Options to power an electric dive compressor?

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Ric

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I have a small Coltrisub electric dive compressor installed in the forepeak of my boat. I can currently only use it when connected to shore power, which is often inconvenient. Are there inverters that can provide enough power for the compressor? I can't remember the KVA of the motor off the top of my head - just looking for advice on whether this is possible. The main engine on my boat is a Volvo Penta MD2020 of about 19hp - so easily enough thermal power - but I don't know whether the existing electrical system would be adequate.
 
The compressor motor won't be less than 2HP and probably no more than 3HP at a guess if single phase. The big problem will be to supply the start up surge current. The inverter you would need would be very large probably at least 2-4KW or KVA, that's big and would need to be capable of supplying it for at least half an hour and the surge so not a cheapie. The steady state current from 12V for 2KW would be about 18A.
 
Nooooo. That should be 180 Amps. Big set of batteries or a big alternator.
Consider a 2kW suitcase generator, but check that it does the job on startup, the startup load will be high.
 
The smallest Coltri that ai found on the web wants 2.2 kW. A suitcase Honda might do the job.
The Coltri specs are confusing as they spec 4kW for startup but also spec 42A for startup on 240v, which is a lot more than 4kW.
I would do 2 things
1. Get Coltri to state what is really needed
2. Rent a Honda generator and try it if consistent with Coltri statement.
 
Would it be possible to arrange to start the compressor in a no-load state? That way the motor is only spinning itself and the compressor without immediately having to compress any air. This should minimise the starting current, though it still won't be low.
It's worth noting that the stated power output of a generator or an inverter is often for a resistive load like a heater, rather than an inductive load like a motor.
Cheers
Rum Run
 
Norman_E said:
It might be better to drive the compressor directly with a small petrol engine. All of the electric dive compressors I have seen are belt driven, so it may be possible to replace the electric motor with a small petrol engine or even rearrange the drive system to give an option of petrol or electric drive by changing the drive belt.

Small petrol engines are cheap enough http://thepowersite.co.uk/evopower-evo210-honda-gx200-replacement-19mm-shaft-7hp-petrol-engine/
Click to expand...

Beware the fumes for heavens sake if you go down that road!
 
I have a 3.3kw cut off saw running at 230volts. The amps at start up with only the blade inertia are 45. (tested with an ampclamp) That is over 10kw.
 
Thanks for the suggestions. I think I would only consider a system that I could power from my main engine but this does not seem possible. I don't really want a Honda suitcase generator in part as it means carrying another fuel source (petrol) which I don't want. Obviously I am not going to install a petrol engine to my compressor in the forepeak - that would be instant death!
 
I was thinking of fittings a compressor onto my main engine and using low pressure feed good for 10mts Until I Had bad thoughts about someone putting it in gear while I was diving under it.
I would try to run dive gear separately or fill tanks
If you are trying to fill tanks you could run compressor by belt of main engine as some of the small ones run by belt of a 5hp petrol unit
 
I run my Coltri with a 6Kw Genset - works fine as long as there isnt anything running with a significant power drain at the same time, which will kick out the Genset breaker.
 
ip485 said:
I run my Coltri with a 6Kw Genset - works fine as long as there isnt anything running with a significant power drain at the same time, which will kick out the Genset breaker.
Click to expand...
Hi I am a bit late in the forum but may I ask which brand/model genset do you have? and your Coltri specs also...
 
I have the MCH6 - fills a bottle in about 30 minutes and runs perfectly well off my compressor. The start up load is high and you might need a soft start, which I have, so I dont know whether it is absolutely required. Other thoughts - as with any compressor it is very noisy, but simple and efficient for a small number of divers and probably not using more than a few bottles at a time. I have found the compressor relaible and easy to service. Diving off a yacht is not always the ideal platform and you need to think about that aspect but can be made to work well. The obvious considerations are getting in and out of the water, moving around relatively heavy kit and the inevitable roll on many dive locations, but I love it and works just fine.
 
A few options come to mind. Remove the compressor and mount it next to the boat engine so it can be belt driven from the boat diesel. Or leave the compressor electric motor powered but fit an alternator to the main engine. Belt driven 240v 50 hertz of sufficient power. This hopefully will cope with start up current surge. This will need to be driven at constant correct speed either 3000 or 1500 RPM. A bit tricky. https://www.ablesales.com.au/indust...e-alternator-22kva-brushless-three-phase.html
Or fit a big engine alternator 12v Dc which might via batteries drivw very large pure sine wave inverter. Not a very good solution.
 
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