DYI Battery Extender

[AntonioAlfaro]

Battery Extender
Continuing with the experiences and learning of the Orbea Gain D50, I have come to the conclusion that it will not be bad to have a battery extension system. We have optimized the administration of the energy available in the main battery to the maximum, we have gotten physically fit, we have reduced our mass and that of the ebike as much as possible, but now we want to make long-lasting and more demanding routes, and always count on our support levels.
It is in these cases where we need an additional battery.
Mahle/Orbea has developed its own battery extender, and I'll start by summarizing its features:
Total capacity: 208.8W/h (5.8A)
Voltage: 36 V
Cells: Panasonic
Charging time: 3 hours
Maximum discharge ratio: 1.9 A
Water resistance: IP57
Color: Anodized black
Charging and ignition display: Iwoc One button Charging port protected by a rubber cover.
Dual charging: The Range Extender and main battery can be charged at the same time by connecting the Range Extender to the main battery and the X35 charger to the Range Extender.
Certifications: EN 15194.2017 Bicycle mounting: Specific X35 bottle holder with Quick Lock rubber band. Exclusive mounting on the seat tube *(diagonal tube on the Optima).
Weight: 1645 g with bottle holde

The Mahle Range Extender works like a portable internal battery charger that charges the main battery while it is turned on. It operates differently from other systems in that on the Ebikemotion X35, only the main battery provides power to the motor, while the Range Extender charges the main battery, regardless of whether the motor demands current from the main battery or not (such as at speeds greater than 25 km/h, when there is no pedaling or the bicycle is not moving).
The Range Extender provides charge to the main battery at a discharge ratio of 2A, while the motor can demand current of up to 9A. Therefore, the Range Extender is not capable of supplying enough current to the motor by itself, and all this current comes from the main battery.

So far so good and very nice, but 1) the price of this battery extender is extremely high 2) they are not available on the market today.
This has motivated many desperate enthusiasts like me to look for a DIY solution.
Of all that I have read and seen on the web, Yako's experiments (see attached YouTube link) are the ones that have shown a functional and tested DIY system.

Allow me to make an explanatory summary about the Mahle extender system and the options we have when building a DIY extender. These conclusions that I will summarize are the result of my careful analysis of the Mahle and Orbea specifications on their battery extender. As a professional I start from the premise that a serious manufacturer does not lie in its specifications.
The Mahle extender is designed to behave like a main battery charger, supplying only 2 Amps of charging current and a voltage that will depend on the level of charge remaining in the extender. It means that in its electronics, the extender includes a current limiter at 2amps max. and also a reverse current block device to prevent the main battery charging the extender. In other words, it is a system equivalent to the 110/220 VAC ---> 42VDC 2Amp charger that we use to charge the main battery at home.
The question that arises at this point is why only 2 amps does the Mahle extender deliver? What's wrong with that? I'd say there's a lot of good in it. I explain.
A battery bank in a 10S2P arrangement, as is the case, requires 2Amp max as recommended for charging. So far the Mahle system is doing well, because the extender system marketed by a manufacturer must be safe and easy to use by any user and in any condition (this will be better understood when I explain the operation of a DIY extender).
Let's remember a basic principle of the theory of movement of charges: for there to be an electric current (movement of electric charges) from point A to point B, point A must be at a higher potential (voltage) than point B. Keeping this in mind, let's assume that the Mahle extender is point A and the internal battery is point B, and that they are fully charged (same voltage, so no current from the extender to the main battery).
The trip begins and we begin to demand assistance from the Ebike, the motor begins to consume energy. From where? From the main battery and the battery extender. But with one big limitation: the extender will never deliver more than 2 amps. Suppose the assistance level demands 4 amps (which is a lot: 4x36=144 W), 2 amps will come from the main battery and 2 from the extender, and both systems are discharged equally at the same voltage. We stop pedaling: nothing happens since there is no difference in potential between both systems, both are at the same level of charge, there are no currents.
Now, what happens if at that moment (both batteries are equalized in voltage) the level of assistance required is so great that it demands 200W ( 200/36=5.6 Amps). For this demand, 3.6 Amps will come from the main battery and only 2 Amps from the extender. The main battery begins to discharge faster than the extender and at the end of that demand we stop pedaling, we will have the main battery more discharged than the extender, that is, there is a difference in potential and the extender begins to charge the main battery at a rate of 2 amps max. only. It may happen that it fully charge it, or that it charges it just a little, because another request for assistance may occur and the differences in potential will never be the same.
As I've mentioned, and this is a very personal conclusion I've come to, the Mahle Battery Extender was designed to function similar to a battery charger with current limiting at 2 amps. Why so? Because it is the safest and easiest way to use by anyone, at any time and without having to take any precautions (plug and play). As the main battery is the one that provides the greatest load demand to the engine, the extender will always go behind the main battery trying to charge it (at times when there is no load demand from the main battery.)
Do they work in parallel? Yes, at times when the motor demands current.

Now let's see what a DIY extender could look like:

1) Like the Mahle, with the main battery charger concept and current limitation always at 2amps.

2) As an additional battery in parallel and with the same current contribution to the load as the main battery. No charger approach.

Why approach 2 is not commonly used? Because it's complicated, risky, and somewhat impractical to use commercially. Not all users would be willing to learn how to use it and it could lead to lawsuits against the manufacturers that market it.

The operating principle of approach 2 is based on the use of 2 battery banks as equal as possible. That is, equal current capacity, equal voltage, equal cell technology. In our case they will be 250Wh 10S2P battery banks. Built from basic Panasonic 18650 cells. One of these banks is just the main battery, the other the extender.
If both batteries are charged to 100% and separately, in theory they will each have the same open circuit voltage. If under these conditions we connect them in parallel, the resulting voltage will be the same and since there is no potential difference between them, there will be no transient current from one battery to the other. The parallel bank will maintain the same voltage while there is no load.
When the motor demands current, that current will be supplied in equal parts by the main and the extender (either high current or low). What happens to the parallel voltage of the bank? Well, go down as current is demanded. One battery charges the other? No. Both batteries are discharged equally until reaching the protection cutoff limit of each of them.
What happens if this procedure is not strictly followed?

 

[AntonioAlfaro]

Allow me to make an explanatory summary about the Mahle extender system and the options we have when building a DIY extender. These conclusions that I will summarize are the result of my careful analysis of the Mahle and Orbea specifications on their battery extender. As a professional I start from the premise that a serious manufacturer does not lie in its specifications.
The Mahle extender is designed to behave like a main battery charger, supplying only 2 Amps of charging current and a voltage that will depend on the level of charge remaining in the extender. It means that in its electronics, the extender includes a current limiter at 2amps max. and also a reverse current block device to prevent the main battery charging the extender. In other words, it is a system equivalent to the 110/220 VAC ---> 42VDC 2Amp charger that we use to charge the main battery at home.
The question that arises at this point is why only 2 amps does the Mahle extender deliver? What's wrong with that? I'd say there's a lot of good in it. I explain.
A battery bank in a 10S2P arrangement, as is the case, requires 2Amp max as recommended for charging. So far the Mahle system is doing well, because the extender system marketed by a manufacturer must be safe and easy to use by any user and in any condition (this will be better understood when I explain the operation of a DIY extender).
Let's remember a basic principle of the theory of movement of charges: for there to be an electric current (movement of electric charges) from point A to point B, point A must be at a higher potential (voltage) than point B. Keeping this in mind, let's assume that the Mahle extender is point A and the internal battery is point B, and that they are fully charged (same voltage, so no current from the extender to the main battery).
The trip begins and we begin to demand assistance from the Ebike, the motor begins to consume energy. From where? From the main battery and the battery extender. But with one big limitation: the extender will never deliver more than 2 amps. Suppose the assistance level demands 4 amps (which is a lot: 4x36=144 W), 2 amps will come from the main battery and 2 from the extender, and both systems are discharged equally at the same voltage. We stop pedaling: nothing happens since there is no difference in potential between both systems, both are at the same level of charge, there are no currents.
Now, what happens if at that moment (both batteries are equalized in voltage) the level of assistance required is so great that it demands 200W ( 200/36=5.6 Amps). For this demand, 3.6 Amps will come from the main battery and only 2 Amps from the extender. The main battery begins to discharge faster than the extender and at the end of that demand we stop pedaling, we will have the main battery more discharged than the extender, that is, there is a difference in potential and the extender begins to charge the main battery at a rate of 2 amps max. only. It may happen that it fully charge it, or that it charges it just a little, because another request for assistance may occur and the differences in potential will never be the same.

 

[AntonioAlfaro]

As I've mentioned, and this is a very personal conclusion I've come to, the Mahle Battery Extender was designed to function similar to a battery charger with current limiting at 2 amps. Why so? Because it is the safest and easiest way to use by anyone, at any time and without having to take any precautions (plug and play). As the main battery is the one that provides the greatest load demand to the engine, the extender will always go behind the main battery trying to charge it (at times when there is no load demand from the main battery.)
Do they work in parallel? Yes, at times when the motor demands current.

Now let's see what a DIY extender could look like:

1) Like the Mahle, with the main battery charger concept and current limitation always at 2amps.

2) As an additional battery in parallel and with the same current contribution to the load as the main battery. No charger approach.

Why approach 2 is not commonly used? Because it's complicated, risky, and somewhat impractical to use commercially. Not all users would be willing to learn how to use it and it could lead to lawsuits against the manufacturers that market it.

The operating principle of approach 2 is based on the use of 2 battery banks as equal as possible. That is, equal current capacity, equal voltage, equal cell technology. In our case they will be 250Wh 10S2P battery banks. Built from basic Panasonic 18650 cells. One of these banks is just the main battery, the other the extender.
If both batteries are charged to 100% and separately, in theory they will each have the same open circuit voltage. If under these conditions we connect them in parallel, the resulting voltage will be the same and since there is no potential difference between them, there will be no transient current from one battery to the other. The parallel bank will maintain the same voltage while there is no load.
When the motor demands current, that current will be supplied in equal parts by the main and the extender (either high current or low). What happens to the parallel voltage of the bank? Well, go down as current is demanded. One battery charges the other? No. Both batteries are discharged equally until reaching the protection cutoff limit of each of them.
What happens if this procedure is not strictly followed?

 

[AntonioAlfaro]

Here are some illustrations of a laboratory scale test. I have used 2 banks 1S 2P of 2550 Ah.
They were separately charged to a certain level and the individual voltages were Bank A = 8.14v, Bank B = 8.13v
connecting both banks in parallel produced a current from A to B of 1.39 mA. Just as expected.
Since there is no load connected to the parallel of batteries, that current is from A charging to B, but as you can see, a load of 1.39 mA to a bank of 2550 mA means that it is charging at a rate of 62x10-3 C. One day it will charged at the same voltage!

 

[AntonioAlfaro]

Let's go one step further in our model of DIY extender.
We have already seen that we can connect two "same" battery banks in parallel as long as both banks have the same charge. How charge and voltage are related according to the cell manufacturer's curves. So we can say "equal volages = equal charges".
Now, if bank A has a higher charge than bank B, when they are connected in parallel, charges from A will pass to B through an electric current limited only by the internal resistance of the battery banks. these internal resistances are of the order of milliohms and that is why large currents would be caused depending on the level of charge imbalance of bank A and B. Destruction could occur. For this reason, battery chargers limit the maximum current delivered to the load.
Here comes the first alert with the DIY extender.
In our lab-scale model, we connected two banks with different charge levels in parallel and measured the current that was produced. See attached figures.

Bank A = 83% charge volt=8.10 v
Bank B = 72% charge volt=7.94 v
Charge imbalance = 15%
At paralleling , I = 44.4 mA from A to B charging rate 0.02C
After some minuts , I = 30.7 mA from A to B charging rate 0.01C
If we let the banks be connect , they will equalize their charges.

One thing you should pay attention to is that the basic cell's voltage curve is almost flat before reaching the point of discharge ( from 4.2v to 3.0v). In the DIY extender and main batt ( from 42v to 30 v).
So small voltage differences between bank A and B can mean large charge differences. Don't forget this point.

 

[AntonioAlfaro]

Support information on internal resitance.
Test of Sanyo NCR18650GA 3500mAh (Red)


Attachments

• 
  
  
  2022-03-25 16_44_18-Panasonic-NCR18650.

 

[AntonioAlfaro]

Next I will show a series of images about the construction process of the DIY extender. A series of manual modification work was necessary but nothing that cannot be achieved with patience and care.

 

[AntonioAlfaro]

The following image shows a cheap and useful instrument to which I have put a connector compatible with the ones we will use in the DIY extender. We can measure voltage and current simultaneously.

 

[AntonioAlfaro]

Here we can see the adaptations and connectorization for the DIY extender.
M2 is an adapter to charge the DIY extender batt with the same Mahle charger that we use for the main batt. This is optional.

 

[AntonioAlfaro]

The first basic measurement we will make in the actual DIY extender and main batt bank will be to charge
separately up to 100% (when the charging current is < 20 mA the ammeter used will mark o mA) both batteries.
After completing these charges up to 100% on both batteries we will take note of the OCV open circuit output voltages of both battery banks.
This record is extremely important.
Main OCV = 41.9 v
DIY extender OCV = 41.4 v
OCV difference = 0.5 v
It is important to keep in mind that we will never find the same OCV. But more important is to always know the voltage difference for our battery banks because they will change as the charge cycles increase.

Knowing the OCV differential we can begin to draw basic conclusions.
I will continue..

 

[AntonioAlfaro]

DIY Extender already finished and installed.
After 44 Km on road test, every thing worked as expected. Very saticfatory results, so Proyect is over. If someone need help please send me PM.

 

[AntonioAlfaro]

Hello,
I am attaching a draft of the test report that I carried out on my the DIY Extender.

 

[AntonioAlfaro]

Hello,
I am attaching a STL file if you want to print in 3D a lid (mimics a bottle) for the DIY extender.
This is a cosmetic upgrade but it looks good.
PD: Pedelecs does not allow me to attach STL files, contact me and send me your email address if you want to receive that file.

 

[AntonioAlfaro]

Hello,
I am attaching a draft of the test 3 that I carried out on my the DIY Extender.

 

[AntonioAlfaro]

Hello,
I have observed that the % of remaining charge recorded during the trip does not correspond to the half of main battery as if the extender did not exist. (But actually the main battery and the extender are both contributing half). This causes the system to disconnect due to a low level of charge when in reality it has only used half the charge.
Have someone seen something like this on your extender? I will greatly appreciate your comments.
Orbea Gain D50 year 2021 is the test environment.

 

[theshade]

Dear Antonio,

Thank you for all the thread and discussion and the testing reports in the pdf. But I was curious that an ideal diode does not limit current of discharge fro the extender to the main battery. So I was a bit worried that the current might be too large >2A if the main battery is lower charged than the extender when you connect the two together... I think it would be wise to prevent current from exceeding the typical charging current from the powersupply ...
So I was looking for current limiting circuits but I don't know if this can be done with minimal power losses or without resulting to complicated circuitry... I found this current detection circuit:

Capteur de détection de courant WCS2702, module de protection contre les courts-circuits et les surintensités de pipeline réglables - AliExpress 502

Smarter Shopping, Better Living! Aliexpress.com

fr.aliexpress.com

which would measure the current but I still need to "limit" the current accordingly.

 

[AntonioAlfaro]

Dear Antonio,

Thank you for all the thread and discussion and the testing reports in the pdf. But I was curious that an ideal diode does not limit current of discharge fro the extender to the main battery. So I was a bit worried that the current might be too large >2A if the main battery is lower charged than the extender when you connect the two together... I think it would be wise to prevent current from exceeding the typical charging current from the powersupply ...
So I was looking for current limiting circuits but I don't know if this can be done with minimal power losses or without resulting to complicated circuitry... I found this current detection circuit:

Capteur de détection de courant WCS2702, module de protection contre les courts-circuits et les surintensités de pipeline réglables - AliExpress 502

Smarter Shopping, Better Living! Aliexpress.com

fr.aliexpress.com

which would measure the current but I still need to "limit" the current accordingly.

Hello theshade,
You are correct, the diode only serves to block reverse current, but in no way limits the current delivered by the extender battery to the main battery. Remember that this extender approach is in parallel with the main battery, and therefore some very strict conditions of use must be followed to avoid over currents and burning out the main system. I must tell you that I have discarded this extend approach and developed one based on the charge concept. If you are interested, you can send me your email and I will gladly send you a descriptive document.
Greetings Antonio

 

[Petemac]

Hello theshade,
You are correct, the diode only serves to block reverse current, but in no way limits the current delivered by the extender battery to the main battery. Remember that this extender approach is in parallel with the main battery, and therefore some very strict conditions of use must be followed to avoid over currents and burning out the main system. I must tell you that I have discarded this extend approach and developed one based on the charge concept. If you are interested, you can send me your email and I will gladly send you a descriptive document.
Greetings Antonio

Hello Antonio, Thanks for your informative posts regarding the range extender. I am very interested in your new charger approach.
Could you please send me the descriptive document to. cametep@gmail.com