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Forum Index : Solar : Float/equalisation for this controller

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davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 493
Posted: 09:46pm 16 Feb 2020
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I think my question will relate to this specific controller this unit

I notice that when the battery is fully charged and there is excess PV that this controller always displays 14.4V (the default equalisation for sealed LA), which is the voltage on the battery.

I thought LA batteries were only suppose to be equalised for short periods of time.  I never see the battery drop back to the float voltage, which is adjustable, during any charge cycle.

I have two units which behave the same and could check a 3rd one.

Thanks,
Dave
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3254
Posted: 11:52pm 16 Feb 2020
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Only a guess...  
But a fairly typical battery charger control strategy might be not to drop down to float unless there is almost zero charging current being detected by the charger.

In other words, it bulk charges up to 14.4v (or whatever) at current limit.

When it reaches 14.4v the voltage then remains constant, and the current slowly ramps down in absorb charge mode.  
When the current falls below some minimum threshold, it then goes into float mode.
That is a fairly common way of doing things.

The problem with that for solar charging, is the battery may be constantly sourcing power to some kind of load, such as an inverter.  
The charger cannot tell where all the charging current is going, and it just sits constantly in absorb mode at the full 14.4v, and will not be able to drop down into float mode.

Its not a problem unless the battery gasses slightly at 14.4v, which it may do if the electrolyte gets hot enough. The very slow loss of water through electrolysis will the require frequent topping up, which is undesirable.

Car alternators typically charge to 14.1 to 14.2v and the battery gets quite warm in the engine compartment, and that all seems to work just fine.  A cooler battery and 14.4v is very likely not going to to be a problem.

Cell equalization should be a fairly infrequent requirement as you say, and its often up at 15v or more, where the battery gasses merrily.
Cheers, Tony.
 
davef
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Location: New Zealand
Posts: 493
Posted: 12:52am 17 Feb 2020
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Thanks Tony,

First off it is a SLA hence my concern with it apparently staying at equalisation, 14.4V in my case.

There should only be 5-10mA draw on the battery during the day when everything is turned off in the caravan.  Maybe, I had better double-check that.

Cheers,
Dave
Edited 2020-02-17 10:54 by davef
 
Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 342
Posted: 02:39am 17 Feb 2020
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I have 2 of those controllers working, on the 12v unit it sits at 13.7 volt and never seen it do any more, it charges the car battery strait after it is parked in the carport, battery would already be charged on the way home.

I do remember setting these up with some annoying amount of button holding and pressing to go through the menu settings.
the other one is running 24v and floats at around 27. something.
not sure if all these cheap units have functioning buttons or program.
Cheers Aaron
Off The Grid
 
davef
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Posted: 03:58am 17 Feb 2020
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Hi Aaron,

Perhaps if you could check if the 13.7V is your float setting and that your equalisation setting is 14.4V, if using the SLA settings ... that would then indicate my units work differently than yours.

Thanks,
Dave
 
Revlac

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Posted: 08:45am 17 Feb 2020
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Ok had a look at the settings and have been using BO3 Flood. float is 13.7V,  The Model is CY3024
Didn't see any adjustable function or equalization.
It might be like the 2 other charge controllers that just go to float and nothing else, Will have a look in the morning and see if the voltage is any higher.


Is this the same?
Cheers Aaron
Off The Grid
 
davef
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Posted: 10:57pm 17 Feb 2020
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Aaron,
yup it is the same.  

Tony,
I measured the current (with solar input) that was been drawn by the rest of the caravan, which includes its own built-in charger and I measured about 1A !! I think that there is some conflict between the two chargers and as you suggest maybe the added solar controller can't fall-back to float.

Looks like I need to get my head around the whole system.

Thanks for your help guys.
 
davef
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Posts: 493
Posted: 02:57am 16 Mar 2020
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Tony and Aaron,

Thought I'd try on a system that only had a PV panel 20Voc and Imp 5A and connected it to a 45AH car battery.

Straight up to 14.4V.  Measured PV current at about 2A.  I had to reduce current to about 1A before the battery voltage dropped below 14.4V.  This battery just started my diesel tractor about an hour ago but I now think what is happening is that both the caravan battery and the tractor battery can not accept enough current to enable the output voltage of the solar controller to drop below 14.4V.

IE they are reaching their EOL :(  Or does a PWM solar controller behave differently than a small mains battery charger?
 
Revlac

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Posted: 10:40am 17 Mar 2020
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You may be right about the old battery not taking the charge.
The 2 units Running one for 12v it has a 10W panel and the other for 24v has 2 10W panels, so only small current available but definitely running at float, checked the panel input voltage was close to Voc.

I do have a 48V version of these, a TX4830 (Model dose not exist anymore), When I get some spare time I will try it with a 2 250W panels and see if it behaves any different with higher wattage panels.  

I have no idea about any mains chargers, never had one with more than one charge stage.
Cheers Aaron
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davef
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Location: New Zealand
Posts: 493
Posted: 05:53pm 17 Mar 2020
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Thanks for the feedback.

I will try the charger on a good battery to see if I can determine the current drop required to go to float.
 
davef
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Location: New Zealand
Posts: 493
Posted: 10:23pm 17 Mar 2020
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Aaron,

Did a test by progressively shading a 150Watt panel and I saw 14.4V drop back to 13.7V when the battery current dropped below 100mA.

I have never had a brand new lead-acid battery to check but <100mA sounds like a reasonable self-discharge value.

The thing I don't understand is that when the battery current is slightly greater than 100mA the terminal voltage shoots straight up to 14.4V.

Say a lead-acid battery (45AH) is at resting voltage of 12.6V and I stuff 200mA into it, I wouldn't expect the terminal voltage to immediately rise to 14.4V.  Sounds to me that it has a rather high internal impedance.
 
Revlac

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Posted: 09:49am 18 Mar 2020
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Ok Dave,

Did some checking today, the 24V setup is running at float 27.3V or 13.7 per 12V battery, disconnected the panels for an hour, these are 5year old batteries and the voltage drop was not much.
Pressed the button once on the controller and its 27.4, that's float, reconnected the panels it went straight to float.

Now the 48V unit setup for testing today had 4 4WD batteries all about 1 year old all charged about a week ago, connected them to the controller, voltage shown was 51.2 pressed the button once, it says 58V (14.6V per battery) so that's defiantly going to equalise.
connected a pair of 250W panels in series and left it run for the rest of the day and it never went to float. (hope it will go to float eventually)

I have had some old batteries need an equalise charge for several days (bit each day) before they would be happy to sit at a float voltage....on a different controller.
Wouldn't want to do that to a good battery though.

So I think you are correct and have worked out exactly whats going on.

Anyway I have learned a bit more about these things now, so far they seem to be good to leave on the 24v volt batteries on the excavator or tractor, but I would not use them on lithium.
Cheers Aaron
Off The Grid
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 493
Posted: 08:41pm 18 Mar 2020
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Another test, this time on an old (like 30+ years) ex-Telecom flooded 13V 550AH system.  
I thought to myself, "now you just try to push this battery to 14.4V!!"  Only about 3A charging current but the charger behaves as expected.

The other thing I noticed with the caravan battery was I could get it to float on a 1.2A mains charger, but after letting it sit overnight when I put the mains charger back on it took another 20 hours to get it to go to float again.  I know charging to float is quite inefficient but maybe that is another indication that the battery is stuffed.

LiFePO4 batteries are different story, ie require a different charging regime.  

Thanks for the support.  Now I have to decide if I am going to convert the caravan to LiFePO4 or buy a $400 deep-cycle leisure battery.


Regards,
Dave
 
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