Charger for LFP cell testing

[karrak]

I'm going to pull the trigger on a Reaktor 300W. The low output power (only 20A) would take ages to individually charge each of my 200Ah cells from empty, but i can charge the pack halfway then finish each cell off with the Turnigy. Then discharge to measure individual cell capacity, so i know which ones are the "weak link". Then reconnect the pack, recharge to 50% again, then disconnect and bring each cell up to whatever 'balance' voltage i end up choosing before reassembling into the pack (you can relax, SK; i will not "top balance" all the way to 3.65vpc). I also need to take this opportunity to make better interconnects.

Rather than charging all cells to around 50% then charging each one individually with the Reakor you could charge them all in series (4p5s or 5p4s) with the Reakor using the balance charge function with the balance leads connected. When the first cell reaches the set charge voltage you could then put all the cells in parallel and charge them up to whatever voltage you want to balance them at. This will be much faster.

Regarding interconnects you might find this article of use http://www.smartgauge.co.uk/batt_con.html. The diagram below shows how I would wire up a 2P8S LFP battery using prismatic cells. The same principle could be applied to your 5P4S battery. A number of us use braided interconnections as detailed here pcsridgway.com/products/flat-and-round-braided-cables/. They are readily available and not expensive. In your situation where vibration may be an issue I would think braided interconnects would be preferable to sold links.
48V2P16SLFP.jpg

Unfortunately i haven't yet found a manual for the Reaktor 300W online, which is usually the first thing i do when considering a product. But the price is okay so i'm willing to try it out.

You could email Hobyking to see if they will give you a manual.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[Sunking]

Was hoping this thread could focus on the chargers,

We can do that, but you have a serious issue which prevents us from doing so.

Of course charging cells is easy, if you have accurate, reliable equipment. A bench power supply would do fine, but i don't have one. And if i'm going to buy a piece of gear, why not get one that does exactly what i want? Isn't a battery charger just an accurate variable power supply with a user interface and some controls baked-in?. I /want/ a PL8 of course, but it's overkill for my application,

This is the serious issue. You want champagne, but not willing to pay for it. Here is the deal, by choosing LFP you just decided to take the most expensive route you can possible take, and LFP batteries require some special attention and equipment which you are not willing to pay for. That is your problem, not mine.

You say a PL-8 is overkill when it is exactly what you want and need, or even a PL-6 assuming you are building a 4S 12 volt battery. Not only will the PL-8 charge your LFP battery, it will charge any battery chemistry from a 1.5 volt AAA battery up to a 36 volt 400 AH lead acid battery.

So you want to do this the most dangerous and ineffective way possible. I cannot help you. You will have to take advice from Karrak as he is the most dangerous and biggest fraud there is here. Good luck with that. My conscious is clear, you will only have, Karrak, and the Forum owners to be held liable. Good luck with that, both are in Australia. I am not a hack or DIY.

Here is one hint. LFP does not take any special battery charger. Any 12 volt charger made for 12 volt Pb can be used if you know what you are doing. You want a huge luxury car, but cannot afford the gas.

[zamboni]

Was hoping this thread could focus on the chargers, both for my benefit and in case someone else is looking for this info in the future. The bottom/top/middle balancing debate seems to rage across every LFP thread on this site regardless of the topic, and doesn't need to be repeated here. I have a question about a tool. Let's talk tools.

Of course charging cells is easy, if you have accurate, reliable equipment. A bench power supply would do fine, but i don't have one. And if i'm going to buy a piece of gear, why not get one that does exactly what i want? Isn't a battery charger just an accurate variable power supply with a user interface and some controls baked-in?. I /want/ a PL8 of course, but it's overkill for my application, and requires a separate power supply to boot. TWO, if i want to really get the full 40A out of it! I live in a medium-sized RV so i'm looking for a "right-sized" solution that i can justify keeping on-board. I built my PV system but i'm not an electronics hobbyist, so a decent bench power supply isn't something i can just take for granted -- even if i had a "bench" to put it on. Right now i have a toolbox and a plastic tote in the back of the truck where i have to fit all my toys, and aside from the wire strippers, crimper, soldering iron, and Amprobe, none of them are electrical ; ) Someday i'm sure i'll buy a decent bench power supply, but for now i think the $ would be better put into a less-powerful but more job-specific battery charger.

I'm going to pull the trigger on a Reaktor 300W. The low output power (only 20A) would take ages to individually charge each of my 200Ah cells from empty, but i can charge the pack halfway then finish each cell off with the Turnigy. Then discharge to measure individual cell capacity, so i know which ones are the "weak link". Then reconnect the pack, recharge to 50% again, then disconnect and bring each cell up to whatever 'balance' voltage i end up choosing before reassembling into the pack (you can relax, SK; i will not "top balance" all the way to 3.65vpc). I also need to take this opportunity to make better interconnects.

Unfortunately i haven't yet found a manual for the Reaktor 300W online, which is usually the first thing i do when considering a product. But the price is okay so i'm willing to try it out.

[karrak]

Don't have any spare cells, but even if i did, i would not likely be messing with my pack unless i had shore power. This is the house battery in my RV (which is also my home), and the entire rig is electric (no propane; trying to be fossil free). So if the battery pack is down, the whole rig is offline. Battery maintenance means sucking it up and paying for an RV park spot for a night or two. We don't carry a genny

We are in the same situation except we are in a house we built. I am tempting providence by saying that our system has been in continuous operation for about four and a half years. As you have cells in parallel you can remove a single cell to test and still use the battery WITH CARE if you monitor the individual cell voltages and re-balance the battery when you have finished the testing.

I went to put my system specs into my signature but there's a 50 character limit, yet i see much longer signatures being used by others. Are those manually pasted in? The system basics are:
- 1220W array (4x 305W Astronergy panels @ 48V)
- 1000Ah LFP house bank (5P4S HiPower 200Ah cells)
- MPPT solar charge controller (MidniteSolar Classic 150)
- 2800W PSW Inverter (Magnum MS2812)
- ME-RC, Trimetric, and JLD404

You are right about the 50 character limit, it is a real pain. I copy and paste my signature.

I started out with the JLD404 before I designed and built my BMS. You can set a small positive current offset in the calibrate menu to make the JLD404 Ah counter take account of the coulomb/current inefficiency of the battery. The Ah counter offset is calibrated correctly when the Ah counter is zero when the charger switches to float. You can also get the JLD404 to automatically reset the Ah counter when the battery is fully charged by soldering some wires to the Ah reset switch (I can't remember which switch it is) and connecting it to the relay output of the JLD404 and set the relay to operate when the battery reahces the fully charged voltage.

I've been using the pack in a narrow voltage range and manually checking cell voltages, but i'd like to get a bit more out of it so i plan to "start over" with a little more knowledge and thoroughness.

You do not need to disassemble the battery to balance it properly. You can do the balance by setting the float voltage to something conservative like 3.4v/cell (13.6V for 4S) , When the charge voltage gets to less than C/50 discharge any cells that are higher than 3.4V with a 3.3ohm 5W resistor or put two or three is parallel to increase the current draw. Remove the resistors when the voltage drops to less than 3.4V. When it is balanced at 3.4V increase the float voltage to 3.45V (13.8V for 4S) and repeat the procedure. Keep increasing by 0.05V until you get to 3.6V/cell. While you are doing this it is important to monitor the individual cell voltages very carefully. I would get a Cellog 8 to monitor the individual voltages and set an alarm voltage of 3.65V. This will give you plenty of warning.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[Sunking]

Charging a a 1SxP LFP battery is the easiest thing in the world to charge. There is no simpler charging algorithm. All you need is a good voltage/current regulated DC Power Supply. All you need to do is set the voltage to 3.6 volts and wait until charge current stops or reaches roughly C/33 to C/50 which is essentially no current. Lots of salvaged 5 volt variable power supply can do that assuming it has enough current capacity so it does not take days. However not so great if you are talking about say 4 x 100 AH cells with a 10 amp, 5-volt supply. Sure you could wire all 4 cells in parallel, charge at 3.6 volts and wait up to 2 days to recharge the 4 cells in parallel.

But what if that same Power Supply was say 3 to 30 volts at 10 amps? What them. Real simple wire them in series, charge at 14.4 volts and now instead of 2 days is 4 times faster at up to a half day. Is that a better way? Beats me, how much time and money do you have?

OK you know about FMA Revoletric PL-8. They make a PL6 and PL10. These are not your ordinary chargers. They will charge any battery chemistry of today and tomorrow with any Algorithm you want or can dream of programing yourself. Could you charge all 4 cells in parallel with any of the PL's. You sure can, but why would you if you had the power supply required to run one?. All the PL series have a max charge current. Does not matter if the battery is 1S or 8S, the PL-8 can charge as high as 40 amps on 1S to 8S. The trick is in the Power Supply. It has to be large enough in terms of Watts vs Voltage. If you use a 24 volt 60-Amp power supply (1440 watts), you can run 1S to 8S at 40 amps.

But here lies the difference. The PL=8 has 1-Amp Balance current, or roughly 10 times more than a BMS. This enables the user to perform Initial aka Bulk Balance Charge. A BMS is not capable of performing the Initial Balance. With only 100 to 300 ma of balance current can take days, weeks, months, years to perform an initial balance or correct an unbalanced pack.

Point here is you must figure out how to do the Initial Balance and it can be Topped Balance or even easier Bottom Balanced. However BB is not for you. The problem with Top Balance is you just threw away half of your cycle life There is no reason to fully charge your cells. Perform an Initial Balance, then charge at 3.4 vpc and forget about it. From time to time check voltage at the end of a charge. If you see more than a .02 volts spread, time to rebalance. Keep in mind a cell resting at 3.3 volts is roughly 20 to 30% capacity, and 3.4 volts is roughly 80% a difference of 50% capacity 3.45 volts rested is fully charged up. Target charge voltage of 13.6 volts is about perfect on a 4S LFP. Stay away from 14 to 14.4 where manufactures recommend. Manufactures do not have your best interest in mind. They want you to charge to 100% so they can generate more replacement revenue. That is why EV manufactures never allow clients to fully charge the EV batteries. What a customer thinks or fooled into thinking is 100 % charged is in reality only 80 to 90% charged. Otherwise they could not offer the warranties they do. Learn from that. EV manufacturres do not Top Balance. They middle balance.

[zamboni]

It is my experience that angry engineers are worth listening to. Knowing your s*** and being angry about it seem to go hand in hand. As a (former?) engineer, i totally get this. I was never a PE, but i did get really, really, angry. Still do. So i'm always going to pay attention to what SK says. And i always take everything i read "on the internet" with a grain of salt.

But at the same time, i have to take a step back and ask SunKing: What 'bad advice" did Karrak give here? Is Turnigy a horrible battery charger manufacturer? Will their products fry my cells or discharge them into reverse polarity? I'm just looking for advice on a small, per-cell charger. Do you have another suggestion?

[zamboni]

Don't have any spare cells, but even if i did, i would not likely be messing with my pack unless i had shore power. This is the house battery in my RV (which is also my home), and the entire rig is electric (no propane; trying to be fossil free). So if the battery pack is down, the whole rig is offline. Battery maintenance means sucking it up and paying for an RV park spot for a night or two. We don't carry a genny.

Which is fine, because i'm not wanting to use this charger daily; I want to "re-commission" my pack -- basically following PNJunctions' "KISS" post -- and then if i need to periodically re-balance cells, i'll still have the charger on-hand to do that. But it sounds to me like if i do everything right, that should be a rare occasion. $120 for a "one-time use" charger is acceptable to me if it means the pack will be more robust. I can use it on the truck's batteries too, and maybe i'll get into RC helicopters someday ; )

I went to put my system specs into my signature but there's a 50 character limit, yet i see much longer signatures being used by others. Are those manually pasted in? The system basics are:
- 1220W array (4x 305W Astronergy panels @ 48V)
- 1000Ah LFP house bank (5P4S HiPower 200Ah cells)
- MPPT solar charge controller (MidniteSolar Classic 150)
- 2800W PSW Inverter (Magnum MS2812)
- ME-RC, Trimetric, and JLD404

Installed in a 2001 Fleetwood Prowler 5th wheel 25 foot, self-rebuilt.

I've been using the pack in a narrow voltage range and manually checking cell voltages, but i'd like to get a bit more out of it so i plan to "start over" with a little more knowledge and thoroughness.

[karrak]

I considered the Multi4, but it doesn't look like that will tell me the Ah consumed during a discharge, which i'd love to have. The PL6 is an okay fit, in that it's much cheaper than the PL8 but has most of the same capabilities...but it still requires a separate power supply to run off mains power. I don't see any way of doing cell-by-cell maintenance on my battery pack without using mains power, since this is my "house" battery.

If your house battery is 12 or 24V and you have cells in parallel or have a spare cell you can use it as the DC supply to do the testing. Doing this could stuff up the overall battery balance which you would have to correct when you have finished the testing.

I would be interested in some details of your system.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[karrak]

My DC only unit tells you the Ah during charge and discharge on the display, it also logs the voltage and current data I think every two seconds. This information can be downloaded as plain text to your computer via USB. From the description it looks like the AC unit does the same. I can't find a link to download the manual for the AC unit to confirm this.

Other thing that would be worth confirming is if you can do regenerative discharge back into a battery connected to the AC unit. It looks like you can as there is a DC input on the unit.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[zamboni]

I considered the Multi4, but it doesn't look like that will tell me the Ah consumed during a discharge, which i'd love to have. The PL6 is an okay fit, in that it's much cheaper than the PL8 but has most of the same capabilities...but it still requires a separate power supply to run off mains power. I don't see any way of doing cell-by-cell maintenance on my battery pack without using mains power, since this is my "house" battery.

Karrak, thanks for that suggestion! It looks like the current version of the Turnigy Reaktor 300W has a built-in AC power supply...starting to look pretty good! Does the logging feature mean it will tell you the Ah used during a charge or discharge cycle? Because that would be ideal. I can totally live with a 20A charge rate.

[SunEagle]

I have the Cellpro Multi4 RC charger made by Revolectrix and I am very happy with it's performance for both my LiPo and LiFe batteries.

[karrak]

I use a Turnigy 6S 300W Reaktor charger to charge my e-bike batteries and test individual LFP cells.

Things I like about this charger are the regenerative discharging and logging so you can easily do charge/discharge testing of individual cells. It is also pretty accurate and very flexible. Could easily be used to do the initial balance charge.

Main issues are that it is only 20A and you will need a 12/24V power supply or battery to power it.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[zamboni]

The various approaches to LFP pack management such as balancing, capacity-matching, etc., always involve measuring individual cells while charging/discharging. This is always followed by: "Use a good RC charger like a cellpro PL8". Okay, i don't mind spending $ to get equipment to take care of my cells.

A PL8 is $190 for a refurb, plus another $50 for the 12V server power supply just so i can run it off mains power (at half capacity)...and then another ~$40 for various cables to actually connect it all up. It does what i need -- and a whole lot more! But i don't forsee using the many additional features. From what i can tell, i only need a way to charge, discharge, and coulomb-count my cells one at a time. Once that's done i'll put the pack back together, adjust my battery management settings accordingly, and likely not touch the charger again for maybe a year (?). That makes the PL8 seem like overkill.

I'm not familiar with the RC world so i don't even know where to start looking for alternatives. Is it possible to find a "good" 1S charger that has the features required to test & measure my prismatic cells, without getting into the full-blown "workstations" like the PL8? I realize the charge rate will probably be very low, but that's okay, especially if i don't have to buy a separate power supply just to operate it...

I'd be grateful for any brand or site recommendations.