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Thread: Doesn't hold standby power if I crank the car right away

  1. #41
    Raw Wave
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    If you mean the 2nd battery drops to that level - agreed. But it shouldn't if the isolator is doing its job.

    [ FYI - That depends on the isolator - one of the problems with the voltage sensing (smart ha ha!) types is they they can be set up differently - ie - to break quickly at voltage drops, or delayed, etc. But if you have just entered the vehicle after a break, why the heck is the isolator still connected? (Answer - they are usually set to disconnect below 12.7 or 12.5V etc. A full battery is (say) 12.6V, but a just charge battery can be up to 13.6V (for up to ~24 hours if open-circuit). ]
    Rats - now I'm giving away a few of the problems I was hoping the voltage-sensing aficionados would work out for themselves!

    And if it is the 2nd battery that is dropping that low, that essentially proves the reverse conduction of your MOSFET isolator (unlike a transistor, it is a "channel" and not a forward PN junction like a diode). In other words, it behaves much like a relay, though probably with a higher resistances hence higher voltage drop (but small - not the 0.2-0.6V drop of diode isolators). (Caveat - I hope my MOSFET theory is correct!? That's all from back in Roman Numerals days.)


    If you are referring to your main battery, that'd be a normal voltage drop (well, a bit too low), but your 2nd batt should be isolated and NOT see that dip. And I assume the M4 is sensing the 2nd battery's voltage etc.... (Or does the Acc or Ign input also sense voltage... That's a clever economical design - except in these types of situations...)

  2. #42
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    Quote Originally Posted by OldSpark View Post
    If you mean the 2nd battery drops to that level - agreed. But it shouldn't if the isolator is doing its job.

    [ FYI - That depends on the isolator - one of the problems with the voltage sensing (smart ha ha!) types is they they can be set up differently - ie - to break quickly at voltage drops, or delayed, etc. But if you have just entered the vehicle after a break, why the heck is the isolator still connected? (Answer - they are usually set to disconnect below 12.7 or 12.5V etc. A full battery is (say) 12.6V, but a just charge battery can be up to 13.6V (for up to ~24 hours if open-circuit). ]
    Rats - now I'm giving away a few of the problems I was hoping the voltage-sensing aficionados would work out for themselves!

    And if it is the 2nd battery that is dropping that low, that essentially proves the reverse conduction of your MOSFET isolator (unlike a transistor, it is a "channel" and not a forward PN junction like a diode). In other words, it behaves much like a relay, though probably with a higher resistances hence higher voltage drop (but small - not the 0.2-0.6V drop of diode isolators). (Caveat - I hope my MOSFET theory is correct!? That's all from back in Roman Numerals days.)


    If you are referring to your main battery, that'd be a normal voltage drop (well, a bit too low), but your 2nd batt should be isolated and NOT see that dip. And I assume the M4 is sensing the 2nd battery's voltage etc.... (Or does the Acc or Ign input also sense voltage... That's a clever economical design - except in these types of situations...)
    I was talking about the aux (isolated) battery that I did see the voltage drop. I am going to have to test it again to be sure although when I did test it I had a friend crank the engine while I watched the voltmeter directly attached to the aux battery. Anyhow I will test again to be sure it wasn't a fluke.

    But you did bring up an excellent point. The M4-ATX has a setting where you can specify the voltage that indicates IGN on. I believe it is set to ON at anything higher than 5.24v I wonder if it is in fact dipping to below that thus causing the rapid on off signals that M4-ATX doesn't like. Im going to have to put a voltmeter on it during crank to see what it dips down too at crank. Also I could put the setting at something like 2 volts.

    Either way i think I like the simplicity of the charge lamp controlled relay, keeps the guesswork out of the isolation circuit
    -Jesus- King of Kings Lord of Lords

  3. #43
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    Quote Originally Posted by antimatter View Post
    ...charge lamp controlled relay, keeps the guesswork out of the isolation circuit
    And there you have it!
    Another question I often ask is "what is the voltage sensing trying to do?".
    Answer: It is trying to determine if the system is charging so that it can connect the other batteries, loads etc.

    So why try to determine that if the alternator is already telling you that?

    End of Story. (Except when voltage sensing is required for other reasons, as opposed to simply is or is-not charging. Note too that the alternator is still charging even if its output is under 12.7 or 12.0V etc - but IMO that is what a dash voltmeter is for.)


    antimatter - a simple dip test could be done by disconnecting the 2nd battery from the isolator. I'd suggest just pull its fuse (which I assume you have - otherwise disconnect (say) at the isolator but DO NOT allow that connection to short to ground etc!!), then crank and test. The 2nd battery should not see any dip (obviously).

  4. #44
    Jesus Freak antimatter's Avatar
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    Yeah, for me I don't have any of the other situations that you mentioned to would require voltage sensing brilliance

    As soon as I can spare some free time (new born and 22 mo) and get an extra set of hands I will be testing that for sure
    -Jesus- King of Kings Lord of Lords

  5. #45
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    Man i am having a tougg time finding the the 70/60 amp horn relay here in the US. I can find plenty of them 50 amp auto reset breakers
    -Jesus- King of Kings Lord of Lords

  6. #46
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    Just thought I would post an update to the issues I am having.

    I did some testing today and it turns out that after I replaced the isolator (warranty replacement) it fixed my issue with the aux battery participating in the engine crank (voltage drop)...that's good news!

    I also did some testing with a voltmeter at various points along the positive and negative from the aux battery to the terminals on the M4-ATX. I found there was a voltage drop from the battery to the M4 terminals of about .3v. This was because of connectors I used. I replaced these with solid connectors with proper gauge wires and the voltage drop was eliminated. The voltage drop here is not such a big deal but it does explain why the standby power was cut when I was setting the M4 to cut standby at 11.02v and the battery read 11.3v.

    I also RMA'd the M4-ATX because of some other issues that I am having. I will send back this one when I get the new one in.

    This brings me to my battery issues... I apparently have a deficit in charging / power draw. I need to find a way to keep my battery fully charged. Today I watched the voltage from my aux battery go from 11.9v down to about 7v in a period of about 8 hours with a .3 amp draw (standby power). Obviously something is wrong here. I should get at least 48 hours on a full charge (probably more). So not knowing the best way to determine whether a battery is good or not I will assume it is bad and I will be replacing it with another battery just to cover all my basis. I have also considered adding a solar panel on my rear deck to supplement the charging system.

    Anyways I think I am making some headway with this situation and hope to have a near flawless system soon.
    -Jesus- King of Kings Lord of Lords

  7. #47
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    That sounds like a bad battery - nothing to do with charging.
    (Unless poor charging and overdraw has wrecked the battery, but you need to replace the battery first. That assumes it has been charging at 13.6-14.4V. And down to 7V will damage any battery!)

  8. #48
    Jesus Freak antimatter's Avatar
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    Quote Originally Posted by OldSpark View Post
    That sounds like a bad battery - nothing to do with charging.
    (Unless poor charging and overdraw has wrecked the battery, but you need to replace the battery first. That assumes it has been charging at 13.6-14.4V. And down to 7V will damage any battery!)
    I think it is charging on the low end (13.6) and I do think there may be an overdraw situation...but I will be replacing the battery first
    -Jesus- King of Kings Lord of Lords

  9. #49
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    13.6V will still charge it (despite what many seem to think; but it is not enough to reverse sulfation that forms when not fully charged), but that might be easy enough to fix/boost later unless it is a single-wire alternator with a D+ (charge-Lamp) terminal only (not counting the obvious B or B+ = 12V output, and the ground via body/chassis/engine).
    [ You merely insert a diode in he alternators Sense line (S else I = Ign). That's a ~0.6V boost = 13.6+.6 = 14.4V for a mere ~5c to ~20c cost (unless you live in Australia where you might prefer to buy a 5c diode or 2 mounted in a fuse for a mere $35 + $7 P&P - after all, you pay for quality don't you... LOL!). ]

    I'd suggest having the battery tested before buying a new one, though your info seems conclusive....
    A good battery will hold charge. Its open circuit rested voltage (ie after its post-charging surface charge is removed) should indicate the percentage of capacity remaining.
    IE - using my Rules Of Thumb, a full battery is 12.67V - ie, 12.7V but let's use 12.6V. Each 0.1V drop is an ~10% drop in capacity (from 12.7 being full to 11.6 to 11.4V being 100% discharged).
    Hence 12.1V = 12.6V - 0.5V = 5 x 10% = 50% discharged.
    The problem is that those voltages are open-circuit - ie, with load(s) removed (and a bit of self recovery time), but at low loads (line 1A etc) any difference should be negligible. For high loads, there is a voltage drop (eg, 12.6V full drops to 12.4V with lights on, but it is still full - the internal resistance drops voltage according to internal resistance (ESR) times current), but that voltage drop will remain fairly constant for a while (it increases as ESR increases with the decreasing capacity remaining).
    Confused?

    Anyhow, a good battery should start from ~12.6V and drop to ~11.6V linearly.
    But that measures its ACTUAL capacity. Like my 6-8 year old batteries that looked okay from 12.7 to ~11.5V but only had maybe 5AH capacity instead of their rated 40AH capacity.
    That's typical of older batteries, or batteries that have had a tough life (excessive flattening; long storage periods; insufficient charging; excessive current demand; high discharge & recharge rates).


    Sorry for the blurb, but that's the FYI info so you can hopefully understand, or confirm yourself.
    Last edited by OldSpark; 06-13-2011 at 04:30 PM.

  10. #50
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    Quote Originally Posted by OldSpark View Post
    13.6V will still charge it (despite what many seem to think; but it is not enough to reverse sulfation that forms when not fully charged), but that might be easy enough to fix/boost later unless it is a single-wire alternator with a D+ (charge-Lamp) terminal only (not counting the obvious B or B+ = 12V output, and the ground via body/chassis/engine).
    [ You merely insert a diode in he alternators Sense line (S else I = Ign). That's a ~0.6V boost = 13.6+.6 = 14.4V for a mere ~5c to ~20c cost (unless you live in Australia where you might prefer to buy a 5c diode or 2 mounted in a fuse for a mere $35 + $7 P&P - after all, you pay for quality don't you... LOL!). ]

    I'd suggest having the battery tested before buying a new one, though your info seems conclusive....
    A good battery will hold charge. Its open circuit rested voltage (ie after its post-charging surface charge is removed) should indicate the percentage of capacity remaining.
    IE - using my Rules Of Thumb, a full battery is 12.67V - ie, 12.7V but let's use 12.6V. Each 0.1V drop is an ~10% drop in capacity (from 12.7 being full to 11.6 to 11.4V being 100% discharged).
    Hence 12.1V = 12.6V - 0.5V = 5 x 10% = 50% discharged.
    The problem is that those voltages are open-circuit - ie, with load(s) removed (and a bit of self recovery time), but at low loads (line 1A etc) any difference should be negligible. For high loads, there is a voltage drop (eg, 12.6V full drops to 12.4V with lights on, but it is still full - the internal resistance drops voltage according to internal resistance (ESR) times current), but that voltage drop will remain fairly constant for a while (it increases as ESR increases with the decreasing capacity remaining).
    Confused?

    Anyhow, a good battery should start from ~12.6V and drop to ~11.6V linearly.
    But that measures its ACTUAL capacity. Like my 6-8 year old batteries that looked okay from 12.7 to ~11.5V but only had maybe 5AH capacity instead of their rated 40AH capacity.
    That's typical of older batteries, or batteries that have had a tough life (excessive flattening; long storage periods; insufficient charging; excessive current demand; high discharge & recharge rates).


    Sorry for the blurb, but that's the FYI info so you can hopefully understand, or confirm yourself.
    Much appreciated!!
    -Jesus- King of Kings Lord of Lords

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