HV Battery Headway 38120HP LiFePo4 70S pack

Lithium batteries have many advantages. They have higher energy per unit weight, but they are also more delicate. It is best to charge them with a balanced charging device to prevent overcharge and overdischarge problems caused by unbalanced series charging and discharging, because if overcharged and discharged, lithium batteries will Shorten the life, the most serious situation may also lead to burning, it is necessary to make a balance charger for real-time or regular balance voltage charging. Lithium iron phosphate batteries are better tolerant of overcharge and overdischarge, but they are also more sensitive than NiMH batteries, so if you want to modify it, it is better to configure more complete monitoring and maintenance accessories to monitor the voltage and temperature of a single cell in real time. The batteries are best in the same batch. Low-end products to ensure the consistency of self-discharge, capacity, and internal resistance characteristics. In short, it is more complicated and troublesome to maintain.
Another idea is to buy old battery packs, disassemble and measure the internal resistance of the battery cells, select the better composition and connect one or more battery packs in parallel to the original battery (may need to connect 4 power cables, because there are The existence of the safety pin), use the space of the spare tire to create a suitable battery box, clamp the battery cell to prevent swelling, and do not need to connect a temperature probe (the temperature will be reduced when used in parallel, because the current has been shunted to about 1/2 of the original).

 

Why not add a second NiMh battery, but connect it 2P28S to create a 12Ah battery that can handle the high current charging and discharging better than the 1P28S pack and have more than twice the regen capacity that could be charged from a mains outlet?
The limitation the original NiMh pack has is the high discharge and recharge rate robs a significant amount of the rated capacity. By halving the discharge and recharge rate across 2 cells in parallel, the battery life would be extended as well as its performance, yet completely compatible with the on board BMS system ....

T1 Terry

 

The super capacitor is connected in parallel to the battery pack. Supercapacitors can be charged and discharged with high currents and have very low internal resistance and loss. Can they be connected in parallel to the original battery pack or the modified lithium battery pack to reduce the temperature, thereby improving safety performance and acceleration and regeneration performance? This is just an idea. No experiment has been done yet. Friends who are interested and qualified may try it.
Moreover, the super capacitor has no limit on low voltage, and it can be discharged to 0, but it cannot exceed its withstand voltage, which is about 2.7-2.8v single. The use of super capacitors in series may need to have a protection circuit to avoid withstand voltage higher than its withstand voltage.

 

The hybrid system has to have some sort of maximum voltage. You could just build the capacitor bank to meet or exceede that voltage and then add a simple balance circuit between cells.

 

Yes, a balanced circuit is required to improve reliability.
The internal charge and discharge of supercapacitors have no chemical energy transformation, only physical transformation. Theoretically, the possibility of being affected by temperature is low, and the lifespan is close to infinite, but the current capacity is low.
For the prius 3gen 2gen supercapacitor may be a good choice, the capacity does not need to be large, because I am not sure that its motor drive circuit can work for a long time, in terms of design, it does not work for a long time, whether long-term electric drive will cause the inverter The temperature is too high and damage, and the working interval of the engine is prolonged, and the temperature change may increase, which may have some impact on the life of the engine and the warm air. If the engine does not work for too long and the temperature drops to uneconomical operating temperature, The economy has a negative impact. So the battery capacity may not need to be too large.

 

This balancers is hard to find. Large voltage runoff between cells?

 

This link may help, from there you can look around to see what other balancers are available. You can use multiple balancers by over lapping the second balancer over cells balanced by the first balancer, that way the excess can move from one end of the battery to the other. The more cells you over lap between the balancers, the better it works .... 5s To 96s Active Lifepo4 Lithium Lto Battery Cell Balancer With 3a 6a Balancing Current - Buy Lithium Battery Balancer,Lead Acid Battery Balancer,Lifepo4 Cell Balancer Product on Alibaba.com

T1 Terry

 

If the battery consistency is ok, not a bad situation, the balancing work does not need to be done every day, once a month or according to the situation. There are model aircraft chargers on the market, 12s or higher, which are not very expensive. It can set the battery type, battery quantity, cut-off voltage, charging current, and balance current, and it is very powerful. If you build a lithium iron phosphate battery pack for 60s, you can charge it 5 times in a balanced manner (try not to charge several chargers at the same time, because the power supply of the chargers is difficult to isolate), it will not take long. To do this, you need to make 5 battery electrode lead-out row sockets (60s), each row of sockets has 13 electric needles (12s) and do insulation work, and pay attention to the order of the wires. It should not be very complicated and can be done.

 

You got me just reading it ...... Just a quick question, if balancing 12 cells at a time, how does cell group 1-12 balance with any of the other 12 cells groups and likewise, how do any of the other 12 cell groups balance with any other group?
How does cell 70 balance with cell 1 for instance?

T1 Terry

 

Balancing usually is just limiting the voltage per cell. So there's no real difference between having a whole 70 cell ballancer or several smaller ones of 12 cells or even just an individual "balancer" on each cell.

The way active cell balancing works is when a cell reaches a certain voltage the balancer doesn't allow it to reach any higher of a voltages by passing the current through a bleed resistor around the cell down to the next cell. As long as charging continues after the weakest cell hits that voltage the whole battery will continue to increase in voltage so eventually more and more cells will reach their limit and stop increasing in voltage as the others keep increasing. Again, this is regardless of how many balancers are put on the whole pack. If the battery is charged up fully then all the cells will have reached their max voltage and the battery will be balanced.

However, battery protection might be kind of hard to pull off with several BMS's on the whole pack. If one BMS detects a low cell voltage or an overcurrent it could try to disconnect. But since that switch, whether it be a power relay (aka contactor) or power transistor of some sort, is in series with several other BMS's in series it would have to be able to cut the current at the voltage of the entire battery, which it may not be designed to do so would fail.

 

It needs to be fully charged in 60s or 70s. It takes several charging times. Be sure to fully charge the cells before starting the vehicle. Set the charging cut-off voltage. Lithium iron phosphate is about 3.65v, and all charging reaches 3.65v.
[COLOR=rgba(0, 0, 0, 0.87)][/COLOR]

 

Ummm. a rather naive view of how that type of cell balancer works .... but not even close to what happens in real life.
The resistor is placed between the positive and negative of the over voltage cell, because the voltage is higher on the positive terminal than the negative terminal, a resistor does just what a resistor does, it turns electrical energy into heat energy and "burns off" some of that cells capacity. This heat has to go some where and most often it goes into the battery terminal with the heat soak material added ... this heat ends up in the cell via the big block on metal that makes up the terminal. Inside the cell, all the plates that are "positive" are connected to that block and all the plates that are negative are connected to the other terminal block. The electrical conductor plates are very thin, under a mm thick and a small tab designed to carry the current to or from the terminal block, not designed to conduct heat. I'll add a photo later so you can see for yourself what damage that causes inside the cell.
These type of balancers are not active balancers, they are lossie type balancers because they actually loose some of the electrical energy as heat.
Active balancers actually transfer the excess capacity from the high voltage cell to the low voltage cell. The most common methods are inductor coils or capacitors. Each cell charges it's coil or capacitor, then the cell is disconnected and the coils or capacitors are all linked, then the voltage balances out an the coil or capacitor either discharges or recharges from the cell they are connected to .... and the process repeats. Naturally, there is some heat generated, but that is in the actual balancing module, not at the cell.

The very latest active balancers use the hive mind principle and watch the voltage of the cell either side of them, report all three voltages to the central control, then the cell with the higher voltage charges a coil or cap to 3 times the cell voltage, then discharges this across the three cells it sees, one third goes to each cell and the capacity moves up or down the chain are the cell capacity dictates ..... a very fast method of cell balancing .... once all the cells are at the same voltage, the voltage is measured to determine if more charging is required and slowly increase the charge current again until a cell goes high voltage, then the process is repeated. At the end, a fully charged and completely balanced battery is achieved .....but this can only work when mains charging, not regen charging ..... but the balancing part of these new modules still does its thing ..... the flashing lights are great value as well, showing just which is the high cell, which is the low cell and the capacity transfer from cell to cell while it attempts to balance the pack, not that you actually need to know any of that, but it sure looks trick :lol:

T1 Terry

 

So, the actual balance is only a matter of all cells being saturation charged and requires plugging into mains charging regularly ..... not a lot of value for a vehicle with a small capacity battery designed for regen type operation is it?

T1 Terry

 

The active balance circuit is too complicated for individual enthusiasts, and the performance of active balance efficiency, heat and accuracy is not easy to do well. For individuals, it is difficult to complete the diy of the 60s or 70s active balancer. If you want When refitting a lithium battery, I think the low-cost solution is to regularly maintain and balance the battery. If the selected lithium battery has a good enough balance, the maintenance interval can be appropriately extended. According to the situation, the ideal situation does not require balancing, that is, the maintenance interval is unlimited.

 

What?!

So first you say that what I explain is not even close to what happens in real life. Then you go on to just reword what I already said. Yes, that is how a balancer works. Cell reaches threshold voltage. Cell gets connected to resistor that bleeds off current. Cell's voltage is now going down instead of up. Threshold is no longer met so bleed resistor is disconnected.

But yes you are right in that I did not use the term "active balancer" correctly as used today. I was differentiating between an electronically controlled balancer and a more simple method, like taking all the cells out of series and putting them all in parallel so their voltages are forced to equalize.

Um, you do realize that most balancers are not placed right next to the cells, but rather have lead wires that go to the buses between each pair of cells as well as the most positive and most negative terminals. That way the resistors can be placed far away from the battery.

You also realize that the amount of balancing energy that is lost is very small, even in a resitive type balancer. Unless the battery is crazy unbalanced, the amount of heat generated by just charging and discharging is going to be way more than the heat dissipated by the balancer.

That sounds good and all, but last I checked most EV manufacturers were still using resistive based balancing since there is so little benefit to active balancing. Balancing makes up for imperfections in the battery. It doesn't improve performance. The amount of unbalanced energy is very small compared to the rest of the battery. Active balancing causes a very small gain in charging efficiency, but not much more than that.

 

It is very difficult for individuals to make a balancer like the 60s. It requires knowledge of microcontroller programming. Active balancing technology is not recommended. It is necessary to know that the more complex the circuit and the more parts, the probability of failure will increase. Unless the applied technology is very mature and the reliability is high enough. At the same time, it is not recommended to refit high-voltage batteries with lithium batteries. Compared with traditional nickel-metal hydride batteries, lithium batteries have more stringent requirements and are not as resistant to harsh conditions as nickel-hydrogen batteries. Risk Larger. This is also the reason why lithium batteries are generally equipped with protectors to prevent accidents. But there are exceptions, that is, assembling large-capacity lithium battery packs, prius battery ecu will limit the capacity used, so that lithium battery packs work in Within a very small capacity range, it is guaranteed to prevent overcharge, overdischarge, and overcurrent to improve reliability and life. You can configure a real-time balancer if you can, or not, and you can balance it regularly. Active balancing sounds great Advanced, efficiency and balance current have advantages, the circuit is relatively complex, and the reliability is estimated to be worse, I think it will be more applied in pure electric vehicles. I agree that high-voltage battery performance will have an impact on mpg, but if the capacity reaches a certain level , the positive effect will be relatively insignificant as the capacity continues to increase. I think configuring a high-voltage battery larger than 6.6Ah will not have a significant impact on mpg, but it may improve the service life. Unless you can invade the battery ecu and modify its battery capacity data, and engine warm-up strategy that can get close to the EV mileage of the plug-in. That would be a feat

 

I've noticed that with some EV's that the max and min charging is purely voltage based. Now with a Prius this does seem to be different to a point. But the thing is, if I put on a 100Ah HV battery, will the Prius really count only some 3Ah and then cut current? Or will it rely on voltage thresholds and keep charging or discharging until it meets one of those thresholds?

Of course in my case I'd be interested in a bigger battery for mountain driving reasons. Even using the 6 "gears" of B mode instead of regen braking in the Avalon I still reach the bottom of mountain passes with a "fully" charged HV battery.

 

This is the part I refereed to as naive and the sort of talk a lossie cell balancer sales brochure uses. It doesn't bypass the current to the next cell, it just burns off a bit of the capacity.
The catch here is just how much it can burn off, the charging wold need to be less than the resistor can burn off, otherwise the resistor is over powered, burns out and the heat often destroys other components on the balance board.

The balancers that are remote from the cell are the type used for bicycle motor batteries, low voltage and charged from the mains at a trickle rate and the balancing resistor can only handle milli amps, fine for a battery with very little capacity but certainly not suitable for a battery used for regen absorption that sees current in the hundred or more amps.
I have 2 amp burn off cell top balance boards here at our workshop, simply removing the negative terminal connection and running a wire to the negative post creates so much heat in the heat soak section of the balance board it burnt a pattern into my fingers ... that is real heat .....

You do realise the new Hyundai Ioniq 5 is an 800v 50 ah battery that can recharge from 10% SOC to 80% SOC in under 18 mins, do you really think a simple lossie type balancer could shift enough current from one cell to accommodate that sort of recharging?
I am involved with the electric vehicle association here in Australia and I can assure you, the lossie type balance boards are well and truely a thing of the past after the number of cells destroyed by these things .....

T1 Terry

 

Usually balancing happens during charging. In that situation a resistor placed from positive to negative terminal on the cell becomes a parallel circuit. If the circuit is advanced enough to "cut" charge current from entering the cell the charge current now passes through the resistor. If the resistance is low enough or the charge current low enough, then yes, the cell would be discharging at the same time. But charge current is usually limited by the time balancing is needed. It shouldn't be hard to size the resistors so the full cells neither charge nor discharge by simply using Ohm's Law.

Again, ohm's law. If balancing is happening, current is limited to X amps because the cell's voltage will be Y and the resistors are already Z, so E=IR and P=IE.

I know the Nissan Leaf uses resistance balancing and has the resitors in a box separated from the cells with leads going to each cell. I'm sure many more car manufacturers do the same.

Thanks for letting me know. If a Hyndai needs balancing before even reaching 80% SOC then I'd never buy one. That would be a terribly unbalanced battery to say the least.