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Sam Neall

Sam Neall

Mechanical
Mar 26, 2020
32
Are power supplys rated in peak power or continuous power? I have a Sabertooth 2x32 motor driver that Peaks at 64 A per channel at 12 V. I was recommended to get a 70 A power supply. It will cover the base amperage of the motor driver, but I’m worried if the motors draw too much amps, the motor driver will peak and the power supply wont be able to supply adequate power. Also do you think that the motor driver I have will be able to power two of these motors? The seller doesn’t know the max current draw, so by the fact that it draws 1200w max at 24v could one of you give me an idea of how close these are to working with my driver that will power them at 12v?
Any support is appreciated thanks!
 
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Way too much variability out there for us to say. Normally those are associated with battery based systems. With a battery based system the battery(ies) can often supply very large currents briefly. They also have the characteristic of letting the voltage drop while being overloaded. This acts to limit the overload.

With a wall powered supply this latter characteristic is typically missing and overloads damage them or blow fuses.
A proper wall supply for bulk driving DC motors is an unregulated one. Unregulated supplies are a large transformer, rectifiers, and a capacitor bank. Sometimes an inductor is added in series with the rectifier bank to improve the conduction angles of the rectifiers and to limit the startup inrush. That type supply roughly approximates a battery supply. Using a regulated supply subjects the supply regulation to every current twitch those motors can present. For reliability you need to supply the peak current even though it may only be for very short moments. With an unregulated supply you can provide a smaller supply.

Regulated supplies are rated in peak which is also the same as their continuous.
Unregulated are rated in continuous but are capable large peaks since their output is just a large charged capacitor.

Keith Cress
kcress -
 
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The sabertooth says that it has overcurrent protection. Does this mean it will protect against more current being drawn than power supply can handle or does it just have a set limit that it cuts out at? Like if it detects a voltage drop from the power supply, signifying it being overworked, with it cut off? I guess that could be considered under voltage protection but the drop in voltage signifies that the motor is drawing too much current from the power supply so I don’t know. Through more contact with the seller he said these draw around 20A at a normal load so I feel like the power supply will have enough headroom with the motors in normal use. However I’m still in testing phases of the simulator and the motors can possibly stall due to the machine making incorrect position readings and crashing the motor into physical boundaries. If they stall, it could mess up my power supply by drawing a max of 128A. I’ve looked for breakers but I couldn’t find any that are rated for my specs. Is there a breaker you could recommend that will work for this use and will cut off power if the motors stall and draw too much for the power supply? By the way it is not listed whether or not the power supply has overcurrent protection itself. It is a Liteon brand 70 A 12 V power supply. I would assume it does but I want to be sure.

If the motors actually draw that much, is it possible to make an un regulated power supply out of the one that I already have?
 
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It depends on how the designers decided to protect the supply. Typically they "fold them back" meaning the voltage collapses to about 1/5th of normal. When the overload is removed it returns to the design voltage. This means in your motor case it may fold back stalling the motor and stopping everything in there tracks.

You need the model number and the data sheet of the supply to understand its protection.

You can't make an unregulated supply out of a regulated one without too many added kludges.

If you already have the motors and the supplies just try them.

Keith Cress
kcress -
 
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I’m going to get the motor soon and I will test them before I do anything crazy. As far as the extra stuff you’re talking about adding to a regulated power supply, I’d be fine with adding it, considering it would be my only choice if the motors aren’t getting enough power. If you don’t mind, could you let me know the most basic form of an unregulated power supply? Couldn’t you just put a 12 V car battery in line with the wires powering the motor driver? At that point, the power supply would be basically charging the battery up so the battery can deliver the appropriate voltage well also having the ability to act as a giant capacitor and push out peak currents. I would assume you would want to use some diodes to eliminate the risk of back current traveling into the power supply, but I don’t see why any other components would be needed for this given that you can already power these motor drivers with the battery itself.
 
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It looks like you are using the crank arms to develop linear motion.
Why don't you consider linear actuators.
Look for actuators with the travel that you want.
they have end of stroke internal limit switches.
image_nfsjmc.png

Amazon

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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If you have room for an automotive battery, use the battery and a cheap trickle charger.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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Linear actuators with rotary encoders are out of my budget. I would definitely use them if I can afford them though.
 
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I suppose I could do that, but how long with that set up last in continuous operation. If I could, I’d rather use the Power supply that I have currently to charge the battery because If the battery gets discharged, that trickle charger won’t be able to deliver power itself. With a power supply I will always have a current being supplied That is enough to power the motors in normal use. If the motors draw too much the battery will just take over from there. This will be designed for hour long sessions on it and i’m not sure if a car battery can stay charged that long.
 
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It is a racing simulator. Around 6 races at 10 minutes each is around the time I play during a session.
 
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OK, so pretty intensive movement over the duration. Ideally the best way IS what waross described as a battery running it all and a charger just keeping the battery topped up. Then 100A spikes are nothing more than hundred amp spikes. You'd then only need a charger that peaks out at the average power demand. It might be just a 25A charger or even a 10A charger. You would want an intelligent charger that would roll back to cut-off or float once the battery was topped up ~ five minutes after you'd quit.


But, since you have supplies now, go ahead and try them.

Keith Cress
kcress -
 
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