Decreasing 24 volts
Decreasing 24 volts
I need to know if it's possible to decrease 24 volts to a desired voltage without decreasing the ampage on the motors. I'm really using 12 volts but to compensate for voltage drop, I am ordering another 12 volt battery. 24 volts will clearly be too much, however I want to decrease it with a pot. I have 4 motors that run 15500 rpm at .5 amps without a load. Can anyone give me a ballpark of what these will draw in water? I have 2.5 inch carbonfiber props on them. I have used a voltage drop calc and I see anything from dropping 2 to 5v depending on the amps entered. Any suggestions are helpful! Thanks!
Re: Decreasing 24 volts
Hi rovdude,
I had the same issue to solve when I first started building my ROV.
Voltage drop depends mainly on amperage, wire gauge and wire length. There are several voltage drop calculators available on the internet to predict the voltage drop of your system if you know these parameters of your system.
In my case, the motor amperage in air (with the props) was 1.3A but in water was 5A. This depends on the props you are using and you can't know until you measure it.
I tried different props, different wire gauge and lengths but I had huge voltage drops in every case. From 24V at the source only 5 to 8V were reaching the motor.
Finally, I decided that I needed a very thick wire (and very heavy) to power the motors in order to compensate voltage drop. This wire was expensive and would affect seriously the buoyancy of the ROV, so I changed my course, sealed a 12V battery and put it on the ROV.
Depending on your specifications, you could use 24V to power the motors and compensate voltage drop but the losses would be quite high.
If you provide some more information about wire gauge and desired wire length we can compare with my testing results.
I had the same issue to solve when I first started building my ROV.
Voltage drop depends mainly on amperage, wire gauge and wire length. There are several voltage drop calculators available on the internet to predict the voltage drop of your system if you know these parameters of your system.
In my case, the motor amperage in air (with the props) was 1.3A but in water was 5A. This depends on the props you are using and you can't know until you measure it.
I tried different props, different wire gauge and lengths but I had huge voltage drops in every case. From 24V at the source only 5 to 8V were reaching the motor.
Finally, I decided that I needed a very thick wire (and very heavy) to power the motors in order to compensate voltage drop. This wire was expensive and would affect seriously the buoyancy of the ROV, so I changed my course, sealed a 12V battery and put it on the ROV.
Depending on your specifications, you could use 24V to power the motors and compensate voltage drop but the losses would be quite high.
If you provide some more information about wire gauge and desired wire length we can compare with my testing results.
Re: Decreasing 24 volts
Thankyou! I'm using 100ft of 22 guage aluminum ribbon wire, mainly because it's cheap. Yes I know that's horrible, but that's why I want to compensate with another battery. I actualy tested the voltage in air and it dropped from reading 12.9 v(Most 12v supply a little more voltage) to 10.3v at the end of 100 feet. But I fear in water testing will raise amperage and shoot voltage drop up.
Re: Decreasing 24 volts
Since you only need 100ft of wire, you could try other quite cheap wires of lower AWG (e.g. 16AWG speaker wires).
Check this site: http://www.powerstream.com/Wire_Size.htm (it also has a vlotage drop calculator)
AWG22 has a very low limit for power transmission (0.7A). Power transimission usually means powering a machine for a long time in long distances (please correct me here if I'm wrong). Although this is not the common practice when driving an ROV, the rating for this gauge is far too low for the expected amperage of your motors in water. I wouldn't even try it, and if I did, I would expect the wire to melt after a minute of continuous powering.
On the contrary, 16AWG has a quite higher rating (3.7A).
Yet again, you have to test your motors in the water before buying the wires.
Check this site: http://www.powerstream.com/Wire_Size.htm (it also has a vlotage drop calculator)
AWG22 has a very low limit for power transmission (0.7A). Power transimission usually means powering a machine for a long time in long distances (please correct me here if I'm wrong). Although this is not the common practice when driving an ROV, the rating for this gauge is far too low for the expected amperage of your motors in water. I wouldn't even try it, and if I did, I would expect the wire to melt after a minute of continuous powering.
On the contrary, 16AWG has a quite higher rating (3.7A).
Yet again, you have to test your motors in the water before buying the wires.
Re: Decreasing 24 volts
Thank you. The problem is i already have the wires cuz they were free. I tested the wiring already for about 20 seconds... i dont see any problems yet but i need to measure the amperage In water
Re: Decreasing 24 volts
After some testing, I found that my motors draw 14 amps! I have decided to get 12 copper gauge wire for these, but I am using 16 for everything else. The 12 gauge I have found appropriate to compensate for voltage loss and will not get too hot with around 15 amps flowing through 100 ft of it. I also have decided on a 12v battery and a 6v battery, coming to 18v. However my motors stall at 15 amps, but draw 14 amps in water at just in the water. Under pressure how much will this number go up??