Thursday, 18 April 2013

Running an event system from batteries

My outdoor event Print and Viewing Stations run from a battery and inverter system.  The battery supplies the basic power in DC (Direct Current) form and the inverter converts this to AC (Alternating Current ie. mains) 230V that my system components (printers, screens, laptops, etc.) can use. I can also run the system from a standard generator if I wanted to but for one day events the battery solution has some plus points. I don't have petrol, diesel or any other explosive or combustible liquid to deal with, it is silent, it is far far cheaper to run and I can run it without worrying about any deadly fumes it may be putting out. However, unless your needs are very simple then the capital cost of a small (1Kw) no-name brand pure sine wave generator will be far less than your capital cost of setting up a battery and inverter solution.

A battery and inverter solution sounds pretty simple on the face of it but there are a ton of wotchas and gotchas to be aware of. Firstly, you will be dealing with mains voltages on the output from the inverter. If kW and VA don't mean a thing to you and RCD sounds like something your doctor jots down in your notes then get a qualified electrician to help you. Seriously, this stuff can kill you.

Sizing your system is an art and again if in any doubt get some professional help. A lot depends on your loadings and how hard each device is working. Eg. a DNP DS40 printer runs at 20W when idle but pushes up to 330W when printing. To size your inverter and batteries you need to know your peak loads (for the inverter) and your average power usage to work out the required battery capacity. It is also handy to know the start up power requirements of anything you are running as some devices can use a surprising amount of power just to get going before they settle down to their average running power requirement.

The type of battery used is nearly as important as the size of battery used. For our purposes a deep discharge leisure battery provides a good balance between capacity and cost. Specialist deep discharge batteries are available for a price but generally you will find it considerably cheaper to just stay within the limits of a good leisure battery. 

A typical leisure battery should ideally never be discharged to more than 50% of  its capacity. The capacity is usually quoted as A/hr (Amp hours). In broad terms a 12 volt 125 Ahr battery can deliver a current of 1 Amp at 12 volts for 125 hours. That is what the 12v 125Ahr is telling us. It could alternatively deliver a current of 5 Amps for 25 hours (5 x 25 = 125). That is the theory but don't forget we can only use half the available power or we damage the batteries.

Work out your average power usage for the day and once you have an average power usage figure then double it. This covers the 50% maximum DOD (Depth of Discharge). Over discharging the batteries will severely reduce their life. A battery rated at 200 to 250 cycles will probably only achieve half this or less cycles before failing if regularly discharged below 50% of capacity. Ideally, you should also make allowances for the inverter efficiency (typically 85% to 92%) and any cable losses. Quoted capacities for batteries are calculated on a 20 hr discharge rate. You will need to add another 20% (typical value) capacity if you are discharging in 8 hours. Batteries need to be recharged immediately after use or at the latest within 24 hours (this too will have a severe effect on the life of the battery).

Lets use a simple example. I have a printer and laptop and the average power consumption for the two is 60 Watts. Ohms law tells us that Power (Watts)  divided by Volts = Current  (Amps).  For a 12 volt system I can divide the 60 by 12 and this will give me 5 Amps of current being drawn. If I have a 125 Ahr battery  then I can divide this by two (to accommodate the maximum DOD of 50%) and then divide the result by 5 (my current). 

125 / 2 = 62.5 Ahr (usable battery capacity)

62.5 / 5 = 12.5 hours of system use before reaching the 50% DOD.

You should have a correctly sized fuse for the DC side just in case you accidentally short the cables or there is a problem with the inverter. Remember that your cable, inverter and fuse must be able to cope with peak power requirements as well as average power requirements. In our example (when the DNP DS40 printer is actually printing) the peak power requirement would be in the order of 350 Watts. That is nearly six times the average load and the cables, fuses etc. must be specified to handle this and have a margin of safety. Cable sizing is very important. Too thin a cable on the DC side and there is a serious risk of fire and you will lose a lot of power in the cables themselves.

I use a 24 volt system to keep cable diameters down (4 x 12 volt 125 Ahr batteries wired as two batteries in series in parallel with two more batteries in series). This then requires a 24 volt charger and 24 volt inverter. This gives me 24 volt at 250 Ahr capacity. I have a 1 Kw pure sine wave inverter which can handle peak powers of up to 2Kw.

For four reasonable quality leisure batteries , good cables, fuses and fuse holders, a good 24 volt 15A charger, an RCD breaker and a good 1Kw pure sine wave inverter you should budget in the order of a £1000 pounds.

Thursday, 11 April 2013

A prediction - Batteries and Electric Vehicles

I have been doing a lot of work in the last 6 months on moving over from generators (petrol/diesel/LPG) to a battery and inverter solution for outdoor events. It has meant a major re-think on how kit is used and what kit is used. I have been surprised by the huge range of power consumption of screens for example. I know that a large traditional glass monitor uses a lot of power (I am a qualified Micro Electronic Design Engineer so I should know that) but what was surprising was the range of power consumption from otherwise similarly specified LED screens.

To achieve what I wanted to do I have had to replace my monitors, viewing system hardware, print station hardware etc. but the end result is I can run for a day using 4 viewing screens and two printers quite happily (with about 50% of maximum power still available) from 4 largish batteries and an inverter.

This has led to me following some off the beaten track reading on the Internet. It recently took me to a site selling large capacity  Ultra or Super Batteries/Capacitors. These are used to store energy in wind farms and for storing energy from regenerative braking on buses etc. Unfortunately they are very expensive and you need quite a few of them to run a system for any length of time. However, they have some huge advantages over traditional Lead Acid/Gel batteries. They weigh a lot less, they can be charged and discharged hundreds of thousands of times, they can be discharged very quickly (if required) and they can also be recharged very quickly. They work at temperature extremes that a traditional battery cannot begin to match.

Here is a quick link which tells you a bit more about ultra capacitors.

Ok, so I'm going off at a bit of a tangent here but understanding how these capacitors are manufactured triggered a couple of thoughts when I saw the following:

So, here is a prediction. I now believe that within 10 years there will be available Electric
Vehicles (EVs) with a range of at least 500 miles and carrying batteries (capacitors) of a fraction of the weight of current devices. They will support braking and coasting regeneration and will recharge from empty to full in less than a hour. These will be affordable replacements for traditionally fueled family vehicles.

Just put a note in your diary for 10 years time and if I'm wrong you can have a chuckle at my expense.

Footnote: 6 days after I posted this the following was in the news
Super-powered battery breakthrough claimed by US team

Sunday, 7 April 2013

Charging to attend Equestrian Events ????

A recent link on a Facebook page highlighting the difficulties being faced by Equestrian Event photographers prompted me to put into words some thoughts and ideas I have been mulling over for a while.

First thing that came up was Uncle Bob and his camera. I'm not convinced that Uncle Bob and his camera are a huge problem. Definitely a problem but how much of a problem? Yes, it affects sales but if I or a one of the team cannot consistently get a better picture then we should not be out there. I use the word 'consistently' as we should be able to take 100 shots and have 97 at a print standard whilst Uncle Bob will probably carefully sift through his and select the best 10 out of his 100.

Does modern kit make it easier? The camera manufacturers are telling you 'buy our camera and produce pro quality images' so it must be true. If it was that simple then there would not be a profession of photography. So, yes, modern cameras do make our job easier but you still need the underlying skills of a photographer to get the best out of the equipment. As an example, if I was a reasonable rider (I'm not by the way) and you put me on a top jumper with a great saddle and gear would you expect me to perform like a pro jumper?

A good part of the difficulty for professional photographers is that we are in a recession and we are offering 'good' and 'great' images for a tenner a piece or you can have 'not quite as good' for a couple of quid or free. Money is tight and 'good enough' is winning the wallet/purse battle at the moment.

There are some basic costs associated with covering equestrian events professionally. Each photographer will be carrying anything from £1500 to £10k in kit, we may have to set up wireless networks (£1000 each) to get images back to the viewing stations, viewing stations are £250 to £300 each (minimum), print stations (usually a £1000 or more), software, printers, generators, petrol for the generators, marquee, insurance, kit maintenance, consumables stock, van etc. It is a serious investment of capital on our part.

A simple multi discipline event (eg. 3 rings and cross country) typically requires 4 photographers at a minimum of £60 each for the day and usually £80 to £120 with travelling expenses etc. Take it as £80 and with 4 photographer we have spent £320 before we have even taken a penny or taken a shot. Two sales assistants at £60 each and we add another £120 to the equation. So, before we start we need to take £440 to cover staffing and that is before we take into account the other costs already mentioned. Hmmm, maybe this is why we charge for a print or usage of an image.

This can be frustrating at times. An organiser will phone with a 300 entry event. Great we say, we ask some more questions and no matter what we ask it is still 300 riders. Turn up on the day and it is actually 80 riders with multiple entries per rider. At this point every single rider needs to buy an image for us to break even and then the organiser will be stretching out their hand at the end of the day looking for a donation to the club. A busy viewing station does not mean we have actually been busy taking money.

We will be out there in all sorts of weather. Wind, rain, sleet, snow, cold, very cold, brass monkey cold and warm and hot. We will shoot when the light is not ideal because we want to get a picture for you of your day. It is not unusual for a photographer covering cross country for example to set out from the marquee at 8am to walk the course and pick a spot and not get back to the marquee until 6pm. That is ten hours on his/her feet making do with a flask and a sandwich and hopefully finding a bush at some point and doing this even when it is lashing it down one minute and blowing a gale the next.

Ok, this is turning into a book But I hope you are seeing where I am coming from here. This is why we get upset when images we have spent a lot of time and money getting are 'lifted'. Talking of time the typical day for us at an event like this starts at 3 to 4 am packing (after preparing everything the day before) and finishes at about 8pm unpacking the van (for a local event). A long long day. Then we still have to get the images on the Internet and sort out the kits and respond to the emails wanting to know where the images are.

Now, a question for any of you that are riders. If a fee was charged which was part of the registration fee (like the fee for the sound system, ambulance coverage etc.) and Facebook size images were free to download but we could not guarantee that we would have an image of everybody would you pay the fee? We would make best efforts to get as many riders an image as possible and would put a camera at the marquee so we could do a natural light portrait if we have not managed to capture you on the course or in the ring.  How would you feel about this and what would you see as a reasonable charge?

A bit like war and peace now in length for a post but I hope you have stuck through it and would really like and appreciate any feedback (positive or negative). Drop me an email and I will put a selection of views together and update this post with the results.

Update: 4th September 2013
Well, I had one response. The response was positive and agreed that paying a small fee at registration would be a nice way of getting Facebook sized images but that was the only response. I have decided not to cover equestrian events in the future as it is just too difficult to actually recover the costs of attending never mind pay myself a wage.

Thank you for taking the time to read this. John

Thursday, 4 April 2013

A NAS rides to the rescue.

For those who think they don't need backup or can't be bothered or one backup is enough here is a little tale to hopefully make you think again. A NAS is simply a network connected storage box (Network Accessible Storage). Stick some drives in a box give it a bit of an operating system and a network card and charge lots of money for it.

I'm upgrading my main PC and network and have recently stuck a couple of brand new 2TB drives in a NAS box and set it up as a mirrored drive ie. even though I have 2 x 2Tb it sees it as 1 x 2TB and mirrors everything on the first drive onto the second. This means that either drive in the NAS can fail and I still have all my data and can stick a new drive in and the NAS will rebuild the data on the new drive and leave me with nicely mirrored one volume two drives set up again.

Righto, so being a Yorkshire man and sometimes a bit tight. I decided that what I should do (as I have the data on my PC as well) is convert the NAS to a single drive and no mirror and use the drive this would release from the NAS for my new PC build.

Not as straight forward as it would sound as to do this you have to convert the RAID volume on the NAS back to a Basic non RAID volume. Easy enough to do though. As I had all the data on my PC it was just a matter of taking the 2nd drive from the NAS box and repartitioning the remaining drive as a Basic volume. This erases all the data on the drive but not a problem as I have it all on my PC and just need to copy it back on to the now single drive on the NAS. All fine in theory. That is until the drive on the PC packs up half way through writing the data back to the NAS. The chances of it happening are probably small but that is exactly what happened. So, now I have corrupt data on the NAS and a dying disk with corrupt data in the PC. Pretty stuffed at that point you would think. Which is pretty much what I thought and was beating myself up for being a tight git.

But, but , but. Yes, there is a 'but' to this tale.

I built the new PC yesterday and decided (thank you God) that I would use another drive for the Operating System and once that was all installed only then would I use the drive that had come out of the NAS as the new data disk and I would copy the data back onto it from the NAS. But the NAS now has corrupted data on it. Aaaarrrgggghhhh. Was my first thought and my second. Swiftly followed by some choice words as a third and fourth set of thoughts.

Then I remembered something. Something deep and very important. All my data was still on the drive that had come out of the NAS and was still configured as a drive in a Raid array. Allleee blooody llluuulllaa. Now I could take the good drive (with corrupted data copied from the PC) out of the NAS box and put this drive back in and the NAS box would tell me that there was a disk failure but would use the data on this good RAID drive. All my data was safe and sound on the mirrored drive and all I now had to do was stick the drive back in the NAS box that I had converted to a Basic partition and the NAS would rebuild the mirrored RAID onto this drive.

The NAS is chugging away rebuilding the data on the 2nd drive and in a couple of hours I will be back to where I was a few days ago with a mirrored two disk RAID on the NAS. I think I'll keep it like that and invest in a new drive for the new PC.