About chargers - some questions and potential solutions.

[alexis57]

Hi !

I'd like to discuss about chargers and I have some questions and I'd like to show you some potential solutions ( maybe you've already given up them, but I'd like to know the reason )

My battery pack is a 13s4p LiPo, 54.6V with BMS.

1#
Reference : http://endless-sphere.com/forums/viewtopic.php?f=4&t=41170&start=75#p1028304

Firstly I'd like to buy this one : http://fr.aliexpress.com/item/48V-3A-E-Bike-Lithium-battery-charger-54-6V-3Amp-13S-Lipo-battery-charger-High-Quality/935973593.html
Looks like same than here ( ).
It is a CC CV charger for LiPo 13s but obviously, I saw he could change the voltage.
Actually, Im looking for a charger where I could choose the final voltage charge.
For this one, it's 54.6V or 4.2V, I'd like to decrease it to 4.1V or 53.3V because of the LiPo ... It's better for the battery life to go to 4.1V instead of 4.2V.
I think the ratio is x2 life cycles !
Is it a good charger ?

2#
Reference : http://endless-sphere.com/forums/viewtopic.php?f=4&t=41170&start=50#p841252

Secondly, I saw he spoke about a DC DC boost converter (step up, it's same) but this is only a DC-DC converter, it's not supposed to be used for charging a LiPo/Ion battery !!
Why ? Because it's not a CC CV charger ...
I would like some advices for this.

I thought about this solution when I go to friends home or somewhere I can found a DC supply (for computer, TV or any other DC supply, 12v or 19v or maybe more) easily.
I thought use a CC-CV charger in serie with this DC-DC boost converter. BUT I didn't find it for 54.6V then I gave up.
The maximum output voltage I found is 30V. I'm not sure it's possible to connect 2 CC-CV chargers in series (see links below)
http://www.ebay.fr/itm/5A-Lithium-Charger-CV-CC-buck-Step-down-Power-Supply-Module-LED-Driver-New-/201114996886?pt=LH_DefaultDomain_0&hash=item2ed3635096
http://www.ebay.fr/itm/5A-CC-CV-LED-Drive-Lithium-Charger-Power-Step-down-With-Voltmeter-Ammeter-Module-/201331804362?pt=LH_DefaultDomain_3&hash=item2ee04f88ca

1) Possible to choose the final voltage 4.2V->4.1v ? My BMS will manage the voltage of each cell for getting 4.1V ? I'm not sure... The BMS on Aliexpress is missing documentation.
2) What about using a cheap DC-DC boost converter for charging a LiPo ? ( I don't know the behavior of the charger when the battery will get 54.6V (4.2V) or 53.3V (4.1V) )
Maybe I could use it only for backup.

Thank you !

 

[dogman dan]

Ask cellman about getting this charger, or one like it, adjusted down to 13s, 54.6v for the max volts.

I do all my RC lipo charging with one, ( I run 14s), and really like the half charge, nearly full, and full settings at a simple flip of a switch.

I diddled mine to be more like 4.15v, 4.1v, and half charge.

The ultimate charger though, would be a satiator. Hoping to get mine this summer.

 

[alexis57]

Ok, thank you !
Then with this kind of charger, we cannot full-charge the battery because there won't be any CV mode. Only CC and cut-off.
Is it good for battery life ?...

 

[dogman dan]

CC and cutoff is what you want for lithium.

Many are of the opinion that charging to just short of full charge does extend cycle lifespan. That's what the 4.1v setting is for. I try to charge to 4.2v only when I need the extra range for a longer ride. I am at least 6 months away from knowing if that helps any. I suspect in my case, my warm climate will make my packs die early either way.

 

[alexis57]

Ok, I read somewhere that it's possible to stop de charge before 4.2V (or at 4.2V) without use the CV mode. Only CC and cut-off. But in this case, the maximum of the capacity we can get is 70% and the final voltage ( after resting ) is not fixed. (that's why we use the CV, to fix the voltage and being sure the battery is full charged)

You tell you charge only to 4.1V, then you charge with only the CC. (DC power supply ?)
I don't know if it helps but I can just try, so far, I don't need a big range.

I think I could try to put 2 CC/CV chargers (the one on ebay, til 30V) in series and with good adjustments, I could well charge at 4.1V. I'll do some experiments later.
(Cause I'm not sure how the both CV chargers will behave in series.)

Thank you !

 

[dnmun]

i found that charging lipo pouches to 4.12V was almost 8% less charge stored than full charge to 4.20V. others may have measured and can report what they found from exact testing of capacity.

there is a utube video on the tesla users website that mitchji had pulled down here and in the lecture the professor explains that the key factor in cycle life is the LENGTH of TIME that the cell is charged to full charge and not the actual fact that it is charged up to full charge.

so the simple and straightforward solution is just charge only when you will use the cells right away. not to leave them fully charged or sitting for long times at full charge, which most do anyway.

if you have no BMS or balancing charger you won't really have much control over individual cell voltages.

 

[alexis57]

Wow, could you give me the link ? Full charge or 90% charge, the time of the charging is linked.
Of course, for me it's obviously to have a BMS with a homemade battery pack.
I saw on this forum that there is a charger where we can chose the final voltage between 3 voltages. ( 4.2, 4.1 and I don't remember) from a certain cellman.
Maybe I'll buy one and check if this charger uses the CV mode or if it's just a basic DC power supply.

 

[dnmun]

the charger that has three select able output voltages does not have a CV stage at the end. it has a latching output that turns off when the charger reaches final voltage. you should not use them if you have a battery with a BMS or it will never balance.