looking for some advice

Control Boards, Controllers, Tethers, Ect.
FJM
Posts: 23
Joined: Nov 6th, 2013, 11:02 am

Re: looking for some advice

Post by FJM »

If 24V at the surface ends up at 12V at the ROV, do you really need a 24V to 12V converter? Would a 12V regulator be enough?

I'm not totally up on my electronics, so enlighten me why if this thinking is not correct.

Fred
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: looking for some advice

Post by rossrov »

No problems with the current rating then! The voltage converter is a regulator of sorts, how well it tolerates variations in input voltage is the question. A typical switchmode regulator would handle a larger variation in input voltage while still maintaining output, but you would probably have trouble finding one for $10 that can do upwards of 10 amps.

In this case I suspect the input voltage is dropping below what the converter needs, or dropping too quickly (spiking), hence the momentary interference, before the output recovers. The spiking issue can probably be solved with a biggish capacitor on the tether side of the converter. In a conventional truck installation, the converter would be connected close to the battery, not on the end of long wires, so the capacitor helps with part of this.

If you can get the specs on the converter, find out what the minimum input voltage needed is, and size the tether gauge to deliver enough volts.

The point often missed is that by using a switchmode converter/regulator (assuming near 100% efficiency) the current on the 24 volt side will be just a bit more than half the current on the 12 volt side, so less voltage drop over the tether. The tether still needs to be of adequate gauge :) .

For the camera and other electronics, maybe including the control part of the motor control board, I would be using a separate switchmode regulator, needing to supply much less current than the motor's converter/regulator. Using a battery just for electronics would be a backward step just complicating things further.
hazzyb
Posts: 24
Joined: Apr 22nd, 2013, 3:51 pm

Re: looking for some advice

Post by hazzyb »

was talking to eddy at work and he suspects it's the wire size as well, you can try my power cable and see if that solves the problem, might also tell me if i'm going to have the same problem!!

ben
jonnyhas
Posts: 55
Joined: Jun 5th, 2012, 7:45 am
Location: highlands, scotland

Re: looking for some advice

Post by jonnyhas »

Ross,

yeah i don't really want to go back to putting a battery in the box, one of the things i have noticed about these regulator spec's on ebay is they seem to require a minimum of 2 volts over the voltage output so that could be one issue, i have a variable out put step up so can boost it to 28 volts which would cover the drop the caps on the step down are rated to 35v but not sure about the regulator itself i may try and push up to 28v and see what happens, i probably also require to measure that actual amps at the rov 12v end as the step up's have current control also and could be limiting the current to the rov but again im not sure what affect this would have on the overall setup.

i will need to do a bit more reading and some testing!


cheers

Jonny
jonnyhas
Posts: 55
Joined: Jun 5th, 2012, 7:45 am
Location: highlands, scotland

Re: looking for some advice

Post by jonnyhas »

So whilst dealing with man flu (Cough Cough), i did some testing in the bath, I raised the voltage up to 30v and am still having the same issues, I was able to adjust the current output which made a difference in air but not in water, i slo purchased some capacitors and tried locating them into the loop at various points to try and smove out any short voltage loss when motors start up etc but this had little affect. so I have a suspicion that my very cheap regulator in the rov is not up to the job, so i have purchased another today (more expensive model) so hopefully this will arrive in a couple of weeks from the other side of the world and solve the issue,

http://www.ebay.co.uk/itm/330844607241? ... 1497.l2649

I have also bought this one for possibly using to power the control side only

http://www.ebay.co.uk/itm/310675455991? ... 1497.l2649


I have also ordered 40mm props as the 50mm dia on 1100L/min rated motors was pulling 4.5 amps, I re-tested with a 40mm prop I borrowed from my brother this pulled 3 amps and appeared to have suitable thrust so this can only help.


cheers

Jonny
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: looking for some advice

Post by rossrov »

I'm guessing you do not have an Oscilloscope (CRO). Most digital voltmeters are not fast enough to show the brief voltage drop that will be happening at the input of the converter that is most likely causing the converter to shut down. With the CRO, you can look at the input volts before and after adding capacitors, altering tether gauge/length etc

Something you could try is to connect the surface power supply directly to the converter, bypassing the length of tether I'm guessing you have in between at present. Might give you a few clues depending what effect that has.

Having said that, the new regulators may be better designed and hopefully that solves the issue, like you say.

CROs used to be a fairly pricey bit of gear for the hobbyist to justify buying, but now there are handheld models with enough bandwidth etc for this sort of work for less than $100, and USB types that use your PC for processing and display that are even cheaper

With respect, be careful with even Extra Low Voltage around water. What one cannot feel in dry conditions could give a serious shock when water enters the equation, lowering body resistance, and increasing current flow.....
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