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NG3 chargers can't current limit on lithium batteries?

60284 Views 144 Replies 21 Participants Last post by  jollmo
We've been using an NG3 charger for the last several years to charge our lead acid pack. We originally had Electric Conversions install an optional low current mode switch on the NG3 so that we could charge on a standard 15 amp outlet while at work.

We're in the process now of upgrading our pack to lithium. Before we purchased the new batteries we had contacted Electric Conversions regarding modifying our NG3 to handle the lithium batteries. They said they would be able to modify the charging profile for our configuration.

Now, after just receiving the charger back from Electric Conversions we noticed that the low power option had been removed from our unit. They failed to mention this little detail to us. I contacted them and all I was told was we can't current limit on lithium batteries and it would take to much time to do. If you can current limit on lead acid why not lithium? If the hardware of the NG3 supports current limiting on lead acid it should be just as capable of current limiting on lithium. I realize that it might require a separate charging profile or something but it can be done.

My plan now is to figure out the profile programming of the NG3 and modify it myself. I have a lot of professional experience in reverse engineering electronic systems and feel that it can be done. I know a lot of people have been down this path before on here and have found some decent information. If anyone has information about the NG3 charger that would help speed up the process it would be appreciated.

Two lessons here, NG3s don't currently have a current limiting capability on lithium and avoid Electric Conversions. After reading some of the other posts on here, I'm not the only one to have problems with this company.
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That is awesome, Dave. Any idea if the same modification will work with the NG1 or the 240V NG3? Also, is it possible to program the charger to stop when the current dropped to a particular value after reaching the CV stage?
Thanks for the info. I found that the Old_NG3_Logic.pdf file can be found at I also found that Greg Solberg could be one of several people including a firmware engineer at Tesla but I didn't search any further. His name is at the bottom of the schematics pages.

I'll open my NG3 and NG1 and take pictures of the control board. Maybe we can determine if this mod can work in the NG1 as well.

As for programing the chip, I have a Melabs U2 Programmer, will this work for programing? I should be able to figure out the code from your example since I've programmed in BASIC, Pascal, FORTRAN, and various command languages 15+ years ago.
Can I set the CV point and then a minimum current cutoff that terminates the charge?
If the minimum current cutoff can't be set then merely lower the ending voltage like I have done with my NG1 and NG3. I'm ending at 3.465vpc right now and the number of Ah which go into the pack after the charger drops into the "yellow" phase is actually quite minimal so charging times really aren't that much longer.

Depending how the timer is done it could be that when the current drops to a particular point the timer counter could be incremented/decremented appropriately to end the charge.
I wonder if the temperature compensation is taken care of in this logic chip? If so, it seems that the pins for temperature input could be used for input to control the charger externally: to turn down the current or shut it off completely.

FWIW, Attached are photos of the logic boards in my 115V NG1 and 230V NG3 both with the same programming. The paper work says it is the ZV curve #7 but the sticker on the chip says ZV6, in any case it is set for 69.3V Saturation and the current just tapers down close to zero until the timer during the "yellow" phase times out.

I don't think there is anything wrong with using a re-purposed lead acid curve except that the proper charge profile for LiFePO4 calls for a CCCV curve which terminates when the current drops to 0.05C. For my 200Ah pack that would be 10A, just barely above what the NG1 can do. I compensate by charging 20 cells to 69.3V or 3.465vpc which may still be a little high.

Here is the NG1 115V control board:

Here is the NG3 230V control board:
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Yes, that is a great thread. What I was wondering is if the chip does the actual controlling of the ending voltage then the replacement unit could be programmed to take input on the same pins and do something different with it.
When I had my NG3 reprogrammed I was told that it couldn't go much high enough in voltage, it was originally a 48V lead acid version, and they wanted to sell me an Elcon. I told them that they programmed my NG1 and it worked fine and that I had personally seen another NG1, programmed for 48V lead acid, put out 72V so they programmed it the same. The NG1 which I got to put out 72V was originally purchased with a NiZn profile which was reprogrammed for "8 T-875s or equivalent" before I got it. I just dialed in the ending voltage to 72V when I initially started charging a LiFePO4 pack before sending in the ones in the pictures I posted to get properly programmed.

From this I assume, like Brent said, that the basic hardware is set for different voltage ranges like both of my Zivans were built for a 48V lead acid setup, and then they have a 72V range and then maybe a 120 or 144V version. The original sticker on both my current Zivans say that 66V is the max voltage they will allow so it makes sense that they could actually put out a little above that. IIRC, the pots are 15-20 turn pots.

I'm not sure what or how I would need to take measurements on mine but let me know and I'll do my best. I have an Extech EX830 meter so I should be able to measure most anything on these if I'm told what and where.

I do want to get a board, maybe two, at some point.
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Thanks for the info, it both reaffirms what I was thinking and confuses me even more. I would expect with a 2.7V cell limit and 24 cells that your limit would be 65V as well. If you adjusted your pot I would expect the limit to only go down from there.?????
I'm guessing that the 66V was a safety limit. I never saw my pack go that high, 62V IIRC. Playing with the voltage pot got it up to 72V on a LiFePO4 pack.

Unfortunately, my logic board is all surface mount and the ones in the pictures are through hole components, making it difficult for me to do a direct comparison.
I'm sure my chargers aren't the newest. :) As long as the control logic is the same it shouldn't matter. I do know that I couldn't have different profiles programmed into my NG3 except that the sticker on the front seemed to indicate that there were different options based on jumper settings. I played around with them one time and found I could get different current settings which appeared to correspond to what I would expect with different capacity packs. Maybe it is only the newer surface mount type which had the option of different charge profiles.

I think at this point the best to get a few boards out and just let you guys help run some tests. I'll work on getting some boards ordered and assembled as soon as I can.
Do you have any idea what could happen in the worst case situation testing the a different logic board? Any chance that something might burn up in the charger due to over current or is there enough in place that maybe the worst that could happen is messed up voltage settings and timeouts? If only the latter then that is easy to deal with. Just babysit the pack when charging and unplug the charger if things go wrong.

For my NG1 I can just plug it into my Kill-a-Watt meter but I might want to get some way to measure the current out of the wall for my NG3. What do you think?
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Have you taken a look under the stickers to confirm both your units are using ST62T25B6 microcontrollers? [...]

BTW, I was reading an old thread from 2005 mention the reprogramming fee was only $40 back then. ZivanUSA is double that now.
No, I'll have to do that next time I get a chance. As for reprogramming cost, that is progress right? :rolleyes: Maybe the extra cost is so they don't have to answer our questions. :(
That's all nice and well, but, I hate to tell you, you don't need to modify the Zivan NG3 to work with Li-ion. On the contrary, the nice thing about the NG3 is that it's a plain old CCCV charger, which is perfectly ideal to use with Li-ion (in conjunction with a BMS).
They are a pain to get reprogrammed to what we want! I had to ask for a profile for 19 cells so that it was at the right voltage for 20 cells given that the ending current tapers to near zero. Furthermore, it costs about $100 to make a simple change.

During balancing, you do not need to ask the charger to lower the current to match the balancing loads' current. Instead, the BMS will take care of not allowing the cells to be overcharged, by switching the charger on and off, such that the average current matches the balancing loads' current.
But if you applied that to my system the way the chargers were originally programmed it would have taken for ever to get my pack charged. I went from 48V lead acid to 20 cell LiFePO4. Your method wouldn't have worked very well with my charger the way it was.

After the pack is balanced, with a plain CCCV charger, the current will naturally go down to 0 A as the pack is topped off. That is due to physics pure and simple, not to a charger profile. So, again, there is no need to tell the charger to reduce the current. (This is true independently of a BMS.)
And my data shows that after the pack is balanced it doesn't need to continually be balanced on every charge. Furthermore, the charge procedure is to charge to 3.6V and end the charge when the current drops to 0.05C which is 10A in my case. If the ending voltage is lower then the ending current can be lower without overcharging the cells.

But now, I am afraid that you're better off leaving the NG3 charger as is, and let your BMS do its job.
And that is where many of us disagree with you. Besides the BMS vs no BMS debate, why would you remove one of the safety mechanisms in a charging system? What you are proposing is that a BMS never fails. It is made by humans so it is not if it will fail it is when it will fail. By having a properly programmed charger to shut off when it should, entirely on its own, you stand a better chance of your pack being protected when the BMS fails to do its job. Why wouldn't you want this redundancy?

Given the data I have on my pack so far, and that of others, the pack does not have to be balanced on every charge provided that there are no bum cells in the pack. Having a user programmable Zivan means that I can do a balance charge and then easily reprogram the unit to not charge to such a high voltage until the BMS signals that a cell is getting out of line and needs to be balanced again. My data suggests this is easily a year or more. I believe others have gone even longer.
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If you wanted to, you could rig something to skip the balancing phase after the first time, but why go through the trouble?
To prolong the life of the pack by not over charging it every time it is charged.
However, setting the correct top voltage of the charger is a redundant safety mechanism, and I am all for it: if the pack is balanced, even if the BMS fails, the pack will not be overcharged.
And that is why this NG mod is being made. It is being made to provide multiple charge current options, a user settable ending voltage, and the option to properly terminate the LiFePO4 charge procedure which includes the ending voltage and ending current. The last item, ending current, is what so many seem to miss/ignore continually.
Balancing does not harm cells. At least not the way balancing is done by all the BMSs I am familiar with.

On the contrary, balancing maximizes pack capacity.
Do you have data to back that up? After balancing, disconnect the cells and let them sit for a few hours. What voltage do they rest at? If it is over 3.4V then the cells were over charged and their life shortened.

As for max pack capacity, have you done your own tests to see how much capacity is really above 3.4V? I have. I started with a TS-LFP100AHA cell resting at 3.397V and charged it 4.00V. The cell accepted only 0.6588Ah. Why over stress the cell for less than 1% of its capacity. I'm giving up less than 1 mile of range for a longer life pack.
I am one of those people. Please do explain. (Seriously.)
Naturally the idea is to be able to fully charge the cell without overcharging. A fully charged LiFePO4 cell rests at 3.4V, if it rests above this voltage it is overcharged. One option is to charge to 3.4V and just hold it there but then it would take a very long time to fully charge the cell. To compensate for the ESR of the cell, which raises terminal voltage while charging, the charging can be to a higher terminal voltage than 3.4V but then the ending cutoff current needs to be increased the farther above 3.4V the ending voltage is set. The most common charging procedure I have seen is to charge to 3.65V and end when the current drops to 0.05C. For my 200Ah 20 cell pack that would mean I should charge to 73.0V and hold that voltage until the current drops to 10A and then terminate charging. When the cells settle down they will be resting at just under 3.4V or 68.0V for my particular pack. Continuing to charge below the cutoff current of 0.05C can/will overcharge the cells. Last I checked your BMS doesn't balance at or above 10A which means you have to continue charging until the current drops to the programmed shunting current (or the BMS tells the charger to begin throttling back the current) and hold that current for a time to maintain the voltage of the highest cell at 3.65V or the shunting voltage until all cells have matched up. Even with a balanced pack this 3.65V is held with a current significantly lower than 0.05C which means that the cells are being over charged.

Test it out like I said in a previous post. "Balance" the cell and disconnect all loads from it and let it sit for a few hours then measure the terminal voltage. If it is resting at over 3.4v it was overcharged.
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David, I am curious if you could point me in the right direction for the data regarding the resting voltage for LiFePo4 cells. This is a very interesting discussion and I want the specs and/or data to look at with regard to what voltage a fully charged cell sits at. Are SE cells different than TS or any of the newer ones in regards to resting voltage?

Sorry for the delay in responding. I've been dealing with two family emergencies at once so I'm a bit behind.

This is really a bit OT for this thread but I'll post a few things to investigate. Unfortunately I haven't found a single definitive source for this information so I have had to glean from multiple sources including user's experience (and mine), user reports, technical papers and the like.

Watch this video for a good overall understanding to LiFePO4 cells. I recommend watching it more than once if you want to get a better understanding of things:

This paper is very technical. I originally read it to learn why manufacturers say not to charge LiFePO4 cells when they are below 0°C. If you know your physics and/or chemistry you can get some info out on voltages. It is not for the "faint of heart". :D

There used to be a CALIB spec sheet which showed 3.4V as the "float" voltage but I can no longer find it. I also had an email from someone who posted on the EVDL, they worked for a LiFePO4 battery manufacturer, that in testing that they could fully charge a cell if it were held at 3.4V long enough. I gathered that this was quite a long time but he didn't say how long. He also wouldn't disclose which manufacturer he worked for.

Jukka Järvinen has been testing and using LiFePO4 cells for many years. Search for his name on the EVDL and you will come up with posts by him. Basically he says that if a cell rests above 3.4V then it is evidence that all the Lithium has been moved from one side to the other indicating a fully charged cell. I do know that it takes very few ions to be transferred for the voltage to go from 0V to 3V so it makes sense that a similar thing happens at the fully charged end which my testing agrees with. For the older TS cells he said that they only need to be pushed to near 4V once in a while and at low currents. Charging them to lower voltages between them is definitely beneficial for life span.

Jack Rickard ( has done quite a bit of battery testing but it takes a while before you can glean enough info from him to understand why he makes the claims he does. Over the past 2-3 years I have pieced together enough info from him to agree with him on the 3.4V number.

The documentation which came with my TS cells in 2009 say to stop charging when the current drops to 1% of what it was to start with where 0.5C was recommended. This would be an ending current of 0.005C which is quite low. Using this method left cells sitting above 3.5V for several days. I don't know how much of that was due to capacitance of the cells and how much was due to actual Li charge storage. Remember, these LiFePO4 cells are also big capacitors with their hundreds of plates separated by a dielectric.

Finally, the best thing you can do is get some cells and equipment and play with them.

HTH, now I'm going to keep watching this thread because I want to be able to program my Zivan chargers for LiFePO4 charging with both a voltage and current cutoff.
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Unfortunately, I don't have a switch on my board so I won't be much help.
Don't you have a row of jumper pins on yours? All three of the NG1s I've opened up and my NG3 have a row of jumper pins. One of the NG1s had a rotary switch which was hooked up to the row of jumper pins. The rest of the chargers use standard jumpers.
I have a NG1 labled max voltage 58.8 volts is anything you folks are doiing with modifying these chargers capable of raisng the voltage on this charger?
Assuming that an NG1 with that ending voltage is the same one used for 48V lead acid packs, based on my NG1 (and NG3) for 48V lead acid, that they can in fact put out as much as 72V. I found this out by adjusting the voltage trim pot to the max while charging a LiFePO4 pack. I subsequently had both of them programmed by the US Zivan dealer for 69.3V saturation for my 20 cell LiFePO4 pack.

Edit: I forgot to add that the factory programming doesn't use current as a cutoff criteria so it will only taper back toward 0A until the timer times out. At least that is how mine ended up working. That is just one reason the control board replacement that this thread is about is such a useful modification.
If you're using this mod I think that you are probably overcharging your pack.

A long discussion resulted in this post:

Which links to the BestGo manufacturing specs that says the cut-off current in the CV phase should be C/20, so 5A for 100Ah cells. The default in the software seems to be 0.2A - 200mA.
What I had to do was top balance my pack and then trim the voltage to 3.455V/cell to keep the standard charger from over charging. I verified it by charging completely and then removing any load on the pack and let it sit several hours and checked the voltage of each cell. Since all of them dropped to just below 3.38V I know that my TS LiFePO4 pack isn't being over charged.

Basically the higher the target voltage used the higher the cutoff current needs to be but it isn't a linear relationship. I've tested this a little with small packs and it appears to hold true. It is better to undercharge than to over charge your pack. Also, I'm going on 3.5 years with no balancing on my pack and it doesn't show signs of cell drift. If you have no unbalanced loads and no bad cells you do not have to balance your pack on every charge. My pack is now 5 years old.
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