Starter battery VS. Reserve Battery

[daletournier]

Thanks, I wasnt sure if the others would come up abit when disconnected.

Originally Posted by a64pilot

Well, first is you have two banks ganged to one through the switch by using the both of all position, you can isolate to which bank by using the selector, the higher voltage bank won’t have the shorted battery.
Then if your charging, almost always the shorted battery will be hot, much hotter than the others and may be off gassing and will often stink, very often this stink is what alerts people to a problem.

But assume you weren’t charging and it went bad in the middle of the night, you can find the bad battery by disconnecting one terminal, I prefer to disconnect the negative as I believe it’s safer and measure each batteries voltage.

Most of the time just disconnecting the shorted battery will allow the rest to rise to a voltage that will start a motor, a battery that is being heavily discharged if disconnected will recover a lot of voltage just resting.

Now my charging system is wired so that only the banks selected by the battery switch are charged, the switch selects which bank is used, but as the charging is wired through the same wires, it also selects which bank is charged.
Some consider that inefficient or not optimum, I like it as it means if I have a short I can discontinue charging that shorted bank.
If you continue to charge a shorted battery it’s possible it can thermal runaway, unlikely maybe, but possible, but that shorted battery will also suck up all the charge and you may not be charging the good bank very well.

As long as you understand how the switch is wired on your boat, cause it may be different, then you’ll understand what is happening and why.

Now many people are incapable of understanding, and or don’t have the tools or the desire to “mess” with it. I ran into a nice couple on a newish 65 Viking with a professional Capt. In the dry Tortugas that had a shorted battery, that got so hot that the fire detection system detected the overheat, arming the fire suppression system, closing the fresh air louvers and not allowing the engines to be started.

I went over to help, once I figured out what was going on, I turned the bank ‘Off” , it had the on / off switches and not the 1,2,both switch. That disconnected the bank, after a couple of hours it cooled down and they could start the motors and go to Key West.

But it was obvious they didn’t have the tools or the knowledge to diagnose what was going on, neither did the Capt.

Very interesting boat though, it showed me how the other half lived, that boat had back up systems for its back up systems

[john61ct]

Originally Posted by Jetx

Seems most (myself included) agree with the idea of having a dedicated house bank, plus an additional battery designated as either reserve or start. The only difference is whether the additional battery is just sitting there, or being used routinely to start the engine.

Reserve should also routinely be used for that.

The definitive difference, is that it is designed for deep cycling as well, and

sized large enough to run the other Essentials loads,

for which it should also routinely be used, as well as for cranking.

Routinely tested that is, as thoroughly as you like, maybe even Full cycled once or twice a month

if you feel that's good for longevity.

[thomm225]

Originally Posted by daletournier

Yes I get that, but I'm suggesting if the bank is already pulled down completely.

Well, then it depends.

You'd have to disconnect the batteries to see if the voltage returned at some point.

If it didn't after disconnecting all batteries, the bank may be fried. If the voltage returned in the disconnecting process, some batteries may still be good and you could reconnect them to get home or continue your voyage

As I mentioned before, it similar to troubleshooting any drain on any power source. You have to disconnect in a way to observe when the shorted component, chassis, or battery was removed.

Sometimes you can turn off all loads by pulling fuses or flipping switches or in this case disconnect batteries until the voltage returns depending on how long the problem existed

[daletournier]

Thom, I understand the basics, I was a motor mechanic in a previous life. I've never had one battery in a bank get a dead short, I understand what it is and I can use a multimeter, ive actually seen a car battery explode but I wasnt sure if by just disconnecting them after theyd been draining all night if the others would rise significantly enough to measure the difference, thus the reason for seeking clarity.

Originally Posted by thomm225

No, not if one battery is pulling down the whole bank. (Your question was what if you have a shorted battery in your battery bank?) And it will depend on when you discovered the problem and how long it was left unchecked.

If you see it in the first few minutes due to equipment failure from lack of voltage etc, you can fix it. Left unchecked, it could destroy your whole bank.

I'm talking basic troubleshooting 101.

You'll just need to study electrical/electronic troubleshooting a bit more. (or you can just continue to disagree)

[thomm225]

Originally Posted by daletournier

Thom, I understand the basics, I was a motor mechanic in a previous life. I've never had one battery in a bank get a dead short, I understand what it is and I can use a multimeter, ive actually seen a car battery explode but I wasnt sure if by just disconnecting them after theyd been draining all night if the others would rise significantly enough to measure the difference, thus the reason for seeking clarity.

There's no clarity until you disconnect them and check the voltage. They may all be shot

I had a car flooded battery blow up on start also due to me not maintaining it properly

A couple years back I had a battery drop to near 10 volts and since it was in parallel with my only other battery it was pulling it down and affecting my autopilot (and radio) while sailing thru a group of 20 or so tankers. The current was strong and the wind heavy. I had to sail thru by hand and troubleshoot later

After troubleshooting the problem and disconnecting the bad battery, I was able to sail the last 30 miles home on autopilot with just the one 12 volt battery with solar assist

[a64pilot]

Originally Posted by john61ct

Reserve should also routinely be used for that.

The definitive difference, is that it is designed for deep cycling as well, and

sized large enough to run the other Essentials loads,

for which it should also routinely be used, as well as for cranking.

Routinely tested that is, as thoroughly as you like, maybe even Full cycled once or twice a month

if you feel that's good for longevity.

Having a reserve bank is by definition dead lead, plus a lot of wasted money.
It also shortens the other banks lifespan because your cycling it deeper than if you had both banks connected as one.

Think of this scenario, in the middle of the night a battery shorts out, hours later it has killed the whole bank down to 12V and your low voltage alarm goes off waking you up. You can quickly determine which bank has the dead battery by watching battery voltage and selecting 1 or 2 , leave the switch to the good bank and go back to bed, deal with it in the morning, or if your worried start the engine or generator and charge for awhile.

I don’t see a scenario where you can wake up to a completely dead bank. Low volt alarms are simple and cheap.

But to carry around a couple hundreds of lbs of lead and not use it in case your bank goes dead is foolish. Make them separate banks, but gang them together as one and use them.

Then just from my experience I’ve not seen a battery short out except when it was being charged, maybe it’s coincidence I don’t know.

[john61ct]

I understand these design principles may not be for you, I'm just clarifying them as an option for consideration, not trying to "convince" anyone to implement it.

Originally Posted by a64pilot

It also shortens the other banks lifespan because your cycling it deeper than if you had both banks connected as one.
…
But to carry around a couple hundreds of lbs of lead and not use it in case your bank goes dead is foolish. Make them separate banks, but gang them together as one and use them.

That is the point of the "Subset of Primary" variation, completely optional, but addresses exactly that concern.

http://www.cruisersforum.com/forums/....php?p=2982422
From "Variation" onwards

Your "dead lead" objection applies just as much to the dedicated Starter design principle, but in reality each owner can choose what to prioritize use of weight/space capacity or of course their money.


> Think of this scenario, in the middle of the night a battery shorts out, hours later it has killed the whole bank down to 12V and your low voltage alarm goes off waking you up. You can quickly determine which bank has the dead battery by watching battery voltage and selecting 1 or 2, leave the switch to the good bank and go back to bed, deal with it in the morning, or if your worried start the engine or generator and charge for awhile.


Your specific design, correct me if I'm wrong:

50/50 split House bank, connected with a manual 1/2/B ?

Auditory LV alarm, has no effect itself, just alerts the owner?

_______
> Low volt alarms are simple and cheap.

Not much different from triggering a relay, no?

[Q Xopa]

Originally Posted by john61ct

I understand these design principles may not be for you, I'm just clarifying them as an option for consideration, not trying to "convince" anyone to implement it.

That is the point of the "Subset of Primary" variation, completely optional, but addresses exactly that concern.


Your "dead lead" objection applies just as much to the dedicated Starter design principle, but in reality each owner can choose what to prioritize use of weight/space capacity or of course their money.


> Think of this scenario, in the middle of the night a battery shorts out, hours later it has killed the whole bank down to 12V and your low voltage alarm goes off waking you up. You can quickly determine which bank has the dead battery by watching battery voltage and selecting 1 or 2, leave the switch to the good bank and go back to bed, deal with it in the morning, or if your worried start the engine or generator and charge for awhile.


Your specific design, correct me if I'm wrong:

50/50 split House bank, connected with a manual 1/2/B ?

Auditory LV alarm, has no effect itself, just alerts the owner?

_______
> Low volt alarms are simple and cheap.

Not much different from triggering a relay, no?

An alarm is a notifycation we can make a decision on and manage the issue.

An automatic LVD just acts, whether that scenerio is most appropriate or not. Ie you could just turn something off, start the engine or generator etc.

The 'variation' suggestion will, as I tried to previously illustrate, cycle the main bank to a lower SOC because it reduces its capacity right when you have a big load on it and therefore want the most capacity.
It is in some ways its a clever concept but I cant see what it actually achieves over a main/ reserve or house/ start bank set up. Im not convinced.

'Dead lead' so what. Like spare fuel containers, spare engine starters, water pump etc. The accountants tell us this is 'dead' undeployed capital bla bla. Sure it is, so what. I am happy to be carry around spare (dead) lead/ fuel/ parts/ cash etc. When you need it, it suddenly comes alive very quickly.

This is an individual call, and I know what my wasteful choice is.

But despite some peoples insistance we still can not have our cake and eat it too.

[Dockhead]

Originally Posted by daletournier

Thom, I understand the basics, I was a motor mechanic in a previous life. I've never had one battery in a bank get a dead short, I understand what it is and I can use a multimeter, ive actually seen a car battery explode but I wasnt sure if by just disconnecting them after theyd been draining all night if the others would rise significantly enough to measure the difference, thus the reason for seeking clarity.

I've had a cell short out probably three or four times over my cruising life. It's been the usual LA failure mode in my experience.


And what happens is then the charger tries to get back to the set voltage by pumping amps in, and the batteries start to overheat and boil out. This is terrible if it happens when you're not on the boat. This is why it's important to have a temp sensor on the batts and a charger which will turn itself down if it senses overheating.



But I do agree with you that you can find the faulty batt with a multimeter and without disconnecting anything. But then you do want to disconnect and isolate the faulty battery. And unfortunately then replace the whole bank, because you don't know when the next one will do the same thing.

[Dockhead]

Originally Posted by Q Xopa

. . . 'Dead lead' so what. Like spare fuel containers, spare engine starters, water pump etc. The accountants tell us this is 'dead' undeployed capital bla bla. Sure it is, so what. I am happy to be carry around spare (dead) lead/ fuel/ parts/ cash etc. When you need it, it suddenly comes alive very quickly.. . .

Indeed!



Using your start batt for anything else greatly increases the risk that it won't work when you need it, plus if it's a deep cycle rather than start battery type it will already be at a disadvantage.


I guess in a really small boat, or some high performance small multihull, where every pound of weight counts, this might make sense, but what's ONE SINGLE ADDITIONAL BATT on a normal cruising boat.


To each his own, but surely best practice is what reduces the risk as much as possible that your engine won't start when you need it. Dedicated start batt, of start battery type, not used for anything else and not connected to anything else, dedicated alternator and charger. Any connection to any other gear is a place where something can go wrong and leave the start batt dead.


Imagine you're sailing off a lee shore, a gale blows up, you're embayed, and start to lose ground towards the shoals. You need that engine RIGHT NOW! Or any one of a thousand other scenarios.

[a64pilot]

Originally Posted by john61ct

Not much different from triggering a relay, no?

No, it’s significantly different than tripping a relay, trip that relay and you have no power, you can’t start an engine etc with a low battery without tripping the relay. Besides a relay is a point of failure that can leave you with no power if it fails.
Now if you day sail and leave the boat on shore power during the week and have no Solar, I could see a relay helping if the pedestal power fails.
An issue with a relay is it would need to be set at a high enough voltage that leaves you with enough power to start an engine and protect the bank, but during high amp loads the voltage can’t drop to the point the relay disconnects.
Those two are incompatible, so now you need to have a way to disable the relay, and enough knowledge to do so.

It’s exactly like an engine low oil pressure alarm, do you want the engine to shut down automatically, or just alarm to tell you you have a problem?

[thomm225]

Originally Posted by Dockhead

But I do agree with you that you can find the faulty batt with a multimeter and without disconnecting anything. But then you do want to disconnect and isolate the faulty battery. And unfortunately then replace the whole bank, because you don't know when the next one will do the same thing.

Very doubtful that you will find it with batteries still connected.

If in parallel which most banks are, you will read the same voltage on each battery in that section which will not help you determine the bad one. (I think I was reading 11.5 volts or so when I had a battery fail on all batteries until I removed the bad one then it went back to above 12 volts and I ran on that one with solar assist. I did this while heaved too one morning)

After disconnecting and finding the bad one, you should be able to simply remove it from the bank plus any others that are low then run on the rest depending on how bad/shorted the failed one was

We do that here quite often also with 12 volt UPS batteries. We've replaced as many as 10 in a 48 battery cabinet and then run for another couple years

We also had one smoke. We replaced that one and went a year or so

Another time the operators smelled a weird burning smell and that UPS Unit had all 30 batteries overheating due to advanced age. We had to replace them all. We ran on bypass until we could replace them

Now we have to replace all batteries every five years which is quite expensive. For 4 systems it will cost about $41,000. One has a 72 battery unit

[a64pilot]

If you have a dedicated start battery, best have a way to connect to another bank for when that one battery dies, which of course it eventually will. Why it will eventually die and you not see it coming is because it’s health isn’t being monitored.
Ever gone to get into you car only to have a dead battery, but it started fine the day before? That’s because it doesn’t take much to start an engine and since it’s capacity isn’t being monitored, it will slowly degrade until one day it suddenly died, except it wasn’t a sudden death, not really.
For aircraft that have a single battery, the battery is an extremely critical piece of equipment, in the event of an alternator failure, it’s needed to operate the navigation equipment and radios, without which if your IFR, your in a real world of hurt, if you survive it will be due to luck.
So therefore every year the “reserve capacity” of the battery has to be checked during an annual, and you replace a battery that is weak, if that’s done I’ve not seen a battery fail.
Very often that required check isn’t done, it’s even required on all new batteries, except a Concorde battery, which of course is the same as a Lifeline battery, it’s not required on them because the factory has already done a cap check after manufacture and can provide documentation.

If you have two banks, connected together and monitored for health on a daily basis, in the event you have that unlikely sudden death of an individual battery, disconnect the bad bank, crank that motor and drive on.

You can try to cover every possibility until you either end up with a nuclear powered wrist watch AKA as a hopelessly complicated mess, or two boats.

So far as having a dedicated charging system for that one battery, why? Is that one alternator more reliable than the other? Wouldn’t it be better if you have two alternators that they could charge all banks?
Wouldn’t the best be that all charge sources can charge all banks, but do so without complicated / expensive gadgets?

On edit, it goes back to the fact that most systems will work, even the way the boat was wired from the factory will work fine and is safe.
IF and this is important, you understand the capabilities and limitations of how that particular system is wired.
In my opinion you don’t need complex systems with a lot of expensive gadgets to work and be safe, and I’d go so far as to say that each gadget you add is another potential point of failure.
Often KISS is good.
I don’t want an automatic system, I want to be in the loop, I want to be required to make a decision.
Some strive for a pure automated system. That multimillion dollar Viking I spoke of had a pure automated system, unfortunately is disabled the boat and the people on board didn’t understand what was going on and why or how to disable it. Their generator was running of course and pumping a charge into that overheated battery, it wasn’t going to resolve itself automatically, but all it took was turning the bank switch to off and letting the bank cool to return function.
I bet the fire / overheat detection system could be overridden, but I knew nothing about it and neither did the Capt.

[Q Xopa]

Originally Posted by a64pilot

No, it’s significantly different than tripping a relay, trip that relay and you have no power, you can’t start an engine etc with a low battery without tripping the relay. Besides a relay is a point of failure that can leave you with no power if it fails.
Now if you day sail and leave the boat on shore power during the week and have no Solar, I could see a relay helping if the pedestal power fails.
An issue with a relay is it would need to be set at a high enough voltage that leaves you with enough power to start an engine and protect the bank, but during high amp loads the voltage can’t drop to the point the relay disconnects.
Those two are incompatible, so now you need to have a way to disable the relay, and enough knowledge to do so.

It’s exactly like an engine low oil pressure alarm, do you want the engine to shut down automatically, or just alarm to tell you you have a problem?

Yes I think you have nailed it.

Sometimes its better to risk toasting a battery, or in you example an engine, to keep you off terra firma and having everything wrecked.

In the situation described you could wake up with run down and disconnected main. Atleast you can start the motor. But if you want lights, radio or nav instruments it might be not so good.

If stuff like a battery is going wrong, IMHO, much to be notified so you can decide what you want to change up to get things back in control.

Hopefully you can simply switch off a less essential load- fridge maybe, and switch on the motor to get charge headed in the credit direction.

Much better than having a load run one bank right down and automatically disconnect.

But it sounds like some are sold on this idea. Thats fine, just not for me.

[a64pilot]

Assuming you leave the boat the way most are wired, that is the battery selector switch selects both use and charge, that way when you disconnect the bad bank, you also isolate it from being charged, with it isolated then the alternator will be charging the good bank only and all electronics etc will be connected to the good bank only and be able to operate fine, assuming of course they don’t draw more than the alternators capacity, which they shouldn’t of course.

However to continue to beat a dead horse, the most important thing I believe is for you to understand how your system works.
For instance I didn’t know at first that my selector switch selected which bank was charged too, I didn’t even think about that until I installed my larger alternator and that little charge wire that the boat came with wasn’t going to hold 165 amps without a voltage drop, so I connected the alternator to the large battery wire going to the starter, then I figured out that I’m only charging what I’m connected to.