Testing Schumacher SP6 LFP / Lead Acid charger

[PNjunction]

Unbelievable - while I have a general disdain for vehicular chargers, I got hold of a Schumacher SP6 powersports charger which so far, seems to be charging LiFeP04 properly.

Problem - with Schumachers, they are heavily patent-protected to the point that voltages and algorithms are unknown, and may leave you guessing trying to figure out the algorithm.

This is what I know so far:

* You must select Lithium or lead acid upon startup. Lithium here means LiFeP04, NOT any other lithium chemistry!! Don't be hasty and be sure to read the ENTIRE scroll - or you may make the wrong selection!

* Page 3, section 2.8 in the first few safety pages that nobody reads, shows that it is meant to support 22-59ah LFP vehicular batts in the lithium mode.

* At first glance, it looks like a 6A CC/CV charger, which absorbs at 14.2v. Ok cool. Not published, so you have to pull out your measuring gear like I did.

My battery is a 40ah 4S GBS bank. Manually balanced for so-called "top balance" non-critical use with no balance boards by initially charging each cell individually, LVD's and whatnot are in place. This topic is covered ad-infinitum elsewhere.

Unlike most lead-acid chargers which may have their absorb voltage wisely set low to 14.0-14.2 for a "fake" gel setting when charging LFP, the Schumacher SP6 correctly continues full-bore 6A bulk right up to the 14.2v absorb point. Many lead-acid based chargers shoe-horned into charging LFP (usually a BAD idea), sense that anything over about 13.8v with the battery still allowing for a full-charge current bulk will safely cut back the charging current sensing that something is wrong. They don't know you have swapped chemistries from lead-acid to LFP and um, smartly go into a lower-current charge thinking your lead-acid battery is wack.

This differs from the standard absorb with lead acid, where the battery actually sets the charge-current tempo, not the charger when it reaches absorb. But, I have seen Pb cc/cv chargers cut back early on sensing that something is wrong in the universe not knowing the owner is using the wrong chemistry!

What I believe is that what the Pb-based "smart" chargers / solar controllers do when presented with an LFP instead, is think that the lead-acid battery has gone into thermal runaway, and instead of doing the classic cc/cv routine, cut back absorb current prematurely as a safety measure thinking it is still dealing with lead-acid.

The average user who shoe-horns a Pb controller might not even be aware of this, unless he compared it to charging with a lab-power supply set to the same values for cc/cv, and then wondered "why does my lab supply go balls-out all the way into absorb, when my solar controller / Pb charger seems to cut back charge current early?" The Aha-moment strikes!

Basically all I'm saying is that the SP6 seems to have been designed for LiFeP04 in mind, and not as a cheap shoe-horn of Pb algorithms. I think they put some thought into it.

I have noticed that a few times it has done a double-absorb of sorts - charging to 14.2v CV, doing some absorb, backing off to 14.1v for a little absorb, and back up again at 14.25v absorb. My source AC voltage was measuring steady during this time, so regulation seems to be good.

The problem for me is that with unpublished patented algorithms, I am placing my sole trust in the Schumacher engineers to do LFP right without question. I have a hard time with that.

After about 10 cycles now, watched over like an eagle especially during the LFP's absorb (monitoring each cell during this process to make sure none is lower than 3.525 and no higher than 3.6v, all seems ok. (voltage under charge is NOT the same thing as voltage under rest, and means nothing capacity wise either).

While I can't swear to it, and haven't put fine-grained measuring gear on it (aside from Fluke's), the secondary absorbs *may* be an attempt to pseudo-balance the bank - perhaps not exactly, but within reason. Yeah, we'll see if that happens - I'm watching that trend.

Keeping an eye out on it - I have no problem immediately recycling stuff that is just a Pb rehash under another name, but I think the SP6's Lithium (LiFeP04 ONLY) seems to have actually been designed by someone who knows I'll be watching like a hawk. So far so good - at least in the 6A category for 22-59ah capacities. (I'd have no problem extending that to a more practical 20 - 60ah capacity battery support).

So the jury is still out for me on this one, but I'm not immediately recycling it. It might be a keeper - at least for my GBS 40ah LiFeP04 bank.

[Sunking]

* At first glance, it looks like a 6A CC/CV charger, which absorbs at 14.2v. Ok cool. Not published, so you have to pull out your measuring gear like I did.

OK nothing new here, 14.2 is industry standard. 14.4 for FLA

Unlike most lead-acid chargers which may have their absorb voltage wisely set low to 14.0-14.2 for a "fake" gel setting when charging LFP, the Schumacher SP6 correctly continues full-bore 6A bulk right up to the 14.2v absorb point. .

Any CC/CV charger does this be it PB or Lithium. Lithium Ion battery chargers are the simplest of all charger, just a simple Float Mode CC/CV with only 1 voltage setting of 14.2 volts for a 12 volt battery.

The difference you see in charge current behaviour is not the charger changing anything as it is a pure CC/CV charger. It is the battery that regulates the current. A Pb battery Internal resistance is higher than lithium and more dynamic. With the higher resistance the charger current starts to taper off at lower voltages. Example lets say we have a 12 volt 100 AH Pb and LFP. with a 10 amp CC/CV charger set to 14.2 volts and both batteries are heavily discharged measuring 10.5 volts. The Pb battery has an Ri = .02 ohms, and LFP has .01 Ohms.

Initially when you connect the chargers, they supply 10 amps as they are in current limit and voltage has folded back to 10.7 volts on the PB, and 10.6 on the LFP. As the batteries continue to charge at 10 amps the voltage begins to rise as the batteries charge up. The charger with the Pb battery will start to taper current when the voltage reaches 14.0 volts, and the LFP will taper when the voltage reaches 14.1 volts. Charger did not do anything except limit maximum charge current to 10 amps and holds 14.2 volts when the battery voltage equals charge voltage.

Keep in mind a battery charger can only do two things.:

1. Limit maximum charge current
2. Regulate voltage.

Want a smart charger. Simple they have more than 1 voltage set point. A lithium charger has only one voltage set point and you can charge them up to 1C or as slow as you want.

Now in a sloar system you want to modify the algorithm in a Lithium just like you do a Pb battery. Initially you want Bulk/Absorb set to 14.2 volts until charge current tapers off to some predetermined value like C/20, then lower the voltage to 13.6 volts and Float so your panels will supply power to the equipment vs taking it from the battery. You use solar til dark then the battery can take over.

[PNjunction]

Absolutely no problem with the above - spot on. Many users don't understand that a CC/CV charger, when it reaches the CV stage does not by itself under normal conditions taper the current - it is the battery that does so. Standard stuff.

However, Pb "smart" chargers / controllers can be on the lookout for thermal-runaway as part of their safety "smart" algo's. If not detected by a temperature probe, that condition can be detected by a lead-acid battery doing no current tapering in the CV stage as it should - or at least *starting* to. You know - battery gets hot, more current flows, battery gets hotter, more current flows and on and on.

So, when a "smart" / safety conscious Pb charger sees an LFP, which does absorb much later on than Pb, it thinks it has a lead-acid battery with a thermal runaway condition, and then (via changing the pwm pulsewidth, etc) tries to protect the runaway Pb by reducing absorb current as a safety measure.

Non-smart things like programmable bench supplies, or bog-standard CC/CV chargers have no clue, and will not try to outsmart the user using the wrong battery chemistry.

My beloved Samlex 15A Pb charger for example, while it does an admirable job, takes longer to charge than does my bench supply set to the same settings, and I was scratching my head as to why. The Samlex is trying to be safe about what it thinks is a runaway lead-acid at the ends of it's clamps, rather than an LFP.

This is exactly why one should test it for themselves. It never really occurred to me, and although it isn't a showstopper, reducing current artificially to an LFP, rather than letting it absorb on it's own, would demand a much lower absorb voltage for those of us who are picky.

Note to lurkers - the other big problem with Pb chargers / controllers, is that if they employ temperature compensation you can easily cook your LFP cells when it does that.

[Sunking]

However, Pb "smart" chargers / controllers can be on the lookout for thermal-runaway as part of their safety "smart" algo's. If not detected by a temperature probe, that condition can be detected by a lead-acid battery doing no current tapering in the CV stage as it should - or at least *starting* to.

I had to think about that for a second because my brain is automatically wired with Thy Shall Have Temp Comp on AGM batteries and the sure fire way to detect Thermal Runaway, you lower the voltage. Then I had my Doh! moment when I realized any Smart Charger made to work with both Pb and LFP, the Pb cycle would have to be either automatically Terminate the charge when Absord Current Tapers off to some predetermined C/x value, or an EVENT TIMER timed out. So which ever happens first, the voltage is lowered which reduces current.

FWIW I have a Schumacher INC 4825 around here somewhere and know a few folks who own them on my recommendation as a 48 olt golf cart charger. Uses what I think is the exact same algo every one of their chargers has. Here is the Feature Spec rigght from the web site

48V FULLY AUTOMATIC, MICROPROCESSOR-CONTROLLED CHARGER
WITH A 15-25A CYCLING OUTPUT CURRENT •
Includes 8 gauge, 6 foot long output cables with a polarized 50 amp quick connect connector •
Charger status LED indicators •
Lighted ON/OFF switch •
Multi-stage charging algorithm •
Safe-start, reverse polarity and short circuit protection ─
the charger will not apply current to the output connector until it is properly connected •
Maintain mode ─ monitors the battery voltage to keep it fully charged •
Patent-pending “thermal runaway” protection ─ stops charging if the charger detects that there is a problem with the battery •
Automatic temperature compensation ─ automatically adjusts the output voltage based on the ambient air temperature •
Temperature controlled cooling fan for efficient operation and peak performance •
Power saving mode ─ uses very little power when in standby mode or maintain mode •
Heavy-duty steel case with a baked enamel finish •
Charges 48 volt lead-acid batteries •
Perfect for golf carts, tow tractors and people transporters
Industrial UL approved

They are a bit pricey but one of the few Golf Cart Chargers made for continuous Industrial use. When you order it they require you to specify the battery so they can match the profile. I figured out real quick how they program it. Inside is a 6-position rotary switch. Each position has a Profile associated with it. Since I ordered mine as Trojan I know Position 2 is Trojan. A buddy has USB which is #5. With a little hacking you can figure it out by Set Point Voltages.

One thing I can pass down to you is do not measure Charger Voltage at the battery or even the output terms of the charger. Reason is simple, if any significant Charge Current is Flowing, the voltage measured will be an ERROR. This is due to the battery Ri interaction with the Voltage/Current Regulator. Only time when you can actually read the Charger Voltage at the battery is right when Absorb switches to Float because all meaningful charge current has stopped and you are not incurring the IR voltage drop error. You gotta get inside and measure the Feed-Back loop or reference voltage. Compare that Reference to Actual Output, and note the point at what current both voltages are equal. That will tell you when you can use the Output Voltage to determine what the actual SP VOLTAGE is. Anything above that current level will be an ERROR. That might be what has you scratching your head wondering what is going on.

Just remember the only time both Battery and Charger voltage are equal means there is no current flowing right? There has to be a difference in potential for current to flow.

In closing allow me to share a link with you and others. You might have ran across it before but it is a great Readers Digest on battery charging covering all Algorithms and Terms like FLOAT some people need help understanding. Take note and read IUI charging. Should ring a Bell.

Battery Chargers and Charging Methods

[PNjunction]

Again, I'm totally with you on that.

Temp comp is SO important if one wants to do Pb right, but that is a no-no for LFP if you use Pb based products to charge it with.

Even with that disabled, sometimes it is easy to forget about the much lower IR for LFP, and hence, the absorb stage (actual tapering from the battery) comes on later as compared to Pb. This raises a red-flag for the "smart" Pb chargers, and they may take steps to protect you, not knowing your chemistry is totally different than the one it was designed for.

The irony about it all is that I don't normally charge to 100% SOC anyway! Sometimes, but not always.

At any rate, the SP6 seems to know that it is truly charging an LFP (you have to make the selection at the start), and is not just "borrowing" the Pb algo with a lower CV setpoint, (14.2 - which is even bad for many gel's, but we don't do gel anyway.)

There is a lot of marketing pressure to "do LiFeP04" charging, and the cheaper ones will just hide behind a Pb based algo. The SP6 charger surprisingly doesn't seem to have fallen into that trap.

[Sunking]

There is a lot of marketing pressure to "do LiFeP04" charging, and the cheaper ones will just hide behind a Pb based algo. The SP6 charger surprisingly doesn't seem to have fallen into that trap.

The only difference between them when it comes right down to it is Charge Termination and Voltage Set Point. And even that is not a given depending on application. Pb can be more complex but does not have to be.

Both use the exact same CC/CV aka Bulk/Absorb with the voltage set to 14.0 to 14.6 volts, LFP falls in at 14.2 to 14.4. You charge both until Current tapers to some C/x value, or Safety Timer times out. When C/x is reached you Terminate LFP, and can either Terminate the Pb, or lower the voltage to FLOAT

Ironically you can also FLOAT LFP just like Pb at roughly the same voltage of 13.6 volts, so with that said no real difference.

However a charger made for LFP should have one feature not normally found on a Pb charger. A Input for NC/NO contacts coming from an external Battery Manager if used. A means to turn off the Charger Off remotely if the BMS detects a problem.

Looks like we are on the same page. If you want a Charger that can do it all, any battery type there are two routes to go. One is a Hobby Charger and you know what that is. Charge any battery type of today and tomorrow up to 36 volts @ 500 AH. For serious battery charging like an EV or large Pb Solar batteries is something like a Elcon PFC series or other like charger manufacture. Those are sold in Wattage of 1500, 2000, 2500, 3000, 4000, or 5000 watts. Voltage and battery type are just a minor detail you specify when you buy one, You set it to any voltage and algorithm your heart desires for precise control. Voltage of 24 to 312 volts.

So for me a Smart Charger is one I tell it what I want, not what the manufacture thinks I want.

[PNjunction]

Yes definitely! A simple 4S LFP bank can be handled by those who know, but for anything more serious, or if one just wants to REALLY be the one in charge, then the hobby types like an iCharger or Revolectrix Powerlab unit is THE way to go.

And that isn't just for so-called balancing, but for those who want to spot trends early on before they become an issue later.

I dream of an Elcon, although I need the applicaton for it first!

[Sunking]

PN not sure if you have thought of this, or might have caught in other threads where I have brought it up before.....

But have you shopped the Salvaged Telco Equipment market for Rectifiers?

Mostly you find tons of 24 and 48 rectifiers, but there are some 12 volt stuff out there too used for Land Mobile Radio equipment. Any made in the last 30 years are super easy to hack, and if your are OK with using two 10-turn pots to adjust Float and EQ voltages are good to go out of the box after you wire up power. I am not talking about the large ones of 500 amps and up. I am talking more like 19 or 23 inch Rack Mounts of 50 amps and less for Distributive Low Power DC Plants like you would use just for a few equipment racks with a 48 volt 200 AH plant. Just keep in mind once cross the 1500-2000 watts line requires 240 VAC circuit. Point here is they are Tanks of a battery chargers with a great deal of precision that can run wide open 24 x 7 You could get a 24 or 48 volt 30 Amp rectifier for less than you have paid for your other chargers. I know you can hack any of them as all you have to do is find the Trim Pot Wiper, and you know where to take over control. That and a Arduiono Uno and you have a SMART CHARGER can match in quality.

[Sunking]

I dream of an Elcon, although I need the applicaton for it first!

Elcon is OK, but as it turned out I did not need it, but I do use it from time to time. I originally bought to use with a 16S GBS in my cart with a Orion Jr BMS a couple or thre years back as you may recall. The Orion and Elcom talk the same CAN buss protocol and work together along with the Motor Controller. Long story short I have moved onto 96 volt Leaf batteries and no BMS using the Elcon reconfig for 96 volts I do not have anymore use for the CAN bus. If I had to do it again might go with a different EV charger. Things get expensive charger wise when you go above 48 volts.

When I think of a SMART CHARGER I think more in terms of Elcon and other manufactures that let the customer specify the profiles he/she wants, and then programs it in. Or use one of the factory profile by at least telling them what make, model, and AH batteries you are running. That is what I really like about the Hobby Chargers. With a good Rectifier or 24 volt power supply of 1500 watts and you have a Charger that will do about everything anyway you want it.