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Sealed Domestic Batteries for Liveaboard

Jim Batty

By Jim Batty
in Boat Equipment

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ditchcrawler Veteran II

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Posted
Posted

I had missed something then. I had a mental image of the alternator attached to two batteries, one in bulk and one in acceptance. If there is some other charger in the circuit, that's a different game altogether.

 

I'm guessing this is a theoretical model, not a real world one with losses due to conversion, and powering complex electronics, and stuff

 

Richard

How about charging battery No.2 (bulk) that is connected to an inverter that in turn feeds a charger that is charging battery No.1 (acceptance) or maybe the other way round.

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Posted
Posted (edited)

How about charging battery No.2 (bulk) that is connected to an inverter that in turn feeds a charger that is charging battery No.1 (acceptance) or maybe the other way round.

Did that once by accident :)

Edited by Guest
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nb Innisfree Veteran II

nb InnisfreeDonate to Canal World

Posted
Posted (edited)

How about charging battery No.2 (bulk) that is connected to an inverter that in turn feeds a charger that is charging battery No.1 (acceptance) or maybe the other way round.

 

But you are still discharging the half sized bank more than twice as much as two connected together (Peukert)

 

i.e. 50ah from a 100ah batt = 50% discharged, 50ah from 200ah batt = less than 25% discharged

Edited by nb Innisfree
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ditchcrawler Veteran II

ditchcrawlerDonate to Canal World

Posted
Posted

But you are still discharging the half sized bank more than twice as much as two connected together (Peukert)

 

i.e. 50ah from a 100ah batt = 50% discharged, 50ah from 200ah batt = less than 25% discharged

Sorry, I thought we had already agreed that the engine was running and the alternator was putting out 14+ volts, so no No 1 battery discharge.

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nb Innisfree Veteran II

nb InnisfreeDonate to Canal World

Posted
Posted

Sorry, I thought we had already agreed that the engine was running and the alternator was putting out 14+ volts, so no No 1 battery discharge.

 

But with two banks one of them has to be discharged between engine running times same as one large bank has to.

 

The road to enlightenment is long.

 

Enlightenment, geddit?

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Gibbo Veteran II

Gibbo

Posted
Posted

Graph for Robin2

 

graph_14.jpg

 

This is a 130Ahr high quality AGM being charged with a 40 amp charger.

 

Green line is battery voltage on a scale of 10 to 15 volts. Red line is current on a scale of 0 to 50 amps. Time scale is 10 mins/div.

 

The periodic dips down to zero amps are when the charger shuts off to see what the battery voltage does (many modern smart chargers do this). These are actually at 15 minute intervals but they don't all show up in that graph due to alias distortion.

 

Roughly in the middle of the graph the voltage stops rising and the current changes from being constant to starting to decrease. Note that they happen as exactly the same time. That is the transistion from bulk to acceptance. Prior to that is bulk, after is acceptance. There is no grey area.

 

If, after entering acceptance, another battery was connected that exceeded the current capability of the charger then the charger would revert to full current output, the voltage would fall and the original battery that was previously in acceptance would see a huge reduction in charge current.

 

Wet cells and gels have a higher internal resistance so, all other things being equal, in this graph (if it was made using wet cells), the voltage would rise faster, the transistion from bulk to acceptance would happen earlier and the acceptance period would last longer with a lower average current.

 

I have some wet cell tests coming up end of next week so I'll post one then.

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RLWP Veteran II

RLWP

Posted
Posted

I thought he was bulking one while the other was on absorption and the engine was running

 

Which one is he using to power the boat electrics? I'm asking because I've lost track of which is doing what

 

Richard

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Robin2 Rising Star

Robin2

Posted
Posted

Which one is he using to power the boat electrics? I'm asking because I've lost track of which is doing what

 

Richard

 

I'm delighted to see some questions.

 

What I am thinking is that today battery A supplies the house load (to not less than 50% depth of discharge; tomorrow battery B meets the load and the day after its back to A again. Each day both batteries get charged when the engine is running. And there is also battery C which is not used for the house load for a few days (perhaps a week) so that it charges back to 100% before it is brought back into use and battery A (for example) is not used for the house load for a week so that it can get to 100%.

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RLWP Veteran II

RLWP

Posted
Posted (edited)

I'm delighted to see some questions.

 

What I am thinking is that today battery A supplies the house load (to not less than 50% depth of discharge; tomorrow battery B meets the load and the day after its back to A again. Each day both batteries get charged when the engine is running. And there is also battery C which is not used for the house load for a few days (perhaps a week) so that it charges back to 100% before it is brought back into use and battery A (for example) is not used for the house load for a week so that it can get to 100%.

 

So, are batteries A and B both connected to the alternator (and C as well?)?

 

Richard

Edited by RLWP
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RLWP Veteran II

RLWP

Posted
Posted

Yes, when the alternator is running, not otherwise.

 

So how do you arrange the power take-off from just one battery. The other will discharge via the two alternator wires. Also the more highly charged battery will charge the other through the same wire. In reality, it's a two battery bank with complicated switched outputs

 

Or is there some subtlety with diodes going on?

 

Richard

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Robin2 Rising Star

Robin2

Posted
Posted

So how do you arrange the power take-off from just one battery. The other will discharge via the two alternator wires. Also the more highly charged battery will charge the other through the same wire. In reality, it's a two battery bank with complicated switched outputs

 

Or is there some subtlety with diodes going on?

 

Richard

 

If the charger voltage is higher than the battery voltages then it will supply the "power take off" and the batteries will be receiving current.

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RLWP Veteran II

RLWP

Posted
Posted

Two batteries, a separate wire from the alternator to the positive terminal of each battery, right? Then a switched take off to the boat electrics from each battery. Is that how you will wire them up? Or is there some other device in the feed from the alternator to each battery?

 

Richard

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Robin2 Rising Star

Robin2

Posted
Posted (edited)

Two batteries, a separate wire from the alternator to the positive terminal of each battery, right? Then a switched take off to the boat electrics from each battery. Is that how you will wire them up? Or is there some other device in the feed from the alternator to each battery?

 

Richard

 

The batteries that are not serving the house load are connected to the alternator via relays that only come on when the alternator is generating. So they are not connected to anything when the alternator is off.

 

Note that there is only a small charge current going through the relays so cheap 30A automotive ones are all that is required (with appropriate fuses).

Edited by Robin2
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Robin2 Rising Star

Robin2

Posted
Posted (edited)

Graph for Robin2

 

 

May I assume that over the period covered by the graph the battery is charged from 50% SOC to 100%?

 

If so, the charger has put about 100Ah into the battery to replace the 65Ah that had been discharged from it - which is consistent with info from my own batteries and the graph in a Sterling brochure.

 

On the other hand the battery seems to be accepting a lot of current in proportion to the remaining deficit which leads me to wonder if it is only charged to 90% at the end of the graph?

 

EDIT

 

I presume your post #49 was addressed to me, though I'm not sure what prompted it.

 

There is little expense for me - I need a new battery anyway. And my time is free - this exploration is entertaining and informative. If it doesn't work I will just be another silly amateur.

Edited by Robin2
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