Stupidist Plan yet to save gas -- muzzling the alternator

Induction refers to a wire coil that is charged up with what ever the cell voltage is and holds what ever cell capacity was required to fully charge the wire coil ..... this may be only milli amp hrs, but the rapid switch combined with the voltage differential, it could be anywhere up to 5 amps of current moving in and out through any single induction coil, but on average, it's generally 1 amp or less ....., switching at a high hertz rate, it can move a fare amount of capacity from one cell or a multiple of cells, to the lowest voltage cell, rapidly bring all the cell voltages to within 15 millivolts, then it shuts down and turns on again at approx. 150millivolts ..... but you have to be either logging the cell voltages or be "Jonny on the spot" to see the switch on point, the high cell voltage drops rapidly from the 150millivolts higher than the other cells ..... 3 cells at 3.5v would see the high cell reach 3.65v before the cell equaliser turned on again .....

T1 Terry

 

Is this related to switch mode power supplies?

 

In ECOmodder forum, there were proposals to eliminate 12 V charging load to improve MPG. If the 12 V battery is replaced with a modern battery and solar panels, this could work. Still carry the alternator for backup but run the low voltage system from a modern battery and stored solar energy.

I would implement it with a solenoid belt tensioner to minimize mechanical drag and the problem is solved. Normal practice is to use solar-battery around town and only when driving longer distances, backup with the belt tensioned, alternator.

Sad to say, I don't have an engine driven alternator. My BMW i3-REx has a two-cylinder engine driven generator used only when the battery charge is too low or I'm doing a long cross country. I prefer to use my battery is backup for the 2.3 gal gas tank.

Bob Wilson

 

A simpler mod was to replace the starter 12V with a deep cycle, take the alternator out of the belt loop, and just charge up at home. Some EV conversions did similar, as the deep cycle 12V was cheaper than a DC-DC converter with controls.

 

So essentially a switch-mode DC/DC converter to boost the voltage to a low cell and move charge into it faster.

 

No, not a converter or a booster, just a basically simple method of moving capacity from a high voltage cell to a lower voltage cell. Similar to using capacitors, but a lot more capacity, negates the risk of a capacity exploding due to surge current and doesn't suffer with the storage capacity loss the capacitors suffer over time and heat degradation.

The inductor coil charges to the cell voltage, disconnects and all the coils link together so the voltage equalises across all the coils, then reconnects to the cell, either discharging current till the coil voltage and cell voltage are the same, or receiving current, charging the coil till it is the same voltage as the cell if that is a high voltage cell, then the process repeats

T1 Terry

 

Not really, more like a better choice than capacitor active balancing ..... the still make an audible squeal that some people can hear when they are working hard, but I have zero upper level hearing now, so I can't hear it

T1 Terry

 

It's a little sketchy to talk about an inductor charging to a voltage. A capacitor charges to a voltage. The work you did raising its voltage to that level is stored in it as electric charge. You can get that work back out by letting it discharge.

An inductor 'charges' to a current. The work you did raising its current to that level is stored around it as a magnetic field. You get that work back (whether you want it or not) if you try to interrupt the current. The inductor's voltage then becomes whatever it takes to give you back the work that you put in. (That's why transistor switches used to switch inductive things like relay coils generally have a diode or the like protecting them from the voltage spike they would otherwise suffer upon trying to turn it off.)

That exact property, exploited by high-frequency switching of the inductor—as you mentioned in post #41—is the basic principle of a DC/DC converter right there. I'm not sure how important it is to try to say this application isn't one.

 

The first post in this link, from a solar power forum (the first to pop up in my search) shows two topology choices in the base post of this thread. People familiar with DC/DC converters and switch-mode power supplies should be able to identify with these very quickly:

https://diysolarforum.com/threads/what-bms-uses-inductive-balancing.39149

 

Rather than trying to explain it, tripping over my tongue and getting another put down, hopefully this will explain it Why does an inductor behave as a capacitor at high frequencies? - Electrical Engineering Stack Exchange

T1 Terry

 

Parasitics inherent to non-ideal real-world devices.

 

Ok, but is the idea of inductive balancing somehow based on exploiting the parasitic capacitance of non-ideal inductors, or just using their inductance in the usual way?

 

Using it as a capacitor really, it can just be charged and discharged with a higher volume faster than the capacitor method can handle, simply because of the size of the capacitor required, yet not lose capacity over time or risk explosion for a high inrush current where a precharge circuit is often required .... that would negate the value of rapid switching .....

I have tried the multiple small capacitor types, but I've been very underwhelmed on their performance ..... the inductive units do fail if used to try and correct and carry an internally shorted cell, the combined shared current capacity between 3 good cells and a very low cell, pushes the current flow above what the units can handle and the inductor linked to the bad cell fails, so a cell voltage monitor and alarm is still a good back up investment ...... but where do you stop when it comes to back up systems checking system functions?

T1 Terry

 

I don't think so, based on these items that I haven't come close to fully wading through yet. They are using inductors in their intended range as inductors:

MIT: Inductive Cell Voltage Balancer and Model of Battery Cells and Cell Balancers

Monolithic Power Systems: Battery Balancing Techniques

DIY Solar Power Forum: What BMS uses inductive balancing? | DIY Solar Power Forum

 

Did you read page 67, 68 of the 2022 MIT thesis?

T1 Terry

 

Provided the "2022 MIT thesis" you mean is the first of the links fuzzy1 provided:

then yes, I have read it just now; that's the "Conclusions and future work" section, and it didn't say anything that surprised my understanding of how inductors are used, and in particular nothing in it suggested they were being selected or used based on properties other than their inductance (and basic criteria like their safe voltage and current limits).

 

On those pages he says that the capacitive balancer doesn't need a control loop, but the inductive balancer does need one. But once that is implemented, it opens up some additional capabilities. I used to do some of those sorts of control loops, but back in the older, simpler, less-capable days before things like power factor controllers were added to switch-mode power supplies.

I don't see anything about this inductive version "Using it as a capacitor really ...". It has been a long time since I used LTSPICE, even longer since PSPICE. His model's net list shows the inductor having a series resistance, but I'm not seeing a parasitic capacitance on it.

 

I'll leave you two to battle out the theoretical V real world operation, all I know for sure is, they have worked well for me over the last 15 yrs in over 200 off grid battery installations from 12v to 48v systems, enough real world evidence to sell me on the merits of them ...... I've seen zero merits from capacitor based and resistor based cell balancing ..... but that might just be me with my lithium battery hands on experience since 2011 .....

T1 Terry

 

There hasn't been any question about "theoretical V real world operation" or about any of the results or merits of inductive balancing circuits.

It simply seems that "they use the inductors as capacitors" isn't a great way of explaining how they work. They use the inductors as inductors, which shouldn't be very surprising or controversial.

 

No one was questioning that they work, only how they work. Never having heard of these before, I was having difficulty with your description, which seemed like a confused word salad.

We asked if these were related to switch-mode power supplies (SMPS) or DC/DC converters. You said no. But then the items I linked did reveal that these devices are indeed closely related to the SMPSs I was designing and building for a major test and measurement equipment maker forty years ago. These schematic images, from my first link above, better explained to me how these things work:





Another item I linked above described them this way:

Implementations

Inductive Balancing: Through a common inductor, the energy from a higher charged cell is transmitted to a lower charged cell in inductive balancing. The energy flow between the cells is handled by controlled switches, and therefore, efficiently balance the charge.

Capacitive Balancing: In capacitive balancing, capacitors are used to store the energy for some time from a higher charged cell and transmitting it back to a lower charged cell. This technique might be more challenging but allows precision control and fast balancing.

DC/DC Conversion: Specialized converters are utilized to do energy transmission between cells in this method of DC/DC conversion. This technique is hugely adaptable and provides the benefit of controlled and isolated energy transmission.