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Subject Topic: battery isolator wiring (Topic Closed Topic Closed)

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james909
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Posted: February 27, 2011 at 1:36 AM - IP Logged  

Hi everyone. I am looking to install a second battery into my boat and just want to make sure my wiring is correct as I've never installed an isolator before. After a little research it seems that installing the batteries with a solenoid type isolator would be the best for my needs. I drew up a schematic showing how I think it should be wired up. There is one battery which powers only the starter and a second battery that powers everything else. When the key is off the batteries are isolated so the accessory battery can be run down without draining the cranking battery. Then when the ignition is turned on the batteries would be wired in parallel so both batteries could supply cranking power, and charge once the engine is running. Is this an acceptable and practical way to wire this? If someone could just look at my diagram and make sure everything is correct I would really appreciate it. Thanks for the help guys.
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bobviper13
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Posted: February 28, 2011 at 9:22 AM - IP Logged  

Looks perfect. Nice diagram.
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oldspark
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Posted: February 28, 2011 at 11:25 AM - IP Logged  

Where are the fuses?
And why use the (first) relay?


Unless the batteries are next to each other (whereby physical security is assumed), each battery should have a fuse or circuit breaker (aka protection) as close as possible (to its +ve terminal) to protect the interconnecting cable and relay(s). (It is (generally) not to protect the battery(s).)
I use auto-resetting circuit breakers (50A) for my nominal 1A-5A secondary load. Hence if the current to the 2nd battery exceeds 50A for too long (eg, due to an initially high recharge current), the breakers will self reset rather than keeping the system isolated. (Initially high recharge currents decrease rapidly.)   


If the isolator itself is a relay, you don't need the first/smaller relay (unless the isolator's coil current is too high for whatever is driving it - but a 200A relay is likely to be no more than 1 or 2 Amps.

If the isolator is a voltage sensing aka "smart isolator", then you do NOT want any other relay - you merely connect its sensing input top the main battery (or as per its instructions).


Normally with plain relays, the connect signal is taken from the alternator charge light circuit (eg, the UIBI), but most marine generators/alternators are fixed or permanent rotor aka stator systems and hence do not have a charge light. In that case, the voltage sensing (smart isolators) must be used for automated operation. (Current sensing can also be used, but I am unaware of commercial units (despite claims of "Priority Charging" posted_image posted_image ).)

Automatic switching (sensing) is used in case you forget to isolate the batteries when not charging (or being used). If left connected and one battery drains or fails, the other battery also drains and may fail.


The UIBI is the "Ultimate Intelligence Battery Isolator" - a mere relay controlled by common (automotive) charge-light circuits. It's name is sarcasm directed at "Smart" or "Intelligent" isolators when being used in systems with charge lights. Smart isolators are so intelligent that each brand/model usually has different voltage settings and delay settings (unadjustable!) and may have extra/optional triggers. Yep - you require the smarts to chose the right one.


PS - Normally the alternator is connected to the main battery.
IE - the 2nd (accessories) battery is added to the existing system.
A voltage-sensing isolator's signal (input) must be from the alternator connected battery (unless dual-battery sensing is used).
Alternators may be connected to the second battery where voltage or current is an issue - eg, higher voltage for lights or audio.
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james909
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Posted: February 28, 2011 at 3:46 PM - IP Logged  

Thanks for the input guys.

oldspark wrote:

Unless the batteries are next to each other (whereby physical security is assumed), each battery should have a fuse or circuit breaker (aka protection) as close as possible (to its +ve terminal) to protect the interconnecting cable and relay(s). (It is (generally) not to protect the battery(s).)


The batteries will most likely be side by side. But if the cables are long enough I will be sure they are fused properly.

oldspark wrote:

If the isolator itself is a relay, you don't need the first/smaller relay (unless the isolator's coil current is too high for whatever is driving it - but a 200A relay is likely to be no more than 1 or 2 Amps.


I didn't realize the isolator's coil would draw so little current. In that case I will eliminate the relay.

oldspark wrote:

Normally with plain relays, the connect signal is taken from the alternator charge light circuit (eg, the UIBI), but most marine generators/alternators are fixed or permanent rotor aka stator systems and hence do not have a charge light. In that case, the voltage sensing (smart isolators) must be used for automated operation. (Current sensing can also be used, but I am unaware of commercial units (despite claims of "Priority Charging" posted_image posted_image ).)

Automatic switching (sensing) is used in case you forget to isolate the batteries when not charging (or being used). If left connected and one battery drains or fails, the other battery also drains and may fail.


The solenoid that I was planning on using is not voltage sensing but it sounds like that may be a better option. Would you recommend that I just use a voltage sensing relay? I like the fact that the second battery doesn't begin charging until the primary battery reaches a certain voltage. This boat is often used as a towboat so sometimes it is turned on and off a couple of times in a relatively short time frame as people board the swim platform.

oldspark wrote:

PS - Normally the alternator is connected to the main battery.
IE - the 2nd (accessories) battery is added to the existing system.
A voltage-sensing isolator's signal (input) must be from the alternator connected battery (unless dual-battery sensing is used).
Alternators may be connected to the second battery where voltage or current is an issue - eg, higher voltage for lights or audio.


I had planned on having the alternator connected to the second battery for wiring simplicity (transferring existing wiring to the accessory battery and only moving the starter wire to the main battery). But I'd rather do it the right way, so I think I will have the starter, alternator, and ignition switch connected to the main battery so that if the isolator or accessory battery fails the boat is still operational.
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oldspark
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Posted: February 28, 2011 at 5:38 PM - IP Logged  

Ah James, yet again it is a pleasure working with a thinker....
You seem to have a good understanding - eg: "But if the cables are long enough I will be sure they are fused properly"....
....And the "buffer" relay in case the BIG relay draws too much current. (That is a concern for the UIBI - just how much current can an alternator's regulator (charge lamp circuit) supply? Though that is solved by a MOSFET which could even replace an 80A to 120A relay - all for $3!!)



But some clarifications:
james909 wrote:
I like the fact that the second battery doesn't begin charging until the primary battery reaches a certain voltage.

NO!! That is what many claim, but it is usually bullsh!
As an example, though Projecta may advertise "priority charging" for their DBC100k & DBC150K etc isolators, all such wording has been removed from their Australian packaging.
Why?
You actually said it.... "until the primary battery reaches a certain voltage".
And when does the primary battery reach that certain voltage (ie, the isolator's connect voltage)? Probably a few seconds after charging commences.
And does that mean it is fully charged? Or how charged do people think a cranking battery etc will be even after 10 seconds at 14.4V?

The point is those isolator's sense voltage.
And the voltage of the primary battery under charge does NOT reflect its state of charge (SOC). Besides, it goes high quite quickly depending on alternator capacity and total load. (Despite my 38AH AGM initially charging at 40A, the voltage from my 75A alternator at the battery is 14.4V within seconds of starting.)

When the primary system hits a certain voltage, the isolator connects irrespective of the SOC of the primary battery.
It may then disconnect if the 2nd battery & circuit loads so much that it drops the voltage, but then it reconnects and repeats the cycle.... (Many voltage sensing isolators have different On & Off delays to overcome such cyclic switching. That is yet another dilemna and compromise for "smart" isolators.)

FYI - the only way to determine a battery's SOC is by monitoring its charge current. Are their any ammeters present in the battery-only lead? There is also impedance-based methods using AC, but isolators will not use that technology....    


Sorry - the above isn't brief, though hopefully I have provided enough detail to educate, and enough detail for anyone that wants to argue the point/s or correct my mistakes. (Anyone? LOL!)


james909 wrote:
I had planned on having the alternator connected to the second battery for wiring simplicity (transferring existing wiring to the accessory battery and only moving the starter wire to the main battery). But I'd rather do it the right way...

Ah - there isn't so much "a right way"...

As I wrote, if secondary voltage is a priority, then you drew the right way. (Like older halogen driving lights being powered from to the alternator instead of the battery - that was for maximum illumination.)

And ease of installation certainly contributes to what might be the right way.
As does consideration of the system during or after a failure.


I wish there were (always) "a right way", but rarely is it so.
It is usually that some ways are better than others in THAT situation with THAT level of reliability or recovery in mind.

A BIG-audio user might have the alternator connected to the 2nd (audio) battery since that uses the most current...

Much depends on the batteries and loads.
It is nice if the batteries can be interchanged if the main battery fails... Or maybe interconnected provided the main-flattery does not drag down the 2nd-full battery (is that a fullery?).


But my brain feels drained for now... (I just arose. 10:00AM. No coffee yet!)    

I think continue as you have - you have the smarts.
Yes - you can omit the first relay assuming your switch can handle a few Amps. (But a st'd relay is ~250mA max for 30A contacts etc; 200A-500A relays seem to have cols/solenoids of ~2A max. But please confirm!!)

As to smart isolators, keep in mind that that can be the trigger/controller for your BIG relay. IE - the "smart isolator" does not have to connect the batteries - it can merely energise the main relay. (Hence not spending $100's for "200A smart isolators" when a cheaper 80A will do....)

I don't like spending the $bucks that smart isolators cost - eg, $80 etc. (And certainly not the >$200-$300 of the aforementioned 100A & 150A Projectas!!!)   
I have used the Oatley Electronics $22 80A "latching relay" dual battery controller - but that is in kit form and required assembly and housing and connectors. (See K227: 12-24V Dual Battery Adapter For A Vehicle)


These days I'd consider using a $20 MW728 "battery protector" with its cig-plug & socket connections for 10A switching; 12.5V connect and 11.2V disconnect. But I'd add diodes to extend the disconnect to (preferably) 12.8V and connect to >13.3V.
It would drive the main relay. And I'd add other relays for the sense-voltage changes (differing series diode numbers) and maybe manual reset etc.
And of course I'd have one on the 2nd battery output to protect it from excessive discharge (since mine powers a fridge).
Why the MW728? Commonly available and cheap. I have a few just in case I want to protect a battery from some load....
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james909
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Posted: March 01, 2011 at 12:23 AM - IP Logged  

Thanks so much for your detailed posts, I've learned a lot.

oldspark wrote:
But some clarifications:
james909 wrote:
I like the fact that the second battery doesn't begin charging until the primary battery reaches a certain voltage.

NO!! That is what many claim, but it is usually bullsh!
As an example, though Projecta may advertise "priority charging" for their DBC100k & DBC150K etc isolators, all such wording has been removed from their Australian packaging.
Why?
You actually said it.... "until the primary battery reaches a certain voltage".
And when does the primary battery reach that certain voltage (ie, the isolator's connect voltage)? Probably a few seconds after charging commences.
And does that mean it is fully charged? Or how charged do people think a cranking battery etc will be even after 10 seconds at 14.4V?

The point is those isolator's sense voltage.
And the voltage of the primary battery under charge does NOT reflect its state of charge (SOC). Besides, it goes high quite quickly depending on alternator capacity and total load. (Despite my 38AH AGM initially charging at 40A, the voltage from my 75A alternator at the battery is 14.4V within seconds of starting.)


That makes sense, thanks for clearing that up.

oldspark wrote:
Are their any ammeters present in the battery-only lead?


No ammeters, just the voltmeter.    

oldspark wrote:

As to smart isolators, keep in mind that that can be the trigger/controller for your BIG relay. IE - the "smart isolator" does not have to connect the batteries - it can merely energise the main relay. (Hence not spending $100's for "200A smart isolators" when a cheaper 80A will do....)

I don't like spending the $bucks that smart isolators cost - eg, $80 etc. (And certainly not the >$200-$300 of the aforementioned 100A & 150A Projectas!!!)   
I have used the Oatley Electronics $22 80A "latching relay" dual battery controller - but that is in kit form and required assembly and housing and connectors. (See K227: 12-24V Dual Battery Adapter For A Vehicle)


These days I'd consider using a $20 MW728 "battery protector" with its cig-plug & socket connections for 10A switching; 12.5V connect and 11.2V disconnect. But I'd add diodes to extend the disconnect to (preferably) 12.8V and connect to >13.3V.
It would drive the main relay. And I'd add other relays for the sense-voltage changes (differing series diode numbers) and maybe manual reset etc.
And of course I'd have one on the 2nd battery output to protect it from excessive discharge (since mine powers a fridge).
Why the MW728? Commonly available and cheap. I have a few just in case I want to protect a battery from some load....


Thanks for the suggestions, but I actually found a good deal on a 120A smart isolator so I decided to go that route. A big factor was that it's waterproof which will hopefully improve reliability as it may occasionally get wet where I would like to mount it. The kit comes with the voltage sensing relay and an on/off/combine battery switch. I also plan to wire both batteries to the dash voltmeter with a SPDT switch. That way when the batteries are isolated I can keep an eye on each batteries voltage.


oldspark wrote:

james909 wrote:
I had planned on having the alternator connected to the second battery for wiring simplicity (transferring existing wiring to the accessory battery and only moving the starter wire to the main battery). But I'd rather do it the right way...

Ah - there isn't so much "a right way"...

As I wrote, if secondary voltage is a priority, then you drew the right way. (Like older halogen driving lights being powered from to the alternator instead of the battery - that was for maximum illumination.)

And ease of installation certainly contributes to what might be the right way.
As does consideration of the system during or after a failure.


I wish there were (always) "a right way", but rarely is it so.
It is usually that some ways are better than others in THAT situation with THAT level of reliability or recovery in mind.

A BIG-audio user might have the alternator connected to the 2nd (audio) battery since that uses the most current...

Much depends on the batteries and loads.
It is nice if the batteries can be interchanged if the main battery fails... Or maybe interconnected provided the main-flattery does not drag down the 2nd-full battery (is that a fullery?).


Since I went with the smart isolator I believe that the alternator has to be connected to the main battery but I think that's best for my application anyway. Nothing too demanding is running off of the second battery, and reliability is the highest priority to me. I'd rather be able to get home without the stereo, than be stranded with music.
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oldspark
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Posted: March 01, 2011 at 1:05 AM - IP Logged  

It all sounds good....

Tee-hee - no ammeters (or shunts etc) eh? So I wonder how they monitor the main battery's state of charge? LOL!
Of course, why would you want to have priority charging? Most want maximum overall recharging which is BOTH batteries.

[ More spouse-tale assassination: Only if you have short runs with underrated alternators so that the main does not recharge would you want priority charging - maybe! But there are those that reckon there is not enough reserve in OEM alternators to charge a 2nd battery. I guess people must drive with lights constantly on (usually more than 10 Amps) & brake lights & reverse lights & wipers and demisters, and have batteries that always draw tens of Amps... I guess they need priority charging too! ]


Re the alternator - it is connected to the "sensing" side of (voltage sensing) isolator.
Such isolators usually use their main input for sensing (ie, 3-wires: heavy in and out, and a thin ground). If that is toward the battery without the alternator, then it never sees >12.8V etc and hence never connects.
But some have dual sensing (both sides) so that another charger on the other side also connects the batteries...
And some have a separate sense wire so you can sense either battery (ie, 4 wires).


And you'd rather get home without music than be stranded with music?
Well, there is simply no way I can account for some peoples priorities!
(Yes, I am joking. I too would rather live to hear music the week after. I think the harps would bore me by the first Sabbath. And if the singing is flat.... arrrghhh!)


Congrats on your system etc.


BTW - a voltmeter is invaluable. IMO essential.
I have a 3-digit blue-LED in my dash. LCDs are ideal but (IMO) need to be backlit.
Hence I see if the system is above ~13V (a max of 14.4V is normal for charging), or if batteries are approaching flattening stages (below 11.5V depending on loads). Or if getting old (eg, not ~12.7V after resting overnight...).
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james909
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Posted: March 01, 2011 at 7:51 PM - IP Logged  

oldspark wrote:

Re the alternator - it is connected to the "sensing" side of (voltage sensing) isolator.
Such isolators usually use their main input for sensing (ie, 3-wires: heavy in and out, and a thin ground). If that is toward the battery without the alternator, then it never sees >12.8V etc and hence never connects.
But some have dual sensing (both sides) so that another charger on the other side also connects the batteries...
And some have a separate sense wire so you can sense either battery (ie, 4 wires).


Thanks, I'm pretty sure that the isolator I bought uses the main input for sensing but I'll be sure to check the instructions once it gets here.
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