Questions about Regeneration while using a Power Supply / Application Note 90727

Hi

I am using a Power supply with a HIM 2360 Roboteq controller connected to a pair of induction motors inside a vehicle similar to a tethered "bumper car"

My power supply is 24 V.

I intend to put two 12 V batteries in series, connected to the Power Supply in parrallel, as per the diagram in Application Note 90727.

When I measure voltage of each battery, it is around 12.6 V, totalling 25.2 in series.

Now I have some questions please as I could not understand some points in AN90727 document:

1) The intro paragraph states that " A solution is to put in parallel to the power supply a rechargeable battery of higher voltage" then "the battery never conducts".

What is exactly meant by the battery "never conducts" please ? Will not the battery output energy to the controller as it has higher voltage than the power supply ?

2) It is indicated below that Zener diode "D2 is needed only if Vbb is too close to Vs so the clamping voltage needs to be slightly increased"

The diagram indicates Vzz, not Vbb, was it a typo ?

3) As my power supply is 24 V, and my two batteries are 25.6 V, do I need to include a D2 Zener Diode ?

Thanks for your help
Sam

What is exactly meant by the battery "never conducts" please ? Will not the battery output energy to the controller as it has higher voltage than the power supply ?

The battery will conduct current if the voltage caused by regeneration is higher than it's output voltage. Therefore the battery should be sized so that this doesn't happen.

The diagram indicates Vzz, not Vbb, was it a typo ?

'

Yes, I believe so.

As my power supply is 24 V, and my two batteries are 25.6 V, do I need to include a D2 Zener Diode ?

The Zener is there to prevent the power supply from charging Vzz directly. The application note assumes that you only want current flow to Vzz in a regenerative condition, which the Zener provides by breaking down during a regenerative condition. Without it there, Vzz should charge and draw current whenever its output voltage drops lower than the power supply. If this is what you want for your application, this is fine, however the circuit isn't really protecting against regeneration anymore. The idea of the Vzz doesn't even necessarily have to be a battery, it could be some kind of capacitor, or even a load resistor if you don't care about storing regenerated energy. The point is to re-route regenerated current flow away from the power supply, which is what the Zener does when it breaks down.

To be honest, I am probably going to add this application note to my list of things to re-write now that it has come to my attention.

Thanks Gabriel for the answers, this clears things up a lot.

Eventually, for my specific application needs , I think I'll experiment without a Zener first : I'll go with the Roboteq manual recommendation on page 33

Place a battery in parallel with the power supply output. This will provide a reservoir
into which regeneration current can flow. It will also be very helpful for delivering
high current surges during motor acceleration, making it possible to use a lower
current power supply. Batteries mounted in this way should be connected for the
first time only while fully charged and should not be allowed to discharge. The power
supply will be required to output unsafe amounts of current if connected directly to a
discharged battery. Consider using a decoupling diode on the power supply’s output
to prevent battery or regeneration current to flow back into the power supply.

In my specific case, I will protect the power supply with a high current diode.

I will put a battery fully charged at 25.6V in parallel with the 24V power supply. So the battery will override the power supply and energize the controller as long as the battery voltage will be superior to the Power supply voltage. If the battery voltage dips under the power supply voltage, it will get recharged.

If regeneration occurs, it will go directly into the battery, ignoring the circuit leg containing power supply thanks to the diode.

The precaution I will take is frequently check battery voltage to see if it does not discharge between uses, which may prompt a great current on startup.

That sounds good, just make sure you application won't run into a condition where it can over charge the battery, which can be very dangerous. We recommend shunting current to a load resistor if this condition will occur.