have i killed my batteries?

[Sea Dog]

Quite an interesting thread, and some good info coming out of it. My 440Ah bank of sealed leisure batteries is getting on a bit at 7 years old, but when charged to full by my engine alternator and I'm still cruising they are typically accepting a little over 1 Amp according to my Victron monitor. 2% would be about 8-9 amps, so what conclusion should be drawn from the low figure charging current gets down to?

[MtB]

What is the charge voltage giving the 1A tail current result?

 

Sounds to me as though your alternator might be goosed.

 

How does the Victron monitor decide the batts are 'fully charged'? Not by the tail current by any chance?

[dmr]

That's hard to believe. Do you have an alternator controller that goes into float mode?

Is the alternator charge voltage very low????

 

................Dave

[nicknorman]

Quite an interesting thread, and some good info coming out of it. My 440Ah bank of sealed leisure batteries is getting on a bit at 7 years old, but when charged to full by my engine alternator and I'm still cruising they are typically accepting a little over 1 Amp according to my Victron monitor. 2% would be about 8-9 amps, so what conclusion should be drawn from the low figure charging current gets down to?

Personally I think 2% is not properly charged. As you say it can get down to 1/2% or less, as mine do. I take it to be a sign that the batteries are in good condition. I think 2% is a compromise for those who don't want to be running engines endlessly just to put a few amps (and hence a few more amphours) in.

What is the charge voltage giving the 1A tail current result?

 

Sounds to me as though your alternator might be goosed.

 

How does the Victron monitor decide the batts are 'fully charged'? Not by the tail current by any chance?

That's hard to believe. Do you have an alternator controller that goes into float mode?

Is the alternator charge voltage very low????

 

................Dave

I see the same, under 2A at 14.5v into the 450AH. You lot just don't cruise enough!

[Iain_S]

Quite an interesting thread, and some good info coming out of it. My 440Ah bank of sealed leisure batteries is getting on a bit at 7 years old, but when charged to full by my engine alternator and I'm still cruising they are typically accepting a little over 1 Amp according to my Victron monitor. 2% would be about 8-9 amps, so what conclusion should be drawn from the low figure charging current gets down to?

 

Your batteries are charged ...

[Sea Dog]

What is the charge voltage giving the 1A tail current result?

 

Sounds to me as though your alternator might be goosed.

 

How does the Victron monitor decide the batts are 'fully charged'? Not by the tail current by any chance?

 

The monitor doesn't decide Mike, I do that! I ignore the SOC figure, but I do take notice of the Ah counter cos that's probably not far off. But I decide when the batteries are topped up after watching the voltage rise and the current drop from 100a or whatever (depending how much I've used) through 40, 30 20, over 2 or 3 hours, then tens and single figures for maybe 2 or 3 more hours before it ends up sub 2 amps for however long until I moor up. It's hovering about 14.6 volts by then.

 

Personally I think 2% is not properly charged. As you say it can get down to 1/2% or less, as mine do. I take it to be a sign that the batteries are in good condition. I think 2% is a compromise for those who don't want to be running engines endlessly just to put a few amps (and hence a few more amphours) in.

 

I see the same, under 2A at 14.5v into the 450AH. You lot just don't cruise enough!

Thanks Nick, that's nice to know. I had taken my figures as being normal enough, so it's good to know that you see more or less the same from your similar engine and alternator configuration.

 

 

My original query was really wondering whether that final current figure when continuing to run beyond full batteries, whatever it was, told us anything about our present battery capacity or whatever?

[nicknorman]

My original query was really wondering whether that final current figure when continuing to run beyond full batteries, whatever it was, told us anything about our present battery capacity or whatever?

No I don't think so, not in my experience anyway. Perhaps it's because the plate area remains the same regardless of lost capacity, although perhaps it depends on why the capacity is lost (sulphation, lost plate material etc).

As SPt said (I think) the increased tail current with age is to do with contamination of the electrolyte over time.

 

As we know, quite young batteries can have low capacity, but no electrolyte contamination. So my best guess is that the tail current does reflect battery age, but not necessarily battery relative capacity.

[emlclcy]

as part of my pwm to mppt upgrade I bought a victron 700 battery monitor, it has a shunt for clocking in/out current. so this is the perfect tool to do a once deep cycle on my batteries to find their capacity. I've not run it up yet but I imagine it can measure varying currents and summarise battery capacity.

[Sea Dog]

as part of my pwm to mppt upgrade I bought a victron 700 battery monitor, it has a shunt for clocking in/out current. so this is the perfect tool to do a once deep cycle on my batteries to find their capacity. I've not run it up yet but I imagine it can measure varying currents and summarise battery capacity.

Exactly where my figures come from, E. The SOC measurements are considered unreliable though, not least because you have to manually input your current battery capacity in Amp Hours and we don't really know what it is. This is why tail current is important in assessing when your batteries are fully recharged, hence this bit of the discussion.

 

Now, what the MPPT input does to your BMV's readings and calculations is another interesting point!

[Graham.m]

Quite an interesting thread, and some good info coming out of it. My 440Ah bank of sealed leisure batteries is getting on a bit at 7 years old, but when charged to full by my engine alternator and I'm still cruising they are typically accepting a little over 1 Amp according to my Victron monitor. 2% would be about 8-9 amps, so what conclusion should be drawn from the low figure charging current gets down to?

 

It depends on what is running in the boat as your cruising. Surely the monitor will show the current going in or out of the battery, so if something is using -5 amps the alternator is producing +6 amps the monitor will show 1. It might even be the alternator is off and it is the solar panels, if you have them, that are producing +6 amps .

[cuthound]

No I don't think so, not in my experience anyway. Perhaps it's because the plate area remains the same regardless of lost capacity, although perhaps it depends on why the capacity is lost (sulphation, lost plate material etc).

As SPt said (I think) the increased tail current with age is to do with contamination of the electrolyte over time.

As we know, quite young batteries can have low capacity, but no electrolyte contamination. So my best guess is that the tail current does reflect battery age, but not necessarily battery relative capacity.

As Nick says, the increased tail current is a result of contamination of the electrolyte by lost active material.

 

These days most batteries are opaque or sealed.

 

Until the 1980's most commercial batteries for the critical power industry had clear cases. Older batteries had a black sludge at the bottom, through which current tracked more easily than the clear electrolyte above it, resulting in a higher tail current. Sometimes "trees" grew from one plate until they touched an adjacent plate, resulting in a short circuit and reducing cell capacity. On the really big open topped batteries, the "trees" could be removed by using an insulated stick (commonly known as Excalibur).

 

Modern batteries require far a less maintenance than the ones I started my career with.

[WotEver]

 

It depends on what is running in the boat as your cruising. Surely the monitor will show the current going in or out of the battery, so if something is using -5 amps the alternator is producing +6 amps the monitor will show 1. It might even be the alternator is off and it is the solar panels, if you have them, that are producing +6 amps .

Huh?

 

What on earth has that drivel got to do with tail current? Are you suggesting he only has a 6A alternator?

 

Tony

[Top cat]

Exactly where my figures come from, E. The SOC measurements are considered unreliable though, not least because you have to manually input your current battery capacity in Amp Hours and we don't really know what it is. This is why tail current is important in assessing when your batteries are fully recharged, hence this bit of the discussion.

Now, what the MPPT input does to your BMV's readings and calculations is another interesting point!

I have a MPPT controller feeding the batteries via a BMV and it does not seem to adversely affect the volt Ah and amp readings, but I take no notice of the SoC or TTG calculations. Like others I rely on the tail current and voltage to estimate when fully charged. My controller has a float mode which can get confused when the solar input is low like it is at the moment.( running at 13 and a bit V round about 0.5A)

 

Top Cat

[Sea Dog]

It depends on what is running in the boat as your cruising. Surely the monitor will show the current going in or out of the battery, so if something is using -5 amps the alternator is producing +6 amps the monitor will show 1. It might even be the alternator is off and it is the solar panels, if you have them, that are producing +6 amps .

 

I have a 175 Amp domestic alternator Graham, so there's plenty of capacity to let the batteries accept whatever they will whilst cruising. There's normally just the fridge cutting in and out which makes no difference at any time, but I have an 1800 watt coffee machine that barely bothers the charging current at cruising revs providing I haven't just started charging.

[Graham.m]

I have a 175 Amp domestic alternator Graham, so there's plenty of capacity to let the batteries accept whatever they will whilst cruising. There's normally just the fridge cutting in and out which makes no difference at any time, but I have an 1800 watt coffee machine that barely bothers the charging current at cruising revs providing I haven't just started charging.

 

I was thinking in that tail-off area where charge rates are down and the effect of the fridge at say -4A could mask 12A as 8A. It depends how sensitive the charger circuits are and how quickly they respond.

[Top cat]

At low charging currents the alternator picks up the load from say the fridge turning on and the charge rate is unnaffected. The load needs to be much larger say a kettle to drop the charge rate at all.

 

Top Cat

[nicknorman]

At low charging currents the alternator picks up the load from say the fridge turning on and the charge rate is unnaffected. The load needs to be much larger say a kettle to drop the charge rate at all.

Top Cat

Same for me.

[emlclcy]

battery update - the bmv700 is hooked up now with an inverter running a slow cooker - 175watts 14amp battery current. interesting thing is after about an hour the battery voltage increased from 12.12v to 12.30v where its sat at now! so things are looking good and i'm cooking an overnight soup at the same time.

will cycle the battery to 10.5v as recommended by the victron chap to see what the Ahr really is then real value can be plumbed into the bmv700 as a 'real' value

all good so far ...

[Graham.m]

battery update - the bmv700 is hooked up now with an inverter running a slow cooker - 175watts 14amp battery current. interesting thing is after about an hour the battery voltage increased from 12.12v to 12.30v where its sat at now! so things are looking good and i'm cooking an overnight soup at the same time.

will cycle the battery to 10.5v as recommended by the victron chap to see what the Ahr really is then real value can be plumbed into the bmv700 as a 'real' value

all good so far ...

 

Sounds very good and hopefully the soup will be good for lunch tomorrow.

 

Just remind me what is the design capacity of the battery?

[MtB]

battery update - the bmv700 is hooked up now with an inverter running a slow cooker - 175watts 14amp battery current. interesting thing is after about an hour the battery voltage increased from 12.12v to 12.30v where its sat at now! so things are looking good and i'm cooking an overnight soup at the same time.

will cycle the battery to 10.5v as recommended by the victron chap to see what the Ahr really is then real value can be plumbed into the bmv700 as a 'real' value

all good so far ...

 

 

"Overnight soup" sounds nice, what flavour is it?!

[emlclcy]

Sounds very good and hopefully the soup will be good for lunch tomorrow.

 

Just remind me what is the design capacity of the battery?

they are 250ah, as I'm at work all day I reduced the load to5amps which means the battery should still be alive when I get home tonight for the beef shin broth! the meat fell apart just nice this morning

[Graham.m]

they are 250ah, as I'm at work all day I reduced the load to5amps which means the battery should still be alive when I get home tonight for the beef shin broth! the meat fell apart just nice this morning

 

That sounds wonderful, just falling off the bone

 

Be careful not to take that battery to far,

[emlclcy]

Battery update, got back to the alarm on the inverter buzzing, it had switched off at 10.98v but the amp hour count was 218 with 9.5% left so this must be in the 250 ah ball park so happy bunny!

[nicknorman]

Battery update, got back to the alarm on the inverter buzzing, it had switched off at 10.98v but the amp hour count was 218 with 9.5% left so this must be in the 250 ah ball park so happy bunny!

Ok well recharge straight away and don't forget that such a deep DoD will cause life reduction.

[Loafer]

Get em back on charge, quick!

Nick beat me.