Lithium LifePO4 charging regime, I’m confused!

[Ian_H]

I have had the same problem with the quoted capacity keep dropping. This is with Vanbitz installed battery, solar and B2B - I am still discussing it with them.

Glad to hear I'm not on my own! What do your various chargers have as a bulk charge voltage?

 

[autorouter]

What do your various chargers have as a bulk charge voltage?

They don't have a bulk charge voltage. The bulk charge stage is a fixed constant current (amps). The voltage during bulk charge is whatever it turns out to be. It gradually rises from whatever it starts at, say 12.0V, up to the absorption voltage. At that point it is about 80% charged.

When it reaches the absorption voltage, the bulk charge stage stops, and it flips to the absorption stage. The absorption stage is a fixed constant voltage, which is the one quoted in the spec and is probably the one you meant. The current (amps) gradually falls from the full output value to a low value, usually about 1/10 of the full output amps. At that point the charger decides the battery is fully 100% charged, so it flips to float mode.

 

[Lenny HB]

Hi Lenny

View attachment 871167I don't think you can wire these b2bs without a D+. I've put a switch in mine so I can turn it off if I want to. The trickle charging switchover is described above. I have no idea what the efficiency >=4% refers to!

 

[Ian_H]

They don't have a bulk charge voltage. The bulk charge stage is a fixed constant current (amps). The voltage during bulk charge is whatever it turns out to be. It gradually rises from whatever it starts at, say 12.0V, up to the absorption voltage. At that point it is about 80% charged.

When it reaches the absorption voltage, the bulk charge stage stops, and it flips to the absorption stage. The absorption stage is a fixed constant voltage, which is the one quoted in the spec and is probably the one you meant. The current (amps) gradually falls from the full output value to a low value, usually about 1/10 of the full output amps. At that point the charger decides the battery is fully 100% charged, so it flips to float mode.

Yes my mistake. I did mean the absorption voltage at which the charger switches over from bulk mode to absorption.

 

[Ian_H]

View attachment 871186

Hi Lenny
I'm not sure what you are showing/meaning with this pic of the connections from the manual?
None of the wiring diagrams or text I can see suggest it can be run in a voltage sensing mode without a D+ signal.,edit: and mine doesn't charge when I switch the D+ off via an inline switch.

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[Whitebirdyman]

Yes my mistake. I did mean the absorption voltage at which the charger switches over from bulk mode to absorption.

Mine are the ones you quoted earlier, as Vanbitz recommended.

 

[Ian_H]

Mine are the ones you quoted earlier, as Vanbitz recommended.

Sorry, being a bit slow today, which ones?

 

[Whitebirdyman]

Sorry, being a bit slow today, which ones?

The ones that you quoted from Headlight.

 

[Ian_H]

The ones that you quoted from Headlight.

Ah, right. It might be worth just trying the mains charger mode on normal to see if the SOC resets at 14.4V? It's easy to change either on the app or using the mode button on the charger.

 

[Lenny HB]

Hi Lenny
I'm not sure what you are showing/meaning with this pic of the connections from the manual?
None of the wiring diagrams or text I can see suggest it can be run in a voltage sensing mode without a D+ signal.,edit: and mine doesn't charge when I switch the D+ off via an inline switch.

You don't need the switch if you connect a D+ signal to the D+ terminal that would be the normal way to install it.

Just had a look that is the first B2B I've seen that doesn't have a voltage sensing mode.

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[TheBig1]

The thing to remember when stuffing a higher voltage into lithium batteries and often with other equipment is that any voltage above the internal bms setting (or voltage regulation) is dissipated as heat. This can be a killer to enclosed circuits if done often or for extended periods. At a very basic level the electronic components don't like heat

Charging profiles are a constant difference between manufacturers, there being no accepted standard used by all yet. Where some advertising implies that lithium cells will suck up all you can throw at them, they are not telling you that doing so can shorten the lifespan. Some claim to be drop in replacements, with inbuilt circuits that take the lead acid settings and adapt them (Buck/Boost) but these will never be as good as a true lithium charge profile. The chemistry in lithium batteries varies a lot

Just part of the reason some cheap chinese batteries have shorter lifespans. Given that we were told to expect 10 year service life, it explains why lithium batteries are failing prematurely if you speak to people in the trade. And why the technology is still evolving

 

[treblid]

You don't need the switch if you connect a D+ signal to the D+ terminal that would be the normal way to install it.

See post #10. Ian_H has put a switch in series with the D+ signal so he can manually terminate B2B charging when the battery if full.

 

[Lenny HB]

See post #10. Ian_H has put a switch in series with the D+ signal so he can manually terminate B2B charging when the battery if full.

So, I can't read properly today.

 

[EML]

There seems to be a consensus among them that the charging regime needs to be at or below 14.2volts with many warnings that charging at a higher voltage would lead to damage to the battery.

I can't imagine that you're ever going to read this far but, if you do, the 14.2V figure is nonsense. Your 12V "battery" is made up of 4 LiFePO4 "cells", each with a nominal voltage of 3.2V. Cell manufacturers (almost?) universally specify a charging cut-off voltage of 3.60 or 3.65V; multiply by 4 to get 14.4V or 14.6V. This is the voltage at which you switch from constant-current/CC charge to constant-voltage/CV charge. See autorouter's post for details, but note that there is no 'float' for LiFePO4.

But... it doesn't matter. You don't charge the cells. Your Battery Management System does (for most people, the BMS is built into the battery housing). The BMS balances the cells, and cuts them off if there's a problem. You have to apply slightly more to your BMS than the nominal 14.4/14.6. How much more? No-one really knows, but the MOSFETs in the BMS will drop maybe 0.2-0.5V, so at least this much more. It doesn't really matter; if your cells need 14.4V, and you supply 14.9V, the extra 0.5V is lost as heat in the BMS (20A times 0.5V = 10 Watts, so not a big deal).

I’ve installing some at the moment. The Sterling (a well known supplier of electronics that has stands at all MH national shows) tells me that I should charge at 14.6v quoting a range of 14.4v to 14.8v (max). They have personally emailed me to confirm that and the manufacturer (AMPS) also gives those figures in their accompanying literature and warranty.

They'll have done the tests (I hope) so stick with their figure.

Fogstar on their site also recommends charging at 14.6v and a float of 13.6v. Both of these supplies give 5year warranties (provided correct charging voltages being adhered to)

If they really say a "float of 13.6V" they need to go back to battery school. You don't float LiFePO4, and it's potentially dangerous (according to one paper I've read; there's no universal agreement on this). But everyone is agreed that you shouldn't do it.

See my confusion? Don’t want to void my warranty OR damage my batteries by over charging. I will use a Victron IP22 and set parameters by Bluetooth.

My own battery (a TN Power) specifies 14.6V charging, +/- 0.2V, like the Stirling one. It's charged via a CTEK D250SE for solar/alternator, and a Victron MultiPlus for mains. Neither of them understands how to properly charge LiFePO4. The CTEK actually shows a charge profile which includes float and pulse phases. The Victron doesn't seem to be much better, and I'm pretty sure the cells never get to 14.6V. But the good news is that it all works, and the battery charges, although it might take longer than it should.

 

[headlight]

From Fogstars site

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[Lenny HB]

From Fogstars site

View attachment 873714

Someone didn't check the copy before that went to press.

 

[headlight]

Someone didn't check the copy before that went to press.

I only posted that to show what Fogstar themselves recommend for their batteries.

 

[Lenny HB]

I only posted that to show what Fogstar themselves recommend for their batteries.

But they have got the charge & float voltages crossed.

 

[headlight]

But they have got the charge & float voltages crossed.

Sorry Lenny I don't follow ?

 

[Raul]

But they have got the charge & float voltages crossed.

The way I read it is: 13.5-13.8v float and 14.2-14.4v absorb, that's fine as they mention victron recommendation after that as 13.5v float and 14.2v absorb.

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[Lenny HB]

Sorry Lenny I don't follow ?

Read it it says something like charge at 13.5 to 13.85 & float at 14.2 to 14.6, unless I read it wrong if so I blame it on Spanish beer.

 

[Raul]

Read it it says something like charge at 13.5 to 13.85 & float at 14.2 to 14.6,

No it doesn't, they just missed a coma after the word float.

Have you hit the Vino?

 

[Lenny HB]

No it doesn't, they just missed a coma after the word float.

Have you hit the Vino?

Only the beer so far will be on the vino soon, it's a hard life this holiday lark.

 

[headlight]

Only the beer so far will be on the vino soon, it's a hard life this holiday lark.

Take more water with it Lenny

 

[Lenny HB]

Take more water with it Lenny

Beer is 90% water.

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[treblid]

But... it doesn't matter. You don't charge the cells. Your Battery Management System does (for most people, the BMS is built into the battery housing)

The BMS does NOT manage charging. The BMS only disconnects the cells for over or under voltage, over or under temperature and over current protection. It does not regulate voltage or current. It protects the cells in the event of adverse conditions.

 

[LithiumConvert]

I’m confused!​

I am not surprised. This topic does not help at all.

 

[EML]

The BMS does NOT manage charging. The BMS only disconnects the cells for over or under voltage, over or under temperature and over current protection. It does not regulate voltage or current. It protects the cells in the event of adverse conditions.

I don't get notifications of quotes, for some reason (should that happen?), and I only log in every week or so.

I didn't say it managed charging. But, in fact, battery balancing, which you didn't mention, does exactly that. The charging voltage you apply doesn't go direct to the cells; it goes via a MOSFET (transistor). There is some voltage drop in the MOSFET. The BMS controls the current to each cell, individually, via a capacitor and the MOSFET to ensure that the cells track each other during charging. There's hundreds of videos on Youtube explaining this process.

If you attempt to charge your LiFePO4 by connecting your charger direct to the cells, then you're in for a big surprise.

I didn't notice the first time around that there's a lot of confusion about floating these batteries. You don't float LiFePO4; it's constant current till it reaches a pre-determined voltage (in real life, it doesn't normally get that far), then constant voltage till the input current reduces to a pre-determined small level. The Fogstar literature is complete bo**ocks; don't buy from them till they've understood what they're trying to sell.

 

[Lenny HB]

I didn't notice the first time around that there's a lot of confusion about floating these batteries. You don't float LiFePO4; it's constant current till it reaches a pre-determined voltage

All Lithium charges have a float voltage but it is not intended as a float as in maintaining a lead battery. It's purpose is to have the availability of power from the charger when under load so you don't use the battery power when mains is available i.e. when on an EHU.

 

[EML]

All Lithium charges have a float voltage but it is not intended as a float as in maintaining a lead battery. It's purpose is to have the availability of power from the charger when under load so you don't use the battery power when mains is available i.e. when on an EHU.

Ok, well, we'll have to disagree on that. Floating LiFePO4 is (1) potentially dangerous and (2) reduces the lifetime of your battery. You need to keep it at about 50-80% SOC to maximise lifetime, and letting the charger take the strain just because the battery SOC has reduced below 90% is not a good idea. Floating LFP is not as dangerous as floating as Li-Ion, but there's no point, so why bother?

If you Google it you will, admittedly, find lots of opinions. The vast majority are second-hand from people who haven't actually bothered to do the experiments or read the papers. Like everything else, you'll have to pay your money and take your choice.

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