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?

I will continue...

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!

I will continue..

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?

I will continue...

 

Do they work in parallel? Yes, at times when the motor demands current.

 

The Orbea manual says it only ever gets used as a charger (and is therefore never parallel), but the MAHLE system pdf (for the same device) may suggest something else; in one example up to 2amps are supplied from the range extender to motor, and it charges the bike battery with the remainder (if there is any). In another example, it says 2amps can be supplied to the motor, with the rest coming from the bike battery. Could these be via a parallel connection that is no longer utilised by official kit?

 

The first example could also explain the existence of two sets of wires, used to power the charging circuit at the same time as supplying current to the motor.

 

But why the discrepancy between Orbea and MAHLE docs for the same device?

 

Perhaps they had issues after writing the PDF and the eventual production MAHLE range extender specification changed by the time Orbea became a reseller, and it now uses canbus to keep the system in charging only mode. I agree this sounds like the safest way, if you are not going to do something like the alternating Bosch system for whatever reason.

 

Devices without canbus then potentially are able to connect to the battery system in parallel and supply more than 2 amps, (in this untested theory, based on a poorly translated PDF which contradicts the mass-produced Orbea manual). Surely they were not considering using an actual electrically parallel battery system? No other manufacturer does that, for good reason!

 

Or is something else going on.

 

I'd be interested to know if there's been a reliable demonstration of more than 2amps being supplied to the system through the charging port.

I'd be interested to know if there's been a reliable demonstration of more than 2amps being supplied to the system through the charging port.

 

A direct current measurement is a bit tricky to do, but using voltage measurements you can come to same conclusions. It is for this reason that Yako's experiment and the voltage measurements that Yako has made, lead to the conclusion that there is consumption of more than 2amps from the DIY extender.

My purpose is to make current measurements directly from the DIY extender through a lab setup and the use of a smart trainer.

But my engineering background makes me go step by step and checking carefully.

I'd be interested to know if there's been a reliable demonstration of more than 2amps being supplied to the system through the charging port.

 

A direct current measurement is a bit tricky to do, but using voltage measurements you can come to same conclusions. It is for this reason that Yako's experiment and the voltage measurements that Yako has made, lead to the conclusion that there is consumption of more than 2amps from the DIY extender.

My purpose is to make current measurements directly from the DIY extender through a lab setup and the use of a smart trainer.

But my engineering background makes me go step by step and checking carefully.

Measuring what the extender is doing is relatively straightforward because you have access to the cable. Either one of those cheap wattmeter things wired in, or for isolated measurement, a LEM LTC6 sensor with an arduino or even just a multimeter showing its output.

Measuring what the extender is doing is relatively straightforward because you have access to the cable. Either one of those cheap wattmeter things wired in, or for isolated measurement, a LEM LTC6 sensor with an arduino or even just a multimeter showing its output.

Great! Just let us know your measurement results. It will be very valuable for this forum.

Great! Just let us know your measurement results. It will be very valuable for this forum.

Sorry, I may have not been clear: I measure on my own bikes, and I am operating parallel batteries, and about to add solar charging, but I do not have an Orbea Gain. Just a strong interest in the work being done in this thread.

Sorry, I may have not been clear: I measure on my own bikes, and I am operating parallel batteries, and about to add solar charging, but I do not have an Orbea Gain. Just a strong interest in the work being done in this thread.

Even if you have measured on other bikes, we can learn the way you did.

Even if you have measured on other bikes, we can learn the way you did.

If you search for solar trailer you will find my project, and my data will go up there as I collect it.

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.

I will continue...

Support information on internal resitance.

https://lygte-info.dk/review/batteries2012/Sanyo%20NCR18650GA%203500mAh%20%28Red%29%20UK.html

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.

I will continue...

The internal resistance seems very high: voltage difference divided by current is resistance round the circuit I think, and unless there is something else in it, will be almost entirely the internal resistance of the two batteries.

 

(8.11 - 7.91) / 0.0444 = 4.73 ohms, or 1.18 ohms per cell. The data sheet indicates 0.1 ohms per cell, so is there a factor of 10 error creeping in somewhere?

 

Something doesn't look right here.

Panny's/sanyo tend to have a higher initial IR.

The internal resistance seems very high: voltage difference divided by current is resistance round the circuit I think, and unless there is something else in it, will be almost entirely the internal resistance of the two batteries.

 

(8.11 - 7.91) / 0.0444 = 4.73 ohms, or 1.18 ohms per cell. The data sheet indicates 0.1 ohms per cell, so is there a factor of 10 error creeping in somewhere?

 

Something doesn't look right here.

What you write down is correct. I would say that it is not the expected result. But it is real for that test fix. The only explanation I have is that these banks are not new and have too many charge and discharge cycles.

We will leave this test phase until there and we will go on to tests with the real benches that we will use in the DIY extender.

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.

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.

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.

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..

DIY Extender already finished and installed.

After 44 Km on road test,

The behavior of the currents and voltages of the Extender and Main Batt, were equal to the measurements in the static test with route simulation in Rouvy and using the Wahoo smart trainer, therefore the project is finished.

For additionalinformation please send me PM.

 

The behavior of the currents and voltages of the Extender and Main Batt, were equal to the measurements in the static test with route simulation in Rouvy and using the Wahoo smart trainer, therefore the project is finished.

 

So, Antonio, have you concluded whether the extender is working as a charger?

 

Hi Yak, more than that. The mistery now is complete clear. Diy Extender has almost 90km road real test and I am putting all my tests and results in a report.

Hi Yak, more than that. The mistery now is complete clear. Diy Extender has almost 90km road real test and I am putting all my tests and results in a report.

Looking forward to it.

Looking forward to it.

Yako, send me your email address.

The internal resistance seems very high: voltage difference divided by current is resistance round the circuit I think, and unless there is something else in it, will be almost entirely the internal resistance of the two batteries.

 

(8.11 - 7.91) / 0.0444 = 4.73 ohms, or 1.18 ohms per cell. The data sheet indicates 0.1 ohms per cell, so is there a factor of 10 error creeping in somewhere?

 

Something doesn't look right here.

Hi. How did you measure the current. The meter itself can introduce an error when reading current at such small voltage differences and you need to take into account the resistance of the measuring device, leads and probes at the scale that you were using. For example, some Fluke meters introduce a 'Burden' of well over an ohm on the current scale.

 

https://www.fluke.com/en-us/learn/blog/electrical/can-you-live-with-the-burden

Edited April 3, 20224 yr by Sturmey

Hi. How did you measure the current. The meter itself can introduce an error when reading current at such small voltage differences and you need to take into account the resistance of the measuring device, leads and probes at the scale that you were using. For example, some Fluke meters introduce a 'Burden' of well over an ohm on the current scale.

 

https://www.fluke.com/en-us/learn/blog/electrical/can-you-live-with-the-burden

I was commenting on the measurements in a previous post, not making my own. It may well be down to the instruments used. I've not got down to that level of detailed analysis in my experiments!