C-Tek D250 SE and lithium charging - Expert required

Everything I have read agrees with you. Lithium at 100% isn’t great.

Its correctly programmed.

Its the behaviour of the Ctek, and how its charging that is in question.

JJ,
From the advice I have received from multiple experet sources, I believe the Ctek behaviour is preferred for Lithium batteries.

Slightly off topic here, but....
This even extends to phones, laptops, cameras, etc, that use lithium batteries. You will get longer battery life if you don't plug them in overnight and leave them sitting at 100% on a charger for however long. There are apps and devices that help you limit the charge if you want to go down that route. Chargie uses a device between your charger and your phone/tablet, plus an app to stop the charge at the desired level. AccuBattery simply uses an app to alert you when you've reached the desired level of charge but will continue to charge if you ignore it.

With so many devices having built-in, non-removable batteries, technologies like this might prevent an otherwise unnecessary expensive device upgrade due to battery failure.

Yes, I am very aware of the best ways to get the best out of lithium, most modern lithium batteries will take care of this for you for the most part..

The question..

Is this behaviour normal for this charger? If it is I will change it.. if not I will get it replaced as it must be faulty..

G'day JJ,
I looked up the owner's manual for the Ctek. ( Link) It says that on its lithium profile after charging to 100% it will maintain the battery between 95% and 100%. So the short answer to your question, I think, is that the Ctek is working properly.

Now, why does the Victron show 85-90% when the Ctek cuts in, when Ctek says it should be 95%?

I think that is due to discrepancies caused by the differing methods of sensing battery state of charge (SOC). The Ctek does it by sensing battery voltage. The Victron is a coulomb counter.

It is difficult to accurately assess SOC in a lithium battery by measuring battery voltage, owing to the very flat discharge curve displayed by lithium batteries. Typically, a 12V lithium battery will hold 13.2-13.3 volts for a large part of its operating range. To estimate SOC using this method the Ctek has to measure hundredths of a volt or smaller and even then the result is approximate.

The Victron battery meter is a coulomb counter, a far more accurate way of measuring SOC. You probably know this, but for those that don't, a properly set up coulomb-counting battery meter will know how many "particles" of electricity (coulombs) are in a fully charged battery. It then counts those going out (discharge) and those coming in (charging) to arrive at a relatively accurate SOC.

Given measurement errors and other unknowns like possible parasitic discharge able to be measured by the Victron but not by the Ctek, it doesn't surprise me that there is a 5-10% difference between the two.

This actually tells me is not working correctly as this one will go down to 85% or so before charging again.. if it were 95% this would be what I expect.

We have tested the Victron and it counts out the 100 AH correctly. The battery BMS is also a major part of the charging, and will turn off the charging when the battery is full. The charger does not have to make this decision. You can charge a Lithium battery with a simple power supply if you wanted to. The BMS will shut down charging when its decides its full.

If the profile of the CTEK is to allow the battery to get to 85% before charging again, this isnt going to work, and it will be changed out for a Redarc

Can't help with the answer JJ but would have thought the 100% charging issue would be taken care of by the battery's BMS as you say above. CTEK's setup might assume that not all BMS's will do that job properly so they'll err on the side of caution?

Most LFP experts I've read/listened to/watched suggest that squeezing the last little bit of charge into the LFP cells is detrimental to their health over the long term, hence any decent BMS should prevent that from occurring. As Will Prowse has said and demonstrated many times when testing 12V LFPs, cell voltages will appear to be high when the battery (with BMS) is fully charged but they soon settle back to a voltage which is slightly under "full". Thus the BMS is doing its job and the charger shouldn't have to be concerned.

I have tried multiple other chargers and they all work the same. The CTEK is the very odd one out..

Letting the battery get to 85% before charging is just not required, and if that’s what CTEK are doing it’s stupid and not required, and I wonder how they manage to sell chargers..

It seems the answer is to bin the CTEK and get a quality charger..

A quality charger to replace the Ctek would be an Enerdrive DC2DC 40A charger. Perhaps a little cheaper than a Redarc, and charging rates can be fine tuned by the user, as well as being able to handle all battery types. Perhaps a bit bulkier than a Redarc?

Bob

Will look them up.. thnks for the tip.

OK, but the question is "is this behavior the normal behavior for a CTEK" as no other charger we have tried works like this. All other chargers will all keep the battery at 100%. The BMS and the battery design will be such that the cells are never actually at 100%.. even if the meters state 100%..

Just like a Tesla does..

Early Enerdrive DCDC chargers charge till they reached the set parameters then turned off. Restarted charging when battery dropped to around 13.3V so that type of behaviour is not unique. Their current version goes to power supply mode.

According to the CTEK manual charger goes into float mode for 2 hours then switches to pulse mode whereby it gives a pulse a 1 hour pulse charge and an auto pulse 10 days. I assume that means when the battery drops to a certain level it will go into charge mode for an hour. If battery not used then it will give a one hour every 10 days.

I agree.. the battery and system design is such that you can just use them like a normal battery and keep them at 100%, which is probably only really 85 to 90% of the actual cell capacity.

After trying a hand full of chargers, they all charge to 100% then maintain this even while appliances are using power.

The CTECH doesn't, at least the one I have. So my question is, is this the way the CTEK works? or do I have a issue with the charger? If it is the way the CTEK works, then it's useless and will be replaced..

And yet there are lithium battery manufacturers who say do not keep at 100% if in storage. If being used constantly 100% is fine.