100AH Lithium cant handle start up draw

[dreadlocks]

@shade, well yeah.. but at least its not trying to overload it for 5-6h.. only a couple (hint: you really should have a DC charger for a LFP, dont trust your alternator not to cook everything.)

@67cj5, yes thats pretty much it.. you hook it up to a 10A charger it'll take 10A til its full.. you hook it to a 100A charger and it'll take 100A til its full.. it behaves nothing like lead batteries, if you drain a 100AH lead battery down to the danger zone, you might see that 20A charger hit peak power.. for 30mins or so, and then slowly starts shedding amps until its sitting in absorb, barely putting out anything.. trying to stuff that last 20% of the charge down the battery's throat.

If you want a bad fluid analogy, charging a lead battery is like a gravity fed system... as more liquid drains out of the tank above you, less pressures on it so the flow goes down and everything slows down... charging a LFP battery is like having a big firetruck pump hooked up to it, its gonna transfer fluid at 100% all the way til its done.. at rates your not gonna get out of a reasonable gravity system.. and if continue my poor analogy, your lead storage tank will rust if its not full and start to take on damage, your LFP tank wont.. in fact it'll last longer if its not always full, counterintuitively.

 

[shade]

well yeah.. but at least its not trying to overload it for 5-6h.. only a couple (hint: you really should have a DC charger for a LFP, dont trust your alternator not to cook everything.)

Yeah, I'll go with a DC charger and a solar controller no matter what I do. My truck has a 130A alternator, so I have a little more power to work with on that end.

 

[67cj5]

@shade, well yeah.. but at least its not trying to overload it for 5-6h.. only a couple (hint: you really should have a DC charger for a LFP, dont trust your alternator not to cook everything.)

@67cj5, yes thats pretty much it.. you hook it up to a 10A charger it'll take 10A til its full.. you hook it to a 100A charger and it'll take 100A til its full.. it behaves nothing like lead batteries, if you drain a 100AH lead battery down to the danger zone, you might see that 20A charger hit peak power.. for 30mins or so, and then slowly starts shedding amps until its sitting in absorb, barely putting out anything.. trying to stuff that last 20% of the charge down the battery's throat.

If you want a bad fluid analogy, charging a lead battery is like a gravity fed system... as more liquid drains out of the tank above you, less pressures on it so the flow goes down and everything slows down... charging a LFP battery is like having a big firetruck pump hooked up to it, its gonna transfer fluid at 100% all the way til its done.. at rates your not gonna get out of a reasonable gravity system.. and if continue my poor analogy, your lead storage tank will rust if its not full and start to take on damage, your LFP tank wont.. in fact it'll last longer if its not always full, counterintuitively.

So my 26 amp Noco Smart Charger would work fine with a 100Ah Lithium Battery, But when it comes to Charging one using Solar, I have a Victron Smart 100/20 Charge controller, So how would you match it to charge a 100Ah Lithium battery so the battery gets charged to the correct voltage/rate of charge, ?

 

[luthj]

I don't think a dc-dc is necessary if your alternator voltage is between 13.6-14.2V. You may want to downsize your charging circuit wiring to provide some current limiting, but thats not hard to work out with minor testing.

There is the fear of overloading alternators, but thats rarely the case with over the road vehicles. When the alternator hits its current limit, it just drops its voltage until the current is under the limit. say from 13.8 to 13.6V. At idle speed that may be about 80% of its "rated" current. Running for hours at this limit can stress an alternator, but with a 100AH battery you are not going to have that problem, as current will start to taper after 20 minutes or so.

With higher alternator voltages, you will want to stop charging the lithium battery when its nearing full. You can use a battery monitor for this. Another option is an accurate voltage triggered relay. Set it to open the charging relay when the battery gets to within 0.1V of the alternators normal voltage. This signals the current has tapered down, some testing needed.

Another option is simply to use a manual switch. Turn it on for 30 minutes, then turn off. This is really only necessary at charge voltages above 13.9V, below that there is minimal aging done to the battery, as you simply won't be driving enough hours in a year to cause significant high SOC aging.

 

[dwh]

So my 26 amp Noco Smart Charger would work fine with a 100Ah Lithium Battery, But when it comes to Charging one using Solar, I have a Victron Smart 100/20 Charge controller, So how would you match it to charge a 100Ah Lithium battery so the battery gets charged to the correct voltage/rate of charge, ?

Bulk to specified full charge voltage, no absorb, float voltage set below the specified full charge resting voltage of the battery.

IIRC, for a BattleBorn, full charge is 14.6v, resting is 13.6v. But LiFePo4 lasts longer if you don't take it all the way to 100%, so I'd probably do something like bulk to 14.4v, no absorb, float at 13.2v.

Being less than full, the resting voltage might be something like 13.4v.

Setting the float voltage below resting voltage basically turns off the charging, because if the charger is at 13.2v and the battery is at 13.4v, no power flows toward the battery.

The BB is dead at like 12.8v or some such (just woke up, no coffee yet, so don't quote me). So if it drops down to 13.2v due to load (which is like...I dunno...50% or something below 100%), the float voltage of the charger will supply some amps (if the sun is up) to service the load and maybe keep the battery from dropping lower, or at least slow down the rate of discharge.


But that's all just generalizing to convey the basic idea. I don't have the bluetooth dongle for my Victron 100|30, so I haven't played with programming it. In particular, I'd wanna know what voltage will cause it to jump back into bulk.

 

[dwh]

As for the correct rate of charge, BB can accept 1C (100a for a 100ah battery) charge current. But they recommended .5C for longer life, which would be 50a for a 100ah battery.

So any charge current below 50a is low stress as far as the battery is concerned.

 

[67cj5]

Today I have been chasing companies re Lithium batteries, One guy told me to forget about them because they are not where they should be in terms of performance, and when I asked about AGM's he said that GEL was the better way to go because they have a higher output and charge faster, then another site said AGM are faster when it comes to charging and then A Solar site said that FLA Deep cycle and AGM is my best option,

So then I read the NOCO manual and it says use the normal charge mode for Deep cycle and GEL and Calcium batteries etc and then another site said that you need a certain type of charger for Gel yet Noco uses the normal mode, My Normal charger manual says it can charge it is for use with lead acid batteries,

Yet the noco classes all of these in the Lead Acid Category

"For charging 12-volt Wet Cell, Gel Cell, Enhanced Flooded, Maintenance-Free and Calcium batteries. When selected, a white LED will illuminate."

Finally you guys got me to thinking about buying Lithium, and then I get on another that recommend Charging Lithium 100Ah Batteries with a Charge that is less than 20 Amps.

And then the Same Site goes on to say This.

• A flooded battery can accept a charge rate of up to 25 percent of its capacity
• A Gel battery has a higher acceptance rate of as much as 30 percent of its capacity
• An AGM battery accepts the highest charging amps, as much as 40 percent of its capacity

Basing those figures on one of my 115Ah FLA DC Batteries @ 25% is a Charge rate of 28.75 Amps, Is just crazy based on the fact that it is common knowledge that the best charge rate should be around 10% and even charging the same battery at around the 12Amp mark with a start up Peak of 16 Amps for 2 to 3 seconds is still too high for a 115Ah Battery and Although the Charge time is a lot longer the start up peak charge rate of around 10 Amps dropping to 8 to 9 Amps gives a far better charge than using the 16/12Ah charge rate,

I even checked out battery University and they mentioned about those high charge rates too, But where this all goes wrong is that No One can agree on the correct charge rates depending on the Battery Types being charged,,

You Guys say how your Lithium batteries can handle High charge and discharge rates yet every where I check says otherwise, Now I know you Guys are running your batteries right down low and hooking up microwaves and coffee machines up to them, So Does anyone know what on earth those clowns are talking about.

 

[67cj5]

Bulk to specified full charge voltage, no absorb, float voltage set below the specified full charge resting voltage of the battery.

IIRC, for a BattleBorn, full charge is 14.6v, resting is 13.6v. But LiFePo4 lasts longer if you don't take it all the way to 100%, so I'd probably do something like bulk to 14.4v, no absorb, float at 13.2v.

Being less than full, the resting voltage might be something like 13.4v.

Setting the float voltage below resting voltage basically turns off the charging, because if the charger is at 13.2v and the battery is at 13.4v, no power flows toward the battery.

The BB is dead at like 12.8v or some such (just woke up, no coffee yet, so don't quote me). So if it drops down to 13.2v due to load (which is like...I dunno...50% or something below 100%), the float voltage of the charger will supply some amps (if the sun is up) to service the load and maybe keep the battery from dropping lower, or at least slow down the rate of discharge.


But that's all just generalizing to convey the basic idea. I don't have the bluetooth dongle for my Victron 100|30, so I haven't played with programming it. In particular, I'd wanna know what voltage will cause it to jump back into bulk.

Awesome Well Done, yeah that makes sense, so all I need to do is use the App and set to where it is not peaking out,

 

[shade]

I don't think a dc-dc is necessary if your alternator voltage is between 13.6-14.2V. You may want to downsize your charging circuit wiring to provide some current limiting, but thats not hard to work out with minor testing.

There is the fear of overloading alternators, but thats rarely the case with over the road vehicles. When the alternator hits its current limit, it just drops its voltage until the current is under the limit. say from 13.8 to 13.6V. At idle speed that may be about 80% of its "rated" current. Running for hours at this limit can stress an alternator, but with a 100AH battery you are not going to have that problem, as current will start to taper after 20 minutes or so.

With higher alternator voltages, you will want to stop charging the lithium battery when its nearing full. You can use a battery monitor for this. Another option is an accurate voltage triggered relay. Set it to open the charging relay when the battery gets to within 0.1V of the alternators normal voltage. This signals the current has tapered down, some testing needed.

Another option is simply to use a manual switch. Turn it on for 30 minutes, then turn off. This is really only necessary at charge voltages above 13.9V, below that there is minimal aging done to the battery, as you simply won't be driving enough hours in a year to cause significant high SOC aging.

There's value in the simplicity of the methods you described. Lower costs and less to fail is appealing. I'll have to confirm this applies to mine, but I believe Toyota typically uses lower voltage alternators, so that's probably going to mean a DC-DC charger will be useful no matter the battery chemistry.

 

[dwh]

The key for lead-acid is that "up to" 25% (or whatever).

Lead-acid batteries build up electrons on the plates, which is called surface charge. Surface charge causes the voltage to rise, even though the battery hasn't actually charged much.

Because the voltage has gone up, the resistance of the charge circuit has gone up, so the amp rate goes down.

Waiting for the builtup electrons to dissipate into the electrolyte (actually charging the battery) is why it takes hours for lead-acid to absorb a full charge.

So you could have a million amp charger charging the battery, but at X voltage, the battery will absorb Y amps per hour...period.

The only way to drive more amps through the thing, is to raise the voltage potential of the supply. That what "constant current" charging is; running the charger flat out without regulating the voltage at all. Of course, you limit the current to some max, like 25a or whatever the charger is rated to, but until the voltage of the battery rises to whatever the bulk voltage is set to, say 14.6v, then the charger is just running wide open.

But, because the electrons are building up on the plates faster than they dissipate into the electrolyte, the battery will ultimately be what is regulating the amps flowing and the rate at which the voltage rises.

Same thing happens with lithiums...but they buildup less surface charge and it dissipates into the electrolyte a hell of a lot faster.


So while a lead-acid might only be accepting 10a...no matter if the charger is limited to 20a or 50a or 100a...the lithium has such a low resistance and dissipates surface charge so fast, it'll suck down however much your charger is capable of producing.

Which is one reason the lithium needs an onboard BMS, to keep it from sucking down too much too fast, overheating and doing an impersonation of magnesium shavings meeting a spark.

 

[luthj]

A BMS does not restrict charge current in the vast majority of cases. And high charge rates generally don't cause any heating or fire danger, unless we are talking about 2C rates. Lithium cells have supremely low internal resistance, and it stays that way almost to 100% charged.

The fire danger with lithium comes from excessive cell voltages. These cause the electrolyte to break down, forming a gas. That gas can build up and escape from the cell. This gas is very flammable, as is the lithium in the cells. This can be caused by too high overall charging voltage, or a cell imbalance that allows one cell to get well above the others during a charging event.

Over discharging can cause the cells polarity to swap, the resulting electrolyte breakdown during the following charge cycle is also a fire danger.

LFP has much lower thermal coefficient, and is less likely to cause a fire by a large margin than other lithium chemistries.

Over heating the cells can cause internal shorts or thermal runaway, same as lead acid. But that temperature should be quite difficult to obtain in an application running at 1C or less.

The primary purpose of the BMS is to prevent over voltage, under voltage, and to balance any drifting cells. On lead acid, you can perform a absorb charge, and let the low cells come up to match the others. With lithium this would cause one or more cells to go dangerously high voltage, and this start turning electrolyte into gas. The balancing system shunts current around the high cells typically, allowing the others to come up to match them.

 

[67cj5]

The key for lead-acid is that "up to" 25% (or whatever).

Lead-acid batteries build up electrons on the plates, which is called surface charge. Surface charge causes the voltage to rise, even though the battery hasn't actually charged much.

Because the voltage has gone up, the resistance of the charge circuit has gone up, so the amp rate goes down.

Waiting for the builtup electrons to dissipate into the electrolyte (actually charging the battery) is why it takes hours for lead-acid to absorb a full charge.

So you could have a million amp charger charging the battery, but at X voltage, the battery will absorb Y amps per hour...period.

The only way to drive more amps through the thing, is to raise the voltage potential of the supply. That what "constant current" charging is; running the charger flat out without regulating the voltage at all. Of course, you limit the current to some max, like 25a or whatever the charger is rated to, but until the voltage of the battery rises to whatever the bulk voltage is set to, say 14.6v, then the charger is just running wide open.

But, because the electrons are building up on the plates faster than they dissipate into the electrolyte, the battery will ultimately be what is regulating the amps flowing and the rate at which the voltage rises.

Same thing happens with lithiums...but they buildup less surface charge and it dissipates into the electrolyte a hell of a lot faster.


So while a lead-acid might only be accepting 10a...no matter if the charger is limited to 20a or 50a or 100a...the lithium has such a low resistance and dissipates surface charge so fast, it'll suck down however much your charger is capable of producing.

Which is one reason the lithium needs an onboard BMS, to keep it from sucking down too much too fast, overheating and doing an impersonation of magnesium shavings meeting a spark.

With my big wheeled charger I noticed that the higher the Amp setting the faster the battery starts gasing, on the 35A setting it will do it within 30 seconds on a 60Ah battery and on the MED setting the voltage gets up around 14,9v as the battery becomes charged, On the lowest setting it takes a while for the voltage to reach 14.5 to 14.7v on a 115Ah battery depending on it's SoC. but it normally takes around 3.5 to 4.5 hours at 50% SoC.

 

[shade]

Which is one reason the lithium needs an onboard BMS

A BMS does not restrict charge current in the vast majority of cases.

I know batteries used in specific applications must do this (hybrid/EV cars come to mind), but are there LFP batteries for this use that offer a direct interface between their internal BMS and an external charger?

 

[luthj]

I know batteries used in specific applications must do this (hybrid/EV cars come to mind), but are there LFP batteries for this use that offer a direct interface between their internal BMS and an external charger?

EV BMS systems usually communicate with the charger. This is to allow max safe charge rates. The BMS will throttle back the charger if there is an overheat, or balancing issue.

I should revise my previous post to include "for applications discussed here". As fully integrated EV and high power systems do use bi-directional communication between BMS and load/sources.

For applications discussed here that is not applicable, as we don't need to get 4 hours of driving from a 20 minute charge...

 

[dwh]

With my big wheeled charger I noticed that the higher the Amp setting the faster the battery starts gasing, on the 35A setting it will do it within 30 seconds on a 60Ah battery and on the MED setting the voltage gets up around 14,9v as the battery becomes charged, On the lowest setting it takes a while for the voltage to reach 14.5 to 14.7v on a 115Ah battery depending on it's SoC. but it normally takes around 3.5 to 4.5 hours at 50% SoC.

Voltage "potential".

Those big chargers are pretty simple. When you switch the "amps" what you are actually doing is switching the voltage from a multi-tap transformer, and a current limit controlled by the circuit board.