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Thread: Question about ground loop.

  1. #11
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    As long as you know you have to dismantle the alternator to get to each diode to test them. Otherwise it's done with a waveform tester (CRO etc).


    Re the GND point, the main issue is a single ground point. Usually that's neither the alternator nor the battery, but some common point - eg chassis or fusebox of DB.

    Common grounding at the alternator body is rare and usually done by non-practical people else for very specific requirements. To a lesser extent, grounding at the engine or gearbox etc is likewise rare.
    Common grounding at the battery -ve terminal is usually impractical or unreliable.

    Interestingly the last argument I saw for "absolute GND" {sic} was by someone with a small sound system. (They grounded at the alternator.)
    Last edited by OldSpark; 11-06-2013 at 03:59 PM.

  2. #12
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    Realize where your power is coming from and it makes sense to go to the battery directly. Anywhere else and you have to upgrade the wires going from the battery. Look at the size of the wire from your alternator to the battery. It is generally quite small in every car I have ever owned. Somewhere in the 10gauge area. It does not provide large bursts of power on a moments notice. That is the batteries job. The alternator is more of a constant battery charger than anything else. You do NOT want to run ANYTHING directly off the alternator without a battery present. There is a reason car manuals specifically state to never run the vehicle without the battery installed...

    I know that people tell you to ground your battery to the Alternator bracket when you jump a dead battery but this is to keep the sparks away from your battery. A charging battery off gases hydrogen and if you mix hydrogen, oxygen and an ignition source things go boom... Like your battery. I have had a battery explode next to me and luckily I was wearing boots otherwise when the pieces hit my ankle it would not have been fun. I was a new employee and the equipment I was testing had not been run in a long time and the battery was bad. My partner was not aware they had abandoned the equipment so we were not supposed to run it.

    So wherever you ground your system you want to make sure it has a good solid path back to the battery. Again this means upgrading all of the wiring from the battery to the place you are using your power.

    In my area it is very common for people with large systems to ground their systems directly to their battery. But it can be expensive otherwise. I remember buying 1/0 high quality wire that was like $10 a foot or more. In my car I needed to run 15 feet of the wire so I ran both positive and ground to the battery. No worry about voltage drop there. The big difference between high quality wire and cheap stuff like welding wire is the size of the wire and the flexibility. The high quality stuff I had was about the size of OEM 4 gauge and was as flexible as a thick rope. Very easy to work with but the copper actually burned when I tried to solder it to a connector. (Had to use a propane torch because of the size of it.) Soldering 1/0 gauge wire is probably not the best solution. In that vehicle the 1/0 wire ran to a series of distribution blocks that fed the 3,000 watts of real power in that system. It was only rated at 500 watts but we used "cheater" amps. I used 2 Optima batteries and originally used a Diode Isolator but ended up with a Constant use Solenoid to charge these batteries. It was after losing 10 different chromed battery connectors to 4 different Optima batteries that I found out that Optima batteries are crap and not intended for use in daily driven vehicles and definitely not for car audio. One of my batteries was a factory replacement and the other was powering the system. One ground wire went to the negative grounding block and it was also grounded against the frame to ensure that the ground potential of the system battery was the same as that of the vehicle battery.

    Sorry if I went a little off topic there.

  3. #13
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    My god Red, you mean we agree - Optima is crap?
    I'm curious how you "lost" the battery connectors tho - Optima like AGMs should not leak acid. Or was it electrolysis, or the brittleness of chromed items?
    Funny you say Optimas are "definitely not for car audio". Audio & car forums I have seen would strongly disagree. But I wonder what else Optimas are good for... AGMs are not as suited to cranking (as wets) except for long standing vehicles (eg, vintage cars only used once or twice a year) provided they are disconnected else have no parasitic loading. Not that I'd use an Optima when far cheaper and better AGMs are available.


    Optimas like all(?) AGMs are easier for a common terminal connection (eg, GND) because they have boltable hard metal terminals unlike most wets that have lead terminals. Not that that prevents internal damage from all the weight/inertia and cables bolted to their terminal(s).
    As you say, it's the battery that provides the power when the alternator is lacking - eg, high loads at idle; audio etc loads that exceed alternator capability; initial inrush currents and step changes. Hence the battery -ve terminal is "the" ground (or absolute ground as some refer to it).
    But normally it is the alternator that supplies the power, hence the alternator is "the" ground.
    The common compromise is an intermediate ground - normally the chassis or some other distribution point. Then infinite wires and bulk can be added and commonly grounded without stressing battery terminals or alternator bolts or having real estate issues, and you avoid the elevated temperatures and vibration of the alternator or engine block terminations.
    Of course certain applications may warrant actual battery or alternator grounding (welders, winches, etc) but IMO that generally implies insufficient ground wire conductance which IMO should be rectified (as in fixed).
    Ye olde rallyers used to terminate driving-light +12V at the alternator output for maximum voltage (a bonus being that no alternator B/B+ output to battery+ cable upgrade was required - hence a fully add-on system), but that is totally redundant with modern HIDs & LEDs.


    FYI - the main reason car manuals specifically state to never run the vehicle without the battery installed is because there is then nothing to absorb high voltage transients that may damage car electronics.
    If driving without a battery, any step change like flashers, brake lights, wipers etc is likely to collapse the alternators output, hence dead electrics as well as a dead engine (except perhaps for diesels and steam cars).
    In old vehicles, no battery usually meant a higher alternator output voltage that could damage or destroy vehicle electrics. The same is still true but modern alternators are usually limited to a max of 16V in such circumstances (typically ~15.5V).

  4. #14
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    My battery terminals were eaten by the battery acid that leached out of the optima batteries. While it is commonly stated that they are leak proof this is simply not true.

    My understanding is that Optima batteries were built for off road racing where they needed quick starts, high load capacities for winches and other related items. Someone decided to try using them in car audio and it took off from there. They are not designed for the type of use someone would get in a daily driver. In my vehicle I used the top mount posts and they swapped out my batteries in warranty twice. It was obvious it was battery acid eating up the connectors because of how it was happening. The guy from the battery shop actually ran his fingers on the battery posts and tasted it and said "yup battery acid". (Won't even get into how bad of an idea THAT was... NEVER taste battery acid... )

    The AGM batteries you mention I believe are the same type of batteries I was told to use many years ago.

    If you read the design specs on the Optima batteries the Sulfuric acid is locked up in some sort of material and wrapped into spirals thus the 6 cylinder style compartments. My understanding is this is similar to racers using foam in the gas tanks to prevent fuel splash. It keeps the liquid in place during high performance maneuvers and was NEVER intended as a leak preventative. I think they used to advertise they were leak proof and this was how I was able to keep swapping out batteries but I don't believe the last ad boasted that anymore.

    And yes I didn't spell it out but those are the same reasons I was referring to for making sure the battery was in place. The electronics in cars now adays are much more sensative to power surges and spikes than they used to. Cars back in the 70's had very few actual digital processors compared to todays vehicles and disconnecting the battery while the car was running didn't do much damage if any. But today's charging systems require the battery to be in place to operate for the reasons stated.

  5. #15
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    Yup - AGM = Absorbent Glass Mat; the mat is soaked in acid. No free acid per se - you can break open an AGM and it should not spill any acid and will probably still hold charge for a day or so.
    However charging is another issue and acid can "boil" off.
    AKA VRLA - Valve Recombination Lead Acid - the discharge hydrogen is held near the plates so it can recombine when charged. (Wiki reckons VRLA include gel cells but I only knew AGMs to be VRLA. But both are "sealed" or "maintenance free".)

    One of their misconceptions is that they don't vent hydrogen or acid. You have experienced the LOL re the latter.

    Another misconception is that people confuse the ability for an AGM to be able supply more current (because they typically have half the internal resistance of an equivalent wet cell) with their suitability for high discharge.
    AGMs do not like high discharge currents, nor high recharge currents, and certainly not over-voltage recharging nor excessive discharge without immediate recharge (AGMs do not recover after an excessive discharge whereas wets usually do albeit with compromised capacity or life).

    They are popular for winches because they typically require hundreds of Amps (500-900A) and are then usually subject to immediate recharge.
    Audio systems do not fare so well except in competitions (ie, high discharge followed by the trip home at rechargeable levels) though I noted the higher use of wet cells at the last comp I attended (ha ha - higher SPL boys - no caps??).
    AGMs are usually ok for campers & RVs and PCs because of the low discharge rates; it's usually excess discharge or delay between recharges that kills them.

    In a previous millennium, Exide/Chloride released their "Torquestarter" battery which was "the ideal" cranking battery for cars. It was withdrawn approx 1 year after release due to the overwhelming warranty returns. IMO it was simply ahead of its time - alternators still often had external electo-mech regulators but others often also charged way above 14.4V. And no vehicle had under-voltage trips; some Euro vehicles had headlights linked to the IGN key; not even headlight/parker warning buzzers were common.
    A great idea in academic theory, but killed by enough overcharges or the one forgotten headlight-on experience. But I often wonder how the Torquestarter would fare today?
    Of course as I often say, an AGM is not the ideal "everyday cranking battery" - wets are far better - but the Torquestarter should have fared better.


    Modern electronics should not be sensitive to voltage spikes etc. Early electronics were because (IMO) they were designed by idiots or people inexperienced with vehicle electrics (theory & practice) - viz jumper leads with spike suppressors (MOVs etc) - how farken ridiculous.
    However modern vehicle electronics should be robust. The idiots learned the usual 8-16V rule etc AND that they needed to handle spikes up to 400V as well as heat extremes & vibration.


    Not that the above helps the OP's groundloops - I too am hijacking. But since it's been a while since I've addressed "absolute grounds" and basic AGM considerations etc and I realise some readers are unaware of my past writings (viz diode isolators)...
    But now I'll bug out. Most relevant groundloop and noise issues have been covered in Settra's other threads. As for an ad hoc system involving inverters, domestic monitors, noisy M4 or Mx PSUs etc, since the preventive measures have not been applied it now rests with problem solving - aka search and destroy - and most know I'm into prevention and not interested in fixing resultant preventable problems. There are plenty of people that earn good money (or whatever) doing that.

  6. #16
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    guys can i ask something, that is either stupid, OR stupid?? my DMM reads zero Ohms, across the battery terminals (one lead at each pole) , of both my batteries, in Open circuit... is this normal? or is my DMM fried? :P

  7. #17
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    Never a stupid question only stupid answers sometimes. You should see nothing on ohms, on volts do you see voltage? ohms is for resistance on same line not pos to neg. SNO

  8. #18
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    yea i know. that is why i asked >_> , i saw it by luck, doing some other mesurements that traced me there... votls are nromal (12 and so). but i DO see 0.00 ohms (not 0.L wich is when there is no electrical path)... but since its on both batteries, i wander if its the DMM broken..

  9. #19
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    Disconnect the leads from battery and then test, when wired up you technically are completing the circuit and should show 0 ohms with no connections on battery it will show open circuit or your 0L SNO

  10. #20
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    i sed its on open circuit.. nothing is atached to the battery. i was reffering to the DMM's leads..

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