Running out of battery. Can we mix sizes?

[VicS]

VicS, I don't think there is any non-destructive way you can tell if your new battery is low PbSb or PbCa. There isn't enough difference in float current or gassing voltage to tell. Going by its oxymoronic title "professional deep cycle leisure" it's most likely one of the Korean imports that dominate the market and almost certainly PbCa.
PS VicS how about a flame test on an acid sample? Do Sb and Ca give distinctive colours in low concentrations? Or a mass spec would do it

It's a Varta. Whether or not made in Korea I have no idea. I thought Varta were one of the major brands and part of a large world wide group so could be made almost anywhere.

Just surprised its not labelled as lead-calcium if that's what it is. Some brands seem to offer lead-calcium as a "better" and more expensive alternative to the standard range.'

I calcium gives a "brick red" colour in a flame test but I've no idea if the concentration in the acid will be sufficiently high for it to show. According to the books antimony gives a blue flame but then so does lead and several other elements!.

No experience of mass spectroscopy. AA might do it but I've very limited experience of that as well. Used ICP/OES a bit and very probably used that for calcium but I would not have been looking for antimony.

 

[Plevier]

OK, Varta currently use "professional" as a range name. I believe both plates are PbCa. The previous "Hobby" range was hybrid, PbCa neg plates and PbSb pos.
I don't know where they are made now, Varta is just a brand name of Johnson Controls.
I have a suspicion it's Eastern Europe but not sure.
Varta used to be top class and probably still are but tend to be premium price.
Bosch are identical, they tend to use that name for OEM and Varta for retail.

 

[JumbleDuck]

I think you could have a problem if you use a modern charger to charge batteries of dissimilar capacities in parallel. Using a three stage charger the different capacity banks would require different charging times during the absorption phase so they could not be optimally charged in parallel.

I wouldn't worry any more about a big battery and a wee battery in parallel than about the LH 2/3 of the plates and the RH 1/3 of the plates in a single battery.

 

[bedouin]

I wouldn't worry any more about a big battery and a wee battery in parallel than about the LH 2/3 of the plates and the RH 1/3 of the plates in a single battery.

I think that is because you don't understand the chemistry of batteries Either that or you are a naturally laid back guy.

What is the mechanism you think will enable both to be optimally charged during the absorption phase? You think they will both always require the same length of time in the absorption phase irrespective of capacity or condition?

 

[JumbleDuck]

What is the mechanism you think will enable both to be optimally charged during the absorption phase? You think they will both always require the same length of time in the absorption phase irrespective of capacity or condition?

No, but I think connecting them together in parallel creates one bigger battery which will have its own combined characteristics . Here's what googling "absorption phase" found me:

The ABSORPTION stage (the remaining 20%, approximately) has the charger holding the voltage at the charger's absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger set points) and decreasing the current until the battery is fully charged.​

Now, if the voltage is being held, the only reason that the current is decreasing is that the battery is taking up less current. I presume that the smart charger monitors this current and then switches to float when it falls. Well, if you have two batteries in parallel, they'll both take a bit of current at this stage, and as long as the smart charger knows the total capacity it should have no problem in recognizing when the batteries are fully charged.

Have you evidence that different capacity batteries of the same chemistry need significantly different times for absorption charging?

 

[chrishelen]

Soooo in summary is it good idea to replace my nacked 75ah engine start batt with a 110ah to match my house batt? or should I replace the pair (which I am not about to do), or just get another 75ah..the old one lasted about 5 years.they are charged via alternator through a 1-2-both switch.

 

[pvb]

Soooo in summary is it good idea to replace my nacked 75ah engine start batt with a 110ah to match my house batt? or should I replace the pair (which I am not about to do), or just get another 75ah..the old one lasted about 5 years.they are charged via alternator through a 1-2-both switch.

Get another start battery. Ah capacity is less important than current-providing ability, but a 75Ah car battery should be more than capable of starting the average boat engine.

 

[JumbleDuck]

Get another start battery. Ah capacity is less important than current-providing ability, but a 75Ah car battery should be more than capable of starting the average boat engine.

I have a medium term plan on my boat of putting the two existing 65Ah batteries permanently in parallel (there is no room to fit bigger ones) and add a small engine start battery. I have a good Nissan Micra K11 battery lying around which should be more than up to the task of starting a 1GM10. 110Ah sounds like a bit of overkill as an engine start ...

 

[pvb]

110Ah sounds like a bit of overkill as an engine start ...

True, especially when you remember than most boat engines are only around 1.0 litre or less.

 

[Andrew G]

I'm happy that you/we have reached a conclusion to NPMR (the OP)'s question but I am not convinced we have fully solved the problem.
In post #10 NPMR says that his battery #3 showed zero V until battery #2 is turned on.
Can somone explain the mechanism?

Could it be that he is not actually exhausing all his battery bank but has a not-connected, fully charged 75Ah battery standing by?
Cheers, Andrew

(admittedly on a 34' boat I have 5x 110Ah batteries, 160W of solar panels, 96A alternator and a Wind Gen - I like my creature comforts even when far from civilisation)

 

[nigelmercier]

I wouldn't worry any more about a big battery and a wee battery in parallel than about the LH 2/3 of the plates and the RH 1/3 of the plates in a single battery.

Which are in series, not parallel.

 

[Rigger Mortice]

Could it be that he is not actually exhausing all his battery bank but has a not-connected, fully charged 75Ah battery standing by?

He said that he keeps one of his domestic batteries back as a "shunt" because that's what he has been advised to do, so that's probably exactly what has happened.

Personally I can't see any reason to use the batteries like that. It just means that one battery is over used and the other spends a lot of its time idly standing by.

 

[bedouin]

No, but I think connecting them together in parallel creates one bigger battery which will have its own combined characteristics . Here's what googling "absorption phase" found me:

The ABSORPTION stage (the remaining 20%, approximately) has the charger holding the voltage at the charger's absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger set points) and decreasing the current until the battery is fully charged.​

Now, if the voltage is being held, the only reason that the current is decreasing is that the battery is taking up less current. I presume that the smart charger monitors this current and then switches to float when it falls. Well, if you have two batteries in parallel, they'll both take a bit of current at this stage, and as long as the smart charger knows the total capacity it should have no problem in recognizing when the batteries are fully charged.

Have you evidence that different capacity batteries of the same chemistry need significantly different times for absorption charging?

That is simple - if they didn't then you could keep a fixed time absorption phase - and that is not the case. In fact to first order the length of the absorption phase is proportional to the capacity of the battery - so a 110Ah battery requires twice as long as a 55Ah.

The principle of the absorption phase is to push as much power as possible into the battery - there is nothing in the battery chemistry to prevent it being overcharged and no sort of feedback that would automatically equalise the charging between different batteries (as there is for discharge or the bulk charging phase).

Of course this is not a problem if your battery charging regime doesn't include an absorption phase

 

[JumbleDuck]

Which are in series, not parallel.

Sorry, I was unclear. I meant that the LH 2/3 of each plate is in parallel with the RH 1/3 of the same plate, and nobody seems to worry about that.

 

[JumbleDuck]

That is simple - if they didn't then you could keep a fixed time absorption phase - and that is not the case. In fact to first order the length of the absorption phase is proportional to the capacity of the battery - so a 110Ah battery requires twice as long as a 55Ah.

Why? I'm really interested. Isn't a 110AH battery just two sets of 55Ah battery plates connected together in the same case?

 

[bedouin]

Why? I'm really interested. Isn't a 110AH battery just two sets of 55Ah battery plates connected together in the same case?

Not entirely - in the bigger battery they are the same plates in the same electrolyte. The state of charge of the battery really relates to the composition of that electrolyte - so charging is really pushing sulphate ions off the plate and back into solution. So while there is a sulphate ion on the plates that will be displaced back into solution (as sulphuric acid) but once fully charged it will start boiling the electrolyte.

With the two batteries in parallel there is not a connection between each individual set of plates, so the charge can't be shared according to need.

 

[NPMR]

Could it be that he is not actually exhausing all his battery bank but has a not-connected, fully charged 75Ah battery standing by?
Cheers, Andrew

On our boat, each battery is brought into use by switching it 'on'. When you switch on the engine battery alone, all systems come live. If you only switch battery No 2 (the 'domestic' battery) on, all systems come alive and you can even start the engine. If you only switch battery No3 on, nothing happens until you switch battery No2 on.

Hence my belief, from what I've read on this thread, that I'll be fine for the rest of this season putting a bigger battery (capacity) into Battery No 3 position.

If it all goes horribly wrong, I'll be the first to let you know!

 

[pvb]

On our boat, each battery is brought into use by switching it 'on'. When you switch on the engine battery alone, all systems come live. If you only switch battery No 2 (the 'domestic' battery) on, all systems come alive and you can even start the engine. If you only switch battery No3 on, nothing happens until you switch battery No2 on.

Hence my belief, from what I've read on this thread, that I'll be fine for the rest of this season putting a bigger battery (capacity) into Battery No 3 position.

If it all goes horribly wrong, I'll be the first to let you know!

As I said in post #13, this sounds overly complicated, and maybe you need to review the wiring. You'll get better use out of the domestic batteries if they are always connected in parallel.

 

[Plevier]

On our boat, each battery is brought into use by switching it 'on'. When you switch on the engine battery alone, all systems come live. If you only switch battery No 2 (the 'domestic' battery) on, all systems come alive and you can even start the engine. If you only switch battery No3 on, nothing happens until you switch battery No2 on.

Hence my belief, from what I've read on this thread, that I'll be fine for the rest of this season putting a bigger battery (capacity) into Battery No 3 position.

If it all goes horribly wrong, I'll be the first to let you know!

Sounds as though #3 is connected to #2 via an isolator and #2 is connected to the "bus" via an isolator.
#1 appears to connect to the same bus I.e. distinguishing start and domestic batteries is meaningless.

 

[pteron]

That is simple - if they didn't then you could keep a fixed time absorption phase - and that is not the case. In fact to first order the length of the absorption phase is proportional to the capacity of the battery - so a 110Ah battery requires twice as long as a 55Ah.

The principle of the absorption phase is to push as much power as possible into the battery - there is nothing in the battery chemistry to prevent it being overcharged and no sort of feedback that would automatically equalise the charging between different batteries (as there is for discharge or the bulk charging phase).

Of course this is not a problem if your battery charging regime doesn't include an absorption phase

So in absorption phase I am holding the terminal voltage constant and monitoring the current. My 50Ah battery is more charged than my 110Ah battery (for some unexplained reason). The more charged battery has a higher concentration of sulphuric acid in its electrolyte which causes it to have a higher internal resistance, so it takes less current than the lower state of charge battery. Eventually, the current into the 110Ah battery also falls as it charges and the charger switches out of absorption mode and into float.