This is why you get a Revolectrix (aka CellPro) PL-8

[zamboni]

I'm writing this as a favor to others out there who are stubborn and cheap like me, and looking for a charger to work with large-ish Lithium battery packs but who think a PL-8 is "overkill". The most commonly repeated suggestion i saw on this forum about chargers was "Get a PL-8", and i believed that was a good choice -- but nobody really explained "why" -- and i am not one to do something "just because". I thought the PL-8 was a little too fancy; i just wanted to charge/discharge individual cells, maybe re-balance if necessary someday. The logging and PC-interface features were certainly cool but i didn't "need" them...and the marketplace is always evolving. So i thought I'd try and find some alternative. There had to be at least one other option out there, right? Well, after several months and a lot of wasted shipping, i'm telling you: Just buy a damn PL-8. You'll save a lot of little details, surprises, and hassles that really add up. For those who just need to hear it though, here's my little story about why:

First i tried a Turnigy Reaktor 300W. This had a built-in power supply so it could run off mains power without buying a separate PSU, and i thought that made a lot of sense. Output was limited to 10A, which seemed reasonable given the size of the unit, and i was willing to accept long charge/discharge times in exchange for less expensive equipment -- I have more time than money these days. At one point, this charger did have a good reputation...but after taking delivery on it i discovered the most recent units were not made as well. My unit barely survived being connected to a car battery - i did it once as a test, and on the second time it failed and would not power up. I did not hook it up with reverse polarity, it just failed. Blech. In retrospect, even if it had worked i'm sure it would have failed anyway. The heat sinks were tiny.

I replaced that with a HiTech brand unit. Again, a built-in power supply, and again the "specs" made it look like it could get the job done. Unfortunately what i could not tell from the specs nor the manual (which i always download before buying), is that the charger's settings could only be adjusted to a handful of "common presets". So: useless. Back it went.

Starting to realize my foolishness, I browsed the Revolectrix website (makers of the PL-8) to see if they offered any "less cadillac" options. At this point i accepted that i'd have to buy a separate power supply to run a "good" charger, but still wasn't willing to go "bells and whistles" with the PL-8. The GT1200 looked like a great option; i could power it with an affordable 12V 750W server PSU and still get 40A charging out of it. More wary by now, i called Revo, got in touch with their in-house engineer, and told him what i wanted to use the charger for. He told me there would not be a problem, so i ordered it. With relief, I used it to do the cell-by-cell charging while building my pack. It has a rotary knob control instead of the usual "4 button" interface, which i liked. And also it actually worked -- which i also liked. I thought the ordeal was over...i had wasted some shipping but i guessed i had learned a lot, so i was ready to move on.

Then, i decided my initial balance had been at too low a voltage. Disassembling the pack and doing the job cell-by-cell was not desirable, and i had included a balance connector when building the pack (both to connect a CellLog8 and for re-balancing purposes), so i topped up the pack from solar then used the GT1200 to do a balance charge. It worked well, but after a day it wasn't done. The next day i repeated the process with the same connections, same settings...and suddenly smoke was blowing out of the GT1200! Revolectrics sent a replacement without any hassle, and i tried again...with the exact same results. I have gone over my setup, settings, everything with Revolectrix - we don't have an explanation. Their designer overseas is supposed to be looking at the units i shipped back, but they have admitted it's low priority for them so i may not get an answer for months. If i do, i'll share it here. My only idea is that some part of the balancing circuit is sized too small, because for the entire first day that i attempted the balance, one of the parallel banks was above the balance setpoint voltage, so the charger was bleeding charge out of that bank and obviously only sending a small current to the other 3. But on all subsequent attempts, all banks started below the target balance voltage so the charger would have been trying for a larger total current into the pack. This still baffles me though, as it failed literally in minutes, wasn't even warm to the touch when it failed, and i was using this charger well under its rated output capacity (full capacity is 60A and requires a 24V PSU). The manual fairly brags that the charger will throw errors and shut itself down if a problem is detected, including wiring, exceeding inputs/outputs, etc. They don't use the word "foolproof" but you can tell they want to ; ) While i did notice a brief error message as i was reaching to unplug the charger (immediately upon noticing the smoke, since i was right there), the charger definitely didn't manage to shut itself down in time to avoid damage. It won't even power up now.

After a week or so of discussion, Revolectrix concluded i had better just pay the difference and upgrade to a PL-8. I agreed, and that's what we did. So now after all that drama...i have a PL-8 just like the rest of you. I would be balancing my cells right now...but unfortunately the PL-8 uses a slightly different balance connector than the GT1200...so i can't plug my pack in to it. The chargers appear to be in physically identical housings...but i guess the PL-8 design is a little older and uses a JST-PA plug instead of JST-XH (like pretty much every other R/C charger on the market these days). So i'm waiting another 3 days for a $3 adapter to arrive (these things are not stocked in local R/C shops, i called all over). The specs on the website are correct...but it's such an easy detail to overlook, especially since the connectors are basically indistinguishable in online photos. So instead of balancing (again), i'm posting my story here, hopefully to save some other cheap, stubborn schmuck from making all my mistakes.

All the manufacturers were great to work with. No hassles from any of them, and Revolectrix especially has been awesome. Great professional attitude, and a general eagerness to help. It's just too hard to figure out "on paper" if any given charger will do the job for larger LFP packs. Specs online aren't always complete, manuals online aren't always adequate, build qualities are variable, and let's be frank -- these things are meant for batteries that are a whole lot smaller than what we're trying to use them on. I get the impression it's almost an accident that the PL-8 even works, due to FMA just overbuilding the hell out of it. But evidently it's the only one that does.

At least, probably. I won't really know for another few days. And even then i plan to throttle back the charge current to 10A just in case, because i'm not in the mood to cope with another smoked charger. I'm going to wait 'till i hear back from the designer in Singapore before i dare running it at rated capacity.

- Jerud
------------------------------------------------------------
1220W array / 1000Ah LFP house bank
MidniteSolar Classic, Magnum MS2812
ME-RC, Trimetric, and JLD404
2001 Fleetwood Prowler 5th wheel 25 foot, self-rebuilt
Full-time 100% electric boondocking (no propane, no genny) since 2015
www.livesmallridefree.com

[Sunking]

I'm writing this as a favor to others out there who are stubborn and cheap like me, and looking for a charger to work with large-ish Lithium battery packs but who think a PL-8 is "overkill". The most commonly repeated suggestion i saw on this forum about chargers was "Get a PL-8", and i believed that was a good choice -- but nobody really explained "why" -- and i am not one to do something "just because". I thought the PL-8 was a little too fancy; i just wanted to charge/discharge individual cells, maybe re-balance if necessary someday. The logging and PC-interface features were certainly cool but i didn't "need" them...and the marketplace is always evolving. So i thought I'd try and find some alternative. There had to be at least one other option out there, right? Well, after several months and a lot of wasted shipping, i'm telling you: Just buy a damn PL-8. You'll save a lot of little details, surprises, and hassles that really add up. For those who just need to hear it though, here's my little story about why:

First i tried a Turnigy Reaktor 300W. This had a built-in power supply so it could run off mains power without buying a separate PSU, and i thought that made a lot of sense.

Hate to say I told you so, and quit listening to Karrak. Glad you figured it out.

I think you mentioned it but you can use a a Desktop PSU as the power supply, but at 12 volts will be limited. About all DIT EV guys use the PL8 or borrow one from someone and use it differently than you do. We know the failures of top balance like you described letting the smoke out. We Bottom Balance and the PL8 is perfect for it. First we just connect the cells in series and discharge until the first cell reaches 2.5 volts. Then disconnect and put all the cells in parallel. Then set the PL8 to discharge to 2.5 volts and walk away. When finished we set discharge to 1 or 2 amps and walk away again and repeat. When done all cells are at 2.5 perfectly balanced at the bottom. Reconnect in series and charge to 3.45 vpc cell average, we do not use Balance as we do not want any cell to go to fully charged. Never have to worry about over or under discharged and no damn balance boards to smoke or destroy cells. No BMS required.

[zamboni]

I deserve a 'told ya so', and you deserve to be the one to dish it out. I do understand more now than i used to, and that's part of why i chose the stubborn road. But...i'd rather not have : ) Top balance (i think you would call it a mid balance -- not aiming for 100% full cells) works better for the equipment/controls i had in my system already, as far as what i can accurately monitor and where the system will be operating most of the time.

We know the failures of top balance like you described letting the smoke out

Are you implying that top-balancing is a risk to the Charger itself? For all the arguments i've seen for/against any form of balancing, i don't remember ever reading statements about being hard on the charger. Obviously i'm curious about this now because the charging+balancing seems to have been what smoked the GT1200s - which appeared to be otherwise very robust chargers, using the very same case/heatsink/cooling fan enclosure as the PL-8. I had planned to post up and tout the GT1200 as an excellent budget-friendly alternative to the PL-8 until this episode happened...

Yes, i'm using a computer PSU and it doesn't seem to bat an eyelash at running the PL-8. It's actually a refurbed server PSU from some monolithic datacenter somewhere - more robust and a bit higher wattage, and can be found online for under $50 which is nice considering the Revolectrix PSU is over $200. I'm sure it's worth it...but i can afford to be limited to 40A output.

[Sunking]

I deserve a 'told ya so', and you deserve to be the one to dish it out. I do understand more now than i used to, and that's part of why i chose the stubborn road. But...i'd rather not have : ) Top balance (i think you would call it a mid balance -- not aiming for 100% full cells) works better for the equipment/controls i had in my system already, as far as what i can accurately monitor and where the system will be operating most of the time.

I was not trying to beat you up, showing you a different way you had not looked into.

Are you implying that top-balancing is a risk to the Charger itself? For all the arguments i've seen for/against any form of balancing, i don't remember ever reading statements about being hard on the charger. Obviously i'm curious about this now because the charging+balancing seems to have been what smoked the GT1200s - which appeared to be otherwise very robust chargers, using the very same case/heatsink/cooling fan enclosure as the PL-8. I had planned to post up and tout the GT1200 as an excellent budget-friendly alternative to the PL-8 until this episode happened...

They are forced to bypass more current that they are capable of over extended periods of time.

Yes, i'm using a computer PSU and it doesn't seem to bat an eyelash at running the PL-8. It's actually a refurbed server PSU from some monolithic datacenter somewhere - more robust and a bit higher wattage, and can be found online for under $50 which is nice considering the Revolectrix PSU is over $200. I'm sure it's worth it...but i can afford to be limited to 40A output.

PSU are good inexpensive chargers.

I knew Karrak was full of it.

[zamboni]

They are forced to bypass more current that they are capable of over extended periods of time.

I considered this...but the GT1200s died in less than 5 minutes, not an extended period. I have no knowledge of how a charger works internally so i can't even guess at the real cause, but i AM nervous that the PL-8 could go up in smoke the same way. I'm going to throttle it back to low current and hope.

I get that you wouldn't ever need to use the PL-8 to balance charge so long as you're building bottom-balanced packs...but have you ever done it, and did it work?

[Sunking]

I considered this...but the GT1200s died in less than 5 minutes, not an extended period. I have no knowledge of how a charger works internally so i can't even guess at the real cause, but i AM nervous that the PL-8 could go up in smoke the same way. I'm going to throttle it back to low current and hope.

Inside the charger are Bleeder Circuits aka Vampire Boards. Technicality called Balance Circuits. Pretty simple really when the cell voltage reaches the set point, 3.6 volts for LFP at 100% SOC, the Circuit turns on and bleeds or bypasses a determined amount of current. It is a Shunt. But there is an inherent problem with the concept in the design. They charger is still supplying more current then the Vampire Board can shunt. Not sure how much current the G1200 bypasses but the PL8 is 1 amp. So say you set charge current to 40 amps, first cell reaches 3.6 volts and the vampire turns on and bypasses 1 amp and leaves 39 amps still going through a fully charged cell. When that happens not only are you damaging the cell, the voltag eis still going up on that cell and felt by the vampire board and can damage it.

Now a Smart Lithium charger can reduce current to the Vampire Current when the first cell triggers. The PL8 and GT1200 can do it but not by default. You have to program it to do so called Balance Start V. Note doing so can mean it can take hours to Balance a pack not in balance. Example if there is a 10 AH difference between high and low cell with 1 Amp Balance is 10 hours after th efirst cell reaches 100%

I get that you wouldn't ever need to use the PL-8 to balance charge so long as you're building bottom-balanced packs...but have you ever done it, and did it work?

I practice what I preach and yes I do it. To both my racing golf carts, 3 EV's I hlped freinds build, and thousands of DIY EV builders Bottom Balance. We started to use Bottom Balance because Top Balance destroys lithium batteries. We bottom Balance for 4 very good reasons.

• No accidental over discharges because BB eliminates that possibility. Just one over discharge of a cell destroys it immediately.
• We limit charge to roughly 90% SOC and limit discharge to no less than 10% which doubles to triples cycle life.
• Vampire Boards fail and destroy cells.
• We are not rich or stupid.

We mimic what commercial EV manufactures do. No EV manufacture allows the customer to ever fully charge or discharge the batteries. If they did the batteries would not last more than a year or two, and increase liability/risk to fires. EV manufactures Middle Balance with matched cells. You cannot do that, but you can mimic that as long as you do not TOP BALANCE. EV manufactures limit charge to 10/90 or 20/80 SOC. Think about that.

[zamboni]

Thanks for your detailed replies...I have spent a lot of time reading old posts in this forum and I see you have been repeating much of this advice for quite a while. The more i use my own system, the more clearly i can understand and appreciate what you're saying.

Re: balance circuits in chargers. Your arguments against vampire boards and "active balancing" were persuasive and convinced me long ago to avoid these approaches. I get it, that when the charger is sending more current than the balancing circuits can bypass, then balancing isn't happening. This makes a lot of sense in the case of BMS and vampire boards which are not necessarily "talking" to the charger. But when that balance circuit is inside the very charger which is sending the current...is it not reasonable to think the charger will dial back its current and avoid exceeding the balance circuit capability? This is, after all, pretty much the one job this product is meant for.

The GT1200 is a pretty darn nice charger, with many safeties and controls baked in. It will tell you if it's wired wrong, if voltages or currents go out of spec, it will even dial back charging current if it starts to draw too much current from the PSU or PSU voltage drops below setpoint. Especially because of that lat point, it's hard for me to accept that this charger would simply pump current into a pack even when it "knows" the balance circuits can't shunt enough. But having said that, the GT1200 did not fail when max charge current was set low (under 20A) yet it smoked when i turned charge current up to 30A or 40A. So yeah, it does sound a whole lot like the balance circuits got overwhelmed...but why would such a capable charger "let" that happen to itself?

It's stubborn of me to keep asking why, i know. But these are the moments where i learn the most. I will probably just have to wait and hope Revolectrix eventually does a post-mortem on my charger and will share it with me. It's a shame really -- i really liked using the GT1200. The interface is really good! In sharp contrast, the interface on the PL-8 is a dog. I can see why they provide software to run it with instead, so people forget how bad the controls are...

[Sunking]

But when that balance circuit is inside the very charger which is sending the current...is it not reasonable to think the charger will dial back its current and avoid exceeding the balance circuit capability? This is, after all, pretty much the one job this product is meant for.

Hold your horses, that may or may not be how a Smart Charge with built-in BMS works and the PL8 is no exception as I explained in my last reply. Most hobby chargers, not all, will have the Vampire Boards inside the box just like your PL8 does. Instead of having passive unintelligent Balance Boards mounted on the battery cells, are just moved inside the charger box. That is the reason for the limit of 8, and is called a Centralized BMS as opposed to Distributive BMS using as many Balance Boards required mounted on the cells. Either way is Passive. Your PL8 and GT1200 are Passive in Default Mode. An the charger is just a plain ole simple CC/CV power supply/charger.

OK now that I got your attention, you can go into the System Setup and enable Balance to: Balance Start V. Look it up. When you do that, when the first cell reaches the set point voltage of say 3.6 volts, it reduces current to 1 amp, in in CC mode like you are thinking. When the last cell reaches 3.6, then the charges switches to CV, until charge current tapers to whatever Finish Current is set too. If finish current is 1 amp or greater it just terminates charge and never goes into CV mode.

So just about every BMS made is passive and used Vampire Boards be it internal or external to the charger. Lower end units are fixed voltage set point, and higher end units allow you to program the set point voltage so you can charge various Li chemistries. Very few can actually reduce the charge current when the first cell goes high. The PL8 can do it but NOT BY DEFAULT.

Now a few high end Li Charges like one say for 16S have in effect 16 chargers inside giving each cell what it needs when it needs it. But as you can imagine cost Big Bucks.

[Sunking]

One last thought while I got your attention. If you go buy a Li battery pack like say an A123 Systems 12 volt car battery using a 4S configuration LFP cells has its BMS built inside the battery Box. Li powered tool battery packs have the BMS built into the inside of the battery pack. No special charger of any kind is required, just th simplest form of a CC/CV exactly like a Pb battery uses. So now you should ask if that is a problem or not and the answer is Nope.

Their BMS has a few more functions and can do something you cannot. First the Li cells are matched in capacity and resistance as they have millions of cells to work with and match up with computers. Second they are Balanced at the factor, so there is very little for the BMS to actually do other than monitor and make minor corrections. They still use Vampire Boards but with a few things added.

1. A electronic relay to disconnect the battery if over or under voltage. Or if the charge discharge current is too high. Lights out and no charging until reset internally after conditions clear.
2. A thermal couple to monitor cell temps. If they get to hot and sometimes too cold operate the relay.

As for the charger any charger that is CC/CV with the right range of voltage like 14.2 to 14.4 volts for 4S LFP of a appropriate current that does not exceed what the battery can accept. The actual Vampire Boards rarely ever are used. It was Balanced at the factory, and the Vampite Boards only make small corrections when necessary at the end of the charge cycle. So drop one in your car, and just about every alternator outputs 14.2 volts an dif lower no problem you just will not ever fully charge the batteries and the BMS has nothing to do unless something goes wrong inside.

[zamboni]

I hear what you're saying about factory-built battery packs with BMS inside. And you're right; there's a lot of territory between those, and the packs schmucks like me are putting together for RE off-grid systems.

I just have a hard time accepting that a $200+ PL-8 doesn't have enough smarts to avoid cooking it's own brains out if balance current exceeds the "max charge current" setting. For the record, my PL-8 shipped with pre-programmed profiles, including one "A123 accurate charge" which is the one i chose to balance my pack (with some modifications). I already verified in the PC software that this profile has "balance start V" set to 3.30VPC by default. So some things have changed, perhaps...the PL-8 at least has this configuration available by default currently.

I'm still scared of smoking my $200 charger so i kept charge current max set to 10A initially, then dialed it all the way back to 1A (which is the limit of the balancing circuit according to docs) for the final pass at balancing the cells. It only took 2 days : )

That said, the GT1200 also had the option of setting "balance start V". It is NOT default, but it's available. As a matter of fact, i had set that value to 3.3VPC in the instance where the GT1200 smoked itself in under 30 seconds. So it doesn't seem to me like this is the "answer" to the problem. Honestly, i miss the GT1200. This PL-8 may be fancy but using it is like driving a barge with the controls in braille. The software is not much better. I slightly hate it, even though i did just use i to finally balance my pack to like 3 decimal places (theoretically). That GT1200 had a slick interface, very fast and easy. It just, you know, killed itself for no damn reason. Shame...

-Jerud

[Sunking]

I just have a hard time accepting that a $200+ PL-8 doesn't have enough smarts to avoid cooking it's own brains out if balance current exceeds the "max charge current" setting.

Hold on there for a minute. Balance current is fixed at 1 amp and cannot be changed. Unless you select a Profile Charge like A123 LFP the Charger does not know the capacity of the battery is or what charge rate to use. You have to tell it what to do. When you plug in the Balance Connector, all the Charger knows is how many cells are in series, but that is all it knows unless you are using a Profile Setting. It does not know the capacity, what current the battery should charge at, or even what Li chemistry it is. You have to program all that in.

My best educated guess is the GT1200 has a design flaw Revoletric has over looked.

[vast]

I want to buy a battery from a salvage Nissan Leaf for my 48V offgrid system. Can I use a PL-8 to perform a Bottom Balance, and how to do it? Note that every pack have inside 2p2s cell pouch.
What is the best method?

Thank you for help.

[Sunking]

Well before I answer any questions tell me how you plan to charge it. Leaf Batteries are not exactly compatible with Pb gizmos. Example any gizmo make to work with a 48 volt tPb battery nominal voltage is 48 volts. Not with a Leaf battery because it either has to be 45 volts which is too low, or 52.5 volts which is too high. It can be done, but charging at 59 volts is going to be a problem for almost every Solar Charge Controller on the market.

[vast]

Yes, if I connect 8s, that mean 8x7.4 = 59.2V, and for 6s, 6x7.4 = 44.4V. But for 7s can handle every charger, 7x7.4 = 51.8V.

I have a Midnite Classic 150 charger and voltage charge range is 12-93V. What do you think, can I connect 8s?

[vast]

I do not want to disturb this topic, so I started a new one HERE.