Homemade Battery Packs

ASK1 said:

...I put together my first parallel group and... well, I'm questioning my whole design altogether. I'm not sure if there is enough compressive force from the rubber bands to maintain a good connection with my tinned copper.

My question is: is there any simple way for me to test this parallel group before I go on, to make sure all batteries have good contact with the rails? I don't have the equipment to do any kind of capacity testing, unfortunately.

This is what it looks like:

...

FYI I'm making a 13s8p pack. Any advice appreciated, thanks!

(And yeah, definitely wishing I had gone with solder tabs at this point. Also, I do not have access to a spot welder.)

Click to expand...

This will not be reliable. You need good electrical contact, either by welding, soldering, or using conductive epoxy. Sorry.

Test For Bulk Charge Feasibility

• Test all cells for:
• Self-discharge
• Comparative IR (Internal Resistance)
• Comparative Capacity

1. Carefully balance charge all packs
2. Confirm all cells of equal voltage, test after removed from charger for 1 hour (multi-meter at balance plugs)
label each cell with precise voltage - .01 needed .001 preferred
tape and felt tip marker works
3. Let set several days ... then re-test the voltage of each cell and compare to 1st measure
voltage loss is the Self-Discharge that must be (eventually) eliminated (some minor loss is to be expected, excessive discharging cells must be eliminated)
4. Connect cells in series ~24s-30s
5. Discharging gently through 2 - 120V 60w light bulbs should provide a 4 hour (1Ah per hour) 1 time evaluation test.
6. At some time into test (1 hour?), measure and note the voltage of each cell.
This is the Comparative IR (Internal Resistance)
Higher voltage sag indicates poor IR
Exceptionally poor IR cells should be (eventually) eliminated
7. Continue discharge while testing voltage of every cell at intervals
Intervals should become closer as cells near "empty"
("empty" varies with battery brand-model and discharge rate)
Pay closest attention to lowest voltage cell and watch for accelerated voltage loss = discontinue test
8. Let set several minutes
9. Measure and note cell voltages
This indicates Comparative Capacity
E.G. - (3 hours) 3000mAh + 3.725V (residual V)
Any notably lower cells should be eliminated-replaced - they diminish entire pack capacity
10. Recharge and balance all cells precisely ... again
Run a typical eBike discharge till your considered "empty"
Test each cell and compare voltages >> as a confirmation via higher discharge rate of cells of similar condition-capacity
11. If there are no notably self discharging cells, no cells of deviant IR and all of similar capacity ...
12. Test a bulk charge at ≤.5C (≤2A for 4Ah pack)
13. If cells return to equal beginning voltages at full charge ...
Congratulations!
Your pack is a good candidate for bulk charging (monitoring and occasional balance charges recommended as needed!)

If not ...
Replacing
#1 self-discharging cells
#2 poor IR cell
#3 poor capacity cells
can put you into good condition for bulk charging!

kje said:

What can I use to bulk charge 18650 batteries 60p at 4.2V? My imax charger can charge max 5a, but it would be great to charge these batteries at 30A in parallel... What charger is best for this job? Anything I can make myself?

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An old power supply from a discarded PC might do the job. I would use the 5V output, and run it through a 25A full wave bridge so you have two diode drops. Most PC supplies can put out 20A+, and there are a lot of old ones surplus at low to no cost. This will only charge you up to ~4V, which seems to be better for battery life anyway. This is top of the head and I have not tried it, but since you asked, it's a simple cheap idea.

An alternative is to get a cheap 5V power supply and adjust the output down, by modifying the circuit. Get something like a Mean Well SE-100-5. You would have to be enough of a tech to suss out the schematic and compute the required values. This is not something to try unless you really know your stuff in electronics, as there are high voltages in switchers that can kill you, or you could just burn up the supply. It's doable, but requires finesse.

25.9V 25.92Ah - Spring 2014 build
Accidentally discharged too deep!
Plugged pack into MeanWell with power turned off (MeanWell has LED volt meter that shows static voltage of pack)
Forgot to turn MeanWell on and discharged to ~3.6V per bank except 1 weak bank dropped below 3.00V.
Good news
1. Recharged to within a 3/100V equalization ... indicates minimal if any damage to weak bank.
2. Pinpointed a weak bank and will add a single 18650 to make weak link the strong link!
Then precisely balance ...
3. Charge showed capacity at 20.678Ah to 4.16V!
Not too bad for hundreds of cycles and thousands of miles

When making a 48v (13s12p) battery is it a good idea to make 13 separate parallel banks and connect them in series with banana plugs or Power Poles connectors so I can charge each bank separatly?

"Modular construction", separate banks, has advantages.
But charging banks individually is a poor and complex alternative to initial testing and trial of cells to build properly balanced banks allowing simple bulk charging.
Light gauge balance leads are adequate for any minor imbalance among reasonably screened cells and balanced banks.

Initial build priorities:
#1 Stringent elimination of self discharging cells - essential for any pack build!
#2 Rate comparative IR - reasonably important-desirable.
#3 Capacity rate cells for balanced capacity banks - fairly important but, easy to adjust later, add, remove or replace cells in any bank.

How about making a modular 13s12p construction and connect the banks in parallel when bulk charging?

And make a series wire like on the picture here when using the 48v ebike motor?

kje said:

How about making a modular 13s12p construction and connect the banks in parallel when bulk charging?

And make a series wire like on the picture here when using the 48v ebike motor?

Click to expand...

Sounds like a lot of work ... to accomplish ... ?

Why not invest in a BMS for 30bucks and a charger for as much. Sure 60bucks extra but imagine how many hours after hours you will save during each charge!

Allex said:

Why not invest in a BMS for 30bucks and a charger for as much. Sure 60bucks extra but imagine how many hours after hours you will save during each charge!

Click to expand...

What is taking so many hours? Charging all the banks in parallel?

What charger can balance charge 13s12p battery?

Open up the battery enclosure, Disconnect all of the wires, connect them to your charger, then reconnect everything together, each and every time before a charge - to you really need all that work?
And how will you charge every group? will you have 13 small chargers or wait for each to be finished? Sounds odd to me.

Just buy a BMS and a regular 13s charger - connect ONE plug and then forget about it, return after a few hours to disconnect one plug when your battery is full AND balanced

if you still want to be wild and crazy buy a rc charger like:
-TP-1430

-Graupner Ultra Duo Plus 45
-Graupner Polaron Pro
-for up to 14S

-Robbe Futaba E-1, or Eternity
-for up to 14S

-Schulze 14-801
-for up to 14S

Allex said:

Open up the battery enclosure, Disconnect all of the wires, connect them to your charger, then reconnect everything together, each and every time before a charge - to you really need all that work?
And how will you charge every group? will you have 13 small chargers or wait for each to be finished? Sounds odd to me.

Just buy a BMS and a regular 13s charger - connect ONE plug and then forget about it, return after a few hours to disconnect one plug when your battery is full AND balanced

if you still want to be wild and crazy buy a rc charger like:
-TP-1430

-Graupner Ultra Duo Plus 45
-Graupner Polaron Pro
-for up to 14S

-Robbe Futaba E-1, or Eternity
-for up to 14S

-Schulze 14-801
-for up to 14S

Click to expand...

Okay I see your point. ☺

How should I configure the cells? First parallel and then series?
What charger should I buy to charge 48v battery?

Used cells(?)

I would recommend parallels 1st,
then a single series connection
then a trial discharge
then carefully measure and label bank voltages
recharge and monitor with bulk charger
adjust for any weak or strong bank (replace or swap some cells)
repeat

I think Angel does series first. But if you look at manufactures it is always parallel first and then series.

Cheap charger:
http://es.aliexpress.com/store/product/100-240VAC-48V-54-6V-DC-2-0A-Lithium-LiPo-Battery-Charger-E-Bike-charger-suitable/313864_1043911845.html?spm=2114.04020208.3.20.W3RpQt&ws_ab_test=searchweb201556_1_79_78_77_80,searchweb201644_5,searchweb201560_9

Better quality:
http://www.aliexpress.com/store/product/High-Quality-Electric-Bicycle-Charger-13S-48V-54-6V-CV-2amp-Li-ion-LiPoly-Battery-Charger/313864_1960232393.html

Cheap BMS:
http://www.aliexpress.com/store/product/13-lithium-battery-protection-board-48v-lithium-battery-BMS-30A-continuous-60A-peak-discharge/313864_1741121963.html

Better quality:
http://bestechpower.com/481v13spcmbmspcbforli-ionli-polymerbatterypack/PCB-D132.html

It's used cells. I ordered this charger:
http://www.ebay.com/itm/121385746161?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Will that work?

Charger is for SLA = not good!
Cancel order ... if possible!
Voltage and charging method too high and wrong.

You need a 48.1V (13s) Li-ion charger (54.6V) or adjustable MeanWell type 48V power supply (53.3V - 54.6V).

EG http://www.ebay.com/itm/AC-110-220V...793055?hash=item3f4bb06cdf:g:CNcAAOSw-W5Uz0cC

DrkAngel said:

Charger is for SLA = not good!
Cancel order ... if possible!
Voltage and charging method too high and wrong.

You need a 48.1V (13s) Li-ion charger (54.6V) or adjustable MeanWell type 48V power supply (53.3V - 54.6V).

EG http://www.ebay.com/itm/AC-110-220V...793055?hash=item3f4bb06cdf:g:CNcAAOSw-W5Uz0cC

Click to expand...

Thank you. I asked the seller about cancelling the order.

Do I need BMS? Can this do the job?
http://www.ebay.com/itm/Batterie-Protection-BMS-PCB-Board-Balance-Pr-13-Packs-48V-Li-ion-Cell-Max-25A-/121713481986?hash=item1c56b05902:g:tx0AAOSw~gRVtKLm

Thorough cell testing before assembly and subsequent monitoring make a BMS not "necessary".

But, otherwise, the BMS you found is rather cheap insurance and capable for discharges ≤25A.

Hi, First time poster so please be gentle …

I’m building a 3s20p pack using the principles espoused by DrkAngel and others in this forum (Thanks).

Do any of the bulk chargers (Modded Meanwell / Other) have automatic shutdown when pack voltage reaches 4.1V ?

My packs will remain in my garage and a buzzer sounding when the pack hits 4.1v @1s (or 12.3 @3s) won’t cut it. Also, given the attention to avoid overcharging, I see value in having automatic charging shutdown @ 4.1v.

So, one option is the Turnigy Reaktor 300w charger with a 24c DC power supply (already have the power supply). Its spec’d at 300w and 20A charge rate. My pack will be conservatively rated @ 30A (Used Lenovo Li-Ion cells, tested 1500 mAh average) . I believe DrkAngel has developed a great procedure to optimize used cells for experimenters and I will follow it strictly. As such, I also don’t plan to use a BMS. So, some options charging at 1C will be:

1) 1s bank charging requirement would be 4.1v x 30A = 123 w. However, charger limited to 20A so charge time will be approx 90 minutes (30/20 x 60 minutes). Charging 3 banks will require swapping banks and take 3 hours.
2) Three 1s banks in parallel would be 4.1v but 90A = 369 w. With charger limited to 20A, charging time will be 4.5 hours (90/20 x60). Have to use parallel connector but benefit is one step charging (no swapping banks) and "natural" balancing of paralleled banks.
3) 3s pack charging requirement would be 12.3v x 30A =369 w. Benefit is no extra charge cables, just plug it in. Charge time approx 4.5 hours but without BMS and constant monitoring, there is a risk of voltage unbalance, one day.

My preference would be option 2, parallel charging @ 4.1v with an RC type charger.

If my desire is to have automatic charger shutdown, besides cost of a reputable RC type charger, what am I missing ?

MeanWells and similar adjustable power supplies automatically end charging when target voltage (1s-4.10 or 3s-12.3V etc.) is attained.
Does "maintain" selected voltage.

30Ah actual pack capacity should only be charged at a ≤15A (.5C) charge rate.

Charging at 3s is much preferable but should be closely monitored during initial charges and discharges.
Cell level Meter-Alarm highly recommended! <$1.50

Shift or add cells to any weak bank after initial tests-trials.

I'll charge at 0.5C and give one of the Meanwells a shot. Thanks again.

MeanWell type PS will adjust for 12.30V or 12.60V easily but might output more than its rated 12A.
Using lighter leads to battery should limit charge to 12A. 12A x 12.3V = 147.6w from 150w PS looks good.

See - MeanWell Mods S-150-12 details mods and tweaks for genuine MeanWell S-150-12.

DrkAngel said:

Light gauge balance leads are adequate for any minor imbalance among reasonably screened cells and balanced banks.

Click to expand...

How can I balance a 13s12p 48v battery pack?

kje said:

DrkAngel said:

Light gauge balance leads are adequate for any minor imbalance among reasonably screened cells and balanced banks.

Click to expand...

How can I balance a 13s12p 48v battery pack?

Click to expand...

#1 Proper screening and build might never, to seldom, ever require re-balancing!
#2 But 1s charges to individual banks can "equalize" manually.
#3 iMax B6 or similar can balance up to 6s at a time ...
#4 13s BMS w/equalization feature is the automatic way ... confirm-monitor for proper, or quality of, function!

DrkAngel said:

kje said:

DrkAngel said:

Light gauge balance leads are adequate for any minor imbalance among reasonably screened cells and balanced banks.

Click to expand...

How can I balance a 13s12p 48v battery pack?

Click to expand...

#1 Proper screening and build might never, to seldom, ever require re-balancing!
#2 But 1s charges to individual banks can "equalize" manually.
#3 iMax B6 or similar can balance up to 6s at a time ...
#4 13s BMS w/equalization feature is the automatic way ... confirm-monitor for proper, or quality of, function!

Click to expand...

OK so if I make this battery pack without balance cables it is still possible to "equalize" manually?