Hi,

So you mean two independent brakes? That is supported today. This is the standard setup for a 2WD hub dyno for example, or a 4WD roller dyno. 

Or if you mean two brakes in parallel, that is fine too. You will use the same control signal to control both brakes. So they will brake the same amount. In series, I am not sure what you mean. 

Can you elaborate the question? 

Cheers,
Jostein

Hello Jostein !

Thanks a lot for your quick reply - i appreciate that.

You wrote:

>In series, I am not sure what you mean. 

I meant to wire two retarders electrically in series to provide exactly the same current,

but then you would need to have apprx. 400V DC

The reason why i am asking is the differential speed:

When you put out the same PWM to both POD retarders they do not get the same rpm due to small physical differences or small different temperatures, etc. 

Questions:

- Do you have experience with two POD´s ?

- When POD´s accelerate slightly different, do you calculate the power of each pod KW separately and add them afterwards to the average rpm value of the two?

e.g.

POD one is accelerating  4.34 Rad/s² while having 1322 rpm
POD two is accelerating  4.32 Rad/s² while having 1344 rpm at the same time

Then you get two different power values for each side, then you add them to get the total power.
Is that total power stored at 1333 rpm at the graph? (or at 1322 rpm or at 1344 rpm)

Additional related question :
Do you have a simulation mode, where the mass  of the car can be specified and the POD´are
simulating that mass (detect acceleration and control POD current depending on this acceleration * mass) ?

This function is great for setting up the carburettor accelerating pump or accelerated enrichment in efi.

Hi,

The standard way to connect it with two brakes is to control the two brakes independently. So you use two RPM sensors and use brake outputs, and there are two PID control loops running, ensuring that both RPMs are the same. 

Controlling two independent brakes with one output will lead to differences in the RPM as you say. You can run two brakes in parallel if they are connected together (this would be if one brake is not strong enough for example). They would then be physically connected together and you could electrically connect them together too, if the power supply is strong enough. The current would double of course. There is nothing wrong with connecting them physically in parallel and electrically in series, but then the voltage will double, and you need a power supply that supports this.

So the control works to keep RPM the same. As you say there can be slight differences in RPM, and the calculation take the average RPM. This will be correct, assuming the Moment of Inertia is the same for the two brakes and axles. This is a reasonable assumption (in most cases it will be exactly the same), and anyway a very small effect since the RPM will be very similar. 

With the RPM brake curves you can set up whatever curve you want, use as many points as necessary. There is no automatic calculation of a "car acceleration mode", but you can calculate it yourself, and adjust the curve to match. 

Cheers,
Jostein

OK, thanks for the clarification!

Now i am clear on this - that´s what i need to have.

(on a first look i did not recognize you have 2x RPM and 2x OUT in the instrumentation kit)