Starter battery VS. Reserve Battery

[john61ct]

Originally Posted by a64pilot

the most important thing I believe is for you to understand how your system works.

100% critical first step, so many don't

> Assuming you leave the boat the way most are wired, that is the battery selector switch selects both use and charge

Not sure what you mean by this.

Short of using a Dual Circuit Plus 5511?

IMO ensuring both sides get charged should always be automated with a combiner, with an override for exceptional circumstances.

[rom]

Originally Posted by a64pilot

Having a reserve bank is by definition dead lead, plus a lot of wasted money.

Probably true for your boat but not universal. My house bank is 1000Ah, my reserve (I'd rather call it emergency) bank is 100Ah. Not that much money or dead lead for me.



Where I think you are universally wrong though is by permanently connecting two banks together by the mean of a switch. You likely end up with a totally unbalanced single bank which is the best way to shorten your battery life. (unless maybe bank 1 & 2 are exactly the same and the cabling behind was well thought out)

[ramblinrod]

Originally Posted by Q Xopa

So your system shuts down everything except allows for a start, if the house (only) battery bank gets drawn doen too far?

What do you do if your house bank battery dies of, lets say an internal short?

I guess normally there is no 'dead lead' to needlessly cart around. That is until the one bank does suddenly die. Of course that would never happen right. Im not sure I would risk my boat, life or my customers, (not that I have any like others here), on that premise.

No.

The LVD relay only isolates the reserve battery (with the starter directly connected) from the house bank.

The house bank is still connected to the distribution panel and will allow the user to drain the batteries to complete dead.

The reserve battery will no longer be drained by house loads when disconnected, and will always be able to start the engine.

When the engine is started, the alternator will charge the house bank, and when the charge voltage rises above the LVD reconnect threshold, the reserve battery becomes part of the house bank again.

For an astute boater who monitors and manages their electrical system reasonably, this reserve battery isolation should never happen; it is just to make full use of all batteries aboard, while preserving capacity to start no matter what the dumb boater does.

Vastly superior to a 1/2/B/Off switch, diode isolator, or ACR (where the start battery is used 0.000001% of the time, normally sits at 99-100% charged, takes up space, adds weight, and isn't used to support normal house loads 24/7.

[john61ct]

Originally Posted by rom

Where I think you are universally wrong though is by permanently connecting two banks together by the mean of a switch. You likely end up with a totally unbalanced single bank which is the best way to shorten your battery life. (unless maybe bank 1 & 2 are exactly the same and the cabling behind was well thought out)

Yes, if stating a 50/50 split House bank, connected with a manual 1/2/B switch is "universally optimal" because

"that's the way most boats are wired" (by the maker?)

does not ring true as a best practice, to me.

If indeed that is what's being asserted here.

[ramblinrod]

Originally Posted by john61ct

Yes, if stating a 50/50 split House bank, connected with a manual 1/2/B switch is "universally optimal" because

"that's the way most boats are wired" (by the maker?)

does not ring true as a best practice, to me.

If indeed that is what's being asserted here.

What post number is this referring to?

[john61ct]

Originally Posted by ramblinrod

Vastly superior to a 1/2/B/Off switch, diode isolator, or ACR

Note the LVC is in fact exactly the same basic functionality as a VSR/ACR/combiner.

The key factors required for this usage case are

sufficient continuous / peak ampacity for the context

adjustable V setpoints, ideally for both Open/isolate and Close/combine independently, and

ability to manually lock/override.

[john61ct]

Originally Posted by ramblinrod

What post number is this referring to?

Added quote, we crossposted

[ramblinrod]

Originally Posted by daletournier

If you get a dead short what's the best way to determine which battery it is in the bank?

Ideally, there is an isolation switch for each nominal system voltage battery in the bank (ie, if system voltage is 12 Volt, isolation switch for each 12 Vdc battery connected to it; if 6 Vdc batteries, isolation switch between each series pair and 12 Vdc system bus.)

Almost as good is to have an isolation switch between ganged batteries. (For example a 1/2/B/Off switch between 2P and 2P 12 Vdc batteries.) Then one cannot isolate each individual battery, but can isolate a bad battery, (and other ganged to it in that group) from the bus, so the opposite gang will still function, until the defective battery issue is resolved.

Least good is removing each battery terminal in turn. (The latter can generate a spark, which if the battery fault has been causing excessive gassing can cause an explosion.) This also takes additional time, tools, is likely more difficult to access, removing battery box covers in a small confined space, and is least easy to do in a heavy seaway.)

[ramblinrod]

Originally Posted by john61ct

Note the LVC is in fact exactly the same basic functionality as a VSR/ACR/combiner.

The key factors required for this usage case are

sufficient continuous / peak ampacity for the context

adjustable V setpoints, ideally for both Open/isolate and Close/combine independently, and

ability to manually lock/override.

I disagree.

An ACR is typically used to combine a start battery to a deep cycle bank if and only if a charge source is applied. The start battery is never used to power house loads.

A reserve battery, is deep cycle, used to power house loads AND start the engine, EXCEPT if the dumb boater drains down the house bank too far. Then and only then is the reserve battery isolated from the house bank by the LVD to preserve starting capability.

[ramblinrod]

Originally Posted by rom

Where I think you are universally wrong though is by permanently connecting two banks together by the mean of a switch. You likely end up with a totally unbalanced single bank which is the best way to shorten your battery life. (unless maybe bank 1 & 2 are exactly the same and the cabling behind was well thought out)

Depends on use.

I install/modify many systems where groups of house batteries are separated by a 1/2/B/Off switch, where the switch is always in the "B" (combined position) so all are charged / drained as one bank, and the switch is used solely for testing/troubleshooting/ and emergency isolation.

In this case, the scheme to isolate/combine the start battery or reserve battery for starting, is a separate issue.

[rom]

Originally Posted by ramblinrod

A reserve battery, is deep cycle, used to power house loads AND start the engine, EXCEPT if the dumb boater drains down the house bank too far. Then and only then is the reserve battery isolated from the house bank by the LVD to preserve starting capability.

So you still have "dead lead" on board, don't you ? Instead of a house+reserve (or house+start) you are advocating house+bigReserve connected permanently and where you need to carefully setup the LVD to a voltage that preserves enough dead lead to start the engine(s). More than that you are adding a big balancing issue between each single battery. I am totally failing to understand where this is a good system.

[john61ct]

Originally Posted by ramblinrod

I disagree.

Just talking about the device operating mechanism, not the batt type nor purpose used.

VSR fixed voltage at a high setpoint is **how** it functions to only close while charge source is active.

The LVC is in effect doing the same thing, just "open when V drops to X" at a lower setpoint

[john61ct]

The key is an overall system where the separation happens only rarely, SoC is usually maintained well above the LVC setpoint.

Originally Posted by rom

Instead of a house+reserve (or house+start) you are advocating house+bigReserve connected permanently and where you need to carefully setup the LVD to a voltage that preserves enough dead lead to start the engine(s). More than that you are adding a big balancing issue between each single battery.

Say 2V lead cells comprise the bank, the Primary/house subset is 5P6S, while

Reserve/starter is 2P6S

Only two batteries in parallel, much less of a balancing issue than what many banks have built from three or more 6V pairs or 12V units.

Again, not "advocating", just clarifying the concept

[Q Xopa]

Originally Posted by ramblinrod

No.

The LVD relay only isolates the reserve battery (with the starter directly connected) from the house bank.

The house bank is still connected to the distribution panel and will allow the user to drain the batteries to complete dead.

The reserve battery will no longer be drained by house loads when disconnected, and will always be able to start the engine.

When the engine is started, the alternator will charge the house bank, and when the charge voltage rises above the LVD reconnect threshold, the reserve battery becomes part of the house bank again.

For an astute boater who monitors and manages their electrical system reasonably, this reserve battery isolation should never happen; it is just to make full use of all batteries aboard, while preserving capacity to start no matter what the dumb boater does.

Vastly superior to a 1/2/B/Off switch, diode isolator, or ACR (where the start battery is used 0.000001% of the time, normally sits at 99-100% charged, takes up space, adds weight, and isn't used to support normal house loads 24/7.

This is all down to personal philosophies of how we choose to operate our boats.

You probably noted my previous comments about this setup a few posts ago.

You hit the nail on the head when you said - "For an astute boater who monitors and manages their electrical system reasonably".

I understand how it works and the reasoning behind it. As Ive said in some ways quite clever. I understand you dont like 'dead lead'.

Yes I also agree with 1 2 B being not a particularly good concept.

Yes this setup gives you less risk than leaving your 12B on B and everything is gone.

But the examples I cited reasoning why I dont like it are- Im a bit confused why someone astute monitoring and managing would not- drain less and charge more, as you say turn the engine on, and turn some loads off. Instead of draining the House bank into oblivion? (Except for bilge pumps but then you got more issues than flat batteries).

Now you might have killed your house bank, so even if you start your engine no radio, nav, lights etc.

I dont see what you have gained over simply an alert, then take action.

Im ok with some 'dead lead'. To me its just keeping your powder dry, or the rainy day stash. I agree its not maximum utilization of battery capacity.

I keep spare water pumps, starters etc. Many dont bother clogging their boats with all that dead weight or space.

Ive seen a similar argument re liferafts.

Thats just my view, feel free to do as you want.

[ramblinrod]

Originally Posted by Q Xopa

Im a bit confused why someone astute monitoring and managing would not- drain less and charge more, as you say turn the engine on, and turn some loads off. Instead of draining the House bank into oblivion?

Because boaters, even really smart ones, sometimes make mistakes.

A manual system is fraught with risk of human error.

I dont see what you have gained over simply an alert, then take action.

The system I proposed is automatic, nobody has to present, astute, or even alive, to prevent discharging batteries to the point the engine cannot be reliably started.

Operating a 1/2/B/off switch based on SOC monitor and/or alarm, requires someone to be there and take action.

Im ok with some 'dead lead'. To me its just keeping your powder dry, or the rainy day stash. I agree its not maximum utilization of battery capacity.

Dead lead is not the end of the world.

But if one has batteries they paid good money for, that take up valuable space, and slow the boat down due to additional weight, I recommend using them to ones best advantage vs just carrying them around "just in case".

Yes, some spares carried aboard are dead weight until they are needed. So is a dedicated starter battery. But if one can easily configure a reserve battery so it supplements the house bank under normal conditions, and starts the engine under normal conditions, and only is isolated to preserve starting in abnormal (heavy house bank discharge) conditions, I just don't see any down side.

It's akin to putting an alternator and H2O heating loop on an auxiliary engine. The auxiliary engine could be used solely for propulsion, but why not also use it for charging batteries and heating water when it can be done so easily.