology, etc. (And describe situations that do not occur with the (auto) isolators I describe - eg, current surges. In setups like yours, one battery cannot discharge into another if using relays and the alternator is charging.)

    To quote one Diode Isolator link "(Diode Isolators are)... not used much these days but can be found on older vehicles".
    That is correct, the industry has moved to OTHER isolators - generally relay, but some newer FET switching types. And they have their reasons.


    But I'll have to defer until later (other-life issues - I hate them!), though a quick look at your http://pysystems.ca/blog/tag/fire-hazard/ support my views entirely - but maybe I'll get your point later.

    And I found another that also reckons relays are not (battery) isolators, but that has some quite funny-cum-ridiculous other statements. And guess what - he sells diode isolators!


    Hopefully I'll be back tomorrow to post my summary. And maybe look properly at your replies above.
    Paralleling is great with optima's, that being said when you leave them paralled all the time.. when you start to separate, drain, and reconnect that bad... do you know how many amps are placed on the wire, relay ect when you flip that back on.. i'd rather have some voltage loss with isolator, then surge and fire that can happen with relays... likewise they both have their disadvantages... but fire, surge, and shorten life of batteries vs 0.3v loss from isolators.. Hmmm thats a no brainer

  8. #38
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    Apologies for the delay, my one-day away extended to two.. At least day 2 was not a repeat of day 1. But still, pending aforementioned summaries and analysis....


    Simbalage22 wrote: ["I]The power waisted alone for the relay to stay in the close position alone is bad..[/I]".
    So the 3W for our typical relays is bad, as is the 7W-13W for 250A relays and 25W for 400A relays?
    Yet Simbalage22 claims that the 0.3V drop for a diode relay is ok? The voltage-drop wastage for that Vanner at 250A is over 150W (in one leg)!. IE - 150W compared to a relay's 13W energisation power.
    Whilst I'd argue that even 25W (2A) is negligible for a 400A islolator (especially since the vehicle is charging) and certainly negligible compared to 10x that power for a Vanner isolator, the dissipation of 150W heat is an issue.

    However, my greater concern is even a mere 0.3V drop (or 0.6V at 250A) compared to 50mV (0.05V) across a relay at 250-400A.
    0.05V loss is not a big deal, but 0.3V and certainly 0.6V is. (People here sell 0.6V "boosters" for alternators for over $40!)


    Take your Optima-paralleling issues to Optima. I wrote the same. I do not recommend the paralleling of any not-in-use batteries. And if paralleled without an isolator, they should be matched and with equal charge-discharge paths as per normal recommendations - certainly not separated into engine bays and trunks and sharing a common ground!


    And as I wrote, there is no battery discharge current surge with the UIBI or similar isolators. Else maybe you can explain how one battery can discharge into another battery when BOTH are being charged - ie, both are above 13.6V? IMO that is a NO brainer!


    Yet again, you have repeated my concerns and views, with the exception that for some reason you now write that the power wastage with isolators (especially the Vanner) is no longer relevant (??!).

    Shortened battery life and fires etc with relays? Sorry - I think you are confusing that with the paralleling of batteries - ESPECIALLY AGMs. But you and Optima reckon that is not problem.
    We have the usual fuses or circuit breakers that help prevent that - not that that'll prevent AGM thermal runaway occurring whilst charging, but neither does the Vanner. And as you know, I dislike paralleling of batteries when not being charged or used - mainly to prevent replacing batteries at up to FOUR times normal rates (for 2 in parallel), but also for such SAFETY reasons (ie, fire).


    If you wish stop now, that's cool. You have an isolator that you like, and it solves your older problems if not your current voltage difference problem.
    But if or when your Vanner blows and you want to solve those SAME problems for $25 instead of ~$250 or more whilst wasting far less power and using something that lasts far longer (as I wrote, generally 10 years or longer), then revisit these posts or contact me if needed. (Relays are even more reliable than the voltage-sensing switch you have referred to.)

    I'll probably still post my summary of your arguments in favor of relay or FET isolators over diode types to both assist your next choice as well as for the benefit of other readers.


    BTW - yes, I was referring to your posted link which is old, but your posts date from 2009 and it seems nothing has changed.
    Also, Simbalage22 wrote above: "...ppl.. drop your isolator and use a relay.. Come on here! is that what you want to hear.. . Others have expressed no opinion nor taken sides. I expect any remaining readers are as curious as I to understand your justifications etc.


    But I do suggest sticking to your basic proposal that there is a current surge between batteries when connecting a UIBI or other voltage-sensing etc battery isolator (WRONG! Except in certain circumstances which are not relevant in your case, nor a typical UIBI/voltage battery isolator set up) - even though as I have written, that may have occurred only in your original set up and does not occur with the isolators we are now discussing (namely, non manual-switches isolators).
    Other issues like connection fire hazards, power wastage, life-span, alternator noise, your previous problems & current alleged non-standard voltage regulator, and the subject of otherwise paralleling batteries, etc, are secondary or irrelevant or proven to be against diode isolators.
    Besides, let's understand one thing at a time. Like I wrote, it is (in retrospect) simple but usually very tricky to initially comprehend. Whilst I may well understand all the related issues, it is too confusing to explain them all at once.


    A despite you choosing not to start a new thread on this issue, I think this thread is now so far hijack-padded that it doesn't matter, so why not continue?

  9. #39
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    using a relay is still technically paralleling tho.. Likewise I am not rich.. When I cant afford an isolator i'd use one in a second. But in my application with the computer the loads need to be separate.. completly. Large lights, starter ect all effect my car pc.. so with my experience with the isolator I dont have the voltage drop when cranking because their separate. Yea I know a switch on the relay works but then they still are parallel when charging so banging the amps loud can bring down the both batteries and make the car pc blip off enough to reboot. So I am happy with it and hope it does last. I have 7.1 in my car and its loud.. I created a thread on this while were on alternator noise.. So trust me I am not saying its wrong, or incorrect.. Just that there are better ways to separate batterys at a cost all ways.. Nothing like using a relay and have more CCA in the winter.. the ability to flip your switch and start a dead car.. I have used it.. works quite well.. but not efficient enough to me for true isolation.. Piece of mind knowing my brand new yellow top never sees the used one under the hood is pricessless and worth the voltage loss to me. My alt is cranking 15v so I dont notice the loss anywho

    BTw who hijacked the thread? I posted about an isolator... you said 260a who uses them nowadays... So of course I am gonna comment
    My comment about you being right was being a smart azz.. you tell me how I can get true separation (or current flowing in 1 way on my batteries) and i'd be willing to give it a try. Also how many amps is your alternator is it greater then 260? I dont know about you but having the amps that your relay carries does risk fire and surge because they are still paralled so you explain your setup,, Draw a diagram.. Isolators (diode type) are self explanitory... LEg 1 leg2 alternator.. Simply put it works with a voltage loss which is not noticable. Even distribution of amps and batteries never ever ever ever see one another even durring charging. I know because I had a dead optima on the second leg for the longest and it never brought down the bat on leg one.. Had this been a relay, or paralled the bad battery would have shorted the good one (running or otherwise) soon as you threw the switch.. Hence why I advise AGAINST the relay unless thats all you got, or your goal is paralleling with option to separate, drain, and throw back in for a fast charge which does hurt the whole electrical system..Might as well be giving the neighbor that has a bad battery a jump every morning, or 6 times a day for that matter.. Ever time you drain, and re-parallel (Which is what your doing from what I am understanding) you are hurting your batteries.. I'd truthfully rather leave them paralled so they drain equily vs separate and drain as I post above.. I have seen batteries explode doing just this.. I was lucky.. So is a relay cheap, yes... are there better ways yes.. does it work.. yes.. but personally if I had to i'd parallel and just reep the rewards of having double runtime vs using a relay.. Or use an isolator to separate and if the 0.3v doesnt effect you have true separation the way it was meant. If your alternator is more the 260a then I could see why one would not want to use an isolator... But 260a charging is alot
    Last edited by Simbalage22; 08-23-2011 at 12:55 PM.

  10. #40
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    First a question for you: The UIBI I described, when does the relay connect the 2 batteries, and when does it disconnect?
    Hint: Ignoring time delays, it is the same as voltage controlled battery isolators.


    Yes, the relay parallels the 2 (or more) batteries.

    That is its intent, though the prime intent is to (only!) parallel the batteries when the alternator is charging (or rather, isolate when NOT charging). Hence no battery to battery current surges that you spoke of.

    It is quite acceptable to parallel batteries when they are being charged. There is no need to have matching batteries, they only have to be the same voltage and lead-acid, ie, 12V flooded (wet cells), gel cells, or AGM (aka VRLA).


    Whereas diode & voltage controlled isolators are expensive, the UIBI is merely a relay which is energised when a vehicles charge light extinguishes - ie, the alternator is charging. The relay is sized to suit whatever current is desired.
    Hence it is the cheapest battery isolator that meets the normal main requirements - ie, NOT leave batteries paralleled when NOT charging but charge all batteries when charging is available - ie, engine running and alternator charging.
    But for stator systems or permanent magnet systems which do not normally have charge lights, diode, FET or voltage controlled isolators must be used. (Not really a must, but charging can only be determined by two methods - ideally current sensing (which does not need time delays) but the norm is voltage sensing (which requires delays to prevent false switching and on-off-on-off "hunting", as well as determining what voltage level to set the cut-in and cut-out voltages; they can both vary depending on what the user wants).

    Hence one important point, the UIBI in its basic form is only suited to systems with charge light circuits, or something that tells the UIBI (relay) when the system is charging. (Actually that is not difficult - a circuit that measures a voltage drop along the alternator output wire. It may only be milli-volts, but that is easy enough to detect. Some remote sensing ammeters use that - they measure the voltage drop across the battery's ground wire (though the +ve wire if single can also be used) and convert that to a current (Amps) display after calibration (based on V=IR where R is the resistance of the wire segment being measured).
    For the UIBI battery isolator, it need only detect current (say above 100mA, though normally any car alternator will output at least a few Amps just for gauges and the engine (management) alone). I'd add polarity in case an alternator power diode shorts. Not that that is a common event, but if it does ever occur, it's bad enough with one battery going through it - you don't want the isolator connecting any more. (That situation is one advantage of a diode isolator, but I stress it is a VERY rare situation, and usually if the diodes have shorted, the main battery will blow them open anyhow. So in practice, it is rarely a consideration.)

    As to hurting batteries, I disagree. Every time you are NOT charging a battery, you are hurting it. That is a bit pedantic, but in an ideal world, batteries would always be on a float charge. (If a battery is not fully charged, it begins to sulfate. And when is a battery not fully charged? Not long after it stops being charged and its internal leakage starts to discharge it. The flatter it is, the greater the sulfation. But car batteries last for years despite that. As I said, I am being pedantic - sulfation is trivial EXCEPT if batteries are left uncharged for a long period (say 3 months for a wet cell), or if left not fully charged (a reasonably discharged battery should be recharged ASAP).

    Ignoring temperature, the best battery life occurs with the least cycles, lowest discharge rates, lowest discharge depths, and prompt recharging - preferably at as low a rate as possible and not exceeding typically 14.4V (for wet/flooded cells). (Maintenance is a different issue. EG - charging above 15V to "equalise" the cells - often done in conjunction with a HIGH current charge (20A or more) if it's been flattened and/or sitting a while.)

    [ FYI: Note that figures I am using are typical for 12V lead-acid batteries. But variations exist, sometimes between different manufactures, or models, or type (AGM) or application (deep discharge, cranking, cyclic, stand-by) or temperature or battery size or... So to my are my "general" statements.]


    So how do we decrease the current drain from a battery?
    What about paralleling the batteries we have? Yeah - that's good, but we don't want to leave them that way. One battery may discharge into another if they differ. A collapsed or faulty battery will bring down and eventually destroy the good battery(s). I know you know that because I greatly appreciated that - especially considering the number of $#%#@@! that do not understand such issues!
    So why not parallel them ONLY when being used or being charged?

    Bingo! Hence the common relay type isolators (whether UIBI or voltage controlled etc).
    They allow the batteries to share the loads and hence reduce a battery's peak current load.
    And they are being charged anyhow - they merely supply the alternator's shortfall for that peak load (eg, brake lights or headlights on, amplifier thumps etc) but the alternator soon recovers and recharging begins. Apart from cranking, that's what batteries are for - to make up for temporary or transient alternator shortfalls. Otherwise the vehicle would most likely stall.
    Undersized alternators is a different issue! But that is not a problem for clever people - eg, those with 250A alternators! (I shall refrain from discussing certain recommendations and view on certain audio forums!)

    Not that typical battery isolators share the load for cranking because the engine/alternator is not charging - that requires a manual bypass feature on voltage sensing isolators. For the UIBI, it is as simple as adding a manual bypass switch, plus 2 diodes (20c 1N4004 etc) to enable a parallel trigger for the relay without having the switch back-feed into the charge light circuit and visa versa. (Simple eh? Or it should be once you see the circuit or wiring diagram.)
    But again, once charging, no problem sharing that load. For many (if not most), that is a very desirable feature. And of course, when not charging, the batteries are isolated from each other so they cannot discharge each other, and you can flatten your aux battery (on accessories, PCs, fridges, amplifiers) but still have the main battery for cranking as normal.

    BTW - yes, connecting a full cranker with a flat 2nd or aux battery is not desirable (again, as you have so rightly pointed out!), but that is NOT how the isolators normally work, and I would hope manual bypassers know what they are doing. (Inhibit circuits could be added to prevent manually connecting a full and flat battery, but why manually bypass (connect) if your cranker is full anyhow?)
    As to connecting flat to full battery, that is common when jump-starting vehicles, and rarely have I seen warnings relating to battery damage etc. (I recently rechecked a few sources and sites as a result of the issues you raised.)

    The normal isolator operation whereby a big battery connects to small battery (or flat) isn't an issue. Because they are both charging - ie, the alternator is above (say) 13.6V which is above any typical battery's full voltage - they cannot discharge into each other.
    And batteries - no matter what size - are specified to charge from up to 14.4V sources. That's constant voltage charging as recommended almost universally.

    Mind you, most batteries have a specified current limit. Exceeding that limit (for both charging and discharging respectively) is considered excessively damaging for the battery. (Noting that the limit is somewhat arbitrary. The lower the better, so what is deemed unacceptable or excessive? But that's just one of the specs that is supposed to allow the battery to last its specified life.)
    And I admit, it often scares the crap out of me when I know that people parallel their small 7AH or 1.2AH etc batteries with the might of a big cranking battery or typical alternator! But in practice, though the battery's charge current may be exceeded, that is usually short lived. The charge current drops quickly as the battery's internal voltage increase. How fast? Well, the higher the current, the faster the recharge and faster the voltage rises. It's a Catch-22, but a good one. The thrashed battery usually doesn't even have time to heat up (heat being a good indicator of battery problem, or being (fully) charged...)
    It shocked me when I found my 38AH AGM was taking 45A when alternator charging began. It's not supposed to exceed 4A, or is it 8A, or maybe ~15A max? But 45A way exceeds that! But withing 10-30 seconds it is down below 10A. And I've been using that 12 year old AGM for probably 12 months as my main cranker. My brother has been using another (same model and age) for about 3 years as his car battery. They are 10-year UPS batteries that were discarded after 5 years (a common preventative maintenance strategy), but IMO they should not be suited for cranking - it's way to much strain for them. Yet they refuse to die.


    But I'll leave it there. I haven't commented directly on your last reply. Instead I've given a mixture of battery considerations. However I think that with that, you may begin to understand what I have been reflecting.

    Also, I thought you did have the Vanner isolator or similar. Ah - you got one cheap...? (Like my 38AH AGMs - normal retail price here is ~$660, though I suspect if I ever wanted a replacement, I'd get the bigger 100AH. Not only would that be ok for cranking (it'd probably last 20 years!), but it is CHEAPER - about $500 (which is cheaper than the RRP of an Optima 75AH yellow-top).)


    But if you are not rich, then I reckon the UIBI (relay) is the way to go. I do know that it is the best and cheapest solution for MOST applications. (So do certain self interested parties - that's why I cop a lot of flak in some circles!) But that comes after years of experience and knowledge.
    And this reply has barely scratched the surface.
    Plus there are some omitted considerations - like enough charge-light drive to energise the relay (a smaller buffer relay might be needed for BIG relays). And the sizing of the battery interlink (most are big enough to supply the secondary recharging and loads - not share cranking currents).
    But non-diode isolators are add-on systems. You can keep the existing alternator-battery wiring; you just add the relay and interlink cable (with fuses or breakers at each end) and the 2nd battery to that.


    BTW - UIBI stands for "Ultimate Intelligence Battery Isolator". It got that name after certain parties aired their views on much of the advertising and false claims of "Smart" isolators (voltage sensing). I like their summation: "What does the voltage sensing isolator try to determine? (and) What does a charge light mean?" (Answer to both: Charging. Problem for voltage sensors is the delays required and (or) the voltage thresholds chosen - a very complex issue indeed! And no unique answer, and no unique set of sags and dips etc.)

    More later. It's 5:30AM. Yep - time for bed.

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