To isolate or not to isolate... that is question

[GILow]

Hello crew,

I'm just weeks away from finally fitting the "real" battery bank to the boat. I've got by since 2012 with a small bank, two 12 volt, 100 amp-hour batteries in parallel. The boat has been a dock queen all this time, so no point in having any more.

House bank is totally independent of engine bank. (Engine bank is 24 volts, house is 12 volts.)

This "real" house bank will be around 600 amp hours and will consist of 6 x 105 AH 12 volt conventional lead-acid deep cycle batteries. Power loads on the boat are reasonably trivial, with the exception of a 1500 Watt inverter that runs the odd power tool or coffee machine for a few minutes at a time.

Here's the thing...

Since 2012 I've had the two batteries in parallel, connected via one of those big round 1, 2, 1 + 2, OFF battery isolation switches. And the whole time since 2012 I have used either 1 + 2 or, when doing major electrical work, OFF.

I am wondering if there is any reason to fit any kind of single battery isolation switches to the new bank?

They seem to me to be additional point of failure.

I would still have a master ON/OFF switch, of course.

How would you do it? Access to the battery bank is pretty good so disconnecting a battery using a spanner is not a big problem.

(And, for the record, this is in Australia, so the ABYC standards, although often helpful and well thought out, are not a technical requirement for me.)

Matt

[john61ct]

Originally Posted by GILow

This "real" house bank will be around 600 amp hours and will consist of 6 x 105 AH 12 volt conventional lead-acid deep cycle batteries.

Confirm with knowledgeable peers whether good model, true deep cycle. Not vendors.

Going to 6V may yield better quality / value than 12V.

___

> Since 2012 I've had the two batteries in parallel, connected via one of those big round 1, 2, 1 + 2, OFF battery isolation switches.

That depends on - connecting what to what. If between the members of a bank, lose it.

If directing output to loads between House and say Starter ir a Reserve, maybe useful.

A VSR / combiner is to connect a bank to a charge source circuits "on the other side" only when the source is active, otherwise isolating.

Doing that with a manual switch means forgetting can leave both banks flat, no cranking.

[Wotname]

Originally Posted by GILow

............

I am wondering if there is any reason to fit any kind of single battery isolation switches to the new bank?

They seem to me to be additional point of failure.

I would still have a master ON/OFF switch, of course.

How would you do it? .........

Matt

Me, I would simply have the master ON/OFF switch. No need to further isolate the batteries within the bank.

[Wotname]

Originally Posted by john61ct

Confirm with knowledgeable peers whether good model, true deep cycle. Not vendors.

Going to 6V may yield better quality / value than 12V.

___

> Since 2012 I've had the two batteries in parallel, connected via one of those big round 1, 2, 1 + 2, OFF battery isolation switches.

That depends on - connecting what to what. If between the members of a bank, lose it.

If directing output to loads between House and say Starter ir a Reserve, maybe useful.

A VSR / combiner is to connect a bank to a charge source circuits "on the other side" only when the source is active, otherwise isolating.

Doing that with a manual switch means forgetting can leave both banks flat, no cranking.

Err... you might have missed the fact that the OP starting circuit is 24V and is completely isolated form his 12V house batteries.

[john61ct]

Originally Posted by Wotname

Err... you might have missed the fact that the OP starting circuit is 24V and is completely isolated form his 12V house batteries.

Ah yes, thanks.

Then a DCDC charger would replace the VSR function.

And the switch would be eliminated, or for other purposes not involving the alt as a charge source.

[GILow]

Originally Posted by john61ct

Ah yes, thanks.

Then a DCDC charger would replace the VSR function.

And the switch would be eliminated, or for other purposes not involving the alt as a charge source.

I've got a DC to DC charger to grab power from the engine alternator/battery-bank in the event of an emergency. Nice little bit of kit, but so far has been mostly unneeded thanks to 760 Watts of solar and a 360 Watt wind gen. But good to have, that's for sure. I do use it when I am wanting to run the inverter at full output, as the existing tiny battery bank does not cope with the sorts of currents the inverter draws. Starting the 100 HP diesel to vacuum-clean the boat does feel a little silly though.

The system is pretty well sorted in terms of inputs and outputs, it all has been stable for a couple of years. Just ready, at last, to put some decent capacity in place.

Sounds like no objections to tossing the isolator switch so far.

Matt

On a side note, just got a much better price than expected for the batteries, starting to think maybe 800 AH....

[smac999]

no need for swtiches on each battery. one main house swtich. inverter should have own switch and feed if it is an inverter / charger.

[GILow]

Originally Posted by smac999

no need for swtiches on each battery. one main house swtich. inverter should have own switch and feed if it is an inverter / charger.

Yep, inverter has its own switch. No parasitic power loss on this old boat. [emoji846]

[tanglewood]

I’ll offer up an alternate view. I like the ability to segment off parts of the house bank, primarily for testing and diagnostics. You could set up two strings using your existing switch. Normally leave the switch set to 1+2 so you are using the whole bank. But periodically check each bank individually to see if performance matched. The reason is that a bad battery in parallel strings can be hard to identify, and do a lot of damage to a bank. The ability isolate strings can help identify and locate problems.

Ideally each string would have isolation. Just an on off switch is fine. A removable fuse can work too, as can simply disconnecting cables. But with flooded batteries, a lot of sparking and metal wrenches that can slip or be dropped is good to avoid.

[GILow]

Originally Posted by tanglewood

I’ll offer up an alternate view. ...

...The ability isolate strings can help identify and locate problems.
.

Agreed. Very much the primary advantage of the isolation switches.

Regarding batteries and spanners, I keep a dedicated battery spanners secured with the batteries. It is wrapped in electrical tape.

I’ve done more than enough welding for one lifetime. [emoji6]

[john61ct]

Each connection or device in a circuit adds resistance and voltage drop.

Within the bank and permanent, not ideal.

Should be designed so not hard to undo jumper wires as needed without incident.

On banks benefiting from equalization this should be happening at least monthly anyway.

[noelex 77]

Originally Posted by tanglewood

I’ll offer up an alternate view. I like the ability to segment off parts of the house bank, primarily for testing and diagnostics. You could set up two strings using your existing switch. Normally leave the switch set to 1+2 so you are using the whole bank.

+1

My only suggestion is that ideally each string should have its own battery switch. On/Off. That way if the battery switch becomes defective there is redundancy. Switching DC is not an easy task and battery switches do sometimes become defective.

Considering the above, if you are going to reuse your old battery switch, check its contact resistance. The best way to do this is to measure the voltage drop with a reasonable current.

Two switches mean you have an easy way of isolating part of the battery bank if a battery becomes suddenly defective (and this usually happens when sailing offshore), or as a means of testing, or equalising the bank.

[john2445]

Back when I was first building a bank of more than one battery, I read about a battery failing. The other batteries tried to pump every amp they had into the failed battery. The result wasn't pretty.

I have only a master cutoff switch (outside the battery compartment) but install a mega fuse between the two 6v in series and between the 12v in parallel.

Nothing's blown up yet! Knock on wood.