NG3 chargers can't current limit on lithium batteries?

GizmoEV said:

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.

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I see. Well it depends on how the probe is wired. The way I understand it, the chip sees a reference voltage that has some relationship with with the actual measured pack voltage. We can manipulate this reference voltage using the voltage pot. If Zivan wired the probe "inline" with this signal line I would think we could only use it only for it's intended purpose of lowering or raising the voltage setpoint. If the probe really is on it's own signal line then we probably can use that as a signal line as you wish to. With the right programming you should be able to signal on the line any number of variables using a multi position switch with different resistance values or just a SPST switch for a simple binary hi/low signal.

If what you're ultimately after is simply a CC/CV charge profile that terminates charge at 0.05C I don't think we need anything more than the mod chip itself. The way I understand it, just like voltage the chip sees a reference signal corresponding in some way to the charger current output, so it would be a simple matter for the chip to terminate charge once the current drops to the specified reference level. The reason I believe the chip must receive a current reference signal is because manipulating the current pot lowers and raises current output of the charger, even in Phase one (CC) mode.

If we can use the temp probe, I'd like to use it as a temp probe, but at proper correction value for LiFePO4 cells. The best reference I have to what that might be is the Thunder Sky owners manual that suggests raising charging voltage 100mVpc at -35degC. This implies a temperature compensation of -1.82mVpc per degC standardized at 25C. At 110 degrees that's a 79mVpc drop in voltage, or almost 2 volts with 25 cells.

I completely agree with everything in that post. The power stage of the charger is great. The control board though is pure crap. I had originally planned on replacing the entire control board until I opened up the charger and saw what was in volved in having to completely dissassemble the charger, cut out and desolder the old control board, resolder in the new one, and hope that everything would go back together without having those extra pieces left over that always seem to show up. I decided on the easier route of just replacing the socketed chip. I figured it would be much easier for others as well to just replace a chip on their own.

Yes, you can use the temperature probe input to control the board anyway you want. The probe input circuitry is shown on page 6 of the original schematics. It's signal just shows up as an analog signal at one of the a/d pins of the PIC. So, in other words, once you sample the voltage you can do anything you want with it. For our own setup, we are not currently using the temp probe so we don't yet have temperature compensation built into our code.

In documenting my code, I'm trying to make it as simple as possible for everyone with different versions of the charger to work with. I understand how my 144Vdc out version works; however, I don't yet have a good feel for all of the different versions (voltage and chemistry types) of chargers out there. For example, my NG3 was originally configured as a 144Vdc 15A lead acid charger. When they modified it to LiFePo all they did was change the chip, add a jumper, and maybe tweak the pots. However, I'm currious if there are any real changes they make for other chemistries. Here is why I'm asking, in Zivan's user manual they discuss the cell tension, which for lead acid is 2.0V. This 2.0V tension is what my 144V charger is based off of, which I will try to explain later. But they state the tension for other chemistries is different. I'm curious if they actually used different hardware settings for the cell tension for example if you originally bought say a NiCd charger.

Here is why I consider my 144Vdc charger to be based off of a 2.0V cell tension. This is all based on the circuitry that is on the right half of page 1 of the control board schematics. U7A generates a buffered reference voltage (Vref) 1.954V. U6D buffers the voltage divided battery input. If my battery pack is at 144V and the voltage pot is set to 0 ohms (left schematically) then the buffered voltage (Vbatt_divided) out is 1.999V. If the battery pack voltage is 144V and the voltage pot is set to 2k ohms (right schematically) then the output is 2.588V. This tells me that there is a 481k ohm voltage divider resistor on the power board. Likewise for a 144V system, they assume 12 batteries with 6 cells each or 72 total cells. Again the voltage divider math works out 6.8k + 2k + 481k =~ 490k, or another way to look at is 6.8k ohms/cell * 72 cells = 490k.

So, the voltage that the A/D (Va/d) of the PIC sees is:

Va/d = ( Vbatt_divided - Vref ) * (100k/15k)

From this, and assuming the pot is at 0 ohms, I can set my CV point anywhere from 140.7V to 195.1V before I clip the A/D input. If the pot is at 2k then it is reduced to between 110V and 150.1V.

The big question is, given the range of possible CV setpoints, do all different versions of the chargers have slightly different hardware or does it skip every 48V or so? Obviously I would expect some differnces beween say a 72V system and a 144V but what about systems that are closer in output? For example I might expect that a 156V system with an additional 6 cells would have a voltage divider resistor on the power board that is 521.8k. Any thoughts or measurements that can be made would be appreciated.

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.

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.?????

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 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.

So here it is, the prototype code. It's not as complete as I'd like yet but I think everyone will be able to figure it out and modify it to their needs. In order to compile it you will need to download Microchip's MPLAB and Hi-Tech's PIC18 Lite C compiler. (both free). The text file is just the code. The zip contains the entire MPLAB workspace and project files.

customcircuits said:

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.?????

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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.

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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.

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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?

Thanks for providing the schematic of the NG3 control board. Now I have a chance to replace the board with one which I'll design using discrete parts. I have been retired for 20 years and never did learn programming so I have to stick with the old fashioned way. I was stonewalled by the NG3 rep when i told him I had changed to lithium. I was always hopeful to get the Zivan reprogrammed, but in the meantime I designed a charger from scratch. It provides 10 amps at 135 volts. It starts with a button and stops when the current reduces to 1 amp. The hot parts are built on a heat sink and there is a fan. So far, so good. I have been thinking of making a 220v version so I could increase the current to 15 amps. BTW, my car is the 914 that I bought from Steve, who has a blog with lots of details of the car. My charger is modular and i will include schematics of each of the 5 modules after I learn how to convert them to pdf files. They are now *.eps.
Bob