Sv: Korrekt lading av Saxo med bly traksjonsbatteri

[BauDemo]

I have been reading that at the end of the charging cicle the Think does something called overcharging. I read that this is relatively bad - can introduce "memory", beacause of enlarged christals, etc.... It can also be good, because it helps equalize the pack... There are many opinions of it, but I can seem to find what is it...

What I can not find is when exactly this overcharge phase starts... does it start after 80% SOC? Or is it after the SOC meter shows 100%? Is there any other way to measure or sense when the overcharge starts?

I searched the forum, but have not been able to find this. Please point me to a thread if that is already discussed.

[Boogie]

When we are talking about an overcharging, we are talking about all above 100% capacity.
NiCd will always have an overcharge. Even if you are talking about a single cell.
So the purpose is not only to make sure your cells are equalized, but also to make sure they are fully charged.

An overcharge is not harmfull in itself, but if you leave the battery fully charged, then it will start to form larger crystals as well having a great selfdischarge of upto 1% per hour for the first 8-10 hours.

A good indicator of a full battery is "boiling" in the battery. The energy supplied is not saved, but will create heat which will make the cell "boil".
You can easily hear it when you are working with the battery out of the car. More complicated when mounted.

[Ken]

Hello BauDemo, l can answer some of your questions off the top of my head.

Overcharging ensures that all the cells in all the blocks are 100% charged otherwise an imbalanse could occur. It is commonly accepted here on the forum that Think cars exagerate this charging phase leading to an unneccesary electrolysis and use of water from the electrolyte. So, some is OK but too much is bad.

Unlike lead/acid batteries, keeping NiCads fully charged all the time will lead to crystal growth and reduced capacity so a relatively deep discharge once a week or two will help to dissolve the crystals.

Overcharge begins at about 97% SOC and 100% will only register after the overcharge sequence has finished. The needle will often go down to 0% afterwards.The overcharge is carried out at 5A  so if you have a plug in energy meter from Clas Ohlsen f.ex. you will be able to see when the current drops from 10 or 15A down to 5A.
The charging voltage is carefully calculated for this phase and after a threshold voltage is reached, the calculated voltage, dependent on battery temperature, is applied for a determined period.

Hope this answers your questions, but ask more because its fun writing in english!

I see that boogie has answered before i posted this. Good english old sport.
 

[BauDemo]

Thank you both!
I always thought that the 5A charging was starting around 80% SOC... but here I am learning everyday!
Wouldn't it be possible to use a current monitoring control relay... something like this
http://www.elfa.se/elfa-bin/setpage.pl?http://www.elfa.se/elfa-bin/dyndok.pl?lang=se&vat=0&dok=11746.htm to automatically switch off the charging when the charging current goes to 5A?

[Ken]

There is a thing called a Revne box that limits overcharging automatically but allows a full cycle now and then, or do as I do and work out in your head how many hours you wish to charge. 15% per hour is typical so set a countdown timer  to the required period.

[elektrolux]

The charging voltage is carefully calculated for this phase and after a threshold voltage is reached, the calculated voltage, dependent on battery temperature, is applied for a determined period.

I'll try to explain this a little easier: Overcharging starts after a preset voltage is reached. This voltage is temperature dependant to a sertain degree, but normally at 8V / battery.

After this, a prosentage of the Ahr supplied during the bulk charge phase, is supplied as overcharge. Saft spesify this persentage to 15%, but it appears Think overdoes this and charges 18+% as overcharge.

Overcharging is nessesary to keep battery capasity intact, and to syncronize cells, but also leads to heat build up witch in turn gives higher self discharge, and desyncronisation and high water consumption.  So, overcharging is designed to syncronice batteries but at the same time leads to desynkronization.

To overcome theese effects its wice to charge car before driving, instead of after driving, and to fill water twice as often as the service light demands. 

[BauDemo]

Thank you for the explanation... Now I see that it is not really that easy to say exactly when the overcharging starts...
If the voltage is used to signal the overcharge, an overvoltage relay could be used... but then again all the batteries do not reach that level at the same time...

I will get myself a timer and use that instead!

Just to confirm - if the car is set at 10A charging, and the SOC arrow shows 40%, I could then set the timer for 4 hours (100% - 40% = 60% charge required, 60% / 15% per hour = 4 hours) and be sure that I will limit the overcharging. Is this the correct way to do it?

[Ken]

Yes, that is OK. Some people give a little overcharge every time so 4,5 hours woulld give a half hour extra. Others only charge enough to cover the expected demand. The battery management system is a bit clever and will register interupted charging and wil try to overcharge even more if given the chance.
Maximum capacity will be acheived by deep discharge and plenty of overcharge but the down side of this is a high use of water and possible cell reversal which is potentially damaging. It partly depends on your driving range requirements but generally one only gets out what one puts in in terms of KWatts.
A battery montoring system like PakTrakr will help ensure that battery reversal doesn``t happen and will enable safe deep discharge.