Homemade Battery Packs

Batteries, Chargers, and Battery Management Systems.
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Re: Homemade Battery Packs

Post by DrkAngel » May 28, 2014 5:22 pm

Built 24.84V 6Ah MeanWell charger (S-150-24) ... for 22.2V LiPo pack.
Yes I labeled it.
Don't want to plug into wrong pack!
18ga computer power cord fit through wire hole.
MW22.2V.jpg
4.14V per bank looks optimal.
Image

MeanWell will be outputting 6A continuously for nearly 5 hours so I felt it advisable to add a 24V fan.
At about 25V it seemed annoyingly loud , so ... I added a 47ohm 2w resistor in series.
Dropped voltage at fan to 21V and quieted to ... acceptable.
Fan placement appears optimal.
MW components.jpg
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Re: Homemade Battery Packs

Post by kje » Jun 04, 2014 5:50 pm

Today I had a long boat trip with my electric trolling motor and my batterypack. At the end the three cells in my batterypack was at 3.72V, 3.73V, and 3.75V. Is that acceptable?

My Imax B6 charger is very hot when charging my 3s50p batterypack at 3A. Can I use a powersupply to charge the batterypack and what voltage and amp should it deliver?

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Re: Homemade Battery Packs

Post by lxgoldsmith » Jun 04, 2014 7:58 pm

From what I've learned, add a little capacity 1-2 cells at a time to the lower cell groups and don't let them fall lower than 3V, stop at 3.5-3.6 for longer life. To charge faster and relieve strain on your hobby charger, use a bulk charger (variable power supply, anything to match the voltage) in parallel and let the hobby charger balance the cells.

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Re: Homemade Battery Packs

Post by Skalabala » Jun 05, 2014 2:46 am

kje wrote:Today I had a long boat trip with my electric trolling motor and my batterypack. At the end the three cells in my batterypack was at 3.72V, 3.73V, and 3.75V. Is that acceptable?

My Imax B6 charger is very hot when charging my 3s50p batterypack at 3A. Can I use a powersupply to charge the batterypack and what voltage and amp should it deliver?
Try your luck and swap on complete string (20P) from the 3.72 with one of the 3.75
Its not to good after one use. After the swap if it goes good then you can fine tune by adding some cells :)
You used 20P strings right? 20P3P3S? 60 cells x 3 ?
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Re: Homemade Battery Packs

Post by kje » Jun 05, 2014 8:41 am

Skalabala wrote:
kje wrote:Today I had a long boat trip with my electric trolling motor and my batterypack. At the end the three cells in my batterypack was at 3.72V, 3.73V, and 3.75V. Is that acceptable?

My Imax B6 charger is very hot when charging my 3s50p batterypack at 3A. Can I use a powersupply to charge the batterypack and what voltage and amp should it deliver?
Try your luck and swap on complete string (20P) from the 3.72 with one of the 3.75
Its not to good after one use. After the swap if it goes good then you can fine tune by adding some cells :)
You used 20P strings right? 20P3P3S? 60 cells x 3 ?
Thank you. Yes I used 20P strings.

Now my Imax B6 charger died when charging my batterypack. Its no power, maybe it was too hot and fried?
What charger should I buy now? My Imax was B6AC with no fan - does it help if I buy an Imax and use external power supply?

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 05, 2014 8:55 am

As explained earlier ...
MeanWell power supplies can be modded and work excellently as bulk chargers.
See - MeanWell chargers
The S series, specifically S-150-12 and S-350-12 are moddable 15 and 24 have been modded for 12.3V.
S-150-24 has the most extensive mods, documentation and instructions.
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Re: Homemade Battery Packs

Post by kje » Jun 05, 2014 7:55 pm

Is there anything wrong with connecting any 12V power supply to my battery pack?

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Re: Homemade Battery Packs

Post by teslanv » Jun 05, 2014 7:58 pm

kje wrote:Is there anything wrong with connecting any 12V power supply to my battery pack?
Probably. What are you trying to accomplish?
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Re: Homemade Battery Packs

Post by kje » Jun 06, 2014 6:08 am

Charging the batterypack...

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Re: Homemade Battery Packs

Post by teslanv » Jun 06, 2014 7:15 am

You would want to match the charger voltage with the max. Voltage of your battery, or slightly less than the max battery voltage. Then monitor it carefully when you charge. Research "Bulk charging".
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Re: Homemade Battery Packs

Post by DrkAngel » Jun 06, 2014 7:48 am

Bulk Charging Review

Lithium ion cells, at moderate rates, will discharge and charge at near 100% efficiency.
This means that batches of cells will tend to charge in the same manner as they discharge.
= Pack will bulk recharge all banks to same equal voltage they began with.

The ideal pack would be constructed of cells of identical manufacture, each cell of equal capacity, age, condition etc.
Nearly impossible with recycled cells.
So ... target should be to produce banks of equal capacity. See - Bulk Capacity Testing
and
If multiple brands of cells used, each bank should be constructed of a representative sampling of each type.
(This helps keep banks of similar IR! Keeping banks equalized during various discharge rates.)
If matched closely, each bank of a pack should begin precisely equal in voltage.
When "fully discharged" (discharged to optimal DOD = possibly 3.7V) at moderate rate, all banks should still be of nearly identical voltage.
Now ... If charged at moderate rate (<.5C for laptop cells) all cells should recharge to the same beginning equal voltages between banks.

Especially with large packs, if banks are not equal at optimal DOD, adding cells to any weak bank will help equalize pack.
Pack should be fully charged 1st, then fully charged cells added.
Or, any stronger bank should have cell-cells removed and added to weaker bank-banks.
Repeat process till banks equalized.

Safety!
Monitor voltages at full and empty!
Especially during preliminary cycles!

Avoid!:
Excessive discharge rate (not >.5C sustained)
Deep discharges (not below ~3.7V per bank - dependent on cell characteristics see - Capacity Mapping )
Excessive charge rates (Keep below .5C)
Excessive charge voltage (4.20V per cell is maximum, some cells designed for 4.10V, lower voltage greatly increases usable life!) See - Optimal Charge Voltage

Most important, any self-discharging cells must be eliminated!
Self-discharging cells will cause their bank to continually bleed down, unequalizing-unbalancing the pack.
Making bulk charging ineffective and dangerous!

Bulk chargers
Your bulk charger should be a CC\CV type.
Constant Current\Constant Voltage
Charger - power supply should be amperage limited to <.5C (for laptop cells) and have sufficient rating-cooling to maintain output continuously.
It must also be voltage limited to the packs target maximum voltage.
When attached the charger will provide the maximum amps, but voltage will sag well below the set target voltage.
As the battery is charged, target voltage will be attained and as it is, the current-amps supplied will diminish to a near ... final 0.00A.
Power supply must be current-Amps regulated ... or it will likely overheat and "burn up", component failure or worse.

Effectively, bulk charging is a relatively safe, inexpensive, effective charging method.
Highly dependent on each bank being of similar condition and capacity ... with no self-discharging cells!!!
Ideally, discharge and charge rates should be similar.
EG 30Ah pack - discharging at 15A and recharging at 15A.
I try to insure that typical discharge is below .5C and with brief surges not exceeding 1C, better for cells, efficiency and lifespan.

Capacity must be actual capacity ... not original rated capacity!
C rate also should be calculated by actual, rather than original, capacity.

EG Over 3 years, with 25.9V 25.92Ah recycled build, I noted a marked decline in capacity with a nearly identical decline in IR (Internal Resistance) numerically higher - more resistance - lower performance.
Heat production, voltage sag etc. seemed based on actual rather than rated AH, of the build.
Last edited by DrkAngel on Jun 06, 2014 2:27 pm, edited 3 times in total.
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Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Homemade Battery Packs

Post by kje » Jun 06, 2014 11:13 am

teslanv wrote:You would want to match the charger voltage with the max. Voltage of your battery, or slightly less than the max battery voltage. Then monitor it carefully when you charge. Research "Bulk charging".
Ok. My max battery voltage is 12.6. So I can connect a 12.6V powersupply direct to my batterypack and monitor it carefully?

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Re: Homemade Battery Packs

Post by teslanv » Jun 06, 2014 12:22 pm

What kind of battery do you have? 3-Cell Lithium?

12.6V is pretty low for motive applications, unless you are breaking your larger battery down to smaller packs for Parallel charging.

But, yes, that should work. You will need to disconnect the battery from the power supply once the current drops to <.25A
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Re: Homemade Battery Packs

Post by Skalabala » Jun 06, 2014 3:12 pm

teslanv wrote:What kind of battery do you have? 3-Cell Lithium?

12.6V is pretty low for motive applications, unless you are breaking your larger battery down to smaller packs for Parallel charging.

But, yes, that should work. You will need to disconnect the battery from the power supply once the current drops to <.25A
He has 60P3S 18650
I am busy with an ATX PSU to charge with. I am sure you can use an automotive 12V battery charger?
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Re: Homemade Battery Packs

Post by kje » Jun 06, 2014 5:36 pm

teslanv wrote:What kind of battery do you have? 3-Cell Lithium?

12.6V is pretty low for motive applications, unless you are breaking your larger battery down to smaller packs for Parallel charging.

But, yes, that should work. You will need to disconnect the battery from the power supply once the current drops to <.25A
Like Skalabala says I have 3-Cell Lithium. (60P3S 18650)

Is 12.6V too low for motive applications like my trolling boat-motor?

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Re: Homemade Battery Packs

Post by teslanv » Jun 06, 2014 10:42 pm

Ah, trolling motor is probably fine at 12v.
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Re: Homemade Battery Packs

Post by kje » Jun 07, 2014 3:24 am

What is the difference on a usual 12V charger and a 12V power supply?

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Re: Homemade Battery Packs

Post by Skalabala » Jun 07, 2014 5:46 am

kje wrote:What is the difference on a usual 12V charger and a 12V power supply?
My guess will be the wave stability? Can not see why a car battery charger will not work for you if the cells are monitored.
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Re: Homemade Battery Packs

Post by DrkAngel » Jun 07, 2014 6:43 am

Skalabala wrote:
kje wrote:What is the difference on a usual 12V charger and a 12V power supply?
My guess will be the wave stability? Can not see why a car battery charger will not work for you if the cells are monitored.
Don't be stupid!

A simple request!

A 12V lead acid charger might output 15V+, pumping 5V into 4.1-4.2V limit cells will damage, possibly destroy, them.
You had better very very very "carefully monitor" ... or your pack, and surroundings, are liable to go up in smoke!
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Homemade Battery Packs

Post by Skalabala » Jun 07, 2014 11:56 am

But you use this http://www.ebay.com/itm/4000W-220V-AC-S ... 27e46e3893 on a charger without this Image :mrgreen:
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Re: Homemade Battery Packs

Post by 999zip999 » Jun 07, 2014 12:44 pm

12.6V is your goal and most all sla car chargers charge to 13.6v or much more.
That being said you can charge the pack with it if you seat and watch the voltage of the parelle cell group and not let it go above 4.2v so 12.6v for pack. But as soon as you think you know how fast it will charge it will run away from you and over charge.
So in a pinch yes if watched, but dangeruls.
As you must keep the 4.2v rule.

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Re: Homemade Battery Packs

Post by Skalabala » Jun 08, 2014 2:00 am

It will be really easy to modify it to be safer. A simple voltage beeper triggering a relay that switches the charger of.
Maybe try a meanwell? Should be cheap?
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Re: Homemade Battery Packs

Post by nioko » Jun 08, 2014 4:55 am

Kje, if I were you, I'd do the following:

Add connectors to each of your 20p Strings
Create a discharge Harness, or whatever you want to call it, to run these strings as 3s (resulting in the 3s20p battery that you have now).

Create a charge harness, that makes those strings 3p, resulting in a 1s60p battery

Charge using a lab power supply, set to your desired voltage per cell (4.1~4.2v), it will do CCCV, and your pack will obviously end up balanced.

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Re: Homemade Battery Packs

Post by Skalabala » Jun 08, 2014 7:22 am

nioko wrote:Kje, if I were you, I'd do the following:

Add connectors to each of your 20p Strings
Create a discharge Harness, or whatever you want to call it, to run these strings as 3s (resulting in the 3s20p battery that you have now).

Create a charge harness, that makes those strings 3p, resulting in a 1s60p battery

Charge using a lab power supply, set to your desired voltage per cell (4.1~4.2v), it will do CCCV, and your pack will obviously end up balanced.
Good idea I think.
Just remember its 20P3P3S so its 180P we want.
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Re: Homemade Battery Packs

Post by kje » Jun 08, 2014 10:01 am

I would never charge my batterypack with a lead acid charger.

Thanks for the inputs folks! I discovered my Imax B6 works with the 11-18V DC input. :D

After charging my batterypack without balancing, all 3 cells was at excatly same voltage! Thats nice. :) But how can that be when they where unbalanced before charging?

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