is a switch needed for a compressor?

Submitted: Tuesday, Apr 16, 2013 at 20:57
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The second switch (15amp 12v) on my compressor has melted. Do I really need a switch? I plug into an Anderson - one each side of the vehicle. Any harm done when plugging in and out when 'live'?

thanks

Markthemilko
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Reply By: Member - PJR (NSW) - Tuesday, Apr 16, 2013 at 21:31

Tuesday, Apr 16, 2013 at 21:31
I don't know about anyone else here but it sounds like the switch may have saved the wiring and/or the compressor.

I wouldn't run one without a dedicated fuse and switch myself.

Ours is mounted in the rear and a 12V run capable of supplying 40 amps has been run to it via a 30 amp switch in the cabin and fused at 25 amps from a separate accessory fuse panel under the bonnet.

What compressor is it and is it portable or vehicle mounted?

Phil

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Follow Up By: Member - Markthemilko - Tuesday, Apr 16, 2013 at 22:13

Tuesday, Apr 16, 2013 at 22:13
Thanks Phil.
It is a Bushranger Super Max (3 years old) and is portable. There is a 30amp fuse in the line close to the battery.

Mark
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Follow Up By: Member - PJR (NSW) - Wednesday, Apr 17, 2013 at 01:51

Wednesday, Apr 17, 2013 at 01:51
Hi Mark

Good. The circuit is fused.

If you look at the specs at Bushranger here it shows that the maximum current draw is 38 amps. That means that even the 30 amp fuse is a tad small. But don't go changing it. The specs may mean the peak current of 35 amps for a micro second at switch on. That's why the 30 amp fuse did not blow. The running current could be around the 15 - 20 amp range and thus too big for the 15 am switch.

So leave the 30 amp fuse in line and get a heavier current switch.

I would still use a switch. Do you turn 240 V power points at home off before putting the plug in and out? Same reason. Surging and sparking. Admittedly the voltage is different but the lesson is the same. Cleaner and safer.

Phil
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Follow Up By: Member - Markthemilko - Wednesday, Apr 17, 2013 at 12:57

Wednesday, Apr 17, 2013 at 12:57
hi Phil,
Yes I was told along time ago to always switch off before removing the plug!

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Follow Up By: Member - PJR (NSW) - Wednesday, Apr 17, 2013 at 13:40

Wednesday, Apr 17, 2013 at 13:40
I installed six of these Cole Hershey rocker, 30 amp switches in the console of the 100 series. See link below for them. Good job also Gee ain't I humble. Our compressor uses 25 amps when running so I anly needed a 30 amp switch. Higher current relays for lights etc are mounted next to the dedicated fuse box under the bonnett near the accessory battery.

Two colours are for: red are for the lockers, two orange ones for the Redarc relay and air compressor and the two green ones are for lights. All are illumited with the dash lights. On off status/indication comes from the individual switched 12V (not dimmed with the dash). The panel has its own loom from a fuse box in the front and can be unplugged and the whole console then removed from the car.

Cole Hershee illuminated switch

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Follow Up By: Member - Markthemilko - Wednesday, Apr 17, 2013 at 22:52

Wednesday, Apr 17, 2013 at 22:52
Thanks Phil.
You did a good job - they look very smart!
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Reply By: Allan B (Member, SunCoast) - Tuesday, Apr 16, 2013 at 21:32

Tuesday, Apr 16, 2013 at 21:32
Mark, you could do away with the switch and simply plug & unplug the Anderson to control the compressor. However you may cause some minor burn damage to the Anderson contacts by doing this.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Apr 16, 2013 at 21:55

Tuesday, Apr 16, 2013 at 21:55
Mark, Perhaps I could add that high-current switches in small format are not easy to come by. An alternative is to fit a high-current relay controlled by a 10A switch.
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Follow Up By: Member - Markthemilko - Tuesday, Apr 16, 2013 at 22:25

Tuesday, Apr 16, 2013 at 22:25
Thanks Allan.
Yes you're right about high-currant switches being hard to come-by!
I have belatedly realised that this Bushranger Supermax would need a 40amp switch! It used to have a 50amp fuse, but the housing cracked so I discarded it.

regards
Mark
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Follow Up By: Member - Scott M (NSW) - Tuesday, Apr 16, 2013 at 22:33

Tuesday, Apr 16, 2013 at 22:33
Mark, raisins or sultanas ?

Sorry, couldn't resist it......
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Follow Up By: Member - Markthemilko - Tuesday, Apr 16, 2013 at 22:45

Tuesday, Apr 16, 2013 at 22:45
neither - black currants!
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Follow Up By: Member - Scott M (NSW) - Tuesday, Apr 16, 2013 at 22:55

Tuesday, Apr 16, 2013 at 22:55
just make sure you don't mix the black currants and the red currants
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Follow Up By: Member - Markthemilko - Wednesday, Apr 17, 2013 at 12:52

Wednesday, Apr 17, 2013 at 12:52
I'll try not to!
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 03:05

Friday, Apr 19, 2013 at 03:05
Hi Mark

What Allan suggested about using a relay is spot on.

You may recall the switches in my photo further up this thread. Four of the switches control four relays relays under the bonnet.

It means that the wiring to the switches only has to carry the small switch illuminating current (negligible for the LEDs) and the operating current of the relays (1/4 amps each relay). I used a 5 amp fuse. This small current means that the wires can be small and easy to install especially if you want it removable with a plug and socket as I have done.

The relays under the bonnet do all the "heavy" work. The relay "outputs" are fused separately according to their role. No big heavy wires or current to the cabin or console. Safe!

Phil

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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 03:19

Friday, Apr 19, 2013 at 03:19
PS If you look up those switches at the Cole Hershey site you will see that they are rated at 30Amp. They were used because they are reliable, look good and had the correct colours. Not for the high current capability.

Missed this in my earlier post.
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Reply By: Allan B (Member, SunCoast) - Tuesday, Apr 16, 2013 at 22:43

Tuesday, Apr 16, 2013 at 22:43
Mark, There is a way to kill two birds with one stone. Use a circuit breaker such as in the photo below from ABR Sidewinder (Business Member).
The breaker can be operated as a switch and also protects against excess current.
These particular breakers have very convenient tunnel-type terminal connections not needing lugs. The terminals are fully shrouded and the breaker is easy to mount.
There are six of them in my Troopy.

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Follow Up By: Member - Markthemilko - Tuesday, Apr 16, 2013 at 22:48

Tuesday, Apr 16, 2013 at 22:48
Thanks Allan. I like the look of them, definitely the best way to go.

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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 07:58

Friday, Apr 19, 2013 at 07:58
Hi Allan

Is that little coloured button a quick "release" actuator? How is it mounted?

No details on the sidewinder site that I could see.

One of them would be handy for the feed to an accessory fuse panel that I installed for all the 4WD accessories that we want to add. Things like fridges, compressor, lights etc. I used a ten way Jaycar fuse panel with 30 amp per circuit one with LEDS from Jaycar. The breaker may be a bit low in rating for me but at the moment the load is way under it's rating.

Phil
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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 09:39

Friday, Apr 19, 2013 at 09:39
Yes Phil, The lever is the Reset or Close and the small button is the Manual Trip or Open. The mounting is through two 4mm holes in the flange just visible in the photo.


I have used them in the Troopy, individually for the battery connections, HF radio, compressors, inverter and as feeds to the several fuse panels for smaller auxiliaries. When not "on the track" I manually trip these breakers as an added safety measure.


ABR Sidewinder only has them in 40A and 60A which were adequate for me. I seem to recall that I have seen them on another site at 80 or 100A but cannot remember where.


What I particularly like about these breakers is that they have tunnel terminals with hex-key grub-screws and brass sleeve inserts to accommodate smaller cables. Then the whole terminal is shrouded with a screw-on clear polycarbonate cover. No need for lugs and no exposed live terminals as in some breakers with stud terminals.


Incidentally, I believe that your arrangement of using control switches with remote relays is the way to go. As well as allowing the use of lower rated switches, it keeps the heavy current cabling out of the cabin and reduces losses in cabling. Good practice indeed.


Incidentally, getting back to your original post, in that fire in your mate's vehicle, was that battery cable appropriately fused at both ends? Probably not considering the severe outcome of a short to earth.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 09:45

Friday, Apr 19, 2013 at 09:45
Sorry Phil, that question in my last paragraph belongs on the thread about "Issues with voltage drop and melting wires". I'll re-ask it on there.
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 10:50

Friday, Apr 19, 2013 at 10:50
I will answer it in both threads.

In a word, no!! No fusing either end. I don't even think there was a device like the redarc. But it was the positive to earth in the back and a long run for the rear negative that allowed the current to go and burn out all the gear in the front. It wasn't protected.

Neither is the cable between my two accessory batteries next to each other under the bonnet. No panels or anything to go through. Yep. Sure is crowded. The two accessory batteries are isolated from the cranking battery though. We used the 200 amp redarc isollator. And that is the one controlled via the "small wires" to the switch on my console.

I agree to keep the big currents our of the cabin. No worries going through bulkheads and no sharp metal edges to worry about. And as a bonus no more holes for water to come into the cabin at water crossings.

I have been keeping my eyes out for just a breaker. Thanks. The fuse panel has a 100 amp and 30 amp per circuit limit so I need around 80 amp for the battery connection. But I need to do some mathematics first (note that word is not math!!!). Excellent. Thanks.

I won't use the small holes though as the idea is to tidy stuff up. I cannot stand untidy work. Easier to fault find a tidy installation. I still have three spare unused fuse slots so I should be right. But never underestimate what the boss wants in the car. She was looking at a small 15 amp oven last night. ???????? But she's worth it so we shall see. I already carry a toilet for her. But then again an oven can hold some "dogs eyes" for me. Hmmmmm!! But I will draw the line at cupachino machines though.

All good stuff and agin thanks for the idea.

Phil

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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 11:10

Friday, Apr 19, 2013 at 11:10
Phil, ..."I won't use the small holes though as the idea is to tidy stuff up"...
Huh?? I'm not with it. How would you mount it then?
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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 12:34

Friday, Apr 19, 2013 at 12:34
Phil, ..."I won't use the small holes though as the idea is to tidy stuff up"...
Huh?? I'm not with it. How would you mount it then?
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 14:16

Friday, Apr 19, 2013 at 14:16
"I was talking about the "tunnel terminals with hex-key grub-screws". I would mount it using "two 4mm holes in the flange".

Easy confusion Allan.

The idea of the fuse panel is to run the "smaller cables" from accessories to the panel and pick up power through a fuse. Stay away from the battery as much as possibe. Ideally the only cables on the battery terminals are the car distribution system, the alternator, winch and the cables to additional fuse boxes. The operative word is "idealy".

Time for me to do some house work and then get pack a snack for the footy tonight. My son and his son are going to the Australia versee NZ Anzac test at Canberra Stadium. I like that. Three generations.

I never knew my grandparents they died very early. Both my own and my wife's parents all died before we were married and had children. So things like family only 4WD treks (Cape York photo - CREB) and the footy are precious.

Catchya

Phil

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Reply By: BluePrint Industries Pty Ltd - Wednesday, Apr 17, 2013 at 14:30

Wednesday, Apr 17, 2013 at 14:30
Hi Mark,

I would think that if your melting switches maybe you need a relay rather than a bigger or better switch.

Most compressors should have a relay installed in them but I have seen a lot that do not despite what the sticker on or advertising brochure says.

Regards

Kurk
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Follow Up By: Member - Markthemilko - Wednesday, Apr 17, 2013 at 22:44

Wednesday, Apr 17, 2013 at 22:44
ok, thanks Kurk.
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Reply By: The Bantam - Thursday, Apr 18, 2013 at 21:42

Thursday, Apr 18, 2013 at 21:42
A lot of people under estimate the current drawn by compressors......even the current written on the plate or in the manual my be well and truly understated.

When compressor starts there will be a quite high surge...sometime twice or three times the running current......the current draw will then settle down, but as the pressure ( or head) the compressor pushes increases the current drawn increases.

I have one compressor that I baught from Aldi for diddley squat......similar to many others

It did not work out of the box...but that is a different issue....it was a silly wiring fault.

While I was fixing it A few things became apparrant.....

When I got it going the factory fitted 25 amp blade fuse blew a replacement 30 amp blew nearly as quickly.....so out with the clamp meter.....running at 30psi this thing was drawing over 35 amps....
The limit of the standard blade fuse format is about 30 amps and many blade fuse holders are only good for 20 amps.

Any way
These things draw a lot of current and the switch on and switch off surges can be realy hard on switch contacts.

They need to have a relay doing the switching...and a fairly solid one....most of them have a relay inside the housing if they have a switch on the body.

The factory relay in this unit was only a standard 30 amp horn relay..and a cheap one.

To cut a long story short...the unit has been given the treatment.
Heavier cable, a maxi blade fuse holder with a 40 amp fuse, a 60 amp horn relay and a remote control.

There was not enough room inside the case, so the relay was mounted on the base plate.

I have a remote control that can be plugged in so that I don't have to go all the way back to the compressor or the outlet to switch off in between checking pressures and moving to the next tyre.

I have a good second compressor for the less than $20 & few bits & time it cost me.

If ya switching any more than 10 amps, best to use a relay.
Don't forget to allow for the start up surge and the disconnection spike working the contacts hard.

As for using a circuit breaker as a switch.......not realy a good idea.....circuit breakers are not designed with frequently repeated operations in mind.
Keep using at a switch and it will get worn and not work too well as a circuit breaker.

cheers
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Apr 18, 2013 at 23:15

Thursday, Apr 18, 2013 at 23:15
Bantam,


The particular circuit breakers I referred to above actually have contacts rated to carry 150 Amps.
They are available with overload settings of 30, 40, 60, 100 & 150 Amps although all have the same 150A rated contacts.
They are specified to safely break the circuit with fault currents exceeding the rating by 250%, that is a prospective fault current of 375A.
They are rated in excess of 2000 switching operations at rated current.


Clearly, if they are capable of not only acting as current carrying and current limiting overload circuit breakers at high currents they are also eminently suitable to repeatedly switch typical compressor currents of 30 to 40 Amps.
I also suggest that their occasional use as a compressor control switch is unlikely to exceed their rating of 2000 operations especially if one simply allows the compressor to run free to air whilst "checking pressures and moving to the next tyre".


Bantam, if you are not in possession of the facts and do not have specific information to the contrary, I suggest that you keep your opinions to yourself, respect the information provided, and refrain from refuting the advice I have given.
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Follow Up By: The Bantam - Friday, Apr 19, 2013 at 00:21

Friday, Apr 19, 2013 at 00:21
I AM very much in possession of the FACTS.
I know the type of breaker I use them

2000 operations is not a very high number of operations for a switch.

that is only 20 days at 10 operations a day....for some that is a design life span less than a single trip operated as a switch.

A quality switch or relay should be in the 10s or 100s of thousands of cycles design life span.

Circuit breakers SHOULD have contacts rated very much higher than their rated current...

further as far as circuit breakers are concerned those fault current ratings quoted look pretty piss weak, when you consider most din rail breakers in the 5 to 40 amp range are rated to inturupt fault currents far higher than 250%....think in terms of 100 times rated

These are not high repitition, high quality breakers....they are a low cost item and a fair thing when used as designed.........so it is very much wise to stick with the generally accepted engineering recommendation and practice of not using circuit breakers as switches

As I say I use these or very similar items....the mechanical feel alone tells me that with excessive wear they will fail to,latch and long before that, wear in the latching mechanism will result in them failing to hold at the rating specified.
If indeed the contacts are only rated for 2000 operations, with frequent and repeated use under load the contacts may indeed weld closed, or become high resistance.

If we are to rely on circuit breakers to work to specification as circuit breakers, it is wise to adhere to the generally accepted engineering recommendation and practice of not using them as switches.


Further...I have a switch on my compressors so that I can turn them off and I do not have to deal with a pissing hose while I connect and disconnect.

In addition, many of these compressors have poor duty cycles and no thermal protection device.... Thus turning the machine off while checking pressures and moving from tyre to tyre may very well extend the life of the machine.

cheers
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Follow Up By: The Bantam - Friday, Apr 19, 2013 at 00:24

Friday, Apr 19, 2013 at 00:24
sorry unable to edit 200 days at 10 operations a day.

I'd put 20 operations on every time I reinflate...what it some mates use my machine

2000 operations still would not last a trip for some.

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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 08:47

Friday, Apr 19, 2013 at 08:47
Bantam if you were more fully familiar with technical specifications of electrical equipment you would recognise that a manufacturer's rated "2000 operations" of an over-current circuit breaker relates to interruptions at fault current values where the contacts are extremely stressed. Operations at lower switching currents or simple isolation would be many, many times more than 2000.
These are DC consumer products not heavy duty industrial breakers intended for mains operation with extreme prospective fault ratings. Keep it within context. Look it up on Sanyang Electric Company site yourself.
I'm sure you could positively contribute here without big noting yourself all the time. It gets a bit onerous mate. Add to the discussion rather than refute and pontificate over the top of earlier contributions. And try learning from the older, wiser and more experienced.
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 14:31

Friday, Apr 19, 2013 at 14:31
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Follow Up By: The Bantam - Friday, Apr 19, 2013 at 14:33

Friday, Apr 19, 2013 at 14:33
The fact remains, it is a well understood and universally accepted principle that you do not use circuit breakers as switches

What I am posting is exactly in context and on subject and pertenent.

2000 operations no matter which way you look at it is a very low number of cycles.

remember this is a situation where there are high start up currents associated with a motor.....start up currents that may be 200% or 300% of the steady state current of the machine.....steady state current that may already be underestimated.

Every closure under load in this situation may indeed see current flowing that approximates the 250% claimed fault current rating

Switches and relays are designed for frequent and repeated operation under load circuit breakers are not.

This is not a switch and should not be used as one.

It gets a bit onerous MATE when I make a simple well founded comment that relates to well understood sound engineering practice and YOU mount a personal attack directly accusing me of not knowing what I am talking about and big noting my self.

I am not the big note in this situation.

cheers
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Follow Up By: Member - PJR (NSW) - Friday, Apr 19, 2013 at 14:40

Friday, Apr 19, 2013 at 14:40
Allan I don't know about you but I thought that we were avoiding the nitty gritty electronic details and staying where most readers would understand and get something positive out of it. Otherwise we run the risk of talking to thin air. Not a bad idea sometimes.

I have done enough of that. Besides the footy calls.

Phil.

If you are watching we three will be right at the fence behind the Kiwis. I am the grey haired gentleman. Er bloke that is!!!
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Follow Up By: Allan B (Member, SunCoast) - Friday, Apr 19, 2013 at 15:02

Friday, Apr 19, 2013 at 15:02
Yes Phil, It's easy to get dragged into arguing 'academic' points of view which wander well away from the simple practical issue of the original post and responses. Over and Out!
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Allan

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Follow Up By: oldtrack123 - Tuesday, Apr 23, 2013 at 12:18

Tuesday, Apr 23, 2013 at 12:18
HI
One practical hint for a simple tyre compressor[no reciever / tank] is never try to start while the hose is connected to a partly inflated tyre

The Surge/start current will be far above normal & the motor may not even be able to start.

The wiring needs to be adequate to cope with the start current or VOLTAGE drop may add to the problems

A stalled motor will draw many many times its normal run current
PeterQ
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Reply By: Member - graeme W (WA) - Saturday, Apr 20, 2013 at 22:21

Saturday, Apr 20, 2013 at 22:21
Hi.
Wire your compressor as close as practical to the battery you will use,then run an air line to a convienent place to plug in your air hose. Use at least 8b@s cable through a relay that matches or is bigger than the current draw of your compressor. Then run some cable to a dash switch this can be lighter as it only switches the relay. Use good connectors and crimp with a little copper showing so you can run some solder down each crimp. No voltage drop and no switches to melt which will mean your compressor will run at full speed. Use a suitable fuse close to the battery.Also pays to use the starting battery for this exersize and keep the car running when pumping tyres as if for example its night and all lights and perhaps spotties are on your auxillary battery may not be charging at the time.My compressor draws 35 amps on its own.
cheers Graeme
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Follow Up By: oldtrack123 - Tuesday, Apr 23, 2013 at 12:22

Tuesday, Apr 23, 2013 at 12:22
HI Graeme
X 2

PeterQ
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