Battery charger voltage

bc100

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My manual says that a charger should not exceed 14.8 Volts, however the Ctek MXS 5 starts out at 15.8Volts. Should I be worried? The car (and charger) has just arrived and I thought it a good idea to put it on a charger as I don't know its past and I'm guessing it is still on its original battery.
 

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it should drop as the battery charges.
 
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bc100

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Agreed, and it drops back to 14.8V. This can be up to 8 hours later if I'm reading the manual correctly.
 

Tony Dyson

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I would be worried, 15.8v is too high for any sustained period, it won't damage the battery, MB restrict in-car battery charging to 14.8v to protect their Electronic Control Modules and damaged they can cost considerably more complications than a discharged battery, to be safe I would disconnect the -ve battery terminal and put the clamp and batt module to one side and connect the charger -ve directly to the batt -ve post, you would be required to do this or remove the battery from the car if you ran any repair or desulphation programme with your charger.
 
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Tony Dyson

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If you read your Charger manual you'll find you're using the wrong charge mode, you should only use the recondition mode with the battery disconnected from your car!



upload_2020-7-27_19-48-29.png
 
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bc100

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If you read your Charger manual you'll find you're using the wrong charge mode, you should only use the recondition mode with the battery disconnected from your car!



View attachment 60621
However on the next page all the modes show the step 1 desulphation process is involved. Many people rate this charger very highly on their Mercedes cars but I'm just being cautious.
 

Tony Dyson

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Your MB OM clearly states "Only use battery chargers with a maximum charging voltage of 14.8v" my advice is not to exceed this voltage while the battery is connected to the car.
 

Tony Dyson

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However on the next page all the modes show the step 1 desulphation process is involved. Many people rate this charger very highly on their Mercedes cars but I'm just being cautious.
Mmm, I wonder if this is a recent change or the Desulphation stage has been overlooked by Ctek owners, it reads as it is an apply if necessary feature, nevertheless if applied it has the potential to do some considerable damage! especially to the more sensitive models!
 
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bc100

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I've watched a few videos on this and it seems to skip through stage one quite quickly, a few seconds in one or two cases. It seems to be spikes 300mS apart and is only a volt after all. However until I find out more I'm not going to risk it. I bought the CTEK at £67 as opposed to the Mercedes branded one (also a CTEK it seems) as it was £98. False economy maybe.
I don't really want to be disconnecting the battery if I can help it. Anyway I'll see what a bit further research turns up. Thanks for your thoughts on this Tony.
 

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Yes the manual for my 209 CLK makes the same remark about charger voltage not exceeding 14.8v. However my charger is a CTEK MXS3600 or something or other and it's maximum voltage is 14.7 and this is why I've never upgraded to the larger charger. That said, it was my understanding that the increased voltage available on the MXS5 is user selectable but maybe not. I'd like to know really as l may upgrade my charger at some point.
 

Tony Dyson

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I wonder if there's a difference in specification between the MB branded one and the MSX5 sold directly by Ctek?
 

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I've used an MXS10 on our r230 for years with no ill effects.
 
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bc100

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I wonder if there's a difference in specification between the MB branded one and the MSX5 sold directly by Ctek?


I'm not sure, but on another thread here (Best Trickle Charger To Use on E200) there is a reference to CTEK Stop Start which is only rated at 3.8 amps but the voltage is limited to 14.5, so this may be the safer route.
 

Tony Dyson

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I've used an MXS10 on our r230 for years with no ill effects.
Yours too has the initial desulphation stage and the description below indicates, if required, could last up to 8 Hrs. The Recondition programme would extend that by 30 Mins to 4 Hrs.

upload_2020-7-28_8-40-43.png
 

Tony Dyson

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I'm not sure, but on another thread here (Best Trickle Charger To Use on E200) there is a reference to CTEK Stop Start which is only rated at 3.8 amps but the voltage is limited to 14.5, so this may be the safer route.
The Ctek Stop Start reads as simply a temperature regulated PSU that will provide a charging voltage 24/7 regardless of what condition the battery is in, with no other functions, hardly a Smart Charger which is what people would expect from Ctek?
I cannot see how MB would advise a charging limit of 14.8v to car connected batteries and then sell a charger that exceeded that limit every time the charger was connected, what we need is a forum member who has bought an MB branded charger to look at the manual? I bought a NOCO charger last year which conforms to the 14.8v rule for all standard in car charging, all other functions have to be manually set, I disregarded the Ctek for other reasons but didn't notice the initial automatic desulphation stage at the time.
 

Tony Dyson

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I found this document on a US site for a MB branded trickle charger, so there is first of all a presumption that it will be the same/similar specification to the European models other than the supply characteristics, I have edited the original PDF doc to remove all generic safety and irrelevant information pages as the file was too big to upload here.
As you can see from the information herein, the MB branded charger is a reduced function charger from any of the current range of smart chargers from the Ctek range, other than the "Stop'Start" model which has no more features than a standard temperature regulated PSU (Power Supply Unit), and when the MB branded charger detects high levels of Sulphation it will display error indication, the charger will not apply a charge voltage in excess of 14.4v.

I don't know when Ctek introduced the Desulphation stage at the start of every setting in their current range of smart chargers but it is clearly in contradiction to the advice and practice of MB for their cars. If the Ctek charger doesn't detect any Sulphation issues it will skip the Desulphation process and this may the saving grace for many Ctek owners until their batteries deteriorate to a level where the Ctek charger decides a standard car connected battery requires Desulphating and decides to launch itself and apply 15.8v to the car's Controller Area Network components!
 

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bc100

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Here is an interesting video that shows what is going on;


On other videos, stage 1 seems to last for less than a second on most batteries , so I may be OK. The NOCO looks like a good bet also but they have a desulphation mode that may use these spikes.
 

flowrider

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I've used an MXS5.0 and an MXS10 on my SL's AGM battery for years without issue. The desulphation stage lasts no time at all and the charger goes to stage 4 in seconds.
 

LostKiwi

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I've used an MXS5.0 and an MXS10 on my SL's AGM battery for years without issue. The desulphation stage lasts no time at all and the charger goes to stage 4 in seconds.
That's what I see too.
 

Tony Dyson

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In the video, the charger is performing as design, there's an evaluation of sulphation and the desulphation mode deals with it but at an operating voltage of 15.8v, the real danger is if the charger senses a deeper level of sulphation and runs the desulphation stage for up to 8 Hrs at 15.8v.
The desulphation stage in the NOCO charger pulses small amounts of current at 14.8v, the Repair function has to be manually chosen and uses 16.5v.
Providing everyone's batteries are in a reasonable condition, the overvoltage applied during the Desulphation stage of a CTEK Charger doesn't appear to be causing much of a problem as @LostKiwi posted at post #12 but I do wonder if it has in fact caused some complications in the numerous posts complaining about electrical anomalies on the forum.
I wrote an E Mail to CTEK this afternoon enquiring about the application of 15.8v and MB guidance notes limiting it to 14.8v, I'll post again if I get an answer. :)
 

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