CTEK issues - erroneously reports full + using an extension

[Jakg]

I've got a CTEK MXS 5.0 battery charger and a car with what I thought was a battery drain issue. After some more investigation, the car showing a green "fully charged" symbol while the battery is only 11.5v, so no wonder the car keeps saying the battery is flat!

I've noticed that when charging a regular (non-AGM) battery it's only doing about 2A (without any extensions) and the quick-connect connector gets warm to the touch.





The CTEK came with a ~0.5m cable which is useless, so I bought the extension which didn't really help much - so I extended the extension with some thick (2.5mm²) cable to give ~5m total. With this, that same test drops to 1A. I think the real problem is not the extension I added but the extra pair of quick connects it adds - as they are getting warm as well.



My suspicion is that the resistance of the connectors is what's confusing the CTEK into giving up charging and declaring it finished.

I could've chopped the ends off but I wanted to keep the unit as-is in case I needed to return it under warranty.
I could've extended the 240v side instead of the 12v side but I thought it'd be safer and easier to run low-voltage wiring and that means the CTEK can be screwed to the wall out of the way.

Has anyone had a similar issue? Or is the real problem I (mis) using a maintainer as a charger/power supply?

For reference - the battery itself is fine - i've tried two different batteries which have the same issue, one is less than a year old. Hence thinking I had a parasitic draw...

[davek_964]

I have a few CTEKs that are extended - probably also about 5m - using whatever cable I had laying around (on the 12V side). I simply cut the 12v feed from the Ctek and extend it - I can't remember how I connected the wires, but I think it was simply a terminal block.

They seem to work fine.

[M11rph]

Are you experiencing this issue when using it with the cable coiled up as shown in the last photo?

It's possible that the higher resulting inductance is either directly affecting the CTEK charger or causing it to respond to what it is seeing as a battery issue?

Easy to eliminate that as a possible cause.

[Huzzah]

Mines extended too, probably 10m. Works fine, not sure of the wire I used, probably thickish speaker wire.

[E-bmw]

As above coiled leads are a no-no under these circumstances and this could be part of the issue.

Also electrical connections/wires getting warm indicates additional resistance causing heat in the area of additional resistance. (for instance a fuse blows because the wire in it melts, the wire is very thin to regulate this current)

If I were in your position the first thing I would do is to remove all extensions and run it direct using a mains extension & see what happens.

If that works then go back to try the extension rolled out, checking for warmth & current flow/voltage at the battery.

[paul_c123]

Given the way smart chargers sense battery condition, any extending of the 12V wires is a no-no. By all means extend the 230V though.

[NDA]

I have the same style of CTEK extender with the same connectors - about 2M in length I should think. It works fine.

As above, coiling the wire won't be a good idea - try a shorter extender or spreading that cable about a bit.

Battery experts could answer this, but I'm sure my battery reports quite a low voltage (maybe around or just under 12V) when the engine's not running - but then runs at about 14.3V when the car's running.

[M11rph]

Fully charged resting voltage should be around 12.5v.

With the engine running you'll be measuring alternator output rather than any battery voltage. Anywhere from 14-15.3v (If you have a Porsche, display the battery voltage and see what happens when you switch from Normal to Sport mode. Spoiler~ charging voltage jumps up).

[Jakg]

E-bmw said:

Also electrical connections/wires getting warm indicates additional resistance causing heat in the area of additional resistance. (for instance a fuse blows because the wire in it melts, the wire is very thin to regulate this current)

To be clear - it's the CTEK connectors itself that gets hot, not the wire, not my extension connections.

M11rph said:

Are you experiencing this issue when using it with the cable coiled up as shown in the last photo?

It's possible that the higher resulting inductance is either directly affecting the CTEK charger or causing it to respond to what it is seeing as a battery issue?

I hadn't thought about that, I'll try it.

E-bmw said:

If I were in your position the first thing I would do is to remove all extensions and run it direct using a mains extension & see what happens.

It charges, but only 2A when the manual says the bulk-charge phase should be 5A. But that could be because I was using a mulimeter to measure the current and that's affected it. But without the extensions, the connector still gets warm - Google seems to suggest that's normal, but to me that's not good at all.

NDA said:

Battery experts could answer this, but I'm sure my battery reports quite a low voltage (maybe around or just under 12V) when the engine's not running - but then runs at about 14.3V when the car's running.

There are voltage->SOC tables for different battery chemistries online, e.g. https://sunonbattery.com/agm-battery-voltage-capac... - but 11.5v would never be fully charged.

[Panamax]

Jakg said:

After some more investigation, the car showing a green "fully charged" symbol while the battery is only 11.5v, so no wonder the car keeps saying the battery is flat!

I don't understand this sentence. What is showing what?

As others have indicated, 11.5v is either "knackered" or "flat". The question is which.

I suspect warmth of the connector can be resolved by cleaning the terminals. Use a cotton bud and meths for the pins and a wooden cocktail stick soaked in meths for the socket holes. After cleaning, give the connector some vigorous connections and disconnections to scratch any oxidation off the contact surfaces.

[E-bmw]

Jakg said:

E-bmw said:

Also electrical connections/wires getting warm indicates additional resistance causing heat in the area of additional resistance. (for instance a fuse blows because the wire in it melts, the wire is very thin to regulate this current)

To be clear - it's the CTEK connectors itself that gets hot, not the wire, not my extension connections.

M11rph said:

Are you experiencing this issue when using it with the cable coiled up as shown in the last photo?

It's possible that the higher resulting inductance is either directly affecting the CTEK charger or causing it to respond to what it is seeing as a battery issue?

I hadn't thought about that, I'll try it.

E-bmw said:

If I were in your position the first thing I would do is to remove all extensions and run it direct using a mains extension & see what happens.

It charges, but only 2A when the manual says the bulk-charge phase should be 5A. But that could be because I was using a mulimeter to measure the current and that's affected it. But without the extensions, the connector still gets warm - Google seems to suggest that's normal, but to me that's not good at all.

NDA said:

Battery experts could answer this, but I'm sure my battery reports quite a low voltage (maybe around or just under 12V) when the engine's not running - but then runs at about 14.3V when the car's running.

There are voltage->SOC tables for different battery chemistries online, e.g. https://sunonbattery.com/agm-battery-voltage-capac... - but 11.5v would never be fully charged.

I got that it was the connectors, you said that earlier, where the heat is generated (regardless of where it is) is where there is an increased resistance. When you say Google suggests it is normal, please don't tell me you are quoting google AI?

The multimeter won't affect the current in the loop as it is effectively a short circuit in itself when set to read current.

11.5v is either goosed of flatter than a flat thing with an elephant sat on it's head! 14.3v means the alternator is charging the battery. It should be 12.6/12.7v for a fully charged healthy battery.

[Jakg]

Jakg said:

I've got a CTEK MXS 5.0 battery charger and a car with what I thought was a battery drain issue. After some more investigation, the car showing a green "fully charged" symbol while the battery is only 11.5v

Panamax said:

I don't understand this sentence. What is showing what?

Sorry, your right that makes no sense. It's the CTEK unit thats showing a green "fully charged" symbol, while the battery is actually flat.

Panamax said:

I suspect warmth of the connector can be resolved by cleaning the terminals. Use a cotton bud and meths for the pins and a wooden cocktail stick soaked in meths for the socket holes. After cleaning, give the connector some vigorous connections and disconnections to scratch any oxidation off the contact surfaces.

It's been having this behaviour (connector getting warm) since new - I don't think it's dirty or corroded but I'll clean it anyway.

E-bmw said:

I got that it was the connectors, you said that earlier, where the heat is generated (regardless of where it is) is where there is an increased resistance. When you say Google suggests it is normal, please don't tell me you are quoting google AI?

Obviously not - what I mean is that if you search for "CTEK connector warm" you get results suggesting this is common (e.g. https://www.porscheclubgb.com/forum/threads/ctek-c...

[E-bmw]

Jakg said:

E-bmw said:

I got that it was the connectors, you said that earlier, where the heat is generated (regardless of where it is) is where there is an increased resistance. When you say Google suggests it is normal, please don't tell me you are quoting google AI?

Obviously not - what I mean is that if you search for "CTEK connector warm" you get results suggesting this is common (e.g. https://www.porscheclubgb.com/forum/threads/ctek-c...

Whether it is common or not, I am not questioning, but I assure you it is not right.

If you remove the connectors & solder/crimp the wires together I bet the wiring join does not get hot.

ETA.
Just done a bit of googling & there are many posts about the charger getting hot, which is to be expected but very few on the connectors getting hot unless I am misreading them.

In fact the only one I found on the first couple of pages was on that porch website.

Edited by E-bmw on Thursday 11th September 13:23

[eltax91]

Is the connector nice and tight? I had an issue with one of mine and it appeared over time the connectors had got dirty and worn slightly. I sent some contact cleaner down it and tweaked the pins slightly with some needle nose pliers and it was back up and running again.