lw395
Well-Known Member
In as much as the 'resistance' of something as non-linear as a battery is a valid concept, yes, sort-of.
The big variable is the state of charge.
Then there's the temperature.
Can a high charging current be harmful, even though the charging voltage is correct?
- Thread starter BabaYaga
- Start date
In as much as the 'resistance' of something as non-linear as a battery is a valid concept, yes, sort-of.
The big variable is the state of charge.
Then there's the temperature.
lw395
Well-Known Member
The wires will have resistance.
The alternator will have an output impedance. Probably mostly dominated by the V/I curve of the output diodes. If you take a typical 150A diode, that will drop something like 0.6V at 10A and 0.8V at 100A.
There's a diode in the path on both + and - sides, so there goes 0.4V.
It's not as simple as that as the alternator is a 3 phase thing sharing current around 3 pairs of diodes. The regulation may or may not correct for the drop on one side. But basic automotive alternators are designed with an output impedance, I doubt it's even a design aim to keep the volts exactly stable regardless of current.
Modern vehicles are not so simple. I think some of them shove quite high currents into lead-acid batteries when braking or going downhill. But they are not simply voltage regulated.
pvb
Well-Known Member
If your charging circuit has such a high voltage drop when charging at higher current, doesn't that simply mean that the wiring is undersized?
Alternators are regulated to maintain a certain output voltage, irrespective of what might happen internally with diodes.
GHA
Well-Known Member
Bearing in mind there's no such thing as bulk voltage, in what's commonly known as the bulk phase on most boats the lead acid batts will take whatever current is available from the charger then the current they will accept will tail off as the voltage rises up to the absorption limit controlled by the charger. Not possible to limit the max current by voltage regulation unless you have the absorption voltage set so low that it will take days to recharge.
PaulRainbow
Well-Known Member
I think you'll find those Trojan figures are "recommended max current" rather than "if you exceed this the World will end" currents.
Perhaps, in an ideal World, we should be charging at the recommended voltages, using equipment that limits max current. In the real World of boats, we don't and batteries seem to last a reasonable time. If we start fitting charging systems grossly mis-matched to the batteries and use of the boats, it might be a different matter. It's all about having as much of a balance between the batteries, the loads they are subjected to and the output of the charging systems.
Perhaps, in an ideal World, we should be charging at the recommended voltages, using equipment that limits max current. In the real World of boats, we don't and batteries seem to last a reasonable time. If we start fitting charging systems grossly mis-matched to the batteries and use of the boats, it might be a different matter. It's all about having as much of a balance between the batteries, the loads they are subjected to and the output of the charging systems.
pvb
Well-Known Member
I didn't suggest there was, I said that battery manufacturers specify the ideal charging voltages for the bulk charge and float charge.
GHA
Well-Known Member
Yet to see anything like that. Datasheets will have recommended voltage maximums for absorption , but by the time the voltage has been pushed up that high the current will have tailed off substantially.
Wrong.
pvb
Well-Known Member
I'm surprised you're not aware of recommended voltages for bulk charge and float charge. Take a look at the Trojan T-105 data sheet for just one example - http://www.trojanbattery.com/pdf/datasheets/T105_Trojan_Data_Sheets.pdf
GHA
Well-Known Member
Yes, limits. There is no such thing as bulk voltage. Not great wording on their part,
https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf
o Phase 1: Constant current bulk chargeA constant current equal to 10-13% of C20 is applied as the voltage slowly increases.The bulk phase ends when the voltage rises to the absorption voltage.
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pvb
Well-Known Member
I think you're being deliberately obtuse. The Trojan data sheet specifies "charger voltage settings", it doesn't say "bulk voltage", nor does it say "maximum" or "limit".
GHA
Well-Known Member
See the edit.
You worded it very badly and got called up on it.
https://www.trojanbattery.com/pdf/Tr...UsersGuide.pdf
o Phase 1: Constant current bulk chargeA constant current equal to 10-13% of C20 is applied as the voltage slowly increases.The bulk phase ends when the voltage rises to the absorption voltage.
That's wrong.
lw395
Well-Known Member
Have you every measured the V/I curve of an alternator across a range of RPM?
Maybe you ought to go and do so before pronouncing with such certitude.
Then do the maths for a typical cable run.
pvb
Well-Known Member
Alternator rpm affects the current it can potentially supply; the voltage is regulated to a maximum by the regulator.
pvb
Well-Known Member
GHA
Well-Known Member
Did you read the previous post? Badly worded on their part as in yours. Give in and admit it. There is no such thing as bulk voltage and talking about bulk voltages is meaningless and unhelpful.
One more time...
https://www.trojanbattery.com/pdf/Tr...UsersGuide.pdf
o Phase 1: Constant current bulk chargeA constant current equal to 10-13% of C20 is applied as the voltage slowly increases.The bulk phase ends when the voltage rises to the absorption voltage.
Wrong. Completely wrong.
pvb
Well-Known Member
I haven't the faintest idea what you're continuing to argue about. If you don't like Trojan's wording, write to them and tell them, I'm really not interested.
BabaYaga
Well-Known Member
Thanks for your further comments.
Some disagreement here, as always on these subjects...
As the OP, I thought I would attempt to sum up some things that I believe to have learned from this thread, so far:
When the maximum available charging current is modest in relation to the overall Ah capacity of the battery (modest' could be 10, 13 or maybe 20 percent of Ah) a well discharged battery will likely accept this maximum current continously during the bulk phase, i.e. while the voltage gradually rises and eventually reaches the set point, which marks the start of absorption.
In this case the current seen will depend, not on the battery, but on what the charging source can supply: For a mains charger the maximum output current or for an alternator the rating and engine RPM.
To me, it seems unlikely that a battery could be harmed because of the charging current being 'too high' in such circumstances.
When the available charging current is higher with respect to the total battery capacity, the course of the bulk phase will be different (if I have understood various comments correctly):
After a period of maximum current output, in some cases a very short time, the current will begin to taper off. Not because of some limitation of the charging source or its regulation, but because the charge acceptance of the battery goes down as the state of charge goes up (despite the battery being far from fully charged, as we are still in bulk phase).
Now, is there potential for the battery to come to harm in this scenario?
Obviously Volvo Penta with their 115A alternators and many mains charger manufacturers do not think so. Trojan batteries might take a different view.
To me at least, it looks like this condition might be a bit more demanding for the battery, perhaps in connection with a rise of temperature? If so, there could be an increased risk for some damage or reduced life span.
But significant or not? Hard to know....
Some disagreement here, as always on these subjects...
As the OP, I thought I would attempt to sum up some things that I believe to have learned from this thread, so far:
When the maximum available charging current is modest in relation to the overall Ah capacity of the battery (modest' could be 10, 13 or maybe 20 percent of Ah) a well discharged battery will likely accept this maximum current continously during the bulk phase, i.e. while the voltage gradually rises and eventually reaches the set point, which marks the start of absorption.
In this case the current seen will depend, not on the battery, but on what the charging source can supply: For a mains charger the maximum output current or for an alternator the rating and engine RPM.
To me, it seems unlikely that a battery could be harmed because of the charging current being 'too high' in such circumstances.
When the available charging current is higher with respect to the total battery capacity, the course of the bulk phase will be different (if I have understood various comments correctly):
After a period of maximum current output, in some cases a very short time, the current will begin to taper off. Not because of some limitation of the charging source or its regulation, but because the charge acceptance of the battery goes down as the state of charge goes up (despite the battery being far from fully charged, as we are still in bulk phase).
Now, is there potential for the battery to come to harm in this scenario?
Obviously Volvo Penta with their 115A alternators and many mains charger manufacturers do not think so. Trojan batteries might take a different view.
To me at least, it looks like this condition might be a bit more demanding for the battery, perhaps in connection with a rise of temperature? If so, there could be an increased risk for some damage or reduced life span.
But significant or not? Hard to know....
halcyon
Well-Known Member
see #2
Get back when I have some work finished.
Brian
Get back when I have some work finished.
Brian
yourmomm
Well-Known Member
Sheesh thanks for this summary. I was losing the will to live, trying to make sense of all of this. My experience is only real-world, I have absolutely no theoretical knowledge, despite trying to learn on a number of occasions (and wiring my own boats, <gulp>).
So, all I know is that as long as my 7 stage 50A charger had the correct battery type selected (liquid/gel/agm, which limits the max voltage), then its never (apparently) harmed any battery I've charged with it at full power: even a measly 74ah....it just down regulates the current, as required, and I've always understood that you'll get less charge accepted, if you charge at a higher rate (you can see this, whilst charging, as the charger will often switch to absorption phase on 50A, even though it remains in bulk charging phase if switched back to lower charging currents). But now I'm also wondering if charging at higher current repeatedly permanently lowers the amount of charge a battery can accept? Or whether, if you just revert to 2A charging, it will just revert to accepting the same charge 2A charge, it always allowed? Can someone give a simple yes / no answer to this?
However, if you accidentally select the wrong battery type (ie select liquid, when charging gel, or gel/liquid batteries in parallel), then you immediately fry the gel batteries. Dont ask me how I found this out....
So, from my perspective, when I'm in a marina, I charge slowly, with lower current, and when I'm charging on a generator (or engine for that matter), I charge at a much higher current. And I always ensure that gel is set to 14.1v, and no higher....
lw395
Well-Known Member
This 'charge accepted' malarkey is really a bit of wooly language.
Where is the charge that is rejected?
A charger set to 50A bulk charging will turn off its 'bulk charging LED' as soon as the current falls below 50A because the voltage limit has been reached.
That 's what 'bulk charging' is. The battery charger is operating as a source with a current limit and a voltage limit. Say 50A and 14.4V. If the load is drawing 50A, the volts will be below 14.4 and the current limit light will be on. If the current drops, the volts will rise to 14.4 and the voltage limit light will be on.
When the battery doesn't draw enough current to hit the current limit, it's charged at the voltage limit and we call that 'absorption'.
If you change the current limit to 25A, the same battery will operate the current limit until it's a lot more charged.
Around the middle of a charge cycle, it doesn't matter much whether we're current or voltage limited, what's happening in the battery is pretty much the same, unless the volts are so high that gassing is excessive.
