Mix new 18650 with old

[bikefan1]

Hi.
I'm ran into a snag with my battery build and that is the supply of recycled laptop batteries
I thinking of buying some new cells and using also good and tested old cells. Is there a problem with that?
These recycled cells would be a good condition cells.

 

[dogman dan]

Your older cells which I would assume to be lower capacity would limit your capacity. And it might balance funny.

 

[bikefan1]

Your older cells which I would assume to be lower capacity would limit your capacity. And it might balance funny.

Yes that is what I was thinking.
Older cells are around 2000 mAh. But new would be 2500 mAh.

 

[ecycler]

It depends on how you build the pack and how hard you are stressing them. If you distribute them evenly by mixing them into the parallel strings with the older batteries it should be fine as long as you make sure none of the old ones are self discharging and limit your DOD based on the older battery capacity. You are just looking to augment a primarily recycled battery pack, right?

 

[bikefan1]

It depends on how you build the pack and how hard you are stressing them. If you distribute them evenly by mixing them into the parallel strings with the older batteries it should be fine as long as you make sure none of the old ones are self discharging and limit your DOD based on the older battery capacity. You are just looking to augment a primarily recycled battery pack, right?

This is for a new pack. I saw this http://lunacycle.com/batteries/bare-cells/lg-18650-he4-18650-50-pack-wholesale/ seems like a good deal.
Then I would add in parallel old cells since 50 cells for 13s pack is too little. Most of the pack would be new cells.

 

[bionicdan]

I always wondered if you could make a 10ah pack using 4x2500 and 5x2000 etc etc. So the lower capacity cells get an extra helper to keep capacity even?

 

[tomjasz]

DO NOT MIX CELLS in any pack. Period. It's a waste of time and energy.

 

[ecycler]

It depends on how you build the pack and how hard you are stressing them. If you distribute them evenly by mixing them into the parallel strings with the older batteries it should be fine as long as you make sure none of the old ones are self discharging and limit your DOD based on the older battery capacity. You are just looking to augment a primarily recycled battery pack, right?

This is for a new pack. I saw this http://lunacycle.com/batteries/bare-cells/lg-18650-he4-18650-50-pack-wholesale/ seems like a good deal.
Then I would add in parallel old cells since 50 cells for 13s pack is too little. Most of the pack would be new cells.

Yikes. In that case I would go a totally different route. We need more info to make a decent recommendation.

What is the config you intend to build with the He4's?
How many recycled cells and what type do you intend to acquire?
Why F are you not just buying more He4's?
How many amps do you intend to draw peak and constant?
What is your target voltage?

Basically if you answer these questions in a way that makes sense, then you should build yourself a good pack with the new cells and use the old recycled cells to make a 'booster pack' to bump up the voltage. Put them in series to avoid damaging the good batteries and run a cycle analyst to make sure you do not deep cycle the good batteries. This is likely not going to work well as there is a huge different between used laptop batteries and He4's in discharge capabilities. My original understanding was that you did not have such disparity between the cells!

 

[bikefan1]

It depends on how you build the pack and how hard you are stressing them. If you distribute them evenly by mixing them into the parallel strings with the older batteries it should be fine as long as you make sure none of the old ones are self discharging and limit your DOD based on the older battery capacity. You are just looking to augment a primarily recycled battery pack, right?

This is for a new pack. I saw this http://lunacycle.com/batteries/bare-cells/lg-18650-he4-18650-50-pack-wholesale/ seems like a good deal.
Then I would add in parallel old cells since 50 cells for 13s pack is too little. Most of the pack would be new cells.

Yikes. In that case I would go a totally different route. We need more info to make a decent recommendation.

What is the config you intend to build with the He4's?
How many recycled cells and what type do you intend to acquire?
Why F are you not just buying more He4's?
How many amps do you intend to draw peak and constant?
What is your target voltage?

Basically if you answer these questions in a way that makes sense, then you should build yourself a good pack with the new cells and use the old recycled cells to make a 'booster pack' to bump up the voltage. Put them in series to avoid damaging the good batteries and run a cycle analyst to make sure you do not deep cycle the good batteries. This is likely not going to work well as there is a huge different between used laptop batteries and He4's in discharge capabilities. My original understanding was that you did not have such disparity between the cells!

What is the config you intend to build with the He4's?
What about 13s6p pack. Have 2 old in parallel with 4 new. Lunacycle is also selling Samsung 18650 INR-18650 25r not sure exactly what is the difference from the LG He4.

How many recycled cells and what type do you intend to acquire?
I have few brands of cells (around 30 cells ca. 2000 mAh). Most of them are Samsung can't rembered what type.

Why F are you not just buying more He4's?
Well the reason I'm not buying more is cost. I want to try at least use the cells that I already have. There is quite a lot of cost that is added with shipping to Iceland, taxes and customs.

How many amps do you intend to draw peak and constant?
BBS02 750W 48V, think it has 25A controller (thats peak amp I assume). Not sure what constant amperage would be. 10A maybe.

What is your target voltage?
48V that is what BBS02 750W 48V is rated for.

 

[DrkAngel]

Best to build a full voltage low capacity pack with recycled cells.

• Pre-test all cells for:
• Self-discharge
• Comparative IR
• Capacity

Test at light load

Build additional pack using new cells
(At minimum, pre-test cells for self-discharge)

Combine in parallel for use
Easy to add to either pack as more cells become available or as budget allows.

See - Homemade Battery Packs #1 post has handy Index

 

[ecycler]

What is the config you intend to build with the He4's?
What about 13s6p pack. Have 2 old in parallel with 4 new. Lunacycle is also selling Samsung 18650 INR-18650 25r not sure exactly what is the difference from the LG He4. It is very important that you have an equal amount of each in parallel to keep things balanced.

>Unless you get 52 new cells that is going to result in too much imbalance. The 25r's are a really good cell too, they seem to be much more common.

Why F are you not just buying more He4's?
Well the reason I'm not buying more is cost. I want to try at least use the cells that I already have. There is quite a lot of cost that is added with shipping to Iceland, taxes and customs.

>I understand. Iceland is a great place. Have not been there for more than 20 years, but really enjoyed my visit. It does actually complicate your build a bit since it means you will be running your bike at colder temperatures than most on this board. This is important because you will get poor performance from the weaker recycled batteries at low temps. Running them near their C rating which you should probably plan on only being 1C-2C will cause them to sag quite a bit.

How many amps do you intend to draw peak and constant?
BBS02 750W 48V, think it has 25A controller (thats peak amp I assume). Not sure what constant amperage would be. 10A maybe.

>That is helpful to know.

FYI- This is going to be quite an advanced battery building/balancing/monitoring scenario for your first pack build.

The numbers are not ideal. You only have enough old batteries to do 13s 2p and if you order 50 new you will only be able to do 13s 3p with a handful of spares. If you were to put these into parallel you would end up with a 48v nominal pack that holds 11.5ah, but you would be left with a bunch of extra unused batteries (4 old cells and 11 new cells!) Which is not ideal. You are literally leaving about ~130 watt-hours on the table with this route, but it should work fairly well and be easier to maintain.

Your biggest risk is a self discharging battery making its way into the pack and ruining other batteries. This is why I recommended doing the new and old batteries in separate packs and running them in series. That way if you have one of the old batteries fail, it can't hurt the new (expensive) batteries.

Your other more advanced (not recommended) option given you are not willing to acquire more cells would be something a little more exotic like:
10s 5p of the new batteries and and running that pack in series with 3s 10p of the old batteries. The advantages to this would be that you are utilizing all of your batteries and now your effective total pack would have 48v nominal with 12.5ah (limited by the larger 10s pack of the new cells.) The problem is since you are using the bafang system you will not have the capability to measure the ah used without getting a cycle analyst or one of the other cheaper meters on the market and you would likely be constantly deep cycling your good batteries since their pack would have less amp hours than the old battery pack. (12.5ah vs 20ah) The good thing about this route is that you would like have less voltage sag in cold weather and overall get more utilization of your battery.

How willing are you to learn and mess around with your battery?

None of this is really recommended, but since you are limited by resources I am doing my best to explain your options so you can learn.\

You would probably be best off just collecting 3-4 times as many recycled cells and learn more about pack building/monitoring etc and possibly ruin a few before trying to mix old and new batteries of different cell types into your first build and then save up so you can buy a larger quantity of new 18650's so you don't have to mix.

 

[999zip999]

I would keep new cells separate in it's own pack. Used laptop cells work well in a parallel of 8 or 10. The lg are some of newer greater cells don't waste them in parallel with old used cells. Do you have a spot welder ? If not buy pre welded in parallel string. Then you have taps to solder too and not to solder on cell. Plus a 80watt iron with a wet sponge to instantaneously cool down.

 

[bikefan1]

What is the config you intend to build with the He4's?
What about 13s6p pack. Have 2 old in parallel with 4 new. Lunacycle is also selling Samsung 18650 INR-18650 25r not sure exactly what is the difference from the LG He4. It is very important that you have an equal amount of each in parallel to keep things balanced.

>Unless you get 52 new cells that is going to result in too much imbalance. The 25r's are a really good cell too, they seem to be much more common.

Why F are you not just buying more He4's?
Well the reason I'm not buying more is cost. I want to try at least use the cells that I already have. There is quite a lot of cost that is added with shipping to Iceland, taxes and customs.

>I understand. Iceland is a great place. Have not been there for more than 20 years, but really enjoyed my visit. It does actually complicate your build a bit since it means you will be running your bike at colder temperatures than most on this board. This is important because you will get poor performance from the weaker recycled batteries at low temps. Running them near their C rating which you should probably plan on only being 1C-2C will cause them to sag quite a bit.

How many amps do you intend to draw peak and constant?
BBS02 750W 48V, think it has 25A controller (thats peak amp I assume). Not sure what constant amperage would be. 10A maybe.

>That is helpful to know.

FYI- This is going to be quite an advanced battery building/balancing/monitoring scenario for your first pack build.

The numbers are not ideal. You only have enough old batteries to do 13s 2p and if you order 50 new you will only be able to do 13s 3p with a handful of spares. If you were to put these into parallel you would end up with a 48v nominal pack that holds 11.5ah, but you would be left with a bunch of extra unused batteries (4 old cells and 11 new cells!) Which is not ideal. You are literally leaving about ~130 watt-hours on the table with this route, but it should work fairly well and be easier to maintain.

Your biggest risk is a self discharging battery making its way into the pack and ruining other batteries. This is why I recommended doing the new and old batteries in separate packs and running them in series. That way if you have one of the old batteries fail, it can't hurt the new (expensive) batteries.

Your other more advanced (not recommended) option given you are not willing to acquire more cells would be something a little more exotic like:
10s 5p of the new batteries and and running that pack in series with 3s 10p of the old batteries. The advantages to this would be that you are utilizing all of your batteries and now your effective total pack would have 48v nominal with 12.5ah (limited by the larger 10s pack of the new cells.) The problem is since you are using the bafang system you will not have the capability to measure the ah used without getting a cycle analyst or one of the other cheaper meters on the market and you would likely be constantly deep cycling your good batteries since their pack would have less amp hours than the old battery pack. (12.5ah vs 20ah) The good thing about this route is that you would like have less voltage sag in cold weather and overall get more utilization of your battery.

How willing are you to learn and mess around with your battery?

None of this is really recommended, but since you are limited by resources I am doing my best to explain your options so you can learn.\

You would probably be best off just collecting 3-4 times as many recycled cells and learn more about pack building/monitoring etc and possibly ruin a few before trying to mix old and new batteries of different cell types into your first build and then save up so you can buy a larger quantity of new 18650's so you don't have to mix.

You should visit Iceland again

I like the idea of having the two parallel packs. One recycled and one new. I'm thinking new pack: 13s4p (would buy 2 indentical cells from somewhere else to get 52 total). And recycled pack would be 13s2p, maybe that is too small to be of any difference?

The two packs should have two BMS right?

I like to tinkering with electronics. But have not much dealt with batteries so I'm very interested reading and learning.

Maybe I will hit the jackpot of recycled batteries then I could make all recycled pack
I don't have a spot welder but I have a soldering gun.

 

[DrkAngel]

Recycled cells must be thoroughly tested and matched.

• At 2p:
• that might not be possible?
• and not worth the cost of an additional BMS!

Recommend a minimum of 4p with spares for testing.
(keep looking for additional before building recycled segment?)

If properly matched cells, and monitored, a BMS is not "necessary".
A cheap BMS might be worse than none?
I recommend using bank level voltage monitor alarms regardless if using a BMS or not. VM 1-8s Alarms <$2
Search local eBay for "1-8S Lipo Battery Alarm", use 2 for 13s