nigelmercier
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Not only that, but the same age and chemistry. With AGM batteries is it less important about the capacity.
Running out of battery. Can we mix sizes?
- Thread starter NPMR
- Start date
Not only that, but the same age and chemistry. With AGM batteries is it less important about the capacity.
pvb
Well-Known Member
AGM batteries are essentially just lead acid batteries! As I said, old wives' tales are difficult to eradicate.
VicS
Well-Known Member
There may be a small problem if the two are of very diffeernt capacities and are charged in parallel using a "smart" multistage charger.
No problem during the bulk charging stage but when the absorption stage is reached, where the voltage is held constant, the small battery will be kept on charge longer at that voltage than it would be on its own before the charger goes into "float" mode
pvb
Well-Known Member
But that voltage won't harm it. Many boaters rely on engine charging, which doesn't even have a "float mode" in most cases.
VicS
Well-Known Member
Not harm it but the absorption stage voltage is likely to be higher than the output from a bog standard alternator. That's why the multistage charger. or even an alternator with a fancy regulator, gets the battery closer to being fully charged.
Possible therefore than a small battery charged in parallel with a large one using multistage charging may need its electrolyte topping up more frequently than it would otherwise.
RogerMayne
Well-Known Member
Batteries should be the same type, eg agm lead acid etc. Beyond that it helps to use the water analogy, think of amp hours as the amount of water in a tank and the voltage as the pressure gradient of the water leaving the tank. I do not believe there will be any harm in using dissimilar sized batteries, all batteries of the same size are inherently different anyway.
pvb
Well-Known Member
Most batteries for boat use now use lead-calcium plates, which are very tolerant of high charge voltages,
VicS
Well-Known Member
Sorry missed that. Didn't realise we were talking about lead calcium batteries.
pvb
Well-Known Member
Almost all boat/leisure batteries now use lead-calcium technology.
VicS
Well-Known Member
I just bought a 60Ah "Professional deep cycle leisure battery" I don't think it's lead-calcium. No mention of it in the description anywhere.
It does not matter one way or the other but how would I know?
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PabloPicasso
Well-Known Member
Seems easier and more sensible to reduce power consumption while on passage. Switch off everything. There's very little you actually need on 24/7. Lights at night, fit LEDs. Auto helm, helm more. Switch off the fridge. Don't charge phones etc while sailing?
I'm not being smart here, this is just how to manage a yacht on passage. Run the engine when the volts start to drop. Monitor the battery state regularly
Surely an poor overnight not to monitor battery state to the point where they run flat?
I'm not being smart here, this is just how to manage a yacht on passage. Run the engine when the volts start to drop. Monitor the battery state regularly
Surely an poor overnight not to monitor battery state to the point where they run flat?
grumpy_o_g
Well-Known Member
What actually matters is the voltage required to charge the battery as they'll both be getting the same voltage whether they like it or not if they are paralleled by two ruddy great cables. That's why it's not recommended to mix AGM and wet cell, etc. One of them will not be getting charged optimally. If you have a smart charger then I would have thought it would get a little confused if one battery is healthier than the other but nothing that I would worry about for the remainder of the season.
As far as discharge is concerned the only issue is that a seriously nadgered battery that doesn't hold charge will end up being charged by the good battery, which will also be running all the services at the same time so it won't last long - that happens with similar batteries too of course. If you have a battery monitoring system that will get very confused when you add the new battery and will need resetting. Once it's worked out what the new battery bank is doing it should work fine though.
I can understand people saying that batteries should be similar as this is more likely to mean that the internal resistance of the battery changes similarly on all batteries in the bank but, unless you have a tiny 50AH battery and a massive 300AH battery in parallel I wouldn't expect the difference to be that great. I can well believe that the majority of marine batteries are now Lead-Calcium as most automotive batteries are. Lead-calcium doesn't like deep discharging as much though so the traditional Lead-acid (which uses Antimony) would probably be a better choice but not something to get too hung up on.
Just about batteries have a date code on them somewhere but it varies from manufacturer to manufacturer as to where it is and how it's interpreted.
As far as discharge is concerned the only issue is that a seriously nadgered battery that doesn't hold charge will end up being charged by the good battery, which will also be running all the services at the same time so it won't last long - that happens with similar batteries too of course. If you have a battery monitoring system that will get very confused when you add the new battery and will need resetting. Once it's worked out what the new battery bank is doing it should work fine though.
I can understand people saying that batteries should be similar as this is more likely to mean that the internal resistance of the battery changes similarly on all batteries in the bank but, unless you have a tiny 50AH battery and a massive 300AH battery in parallel I wouldn't expect the difference to be that great. I can well believe that the majority of marine batteries are now Lead-Calcium as most automotive batteries are. Lead-calcium doesn't like deep discharging as much though so the traditional Lead-acid (which uses Antimony) would probably be a better choice but not something to get too hung up on.
Just about batteries have a date code on them somewhere but it varies from manufacturer to manufacturer as to where it is and how it's interpreted.
charles_reed
Well-Known Member
Please, remain comfortable in your opinion, it is such a small matter on which we can agree to disagree.
We do, it appears, agree on the rather more significant contra-indication of not mixing battery construction types (calcium-hardened with antimony, AGM with open) in the same bank. I'd opine that age is less important, providing both batteries are in good health.
sailinglegend420
Well-Known Member
But Charles this is the whole point of the thread - can we mix battery sizes - not such a small matter.
The point about being the same age is surely that they will stay in "good health" for roughly the same amount of time. If one is twice the age of another then that will die earlier and drag down the others. It is always better with a bad bank to replace all batteries at the same time. If you have a larger bank - or many smaller batteries in one large bank - it is easy when they start failing to just disconnect the bad ones and run on the others as long as you can until you can replace the whole bank. This may also allow skippers to search around and find the batteries they really want - not just be forced to buy the local "Rubbish" because they are desperate.
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Plevier
Well-Known Member
Here's my view as a retired applications engineer from a major battery manufacturer.
The prohibition on parallel banks of different capacities is a hangover of old technology.
Batteries used to be made of lower quality materials using poorer casting methods and high antimony content in the alloy, typically 8-10%. They had high self discharge rates and would gas like mad at the sort of voltages used now for float and recharge even when new. Gassing would worsen through life with antimony migration and local spot deposition on the plates.
Chargers were also much cruder, with little or no automatic voltage control.
The normal regime was to float at under 13V, sometimes as low as 12.3V, and to recharge monthly or after a discharge.
The recharge was normally at constant CURRENT, commonly C/10 or C/20, and would be continued until s.g. was restored and constant. In the latter stages of charging there would be lots of gassing. Voltage could go pretty high. This is a punishing regime for the battery, but in those days they were more heavily built and life expectations were lower.
If you are charging like this, it is important that parallel banks should be identical. It's not really a good idea to have parallel banks at all during this charge.There is definitely a risk of banks being under or over charged.
Since about 1960 (maybe a bit earlier) batteries in Europe improved in purity of ingredients and casting methods and the antimony content brought down to typically 1.5% with big reductions in self discharge, gassing and increased standby life. Simultaneously in the US lead-calcium alloy was developed as an alternative to lead-antimony alloy with similar benefits.
Charger technology has also developed with modern electronics, first to closely regulated constant voltage chargers then smart multi stage chargers.
With this charge regime there is not much problem in using parallel banks of different capacity within reason.
Of course if you have a smart charger it is functioning in constant current mode for part of the charge cycle but with an accurately limited voltage so current declines once that limit is reached. The batteries may get a bit out of step but it is unlikely to go on long enough to do any harm and they should catch up in the constant voltage/declining current stage and on subsequent float.
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.
Manufacturers like PbCa because it is easier for health and safety/pollution - Sb is awful stuff - and has a better shelf life without recharge. Against that PbSb has better cycling and temperature resistance, especially with higher concentrations. Real cycling batteries - fork lift, floor sweeper (e.g T105) etc still tend to use 5-10% Sb. You get cycle life at the expense of more gassing and self discharge.
All the talk from PbCa people about PbSb high self discharge rates relates to traditional high Sb batteries. There isn't much difference between typical PbCa and Pb1.5%Sb.
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
The prohibition on parallel banks of different capacities is a hangover of old technology.
Batteries used to be made of lower quality materials using poorer casting methods and high antimony content in the alloy, typically 8-10%. They had high self discharge rates and would gas like mad at the sort of voltages used now for float and recharge even when new. Gassing would worsen through life with antimony migration and local spot deposition on the plates.
Chargers were also much cruder, with little or no automatic voltage control.
The normal regime was to float at under 13V, sometimes as low as 12.3V, and to recharge monthly or after a discharge.
The recharge was normally at constant CURRENT, commonly C/10 or C/20, and would be continued until s.g. was restored and constant. In the latter stages of charging there would be lots of gassing. Voltage could go pretty high. This is a punishing regime for the battery, but in those days they were more heavily built and life expectations were lower.
If you are charging like this, it is important that parallel banks should be identical. It's not really a good idea to have parallel banks at all during this charge.There is definitely a risk of banks being under or over charged.
Since about 1960 (maybe a bit earlier) batteries in Europe improved in purity of ingredients and casting methods and the antimony content brought down to typically 1.5% with big reductions in self discharge, gassing and increased standby life. Simultaneously in the US lead-calcium alloy was developed as an alternative to lead-antimony alloy with similar benefits.
Charger technology has also developed with modern electronics, first to closely regulated constant voltage chargers then smart multi stage chargers.
With this charge regime there is not much problem in using parallel banks of different capacity within reason.
Of course if you have a smart charger it is functioning in constant current mode for part of the charge cycle but with an accurately limited voltage so current declines once that limit is reached. The batteries may get a bit out of step but it is unlikely to go on long enough to do any harm and they should catch up in the constant voltage/declining current stage and on subsequent float.
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.
Manufacturers like PbCa because it is easier for health and safety/pollution - Sb is awful stuff - and has a better shelf life without recharge. Against that PbSb has better cycling and temperature resistance, especially with higher concentrations. Real cycling batteries - fork lift, floor sweeper (e.g T105) etc still tend to use 5-10% Sb. You get cycle life at the expense of more gassing and self discharge.
All the talk from PbCa people about PbSb high self discharge rates relates to traditional high Sb batteries. There isn't much difference between typical PbCa and Pb1.5%Sb.
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
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NPMR
Well-Known Member
I think I came to the same conclusion - that to get us through the next few weeks it will be Ok to substitute a bigger (capacity AND physical size) battery where we can and then change the other domestic battery over winter when we can get a saw and tools to re-model the actual bay.
The other thread (re 'where' and cable size) has at least given me an idea as to where I might be able to put everything!
bedouin
Well-Known Member
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. Either the larger one is likely to be undercharged, or the smaller one over charged and boil away the electrolyte. However neither of these are critical issues.
charles_reed
Well-Known Member
<< But Charles this is the whole point of the thread - can we mix battery sizes - not such a small matter>>
Yes, but separate them for charging into separate banks.
In fact, as Troubador points out, there are so many other variables that mixing sizes becomes relatively unimportant.
Yes, but separate them for charging into separate banks.
In fact, as Troubador points out, there are so many other variables that mixing sizes becomes relatively unimportant.
ghostlymoron
Well-Known Member
So in other words yes you can mix batteries of different size but no you can't mix battery types in the same bank. As pvb said about three days ago.
pvb
Well-Known Member
We get there in the end...