Charging lithium pack with solar without BMS

[GeorgeF]

Suppose I buy a brandnew quality 12v lithium battery pack without BMS and I charge it with a solar chargecontroller @ 14.1v and automaticly disconnect when it reach 13v also lvd @ 12.5v will the cells stay in balance for a long period of time?

If possible I intend to "bottom balance" first before charging and using it.

Above mentioned voltages are as examples.

In fact is my question what is the concept of max charge (hvd) and at which voltage should i disconnect (lvd) when using a 12v lithium pack without BMS so that the 18650 cells stay in acceptable balance for long period of time

And

in general is it wise to daily use lithium without BMS?

[Mike90250]

Yes it can be done.. Evel Knievel jumped lots of things that were unjumpable. Sometimes it even worked !!

I'd be more comfortable if you were using LFP batteries instead of roman candle batteries.

LFP is a bit safer, and trying to make a large battery pack out of 18650 cells is problematic in itself, with all the connections that can go bad, seals getting ruined from soldering or spot welding heat, and the sheer toxicity of the fumes if it goes bad.

If you absolutely know you have programed the loads to disconnect when the battery is low, and the charger to cease when the top voltage is reached, yes it's possible, but a BMS is really a good idea to save your investment. Voltage set points do nothing if you have a thermal runaway, or a 3rd hand battery in a fresh sleeve shorts.

[GeorgeF]

Ive read on this forum that EV manufactures do not use BMS and that bms is no 1 killer of lithium. So i thought a well balanced brandnew quality pack straight from the manufacurer i do not need a bms and i can use it with a solar system. Daily load is pre defined. Just cc/cv charging and set the setpoints so that the system automatically do the job.

[Mike90250]

Ive read on this forum that EV manufactures do not use BMS and that bms is no 1 killer of lithium. So i thought a well balanced brandnew quality pack straight from the manufacurer i do not need a bms and i can use it with a solar system. Daily load is pre defined. Just cc/cv charging and set the setpoints so that the system automatically do the job.

You might have read some dingbat spouting nonsense . That's the trouble with forums, anybody is an "expert" if they can shout often and loud enough. If you can steer me to that post, i'll put a moderator disclaimer on it.

All EV's have an extensive BMS system to insure the cells all run "middle of the road" and are never cycled deeply. It also monitors/controls temperature and controls charge/discharge to stay within limits. Many EV's have a liquid thermal control system to cool hot batteries.

When dingbats buy a battery pack from a crashed EV at a junkyard, THEY often strip off the BMS because they have no idea how it works. The worst of redneck engineering !

In DIY environments, $10 cell balancers (in actuality "vampire boards") are poorly engineered (if they are even engineered at all) and when they fail (and they often do) they fail shorted and discharge the cell, destroying it. Put 30 of the $10 P.O.S. vampire boards in a battery pack, and in 2 years one of them will fail shorted, kill a batch of cells, and then the other cells get overcharged because a redneck BMS is utilized, again with the cheapest POS parts and poor construction techniques .


Think about it, a $10, 1A vampire board, is supposed to trigger when a cell approaches 90% full ( or whatever it's set to) and your 20A charger is still putting 19A into the full battery. Whoopsie. There are no 20A vampire boards, which is what is needed on a 20A charger system.

[GeorgeF]

I kept a screenprint.

[SunEagle]

I kept a screenprint.

And that file is pure BS. You need a Battery Management system to properly and safely balance any Lithium chemistry battery. Sure you can try to charge without one but as Mike stated you are playing with dynamite and matches.

[GeorgeF]

Its a reply from one of your member Sunking in a thread somewhere in this forum.

If I have a Hvd and Lvd module will the pack stay in balance for a long period of time if I set the setpoints right, cut-off voltages high and low, presuming that the pack is well balanced before the first charge and i know exactly the max load current and duration.

lets say charge till 90% soc and then only 20% discharge.

[jflorey2]

Suppose I buy a brandnew quality 12v lithium battery pack without BMS and I charge it with a solar chargecontroller @ 14.1v and automaticly disconnect when it reach 13v also lvd @ 12.5v will the cells stay in balance for a long period of time?

No. Lithium ions will start to drift from day one. They will likely stay in balance for a long time. But one day one cell will drift until it's at a charge voltage of 4.6 volts, and the fire will start.

In fact is my question what is the concept of max charge (hvd) and at which voltage should i disconnect (lvd) when using a 12v lithium pack without BMS so that the 18650 cells stay in acceptable balance for long period of time

The less you cycle it, and the smaller the window of charge (say, 20% to 70% instead of 10% to 90%) the longer it will last.

in general is it wise to daily use lithium without BMS?

Absolutely not. It's like towing without safety chains. If everything is OK, do you need safety chains? No. But they still save a lot of trailers.

[GeorgeF]

So a solar chargecontroller will not give enough protection for a lithium pack?

[Mike90250]

I kept a screenprint.

And you are reading it out of context. That conversation was talking about consumer BMS, special built race carts, any why nobody uses vampire boards as a substitute for a true BMS

So a solar chargecontroller will not give enough protection for a lithium pack?

Absolutely NOT ( I want that text to blink )

[GeorgeF]

Ok. Thanks for all the answers

[jflorey2]

So a solar chargecontroller will not give enough protection for a lithium pack?

Definitely not. A balancing charger will (at least during charge) but that's a lot of work.

[SunEagle]

Its a reply from one of your member Sunking in a thread somewhere in this forum.

If I have a Hvd and Lvd module will the pack stay in balance for a long period of time if I set the setpoints right, cut-off voltages high and low, presuming that the pack is well balanced before the first charge and i know exactly the max load current and duration.

lets say charge till 90% soc and then only 20% discharge.

A lot of people have made statements that are opposite of what Sunking has posted. It doesn't make them right.

Look if you want to charge an Li battery without a BMS then go ahead. Just don't hurt anyone.

[GeorgeF]

With above hvd and lvd I ment in fact that i really cut-off high and low voltages with low voltage disconnect modules. A chargecontroller for solar charging and extra high voltage disconnect + low voltage disconnect module between the charger and battery pack as most chargecontroller do not cut-off but change to float mode. So when i really cut-off Im wondering then if i need a bms if set the setpoints accordingly.

[inetdog]

With above hvd and lvd I ment in fact that i really cut-off high and low voltages with low voltage disconnect modules. A chargecontroller for solar charging and extra high voltage disconnect + low voltage disconnect module between the charger and battery pack as most chargecontroller do not cut-off but change to float mode. So when i really cut-off Im wondering then if i need a bms if set the setpoints accordingly.

As long as the cells remain sufficiently well balanced and no individual cell failures occur you can get away with overall high and low voltage cutoff points for the multiple cell battery stack. But if you want to be prepared for any contingency you need to monitor the voltage of each individual series connected cell and if you do not have the capability to manage (shunt or remove from the string) individual cells you need to cut off the whole pack when one cell gets out of range.