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battery isolator wiring diagram?

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Member - Posts: 31
Member spacespace
Joined: March 31, 2004
Location: United States
Posted: March 01, 2012 at 3:04 PM / IP Logged  
We're finishing up a party bus with a sound system and led lighting, etc. in the back. I need to charge the main bus batteries (2) and a deep cycle in the rear from the bus alternators or from a gas powered 12vdc generator I put together with a honda motor and an alternator. Here's how it should work:
- When bus is running: alternator should charge both front and rear batteries
- When Generator is running: it should charge the batteries
- If generator nor bus running: isolator should protect main batteries from being run down.
I am unsure what needs to go to chassis ground, vs negative battery terminal, etc. Can someone connect the dots for me?
here's the drawing without connections:
Here's the stereo diagram:
And here's the manual for the battery isolator:
Can I ground the battery in the rear to chassis or do I need to run all the way back to the front batteries negative posts? I really appreciate any help.
Gold - Posts: 4,934
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 02, 2012 at 3:28 AM / IP Logged  
OMG! There is that incorrect diagram of theirs yet again. They have another version that is correct - ie, the LHS side of the left fuse goes to the battery - not the alternator!!!!!
I'd argue that you need TWO isolators - one for each battery other than the designated "main" battery. (And those in the know will most likely agree.)
But you haven't mentioned HOW you want to control them. Normally it will be an automated system - ie, when being charged, the isolators connect the batteries.
However, IMO you have not done the recalcitrant thing and bought a voltage sensing aka "smart" isolator. (They are voltage sensing circuits with varying delays and voltage set-points that switch a relay like your PAC-200. Not the best choice for typical vehicles that have charge-light circuits (typically from the alternator), but they are the best "commercial" option for stator-type chargers as found on boats and some recreational vehicles etc.   
Anyhow, if you want full manual control, it should be easy enough. But that is usually not recommended.
If your alternator has a charge light circuit - ie, a D+ or L terminal - then automation whilst the vehicle (engine) is charging should be easy. [Albeit with an extra relay that switches the PAC-200s - the alternator D+/L is unlikely to handle the ~4A required for 2 PAC-200s (unless it's an old external electro-mechanical type; but I'd recommend upgrading that next time you have charging problems).]
To the above you add the generator circuit.
But you haven't said which has priority... You probably do not want BOTH the alt & genny to charge simultaneously, hence one needs to cut the other's link.
Oh yeah - the genny should have its relay too...
Sorry if that sounds complex, but the control of all the above is (IMO) relatively simple - it's usually a switch or switches and maybe a few diodes and extra relays - you could even chose which charger you want to use if both are running (and if one fails, the other takes over).
Note that the "control" relays (including the "buffer" relay between the alternator's D+/L and the PACs) need only be typical common 30A automotive relays. (Or even smaller, though automotive 30A relays are probably the most common, cheapest, and easiest to mount & connect.)
Chassis & battery ground:
The above is independent of ground except to activate the relays/PAC-200 (ie, 12V across their coils) and noting that it must all be a COMMON ground.
If you have - and can bolt to - a solid chassis, then no ground cable is necessary. However, IMO it never hurts to run a or extra ground lead/s, but they need to match or exceed the +12V cable capacity.
And cable sizing is not only important from the max current POV, but also the voltage drop along the long cable to the distant battery(s). Many undercharge remote batteries due to undersized cables. Those that IMO are gullible solve that by buying expensive dc-dc convertors. Clever ones simply minimise the voltage drop, and probably understand a bit more about what battery charging requires (eg, to be above 13.8V at some time - preferably the "maximum norm" of 14.4V else 14.2V - especially if the battery sat a while when not fully charged.
And don't forget - each battery end needs its fuse (as per that PAC-200 link/diagram).
If the isolators are manually controlled, arguably those fuses (and/else the inter-cabling and (PAC) relays) need to handle at least the starter-motor current. (The alternator-controlled isolator won't (or shouldn't) need that, but some "smart" isolators do...)
So, do you have a charge light (circuit)?
And what is the "both alternator and generator" priority?
And/or would you like to select which is to be used (with a fall-back to the other upon failure)?
Member - Posts: 31
Member spacespace
Joined: March 31, 2004
Location: United States
Posted: March 02, 2012 at 7:12 AM / IP Logged  
oldspark wrote:
So, do you have a charge light (circuit)?
And what is the "both alternator and generator" priority?
And/or would you like to select which is to be used (with a fall-back to the other upon failure)?
Thanks for the reply. Here's what I had come up with. The switch on the ground side of the isolator I am not sure I need. I want the system to be fully automated, ie if the bus alternator or the alternator on the little gas engine is producing power, the system would run on all three batteries. If not, the system would run just on the gel cell in the rear. There will never be times when both would be running that I can foresee. The plan is simply to run the generator (small engine powered alternator) when parked.
Is there a danger in the two alternators back feeding one another or causing a problem that way?
Member - Posts: 31
Member spacespace
Joined: March 31, 2004
Location: United States
Posted: March 02, 2012 at 7:14 AM / IP Logged  
Oh, and the two batteries up front are both the designated main battery for this purpose, the bus uses two batteries from the factory.
Gold - Posts: 4,934
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 02, 2012 at 5:43 PM / IP Logged  
Just a mainly FYI interim reply - I'll consider the "design" later.
Though would the genny be connected to the rear gel-cell, or to the front? I was thinking of two separate "chargers" (alt & genny) with their own battery, then adding the interlink (isolator) to connect the other battery(s) when charging.
And though not envisioning BOTH chargers simultaneously, do you want protection in case someone starts the bus for whatever reason (or genny)? But using both might not be a problem anyhow - see below...
The FYI...
Good practice is that batteries are not left connected in parallel (for significant periods) when not in use. The reason is that a failing battery will fail the other battery.
In simple theory, it means twice the chances of a battery failing, and that causes 2 failed batteries, hence you replace FOUR batteries in the time you'd normally replace either of the batteries if isolated.
But in practice, many have hard-paralleled batteries. I've recently been dealing with big machines (farm and road machinery) where they use 2 parallel strings of s series batteries - ie, 2 parallel 24V batteries - that are hard-wired together (hence 16x the battery replacement frequency).
[ FYI - they have all had +24V from one battery string and the 0V (GND) from the other battery string with equal sized battery interconnects. That's how parallel strings should be interconnected and tapped - ie, all current paths/batteries use equal cabling. ]
Whilst in old days permanent paralleling was unacceptable, with modern reliability it may be. Batteries may have a one in 20 year chance of "self failure" - they will generally fail as a result of usage and aging.
But the effect is still the same - when one fails, it will destroy the others. If undercharged or left uncharged for a significant period, they will fail quickly.
But it often takes days for a battery to fail other batteries, and since buses etc are used daily, the effect is minimised. The longest typical downtime may be a weekend.
And of course if they replace one battery, they replace ALL batteries with the same type (and batch).
Besides, the cost to replace 2 or 4 $200-$400 batteries every year or 2 may be insignificant to operators. (But I get typically 8 years from my car etc $100 batteries.)
But for now, we'll leave the "main battery" as is. You can isolate them later if you find they fail too often. (If leaving the bus unused for long periods, just disconnect at least one of the batteries.)
The important thing is that the rear battery is isolated, especially since it's a different type (and age, and temperature, etc).
Two alternators back feeding one another...
Actually, these days I'm unsure.
Being alternators it shouldn't matter thanks to their diodes - one can not inject into the other. (That assumes typical diode rectification, no shorted diodes, and no excessive voltage spikes.)
As to how the voltages balance out, hmmm... If one senses an over-voltage, it should reduce output so the other supplies full current (until its voltage dips and the other starts cutting in).
But some alternators were destroyed in inter-connected situations. Maybe due to a shorted diode, though my understanding was through "fighting voltage regulators".
That may have changed with more modern alternators - many BIG audio systems have successfully paralleled multiple alternators.
But make sure the genny is an alternator and not a "generator". But gennies have been using alternators for decade - probably since the mid 1960s if cars are anything to go by.
Though "generators" are called gennies, they are usually alternators.   
A generator is a DC-generating machine - essentially a DC motor used as a generator. It has no diodes.
An alternator is an AC-generator with output diodes that convert (rectify) the AC to DC.
The beauty of the AC alternator (apart from slip-rings instead of commutator segments) is that it is far more efficient, and you cannot inject or back-feed voltage/current through the diodes INTO the generator/stator windings. Hence in theory, they can be paralleled with other voltage sources - eg, in vehicles the alternator output is always connected to battery +12V whereas older generators used a big relay to disconnect (its stator winding) from the battery.
Gold - Posts: 4,934
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 05, 2012 at 8:30 PM / IP Logged  
Sorry for burying this thread...
I've been searching for the original .bmp diagrams to modify for your use, but all I found was this gif/jpg previously posted on the12volt:
Whilst it may look complex, it is intended to give the big picture.
The RHS in black is the typical wiring for a vehicle with a charge light - ie, an alternator D+ or L output.
The LHS in grey shows the additional fuses and battery when adding a second/aux battery, and the relay/isolator when battery isolation is used.
The only difference between that circuit and any other battery isolator circuit is what controls the isolator.
A voltage-sensing or "smart"{sic} isolator would have the isolator's coil (#86) controlled by the voltage sensing circuit.
A manually or IGN switched isolator would have #86 go to a +12V switch or IGN +12V.
The alternator-controlled method connects #86 to the alternator's charge light circuit - ie, the D+ or L terminal - ie, the grey wire from #86 to the chargeLamp or D+/L etc.
Normally the lot is contained under the bonnet/hood, but the D+ or L can usually also be intercepted behind the dash, or anywhere between the alternator and dash. Wherever is easiest.
In fact apart from the fuses which should be as close to each battery as possible (but not on top of them), the isolator/relay can be located anywhere as can any added switches or controls.
FYI - to reiterate, the isolator is ON (batteries interconnected) when the charge light is OFF.
And a working charge light is not required for operation (though many alternators require the charge-lamp or similar to initiate or continue charging).
And if the D+/L circuit or alternator fails, simply breaking or disconnecting the D+/L connection from the alternator usually energises the relay - ie, limp home with all batteries powering the vehicle.   
Added switches etc merely involve diodes and the switches.
Switches from +12V are joined to the diagram's grey D+/L circuit, but must go through diodes to prevent +12V feedback. A diode is also inserted in the grey D+/L to #86 to prevent +12V feedback (+12V injection) into the alternator's D+/L circuit (since this is internally connected to GND when the alternator is not charging, or its regulator is faulty.
NOTE: The D+/L circuit is really an output from the alternator's voltage regulator. These were external in old vehicles but are usually integral to the alternator in modern vehicles.
If unsure, getting D+/L from the dash (chargeLight) caters for either case.
So when I write alternator's D+ or L, I am really referring to the alternator's voltage regulator's D+/L terminal or output.
There are diagrams showing additional switches with diodes, but they are on older versions of that diagram.
[Originally it was drawn "functionally" from left to right, but that confused many. So the aux battery etc was moved to the LHS which made it clearer how it was physically arranged, and a mere add on to an otherwise unmodified standard system.]
I was going to modify the diagram above, but not on that crappy gif/jpg version. [My original .bmp version(s) were lost a while ago, and the originator izu069 has stripped the from his system. Note that I - and hence the12volt - have permission to post the above izu069 Copyrighted diagram. But beware others! {That's my friendly warning - izu069 is known for not taking prisoners!!}]
But I posted the above diagram to hopefully show how simple the system is in principle - merely join #86 to the chargeLight circuit instead of a manual switch (which can be forgotten) or the IGN +12V (which parallels batteries during cranking, or could be left on, etc).
It also shows the major standard vehicle wiring that is relevant, but hopefully simply enough to demystify the alternator D+/L workings, and allow simple understanding of operational issues.
EG - if the isolator is energised and the batteries are thus interconnected, they both supply the starter-motor. Not that this a problem - the charge light does not normally extinguish until the alternator is charging - ie, after the engine starts; not during cranking. But if any manual switch is on, or #86 is connected to IGN +12V instead, then both batteries supply the starter-motor and the fuses pop else isolator fuses if insufficiently rated, and one design assumption is that EITHER battery supplies the FULL starter-motor current.
The only warning in your case is that the PAC200 coil takes a lot of current (1A to 2A?) and that can blow the alternator's D+/L circuit. But that is overcome by using smaller relay with its #86 to D+/L and using its #30 & #87 contacts to energise the PAC200's coil (its #86 equivalent).
If that smaller buffer relay is a typical 30A automotive relay, you can switch up to fifteen PAC200s - ie, 15 x 2A = 30A.
In some cases however, maybe even a 30A relay is too much - their coils may draw up to 250mA (1/4 Amp). Newer alternators may have problems even with that - also solvable, but later...
As an aside though still related, I was building a MOSFET interface which could power ANY relay/isolator from any D+/L terminal and most likely any new-age EMS/CPU controlled charging system (the UIBI-2). But now I'm thinking of using a $4 08M2 PICAXE (UIBI-3?) that can not only be programmed or switched for delays or manual operation etc, but could even function as a voltage-controlled or smart isolator. The user would add the relay or relays of THEIR choice thereby minimising costs and destroying the market for other so-called "smart" isolators.
The user could even modify delay times and voltage thresholds as desired (something which is different for each smart-isolator model and none cover varied or universal applications).
Incidentally, the above "charge-Light controlled" D+/L battery isolator method was later dubbed the UIBI - the Ultimate Intelligence Battery Isolator. That was a direct mocking of so-called Smart Isolators which - after expert analysis - are anything but smart (except for the sellers that turn disadvantages into desirables (eg, priority charging - what a load of bullsh!!) and who are smart enough to con the gullible).
But such a PIC-based UIBI would certainly be the ultimate battery isolator!
(All "smart" functions like delays, bypass, low-voltage cut-outs etc can be added to the UIBI, but the PIC version would do away with all peripheral components, except the relays/isolators and manual switches. Let's see - a match-box sized UIBI-3(?) that sells for $49.95...? Hmmm.... And $9.95 or $14.95 to replace if it fails...?)
I do ramble don't I? At least I included a few useful tips (eg, limp-home mode?).
And whilst searching for certain UIBI diagrams for this reply, I did enjoy reading the replies of others. Some just don't get it. Some even ask me to justify what is wrong with voltage-sensing or smart isolators (despite outlining some of their problems, not to mention their different voltage settings and delays, why some include manual activation, and how some contradict the behavior of others!). Not that they could justify spending $50 to $350 extra for an IMO proven inferior system LOL!
None even answered my oft repeated question: "What is the voltage sensing trying to do??" - no wonder we never progressed! (Ans: Determine IF the system is charging.)
But I have digressed...
Ignore the extra gaff for now (woops - too late). Can you pick the basic idea, and its "simplicity" { posted_image }, and does it maybe suit or fit your vehicle (alternator) or desires?
Note that the simple UIBI (D+/L to #86) solves the automated connect whilst charging desire.
And it is merely an added 2 diodes and one switch to interconnect the batteries at any time (eg, for cranking, or if the alternator fails). (And another - else a 3-position switch - to isolate the batteries when charging.)
Not that that prevents both chargers simultaneously, but that may not be a problem, and that too is a relatively simple addition anyhow (I think!.
IMO a simple solution - a minor change to the diagram you posted.
Gold - Posts: 4,934
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 05, 2012 at 8:32 PM / IP Logged  
Geez that was long! My interrupted sessions cause me to lose track!

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