Question Cyrtron MD30C regenerative current protection

Hi everyone,

I ordered 3 Cytron MD30C motorcontrollers for the 500W 24V motors on my new 3dof simulator build.
I have 3 Meanwell RSP-1500-24V PSU 63A , but probable only use 1 or 2.

https://www.xsimulator.net/communit...or-flight-and-space-gaming.19571/#post-257438

The reason for choosing these controllers was price. (I got them for 115 euro) compared to sabertooth (275 euro for 2)

My question is protection against regenerative current , and maybe other electrical problems
I only have basic electrical/soldering skills


The cryton manual states:
If Switching Power Supply is being used as power source for MD30C, we recommend parallel it with same voltage battery. This is to absorb the re-gen power from motor. DC brushed motor will become generator when it is slow down and rotate by external force.

-2 equal 12V battries connected in series would give me 24V (24V are not common here)
is it ok to use 2x12v instead of one 24V?
How many Ampera hour (Ah) does it need to be?

-Another option like Sebastian2 on his build thread with modified shunt regulators with trim pods and load resistors for each psu/controller/motor unit. It looks like a lot of wiring and soldering, going this way

-On the sabertooth controller you can only use load resistors is that possible with the cytron MD30C?
This looks like a very simple and inexpensive solution.
- Also see the use of diodes on some builds.

Can anyone help me out on what choosing the best and safe setup.

Thanks

Maybe my question is not clear ?

I want to protect my Cryton MD30C against regenerative current .
I listed the options I found on this forum.

Does anybody use this driver and protect it anyway ?

The problem you raised is quite complicated. I am not an electronics engineer by training, so I will describe how I solved it in my 6DOF. Generally, from what I understand, regenerative current is dangerous for the power supply, not for the controller itself. So I installed a Schottky diode between the power supply and the + power supply of the motor controller board (I use this controller https://www.xsimulator.net/community/threads/reasonably-priced-100a-motor-controllers.17638/).
The installation has been working for several months without any failures.
The controllers you have chosen support currents up to 30A. My measurements show that the 250W 13A DC motors I use can draw up to 20A at peak times. With your 500W motors, it may be a lot more, so keep that in mind.

Thanks Attyla,

I didn't know the motor controller could handle the regenerative current , but protection is to protect the PSU from shutting down or getting damaged.

I was thinking if you put a diode in front of the PSU , the energie would go into the controller ,
transforming to heat and damaging the controller , or damaging it directly with high/reverse current.

Do you now if polarity changes when regenerative current occurs?

My electronic skills are very basic , but I made a simple drawing of my idea of how to wire things up.

is this a possible setup , the schottky diodes are the part i'm not sure of .
3 of them to a central fuse box ? i have no clue if that would work.

any electronic help will be appreciated.

I got 2 used batteries Varta AGM 12V 95AH for only 50 euro.
So switched to this option for dealing with the regenerative current .

The psu fan is noisy so turning it off when using the rig would be prefered.

With this change new questions arrise.

- Is it save to charge 2 batteries in series with the PSU?
Or should I get a battery charger (maybe a better option anyway).
I have 3 PSU units I have no use for then .

-Can anyone give me advise on the settings on the PSU ?
From the documentation of the battery:
The best working range voltage for the batteries is 12.4 to 12.6Volt. (so 24.8 to 25.2 with the 2 in series)
advised Charging voltage is 28.8V

-Do I need overcharge protection when using the PSU for charging?

-Do I need a fuse between PSU and the batteries?

-What is the best place for the Emergency stop or any other shutdown option ?
I guess in the positive line after the batteries for the terminal block .

To charge the batteries completely to 100% a voltage of at least 28V is required. But 95Ah is way more than you need. I would set the voltage to 25.2V. This charges the batteries only to 50 or 60% but this way you don't need overcharge protection.

The PSU has overcurrent protection on its own. But in the very unlikely case that something in the PSU fails the battery could drive >1000A causing a fire risk. The retifier also avoids current going back into the PSU but a fuse would be better because it doesn't get as hot. The rectifier wastes ~50W.

You definitely need a way to cut off power. The motor drives are still powered by the battery if you only switch the PSU off. It's difficult to find switches that can handle 50A DC. I'd use a power relay like the ones used in trucks or solar power inverters.

If the Cytron boards don't draw too much idle current to drain the batteries within a few days you could also simply pull the fuses if you don't use the rig for more than a day. But it would be better to have some sort of emergency stop.

No, a single 1500W PSU is perfect. If the motors draw more than 1500W for a short time the batteries will buffer that. And the PSU provides enough power so that the batteries never really get discharged.

If the fan is too loud I'd replace it with a bigger one with lower RPM or add a temperature controller.

Thank you very much Aerosmith ,

This helps me a lot

I will set PSU to 25.2 Volts and build in a fuse (60A) before the rectifier.

also an off/on switch (will look for a power relais) and an emergency button to the cryton drivers will be installed ( switching both plus and minus lines)

The PSU has overcurrent protection on its own. But in the very unlikely case that something in the PSU fails the battery could drive >1000A causing a fire risk. The retifier also avoids current going back into the PSU but a fuse would be better because it doesn't get as hot. The rectifier wastes ~50W.

Is a power relais and the wiring like this what you mean?

Yes exactly. I don't know why there is a ground wire to the switch, though. Normally, the emergency stop is a NC pushbutton. When you push it it cuts power to the relais coil.

If the relay can handle >60A you can put it between the battery and the fuse box (3 x 20A).

The ground wire on the switch is indeed strange , and isn't needed for the relay to function.
I was thinking of making the Emergency button with the relais
on the switching side of the relay,
I could use thinner wires and a low amp fuse (1A?), if i understand correctly it only feeds a small coil inside the relay.

For the on/off switch , I found this one, that is used on boats and campers etc.
it cost around 10 euro . so no deal breaker only a circuit breaker


Will update the schematic and add some pictures once connected and hopefully working.

Schematic update

I have frame with 3 volt and amp gauges from an other project , gonna use that to monitor the setup.

-The psu and battery switches will be like in the picture in my previous reply.
-For the emergency button , the power relay will be used .
To limit power to the positive line of the switch , I will use a resistor and a fuse.
U= 24V R= 8 ohm I will be 3A max , 5A fuse in case something goes wrong.

60A fuse and the rectifier in the positive line of the PSU maybe overkill but I got the parts lying around.

Wiring will be all 10awg, for the emergency switch something like 16awg .

Please comment if something is wrong