LITHIUM <span class="highlight">BATTERY</span> CHARGING

I have an enerdrive 40 amp dcdc charger as well as an enerdrive 40 amp 240 v charger. Neither of these float once the lithium is charged. Renogy also make no mention of float for their batteries. Once it is fully charged it simply drops the charge amps dramatically.

"Once it is fully charged it simply drops the charge amps dramatically"

That is what a float charge stage does!

To be more precise, the charger does not drop the amps, the charger holds it charge voltage at its max charge volts, the battery amps then gradually taper off as the battery no longer wants to accept further charge. when the charge current drops to the set point the charger then changes to the float stage which in the Enerdrive 40A unit for Lithium it is 13.5V -14.2V and can not be turned off as detailed in the manual. They call it power supply mode but in reality applying any voltage to the battery once fully charged is float charging by whatever name you wish to call it. Their previous model was a better unit, it actually terminated charging at a specific point and resumed charging when the battery voltage dropped to a predetermined set point set point.

Renogy is states no float stage is required for Lithium. It also doesn't have a current set point to stop charging so one assumes it charges till the current drops to a certain point then what? Does it turn off and just stay off, what if a load is then applied to the battery does the battery just discharge or does the charger resuming charging at some point? They supply little detail of the Lithium functionality, for this reason I would steer clear of it.

The charger starts charging as soon as a load is put on the battery.

So how does it know when to start charging, the terminal voltage of a Lithium drops very little with a load applied. If it was charged to 14.4V for example then it will gradually drop to its fully charged terminal value over a period of time once there it will change very little with load. If it starts charging before the battery voltage drops below whatever its fully charged resting voltage is it is float charging. It may cycle on and off but it is still float charging.

The problem I assume Enerdrive found was they set their original charger to supposed start recharging at around 70% SOC, the problem with that is how do you determine 70%SOC. Different brands and different cells have different terminal volts at 70% SOC. My Lithiums sit around 13.2V@97% SOC and 13.1V@70%SOC with a light load, it doesn't give much to work with. I assume this caused issues for Enerdrive and that is why the new model has float charge or power supply mode as it was to hard to determine when to restart charging.

The Renogy unit does not have the ability to set a float voltage, nor does it have the ability to set at what current to stop charging, they have provide virtually no details:

What charge current does it stop charging at or does it even stop charging when the battery is full, it doesn't indicate it does?

What at what voltage does it restart charging?

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HKB,

You raise a very good point Leigh....... "At what point does a Lithium charger initiate the charging cycle"?
Every article on Lithium charging that I have read begins the description with reference to the charging current but does not indicate how the cycle begins. It seems to assume that you connect the charger to a battery in some state of discharge, switch it on, and the charge cycle begins.

So what happens in the case of a permanently connected and powered charger? As you say, observing cell volt drop as a function of a small applied load produces only a very small voltage change which would not be a reliable instigation. And it would not be desirable to wait until the cell voltage had fallen to a low state of charge. Surely it is not done by Coulomb in/out counting?

So how is the charge cycle initiated? If anyone knows for sure, please let me in on it.

"Surely it is not done by Coulomb in/out counting?"

You've stolen my thunder, Allan. I don't think it is done that way, but I was going to suggest it as a method.

You can buy inexpensive coulomb counter battery monitors that use Hall effect sensors (or shunts) so IMO the technology is there begging to be used.

Add one to the internals, write a few lines of code [:-)], including a user input for battery capacity, determine or have programmable a SOC threshold for return to bulk and away you go.

Simples :-)

Enerdrive goes to power supply mode (float charges) once fully charged and will supply upto max set current, if terminal voltage drops to 13.3V goes to charge. Gives an example of float voltage of around 13.5V being maintained for 7 days then maintenance charge applied then back to float again for 7 days etc. However the actual float voltage is adjustable from 13.5V - 14.2V, it does not state though if the restart voltage of 13.3V changes if you change the float voltage.

Ctek, goes to float mode for upto 10 days then pulse charges for max 1hr pulse, auto pulse 10 days whatever that means. Float can supply upto max amps, reverts to charge stage if battery voltage drops. Very similar to the Enerdrive unit except restarts charging if voltage drops below the float voltage.

Redarc float charges, goes to charge if battery voltage drops but doesn't state what current it will supply in float mode before reverting to charge stage.

It would seem these three decided it was easier to have the charger remain active, ie they all supply a continuous voltage to the battery once fully charged, call it float mode/power supply mode whatever. If the draw on the battery and charger gets to the point where the battery terminal drops below the set point in the case of the Enerdrive unit, or the float voltage of the other two, then they all revert back to the charge stage, ie they will run at maximum output until the max charge voltage is reached and once again revert to float.

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Thanks for that Frank. If ever I get a lithium setup I'll get a Coulomb counter thingummy, dash off a bit of code and giddyap, away we go.
In the meantime can you enlighten me how the typical lithium charger knows when to let the horses out? Ta.

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Even though many expressions are made that it is neither needed nor desirable to float charge lithium batteries, it seems that it is being done in practice by typical chargers (ref. HKB) in order to obtain a voltage point for initiation of the charge cycle.
Beats measuring Coulombs and writing code Frank. lol

I don't know if Enerdrive's DC2DC is typical, Allan, but here's a cut and paste from their owners manual (latest version)



I, too, am somewhat confused by the "don't float lithium batteries" then as far as I can tell, all charger manufacturers do it. Sometimes it's called a "maintenance charge". How that differs from float beats me.

The proprietor of EV-Power says the charger should charge to 100% then switch off and he sells one that does that. (Mains, not dc to dc). But I don't know how it returns to bulk.

EV powers charger, 14.4V peak charge voltage then OFF, automatically restarts charging at ~12.8V. Not really practical for use by most in a mobile situation as you wouldn't want the battery dropping to 12.8V if charge is available. For electric car with planned usage or home use maybe.

Float charging of Lithiums when fully charged is not good for them, hence charger manufacturers renaming of float to supply mode they do it that way as it is the easiest solution. Also keep in mind some lithium batteries aren't good at keeping their cells balanced, they need prolonged charge time to let the BMS balance the cells. Also keep this in mind if you buy a charger from a manufacturer that also has is own line of Lithium batteries as their chargers will no doubt be tuned to meet their batteries specific needs and they may not be suitable for your battery if supplied from another company.

In a mobile situation though you most likely want to fully charge the battery in a day as either you stop driving at days end or the sun goes down. Battery then partially discharge overnight so long periods of floating don't occur. If your going to be parked up in a park for a few days and your not using the batteries you can either disconnect the battery if possible and just leave the charger in supply mode or turn the charger off and on as required. I generally just leave the charger off and turn it back on when the battery drops to around 70% SOC till its charged.

This is from the Renogy 100amp/hr battery manual..

Yep the BMS needs it to cell balance, it shouldn't.

I have had my Lithium for around 6 years now, I have never needed to balance the cells, a good quailty battery will have matched cells and they won't drift out of balance. If a battery manufacturer indicates their battery needs regular cell balancing then something is wrong, they are most likely using low quailty cells or cells haven't been matched during manufacture. A lot of cheap drop ins suffer this issue as they are made of many poor quailty cells in a parallel series combinations to get the required Ah and voltage.

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I guess that it is fortunate that, for touring, the daily routine of 'engine start-up' or 'solar awakening' resets the charger. For van park stays just manually manage it as HKB suggested.
Don't know why I'm interested........ I don't even have lithium. lol

When I did my conversion from AGM to lithium, Ev-power told me that although the ideal setup was dedicated lithium chargers, in a camping environment lead-acid chargers with suitable selectable voltages were ok.

So my mains charger, dc to dc and solar regulator are all lead-acid chargers but all have suitable selectable voltages. Only one is ever in use at a time, so like HKB, when the battery is fully charged I turn off the relevant charger and turn it on again when needed. Fully manual, no smarts except the stages within the chargers and if I don't turn off the charger there is no real issue because the "error" is short term and the float voltage is within the battery spec for the period the charger is on, so no big deal.

Each of my chargers, when I turn it on, goes into bulk mode. So if the partially discharged battery is at, say 13.2 volts, and I turn a charger on it will start in bulk and complete a full cycle. All three chargers, when they go into the constant voltage segment (absorption) don't stay there long and drop into float within maybe 20 minutes, so they're almost as good as dedicated lithium chargers. (With my old 315Ah AGM battery bank they would stay in absorption for hours.)

Being manual, it is not the most efficient system, but I have an abundance of capacity and an abundance of solar for my needs so if I miss the mark a bit it doesn't matter.

In my camping environment the battery typically floats (wrong term, perhaps) between 50 and 100% SOC. And the beauty with lithium is that if you get a prolonged period of poor sun you can wallow around in the 20 to 30% SOC area for as long as required with no detriment to the battery.

For storage I discharge the battery to about 70% and disconnect the negative to isolate it.

I have now a 40 amp Renogy dcdc charger on my 100amp lithium renogy battery. The dcdc charger does not go into float as Renogy says it is not required.

So where back to what conditions have to be met before they charger stops charging and starts charging again?

The fact that the manufacturer provides no detail as to the Lithium functionality is a pretty good reason in itself not to use it.

I was very surprised to also find the unit has to be turned off and on by trigger wire, ie no voltage sensing function, that would be a turn off for a lot of users.

Wouldn't the charger (talking about modern intelligent chargers) consider things like cell temperature, voltage movement, predetermined amperage used and other electronic factors as built into the charger? I can custom set up the parameters on the enerdrive if I so wish. Thats why I thought they were called "intelligent" chargers..they know when to switch on or off. I also use a coulomb meter and find it excellent (actually use 2--one in camper on agm batts and one in rear tub on lithium) @$100 better than most meters I,ve seen with a simple screen, large display and simple to set up.

The renogy unit looks very basic, the fact they provide no information regarding the Lithium functionality is they probably don't know what it is. The unit is no doubt a rebranded Chinese unit. from memory renogy was the company someone mentioned on another forum, they asked renogy what type of cells, who many cells and the brand of cells used in their battery and they could not tell them what them.

Intelligent chargers are only intelligent in that they have tow or more stages and they can run a preset program. Your Enerdrive unit for example if you use user settings you have to tell it the charge voltage, the float voltage, maximum charge rate, what current to stop charging at, absorption time etc. In other words it is still pretty dumb, it has a set program and you tell it what it needs to do at each stage. It can't work out for itself when to start charging the battery, some has to program the start conditions into it.

The early Redarc chargers with a Lithium profile where a perfect example, they were setup to charge the Redarc Lithium batteries, if you used then on other brands they could have easily damaged the battery as the maximum charge voltage was very high.

The enerdrive dcdc unit is 3 stage. The 240 volt is also at least 3 stage...hence..not dumb. The user changes are a smart move because not all lithium batteries are the same. Same can be said of agm batteries as well. Adjusting the charger to suit your battery manufacturers specs is a smart thing in my opinion. The Renogy dcdc is also 3 stage.
Renogy are a very large international company and yes, like majority of battery/equipment companies, source their parts from China...absolutely nothing wrong with that...it all depends on the specs/quality that a company wants to sell. Renogy have an excellent rating in America and after conversing with people here in Oz who have their products I went with their products. I matched the products together for best results.

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Ahh, I finally found something about "return-to-charge". Unsurprisingly, it was from Enerdrive......

"........The “return to bulk” voltage setting in lead acid chargers is normally 12.5-12.7v. This voltage for a lithium battery is way too low. At this voltage the lithium battery will have been depleted to approx 10-15% state of charge. Lithium charge algorithms will normally set a return to bulk voltage of 13.1-13.2V. Just another reason that a standard lead acid charger doesn’t suit lithium batteries."

So, at least with Enerdrive, the return to bulk charging (from float) is by voltage detection. This is what I expected.

The whole Enerdrive charging dissertation can be read here.

Allan, I indicated several posts ago that's how it works!

Bigfish,

Personally I don't purchase anything unless I can see how it will perform and if it will meet my requirements. Most charger manufacturers provide detail specs as to how the unit functions and I can make an informed decision as to if will meet my requirements. As you wrote users specs is a big bonus as I can fine tune it and not have to use a comprise charging regime.

In the case of the renogy charger little information is given as to how the unit behaves in the case of a Lithium battery, therefore I have no way of making an informed decision as to if it is or is not suitable for my needs. If the manufacturer can't or won't provide detail specs then I won't be using their product.

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Yes Leigh, we both had surmised that 'return-to-boost' charge was initiated by sensing voltage but I wanted to hear it from "The Horses Mouth" so to speak. Now I have. OK?

HKB..
"Yep the BMS needs it to cell balance, it shouldn't.

I have had my Lithium for around 6 years now, I have never needed to balance the cells, a good quailty battery will have matched cells and they won't drift out of balance. If a battery manufacturer indicates their battery needs regular cell balancing then something is wrong, they are most likely using low quailty cells or cells haven't been matched during manufacture. A lot of cheap drop ins suffer this issue as they are made of many poor quailty cells in a parallel series combinations to get the required Ah and voltage."

Enerdrive, Renogy,EVPower all have BMS that monitor the cell balance automatically...thus as you say..you have not needed to balance the cells. I would not expect to balance cells as well if the appropriate BMS is matched with the battery. Many of the e-bay specials would indeed be a risky proposition...but then againwe would need to see how they are performing after, say, 5 years to really see if they are duds or god value. I,d love to get rid of my 3 x 120 agm fullrivers in the camper and go to lithium....problem is the buggers wont die!!!..lol

I have an EV works battery, the battery can be purchased with or without cell balancers, I opted to purchase the cell balancers but have never needed to use them. The cell balancers sit on top of the cells but as I rarely charge the battery above 13.8V there is never enough charge voltage for them to do their thing. In my case I only use to detect if a cell should go faulty.

Many don't use cell balancers at all as faulty cell balancers can cause more issues than the likely hood of a quality cell going out of balance or faulty.

My battery will be an AMPTRON 100AH LiFEPO4. It does have an inbuilt BMS.

Do I need a DC to DcC charger as well ?

Thanks

Amptron is an Australian company - or if it is not, it has an Australian presence. If I were you I'd ask them. They'll probably need to know the make and model of your vehicle so they can determine what your alternator does, or if you know that, tell them.

1300 543 376 - 24 hrs according to their website.