PaulRainbow
Well-known member
What batteries are you using that can be on a 25a charge for 24 hours and still accept a 25a current ?
Charging one battery using two Aldi / Didl smart chargers simultaneously
- Thread starter CAPTAIN FANTASTIC
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jakew009
Well-known member
6 x 280Ah LiFePO4 in parallel
But the size of the battery bank is irrelevant, a 60Ah battery behaves exactly the same. Lead will get to absorption at 70% or so.
PaulRainbow
Well-known member
A 1680ah LifePO4 bank, connected to a 25A fixed output charger is hardly relevant to a typical boat with 200ah/300ah of LA batteries.
billskip
Well-known member
Big ones?
Refueler
Well-known member
Awwww Paul ... Don't let that spoil his fun !!
noelex
Well-known member
Here is a practical example showing the effect of one, two, and then three chargers connected to one battery bank.
These are three identical solar chargers, but the algorithm and result would be identical mains-powered chargers.
As you can see:
One charger is delivering 235W.
Two chargers are delivering 464W.
Three chargers are delivering 700W.
If the test was repeated later in the day when the lead-acid batteries had a higher state of charge, the limited charge acceptance would start to kick in. The battery bank would be unable to safely accept the full 700W output, but this is equally true if there was a single 700W charge source.
This shows how three chargers each capable of delivering around 233W are behaving the same as a single charge source capable of delivering 700W.
These are three identical solar chargers, but the algorithm and result would be identical mains-powered chargers.
As you can see:
One charger is delivering 235W.
Two chargers are delivering 464W.
Three chargers are delivering 700W.
If the test was repeated later in the day when the lead-acid batteries had a higher state of charge, the limited charge acceptance would start to kick in. The battery bank would be unable to safely accept the full 700W output, but this is equally true if there was a single 700W charge source.
This shows how three chargers each capable of delivering around 233W are behaving the same as a single charge source capable of delivering 700W.
PaulRainbow
Well-known member
The following screenshot was taken earlier today, with the mains charger off.
I turned the mains charger on and the solar worked OK for a while, but as the batteries SOC rose, the solar reduced
I imagine a couple of people will now claim that the reason the solar yield has now dropped is because the batteries are almost fully charged, but note the shore charger is still putting 29.2A into the batteries.
In addition, after a little longer i turned the shore power off and the solar immediately did this:
I turned the mains charger on and the solar worked OK for a while, but as the batteries SOC rose, the solar reduced
I imagine a couple of people will now claim that the reason the solar yield has now dropped is because the batteries are almost fully charged, but note the shore charger is still putting 29.2A into the batteries.
In addition, after a little longer i turned the shore power off and the solar immediately did this:
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PaulRainbow
Well-known member
I can remotely monitor one of my customers boats, using the Victron VRM portal. He has 400W of solar and has harvested 0.1 kWh today. I have 900W of solar and have harvested 0.9 kWh today. His shore charger has been on all day, mine only comes on at 50% DOD, until the batteries reach 60% DOD, i don't like wasting free electricity. 
billskip
Well-known member
Did you look up to see if there was a big black cloud ,or solar eclipse...
PaulRainbow
Well-known member
I did look, but didn't see oneDid you look up to see if there was a big black cloud ,or solar eclipse...
noelex
Well-known member
The solar panel output has reduced to stop the battery voltage riding above the voltage set point and damaging the battery. The 939W put out by the Multiplus is as much as the battery can accept. The charging system looks to be behaving just as it should. If you had a larger shore charger, it would also be throttling back at this stage to prevent the battery voltage climbing over the voltage set point.
Incidentally, if you increase the voltage set point of the solar controller slightly (and/or decrease the set point of the mains charger), the mains charger will reduce its output first. There is no reason not to utilise the full solar output. I always set up my chargers (including the alternator)this way so the solar output is the last to throttle back when the charging current available is more than the battery bank can accept. Solar is free, has no wear and tear, and is better for the environment.
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PaulRainbow
Well-known member
The two chargers have the same settings, how does that add up to more volts ?
Huh ?
A picture is worth a thousand words.
noelex
Well-known member
The voltage set points are never exactly the same even if set to the same numerical value. There are always minor inaccuracies in the voltage measuring circuitry and voltage drop in the cabling. The Victron units are very good here as the voltage set points can be adjusted in very fine one-hundredth of Volt steps.
For example, if your absorption set point on both a battery charger and solar regulator is 14.20V. If the solar regulator is cutting out first (as your examples show), bump up the set point on the solar controller slightly (for example, to 14.24V). When the battery voltage reaches 14.20V, the battery charger will start reducing its output, but the solar regulator will continue its full output as its slightly higher voltage set points have not been reached. I have used the technique for many years, and it works well.
When the charge sources can output more than the battery is capable of safely accepting, it is helpful to have as much power as possible from solar and less from shore power or the engine alternator.
noelex
Well-known member
I am not sure what you are puzzled about. I am referring to your post #47.
The MultiPlus is putting out 33.5A @ 28.03V or 939W. The battery voltage at 28.03V is obviously at or above the voltage set point of the Victron solar controller, or the current has dropped below the tail current value; otherwise, it would not have stopped charging. If these settings are correct and you wanted the maximum charge voltage to be 28.03V, all is fine. If not, the settings should be changed.
If tail current is the problem, this is easy to disable in the software— something I would strongly recommend if you have multiple charge sources, especially multiple solar controllers.
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PaulRainbow
Well-known member
No tail current on either charger.
noelex
Well-known member
Good
.Did you want the chargers to maintain an absorption voltage of 28.03V (or thereabouts) as achieved with both chargers on as shown in post #47, or did you want another value?
PaulRainbow
Well-known member
Thanks for the input, but everything is working exactly as i want it to.Good
Did you want the chargers to maintain an absorption voltage of 28.03V (or thereabouts) as achieved with both chargers on as shown in post #47, or did you want another value?
noelex
Well-known member
That is what is important.
With multiple chargers, people often feel one charger is becoming "confused" if the output is not equally shared between the charge sources. This is usually not the case (although in rare cases, problems can occur).
For example, if we have two identical 10A chargers, if the battery is discharged, it will likely initially take the full 20A charging current without the battery voltage rising above the bulk/absorption limit, but as the battery becomes more charged, the current the battery will accept without exceeding the bulk/absorption limit will decrease.
When this reaches, for example, 10A, you may expect each charger would contribute 5A. This does happen, but more commonly, one charger predominates and may even contribute the full 10A. This is when it is easy to believe one charger is "confused" by the output of the other. In reality, the battery does not care if 5A comes from each charger, 10A from one, and zero from the other, or some other mix.
jakew009
Well-known member
The graph is literally identical on a 60Ah battery. It just gets to absorption quicker.
Refueler
Well-known member
Now we start to converge on posts .... WOW .. who would have believed it !!