looking for some advice

[jonnyhas]

Hello everybody,
As ever my rov building is sporadic and waiting on parts etc but i have run into some more issues with what i thought was the answer to voltage drop, i have up'ed my supply to 24v and fitted a 24v-12v regulator in the rov, but i am still having similar issues that when i have 4 thrusters activated (2 for forward & 2 for up/down) the voltage drops below the min voltage rating for my control relays then it all starts pulsing ( i will retest when im sure my 12v car battery is fully charged).

my control is via a vellemen K8023 running H-bridge relays

but in the interim is there a way i can stop this im thinking capacitors but not sure the correct set up.

my second problem is the horrible start up power drop when you activated a motor, i.e the camera briefly glitches and led light dips etc, how can i resolve this issue or again im thinking capacitor's but my electronics knowledge is limited but i am learning!!

any help greatly appreciated

Jonny

[scubersteve]

The power requirement for an electric motor is generally greatest at start-up which is why large motors (refrigerators, compressors, etc.) use startup capacitors. So with 4 thrusters running you are momentarily needing way more power than you probably think. Your subsequent voltage drop is below the minimum required by your camera and it drops out accordingly.
From your mention of a car battery I'm guessing you have topside power. How long and of what gauge are your tether power wires? I'm guessing the voltage drop across them is your problem.

[FJM]

My suggestion would be to add a separate on-board battery for any electronics and have the motors run off the surface battery. The drain caused by electronics should be much less so you don't need the same level of amperage as required to run the motors.

As your motor power gets used, the motors may run slower, but the electronics won't be affected by the voltage drop. Not sure how your relays are set up, but if you have the signal to turn them on from the on-board battery then they should respond consistently and not start pulsing.

Fred

[FJM]

My suggestion would be to add a separate on-board battery for any electronics and have the motors run off the surface battery. The drain caused by electronics should be much less so you don't need the same level of amperage as required to run the motors.

As your motor power gets used, the motors may run slower, but the electronics won't be affected by the voltage drop. Not sure how your relays are set up, but if you have the signal to turn them on from the on-board battery then they should respond consistently and not start pulsing.

Fred

[jonnyhas]

FJM,

Yeah thats what im thinking about would be alot easier than more pcb work, am looking at a small 12v lipo that can sit in the otterbox under the control pcb on ebay at the mo.

Scubersteve,

my setup is 12v battery stepped up to 24v then 35m 16 gauge tether to 24/12v regulator the 24v section never drops much but the 12v side drops down although thinking about it i may have caused my own problem by wiring in the rov with 18 gauge wire instead of keeping it 16 for as much as possible!.


cheers guys

[rossrov]

What sort of voltage reducer are you using for the motors, and what is it's current rating? Wouldn't be too concerned about thinner wires in the ROV - they are only short runs.

[FJM]

I'm interested in your regulator as well as well as I'll run into the same problems.

Do the problems continue once the motors are running? If not, then it's definitely a startup issue.

Also, are you sure it's a voltage issue rather than a current draw issue? The voltage may be ok but the motors are robbing the other circuits of enough amps that they power off and then restart when the surge ends.

If you are using a micro controller, you could use PWM to ramp up the speed or offset the start of each motor very slightly so there is not a simultaneous draw. In the short term, can you drop the voltage to each motor to lessen the load (the motors will run slower but should draw less amps/power and the rest of your circuits won't reset).

Fred

[scubersteve]

According to my calculations 24v across 35m of 16 gauge wire at an assumed draw of only 12 amps (and with 4 thrusters you may very well be higher than that) gives you a terminal voltage of 12.18v before you ever run it through your regulator.

Free advice is worth what you pay for it but that seems like undersized tether wire to me.

I would be using 10 gauge...

[jonnyhas]

Scubber,

yeah i will need to do some investigation in the current draw department, i could also boost it up to 36v which would solve the issue, i would however need to change my current regulator.

jonny

[jonnyhas]

Fred / Ross,

this is the regulator im using;

http://www.ebay.co.uk/itm/330808408562? ... 1423.l2649


cheap and cheerful whether it will actually handle 30amps is a nother matter , i have potted it with heat transfer epoxy and it is mounted externally to my rov.


cheers
Jonny