TaxiDriver Posted June 5, 2013 Report Share Posted June 5, 2013 (edited) If a piece of medical equipment will run of a 12v supply and requires 2.5amps...... . How big a leisure battery will I need to run said piece of medical equipment for two nights of 8-10hrs ?? Also, On two core cable(12v) is it usual that the cable with the stripe is the positive (+) It's an Australian manufactured machine, They wire it up for 240v UK mains but the 12v is wired for Australian std whereby the polarity is reversed from UK so they don't import the 12v leads hence I've had to buy the bits from Maplin to make one up. Edited June 5, 2013 by TaxiDriver Quote Link to comment Share on other sites More sharing options...
old rooster Posted June 5, 2013 Report Share Posted June 5, 2013 Multiply the amps by the hours so worst case 2.5 x 20 = 50Ah theoretically but don't rely on a 50Ah battery as that would be expecting 100% efficiency. I'd go for something like 75Ah personally. As for polarity it would be a bit of a guess given the info you've provided. If it is medical equipment it is very likely fuse protected so reversing polarity shouldn't kill the thing, just possibly blow the fuse. Quote Link to comment Share on other sites More sharing options...
Chris Bb Posted June 5, 2013 Report Share Posted June 5, 2013 Will you be recharging between uses? If so, 2.5A x 10h = 25Ah + 25% contingency = 30 - 35Ah minimum. If not, 2.5A x 10h x 2 = 50Ah + 25% = 60 - 65Ah minimum. Black strip usually = positive. I don't understand how the Australian standard is the opposite of UK. Unless in a caravan or some such, why not use it on 240V? Hope that helps a little, but I'm not a qualified electrician. Quote Link to comment Share on other sites More sharing options...
old rooster Posted June 5, 2013 Report Share Posted June 5, 2013 Will you be recharging between uses? If so, 2.5A x 10h = 25Ah + 25% contingency = 30 - 35Ah minimum. If not, 2.5A x 10h x 2 = 50Ah + 25% = 60 - 65Ah minimum. Black strip usually = positive. I don't understand how the Australian standard is the opposite of UK. Unless in a caravan or some such, why not use it on 240V? Hope that helps a little, but I'm not a qualified electrician. Not sure where you dun your maffs but I make 25% of 50 to be 12.5? so in your second suggestion the total would be 62.5 total minimum? I guess the info in both posts is near enough to give the OP an idea of what he needs. Quote Link to comment Share on other sites More sharing options...
Chris Bb Posted June 5, 2013 Report Share Posted June 5, 2013 Not sure where you dun your maffs but I make 25% of 50 to be 12.5? so in your second suggestion the total would be 62.5 total minimum? Which is why I said 60 - 65, I don't believe you can buy a 62.5Ah battery but I stand to be corrected. Oh, I just have been. Quote Link to comment Share on other sites More sharing options...
TaxiDriver Posted June 5, 2013 Author Report Share Posted June 5, 2013 In Oz std the outer part of the socket is positive and the inner pin is the negative whereas the UK has centre pin + positive I need to run the machine for the 2 nights that I'm at this weekends Catton Hall PW Rifle shoot, so, I think it's unlikely that I'll be able to charge the battery in between the 2 nights use. Simpler but more expensive would be a 12v - 240v inverter but I don't have/can't afford one of them. Quote Link to comment Share on other sites More sharing options...
old rooster Posted June 5, 2013 Report Share Posted June 5, 2013 In Oz std the outer part of the socket is positive and the inner pin is the negative whereas the UK has centre pin + positive I need to run the machine for the 2 nights that I'm at this weekends Catton Hall PW Rifle shoot, so, I think it's unlikely that I'll be able to charge the battery in between the 2 nights use. Simpler but more expensive would be a 12v - 240v inverter but I don't have/can't afford one of them. If you used an inverter to run your device you would eat the battery. Basically I would imagine the machine runs on 12 volts and has an internal transformer to take the mains down to that for normal use. If you used an inverter it would just be wasting power by taking the 12 volts up to 240 volts for the machine to then convert it back to 12volts. You know the wiring system polarity so it should be easy enough to wire a battery to the device? Is it running at 2.5A constant or is that the maximum current draw? You might find that the specification shows the max current whereas in practice it doesn't run at that through the full duty cycle. Quote Link to comment Share on other sites More sharing options...
TaxiDriver Posted June 5, 2013 Author Report Share Posted June 5, 2013 (edited) If you used an inverter to run your device you would eat the battery. Basically I would imagine the machine runs on 12 volts and has an internal transformer to take the mains down to that for normal use. If you used an inverter it would just be wasting power by taking the 12 volts up to 240 volts for the machine to then convert it back to 12volts. You know the wiring system polarity so it should be easy enough to wire a battery to the device? Is it running at 2.5A constant or is that the maximum current draw? You might find that the specification shows the max current whereas in practice it doesn't run at that through the full duty cycle. The simplist (and most expensive) way would be to use the machines usual 240v lead plugged into a 12v-240v inverter connected to as big a leisure battery as I can afford. Using a 12v lead I can simply connect to a leisure battery, the machine requires 2.5amps constant, Question IS how big a capacity leisure battery would I need to give me 2x 8-10hrs running time ? As previously explained the Oz polarity of the12v plug/socket is reversed to that of the UK, So I have this sussed out Edited June 5, 2013 by TaxiDriver Quote Link to comment Share on other sites More sharing options...
old rooster Posted June 5, 2013 Report Share Posted June 5, 2013 The simplist (and most expensive) way would be to use the machines usual 240v lead plugged into a 12v-240v inverter connected to as big a leisure battery as I can afford. Using a 12v lead I can simply connect to a leisure battery, the machine requires 2.5amps constant, Question IS how big a capacity leisure battery would I need to give me 2x 8-10hrs running time ? As previously explained the Oz polarity of the12v plug/socket is reversed to that of the UK, So I have this sussed out If you can get a couple of big crocodile clips from Maplins just screw those to the ends of your cables and connect to the battery. The inverter really isn't the way to go as previously explained. You have the calculations for battery size in my original reply....I'd go for 75Ah personally, if you had to carry it around you could always pinch on that a bit but I tend to spec. in a bit of leeway when designing this sort of equipment. Hope this helps? Quote Link to comment Share on other sites More sharing options...
aris Posted June 5, 2013 Report Share Posted June 5, 2013 2.5A for 10 hours would be 25AH (Amp Hours) I believe (I am not an electrical engineer). I think the 'leisure batteries' are also known as deep cycle lead-acid batteries. Plenty in that capacity available - go for 100Ah. Quote Link to comment Share on other sites More sharing options...
stokie Posted June 5, 2013 Report Share Posted June 5, 2013 You need medical equipment at a rifle meet ..... What the hell is Sparkie planning ....lol Quote Link to comment Share on other sites More sharing options...
TaxiDriver Posted June 5, 2013 Author Report Share Posted June 5, 2013 You need medical equipment at a rifle meet ..... What the hell is Sparkie planning ....lol he's not planning nothing I need to run my cpap machine (it's a kinda ventilator thingy) so I don't wake up deceased on the Saturday or Sunday morning (That would really mess up my weekend!! ) Quote Link to comment Share on other sites More sharing options...
Medic1281 Posted June 5, 2013 Report Share Posted June 5, 2013 There's nothing worse than waking up dead in the morning!! Quote Link to comment Share on other sites More sharing options...
clakk Posted June 5, 2013 Report Share Posted June 5, 2013 (edited) try a solar charger the weather forcast is stonkin up here at the weekend .maplins ebay amazon all do em .im sure u can get one to top up whilst running .if you only use breathing device at night itl charge up all day whilst your killing paper. Edited June 5, 2013 by clakk Quote Link to comment Share on other sites More sharing options...
TaxiDriver Posted June 5, 2013 Author Report Share Posted June 5, 2013 There's nothing worse than waking up dead in the morning!! Oh there is, but she couldn't get the weekend off and has had to stay home Quote Link to comment Share on other sites More sharing options...
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