Separate house / starting banks, or not?

Whoever set up your system did a good job.


A simple solution is to not use the both position for one pair and keep it as start or backup house. That way you will know when the on line set gets low and decide then what to do. I am not a fan of paralleled batteries and would switch between banks in normal operation anyway. If one battery in a parallel bank fails it will draw down all the others and in your case all those batteries will dump current into the one failed battery boiling it among other exciting things.

bayview said:

I am not a fan of paralleled batteries and would switch between banks in normal operation anyway. If one battery in a parallel bank fails it will draw down all the others and in your case all those batteries will dump current into the one failed battery boiling it among other exciting things.

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So you're not a fan of 6V golf cart batteries wired in parallel/series to form a large house bank, I take it. Lot of folks do this and understand the meaning of battery bank voltage. When monitored, it can indicate a failed cell or battery.

The big fear with a house only , no dedicated start is FLAT BATT..

Folks with an undervoltage alarm need to be aboard to start the recharge.

Leaving for a day trip , with a light on or a bilge pump stuck on can bring the house to dead in time.

The start batt for the engine solves the DEAD horror with little effort , no Sea Tow , batt cables .....

Andy G said:

I assume that this discussion is aimed at lead acid batteries, can anyone confirm if the discharge percentages etc are the same for AGM batteries? As I have just replaced my old lead acids with AGM's it would be good to know

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Slightly different:

I wired my last boat with 2 35watt panels, one for generator start, one for forward bow thruster. Both stand alone. Thruster batt next to thruster with no big cables strung through the boat for charging or running the thruster, just 12ga for panel charging. House and main start charged from alternator or charger. Charger powered from shore or genset. Controller shared charging for house or main.
I had some jumper cables that would reach from the main start and house to reach Genset start should it go south, and they would reach the thruster from the main/house. Never needed the jumpers. This worked good, and for peace of mind many redundancys.

Andy G said:

I assume that this discussion is aimed at lead acid batteries, can anyone confirm if the discharge percentages etc are the same for AGM batteries? As I have just replaced my old lead acids with AGM's it would be good to know

Click to expand...

Heron said:

Slightly different:

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Heron, I can't quite tell what your meaning is here. Is the pic relevant to Andy's question?

-Chris

ranger42c said:

Heron, I can't quite tell what your meaning is here. Is the pic relevant to Andy's question?

-Chris

Click to expand...

Yes...Shows the different % Charge numbers VS Voltages for both battery types..
I understood that is what he was asking...

Fly:
in series no problem. In parallel if one cell shorts you have a 10.5 V battery in parallel with a 12V battery both being charged by the alternator. I know this is common practice but that does not make it without problems. What do think happens when the one batter in a parallel set up fails?


The OPs switch set up at least allows him to switch things out.

Heron said:

Yes...Shows the different % Charge numbers VS Voltages for both battery types..
I understood that is what he was asking...

Click to expand...

Hmmm... I often have trouble seeing things that are right in front of me...

But all I can see is wet and gels, not AGMs...

??

-Chris

bayview said:

Fly:
What do think happens when the one batter in a parallel set up fails?

Click to expand...

The voltage drops precipitously.

ranger42c said:

Hmmm... I often have trouble seeing things that are right in front of me...

But all I can see is wet and gels, not AGMs...

??

-Chris

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Sorry...As I understand it, Gell Cell's behave similar to AGM types RE. Voltages. I may be wrong:

GEL: The Gel Cell is similar to the AGM style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a Gel Cell has a silica additive that causes it to set up or stiffen. The recharge voltage on this type of cell is lower than the other styles of lead acid battery.

Heron said:

Sorry...As I understand it, Gell Cell's behave similar to AGM types RE. Voltages. I may be wrong:

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Ah. FWIW, I've been under the impression AGMs are more like FLAs for discharge rates. Our charger uses the same profile for those two. From that, I've guessed that the 50% discharge rule-of-thumb is also useful for AGMs, and our batteries reach that state of charge at 12.18V (well, when they were new, anyway).

Both Lifeline and Odyssey cite duty cycles down to 80% discharge... but I suspect that's more advertising than recommendation, especially since Lifeline's first citation (for GC2s) is to 50% SOC.... and their 80% citation might be only to compete with Odyssey

-Chris

>but I suspect that's more advertising than recommendation,<

They do SELL batts , so a short service life is a good deal,,for them.

FF said:

>but I suspect that's more advertising than recommendation,<

They do SELL batts , so a short service life is a good deal,,for them.

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Sure. But Lifeline says 1000 cycles to 50% for their 6V GC2 deep cycle AGM batteries, which doesn't seem too short.

They rate the same batteries at 550 cycles to 80% discharge, compared to Odyssey's 440 cycles to 80%, but the Odyssey in question is a 12V G31, deep cycle in advertising only, probably more accurately a pretty good dual purpose.

-Chris

FF said:

The big fear with a house only , no dedicated start is FLAT BATT..

Folks with an undervoltage alarm need to be aboard to start the recharge.

Leaving for a day trip , with a light on or a bilge pump stuck on can bring the house to dead in time.

The start batt for the engine solves the DEAD horror with little effort , no Sea Tow , batt cables .....

Click to expand...

The "suspenders" in our case is an 8kw genset with a totally separate battery to start it. Fire it up, and it charges the big battery bank.

>Fire it up, and it charges the big battery bank.<

Given enough TIME , and remember all batts do not like to be taken to near 0% SOC , and will usually need replacement afterwards.

Can you get by without a separate engine start batttery, sure! Ditto:

• A wrong type anchor
• No inverter
• No refrigerator
• No AC if you live in FL
• No heat if you live in the North
• No fresh water flush for the head
• No queen sized bed
• No windlass
• And many more

The above dittos could be called a sail boat or Willy, both perfectly acceptable for the many thousands of current owners. As the size, complexity and reliance upon ready amps of the vessel increase, so do the needs. Not to mention the potential requirement to quickly and safely raise anchor in the middle of a stormy night as the rocky shore approaches.

Quote:
Originally Posted by bayview
Fly:
What do think happens when the one batter in a parallel set up fails?

The voltage drops precipitously.

Click to expand...

Exactly, and when that happens the other batteries dump all their charge into the failed battery and it overheats and sometimes spews acid.