The care and feeding of a123-based packs...

[Tom_Cook]

Great thread. Thanks to the OP and other contributers for this wealth of information.

But ehr.... what would be the easiest/best/cheapest way to charge, use and maintain a 12s3p A123 pack?

I was thinking about dividing it into 3 4s3p sub-packs. Each with a built in LVC.
Charging probably with a home built 12s CMS, if I can find a proper scheme for building a CMS hooked up to some power source.

The standard RC chargers don't do charging and balancing of packs larger than 10s, and I don't want to buy another device that lies in the way most of the time. I know... I could just charge the 3 sub-packs separately with a smaller RC charger. Should work OK, until I am in a hurry :wink:

The main reason for splitting the larger pack is weight distribution and "age" distribution. I have 12 older cells and want to order 24 new ones.

Cheers, Tom

 

[ramboman]

Robbe Infinity 3 with external 12s balancer is appropriate, but slow...
iCharger 3010B is appropriate for fast charge, but balance only up to 10s...
But you don't have to balance a123s all the time...
And the balancer of Robbe can be used passively...
I would prefer to split the pack in two 6s3p and balance the separately or coupled in parallel.

 

[Tom_Cook]

Hi, thanks for the tip. That Robbe balancer looks pretty interesting.

When using something like that, does one still need such an expensive charger/balancer?

Having two balancing apparati sounds like a bit of overkill to me
Don't like to spend 280€ either

 

[Desertprep]

What is the best price/source of an a123 pack now?

 

[ramboman]

eBay...

 

[webfootguy]

What is the best price/source of an a123 pack now?

I've got 8 cell Dewalt packs for sale on Ebay right now and can provide raw cells (with tabs) or in groups of up to 8 cells with tabs. PM me if you know what you want.

 

[texaspyro]

What is the best price/source of an a123 pack now?

Forum member cell-man. He will build you any pack you want. He welds them up with copper interconnects for around 6 bucks a cell.

 

[Desertprep]

Is an A123 battery pack well suited for an r/c outrunner? or should I use a lipo pack?

 

[ramboman]

Is an A123 battery pack well suited for an r/c outrunner? or should I use a lipo pack?

YES!
even better, you charge in the plane in 15min, between two flights

 

[The Mighty Volt]

Hi there.

Today I was tabbing some A123 to charge them individually before joining them in a large 10p string.

I was testing the strength of one of the tabs when this happened:

As it happened, the tab was well on, and refused to come off without pulling apart a piece of the cell, I believe the vent of the positive terminal.

Any suggestions as to what effect this might have on the battery? Should I replace it in my string?

Thanks.

 

[steveo]

Hi there.

Today I was tabbing some A123 to charge them individually before joining them in a large 10p string.

I was testing the strength of one of the tabs when this happened:

As it happened, the tab was well on, and refused to come off without pulling apart a piece of the cell, I believe the vent of the positive terminal.

Any suggestions as to what effect this might have on the battery? Should I replace it in my string?

Thanks.

id re-tab it ...

i'm sure she is fine.. they are tough cookies..

or if your wooried just replace..

by tabbing you not placing much heat anyways!

-steveo

 

[The Mighty Volt]

I will try to re-tab it now in a few moments. Did you get your welder going Steveo?

 

[ramboman]

This is not critical at all... I removed the tabs of my early a123 cells to be able to use solderless tubes...

 

[steveo]

I will try to re-tab it now in a few moments. Did you get your welder going Steveo?

I just got my 2 scrs from jeremy yesterday...

I basically have

efx capasitor
4 - .25 farads
2 - .5 farads
*********************
1 - other brand .5 farad capasitor

all bolted up to 24" x 1" x 1/4 thick bus bars

i have some 6 or 4 gauge for the wires... and some 1/4" copper electroides

i'll try to get some welds in this weekend...

got a few tries on it before my scr fails... works good on 2 farads (efx caps only)..strong welds on negative terminals... however..... weak welds on positive terminal thou..

i'll post some pics soon

-steveo

 

[The Mighty Volt]

Good stuff Steveo. Jeremy is a gent- make him your model in all things!

I eventually used solder to just stick it back on.

 

[The Mighty Volt]

Question:

What is the difference, in State of Charge, between two A123 batteries, one of which, at a given point in time, is drawing 3.6v 0.5A CV, and the other of which is drawing 3.6v 0.10A, CV?

I have a PITA standing around trying to charge A123 via the CV method, where the voltage is set to 3.6v from my power supply, and then observe as the current drawn by the battery decreases, until it eventually hits 0.01A, CV. At that point it is, in my opinion, fully charged.

However, it is taking an age to move from 0.10A to 0.01A, 3.6v CV. So, I ask, what is the difference in SOC at these values? Is it so insignificant, as I can safely connect these batteries in parallel without suffering any damage to the lesser charged cells?

Thanks.

 

[ramboman]

Fyi, the iCharger 3010B uses CCCV and stops at 10% of C, i.e. 0.1A. Going further is useless...

 

[The Mighty Volt]

Fyi, the iCharger 3010B uses CCCV and stops at 10% of C, i.e. 0.1A. Going further is useless...

Hi. I am not actually using a dedicated charger, but just a PS with switching function.

DO you know how much difference there is, in SOC, between two cells one of which is drawing 1.0A, decreasing, and the other which has reached 0.5A, decreasing?

THanks.

 

[ramboman]

I use a MasTech HY5020e too, same procedure, set V, connect pack, set A wait...
You can wait forever without risk, better to stop when nothing more goes in...
Difference in current after a long period is probably due to difference in internal resistance...

 

[The Mighty Volt]

Okay, but, when the voltage is constant, at 3.6v, at what stage do the differences in current being drawn become unimportant?

Clearly, a battery which immediately draws 3.0A or so, dropping regularly, is not as charged as a battery which immediately draws 0.5A, dropping slowly.

At what point does the difference in Amperage drawn become less important?

 

[GGoodrum]

The general rule-of-thumb I use is around 1/50th of the total pack capacity, so for a 10Ah pack, it would be when the current drops below 200mV (.2A...). The new Charge Controller we now have for the inexpensive MeanWell supplies has an adjustable shutoff current setting with a range of 0 to 1A.

-- Gary

 

[The Mighty Volt]

The general rule-of-thumb I use is around 1/50th of the total pack capacity, so for a 10Ah pack, it would be when the current drops below 200mV (.2A...). The new Charge Controller we now have for the inexpensive MeanWell supplies has an adjustable shutoff current setting with a range of 0 to 1A.

-- Gary

Okay then...I am charging individual 2.2Ah cells, so 1/50th of that is..........044A which happens to be a pretty low figure. I guess the batteries really aren't fully charged until they are drawing very very little current indeed.
Thanks.

 

[GGoodrum]

Actually, I think anything between 100 and 200mA is fine, even for 2.2Ah cells. The big thing you want to do is try and charge them all to the same level, if you are going to then build them into a pack. It doesn't really matter what the cutoff point is, but it is important to try and pick the same number for all of them.

-- Gary

 

[The Mighty Volt]

Actually, I think anything between 100 and 200mA is fine, even for 2.2Ah cells. The big thing you want to do is try and charge them all to the same level, if you are going to then build them into a pack. It doesn't really matter what the cutoff point is, but it is important to try and pick the same number for all of them.

-- Gary

I just set my power supply for 3.6v, then I leave the battery hooked up to it until it is drawing no more current. Then I know it is fully charged to 3.6v with its full complement of capacity also.

Unfortunately, this has proven to be so time consuming, thats why I asked how much difference there was, SOC, between a battery that had hit 0.1A steady and a battery that was dropping very slowly from say, 0.5A.

My power supply only goes to two decimal places, that is to say XX.XXv, so I will be letting all of the batteries sit there until they draw no more current. Then they are charged.

TMV

 

[lifepo4ever]

hi there , do i need a bms for a 6sp2 A123 pack because i want to add it to my lipo pack for some more range , i know i can use balancer and then charge but some people
say that more you have cell more I have chance to destroy the cell with out a proper balancing , but what is the maximum we can use with out a lvc or bms ?

thank you