TP4056 In series with Isolation

Question

I found this https://www.youtube.com/watch?v=cBM0aUGW87Q&t=22s Idea on YouTube but is interested in extending the Idea.

What I plan to do is to Isolate the TPS4056 with a higher drive DC-DC converter. The only on I could found locally is a URB2405YMD-10WR3 with an input voltage of from 9VDC to 36VDC to an output of 5VDC and a drive of 10Watt. I could thus probably drive each individual TP4056 at the full level of 1A at 5VDC (thus 5W) and thats a safety net for the DC-DC converter.

I would also be able to charge a LiPo stack with either a Lead Acid input of 11VDC to 14.8VDC or a 36 sell PV panel (Max unloaded voltage of 21.4VDC).

If I stack up 6 LiPo cells to provide an output of approximately 24VDC (theoretically and I hope so)

It is then Isolating the Charge circuit of the LiPo's from the input charge.

My problem is to provide a stable enough charge circuit for a 6 stack LiPo cell's ( I plan to use a 6X2 stack thus six in series each with two in parallel).

Thus each stack could be charged with its own TP4056 that is Isolated from the Input (I hope).

As the planned tagged LiPo cells (Panasonic NCR18650B at 3.7VDC 3.4A/h) that do not have protection so I will have to add a BMS to limit the depletion level of each cell (I'm going to use two three cell BMS without balance as this is already done by the Induvidual 6 TP4056.)

The load will be then supplied through the two 3S BMS's in series to provide the required output of 24VDC.

This would then limit the problems with the Charge circuit for a 6 cell stack that is at least 25.2VDC (I hope)

It is very experimental at this stage but I hope it would be successful at the end for a bugout SHTF lithium stack the DIY way. Im still awaiting the components (of which the DC-DC converters is by far the most expensive) and the PCB for this components. (i'm also putting on a Polyfuse (self re-settable fuse) with I-hold of 7A and I-trip of 14A at the input side just for protection of the DC-DC converters (LP30-700 with a Vmax of 30VDC of Way-ON; also locally available))

Please help me regarding this Idea because locally available components is quite limited.

kkazem · Answer

I'll be glad to help you. I'm power electronics engineer with 40+ years experience. But I haven't really heard a question yet. I don't really see much of a need to balance the cell voltages fully charged. Panasonic makes pretty-good LiPo batteries and the datasheet for your model shows the typical to min capacity difference of only about 3%, so I would expect about +/-3% or a maximum capacity difference of 6% total. That's not that much. With a CC-CV charge profile (constant current followed by constant voltage), the cells might have about the same 6% max difference in fully-charged voltage. Since they're in series, only the total voltage really matters to your load. And even if you charge them with a balanced maximum charge voltage system as you described, once the charger is turned off, the cell voltages will revert to their own balance and not the maximum charge voltage of 4.20 V/cell. Remember, all your cells will (should) be at pretty much the same temperature, so no cell-to-cell differences from that. My point is that simply charging in series without a cell balancer in most cases produces very good charge results with little imbalance. Unless you're using cheap batteries that have big capacity differences, I doubt you'll notice much difference between charging with balanced fully-charged voltages compared to series circuit charge with the same current charging all cells in the pack. Having said all that, reply and I'll try to help you.

zagene · Answer

Hi Kamran, TY for the answer. The unfortunate business with this cells is that It is dangerous, to charge and to discharge, and I have to do with what is available at what price in my country. First thing (as from my supplier) there is four main types cells available under this serial number, the tabbed and the un-tabbed and the with protection and these without. Unfortunately I can only get tabbed cells (for easy building a block or series of cells as I am not comfortable to solder on the cells itself or make a Spot welder to tab it) in unprotected format. So this cells will over deplete if I'm not very careful with the load and then its useless. As this cells (or 12 of them in my case) is quite expensive and I do not want to damage it. In a nutshell, the TP4056 is a LiPo battery charger at CC 1A and CV 4.2VDC so in this way it can charge two cells in parallel. But what if I want to build a block of 6 batteries (each containing two cells in parallel) in series. That would require a DC charge voltage of 25.2VDC to fully charge at a CC rate of at the most 1C (6.8A) and a charge controller or a solar MPPT controller is quite expensive. So my Idea is to charge each cell pair in parallel on their own. In that way if the cell is full it will stop the charging process (also with the lipo batteries the recharge cycles is limited so trickle charge is also not a good Idea). In this way if all the TP4056 indicate that all the cells is fully charged then I can remove it from the charger. (The BMS on the battery pack is for short circuit protection and prevention of depleting the cells but that will only come in with the load). The TP4056 modules (unprotected modules) is quite cheap and do work well, but its built for an input of 4.5 to 6 VDC. Trying it it series or parallel also do not work as it seems that the bypass capacitor's capacitance is either to high or too low causing all sorts of problems with damaged modules. (I have lost quite a few of them in the past as well as the TP5100 modules) Thus the isolated supply for each of the modules and if one cell group is full then it will just not draw current to charge. The added advantage of the DC-DC converter is that I may now supply a wide range of inputs to the DC-DC converters and as it is Isolated, the supply to the TP4056 is also isolated and thus the process of charging each cell group. That is theoretically and as you and I know, It does not agree with the real world situation. The DC-DC converter used originally do not do the thing for me as a 1W supply to the TP4056 will take forever to charge 6A/h and also the max Supply voltage of it is 9VDC so its built for a 5VDC USB charger and not for a higher current need of 6 groups in series. PS, I changed the output on the PCB design for a JST XS connector so that the batteries could be unplugged from the charge circuit and it will also enable me to charge one to six cell groups of 4.2VDC via the same as a balanced charger output or an external balancer. And I hope it will work in the long run as time and money for lots of experimenting just is not available.

kkazem · Answer

Here's some comments to help you on this TP4056, 2x6 cell charging circuit: 1. If you're charging close to 1 amp per pair of paralleled cells, you're not going to be using a USB charger to do it as the max I've seen in USB chargers is 2 or 3 amps for hi-current USB chargers & 0.5A for standard USB. Therefore, you need an input power source of 5VDC at 7.5 amps minimum capacity to keep from loading it at 100% and having an overtemp situation in your input power supply. Your charging time will be much greater than 6.5 hours (1 amp*2 cells*3.25 hrs/cell = 6.5 amp-hours). The problem is that the cells typically can't charge that fast at the high rate of 1C or 3.25A/cell in your case. 2. You don't need the dc-dc converters for this. You can get the same results, without damaging your TP4056's, with a series ckt similar to what you showed, but with the TP4056's input leads also in series, but with an added 1N754 zener diode (6.8V) across each TP4056 with the cathode to the positive-side of the TP4056 input, anode to the negative-side. You mentioned that you damaged them previously and without the zeners or some other way of keeping the TP4056 inputs below the 8V max input rating, they'll likely get damaged. With this configuration, your DC charging input to the 6x series TP4056's should be a well-filtered DC power supply (or wall wart) of 26 to 38 VDC at 1.2 amp minimum (1.0 amp is the bare minimum). The zener diodes are there to protect the TP4056's from an input overvoltage. To protect the TP4056's from a negative input voltage below -0.3V, you can put a 1A schottky diode (1N5819 or equiv) in parallel with each of the zener diodes, with the schottky cathode to the zener anode and vice-versa. But I can't see that the shottkys are necessary in this case. 3. Your polymer fuse is perhaps problematic in your case. Keep in mind that it will still draw 3.6 watts from your power source after it opens ( https://belchip.by/sitedocs/00005773.pdf ). Also, it 14 amps it will take 16.6 hrs to open between 7 and 14 amps, the time to open is not specified nor guaranteed. At 40 amps, it still takes 3 seconds to open. You want the fuse to open fast during a fault. Your TP4056 already provides output current limiting, so your batteries are electronically protected against charging overcurrent. I recommend a fast-blow fuse or a picofuse if space is limited. Make sure to use a current rating 20% to 25% above your actual maximum continuous current. I hope this helps.

TP4056 In series with Isolation

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