Dual battery converter / discharger (with energy recovery) and how it works

[SpeGon]

If I'm not completely off the mark, in the circuit diagram of a dual battery converter shown below, two batteries are first equalized in terms of voltage (the battery with the higher voltage potential is brought to the level of the other) and only then discharged in parallel.
I currently use different converters with energy recovery in my e-scooters.
After use, the separate charging process for the batteries of the same size is completed almost simultaneously, which would confirm the above theory.
Who can explain the circuit diagram to me in detail?

 

[RunForTheHills]

I don't see a circuit diagram, but what you described is accurate.

 

[E-HP]

If I'm not completely off the mark, in the circuit diagram of a dual battery converter shown below, two batteries are first equalized in terms of voltage (the battery with the higher voltage potential is brought to the level of the other) and only then discharged in parallel.
I currently use different converters with energy recovery in my e-scooters.
After use, the separate charging process for the batteries of the same size is completed almost simultaneously, which would confirm the above theory.
Who can explain the circuit diagram to me in detail?

I'm trying to imagine the diagram but it's a bit fuzzy. Maybe describe the components some more.

 

[SpeGon]

I don't see a circuit diagram, but what you described is accurate.

... sorry, the first image was not accepted.

 

[SpeGon]

I'm trying to imagine the diagram but it's a bit fuzzy. Maybe describe the components some more.

The converter looks like that and has most likely been mentioned many times before.

 

[E-HP]

The converter looks like that and has most likely been mentioned many times before.

That circuit will never discharge in parallel. It will draw from one pack or the other, since the internal resistance of each pack will differ. You have to actually parallel the two pack in order to obtain the benefits of higher/combined current output.

 

[RunForTheHills]

Honestly, I think it is just Y connectors on the negative and positive terminals. So just the top diagram and not the bottom one in your drawing.

 

[SpeGon]

Okay, there's also a description of the seller...

 

[BatteryMooch]

If I'm not completely off the mark, in the circuit diagram of a dual battery converter shown below, two batteries are first equalized in terms of voltage (the battery with the higher voltage potential is brought to the level of the other) and only then discharged in parallel.
I currently use different converters with energy recovery in my e-scooters.
After use, the separate charging process for the batteries of the same size is completed almost simultaneously, which would confirm the above theory.
Who can explain the circuit diagram to me in detail?

I’m completely confused by your post…
- That image shows two completely different circuits.
- The first circuit will only allow one battery at a time to be used, with either at any voltage.
- The second circuit does not fully parallel the batteries. BTB powers the motor at all times, and voltages, but does it through a Schottky diode which will drop its voltage by about 0.5V-1.0V depending on the diode and current level. BTA can be switched in/out of the circuit at any time but the packs are never truly paralleled due to the diode’s voltage drop. The diode does prevent current from fplowing from BTA into BTB if BTA s at a higher voltage. But that could have easily been handled without the diode since the MCU would be monitoring voltages.
- The second circuit could operate as described in your circuit description post but it’s still not paralleling packs.

Nothing really makes sense. What specifically are you hoping to do…parallel packs when riding but separate them when charging?

 

[SpeGon]

I’m completely confused by your post…
- That image shows two completely different circuits.
- The first circuit will only allow one battery at a time to be used, with either at any voltage.
- The second circuit does not fully parallel the batteries. BTB powers the motor at all times, and voltages, but does it through a Schottky diode which will drop its voltage by about 0.5V-1.0V depending on the diode and current level. BTA can be switched in/out of the circuit at any time but the packs are never truly paralleled due to the diode’s voltage drop. The diode does prevent current from fplowing from BTA into BTB if BTA s at a higher voltage. But that could have easily been handled without the diode since the MCU would be monitoring voltages.
- The second circuit could operate as described in your circuit description post but it’s still not paralleling packs.

Nothing really makes sense. What specifically are you hoping to do…parallel packs when riding but separate them when charging?

Thank you for your detailed reply... as I said, the attachments shown are from my dealer. My e-scooters use the original battery and an additional battery of the same size. To shorten the charging process, both batteries are connected to a separate charger.

 

[RunForTheHills]

The problem with connecting parallel batteries is that there will be an inrush current to the battery with the lower voltage from the one with the higher voltage when they are connected if the voltage doesn't match. This will charge the lower voltage battery if the BMS doesn't shut it down due to the high current. This will happen with the simple Y connectors in the top diagram. I am not sure what that description means by the MCU will send the voltage value by UART (serial communications?). To what? Motor controllers's may monitor input voltage and send that to a display. But that has nothing to do with the "converter".

 

[SpeGon]

The problem with connecting parallel batteries is that there will be an inrush current to the battery with the lower voltage from the one with the higher voltage when they are connected if the voltage doesn't match. This will charge the lower voltage battery if the BMS doesn't shut it down due to the high current. This will happen with the simple Y connectors in the top diagram. I am not sure what that description means by the MCU will send the voltage value by UART (serial communications?). To what? Motor controllers's may monitor input voltage and send that to a display. But that has nothing to do with the "converter".

The converter also has a COM port (probably UART interface), which is not used in my case.

 

[BatteryMooch]

Thank you for your detailed reply... as I said, the attachments shown are from my dealer. My e-scooters use the original battery and an additional battery of the same size. To shorten the charging process, both batteries are connected to a separate charger.

Yes…okay…from your dealer. But their origins don’t really matter.
What is critical is what information or help you would like to get from us…specifically?

Do you want to parallel your batteries when discharging and want to know the specifics for a circuit to do that?

 

[SpeGon]

Yes…okay…from your dealer. But their origins don’t really matter.
What is critical is what information or help you would like to get from us…specifically?

Do you want to parallel your batteries when discharging and want to know the specifics for a circuit to do that?

My question was and still is whether these converters allow parallel connection (aliexpress sells these in bulk), thereby increasing the service life of the batteries (unfortunately an interior view is only available in a destructive form).

 

[BatteryMooch]

My question was and still is whether these converters allow parallel connection (aliexpress sells these in bulk), thereby increasing the service life of the batteries (unfortunately an interior view is only available in a destructive form).

But you never showed us the schematic for the converters (not available it seems) so we can’t possibly know what they really allow or don’t. All we can do is try to interpret the same text you did and it seems pretty straightforward. It say it allows parallel operation

But only you can decide what to do with that. Do you trust what they say? If yes then I recommend buying it and carefully testing.

 

[SpeGon]

But you never showed us the schematic for the converters (not available it seems) so we can’t possibly know what they really allow or don’t. All we can do is try to interpret the same text you did and it seems pretty straightforward. It say it allows parallel operation

But only you can decide what to do with that. Do you trust what they say? If yes then I recommend buying it and carefully testing.

As already mentioned in post #1, I have been using various converters of this design in different e-scooters with electric brake for quite some time.
Summarized from practical experience:
1. Two battery packs with the same total voltage (e.g., 36V in the same cell arrangement 10s2p and capacity) but different states of charge can be connected to this converter without any compensation flow issue.
2. No significant heating of the ribbed aluminum housing is noticeable under continuous load of the battery packs or during recuperation and prolonged electric braking maneuvers (energy-saving operation?).
3. The current consumption appears to be uniform with the converter, as the subsequent separate charging of the battery packs ends at approximately the same time.
To put it simply, I don't have the equipment to gain further insights. Even if the sketches provided by the seller are incorrect, can't we deduce something from these facts (according to a YouTube video, the housing can only be opened destructively)?
If the converter only has a high-frequency switching function, for example, I wouldn't understand the purpose of it.

 

[BatteryMooch]

can't we deduce something from these facts

No.
There are a large variety of circuits than can be used and your experiences with “various converters of this design” won’t help us because we don’t know what the design is, just its broad product category. Every “converter” (they’re not a converter though) you used could have been a very different circuit. A lot more testing is needed to figure out what it’s actually doing and not doing.

You keep responding to my questions by repeating what you said earlier, and saying you said it earlier, but nothing you said earlier answers my questions so that’s why I keep asking. I’m not trying to be difficult, I’d love to give you a one sentence answer but it can’t be done with the extremely limited information you have.

If the units say they allow parallel operation then that’s what they do. We can’t know all of the conditions they can handle (or not handle) though, how well they do their job, etc., because we don’t have the specific circuit (and maybe the firmware too).

If I’m not understanding what you’re looking for you can check the Texas Instruments web site for application notes and introductions to their eFuse, hot-swap controllers, ideal-diode controllers, and OR’ing controllers: Power protection switches & controllers | TI.com.

You can then compare their features and specs to try to determine if the units you are interested in are doing the job you want or not. You can also contact the manufacturer with your questions but I recommend using very simple questions, each requiring only a yes/no answer or number. That way the questions will translate well if they need to do that in order to understand them.

 

[E-HP]

No.
There are a large variety of circuits than can be used and your experiences with “various converters of this design” won’t help us because we don’t know what the design is, just its broad product category. Every “converter” (they’re not a converter though) you used could have been a very different circuit. A lot more testing is needed to figure out what it’s actually doing and not doing.

You keep responding to my questions by repeating what you said earlier, and saying you said it earlier, but nothing you said earlier answers my questions so that’s why I keep asking. I’m not trying to be difficult, I’d love to give you a one sentence answer but it can’t be done with the extremely limited information you have.

If the units say they allow parallel operation then that’s what they do. We can’t know all of the conditions they can handle (or not handle) though, how well they do their job, etc., because we don’t have the specific circuit (and maybe the firmware too).

If I’m not answering understanding what you’re looking for you can check the Texas Instruments web site for application notes and introductions to their eFuse, hot-swap controllers, ideal-diode controllers, and OR’ing controllers: Power protection switches & controllers | TI.com.

You can then compare their features and specs to try to determine if the units you are interested in are doing the job you want or not. You can also contact the manufacturer with your questions but I recommend using very simple questions, each requiring only a yes/no answer or number. That way the questions will translate well if they need to do that in order to understand them.

The same site include two type of battery combiners. One is like the description provided, which allows batteries at different voltage levels to be attached, and the unit only provides power from the higher voltage pack. This description is consistent with using either Schottky diodes, or a mosfet based ideal diode circuit. On the same site, they sell what appears to be a straight paralleling combiner, with no electronics, similar to your first circuit, but hard wired without the switches. In that description they emphasize that both batteries need to be charged to the same voltage before connecting, and highlight the text in yellow as a warning.
"7--Both Batteries Capacity can be different, But Both Batteries Voltage must need same."

For you, out of the two types, the first would be best. The latter is meant for more advanced users that know of the risks and take appropriate measure to mitigate them. The upside is that the are able to receive all of the performance related benefits, not just range, of paralleling the packs.

 

[BatteryMooch]

For you, out of the two types, the first would be best. The latter is meant for more advanced users that know of the risks and take appropriate measure to mitigate them. The upside is that the are able to receive all of the performance related benefits, not just range, of paralleling the packs.

@SpeGon, I think the above reply was for you.

 

[SpeGon]

Yes, I would also say that a converter (with energy recovery function) is preferable to direct Y-wiring of the battery packs for safety reasons. Accidental connection of unequally charged batteries could, in the worst case, result in an unquenchable fire. The slight voltage drop with corresponding converter diodes should be acceptable, as the use of an additional battery can now be done spontaneously.

 

[E-HP]

Yes, I would also say that a converter (with energy recovery function) is preferable to direct Y-wiring of the battery packs for safety reasons. Accidental connection of unequally charged batteries could, in the worst case, result in an unquenchable fire. The slight voltage drop with corresponding converter diodes should be acceptable, as the use of an additional battery can now be done spontaneously.

Yup, best for your case. Most folks that parallel their batteries never disconnect them, so it's a one time deal. Your concerns a valid, especially if your packs and cells aren't fully matched.

 

[SpeGon]

You're right, as long as weight isn't an issue. However, if we take our bike or scooter on public transport or simply need to go to a higher floor in a building without an elevator, a certain amount of flexibility always pays off.

 

[average joe]

Yes, I would also say that a converter (with energy recovery function) is preferable to direct Y-wiring of the battery packs for safety reasons. Accidental connection of unequally charged batteries could, in the worst case, result in an unquenchable fire. The slight voltage drop with corresponding converter diodes should be acceptable, as the use of an additional battery can now be done spontaneously.

Have you found any "converter with energy recovery function" which are commercially availability?

 

[lnanek]

The amount of energy recovered from regenerative braking is practically nothing anyway. Like 10%? If your controller needs somewhere to dump voltage spikes to avoid faults like my Grin Baserunner controller does, and you want to use it with a diode/ideal diode based battery combiner, I'd just slap a resistor module in there like:

ODrive Regen Clamp

The ODrive Regen Clamp provides a high-performance braking energy management solution for ODrives without an external brake resistor driver. It automatically detects power regeneration from downstream motor drives, and diverts excess energy to an external brake resistor. Compatible and shown...

shop.odriverobotics.com

Then you can still use motor braking if desired, it will just feed back into a resistor, not the batteries.

 

[SpeGon]

Have you found any "converter with energy recovery function" which are commercially availability?

You can find this device on AliExpress by searching for: Dual battery converter with energy recovery.