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Inverter/Generator for outland power supply

Hi folk’s, Can anyone recommend a suitable inverter/generator for use with the outland technology power supply for our BlueROV2?
We are currently using a petrol 3.5kva generator that start’s to struggle on anything more than 50% power. (I am also worried about frying the laptop or ROV with not being on an inverter) I realise these probably only put out a few hundred watts at idle and the outland box requires around 1000 watts.
Does anyone have a unit they use already that they would recommend? We are usually land based too so size/weight is of no great concern as long as it can run the blue on full power and not fry anything.

Hi @murf,

I haven’t looked much into generators before, so educated myself a bit with this article comparing inverter and non-inverter generators. That website also has a Reviews and Buyers guide, of which the first two are inverter-generators that both also support being run in parallel with another of the same type to double the power output.

Your company seems to be Scotland based, so I searched online for “best inverter generators Scotland”, which landed me at this comparison of several ‘leading’ options. I’ve also asked our engineering team internally if they’ve got any recommendations and will pass those on as/if they come through :slight_smile:

Hopefully some others in the community have experience with this too, and can chime in with their experiences/suggestions.

In case it’s helpful, I’ve gone through the power requirements and considerations of an OTPS system below, along with some corresponding implications for your current generator and a potential new one.

+EDITED TO INCLUDE TRANSMISSION LOSSES IN TETHER+

Operating Requirements

Supply Inefficiency Losses

Power Conversions

To get a better sense of the operating requirements, I took more of a look into the OTPS specs. While the ROV Power Supply Enclosure can output up to 1000W, that’s at a 92% efficiency (of the DC-DC conversion), so uses up 1000 / 0.92 \approx 1087 W of the available 1600W of output power from the Topside Supply Unit, which uses 1087 / 0.905 \approx 1200 W of the 1800W max input (noting the 90.5% efficiency of the AC to DC conversion).

Power Transfer (Tether)

As per our voltage drop calculator, a 125m High-Power Tether Cable using two pairs of 23AWG wires to carry 400V would have an efficiency of ~91.9%. If you’ve got the longer 250m tether then the efficiency is ~83.7% instead. Accordingly, 1000W of power in the ROV uses 1200 / 0.919 \approx 1300 W of input power at the top side.

Power Usage Estimates

ROV

With a 15V supply (like from the OTPS), a single T200 thruster at 100% throttle will have the following approximate characteristics

Gain Power Usage [W] x6 Thrusters [W] Thrust
100% ~330 ~1980 100%
75% ~170 ~1020 65%
50% ~65 ~390 34%

So assuming you need a max of about ~35W for the 5V electronics (RPi, Pixhawk, Fathom-X, Camera, camera servo, etc - 5V 6A converter w/ imperfect efficiency), another 15W per lumen at max brightness (e.g. 60W for 4 on the standard BlueROV2), so that remaining ~900W of power for your thrusters (and other powered external devices) can get used up pretty easily if you’re driving hard. I’d recommend keeping the gain at or below 75%, or if you want that factored in automatically in ArduSub so you can have finer-grained control in your valid operating region you can build ardusub with a custom frame, and just copy the BlueROV2 thruster contribution factors (or the heavy configuration ones just above that) and scale them all down by your desired percentage.

For choosing a generator I’d go off the assumption that the full 1000W of ROV power is being used, which is the full 1300W of input power (conversion/transfer inefficiencies factored in).

Laptop

Laptop chargers generally don’t get above 100W, so unless you’re also powering other equipment it’s unlikely you’ll exceed that from the laptop charging output (max 250W socket), so assume you’re consistently using something like 1400W of input power all up, with relatively heavy use of the ROV.

Implications

Current Generator

Assuming your current non-inverting generator has a power factor of ~0.8 (the industry standard for non-inverting generators) it’d have a capacity of ~2800W, so generally shouldn’t be running too far above 50% load anyway (assuming I haven’t missed anything major in my estimates/calculations). It’s possible your 3.5kVA is the maximum load though, in which case if I’m understanding correctly the rated load is possibly something like 20% lower, which would have a capacity of ~2240W and would be running at ~62.5% of that. (I’m unsure about that last point, as I’m not certain if the generator VA corresponds to the max/surge power or the rated continuous/running power)

A New Generator

Generators tend to be happiest/last longer if they’re consistently used at low loads relative to their rated maximums. The ones I looked at seemed to generally indicate run time and noise levels at 25-50% usage, so that’s where I’d suggest looking for optimal performance. With that spec you’d be looking at rated running/continuous loads of 2800-4200W.

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Thanks Elliot, That’s a fair bit of info for me to pour through, I’ll have a look at the recommended buyers guide and try choose something a little bigger than required (if budget allows) I will also look into locking down the gain as suggested, We currently have the ROV back at buccaneer for repairs as it seems to have developed some strange control faults and has crossed lines between the thrust and gripper/lights :thinking:

The electric motors can demand power much faster than the smaller generators can respond, so it is easy to bog them down. Any electric motor(s) can demand power somewhat instantaneously, while the generator has to have time to increase engine RPM to keep up with electrical demand. One way to mitigate this, is to feather the throttle on your ROV more or use a bigger generator that has more headroom.
A 3kw generator should have plenty power. However, in many cases, inverter generators have an “eco mode” switch on them. Make sure that is off. That might solve your issue alone.

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Thanks for chiming in @Outland, and great to see you on the forum! :slight_smile:

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I used to used a Inverter generator 2000w 1700 w continusly it was useless before i made a dc box with a drosel from aircondidion and som capacitors rectefied toppside. Then no problem i get ca 1200w subsea now i use electric car batterys 3.7kwh and a 3 kw inverter that is magicsl no sound😄 and i can dive for a long time.

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I’ve wondered how a car battery would go. The generator I was using at my previous company was quite loud, so whenever we were using it I was thinking about how nice a silent battery could be… :slight_smile:

Hiya
We’ve ran on both inverters and gennys for years with loads of different ROV’s - with gennys the important part always has been to “clean up” the supply, so used Honda EU20i inverter gennys with no issues, a really good 3Kw Hyundai with no probs (and ran it on propane gas rather than petrol and it was really quiet) - almost any other genny has “spiked” and I’ve then ran through either a bigish UPS or a power stabiliser to take the spikes away - when using inverters I’ve ran for nearly two days continuous on a videoray from one 110Ah car battery and still had some to go, but again a good inverter - pure sine wave for preference (thing the one I used was actually only rated 800watt but was fine! - they used to come with the videoray’s for a while so they were USA models outputting 110 rather than our UK 240)
Give me a shout Craig once were ready to get your ROV back to you and we can show you what I’ve used in the past.

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That’s brilliant Ian, Cheers. I quite fancied one of the Hyundai ones, good to know you have tested a few. I’ll probably pop up myself again when the ROV’s ready, I hope she’s not giving you too much trouble, Cheers again

We have used an USP between the power generator and the ROV Power Supply to ensure we kill any peaks or even short interruptions in the supply. Esp. after someone stepped onto the cable and pulled it out of the generator once.

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What i always tell people is, You’ve already got a generator, a nice quiet one (probably)…it’s called a car (or for the elite, a truck). In Scotland it’s probably a fuel-efficient 4cyl diesel.

Just get a good 2k watt inverter, hook it to the battery terminals, leave the engine running.

We did think of that originally, We have a fleet of VW crafter’s, I spec’d up adding batteries, dc-dc inverter, etc for under £1000 for 6-9k watt’s of power, sadly being in Scotland access to some of our sites is “challenging” for vehicle’s, There’s the health and safety nightmare of running cable’s on water sites.

You might consider NATO rated cabels with IP 68 rated protection as they are used by Military and Emergency Recovery Team. They are build to work even in water or in mud. So getting power to your control box over some 50+m should be feasible even if you have to connect 2 of them.