Hi All,
I have put together all bits and pieces and I am ready to dive. By accident I reflected on the Asia manual and saw that the input power should be 12-16V, it continues within bracket “depending on user requirements” It also states, the board have circuit over voltage protection (I don’t know what that is). I did all the testing on 12v due to proximity to power source but main plan was always to ship 24V down a tether due to voltage drop, and built that way. Aborted the dive today due to concern to burn the board and tried to contact Asia for advice with no success. It does not make any sense to build a board with limit of 16V, especially when it’s made for top-side-power ROV?
Took the board apart and found 5 X capacitors rated 16V and three seem to be connected in serial. Is there any way you electrical geniuses can determine the boards max voltage input based on the picture attached?
Help would really be appreciated.
Best
Urgent electrical advice needed – Rov Asia
Urgent electrical advice needed – Rov Asia
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Re: Urgent electrical advice needed – Rov Asia
Hello!
You need to regulate your voltage down from 24V to somewhere between 12-16V. You can buy these regulators, or you can build them yourself. You need to know how many amperes you need.
You can not run the ROV-Asia on 24V, because the over voltage protection will then disconnect the power to protect the board. It is usual that circuits are made for a specific voltage (or voltage range) as this makes producing them cheaper. The over voltage protection circuit can be some fuses who blows if the voltage is too high (which you then would have to replace), or it can be a circuit who disconnects the power until it is right. I don't know what is applied in ROV-asia.
You need to regulate your voltage down from 24V to somewhere between 12-16V. You can buy these regulators, or you can build them yourself. You need to know how many amperes you need.
You can not run the ROV-Asia on 24V, because the over voltage protection will then disconnect the power to protect the board. It is usual that circuits are made for a specific voltage (or voltage range) as this makes producing them cheaper. The over voltage protection circuit can be some fuses who blows if the voltage is too high (which you then would have to replace), or it can be a circuit who disconnects the power until it is right. I don't know what is applied in ROV-asia.
Re: Urgent electrical advice needed – Rov Asia
Here is an example of what you need: http://cgi.ebay.com/DC-24V-12V-20A-240W ... 166wt_1206 (DC 24V to 12V 20A 240W Step-down DC to DC Converter)
How long is the power cable? If you have very long cables on low voltages, the voltage drop in the cable is enormous unless the cable diameter is big. Check out this voltage drop calculator to find out what cable diameter you should use: http://www.calculator.net/voltage-drop-calculator.html
A way to get thinner cables is to go up in voltage. You could have 24 Volts DC in your boat, which then was converted into 120/ 230V AC by using an inverter. Then you could run AC down to your ROV with a low voltage loss, and convert it to 12V DC again. All the equipment may cost a bit if you don't already have it though, the inverter is especially expensive..
How long is the power cable? If you have very long cables on low voltages, the voltage drop in the cable is enormous unless the cable diameter is big. Check out this voltage drop calculator to find out what cable diameter you should use: http://www.calculator.net/voltage-drop-calculator.html
A way to get thinner cables is to go up in voltage. You could have 24 Volts DC in your boat, which then was converted into 120/ 230V AC by using an inverter. Then you could run AC down to your ROV with a low voltage loss, and convert it to 12V DC again. All the equipment may cost a bit if you don't already have it though, the inverter is especially expensive..
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SoakedinVancouver
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Re: Urgent electrical advice needed – Rov Asia
Based on the capacitors, you're are stuck with a 16Vdc maximum. If you were to replace the capacitors with some rated higher, your next problem would be the board voltage regulator (most likely the big black thing with 3 legs, lower left, called "U2"). It probably could take 24Vdc at its input, especially with the voltage loss in the umbilical, but the amount of current it could deliver without going into shutdown mode due to heat would be limited, maybe too much for proper operation of the board. (ex. if the regulator is a 9Vdc unit, and the current it gives out, at 9 volts, is 1 amp, while the input it feeds from is 12Vdc. That makes it drop 3 volts (12-9=3), at 1 amp this will give you 3 watts of heat released (P=E time I, 3V X 1 amp = 3 watts). If the input is pushed up to 18Vdc, you end up with 18-9=9, 9X1=9wattts! You can see where this is going... Thermal shutdown!
A solution is to add a pre-regulator at the input of the board you already have. A 15Vdc regulator with a heatsink would do the trick, for a maximum current of about 750mA.
If more current is needed, you could use an adjustable regulator (it requires just a couple more parts), set between 12 to 16 volts, like the LM317T or-K (up to 1 amp), the LM350K (up to 3 amps) or, if I remember well, LM338K (up to 5 amps!). Their voltage input are rated up to 36Vdc, and the current output capabilities are derated accordingly (more input voltage, less current available before the thermal shutdown). Heat sink or metal surface of enough area required!
These regulators are hard to kill, but you must use all the tricks with protective diodes as your load (your existing board) would be a unusual load (capacitors again...)
Get the datasheet for the LM317 from National Instrument or other and check the suggested circuits and the applications. The '338 and the '350 would pretty much used in the same configurations (but maybe not the same pinouts (!!!), always double check with the right datasheet...)
What is the part number of the regulator on your board? If its an LM317, you might be able to get away with changing only the caps...
A solution is to add a pre-regulator at the input of the board you already have. A 15Vdc regulator with a heatsink would do the trick, for a maximum current of about 750mA.
If more current is needed, you could use an adjustable regulator (it requires just a couple more parts), set between 12 to 16 volts, like the LM317T or-K (up to 1 amp), the LM350K (up to 3 amps) or, if I remember well, LM338K (up to 5 amps!). Their voltage input are rated up to 36Vdc, and the current output capabilities are derated accordingly (more input voltage, less current available before the thermal shutdown). Heat sink or metal surface of enough area required!
These regulators are hard to kill, but you must use all the tricks with protective diodes as your load (your existing board) would be a unusual load (capacitors again...)
Get the datasheet for the LM317 from National Instrument or other and check the suggested circuits and the applications. The '338 and the '350 would pretty much used in the same configurations (but maybe not the same pinouts (!!!), always double check with the right datasheet...)
What is the part number of the regulator on your board? If its an LM317, you might be able to get away with changing only the caps...
Re: Urgent electrical advice needed – Rov Asia
Guys, thanks for the info.
I am kind of furious atm. It’s simply ridiculous to make a board specifically made for ROV with top side power and limit it to 12v. This board has been used with 400 feet of tether and that was no mention that you need any step down dc-dc converter on board. With my teather being 80m, sending 12V i get 5v at the ROV end and there is no way in hell I can get the required 10A needed through that.
Not that I doubt you guys but I am now reading that adding capacitors in serial add the total voltage and in parallel the total current hold? Reading now that putting caps in serial is common practices since its difficult to get a desired voltage only with one so they adjust with several smaller??? If so and if the three capacitors are in series then the total voltage would be 48V, which would make perfect sense for a board like this. Is there a small chance this is the case?
There is no room left for a dc-dc converter in the ROV.
It is a LM317 D2
Magic-I have the equipment for AC - DC but I dont wont to run hight voltage in the ocean.
http://rov-asia.com/document/RovMualFull.pdf
knew it was way too easy……………………………..
I am kind of furious atm. It’s simply ridiculous to make a board specifically made for ROV with top side power and limit it to 12v. This board has been used with 400 feet of tether and that was no mention that you need any step down dc-dc converter on board. With my teather being 80m, sending 12V i get 5v at the ROV end and there is no way in hell I can get the required 10A needed through that.
Not that I doubt you guys but I am now reading that adding capacitors in serial add the total voltage and in parallel the total current hold? Reading now that putting caps in serial is common practices since its difficult to get a desired voltage only with one so they adjust with several smaller??? If so and if the three capacitors are in series then the total voltage would be 48V, which would make perfect sense for a board like this. Is there a small chance this is the case?
There is no room left for a dc-dc converter in the ROV.
It is a LM317 D2
Magic-I have the equipment for AC - DC but I dont wont to run hight voltage in the ocean.
http://rov-asia.com/document/RovMualFull.pdf
knew it was way too easy……………………………..
Last edited by manhattan on Jun 23rd, 2011, 5:25 pm, edited 1 time in total.
Re: Urgent electrical advice needed – Rov Asia
Hey, it's not a manufacture mistake, you made the mistake not to read the necessary documentation before you bought it!
Anyways. How many Volts do you get at the ROV end if you run 24 Volts from the surface?
Are you running digital or analogue data on the tether (i.e. for camera)? In general I don't like the idea of running DC voltage in parallell with a tether used for data (allthough I have no experience with it). It might interfere with the signaling, but perhaps this is more relevant with AC power.
Speaking about the voltage loss; why not add a seperate power cable?
Anyways. How many Volts do you get at the ROV end if you run 24 Volts from the surface?
Are you running digital or analogue data on the tether (i.e. for camera)? In general I don't like the idea of running DC voltage in parallell with a tether used for data (allthough I have no experience with it). It might interfere with the signaling, but perhaps this is more relevant with AC power.
Speaking about the voltage loss; why not add a seperate power cable?
Re: Urgent electrical advice needed – Rov Asia
Running one Cat5e for the Axis 221 minus two wires for tx rx and pair of 1mm power cables. Cant measure the drop becouse i havent connected 24v and the drop happens only when load is present. On 12v I get 12 v at the board after 80 meters and when I put on one motor + esc it drops to 6.
Dry I get 3.8 Ohm resistance over 80m.
Dry I get 3.8 Ohm resistance over 80m.
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SoakedinVancouver
- Posts: 117
- Joined: Dec 31st, 2010, 9:38 pm
Re: Urgent electrical advice needed – Rov Asia
Ok... I took another look (standing on my head...) at the picture. First. lets get the capacitors out of the way. C1 and C2 appear to be input and output capacitors for U2, which I assume to be the LM317. C17(?), C18 and C19, the other three electrolitycs capacitors, are connected in PARALLEL from what I can see (all the minusses on the same side, connected by the copper running along the edge of the board, while all the plusses are toward the inside of the board, and again, connected together. Conclusion: total value of capacitance, 3X470uF=1410uF, @ 16VDC (consider the 16VDC I just typed there to be in italic, bold and underlined...). These three capacitors must be for some sort of filtering (electrolitycs are rarely used for precision, and by the way, nobody but people who work with very high voltage electronic circuitry bother to try to mix and match them for precise voltage values. You buy one that has a higher voltage rating than the highest expected voltage in the circuit. Over rating cost money, and even worse, real estate space on the board.
My guess right now, is that the other big black thingy soldered at the bottom right of the board is another voltage regulator. What's the number printed on this one?
Also, I read that this is a receiver board, which could mean it requires more than one regulated voltage. The LM317 supplies one, the other regulator, if that's what it is, the other.
Do you have a voltmeter? If yes, can you measure the voltages at the pins of the regulators, when powered directly (not through the umbilical) by 12VDC? (by the way, if you are using a car-type battery as a power source, please do put a fuse at the battery end, say, 5 amps MAX. And get a bench power supply (variable, 0 to 30Vdc, 3 amps) as soon as you can, you WILL need it to debug your ROV in the future).
All this to let you know that there is hope. The designer might have stated that the maximum input voltage has to be 16VDC because of ONE capacitor (if one regulator also acts as a pre-regulator for the other one), and all the while he was also keeping in mind that people running a top source of 24VDC would necessarily have a loss down the cable.
If only one of the (presumably) two regulators sees the input voltage, you would have to replace only its input capacitor, a rather simple operation, limited only by your soldering (and desoldering) skills and by the space available for a ....25VDC rated 470uF. Or, for a smaller size and with very limited effect on the voltage regulation, a 25VDC 330uF.
Do you have a schematic of the circuit?
My guess right now, is that the other big black thingy soldered at the bottom right of the board is another voltage regulator. What's the number printed on this one?
Also, I read that this is a receiver board, which could mean it requires more than one regulated voltage. The LM317 supplies one, the other regulator, if that's what it is, the other.
Do you have a voltmeter? If yes, can you measure the voltages at the pins of the regulators, when powered directly (not through the umbilical) by 12VDC? (by the way, if you are using a car-type battery as a power source, please do put a fuse at the battery end, say, 5 amps MAX. And get a bench power supply (variable, 0 to 30Vdc, 3 amps) as soon as you can, you WILL need it to debug your ROV in the future).
All this to let you know that there is hope. The designer might have stated that the maximum input voltage has to be 16VDC because of ONE capacitor (if one regulator also acts as a pre-regulator for the other one), and all the while he was also keeping in mind that people running a top source of 24VDC would necessarily have a loss down the cable.
If only one of the (presumably) two regulators sees the input voltage, you would have to replace only its input capacitor, a rather simple operation, limited only by your soldering (and desoldering) skills and by the space available for a ....25VDC rated 470uF. Or, for a smaller size and with very limited effect on the voltage regulation, a 25VDC 330uF.
Do you have a schematic of the circuit?
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SoakedinVancouver
- Posts: 117
- Joined: Dec 31st, 2010, 9:38 pm
Re: Urgent electrical advice needed – Rov Asia
I just read your post about having no drop at 12VDC with only the instrumentation being powered, while losing 50% with one (ouch!) thruster (unloaded, right? I mean, not in water, doing real work, right?) running.
80 meters is a long way for even 24VDC...
Nonetheless, this means that 24VDC would still be pretty much 24VDC at the board, while you have nothing else powered on. Ergo, you must make sure the board can take it, by adding a pre-regulator (but you have no space) or by an hopefully slight modification of the board component(s).
I'll be waiting for an update on the part number for the other (suspected to be) regulator, and for the voltage measurements (these are needed to establish if there is only one regulator seeing the raw input voltage).
Good thinking about the not wanting to send "high" voltage down into a saline environment. This said, the pro's do it, they have too. Their umbilical go from 50m to 1000m+. Safety is inherent in their operation so it is not that much of an additional worry for them. The main problem with higher voltage is that it promote faster corrosion if it leaks to the frame or in the water around the ROV. And of course, if there is a leak to the frame, and somebody with wet feet touches the ROV as it is brought on board, dripping wet, and depending on the grounding system of the ROV, ship, crane, it could be a deadly experience. So they monitor the electrical system accordingly.
80 meters is a long way for even 24VDC...
Nonetheless, this means that 24VDC would still be pretty much 24VDC at the board, while you have nothing else powered on. Ergo, you must make sure the board can take it, by adding a pre-regulator (but you have no space) or by an hopefully slight modification of the board component(s).
I'll be waiting for an update on the part number for the other (suspected to be) regulator, and for the voltage measurements (these are needed to establish if there is only one regulator seeing the raw input voltage).
Good thinking about the not wanting to send "high" voltage down into a saline environment. This said, the pro's do it, they have too. Their umbilical go from 50m to 1000m+. Safety is inherent in their operation so it is not that much of an additional worry for them. The main problem with higher voltage is that it promote faster corrosion if it leaks to the frame or in the water around the ROV. And of course, if there is a leak to the frame, and somebody with wet feet touches the ROV as it is brought on board, dripping wet, and depending on the grounding system of the ROV, ship, crane, it could be a deadly experience. So they monitor the electrical system accordingly.
Re: Urgent electrical advice needed – Rov Asia
Vancuver,
Thanks for your effort, I owe you one. Bigger one if you save me the already made tether. Will measure what you said first thing tomorrow (midnight here)
The other is difficult to read but I make out BA12 and 42 91
No schematics except the above linked manual.
I have always been planning for the voltage drop and calculated the length of tether based on that. I should receive 14 – 16 V at the ROV end if provided with 24v.
But now I am confused. If I connect the 24V through the 80 m tether to the board and no Load is present wouldn’t I get almost the 24v to the board? I tested this with 12V and there was minimum difference at the board until I turned on the engines. Is this not the case?
Ah, Just read your last line and it cleared my last question about the 24 drop.......
Manufacturer dont state any maximum of any kind it only says in the manual “ 14-16 VCD 20A, Depending on user requirements. Note that the picture provided is only for the bottom board. You don’t see the top side with the fuses. Can that be important?
And yes, The topside transmitter board is powered with separate 12v 500ma
Thanks for your effort, I owe you one. Bigger one if you save me the already made tether. Will measure what you said first thing tomorrow (midnight here)
The other is difficult to read but I make out BA12 and 42 91
No schematics except the above linked manual.
I have always been planning for the voltage drop and calculated the length of tether based on that. I should receive 14 – 16 V at the ROV end if provided with 24v.
But now I am confused. If I connect the 24V through the 80 m tether to the board and no Load is present wouldn’t I get almost the 24v to the board? I tested this with 12V and there was minimum difference at the board until I turned on the engines. Is this not the case?
Ah, Just read your last line and it cleared my last question about the 24 drop.......
Manufacturer dont state any maximum of any kind it only says in the manual “ 14-16 VCD 20A, Depending on user requirements. Note that the picture provided is only for the bottom board. You don’t see the top side with the fuses. Can that be important?
And yes, The topside transmitter board is powered with separate 12v 500ma