Lithium questions

[CanuckRV]

I am really hoping on making the switch to Lithium batteries but have some questions and concerns.
All the batteries I have looked at say they can only be paired with batteries of the same type and manufacture. I can understand that for batteries in series but it doesn't make sense for batteries in parallel.
What can happen?
The reason I ask is I would like to build up my bank as finances permit, not all at once. I would like to eventually like to get to about 4oo amp hours.
As always Thanks for the help.

[Rlum]

Originally Posted by CanuckRV

I am really hoping on making the switch to Lithium batteries but have some questions and concerns.
All the batteries I have looked at say they can only be paired with batteries of the same type and manufacture. I can understand that for batteries in series but it doesn't make sense for batteries in parallel.
What can happen?
The reason I ask is I would like to build up my bank as finances permit, not all at once. I would like to eventually like to get to about 4oo amp hours.
As always Thanks for the help.

I have added different manufacturers and amp/hr lithiums in parallel. It is not ideal because the internal cells have different characteristics. They will not stay completely/properly balanced. But they will be closed enough to work OK. You can rebalance by hooking up the shore power and charge for 24 hours. All lithiums will be than reach their full charge capacity.
My van came with 2 100Ah lithiums. I added 2 100Ah Life blues. Than I added two X 200Ah Chinese made lithiums. Total of 800Ah so I could run air conditioner from bank.
Having said this. Battle Born has black friday sale now.
Try to get batteries with build in BMS with blue tooth. Also if you can afford, get the ones with built in heaters if you live where it is cold!

[jakegw2]

Avanti found this link quite a while back. More then you ever needed to know about connecting different batteries in parallel:

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Bottom line: Internal resistance matters a great deal. When connected in parallel even relatively small differences will create significant differences in current loading between batteries. Your array will work, but some of the batteries will work harder than others and will wear out more quickly.

Possible solutions: As Rlum said, making sure you have a charging system that can periodically fully fill the cells and thus rebalance them is a good starting point. The next thing you could do would be to simply accept the differences in wear and recognize that the lifespan of your array will be shorter than the lifespan of your individual batteries. I would choose this option - LiFEPo4 prices have been dropping and this is the simplest and not particularly expensive option.

If you don't want to have reduced array lifespan then there is always the option of using a ammeter to measure the current flowing from each battery under load and manually balance them by adjusting the length of the wire used to connect them to the array so that the total resistance is more closely matched between batteries. This would not be perfect as I don't think internal resistance is constant, but you could balance it for the most typical withdrawl scenario and prolong the life of the otherwise most-stressed batteries. It wouldn't cost much to do this from a material perspective, but if you needed to hire someone skilled enough to do this well it would probably not be cost effective.

[Rlum]

Originally Posted by jakegw2

Avanti found this link quite a while back. More then you ever needed to know about connecting different batteries in parallel:

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Bottom line: Internal resistance matters a great deal. When connected in parallel even relatively small differences will create significant differences in current loading between batteries. Your array will work, but some of the batteries will work harder than others and will wear out more quickly.

Possible solutions: As Rlum said, making sure you have a charging system that can periodically fully fill the cells and thus rebalance them is a good starting point. The next thing you could do would be to simply accept the differences in wear and recognize that the lifespan of your array will be shorter than the lifespan of your individual batteries. I would choose this option - LiFEPo4 prices have been dropping and this is the simplest and not particularly expensive option.

If you don't want to have reduced array lifespan then there is always the option of using a ammeter to measure the current flowing from each battery under load and manually balance them by adjusting the length of the wire used to connect them to the array so that the total resistance is more closely matched between batteries. This would not be perfect as I don't think internal resistance is constant, but you could balance it for the most typical withdrawl scenario and prolong the life of the otherwise most-stressed batteries. It wouldn't cost much to do this from a material perspective, but if you needed to hire someone skilled enough to do this well it would probably not be cost effective.

Very good information. Your right. They charge and discharge differently. Last set of lithiums from China have internal BMS showing individual cells and voltages. Original battery have no BMS or any information. Life blue have just general information such charge and discharge SOC. They work together but not perfectly?

Thanks for information!

[CanuckRV]

So I should be ok mixing as long as I try to stay as close as possible to the original and do periotic maintenance to balance out the batteries.

[ikanode]

Originally Posted by CanuckRV

So I should be ok mixing as long as I try to stay as close as possible to the original and do periotic maintenance to balance out the batteries.

I read the replies as "You might not have major problems other than a shortened life for the bank. You might get by with frequent monitoring and maintenance to keep them in balance."

Frequent could mean daily monitoring, with maintenance daily, or weekly, maybe even longer than that.

It's a gamble with reasonable odds if you closely monitor--but still a gamble.

[JML]

One issue I discover when I explored adding a LiPo battery to my current one was an incompatibility with the built in BMS on my current battery. In the end, I am going with a single, 280 AMP HR Battle Born - for me, size, no more need for power beyond the 280 AMPS, placement, etc. factored into this decision.

[HarryN]

Originally Posted by JML

One issue I discover when I explored adding a LiPo battery to my current one was an incompatibility with the built in BMS on my current battery. In the end, I am going with a single, 280 AMP HR Battle Born - for me, size, no more need for power beyond the 280 AMPS, placement, etc. factored into this decision.

There are only a handful of common, commercial, internal BMS systems in common use in most LiFe based batteries on the market.

The majority of them have fairly high internal resistance at 100 amp discharge rates, even if the battery that is using them is rated for higher currents.

In practice what this means is that very often, you are better off to purchase multiple batteries and design your power system around a 50 - 60 amp discharge rate vs higher.

[JML]

Thanks for the info!