LIFEPO4 pack:right/wrong way to charge for longevity?

Batteries, Chargers, and Battery Management Systems.
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mwinschel   10 mW

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LIFEPO4 pack:right/wrong way to charge for longevity?

Post by mwinschel » Aug 05 2015 9:56pm

Wondering if there is a general good/bad way to maintain an LIFEPO4 battery pack for longevity of cells?
Here is what I have:

48V 16s 10Ah 38120S LiFePO4 Headway Battery Pack (with BMS)
Cycle Satiator charger (its just plain fun to use...)

What is the general philosphy for best pack life (or is there?) - Do I want to deep cycle the battery and then charge it fully or charge after each use and let it float all the time on the charger (or somewhere in between?) or does it even matter?
(Ie using 2AH/day do I charge it daily or once every five days to get the most life out of my pack?)
Can I any damage the pack by leaving the satiator on when not in use? Plenty of information on Lipo's available but not much I can find on the LIFEPO4 chemistry

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by imorton » Aug 06 2015 12:02am

I am curious too, as I have a SunThing 48v 15Ah LifePo4 battery.

Often I only use 2ah per day, and I end up leaving the 3amp charger on overnight... Am I losing longevity, or is it not making any difference, or is it doing good by always being charged & balanced for the next days usage?

IAN.
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wesnewell   100 GW

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by wesnewell » Aug 06 2015 3:44am

The slower the charge rate the better. Only charge if you don't have enough capacity for your next trip. Don't fully charge and let sit that way before using. Don't run your pack lower than 20% soc. Keep your discharge rate as low as possible. Their cycle life of 2000 is based on a 1C discharge rate at 20% soc (80% dod). Run them at their rated rate of 3C and only expect 700 cycles.
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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by mwinschel » Aug 06 2015 4:45am

wesnewell wrote:The slower the charge rate the better. Only charge if you don't have enough capacity for your next trip. Don't fully charge and let sit that way before using. Don't run your pack lower than 20% soc. Keep your discharge rate as low as possible. Their cycle life of 2000 is based on a 1C discharge rate at 20% soc (80% dod). Run them at their rated rate of 3C and only expect 700 cycles.
I thought that was advice for Lipo chemistry. I partially bought the cycle satiator because I thought the claims of increased longevity of 80 percent charging lithium batteries also increased the life only to find out on further inquiry that only applied to lipos. (what is SOC and DOD by the way?)

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by imorton » Aug 06 2015 4:57am

I guess the difficulty I have is how to only charge to 80% of charge with a regular elcheapo 3amp charger. And it is not practical to only charge before using the scooter, since I use it almost everyday.

Sometimes I finish using it at 6pm for the day, throw it on the charger till the green light comes on (usually 1 hr longer to complete any balance function) than disconnect the charger and the scooter is ready for tomorrow (or the following day after).

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by imorton » Aug 06 2015 4:58am

SOC is state of charge

DOD is Depth of Discharge
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dogman dan   100 GW

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dogman dan » Aug 06 2015 6:18am

If you only draw 2 ah per ride, then leaving it on the charger over night is overkill. You only need to leave it charging overnight when it gets unbalanced, which is typical when you discharge deeper than 80%.

But if you drew 45% DOD, then you'd definitely need to charge it daily. To avoid discharging to 90% on day two. Charge it every other day, or even every third day is not a bad plan in your specific case.

The satiator is not going to kill your pack, even if you left it on the charger 23 hours a day. However, what does age a battery faster is sitting around fully charged at all times, especially when it's hot. Since you don't need 80-100% of you capacity daily, it makes sense to wait till it's a little bit deeper discharged to recharge it.

Any time you need to, don't hesitate to discharge 100%, don't turn the motor off and ride without it if you have any juice at all. But if you can do it conveniently, ride till the pack is closer to 50% discharged before you recharge.

Every other day is what I would do, if I were you.

If you want to charge to 90% most of the time, the satiator will let you do that. Then charge to 100% once a week, or once a month, whatever, to get a full balance charge. Ride ASAP when you do charge it to 100%.

Charging to 90% should also help extend the lifespan, but perhaps not as much as it can with other chemistries. One of the things about Lifepo4, is it is very very tolerant of a slight overcharge. Other types are not so tolerant of that.

To charge to 90%, charge fully, then ride till 1 ah is gone. That's the voltage to charge to, for 90%. Set your satiator to that voltage.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by imorton » Aug 06 2015 6:33am

Dogman Dan, what an awesome explanation, thanks a million... :)

There's a lot of little things to remember, but if it keeps the battery healthy, that's what counts.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dogman dan » Aug 06 2015 6:41am

Your case may be very different imorton.

Mine is too, almost no ride I do will use less than 50% of my capacity. I live in the burbs, and everything is down the hill. No way I want to climb back up 1000 vertical feet with less charge.

And it's extremely inconvenient to have the battery half discharged or more, when I want to use it. What I do a lot, is recharge to about half full immediately. Then if I think I'll ride soon, I charge to 90%. Then just before I ride, I can charge to 100% if I really need it all.

This is convenient for me, using my EM3ev charger, that has the three charge levels switch on it. I use that on my lipo packs.

I also have NMC packs with a bms. Those just get charged full, unless I happen to be around to stop the charge at less. Those batteries I can predict better when I'll need them next, so I often leave them uncharged, till the night before next run to town for groceries.

If I rode daily, a morning commute, I'd just do what I used to do. Put it on the charger every night, ride in the morning.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by imorton » Aug 06 2015 12:33pm

Kiriakos GR wrote:I have 10Ah 38120L LiFePO4 Headway Battery Pack (with BMS)


I bet 1000 EUR that I will get those numbers. 8)

You should never bet, with a battery.... They usually win :)
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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by granolaboy » Aug 06 2015 12:51pm

I always leave my pack on the charger overnight.

My BMS disconnects the charger when it's full, then spends the night balancing the pack. By morning it's all balanced and ready to go again.

I tend to drain my battery to 50% daily though, so not charging overnight is simply not an option.
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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dnmun » Aug 06 2015 12:55pm

if not used regularly just don't charge until needed. lithium is different from lead acid batteries which need to be recharged and put on trickle charge or maintenance charge immediately.

if you ride regularly then it is best to use the battery when it is at full charge because the density and mobility of the ions inside the cell is highest then so it has the lowest internal resistance at full charge. so lowest heating in use.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by 999zip999 » Aug 06 2015 6:23pm

It also depends on your controller and the way you ride, plus terrain. I started balance charging with a hyperion 1420 at 9amp, it melted. Then with two thunder power 1220 at 6amp. wouldn't stay booted up. Then two pedago 2amp charger. Now charge at 14amp with a power supply and a mean well from Teslanv. Or a kingpower 5 amp. from Ping 5yrs ago ( repaired travel charger @ 84v ) They like 2amp the best. No bms. B.S. Just because it's 20ah.
Kiriakos GR I take that bet my A123 20ah lifepo4 pack with 693 cycles and 9963 miles. Let justin hold the money. No drachmas.
Last edited by 999zip999 on Aug 07 2015 10:56am, edited 1 time in total.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dogman dan » Aug 07 2015 5:03am

Must be nice, to live in a battery friendly climate. Both of you do. You can expect years longer lifespan than I ever get.

I have two choices, forget using my bike 6 months of the year and put my battery in the refrigerator, or just accept that I get 3-4 years at most from any battery.

Bottom line, if I take that battery outside into the world, it's killing it. Too hot. On the upside, when it's 100F out there, the battery sure does perk up. Better capacity, less sag.

IMO, the single best thing you can do to make a battery last, is decrease the c rate you discharge it at. 1c or less, nearly all cell types last longer, sag less under load, and stay balanced a bit better. Sounds like the way Kriakos rides, he's doing exactly that.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dogman dan » Aug 08 2015 7:15am

Well, yeah. Of course the best way to avoid hammering your battery into dogshit, is to match it's max amps outuput to the EV. And do that conservatively, hence the oft repeated, "cut c rates in half"

In your case, the c rate of your headways is a lot more than your system can potentially draw, so your max potential amps is way less than "cut in half"

All batteries like taking it easy, vs running at max c rate. Yours will be taking it very easy. This is one reason why headways was a great choice for you. For others, other things make headways a less good choice, such as physical size and weight.

No one size fits all perfect ebike, or ebike battery, or when to charge strategy.

Your controller has some nice features in it. I like that being able to tune the amps, or tune the sensitivity of the voltage bars.

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BVH   1 kW

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by BVH » Aug 08 2015 9:58pm

The members at this EV forum are very savvy on LiFeP04 chemistry batteries. Rooting around over there, you'll find the general consensus is there's no benefit to charging over 3.45 - 3.50 per cell and definitely don't go below 80% DOD. Many use a "Bottom Balance" method of cell balance. It's an interesting concept and makes for some good reading.

Some are into building their own very sophisticated, high KW chargers.

http://www.diyelectriccar.com/forums/fo ... 76971d692e&

I've got the Cycle Satiator also. What a great charger! Firmware Vers .99 just released. If owners don't report many issues, it will sort of morph into Vers 1.00. They are also going to most likely introduce higher Voltage models (same power so less Amps) up to and maybe a bit over 100 VDC.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dnmun » Aug 08 2015 11:44pm

that is not correct.

you get more efficient performance and less internal heating of the cell when it is discharged if you charge the cell to full charge before use.

so charging the cell up only partially before use forces it to get hotter during discharge than if you charged it up to full charge before discharging it.

your assumption is incorrect. you will cause your battery to decay in performance and life cycles if you charge it up only part way before use.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by BVH » Aug 09 2015 10:22am

A while back, I performed a test on my two, almost new 51V/12 Ah LiFeP04 packs. One battery at a time, I rode and stopped and rode and stopped with my Cycle Analyst until the resting voltage of each pack was 3.05 Volts per cell. Using the Satiator, I charged them at a 3.5 Amp rate to a set 3.5 Volts per cell termination. I then let them rest overnight. I then used a second profile in the Satiatior to charge them further to a set termination Voltage of 3.65 Volts per cell. On battery 1, an additional .1 Ah was recorded on my in-line Watt meter and on battery 2, an additional .12 Ah was recorded. Is it conceivable that a less than 1% difference in increased charged capacity is going to induce any significant additional heat during the subsequent discharge of those packs?

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by 999zip999 » Aug 09 2015 11:30am

3.45volt is where the lifepo4 cell starts to race to a high voltage. Yes there are people who like to run a cell to 3.8 volt to have the bms bleed it down to 3.6 v. There is Not more over 3.5v to chase.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by dnmun » Aug 09 2015 2:06pm

BVH wrote:A while back, I performed a test on my two, almost new 51V/12 Ah LiFeP04 packs. One battery at a time, I rode and stopped and rode and stopped with my Cycle Analyst until the resting voltage of each pack was 3.05 Volts per cell. Using the Satiator, I charged them at a 3.5 Amp rate to a set 3.5 Volts per cell termination. I then let them rest overnight. I then used a second profile in the Satiatior to charge them further to a set termination Voltage of 3.65 Volts per cell. On battery 1, an additional .1 Ah was recorded on my in-line Watt meter and on battery 2, an additional .12 Ah was recorded. Is it conceivable that a less than 1% difference in increased charged capacity is going to induce any significant additional heat during the subsequent discharge of those packs?
if you wish to understand go google "transconductance lithium ion cell" and look for an equation in any of those documents that describes the transconductance. you will find the term 'N' which is the density of available ion species that conduct the charge through the electrolyte to the electrode. study what causes the term N to maximum value.

why is internal resistance measured at full charge? how is internal resistance related to full charge?

then lecture me.

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by BVH » Aug 09 2015 5:01pm

I don't know where you got the idea I was lecturing? I am simply asking whether in my case, if charging to 99.x% full at 3.45 VPC is going to translate into producing any more meaningful heat upon discharge than would normally be produced at 100% full at 3.65 VPC.

EDIT: When searching using the term you suggested, I'm only getting hits on physical charge limiting devices, not anything dealing with a description of the phenomena you mention. Can you provide a link to a good site?

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Re: LIFEPO4 pack:right/wrong way to charge for longevity?

Post by 999zip999 » Aug 10 2015 1:09am

O.k. do you heat water or boil water for tea ? Limits and flavor. Fried or Burnt ?

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