Charging one battery using two Aldi / Didl smart chargers simultaneously

[jakew009]

What is it with threads about battery chargers and people coming up with hair brained ideas about how chargers work

All battery chargers work in exactly the same way. The ONLY thing a battery charger can directly control is the voltage it is outputting.

If you connect a charger set to output 14.6V to a flat battery that is sitting at 10V, a massive amount of current would be pulled from the charger which it could not possibly supply (say 500A when it’s maximum output is 5A). The charger would immediately go into over current protection mode and shut off.

In order to protect itself, the charger will reduce its voltage until such a point the current is just below it’s maximum output.

Current = voltage / resistance.

As the battery starts to charge, its voltage will increase. As the batteries voltage increase, the current being supplied by the charger would gradually reduce until it stopped entirely when the two voltages were equal.

However, the charger continue to gradually bump up the voltage being supplied to maintain the current flow at just below it’s rated capacity as the battery charges.

Eventually the charger gets to its upper voltage limit where it’s not safe to go any higher (absorption). At this point the current going into the battery reduces (as the voltage differential reduces) until essentially no current is flowing (the tail current).

At this point a smart charger will revert to float mode (at say 13.8V) or some will just switch off entirely.

With the above in mind, it’s pretty easy to work out what will happen if you have two chargers connected:

If the battery is discharged, both battery chargers will work together to charge the battery. Both chargers will be limiting their voltage to limit themselves to 100% rated output.

Once the voltage of the battery rises (and it nears fully charged), one of the chargers may drop to float mode sooner than the other if it has a different absorption voltage configured.

If both chargers are identical they will generally both drop to float mode at basically the same time.

The exact same process applies to a MPPT solar charger. If you configure the solar charger with the same absorption voltage it will not “take a rest” as soon as the mains charger is connected.

Some chargers will have slightly different logic as to when to terminate a charge or when to start a new cycle, but when connected to a deeply discharged battery, they will ALL work the same.

 

[jakew009]

Ok a question, (or two)
If you put the smart charger on the battery terminals that where it gets its information correct?
If that battery allready has a charger connected wll that information be the same?

Just because you connect a battery charger to a battery, does not mean the voltage of the battery will magically rise to the same as the charger. On a deeply discharged healthy battery, the voltage on the terminals with or without the charger connected will be similar.

Therefore it will have virtually no impact on a secondary charger.

 

[jakew009]

You still don't see the wood for the trees !!

If you have two chargers connected to one battery .... they will both be feeding charge to that battery ... but the voltage they are feeding at is over 13V and as far as one or both chargers are concerned - is full charge battery .. so what will the chargers do ??

Forget what level the battery is at ... its what each charger sees from other charger ...

This is absolute cobblers, noelex is 100% correct.

If the voltage one charger is putting out is affecting the other charger, the battery is fully charged anyway (or completely knackered) and it’s a moot point.

If the battery is discharged, both chargers will work at 100% in constant current mode until one of them hits its absorption voltage limit.

 

[jakew009]

I read replies and I think what is missing from most :

The Lidl Smart Charger works by gauging the resistance against the chargers charge to the battery. This is mainly based on Voltage of battery vs the Chargers Voltage.

The Lidl chargers have no user adjustable settings - only fixed mode buttons. So putting two together will have identical outputs (subject to them being budget chargers of course) ... this means that both will be putting out higher voltage than the battery - but each charger will see the 'other' chargers voltage ... so charge rate will be reduced as it thinks battery is at high state.

I suggest that take away one charger and let remaining one do its job properly.

This is absolutely nonsense too, no charger works by “gauging the resistance against the chargers charge to the battery” (what does that even mean?)

Each charger will put out the maximum voltage it can whilst staying within its maximum current limit up to it’s absorption voltage. That’s why it’s called the ‘constant current’ stage..

 

[billskip]

Just because you connect a battery charger to a battery, does not mean the voltage of the battery will magically rise to the same as the charger. On a deeply discharged healthy battery, the voltage on the terminals with or without the charger connected will be similar.

Therefore it will have virtually no impact on a secondary charger.

You didn't answer my question (s)
I have measured the battery voltage at the terminals and have got a reading , connected a charger and got a different reading. So please explain where the battery chargers get their information if not the terminals.

 

[jakew009]

You didn't answer my question (s)
I have measured the battery voltage at the terminals and have got a reading , connected a charger and got a different reading. So please explain where the battery chargers get their information if not the terminals.

Of course the only place they can get their information from is the terminal.

But unless the voltage you measured is up at absorption level and the battery is already almost full, it’s not going to make one jot of difference.

 

[Blue Seas]

I think that there may be more to it than is being implied by some - Yes, if you put two identical chargers on then, at least in the initial charging phases you will get more more charge than you would get with one alone - but, Victron themselves build in algorithms that allow one charger to act as 'Master' in multiple charger set ups thereby controlling then other chargers as 'Slaves'. They also have built-in protection so that if the Master fails then one of the Slaves will be instructed to take over as Master.

Victron themselves say;

Synchronized parallel charging
Synchronize up to ten battery chargers in a VE.Smart network to make them charge a battery as if they were one large charger. The chargers will synchronize the charge algorithm between them. They will simultaneously switch from one charge state to another, for example from bulk to absorption.
Synchronized parallel charging has several interesting advantages:
- Redundancy: if one charger stops for whatever reason, the other chargers will continue to operate. - Flexibility: simply add a charger to the network if more current is needed.
- Cost: several low power chargers will in general cost less than one high power charger.
- Installation: several low power chargers may be easier to fit in a confined space.

 

[Refueler]

This is absolutely nonsense too, no charger works by “gauging the resistance against the chargers charge to the battery” (what does that even mean?)

Each charger will put out the maximum voltage it can whilst staying within its maximum current limit up to it’s absorption voltage. That’s why it’s called the ‘constant current’ stage..

View attachment 187769

Charger will output CC and CV depending on the level of charge in the battery - the level of charge in the battery which creates a resistance to charge. The higher the charged level of the battery - the higher the resistance against the charger ...

Many chargers claim Constant Current - but in reality - they only maintain that for short period before the amp rate starts to drop while voltage stays up ...

My wording may not meet your technical standard - but it was put in simple terms of what is observed ............

I have various chargers from the simple 1A trickle maintainers through to boost 70A unit ... all that have displays show the reducing amp charge rate as battery charges up and resists chargers output. They do not as manufacturers like to BS us with - have sharp change points ....

As to OP and his two chargers ... at best he can only expect a rate barely greater than a single charger on its own ..

 

[noelex]

They do not as manufacturers like to BS us with - have sharp change points ....

There are sharp change points between the absorption and float stages (on modern multistage chargers). Typically the charger will suddenly change from an output voltage of around 14.4V to around 13.7V. This change in output voltage will result in a significant difference in output current as the battery will accept a lower current at a lower voltage. This is easily seen when using battery chargers as well as solar regulators etc if you happen to be watching the battery monitor at the time of the change.

 

[billskip]

The charger maintains a constant voltage during these phases

Typically the charger will suddenly change from an output voltage of around 14.4V to around 13.7V.

You may say this is taken out of context, and maybe it is ...but in the understanding of a complete nonplussed it's confusing.
Time you tried explaining what works in practice rather than how chargers work in theory...

In practice a charger will work on the information it gets from the battery terminals...this information can be distorted with the connection of another charger.

 

[noelex]

Time you tried explaining what works in practice rather than how chargers work in theory...

See post #18 or the graph posted by Jakew in post #24.

In practice a charger will work on the information it gets from the battery terminals...this information can be distorted with the connection of another charger.

Despite the name, smart chargers are really not that intelligent, most are following a simple algorithm or formula to charge the battery.

An analogy would be navigating following simple directions such as "travel 5 miles north, then turn east for 2 miles, and you will arrive at our house". You could walk, run, or drive and arrive at the same point without any confusion.

 

[Refueler]

There are sharp change points between the absorption and float stages (on modern multistage chargers). Typically the charger will suddenly change from an output voltage of around 14.4V to around 13.7V. This change in output voltage will result in a significant difference in output current as the battery will accept a lower current at a lower voltage. This is easily seen when using battery chargers as well as solar regulators etc if you happen to be watching the battery monitor at the time of the change.

I watch displays a lot - its habit generated by charging many different forms of Lithium - where unattended can lead to dire consequences.

 

[Refueler]

You may say this is taken out of context, and maybe it is ...but in the understanding of a complete nonplussed it's confusing.
Time you tried explaining what works in practice rather than how chargers work in theory...

In practice a charger will work on the information it gets from the battery terminals...this information can be distorted with the connection of another charger.

Bill - we are wasting our effort trying to get practical observation through to those who insist on following Technical ...

I particularly like this one :

"This change in output voltage will result in a significant difference in output current as the battery will accept a lower current at a lower voltage"

 

[PaulRainbow]

I'd like someone to explain how you can charge a battery without the charger output voltage being higher than the actual voltage of the battery.

As far as solar controllers not being affected by mains chargers, anyone who believes that needs to treat themselves to a decent battery monitor.

 

[billskip]

Bill - we are

I'd like someone

You two are trying to get me shore leave..

 

[jakew009]

I'd like someone to explain how you can charge a battery without the charger output voltage being higher than the actual voltage of the battery.

Has anyone said you can? The voltage difference between the charger and the battery is what ‘pushes’ current into the battery.

If you have two chargers connected to a battery that both have higher voltages than the battery, they will both charge the battery.

If you have two chargers connected to the battery, one with a higher voltage than the battery and one with a lower voltage than the battery, only the one with a higher voltage will charge the battery whilst the other does nothing.

As far as solar controllers not being affected by mains chargers, anyone who believes that needs to treat themselves to a decent battery monitor.

Here is a battery that has been on charge for the past 24 hours

It is connected to a mains charger that delivers a constant 25A. The graph doesn't show the full 25A because a couple of amps is powering the actual cctv tower that this graph comes from.

You can see the purple line which is the current. The blue line is the voltage which has gradually risen as the battery charged.



When the sun came out at about 10AM, the VIctron solar charger also kicked in. You can see that in this graph. That's why the current increases from 23A to ~30A when the sun was out. It wasn't a very sunny day hence and it's not in a great location or we would have seen a much larger boost from the solar.



I don't know how you can possibly say that a solar charger will be affected by a mains charger. If they both have the same absorption voltage they are both doing exactly the same thing!

Fwiw's this is a Victron solar charger (MPPT 100/50) and a mains charger that we designed. And it's not in a boat but wired in exactly the same way.

 

[WoodyP]

And while you lot are at it, can anybody advise how many angels can dance on the head of a pin. Not helpful, l know, but it's all I've got.

 

[jakew009]

Charger will output CC and CV depending on the level of charge in the battery - the level of charge in the battery which creates a resistance to charge. The higher the charged level of the battery - the higher the resistance against the charger ...

That's partially true but it depends on the type of battery. A lithium battery whatever charge current you can throw at it up to 99% full. A lead acid battery will charge slower as it gets above 70% or so.

Many chargers claim Constant Current - but in reality - they only maintain that for short period before the amp rate starts to drop while voltage stays up ...

The charger can maintain the constant current for eternity. However, as the battery approaches 100% capacity, the rate at which it will accept charge slows down until it eventually stops completely.

My wording may not meet your technical standard - but it was put in simple terms of what is observed ............

With respect, your observations are just plain incorrect.

I have various chargers from the simple 1A trickle maintainers through to boost 70A unit ... all that have displays show the reducing amp charge rate as battery charges up and resists chargers output. They do not as manufacturers like to BS us with - have sharp change points ....

The charge rate may well decrease, but that's a function of how much current the battery will accept rather than anything the charger is controlling.

As to OP and his two chargers ... at best he can only expect a rate barely greater than a single charger on its own ..

Nope. Two identical chargers will result in a charge current that is precisely twice a single charger on it's own (as long as the battery is capable of accepting twice the charge current).

 

[Refueler]

That's partially true but it depends on the type of battery. A lithium battery whatever charge current you can throw at it up to 99% full. A lead acid battery will charge slower as it gets above 70% or so.


The charger can maintain the constant current for eternity. However, as the battery approaches 100% capacity, the rate at which it will accept charge slows down until it eventually stops completely.


With respect, your observations are just plain incorrect.


The charge rate may well decrease, but that's a function of how much current the battery will accept rather than anything the charger is controlling.


Nope. Two identical chargers will result in a charge current that is precisely twice a single charger on it's own (as long as the battery is capable of accepting twice the charge current).

You've already countered your own argument ...

No-one says a charger cannot maintain a rate - amps and voltage - but that rate depends on the charged level of the battery which causes the resistance to accepting charge.

I suggest you go out and try your two charger theory ... because you will be surprised to find you are wrong.

 

[jakew009]

You've already countered your own argument ...

No-one says a charger cannot maintain a rate - amps and voltage - but that rate depends on the charged level of the battery which causes the resistance to accepting charge.

I suggest you go out and try your two charger theory ... because you will be surprised to find you are wrong.

Very happy to try it in the morning. So 2 25A chargers connected to one battery? Any other requirements for the test?