Solar power in garage?

[sjmmarsh]

Having moved house and now keeping the Caterham in a lockup without power, I have added a 20W solar panel to the roof, charging a 120Ah leisure battery feeding a 2000w power inverter to give me mains power to run lights, chargers and power tools.

 

All seems to be well, except the setup doesn't have enough oomph to run the Aldi compressor (1.8 hp). It seems that the initial power drain on start up exceeds the momentary 4000W loading that the inverter will support.

 

1) Has anyone managed to run a compressor on such a set up?

2) Is there any way to work out what size inverter is needed?

 

Oh - and if you are thinking of doing this yourself, total cost for the panel, controller, battery and inverter was just over £300.

 

Steve

[techbod]

Having been down the same route myself (though my solar setup was mainly for running lights and much lower wattage tools) the thing I would comment on is the output of the inverter. Unless it is a true sine wave type, the AC output is often a very loose approximation of a mains output - often described as a 'modified sinewave'. When put on a scope, my first one was nearer a square wave than sine wave .

 

Whilst devices with switch mode powers supplies didn't seem to care and would run of it quite happily, I destroyed a decent drill that just found the output to 'dirty' for it.

 

Running AC motors of modified sine wave inverters might be a bit hit and miss - it might work, it might run badly, it might not run at all. IMHO of course.

 

(Of course, if you have a pure sine wave inverter then none of this applies...)

 

 

Edited by - techbod on 16 Sep 2010 00:32:02

[sjmmarsh]

Thanks techbod.

 

I don't know which I have, but looking at the prices of pure sine wave inverters (6 or 7x what I paid), I suspect I will have a square wave jobbie.

 

Is anybody interested in a lightly used compressor + tools?

 

Steve

[jackb_ms]

I am looking at a compressor + tools! 😬

what kind of size is it?

 

Don't knopw if SWMBO would agree though

 

 

Jack

 

Emily, The Very Yellow 21

 

Edited by - jackb_ms on 16 Sep 2010 09:23:57

[techbod]

Don't give up on the compressor just yet.

 

It might be trickier than just plugging it in but have a look round the web first and see what other people have done to get a compressor running of a modified sine wave type inverter.

[sjmmarsh]

I now have a pure sinewave inverter 2000W/4000W. It still won't run a compressor, but the other motor driven things run much quieter now. 

Still looking for a way to get it to work.  It is one of the Aldi specials - 2.5Hp or 1.87Kw. I suspect the start up current is too high, but some do seem to run looking at YouTube  

Steve

[Jonathan Kay]

Why would a compressor take more power to start it than to keep it running? Has it got a big flywheel? If so is it accessible?

Thanks

Jonathan

[RFF]

You could consider the installation of a soft start unit on the compressor unit. This will limit the inrush of the start current which is approximately 4-6 times the running current, which occurs only momentarily on start up.

There is a point when the expense of the additional equipment is greater than the purchase price of a petrol driven compressor!

Robert.

[Nigel Fox]

I wonder if your battery is big enough. 4000W at 12 Volts would need over 300 Amps!

[Clousta]

Steve,

My first thought when reading your set up was to put a second battery in parallel.

[Roger Ford]

Undo the drain bolt on the bottom of the compressor (letting any stored air out). It will then require less effort to get started. Once started, do the drain bolt up again and it will run up to full pressure.

Of course you have to do this each time it starts up, so not much use for tools which use lots of air and require the compressor to restart regularly.

This is a trick we learned in my motorcycle racing days, when we had to run compressors from generators with marginal capacity. I used to run a 25 litre compressor from a 2KW gennie, so if your inverter is capable of 4KW it ought to be able to start a fairly hefty compressor.

Why would a compressor take more power to start it than to keep it running?

Because it's trying to compress air without the rotational momentum it has when it's running.

[Jonathan Kay]

Thanks.

That's why I asked about the flywheel, and that's the same as your point about rotational momentum. See also starting Diesel engines and "dropping it on the decompressor".

Jonathan

PS: Anyone know how they start big marine Diesel engines when everything is dead and cold, without looking it up?

[Blue C7]

Compressed air

 

[Piers300]

Hi Jonathan

Stating Marine Diesels in a dead ship condition. My company specialises in the manufacture of Hydraulic, Air and Spring starting systems specifically for this requirement. Small engines use Spring starters and larger mainly hydraulic and air systems. If the vessel is classed, the it has to have emergency starting. See our web site: www.ipu.co.uk and finding Starting Division.

Piers

[Jonathan Kay]

Our hospital chief engineer was a great guy who had spent his early career on merchant ships. I once asked him at lunch how they did it after it occurred to me that lead-acid batteries and rather large electric starter motors might not give the required reliability...

But I'd never heard about spring starters. Thanks. How about one of those on the little compressor?

Jonathan

[Piers300]

Jonathan - We do spring starters for diesels up to about 7 Ltrs, so 200/250 BHP. Once the engines get larger, then it is hydraulic start up to around 2000 Bhp, so something like a Caterpillar V16 running at 1500 rpm. The really big slower speed propulsion engines have either an Air starter motor on the flywheel or Direct air injection right into the cylinder head. However, these need a fully charged air receiver to start and the compressors are normally electrically driven.

However, nothing will start if the ship is dead, so all Classed Vessels (i.e Lloyds, DNV, ABS etc etc) have to have an Emergency generator that provides light and power to get the ship started in an emergency. The emergency genset is not meant to be used for anything else, but will run in parallel with the main auxiliary gensets once they are up and running to transfer load without a break in supply.

This emergency genset has two methods of starting and what is called a twin flywheel housing, so it can have two starter motors fitted, being Electric and Hydraulic, or air and hydraulic ect. The Hydraulic system is pressurised and can be hand pumped (hard work) or engine driven to re-charge and has a number of hydraulic receivers based on the number of start attempts required by the Class Society. It will hold pressure for years. In two previous jobs, I used to make these generators. Now I just do the control systems for the main and emergency gensets.

Piers