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Old 03-06-2012, 14:29   #31
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Re: Battery Cabling for Parallel Bank

Thanks for the responses Andina an Jbaffoh. It seems with every new thing I learn electrical, there seems to be 10 more things I need to learn, making me forever feel a novice........sigh.
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Old 05-06-2012, 03:17   #32
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Re: Battery Cabling for Parallel Bank

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Originally Posted by Andina View Post
No, if one battery is 0.2 volts less than another during the bulk charging mode the difference in charging current entering the battery will be negligible compared to other factors like internal battery resistance.*
Small voltage differences make a large difference in the accepted charge current. This is easily shown in practice.

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By the time the charger reaches the threshold of the bulk stage, the curren will no longer be 50 amps. *At that stage the battery voltage has increased and the current has dropped to about 5 amps. *So the 0.2 volts difference is now 0.02 volts.
0.2v is a *measure of the voltage difference I have typically measured while charging when the batteries are wired incorrectly. Try the measurement for yourself.
Th e only reason I used 50A was that was the figure you used. 5A is too low, charge currents at the start of the absorption phase will be much higher than this.*
Quote:
Originally Posted by Andina View Post
You are incorrect. *All battery charging sources are (quasi) CONStANT CURRENT, not constant voltage as you claim. *If they were constant voltage output the battery would have to be at the same voltage. *But in fact the voltage out of the charging source INCREASES as the battery voltage INCREASES. *They start out at (say) 12.4 volts and charge to (say) 14.2. *You will see that voltage both on the battery terminals and on the charger terminals (they are connected together). *That is hardly constant voltage.
When a charge source is connected to a battery the battery will typically accept more current than the charge source can deliver at least for a short time and the voltage will rise. There is no attempt to charge at a constant current. The current will rise and fall as the load, or the output of the charge sources changes.
When the voltage reaches the absorption set point the battery voltage will be kept at a constant voltage for the absorption set time ( usually 2 hours).
*During this time the voltage remains constant
The charge current falls
When the absorption time is finished the voltage is reduced to the float voltage
During this time the voltage remains constant
The charge current falls

Constant current charging is very different and is used for charging *alternative *battery chemistries *like NiCad
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Old 05-06-2012, 19:53   #33
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Quote:
Originally Posted by noelex 77
Small voltage differences make a large difference in the accepted charge current. This is easily shown in practice.

0.2v is a *measure of the voltage difference I have typically measured while charging when the batteries are wired incorrectly. Try the measurement for yourself.
Th e only reason I used 50A was that was the figure you used. 5A is too low, charge currents at the start of the absorption phase will be much higher than this.*

When a charge source is connected to a battery the battery will typically accept more current than the charge source can deliver at least for a short time and the voltage will rise. There is no attempt to charge at a constant current. The current will rise and fall as the load, or the output of the charge sources changes.
When the voltage reaches the absorption set point the battery voltage will be kept at a constant voltage for the absorption set time ( usually 2 hours).
*During this time the voltage remains constant
The charge current falls
When the absorption time is finished the voltage is reduced to the float voltage
During this time the voltage remains constant
The charge current falls

Constant current charging is very different and is used for charging *alternative *battery chemistries *like NiCad
Nolex

A charger in bulk mode is in constant current. The slope of a lead acid battery is fairly linear. The term constant current is widely used and is no difference from ni-cd or li-ion charging. It's constant current once the acceptance rate of the battery is in excess of the charger capacity.

Absorption current is a very low figure typically less then 20% of C in amps

A charger does not regulate battery voltage , it regulates its charge current . The battery terminal voltage follows suit according to its chemistry. For example a charger when absorption is finished does not " reduce the float voltage " what it does is reduce its charge current and accordingly the terminal voltage reduces. ( it in effect presents a higher output impedance )

Andina is quite right in relation to battery cable length. Small/medium length differences have no effect in practice and are drowned out by terminal and connectors resistance and internal battery resistance differences. Obviously taken to extremes it does have a measurable effect but within the confines of a typical battery box it's completely irrelevant.

Dave
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Old 05-06-2012, 20:18   #34
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Re: Battery Cabling for Parallel Bank

In making all of these battery connections, does anyone use any conductive/anti corrosive compound between the lugs on the wire and the battery terminals or do you just stack them dry and make sure the bolts are tight?
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Old 06-06-2012, 09:56   #35
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Re: Battery Cabling for Parallel Bank

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In making all of these battery connections, does anyone use any conductive/anti corrosive compound between the lugs on the wire and the battery terminals or do you just stack them dry and make sure the bolts are tight?
Personally I like Clean and Dry and Tight. Then if it is in a damp, corrosive location a little spray on protectant may help.
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Old 07-06-2012, 00:23   #36
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Re: Battery Cabling for Parallel Bank

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Originally Posted by goboatingnow View Post
Nolex
A charger in bulk mode is in constant current. *The slope of a lead acid battery is fairly linear. The term constant current is widely used and is no difference from ni-cd or li-ion charging. *It's constant current once the acceptance rate of the battery is in excess of the charger capacity.*
In bulk mode their is no regulation. The charge source cannot put out enough current to charge the battery as quickly as possible.The battery will accept whatever current it can get, this varies depending on the load, engine speed, amount of sun or wind.*
During the bulk phase an isolated battery on a mains charger can *be described as constant current, but in a boat system on a mains charger variations in load will mean this is not the case.*
The bulk phase with solar and wind *charging is never constant current. The absorption and float stages are *always constant voltage.

Some other battery chemistries *are *charged using a * constant current algorithm and this is *very different. The charger regulates the current which is kept constant throughout the charge cycle. The current at the beginning of charging and at the end of charging is exactly the same.*
Charging my AA Ni-MHbatteries for example the charge current starts at 2.00A and finishes at 2.00A. The voltage varies continuously during the charging. This is constant current charging.
The same charger will charge lead acid batteries these are charged at 2.4 v per cell for 3 hours then 2.3v per cell. The current varies continuously during charging. This is using a constant voltage algorithm.

The only time a * constant current algorithm is used for charging lead acid batteries is for *those batteries on permanent standby that can be fed a small *current to replace the self discharge. It is a cheap and easy way of maintaing charge. This is not typically *used for boat systems.

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Originally Posted by goboatingnow View Post
Absorption current is a very low figure typically less then 20% of C in amps*
Dave
That would be 80A for my 400AHr battery bank.
80A "very low current"!! That is a higher not a lower current than we have been discussing.*

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Originally Posted by goboatingnow View Post
A charger does not regulate battery voltage , it regulates its charge current . The battery terminal voltage follows suit according to its chemistry. For example a charger when absorption is finished does not " reduce the float voltage " what it does is reduce its charge current and accordingly the terminal voltage reduces. ( it in effect presents a higher output impedance )*
Dave
The voltage set points for absorption and float are controlled by the charger. With a small allowance for wiring The charge source voltage is the battery voltage.*
With the push of few buttons the battery *voltage can be be changed. The battery does not control the voltages durging absorption and float *the setting on the charger, or regulator does.*
Yesterday my batteries were charging for via solar.*
According to my regulator they spent 10 mins at a constant 14.2 v and just over 5 hours at a constant *13.7v . I cannot tell you what the charge current was because at no stage was the current constant. There was no constant current charging, but there was over 5 hours of constant voltage charging.
Did the battery choose these voltages?- no batteries are not that smart.
Even if I substituted a completely different battery the controller would maintain the same voltage. The controller obviously controls or regulates the battery voltage according to the chosen settings.
The charge source when regulating adjusts the battery voltage by altering its output current, but most charge sources do not know how much current is going into the batteries, even the very smart controllers and chargers that measure the actual battery current make no attempt to keep this current constant. They keep the battery voltage constant.

Quote:
Originally Posted by goboatingnow View Post
Andina is quite right in relation to battery cable length. Small/medium length differences have no effect in practice and are drowned out by terminal and connectors resistance and internal battery resistance differences. *Obviously taken to extremes it does have a measurable effect but within the confines of a typical battery box it's completely irrelevant.*
Dave
I agree the major resistance is in the connectors. If you read the posts you will see I pointed this out to Andina.
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Old 07-06-2012, 02:28   #37
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Re: Battery Cabling for Parallel Bank

Quote:
n bulk mode their is no regulation. The charge source cannot put out enough current to charge the battery as quickly as possible.The battery will accept whatever current it can get, this varies depending on the load, engine speed, amount of sun or wind.*
During the bulk phase an isolated battery on a mains charger can *be described as constant current, but in a boat system on a mains charger variations in load will mean this is not the case.*
The bulk phase with solar and wind *charging is never constant current. The absorption and float stages are *always constant voltage.
Its is conventional to regards any current source that is in effect operating at max amps to be in constant current mode. i.e. the load ( which may be battery plus active system loads) are equal to or in excess of the chargers capacity , This is a fairly common situation in bulk mode. Hence for all intents and purposes the charger is in constant current mode. In fact the charger circuits must be designed to operate in such a mode.

Obviously once the charger current falls below the max "constant current", active regulation begins again.


Quote:
According to my regulator they spent 10 mins at a constant 14.2 v and just over 5 hours at a constant *13.7v . I cannot tell you what the charge current was because at no stage was the current constant. There was no constant current charging, but there was over 5 hours of constant voltage charging.
Did the battery choose these voltages?- no batteries are not that smart.
Even if I substituted a completely different battery the controller would maintain the same voltage. The controller obviously controls or regulates the battery voltage according to the chosen settings.
The charge source when regulating adjusts the battery voltage by altering its output current, but most charge sources do not know how much current is going into the batteries, even the very smart controllers and chargers that measure the actual battery current make no attempt to keep this current constant. They keep the battery voltage constant.
Battery chargers are not true regulators, they cannot be. A charger cannot lower the battery terminal voltage to a level unless the battery chemistry allows it.

I wasn't suggesting the battery sets a "particular" voltage. I was pointing out that voltage regulation of a battery voltage by a charger is actually done by varying the charge current. The battery chemistry determines the response, and the charger monitors the resulting voltage, continuously adjusting the charge current to "attempt" to maintain the terminal voltage.

As an example if you "could" set a float voltage say to 12V, do you think your charger could actually regulate a fully charged battery to that voltage , of course not. even if the charger reduced its current to zero the terminal voltage would remain above the "desired" voltage . Equally if you have another voltage source , the charger cannot "regulate" to a lower voltage , why because chargers cannot sink current.

While its technical semantics, I admit, the battery chemistry determines for a given current ( flowing in or out) what the terminal voltage will be ( give or take the effect of the complex impedance model of the battery). The charger merely regulates its one current ( as that is all it can control) to "hopefully" achieve the desired terminal voltage.


Sorry re absorption current I meant to say a 20th of C in amps i.e. 5%.

Dave
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Old 07-06-2012, 10:20   #38
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Re: Battery Cabling for Parallel Bank

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Originally Posted by goboatingnow View Post

While its technical semantics, I admit, the battery chemistry determines for a given current ( flowing in or out) what the terminal voltage will be ( give or take the effect of the complex impedance model of the battery). The charger merely regulates its one current ( as that is all it can control) to "hopefully" achieve the desired terminal voltage.

Dave
The battery determines the current. The charge source - alternator regulator, AC charger, or solar controller - sets voltage. For a given voltage the battery will accept a given amount of current - it cannot be forced in unless the voltage of the source is increased. As long as the battery is not demanding more than the source can supply it will accept the same current from a 40 amp charger as a 400 amp charger set at the same voltage. The charger regulates voltage.
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Old 08-06-2012, 04:50   #39
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Re: Battery Cabling for Parallel Bank

Hi All,

Can someone explain to me battery cable sizes? Cable in Aust seems to some times called gauges and sometimes some other number?

What is a good battery cable size to get?

My local marine shop doesn't sell tinned battery cable, so I'm going to have to get that from the mainline on the internet.

Ted.
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Old 08-06-2012, 05:26   #40
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Re: Battery Cabling for Parallel Bank

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Hi All,

Can someone explain to me battery cable sizes? Cable in Aust seems to some times called gauges and sometimes some other number?

What is a good battery cable size to get?

My local marine shop doesn't sell tinned battery cable, so I'm going to have to get that from the mainline on the internet.

Ted.
Here is a good place to start:
American wire gauge - Wikipedia, the free encyclopedia
and perhaps better
AWG to square mm Wire Gauge Conversion

It essence, most electrical wire in Australia is sold in metric cross sectional area (e.g 6 sq mm) but it can be found in AWG (or B&S) in specialised industries like aviation and marine. Whitworths Marine sell smaller wire in cross sectional mm and battery cable in B & S (AWG).

See https://www.whitworths.com.au/main_l...=Battery+Cable
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Old 08-06-2012, 05:50   #41
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Re: Battery Cabling for Parallel Bank

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..........

My local marine shop doesn't sell tinned battery cable, so I'm going to have to get that from the mainline on the internet.

Ted.
I know you guys in Lonnie have an aversion to the big smoke down south and the apple eating fellas down south will run you outa town like faceless devil if they spot you but perhaps you could wombat down and get your wire in Hobart
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Old 08-06-2012, 09:59   #42
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Re: Battery Cabling for Parallel Bank

2/0 (67.4 mm2) or 1/0 (53.46 mm2) would be good choices for battery cables. I do not use anything smaller than 1/0 normally.
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Old 08-06-2012, 11:03   #43
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Re: Battery Cabling for Parallel Bank

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The battery determines the current. The charge source - alternator regulator, AC charger, or solar controller - sets voltage. For a given voltage the battery will accept a given amount of current - it cannot be forced in unless the voltage of the source is increased. As long as the battery is not demanding more than the source can supply it will accept the same current from a 40 amp charger as a 400 amp charger set at the same voltage. The charger regulates voltage.
HUH? You have it brass ackwards.

"The charger . . . sets the voltage?"

No the state of charge and the amount of current flowing sets the voltage. Read the voltage on your battery and then read the voltage on your charger. Except for slight a slight drop along the cable THEY ARE AT THE SAME VOLTAGE. The charger is not setting a voltage, it is putting out current and the factors setting voltage are the state of charge and internal resistance of the battery. If the charger put out more current the voltage at the battery terminals would be higher. When it goes to the next mode and puts out less current the voltage on the battery terminals drops.

The battery sets the voltage. As current flows in and the charge state increases, the battery terminal voltage increases proportionally.

All the charging source does is decide when the battery voltage has reached the next threshold and CHANGES THE AMOUNT OF CURRENT so the battery is not over charged. Only when you get to the maintenance stage does the charger actively control the amount of current in order to maintiain a constant voltage.

" it will accept the same current from a 40 amp charger as a 400 amp charger set at the same voltage. "

Excuse me but where is the knob to set the voltage? They are all 12 volt chargers. There IS no VOLTAGE adjustment. How would you set the "voltage" on a 15 amp charger to limit it to 5 amps? There is no such adjustment.

On a discharged battery a 400 amp charger will put out a hell of a lot more current than a 40 amp charger and a 15 amp charger will charge a lot faster than a 5 amp charger.

Some of the confusion may be over HOW the charger regulates the current. That process is internal to the charger and can take different forms depending on how it is designed. In older chargers they had a series resistance and a high internal voltage. The current supplied was the difference between the INTERAL voltage (to which we have no access or control) and the battery voltage divided by the internal charger resistance. However that is very inefficient wasting considerable power in the resistor and generating heat. Modern chargers have more sophisticated methods of regulating the current and referring to the inaccessible INTERAL voltage of the charger is meaningless. That voltage is constant and not adjustable. It could be as much as 25 or 30 volts to provide a voltage source for the electronic current regulator.
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Old 08-06-2012, 11:25   #44
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Ok, now I'm confused.

If changes in voltage that accompany changes in charge modes are solely a function of charger current changes, then why do I observe this in my setup? My solar controller will bring the batteries to 14.5 at around 3.5 amps (depending on solar energy). After absorption, the voltage drops to around 13.4, while the current remains around 3.5 amps. As the voltage rises to 13.52, the current begins to taper down near zero.
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Old 08-06-2012, 11:28   #45
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Re: Battery Cabling for Parallel Bank

Thank God Andina, somewhere here understands electronics, its like talking to the deaf.

+1 on you post

mitiempo, what you are describing is how a "lay man " sees it . Its not what actually happens. Most people do not understand circuit theory, equivalent impedance models etc. So they have a "water in the bucket" understanding of electronics. In real life its much more complex and counter intuitive .



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