Leisure Battery Advice needed

[Emzil]

Hi everyone, I'm hoping that some experienced folk might be able to answer a few questions for me.
I have started trading at some events doing airbrush tattoos and was wanting some advice on leisure battery's.
I'm wanting to run some energy saving light bulbs for a couple of hours each night probably 3x20watts and I also want to run a very small air compressor which will be used on and off all day. the air compressor says its 1/8th horse power and it has a 3lt air tank fitted so the compressor only powers up when it needs to fill the tank. Is it possible to run this little compressor from a leisure battery?
What kind of set up would I need to get lights and compressor powered for a weekend. I'm in a normal transit van not a caravan if that makes any difference.
Thank you all in advance for any advice you can offer.

 

[ProfJohnL]

Hello Emzil.

Yes it is possible to run your equipment from a battery based system. I assume the compressor and lights are actually designed to use 230Vac power, in which case you will need battery and power inverter. However How big each of these needs to be depends on more detail about how long you actually use the equipment for. How frequently and long the compressor needs to work every hour. And how you will recharge the battery.

Please don't go and buy anything yet, becasue there are some important considerations about the type and size of batteries and inverters that you will need, and I will cover that in more detail when I have the necessary details itemised below.

I would make one observation now - you tell us you will use 3x20 W light bulbs. My guess is these are Halogen bulbs to light your client's skin where you are working. If you intend to use these on a mobile booking, you will find that they are probably the biggest power consumer. It will make quite a difference to the size of battery you need if you can change them to even more efficient LED (and long terms cost effective) bulbs.

In the meantime please come back with more detailed information about how how many hours you will be offering the service, and how long in every hour does the compressor actually run, and just confirm the bulbs and how long you will be using them.

 

[Emzil]

Hi John,
Iv had a look at the bulbs I was thinking about and i am looking at florescent bulbs rather than halogen ones. They are 45w CFL (studio bulbs) and will only need 2 of them. Usage wise probably a maximum 4 hrs over 2 days (a couple hrs each night). I had tried some of the led strip lights a friend loaned me with a power pack but although they were bright they didn't cover much distance so still struggled to do detailed work.
The air compressor would be used all day 12 hours each day. its difficult to work out how many times it would be going on and off over the hour as it wouldn't be constant, it is only used for 2-3mins each tattoo. but a rough guide at my busiest times id be using it maybe 20mins over an hour, so maybe 3-4hrs each day spray time (running time). so for 2 days 6-8 hrs?
Yes everything is normal 230v household plugs.
Im not sure on charging is it best to leave in the van and charge from the van or best to get a charger i can hook it to at home? I guess my car battery charger would not be a viable option?
Thanks John

 

[ProfJohnL]

Hello again Emzil.

Now I have the chance to look at your revised information and done some calculations, I make the following recommendations:

You will need a minimum of a 110AH leisure (caravan) type battery to provide the source of power you are looking for.

You will need a 1500W 12Vdc to 230Vac inverter with a "Pure" or "Full" sine wave output - I will explain why below.

I would also suggest you arrange for 50W or bigger Solar panel and charge regulator to help keep the battery charged during the day.

When considering specialist equipment for a commercial venture, it's particularly important to consider it reliability. And for that reason I have rounded up several of the values you have given or are calculated to give a greater margin of operational performance.

I'm sure someone will wonder why I have recommended such a big inverter, when the compressor is only a 1/8HP unit. The reason is electric motors are usually shown with their normal running current or power in this case you have 1/8 HP which is the equivalent to 93W (Watts), This needs a current of about 0.5A (Amps) at 230V. What this doesn't cover is the fact that when ever an electric motor is powered up from standstill, the motor will actually use a lot more current just to get it turning. The current drops back to the steady state value as the speed rises.

The surge current for an unloaded motor is usually assessed at about 4 times the steady state current, but becasue most compressors with auto switches turn on when there is still considerable pressure in the receiver tank, this additional pressure increases the load on the motor which increases its surge current, and I am basing my recommendation on a factor of 10x steady current which is going to be in the order of 5A. at 230V. A simple calculation will tell us the required wattage that represents VxA = W; 230 x 5A = 1150W (Watts) or 1.15kW.

We also need to consider the load the lamps will add, which from your specification is 2 x 45W = 90W so that is a total peak power 1.24kW. The inverter needs to be big enough to cope with this amount of power conversion without stress.

You may well find some inverters are specified as having a 1kW capacity with 1500kW overload margin, and on the face of it might be suitable for you, but I would advise against them, as the peak loading they expect is very infrequent, whereas yours is going to be several times an hour.

Inverters of more than 1kW capacity are typically available in 1 2 and 3kW models. You may be lucky and find a 1.5kW model but in my view that is the minimum size you should be considering.

I have specified a "Full" or "Pure" sine wave inverter becasue the output wave form matches what we get from our domestic mains supplies. Quasi and modified sine waves have nasty transient wave shapes and these reduce the efficiency of motors and transformers. You can sometimes hear motors and transformers buzzing or "singing" on these modified outputs, They usually become hotter, and sometimes wont work at all and will ultimately burn out earlier. So only consider Pure or Full Sine wave output inverters.

There is a trade off for using a pure sine wave inverter, The inverters efficiency drops to something around 67%, so we need to add about 1/3 more to battery capacity to cover for the inverters inefficiency.

So to work out the battery capacity you need, we have to add all the Watt Hour (WH) power demands together for the two days you have specified.:-

90W of lamp for 2 hours per day for 2 days = 360WH
93W Compressor for 4 hours per day for two days = 744WH

Grand total = 1104WH
Add 1/3 to cover inverter losses = 1468wh or more conventionally 1.47 kWH

This will require a 12V battery to be able to supply 122AH (Amp Hours) of capacity. You can get leisure batteries of upto 220AH but these are quite expensive.

However there is an alternative strategy, and that is to use a solar panel in conjunction with a smaller battery. This would have three principal benefits, firstly it will to partially top up the battery during daylight hours. This will means you would almost certainly be able to use a typica 110AH caravan battery, which is smaller and more more manageable. Secondly it will help to ensure the battery's terminal voltage will be above the inverters cut off value, and thirdly It may extend the number of hours you could trade in summer.

A minimum panel of 50W but the bigger the better, again for reliability and longevity of the battery the panel would need a charger regulator.

Another power saver could be looking at LED lighting which could see you lighting power needs drop to about 20W. Don't look at led strings but more at the replacement spotlight GU10 fittings. etc.

I wouldn't recommend using ebay to source an inverter, you would be better going to a canal boat or motor home specialist, again for reliability and spares and service when its needed. This wont be a cheap exercise.

As am alternative solution, You can certainly get 12v LED lights and It would not surprise me if you can't get a suitable 12V compressor . This would negate the need for an expensive inverter, But I would still suggest you consider a solar panel to keep the battery being at least trickle charged.

 

[Emzil]

Wow thank you so much John, this has given me plenty to think about.
The good news is it will come within my budget and a lot quieter than a generator which would have been my alternative.
One last question on charging......if I was to charge the battery at home could I use a caravan hook up lead to the house mains? obviously with the correct adapter plugs.

Thanks again John you made things much clearer.

Emma

 

[WoodlandsCamper]

One last question on charging......if I was to charge the battery at home could I use a caravan hook up lead to the house mains? obviously with the correct adapter plugs.

Click here

 

[ProfJohnL]

Hello again Emzil.

Just a few of other points, which you should be made aware of:

Lead acid batteries must be secured so they can't move when in transit. They should also be contained in an enclosure that is only vented to the outside, as the can under some circumstances produce hydrogen gas which is ignites and burns vigorously. The connecting cables should also be fused to protect the wiring in the event of a fault.

Earthing.
Even though the inverter is not connected to the mains supply, it will produce potentially lethal voltages. And especially where you or your clients may come into contact with equipment, there is the small possibility the equipment may carry a lethal potential. For this reason the system must be properly earthed, and you will need to seek advice on how to ensure this. Also do ensure you have the proper insurance for the business.

In terms of installation, If you go with the inverter idea, It's important to keep the thick 12V cables between the battery(ies) and inverter as short as possible, So I would suggest installing both these parts inside your vehicle, and if you need an extension to get power to your working location use camping type extensions with the RCD protected 13A sockets in a shower proof housing. Like this one
http://www.towsure.com/camping-site-mains-supply-unit-3-outlet

You could permanently mount the solar panel to the roof of the van, then the whole system is integrated, and ready to run at a moment's notice. It should also be possible to arrange for the vans engine to charge the battery when its running, using a typical caravanning split charge relay.

They do cost more but several of the Marine inverters also include a good quality mains charger. This negates the need to set up separate chargers. It ha the benefit of making the system act like an uninterruptible power supply. This would allow you to use mains power if it's available or it will switch over to battery power if the mains is interrupted or simply not available at your location. This could be useful at home in a power cut!

 

[Parksy]

To add the the good information already given, don't fall for the ''it must be better because it cost more'' trap with regard to a solar panel. Most of them are manufactured in China and re-sold here often at a premium when it comes to the leisure industry, but there are no moving parts to wear out and a 12v 100 watt solar panel from E-Bay should fit the bill if you use a good tracking current regulator which is important.
MPPT regulators can be bought from around £70 upwards depending on the amperage and any solar panel can be freestanding if you make a stand from waste water pipe tubing and a couple of push fit elbow joints all fastened to the panel using cable ties