CTEK D250s solar input issues

Open circuit measured voltage was 20-21v with no load. When connected all the output on the ctek was showing was the exact same voltage as the battery. I tried this with a fridge connected to the aux batt and without the fridge connected, no difference. As i understand it the ctek is a step up charger, which it does with alternator power as the input, it doesnt with the solar as the input.

That's correct, this particular DC/DC charger only increases (or steps up) the voltage if it's got a beefy supply from the starting battery/alternator.

Having said this, the battery voltage should slowly increase up to the specced 14.4V if only a solar panel receiving sunlight was connected to its input. No stepup DC/DC conversion required for this, because the solar panel open circuits at 21V which is ample for 12V battery charging.
BTW, the output of a solar regulator will always reflect the battery voltage reading, because it's directly connected to the battery. They're the same thing.
The reason why the battery showed 14.4V with the car battery connected to the input is the high charging current abiliity of max 20A. If the battery is old, 20A can push up the battery voltage to 14.4V regardless of SOC, while the smaller solar panel current won't be strong enough to push it up that high instantly.
I suggest to do a load test on your battery because it looks weak (or it is a small capacity unit).

cheers, Peter

The battery is a 3 month old optima yellow top 75a/h. The voltage with solar panel connected doesnt rise whatsoever. I have read that some of theearlirr ctek units dont work on solar unless the current is at a min of 4amps, no so sure about this.

The following doesn't make sense, unless the battery was toast:

...I am not gaining any higher voltage on the output of the ctek to indicate my battery is charging. The voltage on the output of the ctek may read 12.40v (which is the current battery voltage) but when the solar panel is connected this does not increase.
When I turn my engine on this does increase the voltage to 14.4v....

So with the battery giving a voltage reading of 12.4V, it immediatly jumps to 14.4V on application of 20A charging current?
Note, that 12.4V roughly corresponds to 50% SOC.

Only a dried out, or sulphated up battery would exhibit this behaviour.
Thing is, on a healthy battery, you can't just increase the battery voltage without increasing the SOC at the same time. And because 20A of charging current increases the SOC at a rate of 20Ah/hr, it would take at least 60 minutes to reach a battery voltage 14.4V.
And because healthy spiral wound batteries have a low internal resistance, it would take even longer to get to 14.4V.
So please confirm your statement above.
If true, you may have to do a proper load test on the battery because it seems to be defective.

cheers, Peter

I ran two engel fridges for 20min on my battery to draw it down a little. It is m ore likely close to 12.5v but the volt meter showed 12.4v rounding down. The ctek will step up the voltage when the alternator is providing power to the ctek, it increases the voltage to 14.4v as a bulk charge then dropps down as the battery gets to 80% and floats its to full charge, so as for the battery going straight to 14.4v that is the charging output voltage of the ctek not the actual battery voltage at the time.

...it increases the voltage to 14.4v as a bulk charge then dropps down as the battery gets to 80% and floats its to full charge, so as for the battery going straight to 14.4v that is the charging output voltage of the ctek not the actual battery voltage at the time.....

I'm afraid you've got it all wrong.

By definition, bulk charging is the stage before the battery voltage reaches 14.4V. Once the battery voltage reaches 14.4V, the absorption charging stage commences, at which this voltage is held constant by this charger until 12 hours have passed, or until the charging current has decreased to 0.4A, whichever comes first.

During absorption stage charging, at 14.4V battery voltage, charge is being absorbed at a decreasing rate which is reflected by the charging current taper.
Once the charging current has dropped to typically 10% of the bulk charging rate, the battery is very close to 100% SOC.
This particular charger even waits for the taper to reach 0.4A which is only 2% of its max 20A. So it keeps the 14.4V up for quite some time, until it drops back to float voltage level.

I'm still not sure why you think the 'charging output voltage' would be different to the 'actual battery voltage'.
They're one and the same thing, because there's a fat pair of wires connecting the charger output with the battery terminals - not much room for different voltage readings at both ends of this wire pair.
But wait a minute!
Could it be that your charging wires aren't connected properly?
That would show exactly the symptoms you're describing.
Just double check that you've got good connection at the charger and battery ends, and that the wires aren't damaged in any way.

cheers, Peter

I appreciate your feedback but im finding it difficult to work out how a battery can charge without showing an increased voltage from the output of the charging unit? Sorry if it seems black and white but when my alternator runs and provides power my volt meter shows an increased voltage from the ctek unit around 14.4 then drops down as the battery approaches almost full to around 13.2v.

there's a simple explanation:

an ideal battery would not allow an instant increase of its terminal voltage the moment you turn on the charger.
But the charging current comes on to its maximum instantly, and the voltage follows gradually.
Because your battery is new and has very low internal resistance, it's close to an ideal battery, thus it won't allow the charging voltage to rise to 14.4V from a lowish 12.4V within seconds @ only 20A.
If you want to see this jump in voltage, you'd have to apply a charging current of probably 100A or more.

BTW, if this charger drops to 13.2V in the float stage, it'll do more harm than good to any AGM battery. 13.2V is borderline even for flooded antimonial type batteries which have the lowest float charging voltage requirement of all lead acid type batteries.
For new AGM batteries, you want to see at least 13.6V, and for older ones at least 13.75V~13.8V.
If you apply 13.2V to a fully charged AGM battery, you actually discharge the negative electrodes in it, leading to accelerated sulphation.

The only reason why this manufacturer may have chosen such a low float voltage level on this unit has something to do with ageing VRLA batteries becoming thermally unstable when used at elevated operating temps such as under the bonnet. VRLA batteries can fail spectacularly under the right (wrong) conditions.
And THAT's something every charging gear manufacturer is scared s...less of.
So they choose a less spectacular and slow, albeit premature death which most users even won't take any notice of until they discover that the battery 'doesn't hold charge any more'.

cheers, Peter

From FollowUp 8 of 8 -
"For new AGM batteries, you want to see at least 13.6V, and for older ones at least 13.75V~13.8V. If you apply 13.2V to a fully charged AGM battery, you actually discharge the negative electrodes in it, leading to accelerated sulphation."

Not so. You will not get back flow into a charger of the quality of Ctek when they are not charging. If you experience this they will flatten batteries if you don't disconnect them when you switch them off.

Hi Peter,

thanks for pointing this out, but I wasn't actually implying 'back flow' of current from the battery to the charger.

The reason why, at 13.2V float, the negative electrodes inside the AGM battery slowly discharge, has got something to do with the gas recombination cycle.
In a nutshell, oxygen gas formed on the positive plate during charging, diffuses to the negative plate where it effectively reduces the polarisation of the electrode. If the recombination cycle becomes too efficient (like in a partially dried out cell), or the over potential of the cell isn't kept high enough, the negative electrode's polarisation can go to zero, or even negative.
Once it's in the negative region, the negative electrode is being discharged by a portion of the small float charging current.
The cell voltage thresholds below which this can happen are in the vicinity of 2.25V for fresh AGM cells, and 2.31V for aged ones.

So one would have to be brain dead, to suggest a float charging voltage of only 2.2V per cell, like this particular charger manufacturer.
But as I pointed out in my earlier contribution, there's a certain fear factor which has its roots in the thermal instability of AGM batteries, when being operated in very hot conditions, such as under the bonnet.

It's a reputation thing.
If the battery capacity goes away slowly yet prematurely, then the battery must have been of bad quality.
But if it dies at a later stage, in a spectacular and sudden way, then the charger manufacturer cops the blame.

cheers, Peter

It didnt work with the inbuilt regulator connected to the ctek either. Its easier and neater to have everything go through my ctek rather then have to run extra cabling to my undertray toolbox where my battery is located. I dont see the point in running a regulator to a regulator.

Bigfish,

The inbuilt regulators on most solar panels are nothing more than a dumb el cheapo regulator that does not provide enhanced charging capabilities.

I too, have a bypass rigged up on my solar panels.
One cable is connected to the output of the inbuilt regulator for instances when I am not using the camper, but connecting directly to a portable battery system. (eg my Thumper)

I have added another cable which bypasses the inbuilt regulator and which I can connect to the camper's CTEK D250S dual controller, thus utilising it's superior MPPT capability to obtain the maximum amount of charge into the camper batteries.

Simple, the first regulator limits the available power to the second one. The second regulator is a MPPT type and needs full access to the panel to assess its maximum power point and thus get the maximum available power from the panel.

Thanks for the reply that makes sense, ill give it a go tomorrow. I think that is what peter is trying to explain as well. I appreciate everyones feedback on this as i am new to the solar world,

I have set it up this morning and what u say is correct, its very slowly increasing the voltage. See how i go by the end of the day.

Regards
Chris